阅读说明：本技术 黑电平偏移 (Black level shift ) 是由 J·杰普森卡林 J·乔恩松 于 2021-05-31 设计创作，主要内容包括：本发明公开涉及由偏差分析系统(1)执行的用于数字摄像机图像传感器(21)的黑电平偏移评估的方法。针对由图像传感器捕获的图像的像素,偏差分析系统测量(1001)每个像素的各自的亮度值和对应的色度值。偏差分析系统还基于对每个亮度等级对对应的测量色度值进行平均,针对测量亮度值的不同亮度等级来确定(1002)各自的平均色度值。此外,当一个范围(4)的亮度等级的各自的平均色度值指示与其它亮度等级(7)的各自的平均色度值(6)的色度偏差(5)到了可预先确定的程度,偏差分析系统确定(1003)图像传感器的黑电平设置从真实黑电平偏移。本公开还涉及根据前述内容的偏差分析系统、包括这种偏差分析系统的数字摄像机,以及各自的对应计算机程序产品和非易失性计算机可读存储介质。(The present disclosure relates to a method performed by a deviation analysis system (1) for black level shift evaluation of a digital camera image sensor (21). For pixels of an image captured by an image sensor, a variance analysis system measures (1001) a respective luminance value and a corresponding chrominance value for each pixel. The deviation analysis system further determines (1002) respective average chromaticity values for different ones of the measured luminance values based on averaging the corresponding measured chromaticity values for each of the luminance levels. Furthermore, when the respective average chromaticity values of the luminance levels of one range (4) indicate a chromaticity deviation (5) from the respective average chromaticity values (6) of the other luminance levels (7) to a predeterminable extent, the deviation analysis system determines (1003) that the black level setting of the image sensor is shifted from the true black level. The disclosure also relates to a deviation analysis system according to the preceding, a digital camera comprising such a deviation analysis system, as well as a respective corresponding computer program product and a non-volatile computer-readable storage medium.)

1. A method performed by a bias analysis system (1) for black level shift evaluation of a digital camera image sensor (21), the method comprising:

measuring (1001), for each pixel of at least a substantial part of the pixels of the image captured by the image sensor (21), a respective luminance value and a corresponding chrominance value of each pixel;

determining (1002) respective average chromaticity values for different ones of the measured luminance values based on averaging the corresponding measured chromaticity values for each luminance level; and

determining (1003) that the black level setting of the image sensor (21) is shifted from a true black level when the respective average chromaticity value of successive luminance levels of a range (4) indicates a chromaticity deviation (5) from the respective average chromaticity value (6) of other luminance levels (7) to a predeterminable extent, the respective average chromaticity value (6) of other luminance levels (7) indicating a constant and/or substantially constant chromaticity level.

2. The method according to claim 1, wherein the chromaticity bias (5) comprises a bias of respective average chromaticity values that increases with decreasing luminance level.

3. The method according to claim 1 or 2, wherein the range (4) comprises a low brightness level compared to a highest determined brightness level (71), the low brightness level being lower than fifteen percent of the highest determined brightness level (71).

4. The method according to any one of claims 1-3, further including:

-comparing (1004) the chromaticity deviation (5) with one or more different candidates (9) of a predetermined theoretical chromaticity deviation covering a theoretical luminance level and/or extending along a theoretical luminance level, the theoretical chromaticity deviation being expected to shift for the range (4) for respective different theoretical black levels, i.e. a deviation from a true black level, in view of characteristics of the image sensor (21) and/or image processing settings; and

when a matching candidate (91) is found, it is determined (1005) that a black level offset of the image sensor (21) is equal to the theoretical black level offset of the matching candidate (91).

5. The method of claim 4, further comprising:

adjusting (1006) a black level setting of the image sensor (21) based on the theoretical black level offset of the match candidate (91).

6. The method of claim 5, wherein the adjusting (1006) the black level setting comprises: when a chroma deviation of one or more further captured images matches the match candidate (91), adjusting the black level setting based on the theoretical black level offset of the match candidate (91).

7. A bias analysis system (1) for black level shift evaluation of a digital camera image sensor (21), the bias analysis system (1) comprising:

a pixel measurement unit (101) for measuring (1001), for each pixel of at least a substantial part of the pixels of the image captured by the image sensor (21), a respective luminance value and a corresponding chrominance value of each pixel;

an average determining unit (102) for determining (1002) respective average chromaticity values for different ones of the measured luminance values based on averaging the corresponding measured chromaticity values for each luminance level; and

a deviation determining unit (103) for determining (1003) that a black level setting of the image sensor (21) is shifted from a true black level when the respective average chromaticity value of successive luminance levels of a range (4) indicates a chromaticity deviation (5) from the respective average chromaticity value (6) of other luminance levels (7) to a predeterminable extent, the respective average chromaticity value (6) of other luminance levels (7) indicating a constant and/or substantially constant chromaticity level.

