JP2020121443A - Image processing device, image processing method and program - Google Patents

Abstract

To properly control a degree of overlapping of dots between colors according to features in an image.SOLUTION: An image processing device for determining arrangement of dots on each of a plurality of kinds of color materials by using a threshold value matrix based on an image corresponding to each of the plurality of color materials, has: acquisition means for acquiring an output value of a pixel of interest corresponding to a first color for which arrangement of dots has been determined among the plurality of kinds of color materials; calculation means for calculating an exclusion control value for controlling degree of exclusion of dots in the pixel of interest in a second color for which arrangement of dots has not been determined among the plurality of kinds of color materials based on the output value of the pixel of interest corresponding to the first color and the pixel value of the pixel of interest in the first color; and determination means for determining an output value corresponding to the second color of the pixel of interest based on the pixel value, the exclusion control value, and the threshold value matrix of the pixel of interest in the second color.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image processing technique for generating quantized data for forming an image on a recording medium.

A dither method is known as a quantization method when an image is recorded using the pseudo gradation method. The dither method uses a threshold matrix formed by arranging threshold values associated with individual pixels, compares these threshold values with the pixel values indicated by the image data, and records or does not record dots for each pixel. It is a way to decide.

Patent Document 1 describes a method of avoiding excessive dot duplication and improving dispersibility by considering the arrangement of dots of other colors when performing quantization using a threshold matrix. Specifically, when quantization is performed for each color using a distributed threshold matrix, the threshold is shifted based on the dot arrangement of the colors determined in advance to exclusively determine the dots between colors. To do.

International publication number WO2002/005545

However, according to the method described in Patent Document 1, when dots are formed so as to be mutually exclusive between different colors in a region where the pixel value changes abruptly, such as an edge portion of an image, dots of a color having a high priority are edged. Easy to concentrate on the part. As a result, low-priority color dots are arranged around the edge portion, which may cause a decrease in sharpness and local coloring.

Therefore, an object of the present invention is to appropriately control the degree of dot overlap between colors when quantizing images of different colors according to the characteristics of the images.

In order to solve the above problems, the present invention is an image processing device for determining the arrangement of dots for each of the plurality of types of color materials using a threshold matrix based on the images corresponding to each of the plurality of color materials. An acquisition unit that acquires the output value of the pixel of interest corresponding to the first color of which the dot arrangement is determined among the plurality of types of color materials; and the output value of the pixel of interest corresponding to the first color, For controlling the degree of exclusion of dots in the target pixel for the second color of which the dot arrangement is not determined among the plurality of types of color materials based on the pixel value of the target pixel in the first color A calculation unit that calculates an exclusive control value, and an output value corresponding to the second color of the target pixel is determined based on the pixel value of the target pixel in the second color, the exclusive control value, and the threshold matrix. It is characterized by having a determining means.

According to the present invention, the degree of dot overlap between colors can be appropriately controlled according to the characteristics of an image.

Schematic diagram of recording device and recording head Block diagram for explaining the control configuration Flowchart for explaining the image processing steps It is a block diagram for explaining a software configuration. Flowchart for explaining the steps of the quantization processing Diagram showing an example of the threshold matrix 409 Diagram showing an example of the processing area The figure which shows an example of gradation data Ik, Ic, and Im. The figure which shows an example of the quantization process of K ink. Diagram showing the process of C ink quantization It is a block diagram for explaining a software configuration. Flowchart for explaining the steps of the quantization processing A diagram showing an example of division of the processing target area Figure showing a concrete example of quantization processing The figure which shows an example of the quantization process of K ink. The figure which shows an example of the quantization process of C ink. The figure which shows an example of the quantization process of M ink. The figure which shows an example of the quantization process of Y ink. Diagram showing results of inter-color exclusion processing and suppression processing

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not necessarily limited to the configurations shown in the drawings.

<First Embodiment>
1A and 1B are schematic views of a recording apparatus 100 and a recording head 102 used in this embodiment. The recording apparatus 100 used in this embodiment is a serial type inkjet recording apparatus. In the figure, the x direction represents the main scanning direction of the recording head, the y direction represents the transport direction of the recording medium S, and the z direction represents the ejection direction of the color material (ink). As shown in FIG. 1B, in the print head 102, nozzle rows for ejecting cyan (C), magenta (M), yellow (Y), and black (K) inks are arranged in parallel in the x direction. Has been done. Further, in each nozzle row, a plurality of nozzles 101 for ejecting ink in the z direction according to print data are arranged in the y direction. As shown in FIG. 1A, the recording head 102 is mounted on a carriage 103, and the carriage 103 can move in a ±x direction along a carriage shaft 107. While the carriage 103 moves in the ±x direction, the recording head 102 ejects ink from the ejection ports 101 according to the recording data, so that an image for one band is recorded on the recording medium S. A platen 105 made of a flat plate is arranged at a position facing the ejection port surface of the recording head 102. The platen 105 supports the recording medium S in the area to be recorded by the recording head 102 from the back surface, and keeps the distance between the ejection port surface of the recording head 102 and the recording medium S constant.

When the recording scan for one band by the recording head 102 is completed, the two sets of conveying rollers 104 that sandwich the recording medium S rotate to convey the recording medium in the +y direction by a distance corresponding to the one band. An image is gradually formed on the recording medium S by alternately repeating the recording scan for one band by the recording head 102 and the conveying operation of the recording medium S by the conveying roller 104 as described above.

