阅读说明：本技术 用于视频编解码的方法和设备 (Method and apparatus for video encoding and decoding ) 是由 李贵春 李翔 刘杉 于 2021-01-13 设计创作，主要内容包括：本公开的各方面提供用于视频编码/解码的方法和设备。在一些示例中,用于视频解码的设备包括接收电路和处理电路。例如,处理电路从已编码视频比特流解码出分区信息。分区信息指示帧内编码的(I)切片的最小允许四叉树(QT)叶节点大小。I切片的最小允许QT叶节点大小受小于编码树单元(CTU)大小的阈值约束。进一步地,处理电路基于最小允许QT叶节点大小将I切片中的编码树块划分为编码块,并从已编码视频比特流分别重建编码块。(Aspects of the present disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes a receive circuit and a processing circuit. For example, the processing circuitry decodes the partition information from the encoded video bitstream. The partition information indicates a minimum allowed Quadtree (QT) leaf node size for an intra-coded (I) slice. The minimum allowed QT leaf node size of an I slice is constrained by a threshold smaller than the Coding Tree Unit (CTU) size. Further, the processing circuitry divides the coding tree blocks in the I slice into coding blocks based on the minimum allowed QT leaf node size and reconstructs the coding blocks separately from the coded video bitstream.)

1. A method for video decoding in a decoder, comprising:

decoding, by a processor, partition information from an encoded video bitstream, the partition information indicating a minimum allowed quadtree, QT, leaf node size for an intra-coded I-slice, the minimum allowed QT leaf node size for the I-slice being constrained by a threshold value that is less than a coding tree unit, CTU, size;

dividing, by the processor, coding tree blocks in the I slice into coding blocks based on the minimum allowed QT leaf node size; and

reconstructing, by the processor, the encoded blocks from the encoded video bit streams, respectively.

2. The method of claim 1, wherein,

the partition information indicates a minimum allowed QT leaf node size for the luma component.

3. The method of claim 2, wherein,

in response to a binary tree partition being used for the I-slice, a minimum allowed QT leaf node size of the I-slice is constrained by the threshold.

4. The method of claim 2, wherein,

the threshold is determined based on implicit QT split requirements.

5. The method of claim 1, wherein,

the partition information indicates a minimum allowed QT leaf node size for the chroma components.

6. The method of claim 1, wherein,

the partition information is decoded from a sequence parameter set, SPS.

7. The method of claim 1, wherein,

and decoding the partition information from a picture header PH.

8. The method of claim 1, further comprising:

applying QT partitioning to divide the encoded tree block into QT leaf nodes that meet the requirement of the minimum allowed QT leaf node size before applying either binary BT partitioning or ternary TT partitioning.

9. The method of claim 1, wherein,

the base 2 logarithm of the minimum allowed QT leaf node size of the I slice is constrained to be less than the base 2 logarithm of the CTU size.

10. The method of claim 9, wherein,

the minimum allowed QT leaf node size base 2 logarithm of the I slice is 1 less than the base 2 logarithm of the CTU size.

11. An apparatus for video decoding, comprising:

a processing store configured to: decoding partition information from an encoded video bitstream, the partition information indicating a minimum allowed quadtree, QT, leaf node size for an intra-coded I-slice, the minimum allowed QT leaf node size for the I-slice constrained by a threshold value that is less than a coding tree unit, CTU, size;

dividing coding tree blocks in the I slice into coding blocks based on the minimum allowed QT leaf node size; and

reconstructing the encoded blocks separately from the encoded video bitstream.

12. The apparatus of claim 11, wherein,

the partition information indicates a minimum allowed QT leaf node size for the luma component.

13. The apparatus of claim 12, wherein,

in response to a binary tree partition being used for the I-slice, a minimum allowed QT leaf node size of the I-slice is constrained by the threshold.

14. The apparatus of claim 12, wherein,

the threshold is determined based on implicit QT split requirements.

15. The apparatus of claim 11, wherein,

the partition information indicates a minimum allowed QT leaf node size for the chroma components.

16. The apparatus of claim 11, wherein,

the partition information is decoded from a sequence parameter set, SPS.

17. The apparatus of claim 11, wherein,

and decoding the partition information from a picture header PH.

18. The device of claim 11, wherein the processing circuitry is configured to:

applying QT partitioning to divide the encoded tree block into QT leaf nodes that meet the requirement of the minimum allowed QT leaf node size before applying either binary BT partitioning or ternary TT partitioning.

19. The apparatus of claim 11, wherein,

the base 2 logarithm of the minimum allowed QT leaf node size of the I slice is constrained to be less than the base 2 logarithm of the CTU size.

20. The apparatus of claim 19, wherein,

the minimum allowed QT leaf node size base 2 logarithm of the I slice is 1 less than the base 2 logarithm of the CTU size.

Technical Field

The present disclosure describes embodiments that relate generally to video coding.

Background

The background description provided herein is intended to present the background of the disclosure as a whole. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description, is not admitted to be prior art by inclusion in the filing of this disclosure, nor is it expressly or implied that it is prior art to the present disclosure.

Video encoding and decoding may be performed using inter-picture prediction with motion compensation. Uncompressed digital video may include a series of pictures, each picture having spatial dimensions of, for example, 1920x1080 luma samples and associated chroma samples. The series of pictures may have a fixed or variable picture rate (also informally referred to as frame rate), for example 60 pictures per second or 60 Hz. Uncompressed video has certain bit rate requirements. For example, 1080p 604: 2:0 video (1920 x1080 luma sample resolution at 60Hz frame rate) with 8 bits per sample requires close to 1.5Gbit/s bandwidth. One hour of such video requires more than 600GB of storage space.

One purpose of video encoding and decoding is to reduce redundancy of an input video signal by compression. Compression may help reduce the bandwidth and/or storage requirements described above, by two or more orders of magnitude in some cases. Lossless compression and lossy compression, and combinations of both, may be employed. Lossless compression refers to a technique for reconstructing an exact copy of an original signal from a compressed original signal. When lossy compression is used, the reconstructed signal may not be identical to the original signal, but the distortion between the original signal and the reconstructed signal is small enough that the reconstructed signal is useful for the intended application. Lossy compression is widely used for video. The amount of distortion tolerated depends on the application. For example, some users consuming streaming media applications may tolerate higher distortion than users of television applications. The achievable compression ratio reflects: higher allowable/tolerable distortion may result in higher compression ratios.

Video encoders and decoders may utilize several broad classes of technologies, including, for example: motion compensation, transformation, quantization and entropy coding.

The video codec techniques may include known intra-coding techniques. In intra coding, sample values are represented without reference to samples or other data of a previously reconstructed reference picture. In some video codecs, a picture is spatially subdivided into blocks of samples. When all sample blocks are coded in intra mode, the picture may be an intra picture. Intra pictures and their derivatives (e.g., independent decoder refresh pictures) can be used to reset the decoder state and thus can be used as the first picture in an encoded video bitstream and video session, or as still images. Samples of the intra block may be used for the transform and the transform coefficients may be quantized prior to entropy encoding. Intra prediction may be a technique to minimize sample values in the pre-transform domain. In some cases, the smaller the transformed DC value and the smaller the AC coefficient, the fewer bits are needed to represent the entropy encoded block at a given quantization step size.

As known from techniques such as MPEG-2 (moving picture experts group-2) codec, conventional intra-coding does not use intra-prediction. However, some newer video compression techniques include: techniques that attempt to derive data chunks from, for example, surrounding sample data and/or metadata obtained during encoding/decoding of spatially neighboring blocks and prior to the decoding order. This technique was later referred to as an "intra-prediction" technique. It is noted that, at least in some cases, intra prediction uses reference data from only the current picture being reconstructed, and not from the reference picture.

There may be many different forms of intra prediction. When more than one such technique may be used in a given video codec technique, the technique used may be codec in intra-prediction mode. In some cases, a mode may have sub-modes and/or parameters, and these modes may be separately coded or included in a mode codeword. Which codeword is used for a given mode/sub-mode/parameter combination affects the coding efficiency gain obtained by intra-prediction, and so does the entropy coding technique used to convert the codeword into a bitstream.

H.264 introduces an intra prediction mode that is improved in h.265 and further improved in newer codec techniques such as joint development model (JEM), universal video codec (VVC), reference set (BMS), etc. A prediction block may be formed using neighboring sample values belonging to already available samples. Sample values of adjacent samples are copied into the prediction block in a certain direction. The reference to the direction used may be encoded in the bitstream or may itself be predicted.

Referring to fig. 1A, the bottom right depicts a subset of nine prediction directions known from the 33 possible prediction directions of h.265 (33 angular modes corresponding to 35 intra modes). The point (101) where the arrows converge represents the sample being predicted. The arrows indicate the direction in which the samples are being predicted. For example, arrow (102) represents the prediction of a sample (101) from one or more samples at an angle of 45 degrees to the horizontal from the upper right. Similarly, arrow (103) represents the prediction of a sample (101) from one or more samples at an angle of 22.5 degrees to the horizontal at the bottom left.

Still referring to fig. 1A, a square block (104) comprising 4x4 samples is shown at the top left (indicated by the thick dashed line). The square block (104) consists of 16 samples, each labeled with "S" and its position in the Y dimension (e.g., row index) and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample in the Y dimension (starting from above) and the first sample in the X dimension (starting from the left). Similarly, sample S44 is the fourth sample in the block (104) in both the Y dimension and the X dimension. Since the block is a 4 × 4 sample size, S44 is located at the lower right corner. Reference samples following a similar numbering scheme are also shown. The reference sample is labeled with "R" and its Y position (e.g., row index) and X position (e.g., column index) relative to the block (104). In h.264 and h.265, the prediction samples are adjacent to the block being reconstructed, so negative values need not be used.

Intra picture prediction can be performed by copying reference sample values from neighboring samples, which are determined by the signaled prediction direction. For example, assume that the coded video bitstream comprises signaling indicating, for the block, a prediction direction coinciding with the arrow (102), i.e. the samples are predicted from one or more predicted samples having an upper right angle of 45 degrees to the horizontal direction. In this case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Then, from the sample R08, a sample S44 is predicted.

In some cases, the values of multiple reference samples may be combined, for example by interpolation, to compute the reference sample, especially when the direction cannot be divided exactly by 45 degrees.

With the development of video coding and decoding technology, the number of possible directions has increased. In h.264 (2003), nine different directions can be represented. There are 33 increases in H.265 (2013) and JEM/VVC/BMS, and as disclosed herein, up to 65 orientations can be supported. Experiments have been performed to identify the most likely directions, and some techniques in entropy coding are used to represent those possible directions using a small number of bits, with some penalty being accepted for less likely directions. Furthermore, sometimes the direction itself can be predicted from the neighboring directions used in neighboring, already decoded blocks.

Fig. 1B shows a diagram (180) depicting 65 intra prediction directions according to JEM to illustrate the increase in the number of prediction directions over time.

The mapping of the direction from intra prediction to the bits representing the direction in the coded video bitstream may differ from one video codec technique to another, e.g. it may range from a simple direct mapping of the prediction direction of intra prediction modes to codewords, to a complex adaptation scheme including the most probable mode and similar techniques. In all cases, however, there may be certain directions in the video content that are statistically less likely to occur than other directions.

Motion compensation may be a lossy compression technique and may involve the following: a specimen data block from a previously reconstructed picture or a portion of a reconstructed picture (reference picture) is spatially shifted in the direction indicated by a motion vector (hereinafter referred to as MV) for prediction of the newly reconstructed picture or portion of the picture. In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV may have two dimensions X and Y, or three dimensions, where the third dimension represents the reference picture being used (the latter may be indirectly the temporal dimension).

In some video compression techniques, an MV applied to a certain region of sample data may be predicted from other MVs, e.g., those MVs that are related to another region of sample data spatially adjacent to the region being reconstructed and that precede the MV in decoding order. This can greatly reduce the amount of data required to codec MVs, thereby eliminating redundancy and increasing the amount of compression. MV prediction can be performed efficiently, for example, because in the codec of an input video signal derived from a camera (referred to as natural video), there is a statistical possibility that regions having areas larger than the applicable region of a single MV will move in similar directions, and thus, in some cases, prediction can be performed using similar motion vectors derived from MVs of neighboring regions. This results in the MVs found for a given region being similar or identical to the MVs predicted from the surrounding MVs and, after entropy coding, can in turn be represented by a smaller number of bits than the number of bits used when directly coding the MVs. In some cases, MV prediction may be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., a sample stream). In other cases, MV prediction itself may be lossy, for example due to rounding errors that occur when calculating the predicted values from several surrounding MVs.

h.265/HEVC (ITU-T h.265 recommendation, "high efficiency video codec", 2016 month 12) describes various MV prediction mechanisms. Among the various MV prediction mechanisms provided by h.265, the present disclosure describes techniques referred to hereinafter as "spatial merging.

Referring to fig. 2, a current block (201) includes samples found by an encoder during a motion search, which can be predicted from previous blocks of the same size that have been spatially shifted. Instead of directly coding the MV, the MV is derived from the metadata associated with one or more reference pictures, e.g. from the nearest (in decoding order) reference picture, using the MV associated with any of the five surrounding samples. Of these, five surrounding samples are represented by a0, a1 and B0, B1, B2 (202 to 206, respectively). In h.265, MV prediction can use the prediction value of the same reference picture that neighboring blocks are using.

Disclosure of Invention

Aspects of the present disclosure provide methods and apparatuses for video encoding/decoding. In some embodiments, an apparatus for video decoding includes a receiving circuit and a processing circuit. For example, the processing circuitry decodes the partition information from the encoded video bitstream. The partition information indicates a minimum allowed Quadtree (QT) leaf node size for an intra-coded (I) slice. The minimum allowed QT leaf node size of an I slice is constrained by a threshold smaller than the Coding Tree Unit (CTU) size. Further, the processing circuitry divides the coding tree blocks in the I slice into coding blocks based on the minimum allowed QT leaf node size and reconstructs the coding blocks separately from the coded video bitstream.

In some embodiments, the partition information indicates a minimum allowed QT leaf node size for the luma component. In some embodiments, in response to the binary tree partition being used for an I slice, the minimum allowed QT leaf node size of the I slice is constrained by a threshold. In an embodiment, the threshold is determined based on implicit QT split requirements.

In some embodiments, the partition information indicates a minimum allowed QT leaf node size for the chroma components.

In some embodiments, the partition information is decoded from a Sequence Parameter Set (SPS). In another embodiment, the partition information is decoded from a Picture Header (PH).

In some embodiments, the processing circuitry applies QT splitting to divide the coded tree block into QT leaf nodes that meet the requirements of a minimum allowed QT leaf node size before applying binary tree splitting or ternary tree splitting.

In some embodiments, the base-2 logarithm of the I slice's minimum allowed QT leaf node size is constrained to be less than the base-2 logarithm of the CTU size. In some embodiments, the base 2 logarithm of the I slice minimum allowed QT leaf node size is 1 less than the base 2 logarithm of the CTU size.

Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer for video decoding, cause the computer to perform a method for video decoding.

Drawings

Other features, properties, and various advantages of the disclosed subject matter will be further apparent from the following detailed description and the accompanying drawings, in which:

fig. 1A is a schematic diagram of an exemplary subset of intra prediction modes.

Fig. 1B is a diagram of exemplary intra prediction directions.

Fig. 2 is a schematic diagram of a current block and its surrounding spatial merge candidates in one example.

Fig. 3 is a schematic diagram of a simplified block diagram of a communication system (300) according to an embodiment.

Fig. 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to an embodiment.

Fig. 5 is a schematic diagram of a simplified block diagram of a decoder according to an embodiment.

Fig. 6 is a schematic diagram of a simplified block diagram of an encoder according to an embodiment.

Fig. 7 shows a block diagram of an encoder according to another embodiment.

Fig. 8 shows a block diagram of a decoder according to another embodiment.

Fig. 9 illustrates an example of a chroma sub-sampling format according to an embodiment of the present disclosure.

Fig. 10A-10C illustrate nominal vertical and horizontal relative positions of corresponding luma and chroma samples according to an embodiment of the disclosure.

Fig. 11 shows an example of a picture (1100) divided into CTUs (1101) according to an embodiment of the present disclosure.

Fig. 12 shows an example of raster scan slice partitioning of a picture (1200) according to an embodiment of the present disclosure.

Fig. 13 illustrates an example of rectangular slice partitioning of a picture (1300) according to an embodiment of the present disclosure.

Fig. 14 shows an example of a picture (1400) partitioned into tiles (tile), bricks (brick) (1401) - (1411), and rectangular slices (slice) (1421) - (1424) according to an embodiment of the disclosure.

FIG. 15 illustrates exemplary partition types (1521) - (1524) in a multi-type tree (MTT) structure, according to an embodiment of the disclosure.

Fig. 16 illustrates an example of d-split flag signaling in a Quadtree (QT) with a nested MTT coding tree structure according to an embodiment of the disclosure.

Fig. 17 illustrates an example of an MTT split pattern according to an embodiment of the present disclosure.

FIG. 18 shows an example of a QT with nested MTT coding block structure according to an embodiment of the present disclosure.

Fig. 19 illustrates an example of a restriction on the Ternary Tree (TT) partitioning according to an embodiment of the present disclosure.

Fig. 20 illustrates an example of redundant split modes of Binary Tree (BT) splitting and TT splitting according to an embodiment of the disclosure.

