阅读说明：本技术 图像处理装置 (Image processing apparatus ) 是由 下村健二 川岛正裕 于 2021-04-22 设计创作，主要内容包括：提供一种图像处理装置,具备：图像数据受理部(11),其受理图像数据；以及印刷数据生成部(17),其针对图像数据实施半色调处理来至少变换为3值以上的数据,从而生成多值化数据,其中,印刷数据生成部(17)实施除了构成图像数据的所有像素被变换为最大值的情况以外必定包含零值那样的所述半色调处理。(Provided is an image processing device provided with: an image data receiving unit (11) that receives image data; and a print data generation unit (17) that performs halftone processing on the image data to convert the image data into data of at least 3 values and generate multi-valued data, wherein the print data generation unit (17) performs the halftone processing such that all pixels constituting the image data always include zero values except when the pixels are converted to maximum values.)

1. An image processing apparatus includes:

an image data receiving unit that receives image data;

a print data generating section for generating multi-valued data by converting the image data into data of at least 3 values by applying halftone processing to the image data,

the print data generating unit performs the halftone processing so as to include a zero value without fail except when all pixels constituting the image data are converted to a maximum value.

2. The image processing apparatus according to claim 1,

the print data generation unit, in converting the image data into multi-valued data including an n value and an n +1 value according to the density of the image data, places an n +2 value at the same position as the n +1 value in accordance with an increase in the density of the image data after a pixel of zero value in the multi-valued data has reached a level of a predetermined number of pixels and addition of the pixel of the n +1 value is stopped.

3. The image processing apparatus according to claim 1,

the print data generation unit performs the halftone process such that a pixel of zero value is adjacent to a pixel of 1 value, and the pixels of 1 value are not continuous with 2 or more pixels.

4. The image processing apparatus according to claim 1,

the print data generation unit performs the halftone processing such that the larger the multivalued data corresponding to each pixel is, the smaller the proportion of the zero value included in the entire multivalued data is.

5. The image processing apparatus according to claim 1,

further comprising a binary error diffusion processing section for performing binary error diffusion processing on the image data before the print data generating section performs the halftone processing,

the print data generating unit sets, when the halftone processing is to be performed, a quantization value of a pixel determined to be white by the binary error diffusion processing unit and the multivalued data to zero values.

6. The image processing apparatus according to claim 5,

further comprising a white pixel density adjusting section for performing a white pixel density adjusting process for adjusting the density of the pixel determined to be white by the binary error diffusion process on the image data before the binary error diffusion process is performed by the binary error diffusion process section,

the binary error diffusion processing unit performs binary error diffusion processing on the image data subjected to the white pixel density adjustment processing.

7. The image processing apparatus according to claim 5,

the binary error diffusion processing unit sets the quantization value of the pixel determined to be white to a negative value, sets a quantization threshold value based on the negative value and the quantization value of the pixel determined to be black, and performs binary error diffusion processing.

8. The image processing apparatus according to claim 6,

the brighter the density of the image data is, the more sparse the density of the pixels determined to be white is.

9. The image processing apparatus according to claim 7,

the brighter the density of the image data is, the more sparse the density of the pixels determined to be white is.

10. The image processing apparatus according to claim 1, comprising:

a color mode information acquisition unit that acquires color mode information indicating whether to perform color printing or black-and-white printing based on the image data;

a paper type information acquiring unit that acquires paper type information indicating the type of printing paper on which printing processing based on the image data is performed,

wherein the print data generating section performs, as halftone processing including density unevenness suppressing processing for suppressing density unevenness of a print image, halftone processing that necessarily includes a zero value except for a case where all pixels constituting the image data are converted to a maximum value,

the print data generation unit switches between the halftone processing and another halftone processing including density unevenness suppression processing of which the degree of suppression of the density unevenness is different from the degree of suppression of the density unevenness of the halftone processing, based on the color pattern information and the paper type information.

11. The image processing apparatus according to claim 10,

when information indicating that the sheet is a printing sheet having a permeability of a threshold value or less is accepted as the sheet type information, the print data generation unit performs a halftone process including the density unevenness suppression process.

12. The image processing apparatus according to claim 10,

when information indicating that color printing is performed is accepted as the color mode information and information indicating that the permeability is a printing paper having a threshold value or less is accepted as the paper type information, the print data generation unit performs halftone processing including the density unevenness suppression processing for making print data of the K component not include the print data of the largest droplet as the other halftone processing.

13. The image processing apparatus according to claim 10, further comprising:

a K-component ink amount information calculation portion that calculates ink amount information of a K component based on the image data; and

a brightness calculation section that calculates brightness of color components other than the K component based on the image data,

the print data generating section switches between the plurality of other halftone processes based on the ink amount information of the K component and the lightness of the color component.

Technical Field

The present invention relates to an image processing apparatus that performs halftone processing on image data.

Background

Conventionally, there has been proposed an inkjet printing apparatus that performs a printing process by ejecting ink from an inkjet head onto a printing medium conveyed on a conveyance path.

In such an inkjet printing apparatus, an air flow is generated by conveying a printing medium directly below the inkjet head.

When ink is continuously ejected from the nozzles of the inkjet head, the ink droplets are ejected with a self-stream that acts like a wall and shields the stream of air generated by the conveyance of the print medium. Further, the air flow generated by the conveyance of the print medium may collide with the wall of the air flow itself, and the air flow may be extremely disturbed. Due to the turbulent air flow, the landing position of the ink ejected from the ink jet head is deviated from a desired position, and thus, a so-called air-jet uneven density may be generated.

As a method for correcting this concentration unevenness, japanese patent laid-open No. 2016-: when the image data has a high resolution and a density within a predetermined range, the resolution of the image data is converted into a low resolution according to the degree of generation of the self-air flow, thereby making the unevenness of the wind pattern inconspicuous.

Disclosure of Invention

Problems to be solved by the invention

However, when the image data is originally low-resolution, the method described in japanese patent application laid-open No. 2016-013645 cannot be applied. In addition, the method described in japanese patent application laid-open No. 2016-: in the region converted to the low resolution, the droplet size of the ink becomes large, so that the graininess is degraded, and a tone jump occurs in a boundary region where the resolution of the image data is switched to the low resolution. The tone jump is a phenomenon in which the gradation of an originally smooth gradation portion changes sharply and appears like a stripe.

In view of the above circumstances, an object of the present invention is to provide an image processing apparatus capable of suppressing uneven wind patterns even in low-resolution image data without causing deterioration in graininess and color tone jump.

Means for solving the problems

An image processing apparatus of the present invention includes: an image data receiving unit that receives image data; and a print data generation unit that performs halftone processing on the image data to convert the image data into data of at least 3 values and generates multi-valued data, wherein the print data generation unit performs halftone processing that includes density unevenness suppression processing for suppressing density unevenness of the print image, the halftone processing including halftone processing for necessarily including a zero value except for a case where all pixels constituting the image data are converted into a maximum value.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the image processing apparatus of the present invention, when image data is subjected to halftone processing and converted into data of at least 3 values to generate multi-valued data, since density unevenness is suppressed by performing halftone processing so as to include zero values without fail except when all pixels constituting the image data are converted into maximum values, it is possible to suppress wind unevenness even in low-resolution image data without causing deterioration in graininess and color jump.

Drawings

Fig. 1 is a block diagram showing a configuration of an inkjet printing apparatus using an embodiment of an image processing apparatus according to the present invention.

Fig. 2 is a block diagram showing a configuration of an image processing section as one embodiment of an image processing apparatus of the present invention.

Fig. 3 is a flowchart for explaining the processing of the inkjet printing apparatus using the image processing apparatus according to the embodiment of the present invention.

Fig. 4 is a diagram for explaining a concept of a general halftone process.

Fig. 5 is a diagram for explaining an example of the 1-drop removal process.

Fig. 6 is a diagram for explaining the concept of the halftone process including the first density unevenness suppressing process.

Fig. 7 is a flowchart for explaining an outline of the arithmetic processing of the halftone processing including the first density unevenness suppressing processing.

Fig. 8 is a diagram for explaining specific arithmetic processing of the halftone processing including the first density unevenness suppressing processing.

Fig. 9 is a flowchart for explaining specific arithmetic processing of the halftone processing including the first density unevenness suppressing processing.