FIG. 2 is a block diagram for explaining the control configuration in this embodiment. The image processing apparatus 200 includes a host PC and the like, and the CPU 201 executes various processes according to a program stored in the HDD 203, which is a nonvolatile storage unit, while using the RAM 202, which is a volatile storage unit, as a work area. For example, the CPU 201 generates recording data that can be recorded by the recording device 100 according to a command received from the user via the keyboard/mouse I/F 205 or a program held in the HDD 303, and outputs this to the recording device 100. Further, the information received from the recording device 100 via the data transfer I/F 204 is displayed on a display (not shown) via the display I/F 206.

On the other hand, in the recording device 100, the CPU 211 executes various processes according to a program stored in the ROM 213, which is a nonvolatile storage unit, while using the RAM 212, which is a volatile storage unit, as a work area. The recording apparatus 100 further includes an image processing accelerator 216 for performing high-speed image processing and a head controller 215 for controlling the recording head 102. The image processing accelerator 216 is hardware that can execute image processing faster than the CPU 211. The image processing accelerator 216 is activated by the CPU 211 writing parameters and data required for image processing to predetermined addresses in the RAM 212, reads the parameters and data, and then executes predetermined image processing on the data. However, the image processing accelerator 216 is not an essential element, and equivalent processing may be executed by the CPU 211.

The head controller 215 supplies recording data to the recording head 102 and controls the recording operation of the recording head 102. The head controller 215 is activated by the CPU 211 writing print data and control parameters that can be printed by the print head 102 to a predetermined address of the RAM 212, and executes an ejection operation according to the print data.

The carriage controller 217 controls the movement of the carriage 103 in the ±x directions according to the instruction of the CPU 211. Further, the transport controller 218 controls the rotation of the transport roller 104, that is, the transport of the recording medium S according to the instruction of the CPU 211.

As a connection method for the data transfer I/F 204 of the image processing apparatus 200 and the data transfer I/F 214 of the recording apparatus 100, USB, IEEE1394, LAN, or the like can be used.

FIG. 3 is a flowchart for explaining an image processing process executed by the CPU 201 of the image processing apparatus 200 when a print command is generated. This processing is executed by the CPU 201 while using the RAM 202 as a work area according to a program stored in the HDD 203. Hereinafter, each step in the flowchart will be referred to as “S”.

When this process is started, the CPU 201 first acquires image data created by an application program or the like and expands it in the RAM 202. In the present embodiment, it is assumed that image data having pixel values of 8 bits (256 gradations) indicating the brightness of each of red (R), green (G), and blue (B) is acquired for each pixel. Hereinafter, image data composed of pixels having pixel values of a plurality of components such as R, G, and B in this manner will be expressed as RGB data using the components.

In step S301, the CPU 201 executes color correction processing on the image data expanded in the RAM 202. The color correction process is a process for converting image data expressing a standardized color space such as sRGB into image data associated with a color space recordable by the recording apparatus 100. Specifically, the CPU 201 refers to a three-dimensional RGB look-up table stored in advance to convert RGB data having a pixel value of 8 bits (256 gradations) into R data having a pixel value of 8 bits (256 gradations). Convert to'G'B' data.

In S302, the CPU 201 executes color conversion processing on the R'G'B' data generated in S301. The color conversion processing is performed by converting R′G′B′ data indicating luminance information into densities of K, C, M, and Y corresponding to colors (hereinafter, ink colors) of color materials used by the recording apparatus 100. This is a process for converting into data indicating information. Specifically, the CPU 201 refers to a pre-recorded three-dimensional look-up table, and outputs R′G′B′ data of 8 bits (256 gradations) of each pixel for each KCMY of 8 bits (256 gradations). Convert to data. The data corresponding to each ink color that has undergone color conversion processing is collectively called KCMY data.

In S303, the CPU 201 performs a quantization process on the KCMY data generated in S302. Although the quantization process will be described in detail later, by this quantization process, 8-bit (256 gradations) KCMY data is converted into 1-bit K′C′M′Y′ data. In the present embodiment, the K′C′M′Y′ data is binary data that specifies dot recording (1) or non-recording (0) for each pixel for each ink color of KCMY.

In S304, the CPU 201 outputs the K′C′M′Y′ data generated in S303 to the recording device 100 as recording data. This is the end of the process.

Upon receiving the print data, the CPU 211 of the printing apparatus 100 expands the print data in the RAM 212. Then, while controlling the head controller 215, the carriage controller 217, and the transport controller 218, an image is recorded on the recording medium according to the recording data developed in the RAM 212. Although each process shown in each step of FIG. 3 is processed in the inkjet recording system of the present embodiment, it is not necessary to distinguish which process is performed by the host PC 200 and which process is performed by the printer 100. It can be set arbitrarily. For example, when the host PC 200 performs the quantization up to the quantization, the quantized data may be transferred to the printer 100. Further, depending on the performance of the printer 100, it is also possible to directly receive multi-valued RGB image data and perform all the steps of S300 to S304.