Fig. 21 shows an example of disallowed TT and BT partitions according to an embodiment of the disclosure.

Fig. 22 shows an exemplary syntax (2200) related to partition and block sizes in a Sequence Parameter Set (SPS), according to an embodiment of the present disclosure.

Fig. 23 shows an example syntax (2300) for a picture header structure, according to an embodiment of the disclosure.

Fig. 24A-24B illustrate an exemplary syntax (2400) for a coding tree unit according to an embodiment of the disclosure.

Fig. 25A-25D illustrate an exemplary syntax (2500) for a coding tree according to an embodiment of the present disclosure.

Fig. 26 illustrates an example of slice types according to an embodiment of the present disclosure.

Fig. 27 illustrates an exemplary derivation of variables for parallel TT partitioning and coding block size in accordance with an embodiment of the disclosure.

Fig. 28 illustrates an exemplary derivation of variables for coding block size in accordance with an embodiment of the disclosure.

Fig. 29 shows a flowchart outlining a process according to an embodiment of the present disclosure.

Fig. 30 is a schematic diagram of a computer system, according to an embodiment.

Detailed Description

Fig. 3 shows a simplified block diagram of a communication system (300) according to an embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other through, for example, a network (350). For example, a communication system (300) includes a first pair of end devices (310) and (320) interconnected by a network (350). In the embodiment of fig. 3, the first pair of terminal devices (310) and (320) performs unidirectional data transmission. For example, a terminal device (310) may encode video data, such as a video picture stream captured by the terminal device (310), for transmission over a network (350) to another terminal device (320). The encoded video data is transmitted in one or more encoded video bitstreams. The terminal device (320) may receive encoded video data from the network (350), decode the encoded video data to recover the video data, and display a video picture according to the recovered video data. Unidirectional data transmission is common in applications such as media services.

In another embodiment, the communication system (300) includes a second pair of terminal devices (330) and (340) that perform bi-directional transmission of encoded video data, which may occur, for example, during a video conference. For bi-directional data transmission, in one example, each of the end devices (330) and (340) may encode video data (e.g., a stream of video pictures captured by the end device) for transmission over the network (350) to the other of the end devices (330) and (340). Each of terminal devices (330) and (340) may also receive encoded video data transmitted by the other of terminal devices (330) and (340), and may decode the encoded video data to recover the video data, and may display video pictures on an accessible display device according to the recovered video data.

In the embodiment of fig. 3, terminal devices (310), (320), (330), and (340) may be servers, personal computers, and smart phones, but the principles of the present disclosure may not be limited thereto. Embodiments of the present disclosure are applicable to laptop computers, tablet computers, media players, and/or dedicated video conferencing equipment. Network (350) represents any number of networks that transport encoded video data between end devices (310), (320), (330), and (340), including, for example, wired (wired) and/or wireless communication networks. The communication network (350) may exchange data in circuit-switched and/or packet-switched channels. The network may include a telecommunications network, a local area network, a wide area network, and/or the internet. For purposes of this disclosure, the architecture and topology of the network (350) may be immaterial to the operation of this disclosure, unless explained below.

As an embodiment of the disclosed subject matter, fig. 4 illustrates the placement of a video encoder and a video decoder in a streaming environment. The disclosed subject matter is equally applicable to other video-enabled applications including, for example, video conferencing, digital TV, storing compressed video on digital media including CDs, DVDs, memory sticks, and the like.

The streaming system may include an acquisition subsystem (413), which may include a video source (401), such as a digital camera, that creates an uncompressed video picture stream (402). In an embodiment, the video picture stream (402) includes samples taken by a digital camera. The video picture stream (402) is depicted as a thick line to emphasize a high data amount video picture stream compared to the encoded video data (404) (or the encoded video bitstream), the video picture stream (402) may be processed by an electronic device (420), the electronic device (420) comprising a video encoder (403) coupled to a video source (401). The video encoder (403) may comprise hardware, software, or a combination of hardware and software to implement or embody aspects of the disclosed subject matter as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)) is depicted as a thin line to emphasize the lower data amount of the encoded video data (404) (or encoded video bitstream (404)) as compared to the video picture stream (402), which may be stored on a streaming server (405) for future use. One or more streaming client subsystems, such as client subsystem (406) and client subsystem (408) in fig. 4, may access a streaming server (405) to retrieve copies (407) and copies (409) of encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) in an electronic device (430). The video decoder (410) decodes incoming copies (407) of the encoded video data and generates an output video picture stream (411) that may be presented on a display (412), such as a display screen, or another presentation device (not depicted). In some streaming systems, the encoded video data (404), video data (407), and video data (409) (e.g., video bitstreams) may be encoded according to certain video encoding/compression standards. Examples of such standards include ITU-T H.265. In an embodiment, the Video codec standard being developed is informally referred to as universal Video Coding (VVC), and the disclosed subject matter may be used in the context of the VVC standard.

It should be noted that electronic device (420) and electronic device (430) may include other components (not shown). For example, electronic device (420) may include a video decoder (not shown), and electronic device (430) may also include a video encoder (not shown).

Fig. 5 shows a block diagram of a video decoder (510) according to an embodiment of the present disclosure. The video decoder (510) may be disposed in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receive circuit). The video decoder (510) may be used in place of the video decoder (410) in the fig. 4 embodiment.

The receiver (531) may receive one or more encoded video sequences to be decoded by the video decoder (510); in the same or another embodiment, the encoded video sequences are received one at a time, wherein each encoded video sequence is decoded independently of the other encoded video sequences. The encoded video sequence may be received from a channel (501), which may be a hardware/software link to a storage device that stores encoded video data. The receiver (531) may receive encoded video data as well as other data, e.g. encoded audio data and/or auxiliary data streams, which may be forwarded to their respective usage entities (not indicated). The receiver (531) may separate the encoded video sequence from other data. To prevent network jitter, a buffer memory (515) may be coupled between the receiver (531) and the entropy decoder/parser (520) (hereinafter "parser (520)"). In some applications, the buffer memory (515) is part of the video decoder (510). In other cases, the buffer memory (515) may be disposed external (not labeled) to the video decoder (510). While in other cases a buffer memory (not labeled) is provided external to the video decoder (510), e.g., to prevent network jitter, and another buffer memory (515) may be configured internal to the video decoder (510), e.g., to handle playout timing. The buffer memory (515) may not be required to be configured or may be made smaller when the receiver (531) receives data from a store/forward device with sufficient bandwidth and controllability or from an isochronous network. Of course, for use over traffic packet networks such as the internet, a buffer memory (515) may also be required, which may be relatively large and may be of adaptive size, and may be implemented at least partially in an operating system or similar element (not labeled) external to the video decoder (510).

The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the encoded video sequence. The categories of these symbols include information for managing the operation of the video decoder (510), as well as potential information to control a display device, such as a display screen (512), that is not an integral part of the electronic device (530), but may be coupled to the electronic device (530), as shown in fig. 5. The control Information for the display device may be a parameter set fragment (not shown) of Supplemental Enhancement Information (SEI message) or Video Usability Information (VUI). The parser (520) may parse/entropy decode the received encoded video sequence. Encoding of the encoded video sequence may be performed in accordance with video coding techniques or standards and may follow various principles, including variable length coding, Huffman coding, arithmetic coding with or without contextual sensitivity, and so forth. A parser (520) may extract a subgroup parameter set for at least one of the subgroups of pixels in the video decoder from the encoded video sequence based on at least one parameter corresponding to the group. A subgroup may include a Group of Pictures (GOP), a picture, a tile, a slice, a macroblock, a Coding Unit (CU), a block, a Transform Unit (TU), a Prediction Unit (PU), and so on. The parser (520) may also extract information from the encoded video sequence, such as transform coefficients, quantizer parameter values, motion vectors, and so on.

The parser (520) may perform entropy decoding/parsing operations on the video sequence received from the buffer memory (515) to create symbols (521).

The reconstruction of the symbol (521) may involve a number of different units depending on the type of the encoded video picture or portion of the encoded video picture (e.g., inter and intra pictures, inter and intra blocks), among other factors. Which units are involved and the way they are involved can be controlled by subgroup control information parsed from the coded video sequence by a parser (520). For the sake of brevity, such a subgroup control information flow between parser (520) and the following units is not described.

In addition to the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into several functional units as described below. In a practical embodiment operating under business constraints, many of these units interact closely with each other and may be integrated with each other. However, for the purposes of describing the disclosed subject matter, a conceptual subdivision into the following functional units is appropriate.

The first unit is a scaler/inverse transform unit (551). The scaler/inverse transform unit (551) receives the quantized transform coefficients as symbols (521) from the parser (520) along with control information including which transform scheme to use, block size, quantization factor, quantization scaling matrix, etc. The sealer/inverse transform unit (551) may output a block comprising sample values, which may be input into an aggregator (555).

In some cases, the output samples of sealer/inverse transform unit (551) may belong to an intra-coded block; namely: predictive information from previously reconstructed pictures is not used, but blocks of predictive information from previously reconstructed portions of the current picture may be used. Such predictive information may be provided by an intra picture prediction unit (552). In some cases, the intra picture prediction unit (552) generates a block of the same size and shape as the block being reconstructed using the surrounding reconstructed information extracted from the current picture buffer (558). For example, the current picture buffer (558) buffers a partially reconstructed current picture and/or a fully reconstructed current picture. In some cases, the aggregator (555) adds the prediction information generated by the intra prediction unit (552) to the output sample information provided by the scaler/inverse transform unit (551) on a per sample basis.

In other cases, the output samples of sealer/inverse transform unit (551) may belong to inter-coded and potential motion compensated blocks. In this case, the motion compensated prediction unit (553) may access a reference picture memory (557) to fetch samples for prediction. After motion compensating the extracted samples according to the sign (521), the samples may be added to the output of the scaler/inverse transform unit (551), in this case referred to as residual samples or residual signals, by an aggregator (555), thereby generating output sample information. The motion compensated prediction unit (553) fetching prediction samples from an address within the reference picture memory (557) may be motion vector controlled and used by the motion compensated prediction unit (553) in the form of the symbol (521), the symbol (521) comprising, for example, X, Y and a reference picture component. Motion compensation may also include interpolation of sample values fetched from a reference picture memory (557), motion vector prediction mechanisms, etc., when using sub-sample exact motion vectors.

The output samples of the aggregator (555) may be employed by various loop filtering techniques in the loop filter unit (556). The video compression techniques may include in-loop filter techniques that are controlled by parameters included in the encoded video sequence (also referred to as an encoded video bitstream) and that are available to the loop filter unit (556) as symbols (521) from the parser (520). However, in other embodiments, the video compression techniques may also be responsive to meta-information obtained during decoding of previous (in decoding order) portions of the encoded picture or encoded video sequence, as well as to sample values previously reconstructed and loop filtered.

The output of the loop filter unit (556) may be a sample stream that may be output to a display device (512) and stored in a reference picture memory (557) for subsequent inter picture prediction.

Once fully reconstructed, some of the coded pictures may be used as reference pictures for future prediction. For example, once the encoded picture corresponding to the current picture is fully reconstructed and the encoded picture is identified (by, e.g., parser (520)) as a reference picture, current picture buffer (558) may become part of reference picture memory (557) and a new current picture buffer may be reallocated before starting reconstruction of a subsequent encoded picture.

The video decoder (510) may perform decoding operations according to predetermined video compression techniques, such as in the ITU-T h.265 standard. The encoded video sequence may conform to the syntax specified by the video compression technique or standard used, in the sense that the encoded video sequence conforms to the syntax of the video compression technique or standard and the configuration files recorded in the video compression technique or standard. In particular, the configuration file may select certain tools from all tools available in the video compression technology or standard as the only tools available under the configuration file. For compliance, the complexity of the encoded video sequence is also required to be within the limits defined by the level of the video compression technique or standard. In some cases, the hierarchy limits the maximum picture size, the maximum frame rate, the maximum reconstruction sampling rate (measured in units of, e.g., mega samples per second), the maximum reference picture size, and so on. In some cases, the limits set by the hierarchy may be further defined by a Hypothetical Reference Decoder (HRD) specification and metadata signaled HRD buffer management in the encoded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be part of an encoded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and/or more accurately reconstruct the original video data. The additional data may be in the form of, for example, a temporal, spatial, or signal-to-noise ratio (SNR) enhancement layer, a redundant slice, a redundant picture, a forward error correction code, and so forth.

Fig. 6 shows a block diagram of a video encoder (603) according to an embodiment of the disclosure. The video encoder (603) is disposed in an electronic device (620). The electronic device (620) includes a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used in place of the video encoder (403) in the fig. 4 embodiment.

Video encoder (603) may receive video samples from a video source (601) (not part of electronics (620) in the fig. 6 embodiment) that may capture video images to be encoded by video encoder (603). In another embodiment, the video source (601) is part of the electronic device (620).

The video source (601) may provide a source video sequence in the form of a stream of digital video samples to be encoded by the video encoder (603), which may have any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit … …), any color space (e.g., bt.601y CrCB, RGB … …), and any suitable sampling structure (e.g., Y CrCB 4:2:0, Y CrCB 4:4: 4). In the media service system, the video source (601) may be a storage device that stores previously prepared video. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. Video data may be provided as a plurality of individual pictures that are given motion when viewed in sequence. The picture itself may be constructed as an array of spatial pixels, where each pixel may comprise one or more samples, depending on the sampling structure, color space, etc. used. The relationship between pixels and samples can be readily understood by those skilled in the art. The following text focuses on describing the samples.

According to an embodiment, the video encoder (603) may encode and compress pictures of a source video sequence into an encoded video sequence (643) in real-time or under any other temporal constraint required by an application. It is a function of the controller (650) to implement the appropriate encoding speed. In some embodiments, the controller (650) controls and is functionally coupled to other functional units as described below. For simplicity, the couplings are not labeled in the figures. The parameters set by the controller (650) may include rate control related parameters (picture skip, quantizer, lambda value of rate distortion optimization technique, etc.), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) may be used to have other suitable functions relating to the video encoder (603) optimized for a certain system design.

In some embodiments, the video encoder (603) operates in an encoding loop. As a brief description, in an embodiment, an encoding loop may include a source encoder (630) (e.g., responsible for creating symbols, e.g., a stream of symbols, based on input pictures and reference pictures to be encoded) and a (local) decoder (633) embedded in a video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a similar manner as a (remote) decoder creates the sample data (since any compression between the symbols and the encoded video bitstream is lossless in the video compression techniques considered in the disclosed subject matter). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since the decoding of the symbol stream produces bit accurate results independent of decoder location (local or remote), the content in the reference picture store (634) also corresponds bit accurately between the local encoder and the remote encoder. In other words, the reference picture samples that the prediction portion of the encoder "sees" are identical to the sample values that the decoder would "see" when using prediction during decoding. This reference picture synchronization philosophy (and the drift that occurs if synchronization cannot be maintained due to, for example, channel errors) is also used in some related techniques.

The operation of the "local" decoder (633) may be the same as a "remote" decoder, such as the video decoder (510) described in detail above in connection with fig. 5. However, referring briefly to fig. 5 additionally, when symbols are available and the entropy encoder (645) and parser (520) are able to losslessly encode/decode the symbols into an encoded video sequence, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633).

At this point it can be observed that any decoder technique other than the parsing/entropy decoding present in the decoder must also be present in the corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter focuses on decoder operation. The description of the encoder techniques may be simplified because the encoder techniques are reciprocal to the fully described decoder techniques. A more detailed description is only needed in certain areas and is provided below.

During operation, in some embodiments, the source encoder (630) may perform motion compensated predictive coding. The motion compensated predictive coding predictively codes an input picture with reference to one or more previously coded pictures from the video sequence that are designated as "reference pictures". In this way, an encoding engine (632) encodes differences between pixel blocks of an input picture and pixel blocks of a reference picture, which may be selected as a prediction reference for the input picture.

The local video decoder (633) may decode encoded video data, which may be designated as reference pictures, based on the symbols created by the source encoder (630). The operation of the encoding engine (632) may be a lossy process. When the encoded video data can be decoded at a video decoder (not shown in fig. 6), the reconstructed video sequence may typically be a copy of the source video sequence with some errors. The local video decoder (633) replicates a decoding process that may be performed on reference pictures by the video decoder, and may cause reconstructed reference pictures to be stored in a reference picture cache (634). In this way, the video encoder (603) may locally store a copy of the reconstructed reference picture that has common content (no transmission errors) with the reconstructed reference picture to be obtained by the remote video decoder.

Predictor (635) may perform a prediction search for coding engine (632). That is, for a new picture to be encoded, predictor (635) may search reference picture memory (634) for sample data (as candidate reference pixel blocks) or some metadata, such as reference picture motion vectors, block shapes, etc., that may be referenced as appropriate predictions for the new picture. The predictor (635) may operate on a block-by-block basis of samples to find a suitable prediction reference. In some cases, from search results obtained by predictor (635), it may be determined that the input picture may have prediction references derived from multiple reference pictures stored in reference picture memory (634).

The controller (650) may manage the encoding operations of the source encoder (630), including, for example, setting parameters and subgroup parameters for encoding the video data.

The outputs of all of the above functional units may be entropy encoded in an entropy encoder (645). The entropy encoder (645) losslessly compresses the symbols generated by the various functional units according to techniques such as huffman coding, variable length coding, arithmetic coding, etc., to convert the symbols into an encoded video sequence.