Fig. 10 is a block diagram showing a configuration of an image processing section that performs halftone processing including the first density unevenness suppression processing of the second embodiment.

Fig. 11 is a diagram for explaining binary error diffusion processing based on the Floyd-Steinberg (freoude-Steinberg) method.

FIG. 12 is a diagram for explaining binary error diffusion processing equivalent to the Floyd-Steinberg method.

Fig. 13 is a diagram for explaining the multi-valued error diffusion process in the print data generation unit shown in fig. 10.

Fig. 14 is a flowchart for explaining the flow of the arithmetic processing of the halftone processing including the first density unevenness suppressing processing according to the second embodiment.

Fig. 15 is a block diagram showing a configuration of a modification of the image processing section shown in fig. 10.

Fig. 16 is a diagram for explaining an example of density conversion processing for adjusting the density of white pixels.

Fig. 17 is a diagram for explaining a method of adjusting the white pixel density in the binary error diffusion process.

Fig. 18 is a diagram showing a result obtained by applying a conventional multi-valued error diffusion process to a monochrome gradation image.

Fig. 19 is a diagram showing the result of applying the halftone process of the second embodiment to a monochrome gradation image.

Description of the reference numerals

1: an inkjet printing device; 10: an image processing unit; 11: an image data receiving unit; 12: a color conversion unit; 13: a color mode information acquisition unit; 14: a paper type information acquisition unit; 15: a K-component ink amount information calculating section; 16: a lightness calculation section; 17: a print data generation unit; 18: a binary error diffusion processing unit; 19: a white pixel density adjusting unit; 20: a head drive control section; 30: an ink jet head; 40: a conveying part; 50: a control unit.

Detailed Description

An inkjet printing apparatus 1 using an embodiment of an image processing apparatus according to the present invention will be described in detail below with reference to the drawings. Fig. 1 is a schematic configuration diagram of an inkjet printing apparatus 1 according to the present embodiment.

The inkjet printing apparatus 1 performs printing processing by ejecting ink onto printing paper based on image data output from a computer or image data output from a document reading apparatus. As shown in fig. 1, the inkjet printing apparatus 1 includes an image processing unit 10, a head drive control unit 20, an inkjet head unit 30, a conveying unit 40, and a control unit 50.

The image processing unit 10 receives image data output from a computer or a document reading apparatus, and performs various processes on the image data. In the present embodiment, the image processing unit 10 corresponds to one embodiment of the image processing apparatus of the present invention. The image Processing Unit 10 includes a CPU (Central Processing Unit) and a semiconductor memory. The CPU and the semiconductor memory of the image processing unit 10 may be shared with the control unit 50 described later, or may be provided independently.

The image processing unit 10 executes an image processing program stored in advance in a storage medium such as a semiconductor memory or a hard disk, and performs processing of each unit described later by operating an electric circuit.

As shown in fig. 2, the image processing unit 10 includes an image data receiving unit 11, a color conversion unit 12, a color mode information acquisition unit 13, a paper type information acquisition unit 14, a K component ink amount information calculation unit 15, a brightness calculation unit 16, and a print data generation unit 17.

The image data reception unit 11 receives RGB-format image data output from a computer or a document reading apparatus, and outputs the image data to the color conversion unit 12.

The color conversion section 12 converts the RGB format image data into CMYK format image data.

The color mode information acquiring unit 13 acquires color mode information indicating whether color printing or monochrome printing is performed based on the image data. The color mode information may be information set in a print job including the image data output from a computer, or information set and input by a user on an operation panel (not shown) provided in the inkjet printing apparatus 1. Alternatively, it may be acquired based on automatic recognition of color components contained in image data in the CMYK format.

The paper type information acquiring unit 14 acquires information on the type of printing paper on which printing processing based on image data is performed. In the present embodiment, information on a plurality of types of printing paper having different degrees of bleeding is acquired. Specifically, for example, information on plain paper and information on matte paper are acquired. In plain paper and matte paper, the degree of bleeding of plain paper is greater than that of matte paper. That is, matte paper is printing paper having an ink bleeding degree of a threshold value or less, and plain paper is printing paper having an ink bleeding degree greater than the threshold value. In the present embodiment, information on matte paper and plain paper is acquired, but the present invention is not limited to this, and information on printing paper other than matte paper may be acquired as the type of printing paper having an ink bleeding level of a threshold value or less. Further, as the printing paper having the degree of bleeding larger than the threshold value, information of printing paper other than plain paper may be acquired.

The K-component ink amount information calculating portion 15 calculates ink amount information of the K component based on image data of the K (black) component in image data of the CMYK format. In the present embodiment, the sum of all pixel values constituting the image data of the K component is calculated as the ink amount information of the K component.

The lightness calculation section 16 calculates the lightness of color components other than the K component based on the image data of the C (cyan), M (magenta), and Y (yellow) components in the image data of the CMYK format. The brightness calculation unit 16 of the present embodiment performs Lab conversion on the C component, the M component, and the Y component of each pixel constituting the image data, for example, to calculate the L value thereof. Then, the brightness calculation section 16 calculates an average value of the L values of the respective pixels as brightness.

The print data generation section 17 generates print data for inkjet printing based on image data in the CMYK format, and performs density unevenness suppression processing for suppressing density unevenness of a printed image. Specifically, the print data generating unit 17 of the present embodiment generates ink droplet data of each color as print data by applying halftone processing to image data of each of the C component, the M component, the Y component, and the K component. As the halftone processing, for example, dither mask processing using a dither method can be performed, but the halftone processing is not limited to this, and halftone processing by an error diffusion method may be performed. The ink droplet data is data that specifies the number of ink droplets ejected from 1 nozzle of the inkjet head to form 1 dot of a print image.

The print data generation unit 17 of the present embodiment performs density unevenness suppression processing for suppressing density unevenness of a print image when performing halftone processing. The concentration unevenness suppressing process of the present embodiment is a process of suppressing the above-described unevenness of the wind pattern.

The print data generation unit 17 according to the present embodiment can switch between a plurality of types of density unevenness suppression processes having different degrees of suppression of the wind unevenness, and can switch between these density unevenness suppression processes based on the color pattern information and the paper type information. Specifically, the print data generating section 17 of the present embodiment switches between 3 types of density unevenness suppressing processes having different degrees of suppression of the wind unevenness and a process of performing only a normal halftone process without performing the density unevenness suppressing process. In the present embodiment, the concentration unevenness suppression process with the highest degree of suppression of the wind unevenness is set as the first concentration unevenness suppression process, the concentration unevenness suppression process with the highest degree of suppression of the wind unevenness is set as the second concentration unevenness suppression process, and the concentration unevenness suppression process with the lowest degree of suppression of the wind unevenness is set as the third concentration unevenness suppression process.

The print data generation unit 17 of the present embodiment switches the density unevenness suppression processing in accordance with the combination of the color mode information (whether color printing or black-and-white printing) and the paper type information (whether plain paper or matte paper).

Here, the reason why the density unevenness suppressing process is switched according to the combination of the color mode information (whether color printing or monochrome printing) and the paper type information (whether plain paper or matte paper) as described above will be described. First, table 1 below shows the results of evaluating the uneven wind patterns corresponding to each combination when only the normal halftone process is performed without performing the density unevenness suppression process. Note that the evaluation result "a" of the uneven wind pattern shown in table 1 below means that the uneven wind pattern is not conspicuous, the evaluation result "B" means that the uneven wind pattern is inconspicuous, and the evaluation result "C" means that the uneven wind pattern is conspicuous. That is, the uneven wind distribution means that the uneven wind distribution is inconspicuous in the order of the evaluation results A, B and C.

[ Table 1]

As shown in table 1, when the type of printing paper was plain paper, the degree of penetration of the plain paper was large, and therefore the unevenness of the wind pattern appearing in stripes due to the deviation of the landing position of the ink was not noticeable, and the evaluation result was "a". On the other hand, when the type of printing paper is matte paper, since the matte paper has a smaller degree of penetration than plain paper, unevenness of air wrinkles becomes more noticeable than plain paper. In particular, since the difference in shade in black-and-white printing is larger than that in color printing, the moire unevenness in black-and-white printing is more noticeable than that in color printing. Therefore, as a result of the evaluation of the uneven wind pattern, the evaluation result is "B" in the case of the matte paper and the color printing, and the evaluation result is "C" in the case of the matte paper and the black-and-white printing.