FIG. 4 is a block diagram for explaining a functional configuration in the quantization processing of this embodiment. The role of each block will be briefly described below. The KCMY data generated by the ink color separation processing of S302 is input to the area selection unit 401 for each ink color. Hereinafter, the data for each ink color forming the KCMY data is referred to as gradation data in this specification. Each gradation data has the same number of pixels, and the number of pixels in the vertical direction and the number of pixels in the horizontal direction are also the same. In FIG. 4, the first color is black (K), the second color is cyan (C), the third color is magenta (M), and the fourth color is yellow (Y).

The pixel selection unit 401 sets one pixel as a target pixel from the gradation data composed of a plurality of pixels. Then, the gradation value of each color corresponding to the set target pixel is provided to the ink color selection unit 402. That is, here, when the pixel of interest is set, the pixel selection unit 401 outputs the gradation values of the pixel of interest corresponding to four colors to the ink color selection unit 402.

The ink color selection unit 402 refers to the quantization order information 408 stored in the memory, selects a processing target color from the first to fourth colors, and corresponds to the processing target region of the selected ink color. The gradation data is provided to the threshold processing unit 403. The quantization order information 408 is information indicating the color order in which the quantization process is executed.

The threshold processing unit 403 uses the threshold matrix 409 stored in advance in the memory to execute the quantization processing for each pixel. FIG. 6 is a diagram showing a part of the threshold matrix 409 used in this embodiment. In the threshold matrix 409, a plurality of thresholds having different values are randomly arranged so as to correspond to each pixel. By associating the threshold matrix 409 with the image to be processed in a tile shape, each pixel in the image is associated with any threshold. Further, the threshold value processing unit 403 uses the same threshold value matrix 409 in correspondence with the same position for the gradation data of each of CMYK colors.

The exclusive processing unit 404 controls the threshold value corresponding to the color to be processed next so that the dots of different colors do not overlap in the pixel of interest as much as possible. Therefore, the exclusion processing unit 404 updates the threshold value corresponding to the target pixel each time the threshold processing unit 403 quantizes the gradation value of the target pixel.

The contrast calculation unit 405 calculates a contrast value having a correlation with the degree of contrast in a nearby region including the pixel of interest. The contrast is high when the difference between the gradation values is large in the nearby region, and the contrast is low when there is not much difference between the gradation values. The exclusion control unit 406 controls the degree of the exclusion effect by the exclusion processing unit 404.

The quantized data creation unit 407 generates quantized data that can be recorded by the recording apparatus 100 based on the dot arrangement data generated by the threshold processing unit 403, and outputs the quantized data to the recording apparatus 100 as recording data. The quantized data of each color mentioned here corresponds to the K′C′M′Y′ data described in the flowchart of FIG.

Note that, in FIG. 4, the memory is shown by integrating the nonvolatile HDD 203 and the volatile RAM 202 in the image processing apparatus 200 described in FIG. 2. Further, each block described above is substantially a functional unit in software executed by the CPU 201 shown in FIG. In the following description, it is assumed that a single dot size is used and 1-bit quantized data indicating dot ON/OFF for each pixel is generated for each of CMYK.

FIG. 5 is a flowchart for explaining the processing steps executed by the CPU 201 in the quantization processing of S303 using the blocks shown in FIG. Hereinafter, the quantization processing executed in the present embodiment will be described in detail according to the flowchart shown in FIG. 5 with reference to FIGS. 6 and 7A to 7K.

When this process is started, first, in step S501, the pixel selection unit 401 selects a pixel (x, y) to be processed from the image to be printed as a pixel of interest.

Next, in step S502, the ink color selection unit 402 sets a processing target color from black (first color), cyan (second color), magenta (third color), and yellow (fourth color). The color order to be set for the color to be processed is stored in advance in the memory of the HDD 203 as the quantization order information 408, and the ink color selection unit 402 changes the quantization order information 408 to a new color each time this process is performed. Set according to the color order shown. Here, the quantization order is K→C→M→Y.

In step S<b>503, the threshold processing unit 403 acquires the gradation value I(x, y) of the processing target color corresponding to the pixel of interest from the gradation data obtained by the color separation processing (step S<b>302 in FIG. 3 ). In the present embodiment, the gradation data will be described as 8-bit data in which gradation values of 0 to 255 are stored for each pixel.

In step S504, the threshold processing unit 403 acquires the threshold th used for the quantization processing of the pixel of interest. The threshold value corresponding to the pixel of interest (x, y) is expressed as a threshold value th(x, y).

Next, in step S505, the threshold processing unit 403 determines the output value indicating ON/OFF of the dot in the target pixel by comparing the gradation value I(x, y) with the threshold th(x, y). .. More specifically, if I(x,y)>th(x,y), the process proceeds to S507, and the dot of the pixel of interest (x,y) is turned ON (output value=1) in S507. On the other hand, if I(x, y)≦th(x, y), the process proceeds to S506, and the dot of the target pixel (x, y) is turned OFF (output value=0) in S506.