The transmitter (640) may buffer the encoded video sequence created by the entropy encoder (645) in preparation for transmission over a communication channel (660), which may be a hardware/software link to a storage device that will store the encoded video data. The transmitter (640) may combine the encoded video data from the video encoder (603) with other data to be transmitted, such as encoded audio data and/or an auxiliary data stream (sources not shown).

The controller (650) may manage the operation of the video encoder (603). During encoding, the controller (650) may assign a certain encoded picture type to each encoded picture, but this may affect the encoding techniques applicable to the respective picture. For example, pictures may be generally assigned to any of the following picture types:

intra pictures (I pictures), which may be pictures that can be encoded and decoded without using any other picture in the sequence as a prediction source. Some video codecs tolerate different types of intra pictures, including, for example, Independent Decoder Refresh ("IDR") pictures. Those skilled in the art are aware of variants of picture I and their corresponding applications and features.

Predictive pictures (P pictures), which may be pictures that may be encoded and decoded using intra prediction or inter prediction that uses at most one motion vector and reference index to predict sample values of each block.

Bi-predictive pictures (B-pictures), which may be pictures that can be encoded and decoded using intra-prediction or inter-prediction that uses at most two motion vectors and reference indices to predict sample values of each block. Similarly, multiple predictive pictures may use more than two reference pictures and associated metadata for reconstructing a single block.

A source picture may typically be spatially subdivided into blocks of samples (e.g., blocks of 4x4, 8x8, 4x 8, or 16 x 16 samples) and encoded block-wise. These blocks may be predictively encoded with reference to other (encoded) blocks that are determined according to the encoding allocation applied to their respective pictures. For example, a block of an I picture may be non-predictive encoded, or the block may be predictive encoded (spatial prediction or intra prediction) with reference to an already encoded block of the same picture. The pixel block of the P picture can be prediction-coded by spatial prediction or by temporal prediction with reference to one previously coded reference picture. A block of a B picture may be prediction coded by spatial prediction or by temporal prediction with reference to one or two previously coded reference pictures.

The video encoder (603) may perform encoding operations according to a predetermined video encoding technique or standard, such as the ITU-T h.265 recommendation. In operation, the video encoder (603) may perform various compression operations, including predictive encoding operations that exploit temporal and spatial redundancies in the input video sequence. Thus, the encoded video data may conform to syntax specified by the video coding technique or standard used.

In an embodiment, the transmitter (640) may transmit the additional data while transmitting the encoded video. The source encoder (630) may take such data as part of an encoded video sequence. The additional data may include temporal/spatial/SNR enhancement layers, redundant pictures and slices, among other forms of redundant data, Supplemental Enhancement Information (SEI) messages, Visual Usability Information (VUI) parameter set segments, and the like.

The captured video may be provided as a plurality of source pictures (video pictures) in a time sequence. Intra-picture prediction, often abbreviated as intra-prediction, exploits spatial correlation in a given picture, while inter-picture prediction exploits (temporal or other) correlation between pictures. In an embodiment, the particular picture being encoded/decoded, referred to as the current picture, is partitioned into blocks. When a block in a current picture is similar to a reference block in a reference picture that has been previously encoded in video and is still buffered, the block in the current picture may be encoded by a vector called a motion vector. The motion vector points to a reference block in a reference picture, and in the case where multiple reference pictures are used, the motion vector may have a third dimension that identifies the reference picture.

In some embodiments, bi-directional prediction techniques may be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures are used, e.g., a first reference picture and a second reference picture that are both prior to the current picture in video in decoding order (but may be past and future, respectively, in display order). A block in a current picture may be encoded by a first motion vector pointing to a first reference block in a first reference picture and a second motion vector pointing to a second reference block in a second reference picture. In particular, the block may be predicted by a combination of a first reference block and a second reference block.

Furthermore, merge mode techniques may be used in inter picture prediction to improve coding efficiency.

According to some embodiments of the present disclosure, prediction such as inter-picture prediction and intra-picture prediction is performed in units of blocks. For example, according to the HEVC standard, pictures in a sequence of video pictures are partitioned into Coding Tree Units (CTUs) for compression, the CTUs in the pictures having the same size, e.g., 64 × 64 pixels, 32 × 32 pixels, or 16 × 16 pixels. In general, a CTU includes three Coding Tree Blocks (CTBs), which are one luminance CTB and two chrominance CTBs. Further, each CTU may be further split into one or more Coding Units (CUs) in a quadtree. For example, a 64 × 64-pixel CTU may be split into one 64 × 64-pixel CU, or 4 32 × 32-pixel CUs, or 16 × 16-pixel CUs. In an embodiment, each CU is analyzed to determine a prediction type for the CU, such as an inter prediction type or an intra prediction type. Furthermore, depending on temporal and/or spatial predictability, a CU is split into one or more Prediction Units (PUs). In general, each PU includes a luma Prediction Block (PB) and two chroma blocks PB. In an embodiment, a prediction operation in encoding (encoding/decoding) is performed in units of prediction blocks. Taking a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values (e.g., luma values), such as 8 × 8 pixels, 16 × 16 pixels, 8 × 16 pixels, 16 × 8 pixels, and so on.

Fig. 7 shows a schematic diagram of a video encoder (703) according to another embodiment of the present disclosure. A video encoder (703) is used to receive a processing block (e.g., a prediction block) of sample values within a current video picture in a sequence of video pictures and encode the processing block into an encoded picture that is part of an encoded video sequence. In this embodiment, a video encoder (703) is used in place of the video encoder (403) in the embodiment of fig. 4.

In an HEVC embodiment, a video encoder (703) receives a matrix of sample values for a processing block, e.g., a prediction block of 8 × 8 samples, etc. A video encoder (703) determines whether to encode the processing block using intra mode, inter mode, or bi-prediction mode using, for example, rate-distortion (rate-distortion) optimization. When encoding a processing block in intra mode, the video encoder (703) may use intra prediction techniques to encode the processing block into an encoded picture; and when the processing block is encoded in inter mode or bi-prediction mode, the video encoder (703) may encode the processing block into the encoded picture using inter-prediction or bi-prediction techniques, respectively. In some video coding techniques, the merge mode may be an inter-picture prediction sub-mode, in which motion vectors are derived from one or more motion vector predictors without resorting to coded motion vector components outside of the predictors. In some other video coding techniques, there may be motion vector components that are applicable to the subject block. In an embodiment, the video encoder (703) includes other components, such as a mode decision module (not shown) for determining a processing block mode.

In the embodiment of fig. 7, the video encoder (703) includes an inter encoder (730), an intra encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general purpose controller (721), and an entropy encoder (725) coupled together as shown in fig. 7.

The inter encoder (730) is configured to receive samples of a current block (e.g., a processed block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures), generate inter prediction information (e.g., redundant information descriptions, motion vectors, merge mode information according to inter coding techniques), and calculate an inter prediction result (e.g., a predicted block) using any suitable technique based on the inter prediction information. In some embodiments, the reference picture is a decoded reference picture that is decoded based on encoded video information.

The intra encoder (722) is used to receive samples of a current block (e.g., a processing block), in some cases compare the block to a block already encoded in the same picture, generate quantized coefficients after transformation, and in some cases also generate intra prediction information (e.g., intra prediction direction information according to one or more intra coding techniques). In an embodiment, the intra encoder (722) also calculates an intra prediction result (e.g., a predicted block) based on the intra prediction information and a reference block in the same picture.

The general purpose controller (721) is used to determine general purpose control data and control other components of the video encoder (703) based on the general purpose control data. In an embodiment, a general purpose controller (721) determines a mode of a block and provides a control signal to a switch (726) based on the mode. For example, when the mode is intra mode, the general purpose controller (721) controls the switch (726) to select an intra mode result for use by the residual calculator (723), and controls the entropy encoder (725) to select and add intra prediction information in a bitstream; and when the mode is an inter mode, the general purpose controller (721) controls the switch (726) to select an inter prediction result for use by the residual calculator (723), and controls the entropy encoder (725) to select and add inter prediction information in the bitstream.

A residual calculator (723) is used to calculate the difference (residual data) between the received block and the prediction result selected from the intra encoder (722) or the inter encoder (730). A residual encoder (724) is operative to operate on the residual data to encode the residual data to generate transform coefficients. In an embodiment, a residual encoder (724) is used to convert residual data from the spatial domain to the frequency domain and generate transform coefficients. The transform coefficients are then subjected to a quantization process to obtain quantized transform coefficients. In various embodiments, the video encoder (703) also includes a residual decoder (728). A residual decoder (728) is used to perform the inverse transform and generate decoded residual data. The decoded residual data may be suitably used by an intra encoder (722) and an inter encoder (730). For example, inter encoder (730) may generate a decoded block based on decoded residual data and inter prediction information, and intra encoder (722) may generate a decoded block based on decoded residual data and intra prediction information. The decoded blocks are processed appropriately to generate a decoded picture, and in some embodiments, the decoded picture may be buffered in a memory circuit (not shown) and used as a reference picture.

The entropy encoder (725) is used to format the bitstream to produce encoded blocks. The entropy encoder (725) generates various information according to a suitable standard such as the HEVC standard. In an embodiment, the entropy encoder (725) is used to obtain general control data, selected prediction information (e.g., intra prediction information or inter prediction information), residual information, and other suitable information in the bitstream. It should be noted that, according to the disclosed subject matter, there is no residual information when a block is encoded in the merge sub-mode of the inter mode or bi-prediction mode.

Fig. 8 shows a schematic diagram of a video decoder (810) according to another embodiment of the present disclosure. A video decoder (810) is for receiving an encoded picture that is part of an encoded video sequence and decoding the encoded picture to generate a reconstructed picture. In an embodiment, a video decoder (810) is used in place of the video decoder (410) in the fig. 4 embodiment.

In the fig. 8 embodiment, video decoder (810) includes an entropy decoder (871), an inter-frame decoder (880), a residual decoder (873), a reconstruction module (874), and an intra-frame decoder (872) coupled together as shown in fig. 8.

An entropy decoder (871) is operable to reconstruct from an encoded picture certain symbols representing syntax elements constituting the encoded picture. Such symbols may include, for example, a mode used to encode the block (e.g., intra mode, inter mode, bi-prediction mode, a merge sub-mode of the latter two, or another sub-mode), prediction information (e.g., intra prediction information or inter prediction information) that may identify certain samples or metadata for use by an intra decoder (872) or an inter decoder (880), respectively, residual information in the form of, for example, quantized transform coefficients, and so forth. In an embodiment, when the prediction mode is inter or bi-directional prediction mode, inter prediction information is provided to an inter decoder (880); and providing the intra prediction information to an intra decoder (872) when the prediction type is an intra prediction type. The residual information may be inverse quantized and provided to a residual decoder (873).

An inter decoder (880) is configured to receive inter prediction information and generate an inter prediction result based on the inter prediction information.

An intra-decoder (872) is configured to receive intra-prediction information and generate a prediction result based on the intra-prediction information.

A residual decoder (873) is used to perform inverse quantization to extract dequantized transform coefficients and process the dequantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residual decoder (873) may also need some control information (to obtain the quantizer parameters QP) and that information may be provided by the entropy decoder (871) (data path not labeled as this is only low-level control information).

The reconstruction module (874) is configured to combine the residuals output by the residual decoder (873) and the prediction results (which may be output by the inter prediction module or the intra prediction module) in the spatial domain to form a reconstructed block, which may be part of a reconstructed picture, which in turn may be part of a reconstructed video. It should be noted that other suitable operations, such as deblocking operations, may be performed to improve visual quality.

It should be noted that video encoder (403), video encoder (603), and video encoder (703), as well as video decoder (410), video decoder (510), and video decoder (810), may be implemented using any suitable techniques. In an embodiment, video encoder (403), video encoder (603), and video encoder (703), and video decoder (410), video decoder (510), and video decoder (810) may be implemented using one or more integrated circuits. In another embodiment, the video encoder (403), the video encoder (603), and the video encoder (703), and the video decoder (410), the video decoder (510), and the video decoder (810) may be implemented using one or more processors executing software instructions.

Aspects of the present disclosure provide techniques for constraining a minimum size of a quadtree partitioning.

An exemplary relationship between a source picture given via a bitstream and a decoded picture is described below. The video source represented by the bitstream may be a sequence of pictures arranged in decoding order. The source picture and decoded picture may each include one or more sample arrays, such as (1) luminance (Y) only (monochrome), (2) luminance and two chromaticities (e.g., YCbCr or YCgCo), (3) green, blue, and red (GBR, also referred to as RGB), and (4) arrays representing other unspecified monochrome or tristimulus color samples (e.g., YZX, also referred to as XYZ).

For convenience of notation and nomenclature in this disclosure, variables and nomenclature associated with the above arrays may be referred to as luma (or L or Y) and chroma, where the two chroma arrays may be referred to as Cb and Cr, regardless of the color representation method actually used. The actually used color representation method can be further represented by syntax.

In some embodiments, when multiple sample arrays are used, one of the sample arrays may be used as a reference sample space, and the other sample arrays may be derived from the reference sample space based on a sampling ratio. In an example, when one or more luma and chroma arrays (or blocks) are used, the luma sample array may be used as a reference sample space, and the chroma arrays may be derived from the reference sample space based on a sub-sampling factor. In an example, luma and chroma arrays are included in the source picture and the decoded picture, and then sub-sampling factors, such as a chroma horizontal sub-sampling factor (e.g., SubWidthC) and a chroma vertical sub-sampling factor (e.g., subwehightc) between one or more chroma blocks and corresponding luma blocks may be specified.

Fig. 9 shows a table (table 1) for specifying variables subwidth hc and subheight c (also referred to as chroma subsampling ratio). In an example, the chroma format may be specified using an index and flags, such as chroma _ format _ idc and separate _ colour _ plane _ flag, and then the variables SubWidthC and subwight may be determined based on the chroma format. In another example, the chroma format may be specified using an index such as chroma format idc, and then the variables SubWidthC and subwight c may be determined based on the chroma format. It should be noted that in some examples, chroma _ format _ idc and other suitable values for corresponding SubWidthC and subwight c may also be specified.

Referring to fig. 9, when the chroma format index (e.g., chroma format idc) is 0, the chroma sub-sampling format may be "monochrome", corresponding to monochrome sampling with only one sample array, which is nominally considered to be a luma array.

When the chroma format index is 1, the chroma sub-sampling format may be 4:2:0 or 4:2:0 samples, each of the two chroma arrays having half the height and half the width of the corresponding luma array.

When the chroma format index is 2, the chroma sub-sampling format may be 4:2:2 or 4:2:2 sampling, each of the two chroma arrays having the same height and half the width of the luma array width.

When the chroma format index is 3, the chroma sub-sampling format may be 4:4:4 or 4:4:4 samples, depending on the value of an individual color plane flag (e.g., separate _ color _ plane _ flag), the following applies: (i) if the individual color plane index is equal to 0, then each of the two chroma arrays has the same height and width as the luma array; (ii) otherwise, the individual color plane flag is equal to 1, and the three color planes can be processed individually as a monochrome sample picture.

The number of bits used to represent each sample in the luma and chroma arrays in the video sequence may range from 8 bits to 16 bits (inclusive), and the number of bits used in the luma array may be different from the number of bits used in the chroma array.

Fig. 10A-10C illustrate nominal vertical and horizontal relative positions of corresponding luma and chroma samples in respective pictures according to embodiments of the present disclosure. Alternative chroma sample relative positions may be indicated in the video usability information.

Referring to fig. 10A, in an example, the value of the chroma format index (e.g., chroma format idc) is equal to 1, and thus the chroma format is 4:2: 0. Fig. 10A shows an example of nominal vertical and horizontal positions of corresponding luma and chroma samples in a picture. In some examples, the chroma samples are located vertically between two adjacent luma sample locations and horizontally at the luma sample locations.

Referring to fig. 10B, the value of the chroma format index is equal to 2, and thus the chroma format is 4:2: 2. In some examples, chroma samples are co-located (or co-located) with corresponding luma samples in a picture. Fig. 10B shows an example of nominal vertical and horizontal positions of corresponding luma and chroma samples in a picture.

Referring to fig. 10C, when the value of the chroma format index is equal to 3, all array samples (e.g., a luma array sample and two chroma array samples) may be co-located (or co-located). Fig. 10C shows an example of nominal vertical and horizontal positions of corresponding luma and chroma samples in a picture.

Examples of partitions are described below, such as in VVC. In an embodiment, a picture may be partitioned into CTUs. The plurality of pictures may be divided into a CTU sequence. For a picture with three arrays of samples, a CTU may include an nxn block of luma samples (e.g., a luma block) and two corresponding blocks of chroma samples (e.g., two chroma blocks). Fig. 11 shows an example of a picture (1100) divided into a plurality of CTUs (1101) according to an embodiment of the present disclosure. In an example, the maximum allowed size of a luminance block in a CTU is specified as 128 × 128. In an example, the maximum size of the luminance transform block is 64 × 64.

The picture may be partitioned into slices, tiles, and/or bricks. A picture may be divided into one or more tile rows and one or more tile columns. A tile may be a sequence of CTUs covering a rectangular region of a picture. A tile may be divided into one or more bricks, each of which may include multiple rows of CTUs within the tile. Tiles that are not partitioned into multiple bricks may also be referred to as bricks. However, bricks that are a true subset of tiles are not referred to as tiles.