In contrast, for example, in any combination shown in table 1, the air mark unevenness is inconspicuous as long as the first density unevenness suppression processing is performed, but in this case, only the processing time of the first density unevenness suppression processing requires a data processing time, and thus the printing processing speed is lowered. In particular, in the case of matte paper, high-resolution printing is often performed, and therefore the required printing processing speed is slow, but in the case of plain paper, printing with high resolution, unlike matte paper, is not performed, and therefore the required printing processing speed is fast.

Table 2 shows the evaluation results of the achievement degree of the required printing process speed when the first density unevenness suppressing process was performed in each combination. Note that the evaluation result "a" of the printing process speed shown in table 2 below means that the required printing process speed can be sufficiently achieved, the evaluation result "B" means that the required printing process speed can be achieved, and the evaluation result "C" means that the required printing process speed cannot be sufficiently achieved.

[ Table 2]

As shown in table 2, when the type of printing paper was plain paper, the evaluation result was "C" because the required printing processing speed was higher than that of matte paper. On the other hand, when the type of printing paper is matte paper, the evaluation result is "B" or "a" because the required printing processing speed is lower than that of plain paper. In the case of comparing color printing with monochrome printing, the processing time of the first density unevenness suppressing process in color printing is longer, and therefore the evaluation result is "B", and in the case of monochrome printing, the evaluation result is "a".

From the evaluation results in tables 1 and 2, in the present embodiment, the density unevenness suppressing process was switched as shown in table 3 so that both the evaluation results of the wind unevenness and the printing process speed were "a".

[ Table 3]

As shown in table 3, when the paper type information is plain paper, the print data generation unit 17 does not perform the density unevenness suppression processing and performs only the normal halftone processing because the air-jet unevenness is not noticeable regardless of the color mode information. This makes it possible to increase the data processing speed, and thus it is possible to sufficiently achieve a desired printing processing speed.

On the other hand, for example, when the paper type information is matte paper and the color mode information is black-and-white printing, the print data generation unit 17 performs the first density unevenness suppression process because the air-jet unevenness is most noticeable.

When the paper type information is matte paper and the color pattern information is color printing, the print data generating unit 17 performs the second density unevenness suppressing process or the third density unevenness suppressing process based on the ink amount information of the K component and the brightness of the color components other than the K component.

The contents of the first to third density unevenness suppressing processes and the switching between the second density unevenness suppressing process and the third density unevenness suppressing process will be described in detail later.

The image processing unit 10 is not limited to performing the above-described processing, and may perform various known image processing such as gamma correction processing and edge enhancement processing.

The head drive control unit 20 drives the ink jet head 30 to eject ink from each nozzle of the ink jet head of each color based on the ink droplet data of each color generated by the print data generation unit 17.

The ink jet head 30 includes a plurality of ink jet heads that eject ink of C, M, Y and K colors. As described above, each inkjet head is controlled by the head drive control unit 20 based on the drop data of each color to eject ink onto the print medium, thereby forming an image on the print medium.

The conveying unit 40 includes a conveying mechanism for conveying the print medium to the ink jet head unit 30.

The control Unit 50 includes a CPU (Central Processing Unit) and a semiconductor memory, and controls the entire inkjet printing apparatus 1. The control unit 50 controls the operations of the respective units of the inkjet printing apparatus 1 by operating an electric circuit while executing a control program stored in advance in a storage medium such as a semiconductor memory or a hard disk.

Next, the flow of the processing of the inkjet printing device 1 according to the present embodiment will be described with reference to the flowchart shown in fig. 3. Here, the description will be given mainly on switching of the first to third density unevenness suppressing processes.

First, a print job output from a computer or the like is input to the inkjet printing apparatus 1, and the image data reception unit 11 receives image data in RGB format included in the print job (S10).

Further, the color mode information set in the print job is acquired by the color mode information acquiring unit 13, and the paper type information set in the print job is acquired by the paper type information acquiring unit 14 (S12).

Then, the RGB-format image data received by the image data receiving unit 11 is input to the color conversion unit 12, and is converted into CMYK-format image data (S14).

Next, the print data generating section 17 performs halftone processing on the input CMYK format image data to generate ink droplet data of each color, but at this time, the density unevenness suppressing processing is switched based on the color pattern information and the paper type information.

Specifically, the print data generating unit 17 determines whether the color mode information is color printing or monochrome printing (S16), and if the color mode information is monochrome printing (S16, monochrome), determines whether the paper type information is plain paper or matte paper (S18). When the paper type information is matte paper (S18, matte paper), the print data generation unit 17 performs halftone processing including the first density unevenness suppression processing on the CMYK format image data (S20) to generate ink droplet data of each color.

On the other hand, when the paper type information is plain paper (S18, plain paper), the print data generation unit 17 performs normal halftone processing on the CMYK format image data without performing the density unevenness suppression processing (S22) to generate ink droplet data of each color.

When the color mode information is color printing (S16, color), the print data generating unit 17 determines whether the paper type information is plain paper or matte paper (S24). When the paper type information is plain paper (S24, plain paper), the print data generation unit 17 performs normal halftone processing on the CMYK format image data without performing the density unevenness suppression processing (S22) to generate ink droplet data for each color.

On the other hand, when the print data generating section 17 determines that the paper type information is matte paper (S24, matte paper), the K-component ink amount information calculating section 15 calculates the ink amount information of the K component based on the image data of the K component in the image data of the CMYK format (S26). Further, in the lightness calculation section 16, the lightness of the color component other than the K component is calculated based on the image data of the C component, the M component, and the Y component in the image data of the CMYK format (S26).

Then, the print data generating section 17 refers to a preset table based on the ink amount information of the K component and the lightness of the color components other than the K component (S28) to switch the density unevenness suppressing process. Table 4 below shows an example of the above table.

[ Table 4]

Ink amount information of K component	Lightness of color component other than K component	Processing content
			80～100	0～100	Usual halftone processing
40～80	0～50	Usual halftone processing
			40～80	50～80	Third concentration unevenness suppressing treatment
40～80	80～100	Second concentration unevenness suppressing treatment

As shown in table 4, for example, when the ink amount information of the K component is 80 to 100, the print data generating section 17 generates ink droplet data of each color by applying a normal halftone process to the image data of the CMYK format without performing the density unevenness suppressing process (S22). In this case, since the ink amount information of the K component is large, the degree of penetration is large even in the matte paper, and the air unevenness is not noticeable, and therefore, the density unevenness suppression processing is not performed regardless of the lightness (0 to 100).

For example, when the ink amount information of the K component is 40 to 80 and the lightness of the color components other than the K component is 0 to 50, the print data generating section 17 does not perform the density unevenness suppressing process, but performs a normal halftone process on the image data of the CMYK format (S22) to generate ink droplet data of each color. In this case, the ink amount information of the K component is small, but the lightness of the color components other than the K component is low. That is, when the lightness of the color components other than the K component is low, the ink amount of the color components other than the K component tends to be large, and therefore, the degree of bleeding tends to be large, and the shading difference also tends to be small, and therefore, the unevenness of the air flow is not noticeable. Therefore, in this case, the density unevenness suppressing process is not performed.

For example, when the ink amount information of the K component is 40 to 80 and the lightness of the color components other than the K component is 50 to 80, the print data generating unit 17 performs halftone processing including the third density unevenness suppressing processing (S30) to generate ink droplet data of each color. In this case, the ink amount information of the K component is small, and the lightness of the color components other than the K component is high to some extent. That is, when the lightness of the color components other than the K component is high to some extent, the ink amount of the color components other than the K component tends to be small, and the degree of bleeding is not so large, so that the unevenness of the air marks becomes conspicuous to some extent. Therefore, in this case, the halftone processing including the third density unevenness suppressing processing is performed.

For example, when the ink amount information of the K component is 40 to 80 and the lightness of the color component other than the K component is 80 to 100, the print data generating unit 17 performs halftone processing including the second density unevenness suppressing processing (S32) to generate ink droplet data of each color. In this case, the ink amount information of the K component is small, and the lightness of the color components other than the K component is high. That is, when the lightness of the color components other than the K component is high, the ink amount of the color components other than the K component tends to be small, and the degree of bleeding is small, so that the unevenness of the air flow is conspicuous. Therefore, in this case, the halftone processing including the second density unevenness suppressing processing is performed.