Next, in step S508, the exclusion processing unit 404 changes the threshold value th(x, y) corresponding to the target pixel used in the subsequent processing target color. More specifically, the threshold value th(x, y) is set to the threshold value th'(x, y) so that it becomes difficult to arrange dots of other colors in the pixel of interest (x, y) whose dot is turned on in S507. And update. In the present embodiment, the exclusive processing unit 404 updates the threshold value by the expression (1).
th'=th(x,y)-I(x,y) (1)

When the maximum value 255 of the grayscale data is added to the threshold value th′ calculated here and used for the quantization processing, the threshold value th′ is larger than the original threshold value th in the pixel in which the dots are arranged. Therefore, it becomes difficult to arrange dots in the subsequent processing, and the exclusive effect is obtained. The exclusive control unit saves the new threshold th(x, y) in the memory. The fact that the dots between the colors are exclusively arranged in the pixel of interest by updating the threshold value will be described later.

Next, in step S509, the contrast calculation unit 405 calculates the cumulative gradation data S for each pixel included in a predetermined area centered on the pixel of interest. For example, assume that the pixel 701 is the target pixel in the input image 700 as shown in FIG. At this time, the contrast calculation unit 405 sets a block of 3 pixels×3 pixels around the pixel of interest 701 as a processing area. If the pixel position is at the edge of the image, such as the pixel 702, and a processing area of 3 pixels×3 pixels cannot be secured, a smaller block such as 2×2 is used as the processing area. In the present embodiment, the contrast calculation unit 405 calculates the sum of the gradation value of the processed color and the gradation value I of the color to be processed in the target pixel as the cumulative gradation data S.

For example, assume that the target color of interest in the target pixel is K. In the present embodiment, since the quantization order is K→C→M→Y, the processed color does not yet exist in the pixel of interest, and the cumulative gradation data S of each pixel in the processing region is the gradation value Ik of the K ink. Becomes When the target color is C ink, the sum of the gradation value Ik of the K ink of the processed color and the gradation value Ic of the target color C ink of the target pixel is cumulative for each pixel in the processing area. It is calculated as gradation data S. Similarly, when the color to be processed in the target pixel is M ink, the sum of the gradation value Ik, the gradation value Ic, and the gradation value Im is calculated as cumulative gradation data for each pixel in the processing area. Furthermore, when the target color of the pixel of interest is Y ink, the sum of the gradation values Ik, Ic, Im, and Iy is calculated as cumulative gradation data for each pixel in the processing area. FIG. 8 shows an example of the gradation values Ik, Ic, and Im of the K, C, and M inks of each pixel in the processing area. Here, when the color to be processed in the pixel of interest is M ink, the cumulative gradation data S of each pixel calculated in S509 has the values shown in FIG.

Next, in step S510, the contrast calculation unit 405 calculates the contrast value cnt indicating the contrast in the processing area based on the cumulative gradation data S of each pixel in the processing area. Specifically, in this embodiment, the contrast value cnt is calculated by the following equation (2). However, of the cumulative gradation data S of each pixel in the processing area, the maximum value is max_S and the minimum value is min_S.
cnt=(max_S-min_S)/(max_S+min_S) (2)

However, when max_S=0, cnt=0. The contrast value cnt calculated by the equation (2) is a value between 0 and 1, and the higher the contrast in the processing area, the larger the value.

In step S511, the exclusion control unit 406 performs a process of suppressing the intensity of the exclusion process for the pixel of interest based on the contrast cnt in the processing region corresponding to the pixel of interest. More specifically, the threshold value th(x, y) corresponding to the pixel of interest is further updated so that the change in the threshold value in S508 is canceled as the value of the contrast value cnt corresponding to the processing region is larger (the contrast is higher). To do. In the present embodiment, the exclusive control unit 406 calculates a new threshold th″ by the following equation (3) and stores the threshold th″ in the memory as the threshold corresponding to the pixel of interest.
th″=th′(x,y)+I(x,y)×cnt (3)

In Expression (3), I(x, y)×cnt functions as an exclusive control value that controls the degree of exclusion. That is, the threshold value th′ for exclusively arranging the dots is maintained for the pixels having a low contrast value (low contrast) in the neighboring region. On the other hand, the threshold value th'is updated for a pixel having a high contrast value (high contrast) in the neighboring area. In particular, when the contrast value of the pixel of interest is 1, the threshold value is updated to the original threshold value th. Details of this processing will be described later.

Next, in step S512, the exclusion controller 406 determines whether the threshold th″(x, y) is smaller than 0. When the threshold value th″(x, y) is smaller than 0, the process proceeds to S513. In step S513, the exclusive control unit 406 sets a value obtained by adding the upper limit value i_max (here, 255) in the grayscale data to the threshold value th″(x, y) as a new threshold value th″″ so that the pixel of interest is selected. Update the threshold. On the other hand, when the threshold value th″(x, y) is 0 or more, S513 is skipped and the process proceeds to S514.

Next, in step S514, the ink color selection unit 402 determines whether or not the quantization processing for all the colors has been performed on the pixel of interest according to the quantization order 408. If the quantization processing of all colors in the pixel of interest is completed, the process proceeds to S515. If there is an unprocessed color, the process proceeds to S502, the color to be processed in the pixel of interest is selected, and the quantization process in the pixel of interest is continued.

In S515, the quantized data creation unit 407 outputs the quantized value of each color of the pixel of interest to the RAM 212. In step S516, the pixel selection unit 401 determines whether or not the quantization processing has been performed on all the pixels of the input image. For example, when pixels are selected in order from the upper left, it may be determined whether or not the quantized data of the lower right pixel has been created. If the result of determination is that quantization processing has been executed for all pixels of the input image, quantization processing ends. If there are uncreated pixels, the process returns to S501 to newly select the pixel of interest and continue the quantization process.