A slice may include multiple tiles in a picture or multiple bricks in a tile. Two slice modes may be supported, such as a raster scan slice mode and a rectangular slice mode. In raster scan slice mode, a slice may comprise a sequence of tiles in a tile raster scan of a picture. In the rectangular slice mode, a slice may comprise a plurality of bricks of a picture, which together may form a rectangular region of the picture. The bricks in the rectangular slices are arranged in the sequence of raster scanning of the bricks of the slices.

A picture may be partitioned into tiles and raster scan slices. Fig. 12 shows an example of raster scan slice partitioning of a picture (1200) according to an embodiment of the present disclosure. The picture (1200) may be divided into 12 tiles (1201) - (1212) (e.g., 12 tiles in 3 columns (or tile columns) and 4 rows (or tile rows)) and 3 raster scan slices (1221) - (1223). For example, the raster scan slice (1221) includes tiles (1201) - (1202), the raster scan slice (1222) includes tiles (1203) - (1207), and the raster scan slice (1223) includes tiles (1208) - (1212).

A picture may be partitioned into tiles and rectangular slices. Fig. 13 illustrates an example of rectangular slice partitioning of a picture (1300) according to an embodiment of the present disclosure. The picture (1300) may be divided into 24 tiles (1301) - (1324) (e.g., 24 tiles in 6 columns (or tile columns) and 4 rows (or tile rows)) and 9 rectangular slices (1331) - (1339). For example, a rectangular slice (1331) includes tiles (1301) - (1302); the rectangular slice (1332) includes tiles (1303) - (1304); the rectangular slice (1333) includes tiles (1305) - (1306); the rectangular slice (1334) includes tiles (1307), (1308), (1313), and (1314); the rectangular slice (1335) includes tiles (1309), (1310), (1315), and (1316); the rectangular slice (1336) includes tiles (1311), (1312), (1317), and (1318); the rectangular slice (1337) includes tiles (1319) - (1320); the rectangular slice (1338) includes tiles (1321) - (1322); and the rectangular slice (1339) includes tiles (1323) - (1324).

The picture may be partitioned into tiles, bricks, and rectangular slices. Fig. 14 shows an example of a picture (1400) partitioned into tiles, bricks (1401) - (1411), and rectangular slices (1421) - (1424) according to an embodiment of the disclosure. The picture (1400) may be divided into four tiles (e.g., two tile columns and two tile rows), eleven tiles (1401) - (1411), and four rectangular slices (1421) - (1424). The upper left block includes one brick (1401), the upper right block includes five bricks (1402) - (1406), the lower left block includes two bricks (1407) - (1408), and the lower right block includes three bricks (1409) - (1411). The rectangular slice (1421) includes bricks (1401), (1407), and (1408); the rectangular slice (1422) includes bricks (1402) and (1403); the rectangular slice (1423) includes bricks (1404) - (1406); and the rectangular slice (1424) includes bricks (1409) - (1411).

The CTUs may be partitioned using a tree structure. In embodiments, such as in HEVC, a CTU may be partitioned into one or more CUs by using a quadtree or QT structure, represented as a coding tree, to accommodate various local characteristics. The decision whether to encode a picture region using inter-picture (or temporal) or intra-picture (or spatial) prediction may be made at the leaf-CU level. Each leaf-CU may be further partitioned into one, two, or four PUs according to the PU partition type. Within a PU, the same prediction process may be applied and the relevant information may be transmitted to the decoder on a PU basis. After obtaining the residual block by applying a prediction process based on the PU partition type, the leaf-CU may be partitioned into Transform Units (TUs) according to a QT structure similar to the coding tree used for the CU. In an example, such as in an HEVC structure, multiple partition units, such as CUs, PUs, and TUs, may be different.

In embodiments, quadtrees with nested multi-type trees using binary and ternary partition segmentation structures, such as in VVCs, may replace the concept of multi-partition unit types and thus may remove the separation of CU, PU, and TU concepts and may provide greater flexibility for CU partition shapes. In some examples, when a CU has a size that is too large for the maximum transform length, different sizes may be used for the CU, PU, and/or TU. In the coding tree structure, a CU may have a square or rectangular shape. The CTU may be partitioned first through the QT structure. The QT leaf nodes may then be further partitioned through a Multi-type Tree (MTT) structure.

Fig. 15 illustrates exemplary segmentation types (1521) - (1524) in an MTT structure according to an embodiment of the disclosure. The partition types (1521) - (1524) may include vertical binary partition (SPLIT _ BT _ VER) (1521), horizontal binary partition (SPLIT _ BT _ HOR) (1522), vertical ternary partition (SPLIT _ TT _ VER) (1523), and horizontal ternary partition (SPLIT _ TT _ HOR) (1524). MTT leaf nodes may be referred to as CUs and unless a CU is too large for the maximum transform length, the segments (or CUs) may be used for prediction and transform processing without any further partitioning. Thus, in most cases, a CU, PU, and TU may have the same block size in a QT with a nested MTT coding block structure. An exception may occur when the maximum supported transform length is less than the width or height of the color component of the CU.

Fig. 16 shows an example of split flag signaling for QT with nested MTT coding tree structure according to an embodiment of the present disclosure. Fig. 16 illustrates an exemplary signaling mechanism for partition partitioning information in a QT having a nested MTT coding tree structure. A node (1611), such as a CTU, may be considered the root of the QT, and may first be partitioned as a QT node by the QT structure when a QT split flag (e.g., QT _ split _ flag) is true (e.g., value "1") to generate the QT node (1621). When the QT split flag (e.g., QT _ split _ flag) is false (e.g., value "0"), the node (1611) is not split using QT split and thus may be referred to as a QT leaf node (1611). Each QT leaf node (when large enough to allow it) may be further partitioned through the MTT fabric and may be referred to as an MTT node. Referring to FIG. 16, the QT leaf node or MTT node (1611) may be further partitioned using MTT partitioning.

In the MTT structure, a first flag (e.g., MTT _ split _ cu _ flag) may be signaled to indicate whether the node (1611) is further partitioned. When the node (1611) is not partitioned (e.g., MTT _ split _ cu _ flag is "0"), the node (1611) is referred to as a MTT leaf node (1611). When the node (1611) is further partitioned (e.g., mtt _ split _ cu _ flag is "1"), a second flag (e.g., mtt _ split _ cu _ vertical _ flag) may be signaled to indicate the split direction (horizontal split or vertical split), and then a third flag (e.g., mtt _ split _ cu _ binary _ flag) may be signaled to indicate whether the split is a binary split or a ternary split. Accordingly, the MTT node (1651) is generated based on a vertical binary partition (e.g., BT _ VER _ split) of the node (1611), the MTT node (1652) is generated based on a vertical ternary partition (e.g., TT _ VER _ split) of the node (1611), the MTT node (1653) is generated based on a horizontal binary partition (e.g., BT _ HOR _ split) of the node (1611), and the MTT node (1654) is generated based on a horizontal ternary partition (e.g., TT _ HOR _ split) of the node (1611).

Referring to fig. 17, based on values of the second flag (e.g., MTT _ split _ CU _ vertical _ flag) and the third flag (e.g., MTT _ split _ CU _ binary _ flag), a MTT split mode (e.g., mttssplit mode) of a CU may be derived, as shown in table 2. The MTT SPLIT mode may include vertical binary SPLIT (e.g., BT _ VER _ SPLIT or SPLIT _ BT _ VER), vertical ternary SPLIT (e.g., TT _ VER _ SPLIT or SPLIT _ TT _ VER), horizontal binary SPLIT (e.g., BT _ HOR _ SPLIT or SPLIT _ BT _ HOR), and horizontal ternary SPLIT (e.g., TT _ HOR _ SPLIT or SPLIT _ TT _ HOR).

FIG. 18 shows an example of a QT with nested MTT coding block structure according to an embodiment of the present disclosure. The CTU (1800) may be partitioned into CUs having a QT and nested MTT coding block structure, where the bold block edges represent QT partitions and the remaining edges represent MTT partitions. A QT with nested MTT partitions may provide a content adaptive coding tree structure that includes CUs. The size of a CU may be any suitable size. The size of a CU may be as large as the CTU (1800) or as small as 4 × 4 in units of luma samples. In an example, for a 4:2:0 chroma format, the maximum chroma CB size may be 64 × 64 and the minimum chroma CB size may be 2 × 2.

In examples such as VVC, the maximum supported luma transform size is 64 × 64, and the maximum supported chroma transform size is 32 × 32. When the width or height of the CB is greater than the maximum transform width or height, the CB may be automatically divided in the horizontal and/or vertical direction to satisfy the transform size limit in the corresponding direction.

The following parameters may be defined and specified by a Sequence Parameter Set (SPS) syntax element for QT with nested MTT coding tree scheme. The following parameters may include (1) CTU size as the root node size of the QT tree, (2) MinQTSize as the minimum allowed QT leaf node size, (3) MaxBtSize as the maximum allowed BT root node size, (4) maxttssize as the maximum allowed TT root node size, (5) MaxMttDepth as the maximum allowed hierarchical depth of MTTs segmented from the QT leaf, (6) MinBtSize as the minimum allowed BT leaf node size, (7) MinTtSize as the minimum allowed TT leaf node size, and the like.

In the example of QT with nested MTT coding tree structure, the CTU size is set to 128 × 128 luma samples, two corresponding 64 × 64 blocks with 4:2:0 chroma samples, MinQTSize is set to 16 × 16, MaxBtSize is set to 128 × 128, MaxTtSize is set to 64 × 64, MinBtSize and MinTtSize (for both width and height) are set to 4 × 4, and MaxMttDepth is set to 4. The QT partition may first be applied to the CTU to generate QT leaf nodes. QT leaf nodes may have sizes from 16 × 16 (e.g., MinQTSize) to 128 × 128 (e.g., CTU size). In an example, if a QT leaf node is 128 × 128, the QT leaf node is not further split by BT because its size exceeds MaxBtSize and MaxTtSize (e.g., 64 × 64). Otherwise, the QT leaf node may be further partitioned through MTT. Thus, the QT leaf node may also be the root node of the MTT and may have an MTT depth of 0 (e.g., MttDepth). When the MTT depth reaches MaxMttDepth (e.g., 4), no further segmentation is considered. When the MTT node has a width equal to MinBtSize and less than or equal to 2 × MinTtSize, no further horizontal partitioning is considered. Similarly, when the MTT node has a height equal to MinBtSize and less than or equal to 2 × MinTtSize, no further vertical partitioning is considered.

In an embodiment, to allow for 64 × 64 luma block and 32 × 32 chroma pipeline designs, such as in a VVC hardware decoder, TT partitioning may be disabled when the width or height of a luma coded block is greater than a first threshold (e.g., 64), as shown in fig. 19. Therefore, TT partitioning is not applied to luma coding blocks larger than 64, such as 128 × 128 luma coding blocks. TT partitioning may also be disabled when the width or height of the chroma coding block is greater than a second threshold (e.g., 32). Referring to fig. 19, the first threshold is 64, and TT division is prohibited in luma coding blocks (1911) - (1915) because luma coding blocks (1911) - (1915) have a size of 128x 128. For example, luma coding block (1911) is not partitioned, while luma coding blocks (1912) - (1913) are partitioned using BT. Luma coding blocks (1914) - (1915) are first split by QT into 64x64 blocks. TT segmentation may then be applied to luma coding blocks (1921) - (1922) having a size of 64x 64.

In an embodiment, the coding tree scheme supports the ability for the luma component and the corresponding chroma components to have separate block tree structures. In an example, luma and chroma CTBs in a CTU share the same coding tree structure (e.g., a single tree) for P and B slices. For I slices, luma and chroma CTBs in a CTU may have separate block tree structures (e.g., binary trees), and the partitioning case of CTUs using separate block tree structures is referred to as binary tree partitioning. When applying binary TREE partitioning, LUMA CTB may be partitioned into LUMA CUs by a LUMA coding TREE structure (e.g., DUAL _ TREE _ LUMA) and CHROMA CTB may be partitioned into CHROMA CUs by a CHROMA coding TREE structure (e.g., DUAL _ TREE _ CHROMA). Thus, a CU in an I slice may comprise coded blocks of a luma component or may comprise coded blocks of two chroma components, and a CU in a P or B slice comprises coded blocks of all three color components, unless the video is monochrome.

As described below, a CU may be partitioned at picture boundaries (also referred to as boundaries). In an example, such as in HEVC, when a portion of a tree node block exceeds a bottom picture boundary or a right picture boundary, the tree node block is forcibly split until all samples of each encoded CU are within a picture boundary.

In some examples, the following segmentation rules may be applied:

-if a part of a tree node block exceeds both the bottom picture boundary and the right picture boundary,

if the tree node block is a QT node and the size of the tree node block is greater than the minimum QT size, the tree node block is forced to be split in QT split mode.

Else, the tree node block is forced to be SPLIT in SPLIT _ BT _ HOR mode.

Else, if a part of the tree node block exceeds the bottom picture boundary,

if the tree node block is a QT node, and the size of the tree node block is greater than the minimum QT size, and the size of the tree node block is greater than the maximum BT size, the tree node block is forced to be split in QT split mode.

Else, if the tree node block is a QT node, and the size of the tree node block is greater than the minimum QT size, and the size of the tree node block is less than or equal to the maximum BT size, then the tree node block is forced to be SPLIT in QT SPLIT mode or SPLIT _ BT _ HOR mode.

Else (tree node block is BTT node or size of tree node block is less than or equal to minimum QT size), tree node block is forced to be SPLIT in SPLIT _ BT _ HOR mode.

Else, if a part of the tree node block exceeds the right picture boundary,

if the tree node block is a QT node, and the size of the tree node block is greater than the minimum QT size, and the size of the tree node block is greater than the maximum BT size, the tree node block is forced to be split in QT split mode.

Else, if the tree node block is a QT node, and the size of the tree node block is greater than the minimum QT size, and the size of the tree node block is less than or equal to the maximum BT size, then the tree node block is forced to be SPLIT in QT SPLIT mode or SPLIT _ BT _ VER mode.

Else (tree node block is BTT node or size of tree node block is less than or equal to minimum QT size), tree node block is forced to be SPLIT in SPLIT _ BT _ VER mode.

Restrictions on redundant CU partitioning may be used. QTs with nested MTT coding block structures may provide a flexible block partitioning structure. Different fragmentation patterns may result in the same coded block structure due to the type of fragmentation supported in the MTT. In an example, such as in VVC, certain redundant split modes are not allowed.

Fig. 20 illustrates an example of redundant split modes of BT splitting and TT splitting according to an embodiment of the present disclosure. Two-level sequential BT partitions in one direction may have the same coding block structure as the BT partition followed by the center partition. In the above case, BT partitioning (in a given direction) for the center partition of TT partitioning may be prevented (e.g., not allowed), e.g., by syntax. In an example, the above-described restrictions are applied to CUs in each picture.

In an example, a coding block structure (2001) is generated by two levels of consecutive BT partitions in the vertical direction (e.g., a first level BT partition (2011) followed by second level BT partitions (2021) - (2022)). The coding block structure (2002) may be generated by a vertical TT partition (2012) followed by a vertical BT partition (2023) of the center partition of the vertical TT partition (2012). The coding block structure (2001) may be the same as the coding block structure (2002), so BT partitioning (2023) (in the vertical direction) for the center partition of TT partitioning (2012) is prevented, e.g., by syntax.

In an example, a coding block structure (2003) is generated by two levels of consecutive BT partitions in the horizontal direction (e.g., a first level BT partition (2013) followed by second level BT partitions (2024) - (2025)). The coding block structure (2004) may be generated by horizontal TT partitioning (2014) followed by horizontal BT partitioning (2026) of the center partition of the horizontal TT partitioning (2014). The coding block structure (2003) may be the same as the coding block structure (2004), thus preventing BT partitioning (2026) (in the horizontal direction) of the center partition of TT partitioning (2014), for example, by syntax.

When segmentation is prohibited as described above, the signaling of the corresponding syntax element may be modified to address the prohibited case. For example, referring to fig. 20, when a case where BT partition (2023) or (2026) is prohibited, for example, for a CU of a center partition is identified, a syntax element (e.g., mtt _ split _ CU _ binary _ flag) for specifying whether the partition is BT partition or TT partition is not signaled and is inferred by the decoder to be equal to 0. Therefore, BT division is prohibited for the CU.

A Virtual Pipeline Data Unit (VPDU) can be defined as a non-overlapping unit in a picture. In a hardware decoder, successive VPDUs can be processed simultaneously by multiple pipeline stages. The VPDU size may be roughly proportional to the buffer size in most pipeline stages, so it is important to keep the VPDU size relatively small. In various examples, for example in most hardware decoders, the VPDU size may be set to the maximum Transform Block (TB) size. In some examples, such as in VVC, TT and BT partitions may result in an increase in VPDU size. To keep the VPDU size at a particular size, such as 64x64 luma samples, the following canonical partition restriction (with exemplary syntax signaling modifications) can be applied, as shown in fig. 21. Fig. 21 shows an example of disallowed TT and BT partitions according to an embodiment of the disclosure.

For CUs with width, height, or both width and height equal to 128, TT partitioning is not allowed. For example, TT segmentation (2001), (2002), and (2005) - (2008) are not allowed.