8. The deviation analysis system (1) according to claim 7, wherein the chromaticity deviation (5) comprises a deviation that increases the respective average chromaticity value as the luminance level decreases.

9. The deviation analysis system (1) according to claim 7 or 8, wherein the range (4) comprises a low brightness level compared to a highest determined brightness level (71), the low brightness level being lower than fifteen percent of the highest determined brightness level (71).

10. The bias analysis system (1) according to any one of claims 7-9, further including:

a deviation comparing unit (104) for comparing (1004) the chromaticity deviation (5) with one or more different candidates (9) of a predetermined theoretical chromaticity deviation covering a theoretical luminance level and/or extending along a theoretical luminance level in view of characteristics and/or image processing settings of the image sensor 21, the theoretical chromaticity deviation being expected to shift for the range (4) for respective different theoretical black levels, i.e. deviations from a true black level; and

an offset determination unit (105) for determining (1005) that a black level offset of the image sensor is equal to the theoretical black level offset of the matching candidate (91) when the matching candidate (91) is found.

11. The bias analysis system (1) according to claim 10, further comprising:

an offset adjustment unit (106) for adjusting (1006) a black level setting of the image sensor (21) based on the theoretical black level offset of the matching candidate (91).

12. The bias analysis system (1) according to claim 11, wherein the offset adjustment unit (106) is adapted to adjust the black level setting based on the theoretical black level offset of the matching candidate (91) when a chrominance bias of one or more further captured images matches the matching candidate (91).

13. A digital camera (2) comprising a deviation analysis system (1) according to any one of claims 7 to 12.

14. A computer program product comprising a computer program comprising computer program code means arranged to cause a computer or processor to perform the steps of the method according to any one of claims 1-6, the computer program product being stored on a computer readable medium or carrier wave.

15. A non-transitory computer readable storage medium having stored thereon the computer program product of claim 14.

Technical Field

The present disclosure relates to black level offset estimation for digital camera image sensors.

Background

With the use of digital cameras (e.g., video cameras), it is possible to capture (e.g., for monitoring purposes) what is happening in a particular environment (e.g., an office, an industrial site, a portion of a city, an open square, a city block, a road, etc.) as it is happening and/or at a later time. The image of the surrounding environment (i.e., the scene) may help provide insight and information about the scene that may be, in one way or another, revealing and/or appealing to people.

Recurring problems associated with image processing of captured images are related to black level (black level) shift, i.e., the black level setting of the digital camera image sensor with which an image may be captured is erroneous (i.e., shifted compared to the true black level). The offset may occur over time, be related to temperature variations, and/or be due to variations in the characteristics and/or tolerances of the image sensor, for example. The problem of black level shift becomes more relevant as image processing can be further pushed, for example, with local tone (tone) mapping. Since the black level error is an offset of the true signal, the relative error may be greatest for small signals (i.e., dark regions and/or near black). Errors may be amplified by the gain applied to the image and may be displayed in dark areas in a coloured tint (tint), typically green or magenta, depending on whether the offset is positive or negative, for example because different gains may be applied to e.g. red (R), green (G) and blue (B) using white balance.

To overcome the black level shift problem, it is known to attempt to determine the black level error of the camera image sensor, and then adjust the image sensor settings based on the black level error to presumably correspond to the true black level. However, determining the image sensor black level offset can be difficult, complex, and/or expensive, and thus remains a challenge.

Disclosure of Invention

It is therefore an object of embodiments herein to provide a method for evaluating black level shift of a digital camera image sensor in an improved and/or alternative manner.

The above objects can be achieved by the presently disclosed subject matter. Embodiments are set forth in the appended claims, the following description and the accompanying drawings.

The disclosed subject matter relates to a method performed by a bias analysis system for black level shift evaluation of a digital camera image sensor. The deviation analysis system measures, for pixels of an image captured by the image sensor, a respective luminance (luminance) value and a corresponding chrominance (chromaticity) value for each pixel. The deviation analysis system also determines respective average chromaticity values for different ones of the measured luminance values based on averaging the corresponding measured chromaticity values for each of the luminance levels. Further, when the respective average chromaticity values of a range of luminance levels indicate chromaticity deviations from the respective average chromaticity values of other luminance levels to a predeterminable degree, the deviation analysis system determines that the black level setting of the image sensor is shifted from the true black level.

The disclosed subject matter also relates to a bias analysis system for black level shift evaluation of digital camera image sensors. The deviation analysis system comprises a pixel measurement unit for (and/or adapted to) measure a respective luminance value and a corresponding chrominance value of each pixel for a pixel of an image captured by the image sensor. The deviation analysis system further comprises an average determination unit for (and/or adapted to) determine respective average chromaticity values for different ones of the measured luminance values based on averaging the corresponding measured chromaticity values for each luminance level. Furthermore, the deviation analysis system comprises a deviation determination unit for (and/or adapted to) determine that the black level setting of the image sensor is shifted from the true black level when the respective average chromaticity value of one range of the luminance levels indicates a chromaticity deviation from the respective average chromaticity values of the other luminance levels to a predeterminable extent.