The quantization processing in this embodiment will be specifically described below with reference to FIGS. 9 and 10. FIG. 9A shows gradation data of K ink in the partial area of the input image. A rectangle represents one pixel, and a gradation value is stored in each pixel. FIG. 9B shows a threshold group corresponding to the partial area shown in FIG. 9A. FIG. 9C shows the result of the K ink quantization process. In FIG. 9C, the black-painted pixels indicate that K ink dots (hereinafter, simply referred to as K dots) are arranged (the output value is 1). Since the K ink is the first color, the output value is 1 for the pixel whose gradation value of each pixel is larger than the corresponding threshold value. When performing the K ink quantization process, at least a part of the threshold value corresponding to each pixel is updated by the processes of S508 to S514. FIG. 9D shows the threshold value th′ set by the equation (1) in S508. For the pixel having an output value of K ink of 0, the threshold value is not changed and the same threshold value as that shown in FIG. 9B is held. On the other hand, for a pixel having an output value of K ink of 1, a value obtained by subtracting the gradation value from the threshold value is stored as the threshold value th'. Here, the output value being 1 means that the gradation value of the pixel is larger than the threshold value. Therefore, the threshold value th'will always be a negative value for a pixel having an output value of 1.

FIG. 9E shows the contrast value cnt of each pixel calculated in S510. However, what is the processing area for calculating the contrast value? An area of 3 pixels×3 pixels centered on the pixel of interest is set. A pixel having a flat (no change in pixel value) and low contrast in a nearby region has a small contrast value (0.00). It can also be seen that the higher the contrast in the neighboring region, the higher the contrast value.

FIG. 9F shows the threshold value th″ calculated based on the exclusion control value that controls the strength of the exclusion process. However, when th″<0, i_max=255 is added to th″. As a result of the exclusive control, a K dot is arranged like the lower right pixel in the partial region, and for a pixel with low contrast, a value larger than the original threshold value 19 is adopted as the threshold value. Further, it can be seen that the K dot is arranged like the lower two pixels in the second column and the pixel having a low contrast has a value smaller than the original threshold value and the strength of the exclusion process is suppressed. Further, for pixels in which K dots are not arranged, such as the upper right pixel and the pixel in the second column and the second row, a value smaller than the original threshold value is adopted.

Next, C ink is selected as the color to be processed. FIG. 10A shows gradation data of C ink in the same partial area as the partial area shown in FIG. 9A.

In the present embodiment, not the threshold value group shown in FIG. 9B, but the threshold value group after exclusive control shown in FIG. 9F is used to quantize each gradation value of the C ink shown in FIG. 10A. To do. The result of the quantization in this embodiment is shown in FIG. Here, in order to explain the effect of this embodiment, a result of quantization using the threshold value group shown in FIG. 9B is shown in FIG. FIG. 9C shows the result of quantization using the threshold value th′ after the exclusion process. It should be noted that FIG. 10 shows that dots of C ink (hereinafter referred to as C dots) are arranged in pixels filled in black in the drawing.

From FIG. 9C and FIG. 10B, when the tone values of the respective colors are quantized using the same threshold value group, C dots are formed in any pixel in which K dots are formed. I understand that it will be done. That is, when the same threshold value group is used for different ink colors, the overlapping rate of dots of different colors increases. 9(a) and 10(a) both have a 1-pixel-width line in the second column from the left, especially when the characteristics of the grayscale data are similar, the same threshold value group is used to quantize. If it is changed, the dot overlap rate tends to increase. However, when the recording apparatus 200 ejects ink onto the recording medium based on the quantized data, dot overlap and paper white exposure are mixed in a flat area. As a result, the contrast is high even though the area is flat, and the overlapping dots may deteriorate the graininess and deteriorate the image quality. In the partial area shown in FIG. 10B, the right three columns are flat areas, and there is a possibility that image quality may deteriorate due to overlapping of dots. In addition, the paper white increases due to the increased number of overlapping dots, and the desired density may not be achieved.

Here, when the gradation value of each pixel is quantized using the threshold value th′ after the exclusive processing shown in FIG. 9D, the quantized data shown in FIG. 10C is obtained. As described above, for the exclusion effect, when the threshold value th'<0, th_ is quantized by adding i_max=255. From FIG. 9C and FIG. 10C, it can be seen that when the threshold th′ after the exclusion process is used, the C dot is not formed in the pixel in which the K dot is formed. That is, it is understood that the dots of different colors are mutually exclusively arranged by changing the threshold value in S508. By exclusively arranging the dots between the colors as described above, it is possible to suppress deterioration of the graininess in a flat region.

On the other hand, it may not be preferable to arrange dots of different colors mutually exclusively in a high-contrast region. For example, in the grayscale data shown in FIGS. 9A and 10A, the grayscale value of the second column from the left is larger than the grayscale values of the other columns, and a K+C line is formed. .. However, when the recording apparatus 200 ejects ink onto the recording medium based on the quantized data of the C ink shown in FIG. 10C, a high density line where K and C overlap is supposed to be formed. Nevertheless, there is no dot where the K ink and the C ink overlap. As a result, since the K dots and the C dots are arranged dispersedly, the partial area has a flat density. As a result, the K+C line is difficult to perceive on the recording medium.