The density unevenness suppressing process corresponding to the combination of the ink amount information and the lightness of the color component other than the K component shown in table 4 is an example, and is not limited to this. In short, since the air-streak unevenness tends to be more conspicuous as the ink amount information is smaller, and the air-streak unevenness tends to be more conspicuous as the lightness of the color component other than the K component is larger, it is preferable that the density unevenness suppression process is performed to a greater degree to suppress the air-streak unevenness as the ink amount information is smaller and the lightness of the color component other than the K component is larger.

In this way, by switching the density unevenness suppressing process in accordance with the combination of the ink amount information of the K component and the lightness of the color component other than the K component, the density unevenness suppressing process can be switched in accordance with the degree of bleeding, and the wind unevenness can be more appropriately suppressed.

Then, the print data generating unit 17 inputs the ink droplet data of each color generated by performing the predetermined halftone process as described above to the head drive control unit 20.

The head drive control section 20 drives the ink jet head section 30 based on the input ink droplet data of each color to eject ink from each nozzle of the ink jet head of each color to form a print image (S34).

According to the inkjet printing apparatus 1 of the present embodiment, since the color mode information indicating whether color printing or black-and-white printing is performed is acquired, the information of the type of printing paper is acquired, and the density unevenness suppressing process is switched based on the acquired color mode information and paper type information, it is possible to suppress the wind unevenness and maintain the image quality, and it is possible to achieve a required printing process speed.

Further, according to the inkjet printing apparatus 1 of the present embodiment, since the density unevenness suppressing process is performed when information indicating that the printing paper has a permeability of a threshold value or less is accepted as the paper type information, the density unevenness suppressing process can be switched according to the degree of bleeding which affects the occurrence of the wind unevenness.

As described above, in the present embodiment, whether the image is a color print or a monochrome print is determined based on the color mode information, and the density unevenness suppressing process is switched according to the determination result. This is because, in the case of monochrome color, the amount of ink is small compared to full-color printing, and the mode of occurrence of uneven air flow is close to that in monochrome printing, as in monochrome printing.

Next, a normal halftone process performed by the print data generation unit 17 of the present embodiment and a halftone process including the first to third density unevenness suppression processes will be described.

First, a general halftone process is described. Since the normal halftone processing of the present embodiment is similar to the conventional halftone processing, detailed description thereof will be omitted, but the concept thereof will be described with reference to fig. 4. Here, although the maximum number of droplets of ink ejected to each pixel is 3 droplets, the actual maximum number of droplets is 5 droplets, 7 droplets, or the like. The conventional halftone process described here is a halftone process using a dither method, and is a halftone process using a 4 × 4 dither matrix.

Fig. 4 (1) to (49) are diagrams showing results obtained by applying the halftone processing to predetermined 4 × 4 pixels in the image data, and show the halftone processing results when the print density changes from the lowest density (zero) to the maximum density. As the number in brackets increases, the print density increases by 1 step each time. The 1 grid in each of (1) to (49) of fig. 4 represents 1 pixel.

Fig. 4 (1) to (17) show halftone processing results in the case where the print density changes from zero to the 17 th level. As shown in (1) to (17) of fig. 4, when the print density changes from zero to the 17 th level, 1 data of "1" is added every time the print density increases by 1 level in accordance with the distribution of each dither threshold of the dither matrix, and the data of "1" indicates that the number of ink drops is "1". When the print density is 17 levels, all pixels are set to data of "1".

Next, as shown in (18) to (33) of fig. 4, in the printing density from 18 levels to 33 levels, from the state of the data in which all the pixels are "1", every time the printing density increases by 1 level, the data of "2" is added by 1 for each distribution of the dither thresholds of the dither matrix, and the data of "2" indicates that the number of ink drops is "2". When the print density is 33 levels, all pixels are data of "2".

Next, as shown in (34) to (49) of fig. 4, in the printing density from 34 levels to 49 levels, 1 data of "3" is added every time the printing density increases by 1 level from the state where all the pixels are data of "2", and the data of "3" indicates that the number of ink drops is "3" according to the distribution of each dither threshold of the dither matrix. When the print density is 49 steps, all pixels are data of "3". That is, all pixels become the maximum value (maximum number of drops).

As described above, in the case of the conventional halftone processing, data of "2" or "3" is added in order after the print density is 18 levels, with all pixels being data other than 0 at the time point when the print density is 17 levels. That is, since the print density is 17 levels or less, zero values are not included between pixels, and the state where the density of printed dots is high is maintained, and thus the above-described state where self-air flow is easily generated by ink ejection is obtained, and there is no effect of suppressing the air unevenness. However, the arithmetic processing speed is higher because the arithmetic processing is simpler than the halftone processing including the first to third density unevenness suppression processing described later.

In addition, 1 additional print data is added for 4 or more data after 4 drops every time the print density increases by 1 step, as described above.

The above is a description of a normal halftone process using a dither matrix.

Next, halftone processing including the third density unevenness suppression processing will be described.

As described above, the third concentration unevenness suppression process is the concentration unevenness suppression process with the smallest suppression degree of concentration unevenness, but in the present embodiment, a so-called 1-drop removal process is performed as the third concentration unevenness suppression process. The 1-drop removal processing is processing for excluding data of 1 drop, which is the smallest droplet, from the ink droplet data. In the present embodiment, when the above-described normal halftone processing is performed, the 1-drop removal processing is performed only on the K-component ink droplet data. The reason why the 1-drop removal processing is performed only on the ink droplet data of the K component in this manner is to maximize the influence of the K component on the air streak unevenness and to increase the data processing speed.

As a method of the 1-drop removal process, for example, ink droplet data for 1 drop may be deleted simply by setting the ink droplet data for 1 drop included in the ink droplet data to "0". Further, without being limited to this, for example, as shown in fig. 5, when the ink droplet data of a predetermined pixel is ink droplet data of 1 droplet, the ink droplet data of 1 droplet may be deleted by converting the ink droplet data of the 1 pixel into ink droplet data of 2 pixels of "0" and "2". In addition, 1 square shown in fig. 5 indicates 1 pixel, and the numerical value within 1 square indicates the number of drops of the ink droplet data.

By converting the ink droplet data of "1" into the ink droplet data of 2 pixels of "0" and "2" as described above, the ink data of 1 droplet, which has a small amount of ink droplets and is likely to cause landing deviation, can be deleted, and thus the air mark unevenness can be suppressed. In addition, substantially the same concentration can be maintained. The method of removing 1 drop is not limited to the above-described method, and other known methods can be used.

The above is a description of the halftone process including the third density unevenness suppressing process.

Next, halftone processing including the second density unevenness suppression processing will be described.

As described above, the second concentration unevenness suppression process is a concentration unevenness suppression process whose suppression degree of concentration unevenness is second only than that of the first concentration unevenness suppression process, but in the present embodiment, a so-called 2-drop removal process is performed as the second concentration unevenness suppression process. The 2-drop removal processing is processing for excluding data of 1 drop and 2 drops from the ink drop data. In the present embodiment, when the above-described normal halftone processing is performed, the 2-drop removal processing is performed only on the K-component ink droplet data.

As a method of the 2-drop removal process, for example, the ink drop data of 1 drop and 2 drops may be deleted simply by setting the ink drop data of 1 drop and 2 drops included in the ink drop data to "0". Further, not limited to this, as in the 1-drop removal process, when the ink droplet data of a predetermined pixel is ink droplet data of 1 drop, the ink droplet data of 1 drop may be deleted by converting the ink droplet data of 1 pixel into ink droplet data of 2 pixels of "0" and "2", and the ink droplet data of 2 drops may be deleted by converting the ink droplet data of 2 drops into ink droplet data of 2 pixels of "0" and "3".

By converting the ink droplet data of "1" and "2" into the ink droplet data of 2 pixels of "0" and "3" as described above, it is possible to delete the ink data of 1 droplet and 2 droplets in which the ink droplet amount is small and landing deviation is likely to occur, and therefore it is possible to further suppress the wind unevenness as compared with the third density unevenness suppressing process. In addition, substantially the same concentration can be maintained. The method of the 2-drop removal process is not limited to the above-described method, and other known methods can be used.

The above is a description of the halftone process including the second density unevenness suppressing process.