For 128xN CU (i.e. width equal to 128 and height less than 128) with N ≦ 64, horizontal BT partitioning is not allowed. For example, for a 128x64 CU, horizontal BT partitioning is not allowed (2004).

For Nx128 CU (i.e. height equal to 128 and width less than 128) with N ≦ 64, vertical BT partitioning is not allowed. For example, for a 64x128 CU, vertical BT partitioning is not allowed (2003).

Intra chroma partitioning and prediction limits are described below. Since a binary tree in an intra picture can apply different partitions in the chroma coding tree compared to the luma coding tree, the binary tree can introduce a longer coding pipeline. The range of values for QTBT MinQTSizeC, MinBtSizeY and MinTTSizeY in the chroma coding tree may allow for small chroma blocks, such as 2x2, 4x2 and 2x 4. In the example, MinQTSizeC refers to the minimum allowed chroma QT leaf node size. Thus, practical decoder designs can be extremely challenging. In addition, certain prediction modes such as cross-component linear model (CCLM), planar mode, and angular mode may use multiplication. To mitigate the above challenges, small chroma block sizes (e.g., 2x2, 2x4, and/or 4x2) may be limited in the binary tree as a partitioning constraint.

In various hardware video encoders and decoders, for example, processing throughput may be reduced when a picture has more small intra blocks due to sample processing data dependencies between adjacent intra blocks. Predictor generation for intra blocks may reconstruct samples using the upper and left boundaries from neighboring blocks. Thus, in an example, intra prediction will be processed sequentially block by block.

In some examples, for example in HEVC, the smallest intra CU is an 8x8 luma sample. The luma component of the smallest intra CU may be further partitioned into four 4x4 luma intra PUs, while the chroma component of the smallest intra CU cannot be further partitioned. Thus, in an example, a worst-case hardware processing throughput may result when processing a 4x4 chroma intra block or a 4x4 luma intra block. In some examples, chroma intra CB smaller than 16 chroma samples are prohibited by constraining the partitioning of chroma intra CB in order to improve worst case throughput. In a single coding tree, a minimum chroma intra prediction unit (SCIPU) may be defined as a coding tree node whose chroma block size is greater than or equal to 16 chroma samples and has at least one sub-luma block smaller than 64 luma samples. In each SCIPU, all CBs are inter-predicted or non-inter-predicted (e.g., intra-prediction or Intra Block Copy (IBC)). For non-inter SCIPU, in an example, the chroma CB(s) of the non-inter SCIPU are not further partitioned, and the luma CB of the SCIPU is allowed to be further partitioned. Accordingly, the minimum chroma intra CB size may be 16 chroma samples, and thus 2x2, 2x4, and 4x2 chroma CBs may be removed. Additionally, in the example, chroma scaling does not apply to non-inter SCIPU. Here, no additional syntax is signaled, and whether SCIPU is non-inter predicted can be derived from the prediction mode of the first luma CB in SCIPU. If the current slice is an I-slice or SCIPU has a 4x4 luma partition in it after being further partitioned once (because intra 4x4 is not allowed in VVC, for example), the type of SCIPU (intra SCIPU or non-intra SCIPU) may be inferred as non-intra SCIPU; otherwise, the type of SCIPU may be indicated by a flag before parsing the CU in the SCIPU. In addition, constraints on picture size may be considered by considering picture width and height as multiples of max (8, MinCbSizeY) to avoid 2x2, 2x4, or 4x 2intra chroma blocks at picture corners.

According to some aspects of the present disclosure, various levels of information, such as sequence level (SPS), picture level (in picture header), coding tree unit level, etc., may include syntax related to partition and block size.

Fig. 22 shows an example syntax (2200) for a Sequence Parameter Set (SPS) according to an embodiment of the present disclosure. The syntax (2200) may include an original byte sequence payload (RBSP) syntax. An RBSP may refer to a syntax structure that includes an integer byte that is encapsulated in a Network Abstraction Layer (NAL) unit and is empty or in the form of a data bit string that includes a syntax element followed by an RBSP stop bit and zero or more subsequent bits equal to 0. In an example, the RBSP stop bit is the last non-zero bit in the RBSP.

Fig. 23 shows an example syntax (2300) for a picture header structure, according to an embodiment of the disclosure.

Fig. 24A-24B illustrate an exemplary syntax (2400) for a coding tree unit according to an embodiment of the disclosure.

Fig. 25A-25D illustrate an exemplary syntax (2500) for a coding tree according to an embodiment of the present disclosure.

Grammars (2200), (2300), (2400), and (2500) include semantics related to partitions and block sizes that may be described below.

In an example, the sequence parameter set RBSP semantics are described below.

qtbtt _ dual _ tree _ intra _ flag equal to 1 can specify that for an I slice, each CTU is partitioned into CUs with 64x64 luma samples using implicit QT partitioning, and a CU can be the root of two separate coding _ tree syntax structures for luma and chroma. qtbtt _ dual _ tree _ intra _ flag equal to 0 may specify that a separate coding _ tree syntax structure is not used for I slices. When qtbtt _ dual _ tree _ intra _ flag is not present, it can be inferred to be equal to 0.

The variable log2_ min _ luma _ coding _ block _ size _ minus2 plus 2 (i.e., log2_ min _ luma _ coding _ block _ size _ minus2+2) may specify the minimum luma coding block size. The value range of log2_ min _ luma _ coding _ block _ size _ minus2 may be in the range of 0 to log2_ ctu _ size _ minus5+3 (inclusive).

The variables MinCbLog2SizeY, MinCbSizeY, IbcBufWidthY, IbcBufWidthC, and Vsize can be derived as follows:

MinCbLog2SizeY＝log2_min_luma_coding_block_size_minus2+2 (1)

MinCbSizeY＝1<<MinCbLog2SizeY (2)

IbcBufWidthY＝256×128/CtbSizeY (3)

IbcBufWidthC＝IbcBufWidthY/SubWidthC (4)

VSize＝Min(64,CtbSizeY) (5)

the MinCbSizeY value can be less than or equal to VSize.

The variables CtbWidthC and ctbhightc, which specify the width and height, respectively, of the array for each chroma CTB, can be derived as follows:

if chroma _ format _ idc is equal to 0 (monochrome) or separate _ colour _ plane _ flag is equal to 1, both CtbWidthC and ctbhight c are equal to 0.

Otherwise, CtbWidthC and ctbhight c are derived as follows:

CtbWidthC＝CtbSizeY/SubWidthC (6)

CtbHeightC＝CtbSizeY/SubHeightC (7)

for log2BlockWidth ranging from 0 to 4 (inclusive) and log2BlockHeight ranging from 0 to 4 (inclusive), the upper right diagonal and Raster scan order array initialization process can be invoked using 1< < log2BlockWidth and 1< < log2BlockHeight as inputs, and the outputs can be assigned to DiagScanOrder [ log2BlockWidth ] [ log2BlockHeight ] and Raster2DiagScanPos [ log2BlockWidth ] [ log2BlockHeight ].

For log2BlockWidth ranging from 0 to 6 (inclusive) and log2BlockHeight ranging from 0 to 6 (inclusive), the horizontal and vertical traversal scan order array initialization process can be invoked using 1< < log2BlockWidth and 1< < log2BlockHeight as inputs, and the outputs can be assigned to HorTravScanOrder [ log2BlockWidth ] [ log2BlockHeight ] and VerTravScanOrder [ log2BlockWidth ] [ log2BlockHeight ].

The partial _ constraints _ overridden _ enabled _ flag equal to 1 may specify that the partial _ constraints _ overridden _ flag is present in a Picture Header (PH) of the reference SPS.

The partition _ constraints _ overrides _ enabled _ flag equal to 0 may specify that the partition _ constraints _ overrides _ flag does not exist in the PH of the reference SPS.

SPS _ log2_ diff _ min _ QT _ min _ cb _ intra _ slice _ luma may specify a default difference between the base-2 logarithm of the minimum size in luma samples of the luma leaf block resulting from the QT segmentation of the CTU and the base-2 logarithm of the minimum coded block size in luma samples of the luma CU in a slice with a reference SPS slice _ type equal to 2 (indicating an I slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference value may be overwritten by pic _ log2_ diff _ min _ qt _ min _ cb _ luma present in the PH of the reference SPS. The value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma may range from 0 to CtbLog2SizeY-MinCbLog2SizeY, inclusive. The base-2 logarithm of the minimum size in luminance samples of a luminance leaf block resulting from the QT segmentation of the CTU can be derived as follows:

MinQtLog2SizeIntraY＝

sps_log2_diff_min_qt_min_cb_intra_slice_luma+MinCbLog2SizeY (8)

SPS _ log2_ diff _ min _ QT _ min _ cb _ inter _ slice may specify a default difference between the base-2 logarithm of the minimum size in luma samples of the luma leaf block resulting from the QT segmentation of the CTU and the base-2 logarithm of the minimum luma coding block size in luma samples of the luma CU in a slice with a reference SPS slice _ type equal to 0 (indicating a B slice) or 1 (indicating a P slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference value may be overwritten by pic _ log2_ diff _ min _ qt _ min _ cb _ luma present in the PH of the reference SPS. The value of sps _ log2_ diff _ min _ qt _ min _ cb _ inter _ slice may range from 0 to CtbLog2SizeY-MinCbLog2SizeY, inclusive. The base-2 logarithm of the minimum size in luminance samples of a luminance leaf block resulting from the QT segmentation of the CTU can be derived as follows:

MinQtLog2SizeInterY＝sps_log2_diff_min_qt_min_cb_inter_slice+MinCbLog2SizeY (9)

SPS _ max _ MTT _ hierarchy _ depth _ inter _ slice may specify a default maximum hierarchical depth of a coding unit resulting from MTT partitioning of QT leaves in slices of a reference SPS for which slice _ type is equal to 0 (indicating a B slice) or 1 (indicating a P slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default maximum hierarchical depth may be covered by pic _ max _ mtt _ hierarchy _ depth _ inter _ slice present in the PH of the reference SPS. The value of sps _ max _ mtt _ hierarchy _ depth _ inter _ slice may be in the range of 0 to 2x (CtbLog2SizeY-MinCbLog2SizeY), inclusive.

SPS _ max _ MTT _ hierarchy _ depth _ intra _ slice _ luma may specify the default maximum layered depth of a coding unit resulting from MTT partitioning of QT leaves in slices with slice _ type equal to 2 (indicating I slices) that reference SPS. When partition _ constraints _ override _ enabled _ flag is equal to 1, the default maximum hierarchical depth may be covered by pic _ max _ mtt _ hierarchy _ depth _ intra _ slice _ luma present in the PH of the reference SPS. The value of sps _ max _ mtt _ hierarchy _ depth _ intra _ slice _ luma may be in the range of 0 to 2x (CtbLog2SizeY-MinCbLog2SizeY), inclusive.

SPS _ log2_ diff _ max _ bt _ min _ QT _ intra _ slice _ luma may specify a default difference between the base-2 logarithm of the maximum size (width or height) in luma samples of a luma coded block that may be partitioned using binary partitioning and the minimum size (width or height) in luma samples of a luma leaf block resulting from QT partitioning of CTUs in a slice of slice _ type equal to 2 (indicating an I slice) referencing SPS. When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference value may be overwritten by pic _ log2_ diff _ max _ bt _ min _ qt _ luma present in the PH of the reference SPS. The value of sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ luma may range from 0 to CtbLog2SizeY-MinQtLog2 sizeinray (inclusive). When sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ luma is not present, the value of sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ luma may be inferred to be equal to 0.

SPS _ log2_ diff _ max _ tt _ min _ QT _ intra _ slice _ luma may specify a default difference between the base-2 logarithm of the maximum size (width or height) in luma samples of a luma coded block that may be partitioned using ternary partitioning and the minimum size (width or height) in luma samples of a luma leaf block resulting from QT partitioning of CTUs in a slice of reference SPS where slice _ type is equal to 2 (indicating an I slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference may be overridden by pic _ log2_ diff _ max _ tt _ min _ qt _ luma present in the PH of the reference SPS. The value of sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ luma may range from 0 to CtbLog2SizeY-MinQtLog2 sizeinray, inclusive. When sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ luma is not present, the value of sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ luma may be inferred to be equal to 0.

SPS _ log2_ diff _ max _ bt _ min _ QT _ inter _ slice may specify a default difference between the base 2 logarithm of the maximum size (width or height) in luma samples of a luma coded block that may be partitioned using binary partitioning and the minimum size (width or height) in luma samples of a luma leaf block resulting from QT partitioning of CTUs in a slice of reference SPS where slice _ type is equal to 0 (indicating a B slice) or 1 (indicating a P slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference value may be overwritten by pic _ log2_ diff _ max _ bt _ min _ qt _ luma present in the PH of the reference SPS. The value of sps _ log2_ diff _ max _ bt _ min _ qt _ inter _ slice may range from 0 to CtbLog2SizeY-MinQtLog2 sizeiny, inclusive. When sps _ log2_ diff _ max _ bt _ min _ qt _ inter _ slice is not present, the value of sps _ log2_ diff _ max _ bt _ min _ qt _ inter _ slice may be inferred to be equal to 0.

SPS _ log2_ diff _ max _ tt _ min _ QT _ inter _ slice may specify a default difference between the base-2 logarithm of the maximum size (width or height) in luma samples for a luma coded block that may be partitioned using ternary partitioning and the minimum size (width or height) in luma samples for a luma leaf block resulting from QT partitioning of CTUs in a slice of reference SPS for which slice _ type is equal to 0 (indicating a B slice) or 1 (indicating a P slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference may be overridden by pic _ log2_ diff _ max _ tt _ min _ qt _ luma present in the PH of the reference SPS. The value of sps _ log2_ diff _ max _ tt _ min _ qt _ inter _ slice may range from 0 to CtbLog2SizeY-MinQtLog2 sizeiny, inclusive. When sps _ log2_ diff _ max _ tt _ min _ qt _ inter _ slice is not present, the value of sps _ log2_ diff _ max _ tt _ min _ qt _ inter _ slice may be inferred to be equal to 0.

SPS _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ CHROMA may specify a default difference between the base-2 logarithm of the minimum size in units of luma samples of a CHROMA leaf block resulting from quadtree partitioning of a CHROMA CTU with treeType equal to DUAL _ TREE _ CHROMA and the base-2 logarithm of the minimum coded block size in units of luma samples of a CHROMA CU with treeType equal to DUAL _ TREE _ CHROMA in a slice (indicating I slice) of the reference SPS where slice _ type is equal to 2. When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference may be overwritten by pic _ log2_ diff _ min _ qt _ min _ cb _ chroma present in the PH of the reference SPS. The value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma may range from 0 to CtbLog2SizeY-MinCbLog2SizeY, inclusive. When not present, the value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma may be inferred to be equal to 0. The base-2 logarithm of the minimum size in luminance samples of the CHROMA leaf block resulting from a QT split of CTU with treeType equal to DUAL _ TREE _ CHROMA can be derived as follows:

MinQtLog2SizeIntraC＝sps_log2_diff_min_qt_min_cb_intra_slice_chroma+MinCbLog2SizeY (10)

SPS _ max _ mtt _ hierarchy _ depth _ intra _ slice _ CHROMA may specify a default maximum hierarchical depth of a CHROMA coding unit resulting from multi-type TREE splitting of a CHROMA quad-TREE leaf with treeType equal to DUAL _ TREE _ CHROMA in a slice with slice _ type equal to 2 (indicating I slice) referring to SPS. When partition _ constraints _ override _ enabled _ flag is equal to 1, the default maximum hierarchical depth may be overwritten by pic _ max _ mtt _ hierarchy _ depth _ chroma present in the PH of the reference SPS. The value of sps _ max _ mtt _ hierarchy _ depth _ intra _ slice _ chroma may be in the range of 0 to 2x (CtbLog2SizeY-MinCbLog2SizeY), inclusive. When not present, the value of sps _ max _ mtt _ hierarchy _ depth _ intra _ slice _ chroma may be inferred to be equal to 0.

SPS _ log2_ diff _ max _ bt _ min _ QT _ intra _ slice _ CHROMA may specify a default difference between the base-2 logarithm of the maximum size (width or height) in units of luma samples of a CHROMA coded block that may be partitioned using binary partitioning and the minimum size (width or height) in units of luma samples of a CHROMA leaf block resulting from QT partitioning of a CHROMA CTU of a slice of reference SPS, with slice _ type equal to 2 (indicating I slices), with treeType equal to DUAL _ TREE _ CHROMA. When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference value may be overwritten by pic _ log2_ diff _ max _ bt _ min _ qt _ chroma present in the PH of the reference SPS. The value of sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ chroma may range from 0 to CtbLog2SizeY-MinQtLog2 sizeintranrac (inclusive). When sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ chroma is not present, the value of sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ chroma may be inferred to be equal to 0.

SPS _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ CHROMA may specify a default difference between the base-2 logarithm of the maximum size (width or height) in units of luma samples for CHROMA coded blocks that may be partitioned using ternary partitioning and the minimum size (width or height) in units of luma samples for CHROMA leaf blocks resulting from quadtree partitioning of CHROMA CTUs in slices of the reference SPS where slice _ type is equal to 2 (indicating I slices) and where treeType is equal to DUAL _ TREE _ CHROMA. When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference may be overridden by pic _ log2_ diff _ max _ tt _ min _ qt _ chroma present in the PH of the reference SPS. The value of sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ chroma may range from 0 to CtbLog2SizeY-MinQtLog2SizeIntrac (inclusive). When sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ chroma is not present, the value of sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ chroma may be inferred to be equal to 0.

sps _ max _ luma _ transform _ size _64_ flag equal to 1 may specify a maximum transform size in units of luma samples equal to 64. sps _ max _ luma _ transform _ size _64_ flag equal to 0 may specify a maximum transform size in units of luma samples equal to 32. When CtbSizeY is less than 64, the value of sps _ max _ luma _ transform _ size _64_ flag may be equal to 0.