Therefore, in the present embodiment, a process of controlling the exclusion degree of intercolor dots for each pixel is performed based on the contrast in S511. FIG. 10D shows quantized data of C ink obtained by the threshold matrix after exclusive control shown in FIG. 9F for the threshold group after exclusive control. From FIGS. 9C and 10D, the K+C line is reproduced by overlapping the dots in the vicinity of the K+C line with high contrast, while the C dot and the K dot are mutually exclusive in the uniform region on the right side. I understand that

As described above, in the present embodiment, the inter-color exclusion process and the intensity of the exclusion process are controlled. Control is performed so that dots of different colors are likely to overlap in a high contrast region, and control is performed so that dots of different colors are difficult to overlap in a low contrast region. As a result, a high-quality image can be realized when dots of different colors are appropriately overlapped and recorded on the recording medium.

The processing area for calculating the contrast value cnt is not limited to 3 pixels×3 pixels. Further, the pixel of interest does not have to be the center, and the contrast cnt may be calculated in a 4×4 region with the pixel of interest in the upper left. Alternatively, instead of the continuous area, a staggered grid or a processing area in which only pixels in odd or even columns are calculated may be used. Further, as a method for calculating the contrast value cnt, a method other than the calculation method by the equation (2) can be applied. For example, the contrast value cnt may be calculated based on the histogram of the cumulative gradation data S. Specifically, the kurtosis calculated from the histogram in a predetermined area centered on the pixel of interest may be calculated, and the smaller the kurtosis, the higher the contrast cnt may be set.

<Second Embodiment>
In the first embodiment, in the method of using the same threshold value matrix for the gradation data of each color, the method of controlling the degree of exclusion of dots between colors has been described. In the present embodiment, the number of dots is calculated using the average value within a predetermined area, and then the arrangement of the number of dots is determined, so that the degree of exclusion between different colors is controlled even if different threshold matrices are used. The method will be described below. The same configurations as those in the first embodiment will be described using the same names, and detailed description will be omitted.

FIG. 11 is a block diagram for explaining the functional configuration in the quantization processing of this embodiment. The area selection unit 1101 divides the gradation data composed of a plurality of pixels into a plurality of unit areas, and sets one unit area out of the plurality of unit areas as a processing target area. At this time, the area selection unit 401 divides the gradation data of each color into a plurality of unit areas at the same position.

The ink color selection unit 1102 determines the ink color to be processed for each area.

A threshold matrix 1110 for each ink color is stored in the memory. The dot history information 1111 stores output values of pixels of each color in the unit area. That is, the dot history information 111 indicates the presence/absence of a dot for each ink color determined in advance for each pixel in the processing target area. Since there are four ink colors in this embodiment, the dot history information 1111 is configured to be able to store the output values of the unit areas for three colors.

The target dot number setting unit 1103 sets the target dot number D to be arranged in the processing target area for each color. The target number of dots is the number of dots to be arranged in the processing target area. Here, each pixel is converted into a binary value which specifies dot recording (1) or non-recording (0) for each pixel by a quantization process. That is, the target dot number can be rephrased as the number of pixels included in the processing target area that should be set to a value indicating recording (1 in this case) by quantization.

The evaluation value setting unit 405 sets the evaluation value H for each pixel included in the processing target area of the processing target color based on the gradation data of the processing target area, the threshold group corresponding to the processing target area, and the dot history information. Set. The detailed calculation method will be described later. The dot arrangement unit 1107 determines the dot arrangement in the processing target area based on the target number of dots and the evaluation value of each pixel. The quantized data creation unit 407 creates and outputs quantized data of an image.

FIG. 12 is a flowchart for explaining processing steps executed by the CPU 201 in the quantization processing of S303 while using each block shown in FIG.

First, in step S1200, the area selection unit 1101 sets one unit area as an area to be processed from the image areas to be printed. FIG. 13 is a conceptual diagram for explaining the method of setting the processing target area. The area selection unit 1101 divides the image 1300 to be printed into a plurality of unit areas of the same type, and sets one unit area among them as a processing target area. In the present embodiment, the image area to be printed is divided in units of 4 pixels×4 pixels, and each 4 pixel×4 pixel area is treated as a unit area. Then, the plurality of unit areas are sequentially set as the processing target areas, and predetermined quantization processing is performed. The order in which the processing target areas are set is not particularly limited, but in the present embodiment, the order is set in the +x direction from the upper left of the figure, and when the processing of the end portion is completed, the order of moving to the adjacent stage in the +y direction is set. And

When the processing target area is set in S500, the ink color selection unit 1102 in S1201 uses black (first color), cyan (second color), magenta (third color), and yellow based on the quantization order information 1108. A processing target color is set from among (fourth color).

Next, in step S1202, the dot number determination unit 1103 expands the gradation data of the processing target color of the processing target area in the memory among the gradation data obtained by the ink color separation processing (S302 of FIG. 3). FIG. 14A shows an example of gradation data developed in S1202. A gradation value I of 0 to 255 is associated with each of the 4×4 pixels included in the processing target region 1301. In step S1203, the target dot number determination unit 1103 acquires the threshold value th(x, y) corresponding to each of 16 pixels included in the processing target area from the processing target color threshold value matrix 1110. FIG. 14B is a diagram showing a part of the threshold matrix of the processing target color. The target dot number determination unit 1103 reads 16 threshold values at a position corresponding to the processing target area from the memory from the threshold matrix.