As described above, when information indicating that color printing is performed is accepted as color mode information and matte paper is accepted as paper type information, since only the K component is subjected to halftone processing including 1-drop removal processing or 2-drop removal processing, it is possible to suppress wind streak unevenness by processing simpler than halftone processing including the first density unevenness suppression processing described later, and it is possible to increase the data processing speed, and thus it is possible to sufficiently achieve a required print processing speed.

Next, halftone processing including the first density unevenness suppression processing will be described.

The first concentration unevenness suppressing process is the concentration unevenness suppressing process in which the suppression degree of the concentration unevenness is the greatest as described above. First, the concept of the halftone process including the first density unevenness suppression process will be described with reference to fig. 6. Here, although the maximum number of ink droplets ejected to each pixel is 3 droplets, the actual maximum number of ink droplets is 5 droplets or 7 droplets. The halftone processing including the first density unevenness suppression processing described here is also halftone processing using a 4 × 4 dither matrix.

Fig. 6 (1) to (37) are graphs showing results obtained by applying halftone processing including the first density unevenness suppression processing to predetermined 4 × 4 pixels in image data, and show halftone processing results when the print density changes from the lowest density (zero) to the maximum density. As the number in brackets increases, the print density increases by 1 step each time. Here, for easy understanding of the description, it is assumed that all of the 4 × 4 pixels have the same density.

In the halftone processing including the first density unevenness suppressing processing, first, the number of ink droplets "1" is sequentially added in accordance with an increase in print density, but the addition of data of "1" is stopped in a state where a zero value remains. That is, the addition of the data of "1" is stopped when the number of zero-valued pixels becomes the level of the predetermined number of pixels.

Next, data of "2" is added in order according to the increase in print density, but in this case, the data is arranged in the same rule as the arrangement rule in the case of arranging the data of "1". Then, the addition of the data of "2" is stopped in a state where zero value remains. Further, data of "3" is sequentially added in accordance with the increase in print density, but in this case, the data is arranged in the same rule as the arrangement rule in the case of arranging the data of "2". Then, a state is assumed in which zero remains until the print density reaches the maximum density, and all pixels become maximum values at the time point when the print density reaches the maximum density ("data of 3"). Hereinafter, the description will be more specifically made with reference to fig. 6.

Fig. 6 (1) to (9) show halftone processing results in the case where the print density changes from zero to the 9 th level. As shown in (1) to (9) of fig. 6, when the print density changes from zero to the 9 th level, 1 data of "1" is added every time the density increases by 1 level in accordance with the distribution of each dither threshold of the dither matrix, and the data of "1" indicates that the number of ink drops is "1". Then, as described above, the addition of the data of "1" is stopped in a state where zero remains, and in this case, the addition of the data of "1" is stopped at a time point when the print density is 9 levels. The print density of the data for which the addition of "1" is stopped is not limited to 9 levels, and can be set to a level capable of suppressing the unevenness of the wind pattern.

Next, as shown in (10) to (21) of fig. 6, data of "1" or "0" is replaced with data of "2" in the printing density from level 10 to level 21.

First, as shown in (10) to (17) of fig. 6, in the printing density from 10 levels to 17 levels, for example, the same arrangement rule as that of the data of "0" in the case where the printing density changes from zero to 9 levels is used to replace the data of "1" with the data of "2". This enables the data of "1" to be replaced with the data of "2" while maintaining the number of zero values of 9 stages. Therefore, the effect of suppressing the uneven wind can be maintained, and the print density gradation can be smoothed, so that the tone jump can be suppressed. The tone jump is a phenomenon in which the gradation of an originally smooth gradation portion changes sharply and appears like a stripe.

Next, as shown in (18) to (21) of fig. 6, in the printing density from 18 levels to 21 levels, data of "0" is replaced with data of "2" in accordance with the distribution of the jitter thresholds of the jitter matrix. In the halftone processing including the first density unevenness suppression processing, the addition of the data of "2" is stopped in a state where zero remains as described above, but the data of "2" is stopped at a point in time when the print density is 21 levels. The print density of the data for which the addition of "2" is stopped is not limited to 21 levels, and can be set to a level capable of suppressing the unevenness of the wind pattern.

Further, the number of zeros at the time point when the addition of the data of "2" is stopped can be made smaller than the number of zeros at the time point when the addition of the data of "1" is stopped. This is because, as the number of ink droplets increases, the size of the ink droplets increases, and thus gaps between dots on the printing surface become small or overlap, and therefore, even if the landing positions are shifted by the influence of the air flow, uneven air lines are less likely to occur.

In addition, by performing the halftone processing such that the number of zeros at the time point when the addition of the data of "2" is stopped is smaller than the number of zeros at the time point when the addition of the data of "1" is stopped, that is, the proportion of zeros included in the whole multivalued data is reduced as the multivalued data is larger, the print density gradation can be increased, and the image quality of the printed image can be improved.

Next, as shown in (22) to (37) of fig. 6, data of "2" or "0" is replaced with data of "3" in the printing density from 22 levels to 37 levels.

First, as shown in (22) to (33) of fig. 6, in the printing density from 22 levels to 33 levels, from the state where the data of "2" of 21 levels is maintained, for example, the same arrangement rule as that of the data of "2" in the case where the printing density changes from 10 levels to 21 levels is used, and the data of "2" is replaced with the data of "3". Thus, the data of "2" can be replaced with the data of "3" while maintaining the number of zero values of 21 stages. Therefore, the effect of suppressing the uneven wind can be maintained, and the print density gradation can be smoothed, so that the tone jump can be suppressed.

Next, as shown in (34) to (37) of fig. 6, in the printing density from 34 levels to 37 levels, the data of "0" is replaced with the data of "3" in accordance with the distribution of the jitter threshold values of the jitter matrix. Then, a state is assumed in which zero remains until the print density reaches the maximum density, and all pixels become the maximum value at the time point when the print density reaches the maximum density ("data of 3").

As shown in (1) to (37) of fig. 6, when the print data generating unit 17 of the present embodiment performs the halftone processing including the first density unevenness suppressing processing, the halftone processing is performed so as to always include a zero value except for the case where all pixels constituting the image data are converted to the maximum value (the case of (37) of fig. 6). This makes it possible to reduce the generation of the self-air flow due to the ink ejection and suppress the air-jet unevenness, because the dot density of the printed dots can be made lower than that of the conventional halftone processing. Further, it was confirmed through experiments that the halftone treatment including the first density unevenness suppression treatment has a more moire unevenness suppression effect than the halftone treatment including the 1-drop removal treatment and the halftone treatment including the 2-drop removal treatment.

In addition, as shown in (1) to (9) of fig. 6, when converting data of "0" into data of "1", it is preferable that the pixel of data of "0" is adjacent to the pixel of data of "1" so that the pixels of data of "1" are not consecutive by 2 pixels or more in the vertical and horizontal directions. However, the arrangement of the data of "0" and the data of "1" depends on the density of each pixel of the image data. Therefore, for example, in the halftone processing, after each pixel of the image data is converted into data of "0" and "1" using the dither matrix, the following processing may be performed: the data of "1" is detected in a portion of 2 pixels or more continuous in the up-down direction or the left-right direction, and the data of "1" in the detected portion is converted into data of "0". Thus, the pixels of the data "1" are not continuous by 2 pixels or more in the vertical, horizontal, and vertical directions. This makes it possible to maintain a state where the density of printed dots is low without depending on image data.

Next, an outline of the arithmetic processing of the halftone processing including the first density unevenness suppression processing will be described with reference to a flowchart shown in fig. 7. The processing of the flowchart shown in fig. 7 is similar to the above-described normal halftone processing except for the specific arithmetic processing of the ink droplet data of S46.

First, the print data generating unit 17 sets the y coordinate of the pixel constituting the image data to 0(S40) and sets the x coordinate to 0 (S42). Further, the initial values of the x-coordinate and the y-coordinate of the pixels constituting the image data are zero.

Then, the density data [ x ] [ y ] of the pixel at the position of the x coordinate and the y coordinate set in S40 and S42, and the dither threshold Dth of the dither matrix Dth corresponding to the position of the x coordinate and the y coordinate are acquired (S44). For example, the position of the dither threshold value Dth in the dither matrix Dth is obtained by calculating the remainder obtained by dividing the x coordinate of data [ x ] [ y ] by the size in the x direction of the dither matrix Dth and the remainder obtained by dividing the y coordinate by the size in the y direction of the dither matrix Dth. The jitter matrix Dth and the jitter threshold Dth will be described in detail later.