The variables MinTbLog2SizeY, maxtlog 2SizeY, MinTbSizeY, and maxtbssizey may be derived as follows:

MinTbLog2SizeY＝2 (11)

MaxTbLog2SizeY＝sps_max_luma_transform_size_64_flag6:5 (12)

MinTbSizeY＝1<<MinTbLog2SizeY (13)

MaxTbSizeY＝1<<MaxTbLog2SizeY (14)

further, in an example, the picture header structure semantics are described as follows.

Specifically, ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma is used to specify the difference between the base-2 logarithm of the minimum size in luma samples of the luma leaf block resulting from the quadtree partitioning of the CTU and the base-2 logarithm of the minimum encoding block size in luma samples of the luma CU in a slice with slice _ type equal to 2 (indicating an I slice) associated with the picture header. In an example, the value of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma is in the range of 0 to CtbLog2SizeY-MinCbLog2SizeY (inclusive). When not present, the value of ph _ log2_ diff _ min _ qt _ min _ cb _ luma can be inferred to be equal to sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma.

Further, ph _ max _ mtt _ hierarchy _ depth _ intra _ slice _ luma is used to specify the maximum hierarchical depth of a coding unit resulting from multi-type tree segmentation of the quadtree leaves in slices associated with the picture header having slice _ type equal to 2 (indicating I slices). In an example, the value of ph _ max _ mtt _ hierarchy _ depth _ intra _ slice _ luma is in the range of 0 to 2x (CtbLog2SizeY-MinCbLog2SizeY), inclusive. When not present, the value of ph _ max _ mtt _ hierarchy _ depth _ intra _ slice _ luma may be inferred to be equal to sps _ max _ mtt _ hierarchy _ depth _ intra _ slice _ luma.

Further, ph _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ luma is used to specify the difference between the base 2 logarithm of the maximum size (width or height) in units of luma samples for luma coded blocks that can be partitioned using binary partitioning and the minimum size (width or height) in units of luma samples for luma leaf blocks resulting from quadtree partitioning of CTUs in slices associated with the picture header where slice _ type is equal to 2 (indicating I slices). In an example, the value of ph _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ luma is in the range of 0 to CtbLog2SizeY-MinQtLog2 sizeintranay (inclusive). When not present, the value of ph _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ luma can be inferred to be equal to sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ luma.

Further, ph _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ luma is used to specify the difference between the base 2 logarithm of the maximum size (width or height) in luma samples for a luma coded block that can be partitioned using ternary partitioning and the minimum size (width or height) in luma samples for a luma leaf block resulting from quadtree partitioning of CTUs in a slice associated with the picture header with slice _ type equal to 2 (indicating an I slice). In an example, the value of ph _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ luma should be in the range of 0 to CtbLog2SizeY-MinQtLog2 sizeintrany, inclusive. When not present, the value of ph _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ luma can be inferred to be equal to sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ luma.

Further, ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ CHROMA is used to specify the difference between the base-2 logarithm of the minimum size in units of luma samples of a CHROMA leaf block resulting from quadtree partitioning of a CHROMA CTU whose treeType is equal to DUAL _ TREE _ CHROMA, and the base-2 logarithm of the minimum size in units of luma samples of a CHROMA CU whose treeType is equal to DUAL _ TREE _ CHROMA in a slice associated with the picture header and whose slice type is equal to 2 (indicating I slice). In an example, the value of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma ranges from 0 to CtbLog2SizeY-MinCbLog2SizeY (inclusive). When not present, the value of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma can be inferred to be equal to sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma.

Further, ph _ max _ mtt _ hierarchy _ depth _ intra _ slice _ CHROMA is used to specify the maximum hierarchical depth of a CHROMA coding unit resulting from multi-type TREE splitting of CHROMA quad-TREE leaves with treeType equal to DUAL _ TREE _ CHROMA in slices associated with a picture header with slice _ type equal to 2 (indicating I slices). In an example, the value of ph _ max _ mtt _ hierarchy _ depth _ intra _ slice _ chroma is in the range of 0 to 2x (CtbLog2 size-MinCbLog 2 size), inclusive. When not present, the value of ph _ max _ mtt _ hierarchy _ depth _ intra _ slice _ chroma may be inferred to be equal to sps _ max _ mtt _ hierarchy _ depth _ intra _ slice _ chroma.

Further, ph _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ CHROMA is used to specify the difference between the base-2 logarithm of the maximum size (width or height) in units of luma samples for CHROMA coding blocks that can be partitioned using binary partitioning and the minimum size (width or height) in units of luma samples for CHROMA leaf blocks resulting from quadtree partitioning of CHROMA CTUs in slices associated with the picture header where slice _ type is equal to 2 (indicating I slices) and where treeType is equal to DUAL _ TREE _ CHROMA. In an example, the value of ph _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ chroma should be in the range of 0 to CtbLog2SizeY-MinQtLog2 sizeintranac (inclusive). When not present, the value of ph _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ chroma can be inferred to be equal to sps _ log2_ diff _ max _ bt _ min _ qt _ intra _ slice _ chroma.

Further, ph _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ CHROMA is used to specify the difference between the base-2 logarithm of the maximum size (width or height) in units of luma samples for CHROMA coded blocks that can be partitioned using ternary partitioning and the minimum size (width or height) in units of luma samples for CHROMA leaf blocks resulting from quadtree partitioning of CHROMA CTUs with treeType equal to DUAL _ TREE _ CHROMA in slices associated with the picture header, where slice _ type is equal to 2 (indicating I slices). In an example, the value of ph _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ chroma should be in the range of 0 to CtbLog2SizeY-MinQtLog2 sizeintranac (inclusive). When not present, the value of ph _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ chroma can be inferred to be equal to sps _ log2_ diff _ max _ tt _ min _ qt _ intra _ slice _ chroma

Furthermore, some slice header semantics may be described below.

For example, slice _ type is used to specify the type of encoding and decoding of a slice, e.g., according to table 3 in fig. 26. In an example, when the value of slice _ type of a slice is 0, the slice is a B slice; when the value of slice _ type of a slice is 1, the slice is a P slice; when the value of slice _ type of a slice is 2, the slice is an I slice. In an example, when slice _ type does not exist, the value of slice _ type is inferred to be equal to 2.

In another example, when ph _ intra _ slice _ allowed _ flag is equal to 0, the value of slice _ type may be 0 or 1. When nal _ unit _ type is in a range of IDR _ W _ RADL to CRA _ NUT (inclusive), and vps _ independent _ layer _ flag [ general layer idx [ nuh _ layer _ id ] ] is equal to 1, slice _ type may be 2.

In some examples, the variables minqtlg 2SizeY, minqtlg 2SizeC, MinQtSizeY, MinQtSizeC, MaxBtSizeY, MaxBtSizeC, MinBtSizeY, MaxTtSizeC, MinTtSizeY, maxtttsipey, MaxMttDepthY, and MaxMttDepthC are derived as follows.

For example, if slice _ type is equal to 2 (indicating I slices), the following may apply:

MinQtLog2SizeY＝MinCbLog2SizeY+ph_log2_diff_min_qt_min_cb_intra_slice_luma (15)

MinQtLog2SizeC＝MinCbLog2SizeY+ph_log2_diff_min_qt_min_cb_intra_slice_chroma (16)

MaxBtSizeY＝1<<(MinQtLog2SizeY+ph_log2_diff_max_bt_min_qt_intra_slice_luma) (17)

MaxBtSizeC＝1<<(MinQtLog2SizeC+ph_log2_diff_max_bt_min_qt_intra_slice_chroma) (18)

MaxTtSizeY＝1<<(MinQtLog2SizeY+ph_log2_diff_max_tt_min_qt_intra_slice_luma) (19)

MaxTtSizeC＝1<<(MinQtLog2SizeC+ph_log2_diff_max_tt_min_qt_intra_slice_chroma) (20)

MaxMttDepthY＝ph_max_mtt_hierarchy_depth_intra_slice_luma (21)

MaxMttDepthC＝ph_max_mtt_hierarchy_depth_intra_slice_chroma (22)

CuQpDeltaSubdiv＝ph_cu_qp_delta_subdiv_intra_slice (23)

CuChromaQpOffsetSubdiv＝ph_cu_chroma_qp_offset_subdiv_intra_slice (24)

otherwise, slice _ type is equal to 0(B) or 1(P), then the following may apply:

MinQtLog2SizeY＝MinCbLog2SizeY+ph_log2_diff_min_qt_min_cb_inter_slice (25)

MinQtLog2SizeC＝MinCbLog2SizeY+ph_log2_diff_min_qt_min_cb_inter_slice (26)

MaxBtSizeY＝1<<(MinQtLog2SizeY+ph_log2_diff_max_bt_min_qt_inter_slice) (27)

MaxBtSizeC＝1<<(MinQtLog2SizeC+ph_log2_diff_max_bt_min_qt_inter_slice) (28)

MaxTtSizeY＝1<<(MinQtLog2SizeY+ph_log2_diff_max_tt_min_qt_inter_slice) (29)

MaxTtSizeC＝1<<(MinQtLog2SizeC+ph_log2_diff_max_tt_min_qt_inter_slice) (30)

MaxMttDepthY＝ph_max_mtt_hierarchy_depth_inter_slice (31)

MaxMttDepthC＝ph_max_mtt_hierarchy_depth_inter_slice (32)

CuQpDeltaSubdiv＝ph_cu_qp_delta_subdiv_inter_slice (33)

CuChromaQpOffsetSubdiv＝ph_cu_chroma_qp_offset_subdiv_inter_slice (34)

the following also applies:

MinQtSizeY＝1<<MinQtLog2SizeY (35)

MinQtSizeC＝1<<MinQtLog2SizeC (36)

MinBtSizeY＝1<<MinCbLog2SizeY (37)

MinTtSizeY＝1<<MinCbLog2SizeY (38)

in an example, the following coding tree semantics can be described. In some examples, the variables allowslitqt, allowslitbtver, allowslitbthor, allowslitttver, and allowslittthor may be derived as follows.

In an example, the allowed quaternion partitioning process may be invoked with the coding block size cbSize, set equal to cbWidth, the current multi-type tree depth, mttDepth, treetypeccrr, and modeTypeCurr, as inputs, and the output allocated to allowslitqt.

The variables minQtSize, maxBtSize, maxTtSize, and maxMttDepth may be derived. If treeType equals DUAL _ TREE _ CHROMA, minQtSize, maxBtSize, maxTtSize, and maxMttDepth are set equal to MinQtSizeC, maxBtSizeC, maxTtSizeC, and maxMttDepthC + depthOffset, respectively; otherwise, minQtSize, maxBtSize, maxTtSize, and maxMttDepth are set equal to MinQtSizeY, maxBtSizeY, maxTtSizeY, and maxMttDepthY + depthOffset, respectively.

The allowed binary partition process may be invoked with the binary partition mode SPLIT _ BT _ VER, the coding block width cbWidth, the coding block height cbHeight, the position (x0, y0), the current multi-type tree depth mttDepth, the maximum multi-type tree depth with offset maxMttDepth, the maximum binary tree size maxBtSize, the minimum quad tree size minQtSize, the current partition index partdix, treeTypeCurr, and modeTypeCurr as inputs, and the output assigned to allowssplitbuty VER.

The allowed binary segmentation process may be invoked with the binary segmentation mode SPLIT _ BT _ HOR, the coding block height cbHeight, the coding block width cbWidth, the position (x0, y0), the current multi-type tree depth mttDepth, the maximum multi-type tree depth with offset maxMttDepth, the maximum binary tree size maxBtSize, the minimum quad-tree size minQtSize, the current partition index partdix, treetypercurr, and modeTypeCurr as inputs, and the output is assigned as allowssplittbthor.

The allowed tri-partition process may be invoked with the tri-partition mode SPLIT _ TT _ VER, the coding block width cbWidth, the coding block height cbHeight, the position (x0, y0), the current multi-type tree depth mttDepth, the maximum multi-type tree depth with offset maxMttDepth, the maximum tri-ary tree size maxTtSize, treeTypeCurr, and modeTypeCurr as inputs, and the output assigned to allowslitttver.

The allowed ternary partition process may be invoked with the ternary partition mode SPLIT _ TT _ HOR, the coding block height cbHeight, the coding block width cbWidth, the position (x0, y0), the current multi-type tree depth mttDepth, the maximum multi-type tree depth with offset maxMttDepth, the maximum ternary tree size maxTtSize, treeTypeCurr, and modeTypeCurr as inputs, and the output is assigned as allowssplitthold.

In an example, split _ cu _ flag is a flag to specify whether or not a coding unit is split. For example, split _ cu _ flag equal to 0 specifies that the coding unit is not partitioned; split _ cu _ flag equal to 1 specifies that a coding unit is split into four coding units using a quaternary partition, as indicated by the syntax element split _ qt _ flag, or into two coding units using a binary partition or into three coding units using a ternary partition, as indicated by the syntax element mtt _ split _ cu _ binary _ flag. The binary or ternary partitioning may be vertical or horizontal as indicated by the syntax element mtt _ split _ cu _ vertical _ flag.

When the split _ cu _ flag is not present, the value of the split _ cu _ flag is inferred as follows. The value of split cu flag is inferred to be equal to 1 if one or more of the following conditions is true. The conditions include (1) x0+ cbWidth is greater than pic _ width _ in _ luma _ samples and (2) y0+ cbHeight is greater than pic _ height _ in _ luma _ samples. Otherwise (none of the conditions is true), the value of split _ cu _ flag is inferred to be equal to 0.

Further, split _ qt _ flag specifies whether the coding unit is divided into coding units having half horizontal and vertical sizes. In some examples, when split _ qt _ flag is not present, the following applies. If all of the following conditions are true, split _ qt _ flag is inferred to be equal to 1. The conditions include (1) split _ cu _ flag is equal to 1; and (2) allowslitQt, allowslitBhor, allowslitBtVer, allowslitTtHor, and allowslitTtVer are equal to FALSE. Otherwise (not all conditions are TRUE), if allowslitqt is equal to TRUE, the value of split _ qt _ flag is inferred to be equal to 1; otherwise (allowSplitQt not equal to true), the value of split _ qt _ flag is inferred to be equal to 0.

Further, mtt _ split _ cu _ vertical _ flag equal to 0 specifies that the coding unit is horizontally split. mtt _ split _ cu _ vertical _ flag equal to 1 specifies that the coding unit is vertically partitioned. When mtt _ split _ cu _ vertical _ flag is not present, mtt _ split _ cu _ vertical _ flag is inferred. For example, if allowslitbthor is equal to TRUE or allowslittthor is equal to TRUE, the value of mtt _ split _ cu _ vertical _ flag is inferred to be equal to 0. Otherwise, the value of mtt _ split _ cu _ vertical _ flag is inferred to be equal to 1.

Further, mtt _ split _ cu _ binary _ flag equal to 0 specifies that the coding unit is partitioned into three coding units using ternary partitioning. mtt _ split _ cu _ binary _ flag equal to 1 specifies that a coding unit is split into two coding units using binary splitting. When mtt _ split _ cu _ binary _ flag is not present, mtt _ split _ cu _ binary _ flag can be inferred as follows:

-if allowslitbtver is equal to FALSE and allowslitbthor is equal to FALSE, the value of mtt _ split _ cu _ binary _ flag is inferred to be equal to 0.

Otherwise, if allowslitttver is equal to FALSE and allowslittthor is equal to FALSE, the value of mtt _ split _ cu _ binary _ flag is inferred to be equal to 1.

Otherwise, if allowslitbthor is equal to TRUE and allowslitttver is equal to TRUE, the value of mtt _ split _ cu _ binary _ flag is inferred to be equal to 1-mtt _ split _ cu _ vertical _ flag.

Otherwise (allowslitbtver equal to TRUE and allowslittthor equal to TRUE), the value of mtt _ split _ cu _ binary _ flag is inferred to be equal to mtt _ split _ cu _ vertical _ flag.

In some examples, the variable mtttsplitmode [ x ] [ y ] [ mttDepth ] is derived from the value of mtt _ split _ cu _ vertical _ flag and from the value of mtt _ split _ cu _ binary _ flag, as defined in table 2 of fig. 17 for x x0., x0+ cbWidth-1 and y y0., y0+ cbHeight-1.

In some examples, the variable MttSplitMode [ x0] [ y0] [ mttDepth ] represents the horizontal and vertical binary and ternary partitioning of the coding unit within the multi-type tree as shown in fig. 15. The array index x0, y0 specifies the position of the top left luma sample of the coding block under consideration relative to the top left luma sample of the picture (x0, y 0).

In some examples, the variable modeTypeCondition is derived as follows:

-modeTypeCondition is set equal to 0 if one or more of the following conditions is true:

-slice _ type equal to I and qtbttt _ dual _ tree _ intra _ flag equal to 1.