Furthermore, the disclosed subject matter relates to a digital camera comprising a deviation analysis system as described herein.

Furthermore, the disclosed subject matter relates to a computer program product stored on a computer readable medium or carrier wave, comprising a computer program comprising computer program code means arranged to cause a computer or processor to perform the steps of the deviation analysis system described herein.

The disclosed subject matter also relates to a non-transitory computer-readable storage medium having the computer program product stored thereon.

Thus, a method is introduced according to which an offset from the true black level can be determined in the setting of the digital camera image sensor. That is, since the respective luminance value and the corresponding chrominance value of each pixel are measured for the pixels of the image captured by the image sensor, the luminance and the chrominance can be derived for the respective pixels of the captured image. Also, that is, respective average chromaticity values are determined for different ones of the measured luminance levels based on averaging the corresponding measured chromaticity values for each luminance level by combining together the measured chromaticity values of pixels having the same and/or substantially the same measured luminance values and averaging the chromaticity values, and thus, respective average chromaticity values may be established for the respective luminance levels. Thus, the respective determined average chrominance levels may be mapped to the respective luminance levels. Furthermore, that is, by evaluating the determined average chromaticity values, it is determined that the black level setting of the image sensor is shifted from the true black level when the respective average chromaticity values of a range of luminance levels indicate a chromaticity deviation from the respective average chromaticity values of the other luminance levels to a predeterminable extent, and therefore, if the average chromaticity values of a portion of successive luminance levels deviate from the average chromaticity values of the other luminance levels to an extent considered sufficient (the average chromaticity values of the other luminance levels may indicate, for example, a substantially constant chromaticity level), it may be determined that the image sensor has an erroneous black level setting shifted from the true black level. That is, given that the known (e.g. commonly used in white balance applications) principle of "gray world" has the potential logic (average surface color and/or reflectance in an image with sufficiently different surfaces is grey), using the concepts presented herein, for a correct black level image sensor setting it may be desirable that the respective determined average chromaticity values are constant or substantially constant, i.e. have the same or substantially the same chromaticity level. However, in the case of an erroneous black level setting, the "gray world" principle would be expected to become invalid, especially in dark areas such as for low brightness levels, which are detected by using the concepts presented herein, by: it is determined that the determined average chrominance values of a range, e.g. dark-area luminance levels, deviate to a sufficient extent from the determined (e.g. constant) average chrominance values of other, e.g. higher, luminance levels.

Accordingly, a method for evaluating a black level shift of a digital camera image sensor in an improved and/or alternative manner is provided.

The technical features and corresponding advantages of the above-described method will be discussed in further detail below.

Drawings

Various aspects of the non-limiting embodiments, including the specific features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of an exemplary chromaticity as a function of luminance determined by an exemplary bias analysis system according to an embodiment of the present disclosure;

fig. 2 shows a schematic diagram of exemplary different candidates for theoretical chromaticity bias according to an embodiment of the present disclosure;

FIG. 3 is a schematic block diagram illustrating an exemplary bias analysis system, in accordance with embodiments of the present disclosure, an

FIG. 4 is a flow chart depicting an exemplary method performed by the deviation analysis system according to an embodiment of the present disclosure.

Detailed Description

Non-limiting embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like reference symbols throughout the various drawings indicate like elements. The dashed lines in some of the blocks in the figures indicate that these elements or actions are optional and not mandatory.

In the following, according to embodiments herein relating to black level shift evaluation of digital camera image sensors, a method will be disclosed according to which a shift in settings of a digital camera image sensor from a true black level can be determined.

Referring now to the drawings, and in particular to FIG. 1, a schematic diagram of an exemplary chromaticity as a function of luminance determined by an exemplary bias analysis system 1 according to an embodiment of the present disclosure is depicted. It may be noted that the luminance and chrominance axes of fig. 1 are not drawn to scale for illustrative purposes.