Then, the print data generating section 17 calculates the ink droplet data corresponding to the density data [ x ] [ y ] by performing arithmetic processing using the density data [ x ] [ y ] and the dither threshold dth obtained in S44 (S46). The specific calculation processing will be described later.

Subsequently, the print data generator 17 adds 1 to the x coordinate (S48), and when the value of x is smaller than the size (x _ size) of the image data in the x direction (yes in S50), repeats the processing from S44 to S48.

When x is not less than x _ size in S50 (no in S50), the print data generation unit 17 adds 1 to the y coordinate (S52), and when the value of y is smaller than the y-direction size of the image data (y _ size) (yes in S54), the processing from S42 to S52 is repeated.

Then, at a time point when y ≧ y _ size in S54 (S54: NO), the print data generation section 17 ends the process. This enables the ink droplet data to be obtained for all the pixels constituting the image data.

Next, the operation processing of S46 in fig. 7 in the halftone processing including the first density unevenness suppression processing will be specifically described. Here, the density data of each pixel of the image data is set to 0 to 255, and converted to 0 to 3 ink drop data by performing halftone processing as shown in fig. 6.

First, the density threshold Th and the dither matrix Dth used in the halftone processing including the first density unevenness suppressing processing will be described. In the present embodiment, as shown in fig. 8, the concentration range of 0 to 255 is divided into 3 ranges. The values of the boundaries are set as density threshold values Th [0], Th [1], Th [2], and Th [3 ]. Th [0] is 0 and Th [3] is 255. Th [1] is a value for determining a print density range of data to which "1" is added by the halftone processing, and is a value for determining a print density range from 0 level to 9 levels shown in fig. 6. That is, the print density at which the addition of the data of "1" is stopped. For example, Th [1] is set to 30. When Th [1] is made large, the density of data of "1" is high, that is, the print dot density is high, and the moire unevenness occurs, and when Th [1] is made small, the moire unevenness does not occur any more, but the small dots are small and the graininess is large, so Th [1] is set to a value at which the balance between the moire unevenness and the graininess is obtained by an experiment or the like.

Th 2 is a value for determining the print density range of data to which "2" is added by the halftone processing, and is a value for determining the print density range from 10 levels to 21 levels shown in fig. 6. That is, the print density at which the addition of the data of "2" is stopped. For example, Th [2] ═ 110 is set. As for Th [2], similarly to Th [1], a value in which a balance between the uneven wind pattern and the graininess is obtained is set by an experiment or the like.

In the present embodiment, concentration range index m is 0 for Th [0] to Th [1], concentration range index m is 1 for Th [1] to Th [2], and concentration range index m is 2 for Th [2] to Th [3 ]. The concentration range index m is 0 to 2, and is used in the following description of a specific calculation process.

Next, in the present embodiment, halftone processing is performed using 3 dither matrices Dth [1], Dth [2] and Dth [3] according to 3 density ranges of image data.

The dither matrix Dth [1] is a dither matrix for converting image data in a first density range of 0 to 105 into data of "0" or "1" by halftone processing. The dither matrix Dth [1] is obtained by normalizing a dither matrix formed by a blue noise mask with a density value in a first density range of 0 to 105. For example, when 1 threshold of a dither matrix formed by a blue noise mask is Dth and 1 threshold corresponding to the dither matrix Dth [1] is Dth [1], the calculation is performed by the following equation. In the present embodiment, the dither matrix formed by the blue noise mask is used, but a halftone dot type dither matrix may be used.

dth [1] (first normalized value × dth)/256

The first normalized value in the above equation is a value for controlling the speed at which the dots become dense. For example, when the first normalization value is 256, and when dth is 10 or 100, dth [1] is 10 or 100, but when the first normalization value is 128, dth [1] becomes 5 or 50, which is smaller than the threshold value, and is easier to print. That is, this means that the smaller the first normalized value is, the faster the speed of densification becomes. In the present embodiment, 105 is set as the first normalization value.

The dither matrix Dth [2] is a dither matrix obtained by converting image data in a second density range of 30 to 135 into data of "2" by halftone processing. The dither matrix Dth 2 is obtained by normalizing a dither matrix formed by a blue noise mask with a density value in a second density range of 30 to 135. For example, when 1 threshold of a dither matrix formed by a blue noise mask is Dth and 1 threshold corresponding to the dither matrix Dth [2] is Dth [2], the calculation is performed by the following equation. Note that the meaning of the second normalized value is the same as that of the first normalized value, and in the present embodiment, 105 is set as the second normalized value.

dth 2 ═ second normalized value x dth)/256

The dither matrix Dth [3] is a dither matrix obtained by converting image data in a third density range of 105 to 255 into data of "3" by halftone processing. The dither matrix Dth [3] is obtained by normalizing a dither matrix formed by a blue noise mask with a density value in a third density range of 105 to 255. For example, when 1 threshold of a dither matrix formed by a blue noise mask is Dth and 1 threshold corresponding to the dither matrix Dth [3] is Dth [3], the calculation is performed by the following equation. Note that the meaning of the third normalized value is similar to that of the first normalized value, and in the present embodiment, the third normalized value is 255 to Th [2 ]. By setting such a value, it is possible to set the full print data of the ink droplet to "3" when the density data is 255.

dth 3 ═ (third normalization value × dth)/256

Fig. 8 shows an area (0, 1 drop area) converted into ink drop data of "0" and "1", an area (0, 1, 2 drop area) converted into ink drop data of "0", "1" and "2", an area (0, 2 drop area) converted into ink drop data of "0" and "2", an area (0, 2, 3 drop area) converted into ink drop data of "0", "2" and "3", and an area (0, 3 drop area) converted into ink drop data of "0" and "3".

Next, halftone processing using the density threshold values Th [0] to Th [3] and the dither matrices Dth [1] to [3] will be described with reference to a flowchart shown in fig. 9.

First, the print data generating unit 17 acquires density data of a predetermined pixel constituting the image data, and determines to which of the density range indexes m0 to 2 the density data belongs (S60). Specifically, m satisfying data < Th [ m +1] with Th [ m ] being not more is determined.

Next, the print data generation unit 17 calculates the above-mentioned dth 1 to dth 3 (S62).

Then, when the value of m determined in S64 is zero (S64: YES), the density data of the pixel is compared with the dither threshold value Dth [1] of the dither matrix Dth [1] of the position corresponding to the pixel, and when the data > Dth [1] (S66: YES), the ink droplet data of the pixel is set to "1" (S68).

On the other hand, if data ≦ dth [1] (S66: NO), the ink droplet data for the pixel is set to "0" (S70).

When the value of m determined in S64 is not zero (no in S64), the print data generation unit 17 compares a value (data-Th [ m ]) obtained by subtracting Th [ m ] from the density data of the pixel with the dither threshold value Dth [ m +1] of the dither matrix Dth [ m +1] at the position corresponding to the pixel (S72). data-Th [ m ] is an operation for setting the density data of the pixel as input data with reference to Th [ m ].

When the input data is larger than dth [ m +1] (S72: YES), the print data generation unit 17 sets the ink droplet data of the pixel to m +1 (S74).

Specifically, for example, when m is 1, the print data generation unit 17 compares data-Th [1] with dth [2 ]. Then, when data-Th [1] is larger than dth [2], the ink drop data of the pixel is set to 2. Thus, data of "2" shown in (10) to (21) of fig. 6 is arranged.

On the other hand, in the case of data-Th [ m ] ≦ dth [ m +1] in S72 (S72: No), the dither threshold value dth [ m ] of the dither matrix D [ m ] of the position corresponding to the above-mentioned pixel is compared with Th [ m ] -Th [ m-1] (S76).

Here, regarding Th [ m ] -Th [ m-1], for example, Th [1] -Th [0] when m is 1, indicates a concentration interval from the start of addition of data of "1" to the stop of addition of data of "1" as shown in (1) to (9) of fig. 6. Then, as shown in (10) to (17) of fig. 6, the data of "2" needs to be arranged at the same position as the data of "1", and this is achieved by arranging the data of "2" based on the condition of S72.

However, when the condition of S72 is not satisfied, it is necessary to maintain the concentration at the Th 1 time point. Therefore, if the data of "2" is not arranged in S72, the data of "1" needs to be arranged at the position where the data of "1" is arranged at the time point of Th [1 ].