-modeTypeCurr is not equal to MODE _ TYPE _ ALL.

Chroma format idc equal to 0.

-chroma format idc equal to 3.

Else, modeTypeCondition is set equal to 1 if one of the following conditions is true:

cbWidth × cbHeight equals 64 and split _ qt _ flag equals 1.

-cbWidth × cbHeight equals 64 and MttSplitMode [ x0] [ y0] [ mttDepth ] equals either SPLIT _ TT _ HOR or SPLIT _ TT _ VER.

-cbWidth × cbHeight equals 32 and MttSplitMode [ x0] [ y0] [ mttDepth ] equals SPLIT _ BT _ HOR or SPLIT _ BT _ VER.

Else, modeTypeCondition is set equal to 1+ (slice _ type | ═ I1:0) if one of the following conditions is true:

-cbWidth × cbHeight equals 64 and MttSplitMode [ x0] [ y0] [ mttDepth ] equals SPLIT _ BT _ HOR or SPLIT _ BT _ VER and chroma _ format _ idc equals 1.

-cbWidth × cbHeight equals 128 and MttSplitMode [ x0] [ y0] [ mttDepth ] equals either SPLIT _ TT _ HOR or SPLIT _ TT _ VER and chroma _ format _ idc equals 1.

-cbWidth equals 8 and MttSplitMode [ x0] [ y0] [ mttDepth ] equals SPLIT _ BT _ VER.

-cbWidth equals 16 and MttSplitMode [ x0] [ y0] [ mttDepth ] equals SPLIT _ TT _ VER.

Else, modeTypeCondition is set equal to 0.

In some examples, mode _ constraint _ flag equal to 0 specifies that coding units within the current coding tree node may only use the inter-prediction codec mode; mode _ constraint _ flag equal to 1 specifies that the coding unit within the current coding tree node cannot use the inter-prediction codec mode.

An example of a partition availability related process, such as VVC, is described below.

In an embodiment, the following describes an allowed quaternion segmentation method. The inputs to the allowed quaternion segmentation process may include:

a) the coded block size in units of luma samples (or cbSize),

b) MTT depth (or mttDepth),

c) a variable TREE type (or treeType) which specifies whether a SINGLE TREE (or SINGLE _ TREE) or a binary TREE is used to partition the coding TREE nodes, and when a binary TREE is used, whether LUMA (DUAL _ TREE _ LUMA) or CHROMA components (DUAL _ TREE _ CHROMA) are currently processed,

d) the variable MODE TYPE (also referred to as a prediction MODE TYPE, e.g., modeType) specifies whether an INTRA MODE (or INTRA prediction MODE, MODE _ INTRA), an IBC MODE (or MODE _ IBC), and an INTER codec MODE (i.e., MODE _ TYPE _ ALL) may be used for a coding unit within a coding tree node, or whether only INTRA and IBC codec MODEs (i.e., MODE _ TYPE _ INTRA) may be used, or whether only an INTER codec MODE (i.e., MODE _ TYPE _ INTER) may be used. In an example, MODE _ TYPE _ ALL indicates that intra, IBC, and inter codec MODEs may be used.

The coding block size (or cbSize) in units of luma samples may represent the block size of a chroma coding block (or chroma block) in luma samples. Accordingly, the block size of a chroma coding block in units of chroma samples may be determined based on the coding block size in units of luma samples (or cbSize) and a corresponding chroma sub-sampling ratio, such as a chroma horizontal sub-sampling ratio or a chroma sub-sampling ratio in the horizontal direction (e.g., SubWidthC). For example, for chroma format 4:2:0, the coding block size in units of luma samples (or cbSize) is 16, so the block size of chroma coding blocks is 16 when represented using luma samples as a unit, or 8 when represented using chroma samples as a unit.

In an example, the encoding block size cbSize is set equal to the width (cbWidth) of the encoding block size in units of luma samples. For example, for chroma format 4:2:2, the width of the coding block size in units of luma samples is 16 luma samples and the chroma level sub-sampling ratio (SubWidthC) is 2, so the block size of the chroma coding block can be 16 in units of luma samples or 16/2 (or 8) in units of chroma samples. Also, for chroma format 4:2:2, the height of the coding block size in units of luma samples is 16 luma samples and the chroma vertical sub-sampling ratio (sub-height c) is 1, so the height of a chroma coding block may be 16 in units of luma samples or 16 in units of chroma samples.

The output of the allowed quadportion process may include a variable allowslitqt that indicates whether QT segmentation is allowed (e.g., allowslitqt is TRUE) or not allowed (e.g., allowslitqt is FALSE). The variable allowSplitQt can be derived as follows:

the variable allowslitqt can be set equal to FALSE and QT segmentation (or QT segmentation) is not allowed if one or more of the following conditions (also referred to as conditions for QT segmentation) are true:

omicron (a) treeType is equal to SINGLE _ TREE or DUAL _ TREE _ LUMA, and cbSize is less than or equal to MinQtSizeY

Omicron (b) treeType equal to DUAL _ TREE _ CHROMA, and cbSize/SubWidthC less than or equal to MinQtSizeC

O (c) mttDepth not equal to 0

Omicron (d) treeType equal to DUAL _ TREE _ CHROMA, and (cbSize/SubWidthC) less than or equal to 4

Omicron (e) treeType equals to DUAL _ TREE _ CHROMA, and modeType equals to MODE _ TYPE _ INTRA

Else, allowslitqt may be set equal to TRUE. Thus, QT splitting (or QT) may be allowed.

In various examples, certain conditions, such as conditions (b), (d), and (e) above, including treeType equal to DUAL _ TREE _ CHROMA, may be true when QT segmentation is applied to CHROMA blocks and not true when QT segmentation is applied to luma blocks. Therefore, the conditions (b), (d), and (e) for the QT partition may be referred to as conditions for the chroma QT partition (or the chroma QT partition).

One or more of conditions (a) - (e) may be modified and/or omitted. Additional conditions may be added to the conditions (a) to (e).

In an example, the coding tree semantics include a variable allowslitqt that can be derived as follows: the allowed quaternion segmentation process may be invoked with the coding block size cbSize, set equal to cbWidth (e.g., in units of luma samples), the current multi-type tree depth, mttDepth, treetypeccurr, and modeTypeCurr, as inputs, and the output may be assigned to allowslitqt.

In an embodiment, the following describes an allowed binary segmentation process. The inputs to the allowed binary segmentation process may include:

a) binary split mode (or btSplit),

b) the coded block width (or cbWidth) in units of luma samples,

c) the coded block height (or cbHeight) in units of luma samples,

d) the position of the top left luminance sample of the considered coding block relative to the top left luminance sample of the picture (x0, y0),

e) a multi-type tree depth (or mttDepth),

f) the maximum multi-type tree depth with offset (or maxMttDepth),

g) the maximum binary tree size (or maxBtSize),

h) the minimum QT size (or minQtSize),

i) the partition index (or partIdx),

j) variable TREE type (or treeType) that specifies whether a SINGLE TREE (SINGLE _ TREE) or a TREE is used

A binary TREE is used to divide the coding TREE nodes and, when a binary TREE is used, whether a luminance (DUAL _ TREE _ LUMA) or a chrominance component (DUAL _ TREE _ CHROMA) is currently processed,

k) a variable MODE TYPE (or modeType) specifying whether INTRA (MODE _ INTRA), IBC (MODE _ IBC), and INTER codec MODEs (i.e., MODE _ TYPE _ ALL) are usable, or whether only INTRA and IBC codec MODEs (i.e., MODE _ TYPE _ INTRA) are usable, or whether only INTER codec MODEs (i.e., MODE _ TYPE _ INTER) are usable, for a coding unit within a coding tree node.

The output of the allowed binary split process may include the variable allowbtssplit.

In an example, the variables parallelTtSplit and cbSize are derived based on the variable btSplit, as shown in table 4 (fig. 27).

The variable allowBtSplit can be derived as follows:

-the variable allowbtbsplit can be set equal to FALSE if one or more of the following conditions is true:

omicron cbSize is less than or equal to MinBtSizeY

Omicron cbWidth is greater than maxBtSize

Omicron cbHeight greater than maxBtSize

Omicron mttDepth is greater than or equal to maxMttDepth

Omicron type is equal to DUAL _ TREE _ CHROMA, and (cbWidth/SubWidthC) x (cbHeight/SubHeight C) is less than or equal to 16

Omicron TreeType equals Dual _ TREE _ CHROMA, and (cbWidth/SubWidthC) equals 4, and btSplit equals SPLIT _ BT _ VER

Omicron TYPE is equal to DUAL _ TREE _ CHROMA, and modeType is equal to MODE _ TYPE _ INTRA

Omicron cbWidth × cbHeight is equal to 32, and modeType is equal to MODE _ TYPE _ INTER

Otherwise, the variable eadlowbtsplit may be set equal to FALSE if all of the following conditions are true:

omicron btSplit equals SPLIT _ BT _ VER

Y0+ cbHeight is greater than pic _ height _ in _ luma _ samples

Otherwise, the variable allowbtbsplit may be set equal to FALSE if all of the following conditions are true:

omicron btSplit equals SPLIT _ BT _ VER

Omicron cbHeight is greater than 64

X0+ cbWidth is greater than pic _ width _ in _ luma _ samples

Otherwise, the variable allowbtbsplit may be set equal to FALSE if all of the following conditions are true:

omicron btSplit is equal to SPLIT _ BT _ HOR

Omicron cbWidth is greater than 64

Y0+ cbHeight is greater than pic _ height _ in _ luma _ samples

Otherwise, the variable allowbtbsplit may be set equal to FALSE if all of the following conditions are true:

x0+ cbWidth is greater than pic _ width _ in _ luma _ samples

Y0+ cbHeight is greater than pic _ height _ in _ luma _ samples

Omicron cbWidth is greater than minQtSize

Otherwise, the variable allowbtbsplit may be set equal to FALSE if all of the following conditions are true:

omicron btSplit is equal to SPLIT _ BT _ HOR

X0+ cbWidth is greater than pic _ width _ in _ luma _ samples

Y0+ cbHeight is less than or equal to pic _ height _ in _ luma _ samples

Otherwise, the variable allowbtbsplit may be set equal to FALSE if all of the following conditions are true:

omicron mttDepth greater than 0

Omicron paratidx equals 1

Omicron MttSplitMode [ x0] [ y0] [ mtDepth-1 ] is equal to paralleltTsSplit

Otherwise, the variable allowbtbsplit may be set equal to FALSE if all of the following conditions are true:

omicron btSplit equals SPLIT _ BT _ VER

Omicron cbWidth is less than or equal to 64

Omicron cbHeight is greater than 64

Otherwise, the variable allowbtbsplit may be set equal to FALSE if all of the following conditions are true:

omicron btSplit is equal to SPLIT _ BT _ HOR

Omicron cbWidth is greater than 64

Omicron cbHeight is less than or equal to 64

Otherwise, the variable allowbtbsplit may be set equal to TRUE.

In an embodiment, the following describes an allowed ternary partitioning process. The inputs to the allowed ternary partitioning process may include:

a) a ternary partitioning pattern (or ttSplit),

b) the coded block width (or cbWidth) in units of luma samples,

c) the coded block height (or cbHeight) in units of luma samples,

d) the position of the top left luminance sample of the considered coding block relative to the top left luminance sample of the picture (x0, y0),

e) multiclass tree depth (or mttDepth)

f) The maximum multi-type tree depth with offset (or maxMttDepth),

g) the maximum ternary tree size (or maxTtSize),

h) a variable TREE type (or treeType) which specifies whether a SINGLE TREE (SINGLE _ TREE) or a binary TREE is used to partition the coding TREE nodes, and when a binary TREE is used, whether LUMA (DUAL _ TREE _ LUMA) or CHROMA components (DUAL _ TREE _ CHROMA) are currently processed,

i) a variable MODE TYPE (or modeType) which specifies whether INTRA (MODE _ INTRA), IBC (MODE _ IBC), and INTER codec MODEs (i.e., MODE _ TYPE _ ALL) can be used, or whether only INTRA and IBC codec MODEs (i.e., MODE _ TYPE _ INTRA) can be used, or whether only INTER codec MODEs (i.e., MODE _ TYPE _ INTER) can be used, for a coding unit within a coding tree node.

The output of the allowed ternary partitioning process may include the variable allowtsplit.

In an example, the variable cbSize is derived based on the variable ttSplit, as shown in table 5 (fig. 28).

The variable allowtsplitt can be derived as follows:

-the variable allowtsplit may be set equal to FALSE if one or more of the following conditions is true:

omicron cbSize is less than or equal to 2 MinTtSizeY

Omicron cbWidth is greater than Min (64, maxTtSize)

Omicron cbHeight is greater than Min (64, maxTtSize)

Omicron mttDepth is greater than or equal to maxMttDepth

X0+ cbWidth is greater than pic _ width _ in _ luma _ samples

Y0+ cbHeight is greater than pic _ height _ in _ luma _ samples

Omicron type is equal to DUAL _ TREE _ CHROMA, and (cbWidth/SubWidthC) x (cbHeight/SubHeight C) is less than or equal to 32

Omicron TreeType equals Dual _ TREE _ CHROMA, and (cbWidth/SubWidthC) equals 8, and ttSplit equals SPLIT _ TT _ VER

Omicron TYPE is equal to DUAL _ TREE _ CHROMA, and modeType is equal to MODE _ TYPE _ INTRA

Omicron cbWidth × cbHeight is equal to 64, and modeType is equal to MODE _ TYPE _ INTER

Otherwise, the variable allowtsplit may be set equal to TRUE.

The derivation process for neighboring block availability may be described as follows.

The inputs to the derivation process for the availability of neighboring blocks may include:

a) the luminance position (xCurr, yCurr) of the upper left sample of the current block relative to the upper left luminance sample of the current picture,

b) luminance positions (xNbY, yNbY) of the top-left luminance samples relative to the current picture covered by the neighboring blocks,

c) a variable checkpredmode specifying whether availability depends on the prediction mode,

d) a variable cIdx specifying the color component of the current block.

The output of the derivation process may include the availability of neighboring blocks, denoted availableN, that cover the position (xNbY, yNbY). Neighboring block availability (or availableN) may be derived as follows:

-availableN is set equal to FALSE if one or more of the following conditions is true:

omicron xNbY is less than 0.

Omicron yNbY is less than 0.

Omicron xNbY is greater than or equal to pic _ width _ in _ luma _ samples.

Omicron y is greater than or equal to pic _ height _ in _ luma _ samples.

Omicron IsAvailable [ cIdx ] [ xNbY ] [ yNbY ] equals FALSE.

O neighboring blocks are included in a different slice than the current block.

O neighboring blocks are included in a different tile than the current block.

Omicron _ coding _ sync _ enabled _ flag is equal to 1, and (xNbY > > CtbLog2SizeY) is greater than or equal to (xCurr > > CtbLog2SizeY) + 1.

Otherwise, the variable availableN may be set equal to TRUE.

The variable availableN may be set equal to FALSE when all of the following conditions are true:

-checkpredmode equals TRUE.

-CuPredMode [0] [ xNbY ] [ yNbY ] is not equal to CuPredMode [0] [ xCyrr ] [ yCurr ].

According to some aspects of the present disclosure, there may be conflicts associated with the minimum QT size. Taking the binary tree luma case in the current VVC draft as an example, the minimum luma QT size (MinQTSizeY) may be set to 128 and the maximum luma multi-type tree depth (maxmtdepthy) is greater than zero, then it is not allowed to set the maximum luma binary tree node size (MaxBTSizeY) or the maximum luma ternary node size (maxttssizey) to 64, since they must be greater than or equal to the minimum luma QT size (MinQTSizeY). But since when using a binary tree, the implicit partitioning of the binary tree is applied to a luma coded block of size 128. This in fact results in an actual minimum luminance QT size of 64 luminance samples, and therefore a maximum luminance BT size of 64 and/or a maximum luminance TT size of 64 may be applied.

Aspects of the present disclosure provide techniques for constraining the range of syntax elements on the minimum QT size in consideration of the CTU size and whether a binary tree is used (or whether a dual _ tree _ explicit _ QT _ split is used).

In some embodiments, when using binary tree partitioning and applying implicit QT partitioning at/above some threshold of block size, the range of minimum QT sizes may be defined to exclude QT sizes that will be implicitly partitioned into smaller sizes.

In an example, a binary tree luma block having a size of 128 luma samples is implicitly partitioned into QT nodes having a size of 64 luma samples. In this case, the semantics of the syntax element sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma may be changed. Specifically, SPS _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma is used to specify a default difference between the base-2 logarithm of the minimum size in luma samples of the luma leaf block resulting from the quadtree partitioning of the CTU and the base-2 logarithm of the minimum encoding block size in luma samples of the luma CU in a slice of the reference SPS where slice _ type is equal to 2 (indicating an I slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference value may be overwritten by PH _ log2_ diff _ min _ qt _ min _ cb _ luma present in the Picture Header (PH). In some embodiments, the value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma is in the range of 0 to CtbLog2SizeY-MinCbLog2SizeY- (CtbLog2SizeY >6& & qtbttt _ dual _ tree _ intra _ flag), inclusive. The base 2 logarithm of the minimum size in luminance samples of the luminance leaf block resulting from the quadtree splitting of the CTU is derived as equation (39):

MinQtLog2SizeIntraY＝sps_log2_diff_min_qt_min_cb_intra_slice_luma+MinCbLog2SizeY (39)

similarly, the semantics of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma in the picture header may be changed. Specifically, ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma is used to specify the difference between the base-2 logarithm of the minimum size in luma samples of the luma leaf block resulting from the quadtree partitioning of the CTU and the base-2 logarithm of the minimum coding block size in luma samples of the luma CU in a slice with slice _ type equal to 2 (indicating an I slice) associated with the picture header. The value of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma may be in the range of 0 to CtbLog2SizeY-MinCbLog2SizeY- (CtbLog2SizeY >6& & qttt _ dual _ tree _ intra _ flag), inclusive. When not present, the value of ph _ log2_ diff _ min _ qt _ min _ cb _ luma is inferred to be equal to sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma. When partition _ constraints _ override _ enabled _ flag is equal to 1, ph _ log2_ diff _ min _ qt _ min _ cb _ luma is used instead of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma in equation (39).