The deviation analysis system 1 is suitable for black level shift evaluation of an image sensor 21 (shown in fig. 3) of the digital camera 2. The digital camera 2 may refer to any arbitrary, e.g. known, digital camera, e.g. a digital video camera. According to an example, the digital camera 2 may further be comprised in a digital camera arrangement and/or network comprising additional components, for example as part of an exemplary monitoring system. Moreover, the image sensor 21 of the digital camera 2 may refer to any arbitrary, e.g. known, image sensor suitable for image capturing. The image sensor 21 may be at least partially included in the digital camera 2 and/or at least partially disposed thereon and/or associated therewith. The scene that the digital camera 2 and/or its image sensor 21 may be adapted to capture may be represented by any arbitrary scene, such as an office, an industrial site, a part of a city, an open square, a city block, a road, etc. The scene may also optionally be a scene of interest for monitoring. Furthermore, the deviation analysis system 1 may be included in the digital camera 2. Alternatively, the deviation analysis system 1 may be provided, for example, at least partially outside the digital camera 2, for example in the exemplary digital camera arrangement or monitoring system discussed above, and/or in one or more servers. The digital camera 2, the image sensor 21 and/or the deviation analysis system 1 may further support image processing such as white balancing, local tone mapping and/or comprise components supporting image processing.

The phrase "deviation analysis system" may refer to a "processing system," a "black level shift analysis system," and/or an "image sensor setting analysis system," while "black level shift evaluation for a digital camera image sensor" may refer to "black level shift evaluation for a digital video camera image sensor," and/or "image sensor setting evaluation for a digital camera image sensor. Furthermore, the phrase "evaluation of the black level shift of the digital camera image sensors" may refer to "evaluation of the black level shift of at least a first digital camera image sensor" and/or "evaluation of the black level shift of one or more digital camera image sensors" and, according to an example, further to "evaluation of the black level shift of the image sensors of the surveillance digital camera" and/or "evaluation of the black level shift of the image sensors of the digital camera adapted to capture the surveillance scene".

The deviation analysis system 1 is adapted and/or configured, for example by means of a pixel measurement unit 101 (shown in fig. 3), to measure for a pixel of an image captured by the image sensor 21 a respective luminance value and a corresponding chrominance value of each pixel. Thereby, the luminance and the chrominance may be derived for respective pixels of the captured image and/or respective pixels of a part of the pixels.

The luminance and chrominance values of the respective pixels of an image may depend on the captured scene (e.g., the features of one or more objects (e.g., people therein)) and the environment and/or conditions in which the image was captured (e.g., lighting conditions, weather conditions, etc.). Further, an image may be captured and/or already captured by the digital camera image sensor 21 in any arbitrary, e.g., known, feasible manner, and may refer to any arbitrary captured image. The respective luminance value and corresponding chrominance value of each pixel of the image may be measured and/or derived in any arbitrary, e.g. known, feasible way. Furthermore, the luminance values and/or the chrominance values may be quantized in any arbitrary, e.g. known, feasible way, e.g. based on a commonly known RGB color model.

The phrase "measuring pixels of an image" may refer to "deriving, detecting, identifying, and/or determining pixels of an image" and/or "measuring pixels of at least a first image", may also refer to "measuring for each of at least a portion of pixels of an image", and/or "measuring for each of at least a predeterminable portion of pixels of an image". It may be further noted that "image sensor" throughout this disclosure may be equivalent to "digital camera image sensor". Furthermore, the phrase "respective luminance value and corresponding chrominance value of each pixel" may refer to "respective luminance value and associated chrominance value of each pixel" and/or "respective luminance value and respective chrominance value of each pixel", and further refer to "luminance value and corresponding chrominance value for respective pixel". On the other hand, according to an example, "luminance values" may refer to "RGB-based luminance values", while "chrominance values" according to an example may refer to "RGB-based chrominance values" and/or "R/G, B/G and/or R/B chrominance values".

The deviation analysis system 1 is adapted and/or configured, for example by means of an average determination unit 102 (as shown in fig. 3), to determine respective average chromaticity values of different ones of the measured luminance levels based on averaging the corresponding measured chromaticity values for each luminance level. Thus, by combining together the measured chrominance values of pixels having the same and/or substantially the same measured luminance value, and averaging these chrominance values, a respective average chrominance value may be established for the respective luminance value levels. Thus, the respective determined average chromaticity level may be mapped to a respective luminance level, which is shown in fig. 1 as an exemplary plot 3 comprising the determined average chromaticity as a function of luminance level.

The brightness levels may be different from each other to any feasible extent, e.g. in units of one, ten, one tenth, etc., and the extent may further vary between different brightness values. Furthermore, the averaging of the chrominance values may be achieved in any feasible manner for the respective luminance levels, e.g. by calculating respective mean, median and/or weighted chrominance values for the respective luminance levels. Furthermore, averaging the chrominance values for a particular luminance level may comprise averaging all measured chrominance values, or a selected and/or predeterminable portion thereof, for said particular luminance level.