Therefore, if the data of "2" is not arranged in S72, the data of "1" is arranged if the jitter threshold dh [1] for the data of "1" in the comparative formula of S76 is smaller than the density of the data of "1" whose addition is stopped (S78). This is because, in the case where the jitter threshold dh [1] is smaller than Th [1] -Th [0], it indicates that data of "1" has been arranged at that position.

On the other hand, in the comparative formula of S76, if dth m ≧ Th m-1, the ink droplet data of the pixel is set to 0 (S80).

Thus, when the density data of a pixel of the image data is a density section in which m is 1, the data can be converted into data of "0", "1", or "2". That is, the data of "0" can be mixed together, and the print density variation can be smoothed.

In the above description, although the case where m is 1 has been described, the density data in the density range where m is 2 can be converted into data of "0", "2", or "3" by performing the processing based on the comparison formula of S72 and S76 even when m is 2. That is, the data of "0" can be mixed together, and the print density variation can be smoothed.

The above is a description of the halftone processing including the first density unevenness suppressing processing.

Next, another embodiment of the halftone process including the first density unevenness suppression process will be described. Note that the halftone process including the first density unevenness suppression process described above is defined as a first embodiment, and another embodiment described below is defined as a second embodiment.

The halftone processing including the first density unevenness suppression processing of the first embodiment performs the halftone processing using the dither method as described above, but the halftone processing including the first density unevenness suppression processing of the second embodiment performs the halftone processing using the multi-value error diffusion method. In the case of the halftone processing using the dither method as in the first embodiment, a memory capacity for storing a dither matrix is required. For example, in the case of using a 256 × 256 dither matrix, a memory capacity of 64 kbytes is required. In contrast, since the multi-value error diffusion process does not need to store a dither matrix, the memory capacity can be reduced, and the arithmetic process can be realized by simple hardware, so that the entire hardware can be reduced. Further, the memory capacity required for the multivalued error diffusion processing is described in detail later.

Fig. 10 is a block diagram showing a configuration of an image processing section 10 that performs halftone processing including the first density unevenness suppression processing of the second embodiment. The print data generating unit 17 shown in fig. 10 also performs halftone processing so as to always include a zero value except when all pixels constituting the image data are converted to the maximum value (maximum number of drops) as in the first embodiment, but the image processing unit 10 shown in fig. 10 includes a binary error diffusion processing unit 18 in order to perform such halftone processing. The print data generating section 17 shown in fig. 10 performs the multilevel error diffusion process based on the processing result of the binary error diffusion processing section 18, thereby performing the halftone process that always includes the zero value as described above.

Before the print data generating unit 17 performs the halftone processing, the binary error diffusion processing unit 18 performs binary error diffusion processing on the C, M, Y and K image data. As the binary error diffusion process, for example, a binary error diffusion process based on the Floyd-Steinberg method using diffusion coefficients as shown in fig. 11 is known, but in the second embodiment, the binary error diffusion process is performed using a method equivalent thereto. As shown in fig. 11, the Floyd-Steinberg method is a method of multiplying peripheral pixels by diffusion coefficients to disperse errors occurring in a pixel of interest, but in the second embodiment, as shown in fig. 12, a method of multiplying errors of peripheral pixels by diffusion coefficients to assign them to a pixel of interest is used. In this method, the error err _ bin assigned to the pixel of interest is expressed by the following equation. Furthermore, err _ mem0[ ] in the following equation is a memory that holds the error of the first 1 line of the pixel of interest, err _ pre is the error of the first 1 pixel of the pixel of interest, and err _ mem1[ ] is a memory that holds the error used for the next 1 line of the pixel of interest.

err_bin＝err_mem0[x-1]*1/16+err_mem0[x]*3/16+err_mem0[x+1]*5/16+err_pre*7/16

When the density data of the pixel of interest is D, the pixel data Derr to which the error is assigned is expressed by the following equation.

Derr＝D+err_bin

When Derr >127, the color is determined to be black, and the quantization value is 255. On the other hand, when Derr is less than or equal to 127, it is determined to be white, and the quantization value is set to 0.

Then, err _ mem1[ x ] ═ err is calculated as err _ Derr-quantized value, and err _ pre is set as err.

By performing the binary error diffusion process by the above-described arithmetic processing, a total of 2 lines of memories of err _ mem0[ ] and err _ mem1[ ] can be used as hardware. Further, if the error storage timing (timing) is shifted, the error of the pixel of interest can be written back in the use completion area of err _ mem0[ ] after the error is read, and therefore, a memory of substantially 1 line is sufficient. The error assigned to the pixel in the 1 st row (y is 0) may be set in advance.

Then, the binary error diffusion processing unit 18 applies binary error diffusion processing to the C, M, Y and K image data, and as a result, adds a white pixel flag to the pixel determined to be white, that is, the pixel whose quantization value is 0.

When the halftone processing is performed by the multi-value error diffusion processing, the print data generation unit 17 sets the pixel determined to be white by the binary error diffusion processing unit 18 to a zero value without fail. Next, the multi-value error diffusion process in the print data generating section 17 will be described.

Similarly to the binary error diffusion process, the print data generation unit 17 quantizes the density data of each pixel using a quantization threshold value, and calculates an error from the quantization value and the density data.

Specifically, when the quantization value is q [ i ], the quantization threshold value is q _ th [ i ], and the density data of each pixel is D, each value can be set as shown in fig. 13, for example, when the maximum drop number is 3.

Further, similarly to the binary error diffusion process, when the error assigned to the target pixel from the peripheral pixel is err _ mlt, the value of i for determining which one of the quantization thresholds q _ th [0] to q _ th [2] shown in fig. 13 is used is obtained by the following equation. Further, INT () is a function that rounds a decimal point or less to return a maximum integer not exceeding the original number.

i＝INT((D+err_mlt)*maxdrop/255)

For example, as shown in fig. 13, when D + err _ mlt is 150, i is calculated by the following equation, and i is 1.

i＝INT(150*3/255)＝INT(1.76)＝1

At this time, the quantization threshold is quantized as q [1] ═ 85 or q [2] ═ 170 using q _ th [1] ═ 127 and D + err _ mlt ═ 150, but since D + err _ mlt ═ 150 is larger than q _ th [1] ═ 127, the quantization value is q [2] ═ 170. Then, the multivalued data (ink droplet data) becomes "2" corresponding to q [2] 170.

More specifically, first, after the above Derr is calculated, the value of i is calculated. Then, if i > maxdrop, i is set to maxdrop. Then, in the case of i ═ maxdrop, the quantized value is q [ maxdrop ], and the multivalued data is maxdrop.

When the value is not i ═ maxdrop, it is checked whether or not a white pixel flag is added to the pixel, and when the white pixel flag is added, zero is calculated as the quantization value of the pixel, and the multi-valued data is also zero. In addition, although the quantization value is zero for the pixel to which the white pixel flag is added as described above, the error between the input density and the quantization value is compensated for by the peripheral pixels, and therefore the density does not decrease in the feature of error diffusion.

On the other hand, when the white pixel flag is not added, when Derr > q _ th [ i ], q [ i +1] is calculated as a quantization value, and the multivalued data is i + 1. In the case where Derr is less than or equal to q _ th [ i ], q [ i ] is calculated as a quantization value, and multivalued data is i.

Next, the flow of the arithmetic processing of the halftone processing using the above-described multilevel error diffusion processing will be described with reference to a flowchart shown in fig. 14.

First, the print data generating unit 17 sets the y coordinate of the pixel constituting the image data to 0(S90) and sets the x coordinate to 0 (S92). Further, the initial values of the x-coordinate and the y-coordinate of the pixels constituting the image data are zero.

Then, binary error diffusion processing is performed on the density data of the pixels at the positions of the x-coordinate and the y-coordinate set in S90 and S92 (S94). When it is determined to be white, a white pixel flag is added to the pixel (S96).

Next, the multi-valued error diffusion processing is performed on the density data of the pixel at the x-coordinate and y-coordinate positions set in S90 and S92, and the multi-valued data of the pixel is calculated (S98). In the multi-value error diffusion process, the white pixel flag added in S96 is referred to as described above.

Subsequently, the print data generation unit 17 adds 1 to the x coordinate (S100), and when the value of x is smaller than the size (x _ size) of the image data in the x direction (yes in S102), repeats the processing from S94 to S100.