In some embodiments, a binary tree chroma block with a size of 128 luma samples may be implicitly partitioned into QT nodes with a size of 64 luma samples. In this case, the semantics of the syntax element sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma may be changed. Specifically, SPS _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ CHROMA is used to specify a default difference between the base-2 logarithm of the minimum size in units of luma samples of a CHROMA leaf block resulting from quadtree partitioning of a CHROMA CTU with treeType equal to DUAL _ TREE _ CHROMA and the base-2 logarithm of the minimum coded block size in units of luma samples of a CHROMA CU with treeType equal to DUAL _ TREE _ CHROMA in a slice of the reference SPS, slice _ type equal to 2 (indicating I slice). When partition _ constraints _ override _ enabled _ flag is equal to 1, the default difference value may be overwritten by PH _ log2_ diff _ min _ qt _ min _ cb _ chroma present in PH. The value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma ranges from 0 to CtbLog2SizeY-MinCbLog2SizeY- (CtbLog2SizeY >6& & qttt _ dual _ tree _ intra _ flag), inclusive. When not present, the value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma may be inferred to be equal to 0. The base 2 logarithm of the minimum size in units of luma samples of the CHROMA leaf blocks resulting from quadtree partitioning of a CTU with treeType equal to DUAL _ TREE _ CHROMA is derived as equation (40):

MinQtLog2SizeIntraC＝sps_log2_diff_min_qt_min_cb_intra_slice_chroma+MinCbLog2SizeY (40)

similarly, the semantics of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma in the picture header may be changed. Specifically, ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ CHROMA is used to specify the difference between the base-2 logarithm of the minimum size in units of luma samples of the CHROMA leaf blocks resulting from quadtree partitioning of CHROMA CTUs with treeType equal to DUAL _ TREE _ CHROMA and the base-2 logarithm of the minimum size in units of luma samples of the CHROMA CU with treeType equal to DUAL _ TREE _ CHROMA in the slice associated with the picture header, slice _ type equal to 2 (indicating I slice). The value of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma may range from 0 to CtbLog2SizeY-MinCbLog2SizeY- (CtbLog2SizeY >6& & qttt _ dual _ tree _ intra _ flag), inclusive. When not present, the value of ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma is inferred to be equal to sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma. When partition _ constraints _ override _ enabled _ flag is equal to 1, ph _ log2_ diff _ min _ qt _ min _ cb _ chroma is used instead of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma in equation (40).

Fig. 29 shows a flowchart outlining a process (2900) according to an embodiment of the present disclosure. The process (2900) may be used to reconstruct blocks (e.g., CBs) in pictures of a coded video sequence. The term block may be interpreted as a prediction block, CB, CU, etc. In various embodiments, process (2900) is performed by processing circuitry, such as processing circuitry in terminal devices (310), (320), (330), and (340), processing circuitry that performs the functions of video encoder (403), processing circuitry that performs the functions of video decoder (410), processing circuitry that performs the functions of video decoder (510), processing circuitry that performs the functions of video encoder (603). In some embodiments, process (2900) is implemented in software instructions, so when processing circuitry executes the software instructions, processing circuitry executes process (2900). The process starts from (S2901) and proceeds to (S2910).

At (S2910), partition information is decoded from the encoded video bitstream. The partition information indicates a minimum allowed Quadtree (QT) leaf node size for an intra-coded (I) slice. The minimum allowed QT leaf node size of an I slice is constrained by a threshold smaller than the Coding Tree Unit (CTU) size.

In some embodiments, the base 2 logarithm of the minimum allowed QT leaf node size of an I slice (e.g., minqtlg 2SizeIntraY, minqtlg 2SizeIntraC) is constrained to be less than the base 2 logarithm of the CTU size (e.g., CtbLog2 SizeY). In some examples, the base 2 logarithm of the minimum allowed QT leaf node size of an I slice is less than the base 2 logarithm of the CTU size by 1 (e.g., CtbLog2SizeY >6& & qtbttt _ dual _ tree _ intra _ flag is equal to 1). In an example, the CTU size is 128, the base 2 logarithm of the CTU size is 7, and the minimum allowed QT leaf node size base 2 logarithm of an I-slice (e.g., MinQtLog2 sizeintrany, MinQtLog2 sizeintranc) is 6 constrained (e.g., equal to or less than 6).

In some embodiments, the partition information indicates a minimum allowed QT leaf node size for the luma component (e.g., MinQtLog2 sizeintrany). In an embodiment, in response to the binary tree partition being used for an I slice (e.g., qtbttt _ dual _ tree _ intra _ flag is equal to 1), the minimum allowed QT leaf node size of the I slice is constrained by a threshold. In some examples, the threshold is determined based on implicit QT segmentation requirements (e.g., applying implicit QT segmentation at/above a block size of 128).

In some embodiments, the partition information indicates a minimum allowed QT leaf node size for the chroma components (e.g., MinQtLog2 sizeintranac).

In an example, partition information is present in the Sequence Parameter Set (SPS), e.g., in the form of SPS _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma, SPS _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma, etc. In another example, partition information is present in the Picture Header (PH), e.g., in the form of PH _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma, PH _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma, etc.

In an example, the sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma is constrained to be in the range of 0 to CtbLog2SizeY-MinCbLog2SizeY- (CtbLog2SizeY >6& & qtbtt _ dual _ tree _ intra _ flag). When the CTU size is 128, CtbLog2SizeY is 7. Further, when qtbtt _ dual _ tree _ intra _ flag is equal to 1, the maximum value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma is (6-MinCbLog 2 SizeY). Then, the maximum value of MinQtLog2IntraY is 6 according to equation (39), and the minimum allowed quad-tree (QT) leaf node size is constrained by a threshold 64.

Note that in the above example, when partition _ constraints _ override _ enabled _ flag is equal to 1, ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma may be used instead of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ luma.

In an example, the sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma is constrained to be in the range of 0 to CtbLog2SizeY-MinCbLog2SizeY- (CtbLog2SizeY >6& & qtbttt _ dual _ tree _ intra _ flag). When the CTU size is 128, CtbLog2SizeY is 7. Further, when qtbtt _ dual _ tree _ intra _ flag is equal to 1, the maximum value of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma is (6-MinCbLog 2 SizeY). Then, the maximum value of MinQtLog2IntraC is 6 according to equation (40), and the minimum allowed Quadtree (QT) leaf node size is constrained by a threshold of 64 luma samples (e.g., a block of 64 luma samples by 64 luma samples). Based on the chroma format, a corresponding chroma block size of a minimum allowed Quadtree (QT) leaf node size may be determined.

Note that in the above example, when partition _ constraints _ override _ enabled _ flag is equal to 1, ph _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma may be used instead of sps _ log2_ diff _ min _ qt _ min _ cb _ intra _ slice _ chroma.

At (S2920), the coding tree blocks in the I slice are divided into coding blocks based on the minimum allowed QT leaf node size. In some embodiments, prior to applying BT partitioning or TT partitioning, QT partitioning may be applied to partition the coding tree block into QT leaf nodes that meet the requirements of the minimum allowed QT leaf node size.

At (S2930), encoded blocks are respectively reconstructed from the encoded video bit streams. Then, the process proceeds to (S2999) and terminates.

The embodiments in the present disclosure may be used alone or in any order in combination. Further, each of the method (or embodiment), encoder and decoder may be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits). In one example, one or more processors execute a program stored in a non-transitory computer readable medium.

The techniques described above may be implemented as computer software via computer readable instructions and physically stored in one or more computer readable media. For example, fig. 30 illustrates a computer system (3000) suitable for implementing certain embodiments of the disclosed subject matter.

The computer software may be encoded in any suitable machine code or computer language, and by assembly, compilation, linking, etc., mechanisms create code that includes instructions that are directly executable by one or more computer Central Processing Units (CPUs), Graphics Processing Units (GPUs), etc., or by way of transcoding, microcode, etc.

The instructions may be executed on various types of computers or components thereof, including, for example, personal computers, tablets, servers, smartphones, gaming devices, internet of things devices, and so forth.

The components illustrated in FIG. 30 for computer system (3000) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing embodiments of the disclosure. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiments of the computer system (3000).

The computer system (3000) may include some human interface input devices. Such human interface input devices may respond to input from one or more human users through tactile input (e.g., keyboard input, swipe, data glove movement), audio input (e.g., sound, applause), visual input (e.g., gestures), olfactory input (not shown). The human-machine interface device may also be used to capture media that does not necessarily directly relate to human conscious input, such as audio (e.g., voice, music, ambient sounds), images (e.g., scanned images, photographic images obtained from still-image cameras), video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

The human interface input device may include one or more of the following (only one of which is depicted): keyboard (3001), mouse (3002), touch pad (3003), touch screen (3010), data glove (not shown), joystick (3005), microphone (3006), scanner (3007), camera (3008).

The computer system (3000) may also include certain human interface output devices. Such human interface output devices may stimulate the senses of one or more human users through, for example, tactile outputs, sounds, light, and olfactory/gustatory sensations. Such human interface output devices may include haptic output devices (e.g., haptic feedback through a touch screen (3010), data glove (not shown), or joystick (3005), but there may also be haptic feedback devices that do not act as input devices), audio output devices (e.g., speakers (3009), headphones (not shown)), visual output devices (e.g., screens (3010) including cathode ray tube screens, liquid crystal screens, plasma screens, organic light emitting diode screens, each with or without touch screen input functionality, each with or without haptic feedback functionality — some of which may output two-dimensional visual output or more-than-three-dimensional output by means such as stereoscopic picture output; virtual reality glasses (not shown), holographic displays, and smoke boxes (not shown)), and printers (not shown).

The computer system (3000) may also include human-accessible storage devices and their associated media, such as optical media including compact disc read-only/rewritable (CD/DVD ROM/RW) (3020) or similar media (3021) with CD/DVD, thumb drive (3022), removable hard disk drive or solid state drive (3023), conventional magnetic media such as magnetic tape and floppy disk (not shown), ROM/ASIC/PLD based application specific devices such as a security dongle (not shown), and so forth.

Those skilled in the art will also appreciate that the term "computer-readable medium" used in connection with the disclosed subject matter does not include transmission media, carrier waves, or other transitory signals.

The computer system (3000) may also include an interface (3054) to one or more communication networks (3055). For example, the network may be wireless, wired, optical. The network may also be a local area network, a wide area network, a metropolitan area network, a vehicular network, an industrial network, a real-time network, a delay tolerant network, and so forth. The network also includes ethernet, wireless local area networks, local area networks such as cellular networks (GSM, 3G, 4G, 5G, LTE, etc.), television wired or wireless wide area digital networks (including cable, satellite, and terrestrial broadcast television), automotive and industrial networks (including CANBus), and so forth. Some networks typically require external network interface adapters for connecting to some general purpose data ports or peripheral buses (3049) (e.g., USB ports of computer system (3000)); other systems are typically integrated into the core of the computer system (3000) by connecting to a system bus as described below (e.g., an ethernet interface to a PC computer system or a cellular network interface to a smart phone computer system). Using any of these networks, the computer system (3000) may communicate with other entities. The communication may be unidirectional, for reception only (e.g., wireless television), unidirectional for transmission only (e.g., CAN bus to certain CAN bus devices), or bidirectional, for example, to other computer systems over a local or wide area digital network. Each of the networks and network interfaces described above may use certain protocols and protocol stacks.

The human interface device, human accessible storage device, and network interface described above may be connected to the core (3040) of the computer system (3000).

The core (3040) may include one or more Central Processing Units (CPUs) (3041), Graphics Processing Units (GPUs) (3042), special purpose programmable processing units in the form of Field Programmable Gate Arrays (FPGAs) (3043), hardware accelerators for specific tasks (3044), graphics adapters (3050), and so forth. These devices, as well as Read Only Memory (ROM) (3045), random access memory (3046), internal mass storage (e.g., internal non-user accessible hard drives, solid state drives, etc.) (3047), etc. may be connected via a system bus (3048). In some computer systems, the system bus (3048) may be accessed in the form of one or more physical plugs, so as to be expandable by additional central processing units, graphics processing units, and the like. The peripheral devices may be attached directly to the system bus (3048) of the core or connected through a peripheral bus (3049). In an example, the display (3010) may be connected to a graphics adapter (3050). The architecture of the peripheral bus includes peripheral component interconnect PCI, universal serial bus USB, etc.

The CPU (3041), GPU (3042), FPGA (3043) and accelerator (3044) may execute certain instructions, which in combination may constitute the computer code. The computer code may be stored in ROM (3045) or RAM (3046). Transitional data may also be stored in RAM (3046), while persistent data may be stored, for example, in internal mass storage (3047). Fast storage and retrieval of any memory device may be achieved through the use of caches, which may be closely associated with one or more of CPU (3041), GPU (3042), mass storage (3047), ROM (3045), RAM (3046), and the like.

The computer-readable medium may have computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the kind well known and available to those having skill in the computer software arts.

By way of example, and not limitation, a computer system having an architecture (3000), and in particular a core (3040), may provide functionality as a processor (including CPUs, GPUs, FPGAs, accelerators, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media may be media associated with the user-accessible mass storage described above, as well as particular storage having a non-volatile core (3040), such as core internal mass storage (3047) or ROM (3045). Software implementing various embodiments of the present disclosure may be stored in such devices and executed by the core (3040). The computer-readable medium may include one or more memory devices or chips, according to particular needs. The software may cause the core (3040), and in particular the processors therein (including CPUs, GPUs, FPGAs, etc.), to perform certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (3046) and modifying such data structures in accordance with the software-defined processes. Additionally or alternatively, the computer system may provide functionality that is logically hardwired or otherwise embodied in circuitry (e.g., accelerator (3044)) that may operate in place of or in conjunction with software to perform certain processes or certain portions of certain processes described herein. Where appropriate, reference to software may include logic and vice versa. Where appropriate, reference to a computer-readable medium may include circuitry (e.g., an Integrated Circuit (IC)) storing executable software, circuitry comprising executable logic, or both. The present disclosure includes any suitable combination of hardware and software.

Appendix A: acronyms

JEM: joint development model (joint implementation model)

VVC: general purpose video encoding and decoding (versatile video coding)

BMS: reference set (benchmark set)

MV: motion Vector (Motion Vector)

HEVC: high Efficiency Video Coding and decoding (High Efficiency Video Coding)

SEI: auxiliary Enhancement Information (supplement Enhancement Information)

VUI: video Usability Information (Video Usability Information)

GOPs: picture group (Groups of Pictures)

TUs: transformation unit (Transform Units)

And (4) PUs: prediction Units (Prediction Units)

CTUs: coding Tree unit (Coding Tree Units)

CTBs: coding Tree (Coding Tree Blocks)

PBs: prediction block (Prediction Blocks)

HRD: hypothetical Reference Decoder (Hypothetical Reference Decoder)

SNR: Signal-to-Noise Ratio (Signal Noise Ratio)

CPUs: central Processing unit (Central Processing Units)

GPUs: graphic Processing unit (Graphics Processing Units)

CRT: cathode Ray Tube (Cathode Ray Tube)

LCD: LCD Display (Liquid-Crystal Display)

An OLED: organic Light Emitting Diode (Organic Light-Emitting Diode)

CD: compact Disc (Compact Disc)

DVD: digital Video Disc (Digital Video Disc)

ROM: Read-Only Memory (Read-Only Memory)

RAM: random Access Memory (Random Access Memory)

ASIC: Application-Specific Integrated Circuit (Application-Specific Integrated Circuit)

PLD: programmable Logic Device (Programmable Logic Device)

LAN: local Area Network (Local Area Network)

GSM: global System for Mobile communications (LTE): long Term Evolution (Long-Term Evolution)

CANBus: controller Area Network Bus (Controller Area Network Bus)

USB: universal Serial Bus (Universal Serial Bus)

PCI: peripheral Component Interconnect (Peripheral Component Interconnect)

FPGA: field Programmable Gate array (Field Programmable Gate Areas)

SSD: solid state Drive (Solid-state Drive)

IC: integrated Circuit (Integrated Circuit)

CU: coding Unit (Coding Unit)

While this disclosure has described several exemplary embodiments, various modifications, permutations and various equivalents thereof are within the scope of this disclosure. It will thus be appreciated that those skilled in the art will be able to devise various systems and methods which, although not explicitly shown or described herein, embody the principles of the disclosure and are thus within its spirit and scope.