The phrase "determining respective average chromaticity values" may refer to "calculating and/or deriving respective average chromaticity values", whereas "average chromaticity values" may refer to "representative chromaticity values", and may also refer to "mean and/or median chromaticity values" and/or "weighted average chromaticity values", according to an example. On the other hand, the phrase "for different brightness levels" may refer to "for brightness levels different to a predeterminable extent", "for different ranges of brightness levels", "for at least a part of different brightness levels" and/or "for at least a predeterminable part of different brightness levels", while "brightness level" may refer to "brightness level". Further, "different brightness levels" may refer to "respective brightness levels" and/or "respective unique brightness levels". On the other hand, the phrase "averaging the corresponding measured chromaticity values based on each luminance level" may refer to "averaging the corresponding measured chromaticity values based on calculating an average, a weighted average, a mean, and/or a mean value for each luminance level", "averaging the corresponding measured chromaticity values based on averaging for each of a plurality of different luminance levels", and/or "averaging at least a portion and/or at least a predeterminable portion of the corresponding measured chromaticity values based on averaging for each luminance level".

As shown in fig. 1, the deviation analysis system 1 is adapted and/or configured, for example by means of a deviation determination unit 103 (as shown in fig. 3), to determine that the black level setting of the image sensor 21 deviates from the true black level when a chrominance deviation 5 from the respective average chrominance value 6 of the other luminance level 7 is indicated on the respective average chrominance value of the luminance levels of the range 4 to a predeterminable extent. Thus, by evaluating the determined average chromaticity values, it may be determined that the image sensor 21 has an erroneous black level setting that deviates from the true black level if the average chromaticity values for a portion 4 of the successive luminance levels deviate from the average chromaticity values 6 of the other luminance levels 7 (which may, for example, indicate a substantially constant chromaticity level) to an extent 5 that is considered sufficient. That is, given that the known "gray world" principle (e.g. as commonly used in white balance applications) has the underlying logic that the average surface color and/or reflectance in an image with sufficiently different surfaces is grey, using the concepts described herein, for a correct black level image sensor setting it may be desirable that the respective determined average chromaticity values are constant or substantially constant, i.e. have the same or substantially the same chromaticity level. However, in the case of an erroneous black level setting, the "gray world" principle would be expected to become invalid, especially in dark areas for e.g. low brightness levels, which are detected by using the concepts presented herein: it is determined that the determined average chrominance values (e.g. of the dark-space luminance levels) of one range 4 of luminance levels deviate 5 to a sufficient extent from the determined average chrominance values 6 (e.g. of the higher luminance levels) of the other luminance levels 7 (e.g. are expected to be substantially constant).

The brightness level of range 4 may be represented by any portion of the succession of measured brightness levels and may include any feasible number of brightness levels. Alternatively, the range 4 may comprise low brightness levels compared to the highest determined brightness level 71, for example brightness levels below fifteen percent, preferably below ten percent, more preferably below five percent of the highest determined brightness level 71. Thus, the gray world principle is expected to become ineffective due to erroneous black level settings as described above, especially in dark areas such as for low brightness levels, which are detected by using the concepts presented herein, by: it is determined that the determined average chrominance values (e.g. of the dark-space luminance levels) of one range 4 of luminance levels deviate 5 to a sufficient extent from the determined average chrominance values 6 (e.g. expected to be substantially constant) of the other, e.g. higher, luminance levels 7, so that a shift in the black level can be more easily detected for relatively low luminance levels.

The chromaticity deviation 5 may be represented by any feasible anomaly or anomalies of the determined average chromaticity value of the range of luminance levels 4 compared to the determined average chromaticity value 6 of the other luminance levels 7, for example by a deviation from a constant chromaticity level (as shown in the example of fig. 1). Assuming that the black level of the image sensor 21 is set much higher than the true black level, the chromaticity deviation 5 may (as exemplarily shown in fig. 1) be represented by a higher average chromaticity value for the luminance range 4 than the average chromaticity value 6 (which may be a constant chromaticity level) of the other luminance levels 7 of the measured luminance values. In contrast, in a similar manner, assuming that the black level setting of the image sensor 21 is set too low compared to the true black level, the chromaticity deviation 5 may be represented by a lower average chromaticity value for the luminance range 4 than the average chromaticity value 6 of the other luminance levels 7. Optionally, the chromaticity deviation 5 may include: the deviation of the respective average chromaticity values increases as the luminance level decreases. Thus, as shown in an exemplary manner in fig. 1, chroma anomaly 5 may increase as the luminance level decreases.

The chromaticity deviation 5 should differ from the respective average chromaticity values 6 of the other luminance levels 7 to an extent that is considered to reflect that the black level setting of the image sensor 21 deviates from the true black level, which extent can be arbitrarily selected when considered feasible and/or relevant, for example in view of the implementation at hand. The degree may for example be specified in magnitude and/or percentage and may further differ between brightness levels, e.g. the lower the brightness level the higher the deviation required. Furthermore, the true black level may be represented by any feasible luminance value and/or level applicable to the implementation at hand, e.g. zero or substantially zero. It may be noted that the luminance values derived from the image sensor 21 may in a generally known manner be provided with a spontaneous and/or intentional predeterminable offset (which may for example be set in dependence on the AD converter selection) in order to avoid that the luminance values derived from the image sensor 21 vary around zero. For example, when a 12-bit AD converter providing a resolution of 4096 in a known manner is used, the spontaneous offset may be set to an example value of 200, whereas when a 10-bit AD converter providing a resolution of 1024 in a known manner is used, the spontaneous offset may be set to an example value of 50. It should also be noted that such optional spontaneous luminance shifts may need to be compensated for (e.g. subtracted from) before the luminance values are further processed and/or handled.