Next, in S1204, the target dot number determination unit 1103 determines the number of dots to be arranged in the processing target area based on the gradation data acquired in S1202 and the threshold value th(x, y) acquired in S1203. .. Specifically, an average value obtained by dividing the total sum SUM of gradation data in the processing area by the number of pixels 16 is compared with each threshold value of the processing target area, and the number of pixels satisfying the average value>threshold value Let it be a number. In the present embodiment, the threshold th is acquired from the threshold matrix that differs for each color to be processed. For example, in the case of the processing target area shown in FIG. 14A, the target dot number determination unit 1103 first calculates the average gradation value 109.75 (=1756/16) of the processing target area. Next, by comparing the average value with each threshold value, the number of pixels where average value>threshold value=7 is calculated as the number of dots in the processing target area.

Next, in step S1205, the arrangement evaluation unit 1104 calculates an evaluation value E for evaluating the priority of dot arrangement for each of 16 pixels in the processing target area. The evaluation value E is a real number indicating that the larger the value, the more preferentially the dots are arranged. Specifically, the arrangement evaluation unit 1104 calculates the evaluation value E of each pixel based on the following formula (4).
E=I/I_max-th/th_max (4)

However, I is the gradation value of the pixel of interest, and I_max is the upper limit value of the gradation data. For example, I_max=255 when the gradation data is 8 bits, and I_max=65535 when the gradation data is 16 bits. That is, I/I_max is a real number from 0 to 1, and the larger the value, the easier the dots are arranged. Further, th is a threshold value corresponding to the pixel of interest, and th_max is an upper limit value of the threshold value. For example, if the threshold value is 0 to 254, th_max=254 may be set. At this time, th/th_max is a real number from 0 to 1, and the larger the value, the more difficult the dots are arranged.

Subsequently, in step S1206, the exclusive processing unit 1105 acquires the cumulative value of dots in each pixel from the dot history information 1111 stored in the memory for each of the 16 pixels in the processing target area.

For example, when the color to be processed is C, the output value of the processed K ink is stored in the dot history information 1111. Similarly, when the processing target color is M, the sum of the output values of the K ink and the C ink is included in the dot history information 1111. When the processing target color is Y, the K, C, and M inks are respectively printed. The total output value of is stored. When the processing target color is K ink, there is no processed ink color, and the exclusive processing unit 1105 does not acquire anything from the dot history information 1111.

Next, in step S1207, the exclusion processing unit 1105 corrects the evaluation value E of each pixel based on the dot history information 1111. Specifically, the exclusion processing unit 1105 calculates the evaluation value E′ after the exclusion processing by the equations (5) and (6).
E'=E-H/H_max (5)
However, H=Σ(wi×Di) (6)

H in the equation (5) is an exclusive control value calculated from the history information, and is a real number indicating that the larger the value, the less likely the dots are arranged. In the present embodiment, the exclusion control value H has a larger value in a pixel in which more high density dots are arranged.

Further, in the above equation (6), i is a number indicating the processing order of the processing target color. For example, in the present embodiment, the processing order is K→C→M→Y, so i=1 when the processing target color is K, and i=2 when C is the processing target color. Also, wi is a weight for a preset i-th ink color. In this embodiment, the higher the density of ink color, the greater the weight. Specifically, the weight of each ink color is set to K:C:M:Y=4:2:2:1. That is, w1=4, w2=2, w3=2, w4=1. By determining the weight in this way, the exclusion control value H is calculated as a larger value as the higher density dots are arranged.

Di represents the number of dots of the i-th ink color. For example, when one K ink dot is arranged in the pixel of interest, D1=1. Further, Σ represents the sum up to the i−1th. However, when i=1, H=0. The exclusive control value H calculated as described above is calculated according to the number of dots already arranged and the density of the arranged dots. The larger the number of dots and the higher the density of the arranged dots, the larger the value.

H_max indicates the maximum value of the exclusive control value H in the processing area. The exclusive control value H in the processing area is normalized to 0 to 1 by dividing the exclusive control value H by H_max. In addition, in Formula (5), when H_max=0, it is set as E'=E. That is, when the color to be processed is the first color, the evaluation value E is not corrected because the dots have not been arranged yet.

Next, in step S1208, the exclusive control unit 1106 recorrects the evaluation value E′ so as to cancel the correction effect of the evaluation value in step S1207 based on the cumulative gradation data S in each pixel. Specifically, the exclusive control unit 1106 calculates the evaluation value E″ after exclusive control of each pixel by the following formula (7).
E″=E′+S/S_max (7)
However, S=Σ(wi×Ii) (8)

Here, the cumulative gradation data S is the weighted sum of the gradation values I of the ink colors that have already been processed. For example, if the color to be processed is K, the cumulative gradation data S of each pixel is 0. If the color to be processed is C ink, the product of the gradation value Ik of K ink and the weight w1 for K ink is acquired as cumulative gradation data S for each pixel. Similarly, if the color to be processed is M ink, Ik×w1+Ic×w2 is acquired for each pixel.