When x is not less than x _ size in S102 (no in S102), the print data generation unit 17 adds 1 to the y coordinate (S104), and when the value of y is smaller than the y-direction size of the image data (y _ size) (yes in S106), the processing from S92 to S104 is repeated.

Then, at a time point when y ≧ y _ size in S106 (S106: NO), the print data generation section 17 ends the process. This makes it possible to obtain multivalued data (ink droplet data) for all pixels constituting the image data.

Next, a modified example of the halftone processing using the multi-valued error diffusion processing of the second embodiment will be described. In the halftone processing using the multilevel error diffusion processing of the second embodiment, the binary error diffusion processing is performed to add a white pixel flag to a pixel determined to be white, and the multivalued data is forcibly set to zero for this pixel, but for example, the density of the white pixel is originally high for a portion with a bright density, and therefore, when the processing as described above is performed, the quantization values of the multivalued error diffusion processing for almost all the pixels become zero. In such a state, in the process of the multi-level error diffusion process, errors of pixels whose quantized values become zero are accumulated, and the quantized values suddenly become large in a printable area. For example, in a portion where the density is bright, it is desirable to mix 0 drops and 1 drop, but it becomes 0 drops and 3 drops, resulting in deterioration of graininess of the printed image.

Therefore, in the modification of the second embodiment, the density of the white pixels is not excessively increased after the binary error diffusion process. Fig. 15 is a diagram showing a configuration of a modification of the image processing unit 10 according to the second embodiment. As shown in fig. 15, the image processing unit 10 according to the second embodiment further includes a white pixel density adjusting unit 19.

The white pixel density adjusting unit 19 performs density conversion processing as white pixel density adjustment processing on each of the inputted C, M, Y and K image data. Specifically, as shown in fig. 16, the white pixel density adjusting unit 19 performs the following density conversion processing on each image data: the brighter or darker the input density of the image data, the more sparse the density of the pixels determined to be white is, and the maximum the density of the pixels determined to be white is at the intermediate density.

In the graph shown in fig. 16, the output density is controlled to be a white pixel density sufficient to reduce the wind unevenness at the intermediate density, and the output density with respect to the input density is darker (the white pixel density is more sparse) at a portion brighter than the intermediate density, and the output density with respect to the input density is darker (the white pixel density is more sparse) at a portion darker than the intermediate density. The density conversion process may be implemented by a lookup table or a function such as a predetermined linear expression.

Then, the binary error diffusion processing unit 18 performs binary error diffusion processing on each image data subjected to the density conversion processing by the white pixel density adjusting unit 19. Other configurations of the modification of the second embodiment described above are the same as those of the second embodiment.

According to the modification of the second embodiment, the brighter the input density of the image data is, the more sparse the density of the pixels determined to be white is, and therefore, the deterioration of graininess can be prevented.

The method of adjusting the density of the white pixel after the binary error diffusion process is not limited to the above method, and the density of the pixel determined to be white may be adjusted in the binary error diffusion process unit 18.

Specifically, the quantization value of the pixel determined as white is set to a negative value, and a quantization threshold is set based on the negative value and the quantization value of the pixel determined as black, and binary error diffusion processing is performed. Specifically, as shown in fig. 17, the quantization value of the pixel determined to be white is set to a negative value white _ dens (for example, -20), and the quantization threshold value (137) is calculated based on the negative value white _ dens and the quantization value black _ dens (255) of the pixel determined to be black, and binary error diffusion processing is performed. When the quantized value is set to a negative value (-20) as described above, the error is equal to 20 from the input density (0) to the quantized value (-20) even if the input density is 0, for example, and therefore a positive error is assigned to the peripheral pixel. That is, the density of the white pixels becomes sparse by the action of making the density of the peripheral pixels dense.

By performing such binary error diffusion processing on a portion where the intermediate density is bright in contrast in the image data, the density of the white pixel after the binary error diffusion processing can be thinned. Thus, similarly to the above modification, deterioration of graininess can be prevented even in a portion where the density is bright.

Fig. 18 a to 18D are diagrams showing results obtained by applying a conventional multi-value error diffusion process to a monochrome gradation image. Fig. 18 a to 18D are diagrams obtained by extracting a part of the gradation image subjected to the multilevel error diffusion process, and the density gradually decreases from a to D. A of fig. 18 includes a portion shifted to the maximum density. If only the conventional multi-value error diffusion processing is performed, the wind unevenness is liable to occur in the concentration range R.

Fig. 19 a to 19D are diagrams showing results obtained by applying the halftone processing according to the second embodiment to the same single-color gradation images as those in fig. 18 a to 18D. In fig. 19 a to 19D, all but the portion converted to the maximum density are converted so as to include a white pixel (zero value). In particular, it is found that the fully printed portion in fig. 19B and 19C includes white pixels. This can suppress the influence of the wind unevenness in the concentration range R.

The following remarks are also disclosed with respect to the image processing apparatus of the present invention.

(attached note)

In addition, the image processing apparatus of the present invention may include: a color mode information acquisition unit that acquires color mode information indicating whether to perform color printing or black-and-white printing based on the image data; and a paper type information acquiring unit that acquires paper type information indicating information of a type of printing paper on which a printing process based on the image data is performed, wherein the printing data generating unit performs a halftone process that includes a density unevenness suppressing process for suppressing density unevenness of the printed image, the halftone process including a zero value that is always included except when all pixels constituting the image data are converted to a maximum value, and the printing data generating unit switches between the halftone process and another halftone process that includes a density unevenness suppressing process for suppressing density unevenness of the printed image, based on the color pattern information and the paper type information, the other halftone process including a density unevenness suppressing process for suppressing density unevenness to a degree different from a degree of suppressing density unevenness of the halftone process.

In the image processing apparatus according to the present invention, the print data generating unit may perform the halftone process including the density unevenness suppressing process when receiving information indicating that the sheet is a print sheet having a permeability of a threshold value or less as the sheet type information.

In the image processing apparatus according to the present invention, the print data generating unit may perform, as the other halftone processing, halftone processing including density unevenness suppressing processing for suppressing density unevenness of print data not including a droplet in K-component print data when information indicating that color printing is performed is received as color mode information and information indicating that permeability is equal to or less than a threshold value is received as paper type information.

In addition, the image processing apparatus of the present invention may further include: a K-component ink amount information calculating portion that calculates ink amount information of the K component based on the image data; and a brightness calculation unit that calculates brightness of color components other than the K component based on the image data, wherein the print data generation unit is capable of switching between the plurality of other halftone processes based on the ink amount information of the K component and the brightness of the color components.

In the image processing apparatus according to the present invention, the print data generating section may be configured to, in the process of converting the image data into multi-valued data including an n value (n is an integer equal to or greater than 0) and an n +1 value in accordance with the density of the image data, place the n +2 value at the same position as the n +1 value in accordance with an increase in the density of the image data after the pixel having a zero value in the multi-valued data is changed to a level of a predetermined number of pixels and the increase in the n +1 value is stopped.

In the image processing apparatus of the present invention, the print data generating unit may perform the halftone process such that a pixel of zero value is adjacent to a pixel of 1 value, and the pixel of 1 value is not continuous by 2 or more pixels.

In the image processing apparatus according to the present invention, the print data generating section may perform the halftone processing such that the larger the multi-valued data corresponding to each pixel is, the smaller the proportion of zero values included in the whole multi-valued data is.

In the image processing apparatus according to the present invention, the image processing apparatus may further include a binary error diffusion processing unit that performs binary error diffusion processing on the image data before the print data generating unit performs the halftone processing, and the print data generating unit may set the quantization value and the multi-valued data of the pixel determined to be white by the binary error diffusion processing unit to zero values when performing the halftone processing.

In the image processing apparatus according to the present invention, the binary error diffusion processing section may perform binary error diffusion processing on the image data, and the white pixel density adjusting section may perform binary error diffusion processing on the image data after the binary error diffusion processing section performs binary error diffusion processing on the image data.

In the image processing apparatus according to the present invention, the binary error diffusion processing unit may set the quantization value of the pixel determined as white to a negative value, and set the quantization threshold value based on the negative value and the quantization value of the pixel determined as black, thereby performing the binary error diffusion processing.

In the image processing apparatus according to the present invention, the density of the pixel determined to be white may be made lower as the density of the image data is higher.