The phrase "determining [ … ] that the black level setting of the image sensor deviates from a true black level" may refer to "identifying that the black level setting of the image sensor deviates from a true black level", while "when.. the respective average chromaticity value [ … ] indicates" may refer to "if and/or assuming that the respective average chromaticity value [ … ] indicates". Further, "respective chroma values of a range of luminance levels" may refer to "respective chroma values of a continuous range of luminance levels", and "a range of luminance levels" may refer to "a portion of a continuous luminance level". On the other hand, the phrase "indicating a chromaticity deviation to a predeterminable extent" may refer to "indicating and/or reflecting a chromaticity deviation to a predeterminable extent", "differing to a predeterminable extent" and/or "indicating a chromaticity deviation exceeding one or more predeterminable thresholds and/or standards". Further, the phrase "to a predeterminable extent" may refer to "a predeterminable magnitude and/or percentage". On the other hand, the phrase "chromaticity deviation from the respective average chromaticity values" may refer to "chromaticity anomalies from the respective average chromaticity values" and/or "a deviated chromaticity distribution compared to the respective average chromaticity values". Furthermore, according to an example, the phrase "chromaticity deviation from respective average chromaticity values of other luminance levels" may refer to "chromaticity deviation from constant or substantially constant average chromaticity values", "chromaticity deviation from respective average chromaticity values of other equivalent or substantially equivalent other of the other luminance levels", "chromaticity deviation from respective average chromaticity values of other and/or remaining luminance levels", and/or "chromaticity deviation from respective average chromaticity values of luminance levels of other ranges of luminance levels, which may be predetermined". Furthermore, the phrase "the black level setting of the image sensor is shifted from a true black level" may refer to "the black level setting of the image sensor has been shifted from a true black level", "the black level setting of the image sensor is shifted, deviated, and/or erroneous as compared to a true black level" and/or "there is an image sensor black level shift with respect to a true black level", and "a true black level" may refer to a "hypothetical and/or virtual true black level" and/or a "correct black level". Further, one and/or more "settings" throughout the disclosure may refer to "one or more parameters and/or configurations".

The determination of the black level shift can be done in various ways using the determined chromaticity deviation 5 as input. However, optionally, as shown in fig. 2 (which shows a schematic diagram of exemplary different candidates 9 of theoretical chromaticity shift according to embodiments of the present disclosure), the deviation analysis system 1 is adapted and/or configured, for example by means of a deviation comparison unit 104 (as shown in fig. 3), to compare the chromaticity shift 5 with one or more different candidates 9 of predetermined theoretical chromaticity shift expected for respective different ranges 4 of theoretical black level shift, in view of characteristics of the image sensor 21 and/or image processing settings. Then, the deviation analysis system 1 may be adapted and/or configured, for example by means of the offset determination unit 105 (as shown in fig. 3), to determine that the black level offset of the image sensor 21 is equal to the theoretical black level offset of the matching candidate 91, when the matching candidate 91 is found. Thus, by comparing the chromaticity deviation 5 with the predetermined theoretical candidates 9 and finding a match 91 among the predetermined theoretical candidates 9, the current black level shift of the image sensor 21 can be identified as the virtual black level shift of the match candidate 91, wherein the predetermined theoretical candidates 9 respectively have different virtual chromaticity deviations representing and reflecting the different virtual black level shifts.

The matching candidate 91 may be found by comparing at least a part of the chromaticity deviation 5 with at least a part of the one or more candidates 9 (at least partly overlapping the luminance value range 4). When a matching candidate 91 matches at least the chroma deviation 5 to a predeterminable degree, the candidate 91 may be further considered as matching. The respective one of the different candidates 9 may deviate based on a unique virtual black level and then the respective candidate may reflect a unique theoretical chromaticity deviation. Depending on the different theoretical black level deviations of the different candidates 9, the respective theoretical chromaticity deviations deviate from each other. Respective theoretical chromatic deviations may further and/or have been determined and/or calculated based on and/or taking into account characteristics and/or image processing settings corresponding to and/or expected to correspond to applicable and/or expected image sensors 21. For example, the different candidates 9 may be pre-stored, such as in an exemplary database, for example in the deviation analysis system 1, and/or may be retrieved with the support of the deviation analysis system 1.

One or more different candidates 9 may be represented by any arbitrary number of candidates 9. Furthermore, different candidates 9 may have been determined and/or calculated to provide a theoretical chromaticity deviation covering and/or extending along any arbitrary number of theoretical luminance levels and/or values, e.g. a variation along lower regions thereof and/or black regions. Moreover, the respective theoretical black level offsets of the different candidates 9 may each be represented by any arbitrary feasible different virtual offset deviating from the true black level, e.g. varying from an offset of one or two cells up to an offset of tens or even hundreds of cells. In the example of fig. 2, the first theoretical offset associated with the first candidate 91 (found here to be the matching candidate 91) is an offset (represented for example by a value of 2) that deviates (represented for example by a value of 0) from the positive two units of the true black level. In a similar manner, an exemplary second theoretical offset associated with the second candidate 92 is a positive one-unit offset (e.g., represented by a value of 1), while an exemplary third theoretical offset associated with the third candidate 93 is a negative one-unit offset (e.g., represented by a value of negative 1). Since the exemplary first and second candidates are based on a positive virtual offset, their respective associated virtual chromaticity bias 91, 92 may (as illustrated in exemplary fig. 2) include a chromaticity value and/or level that is greater than an exemplary constant chromaticity level 90 that is luminance independent, where the exemplary constant chromaticity level 90 represents an offset from the true black level of zero. In contrast, since the exemplary third candidate is based on a negative virtual offset, its associated virtual chromaticity bias 93 may (as illustrated in exemplary fig. 2) include chromaticity values and/or levels that are lower than the constant chromaticity 90 level.

The phrase "comparing the chromaticity shift" may refer to "comparing at least a portion of the chromaticity shift", while "different candidates" may refer to "different sets" and/or "different and/or unique candidates". On the other hand, the phrase "predetermined theoretical chromaticity deviation" may refer to "predeterminable and/or prestored theoretical chromaticity deviation", "predetermined virtual and/or imaginary chromaticity deviation" and/or "predetermined theoretical chromaticity deviation associated with luminance". According to one example, "theoretical chromaticity bias" may refer to "theoretical chromaticity distribution, model, curve, and/or plotted curve. Further, "theoretical chromaticity bias expected for the range" may refer to "theoretical chromaticity bias applicable, feasible and/or expected for the range," and "different theoretical black level shift" may refer to "different and/or unique theoretical black level shift", "different virtual and/or imaginary black level shift" and/or "different theoretical black level bias". On the other hand, the phrase "in view of characteristics and/or image processing settings of the image sensor" may refer to "in view of characteristics and/or image processing settings corresponding or substantially corresponding to those of the image sensor", "in view of expected characteristics and/or image processing settings of the image sensor", "related characteristics and/or image processing settings of the image sensor" and/or "based on characteristics and/or image processing settings of the image sensor", and further "in view of settings of the image sensor" according to one example. Further, the phrase "when a matching candidate is found" may refer to "when a matching candidate is found among the candidates," when a matching candidate is considered to be found, "and/or" when a matching candidate is found based on the chroma deviation being related to, consistent with, and/or similar to the matching candidate to a predeterminable degree. On the other hand, the phrase "the black level shift of the image sensor is equal to the theoretical black level shift of the matching candidate" may refer to "the black level shift of the image sensor is substantially equal to and/or close to the theoretical black level shift of the matching candidate".

The adjustment of the black level setting of the digital camera image sensor 21 may be done in various ways using as input the determined chromaticity shift 5 and the obtained knowledge of the deviation of the black level setting of said image sensor 21 from the true black level. Alternatively, however, the deviation analysis system 1 may be adapted and/or configured, for example by means of the offset adjustment unit 106 (as shown in fig. 3), to adjust the black level setting of the image sensor 21 based on the theoretical black level offset of the match candidate 91. Thus, based on the theoretical black level deviation of the found matching candidate 91 being identified as equal to or substantially equal to the current or substantially current black level offset of the image sensor 21, the image sensor black level setting may be adjusted accordingly to reflect the true or presumed true black level. The phrase "adjusting the black level setting" may refer to "setting the black level setting", and "based on the theoretical black level shift of the matching candidate" may refer to "based on the determined black level shift".

Further optionally, the deviation analysis system 1 may be adapted and/or configured, e.g. by means of the offset adjustment unit 106, to adjust the black level setting based on a theoretical black level offset of the matching candidate 91 when the chromaticity deviation of one or more further captured images matches the matching candidate 91. Thus, by considering a black level shift evaluation as described herein (which may similarly be found to match the match candidate 91) of one or more additional images before adjusting the image sensor black level setting, a method is provided that is considered more robust. The phrase "one or more further captured images" may refer to "one or more further images captured by the image sensor" and/or "one or more additional captured images".

As further shown in fig. 3, the deviation analysis system 1 may comprise a pixel measurement unit 101, an average determination unit 102, a deviation determination unit 103, an optional deviation comparison unit 104, an optional offset determination unit 105 and an optional offset adjustment unit 106, which have been described in more detail above. Further, embodiments herein for black level shift evaluation of the digital camera image sensor 21 may be implemented by one or more processors (e.g., processor 107, represented herein as a CPU) and computer program code for performing the functions and acts of embodiments herein. The program code may also be provided as a computer program product, for example in the form of a data carrier carrying computer program code, to perform embodiments herein when being loaded into the deviation analysis system 1. One such carrier may be in the form of a CD ROM disc, optical disc, solid state disc, flash memory and/or hard disk drive, although the use of other data carriers is also feasible. Furthermore, the computer program code may be provided as pure program code on a server and downloaded to the deviation analysis system 1. The deviation analysis system 1 may further comprise a memory 108, the memory 108 comprising one or more memory units. The memory 108 may be arranged to store, for example, information and further store data, configurations, schedules, and applications to perform the methods herein when executed in the bias analysis system 1. For example, the computer program code may be implemented in firmware of the embedded processor 107 that is stored in the flash memory 108. Furthermore, the unit 101, the optional processor 107 and/or the optional memory 108 may be at least partly comprised in, associated with and/or connected to the digital camera 2 and/or used for example in a monitoring system optionally comprising the digital camera 2. Those skilled in the art will also appreciate that the above-described means 101-106 may refer to a combination of analog and digital circuitry, and/or one or more processors configured with software and/or firmware, for example, stored in a memory such as the memory 108, that when executed by one or more processors such as the processor 107, performs as described herein. One or more of these processors and other digital hardware may be contained in a single application specific integrated circuit ASIC, or several processors and various digital hardware may be distributed in several separate components, whether packaged separately or assembled into a system on chip Soc.

Fig. 4 is a flow chart illustrating an exemplary method performed by the deviation analysis system 1 according to an embodiment of the present disclosure. The method is used for black level shift evaluation of the digital camera image sensor 21. Exemplary methods that may be repeated in succession include one or more of the following actions discussed in support of fig. 1-3. Further, where applicable, acts can be taken in any suitable order and/or one or more acts can be performed concurrently and/or in an alternating order.

Act 1001

In act 1001, the variance analysis system 1 (e.g., with the support of the pixel measurement unit 101) measures, for pixels of an image captured by the image sensor 21, a respective luminance value and a corresponding chrominance value for each pixel.

Act 1002

In act 1002, the variance analysis system 1 (e.g., with the support of the average determination unit 102) determines respective averaged chromaticity values for different ones of the measured luminance values based on averaging the corresponding measured chromaticity values for each luminance level.

Act 1003

In action 1003, when the respective average chromaticity value of the luminance levels of one range 4 indicates a chromaticity deviation 5 from the respective average chromaticity value 6 of the other luminance level 7 to a predeterminable extent, the deviation analysis system 1 (e.g. with the support of the deviation determination unit 103) determines that the black level setting of the image sensor 21 is shifted from the true black level.

Alternatively, the chromaticity deviation 5 may include a deviation of the respective average chromaticity values that increases with decreasing luminance levels.

Further optionally, the range 4 may comprise a low brightness level compared to the highest determined brightness level 71, for example a brightness level lower than fifteen percent, preferably lower than ten percent, and more preferably lower than five percent of the highest determined brightness level 71.

Act 1004

In an optional act 1004, the deviation analysis system 1 may compare (e.g., with the support of the optional deviation comparison unit 104) the chromaticity deviation 5 with one or more different candidates 9 of predetermined theoretical chromaticity deviations expected for respective different ranges 4 of theoretical black level shift in view of characteristics of the image sensor 21 and/or image processing settings.

Act 1005

In optional act 1005, which may be performed after optional act 1004, when a match candidate 91 is found, the deviation analysis system 1 may (e.g., with the support of the optional offset determination unit 105) determine that the black level offset of the image sensor 21 is equal to the theoretical black level offset of the match candidate 91.

Act 1006

In optional act 1006, which may be performed after optional act 1004 and/or optional act 1005, the deviation analysis system 1 may (e.g., with the support of optional offset adjustment unit 106) adjust the black level setting of the image sensor 21 based on the theoretical black level offset of the match candidate 91.

Optionally, the adjusting of act 1006 may include: when the chroma deviation of one or more further captured images matches the match candidate 91, the black level setting is adjusted based on the theoretical black level offset of the match candidate 91.

The person skilled in the art realizes that the present disclosure by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It should also be noted that the figures are not necessarily drawn to scale and that the dimensions of some features may have been exaggerated for clarity. Instead, emphasis is placed upon illustrating the principles of the embodiments herein. In addition, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.