Note that S_max in the equation (7) represents the theoretical upper limit value of the cumulative gradation data S. For example, if w1=4 and the gradation data is 8-bit data that can take a value of 0 to 255, the value of S_max at i=2 is 1020 (=255×4). Furthermore, if w2=2, the value of S_max at i=3 is 1530 (=255×4+255×2). When S_max=0, E″=E′.

In the present embodiment, the weights wi of the inks in formulas (6) and (8) are common, but different weights for the same ink can be used in the respective formulas.

Next, in step S1209, the dot arrangement unit 1107 determines the dot arrangement of the processing target area based on the evaluation value E″ of each pixel in the processing target area. Specifically, the dots are arranged in the area in order from the pixel with the largest evaluation value E″ by the target number of dots calculated in step S1204. When the evaluation value E″ is the same value, the pixel having the larger gradation value I is preferentially arranged. As a result, the dot arrangement is determined for the processing unit area as shown in FIG. Alternatively, a pixel having a priority value may be randomly selected from pixels having the same evaluation value, or the upper left pixel may be preferentially arranged. The dot arrangement unit 1107 determines that the output value of the pixel in which the dots are arranged in the processing target area is 1, and the output value of the pixel in which the dots are not arranged is 0. FIG. 14D is a diagram showing the output value of each pixel.

Next, in step S1210, the dot arrangement unit 1107 updates the dot history information 1111. Specifically, it is stored in the memory in association with the output value ink color of each pixel determined in S1209. The stored dot history information is acquired as the dot history of the ink color that has been processed in the subsequent ink color S1206.

Next, in S1211, the quantized data creation unit creates quantized data of the image from the output value for each unit area determined in S1209, and outputs the quantized data to the RAM 212.

Next, in step S1212, the ink color selection unit 1102 determines whether or not quantized data of all ink colors has been created for the processing target area in accordance with the quantization order. If it is determined that the quantized data for all ink colors have been created, the process advances to step S1213. If there is uncreated ink, the process advances to step S1201 to reselect the processing target color and continue the quantization process.

In step S1213, the region selection unit 1101 determines whether quantized data has been created for all pixels of the input image. That is, all blocks divided by 4 pixels×4 pixels shown in FIG. 13 are selected as the processing target area, and it is determined whether or not the quantized data has been created. For example, when blocks are selected in order from the upper left, it may be determined whether or not the processing area is the lower right block. If the result of determination is that quantized data has already been created for all pixels of the input image, the quantization processing ends. If there are uncreated pixels, the process advances to step S1200 to select a processing region and continue the quantization process.

The quantization processing in this embodiment will be specifically described below with reference to FIGS. 15 and 16. Note that the quantization process for the first color K ink will be described with reference to FIG.

FIG. 15A shows gradation data Ik of K ink in the processing target area. FIG. 15B shows a threshold group corresponding to the processing target area.

At this time, in S1204, the target dot number=4 is calculated from the comparison between the average value 60 of the gradation data Ik shown in FIG. 15A and each threshold shown in FIG. 15B.

Further, FIG. 15C shows the evaluation value E calculated using the equation (3) in S1205. FIG. 15D shows the exclusive control value H before normalization. Since the K ink is the first color (w=1), H=0 for all pixels in the area. Therefore, as shown in FIG. 15E, the evaluation value E′ after the exclusive processing in S1207 is E′=E.

Similarly, the cumulative gradation data S shown in FIG. 15(f) is S=0 for all pixels in the area, and the evaluation value E″ after the exclusive control processing shown in FIG. 15(g) is E′. ′=E. At this time, by arranging four dots (the number of dots=4) in order from the pixel with the highest evaluation value E″ shown in FIG. 15G, the K ink dot arrangement shown in FIG. 15H is obtained. To be The quantized data shown in FIG. 15I is stored as dot history information 1111 in the memory in association with the weight w1=4.

Next, FIG. 16 shows a process of quantization processing of the second color C ink. First, the gradation data Ic of C ink in the processing target area and the threshold groups corresponding to the processing target area are shown in FIGS. 16A and 16B, respectively. At this time, the evaluation value E and the number of dots=4 shown in FIG. 16C are calculated.

Further, the exclusive control value H of each pixel shown in FIG. 16D is calculated from the quantized data of K ink shown in FIG. 15I and the weight w1=4 for K ink. At this time, H_max=4.

Further, the evaluation value E′ after the exclusion process shown in FIG. 16E is calculated from the evaluation value E shown in FIG. 16C and the exclusion control value H normalized by H_max.

Similarly, the cumulative gradation data S of each pixel shown in FIG. 16F is calculated from the gradation data of K ink shown in FIG. 15A and the weight w1=4 for K ink. From w1=4, S_max=1020. Further, the evaluation value E″ after the exclusive control processing shown in FIG. 16G is calculated from the evaluation value E′ after the exclusive processing and the cumulative gradation data S normalized by S_max.

At this time, by arranging four dots (the number of dots=4) in order from the pixel with the highest evaluation value E″ shown in FIG. 16G, the C ink dot arrangement shown in FIG. 16H is obtained. To be Further, the quantized data shown in FIG. 16I is stored in the memory as dot history information 1111 in association with the weight w2=2 for the C ink.

Similarly, FIG. 17 shows the process of the quantization process for the M ink of the third color. In this example, H_max=6, S_max=1530, and the number of dots=4. Therefore, the quantized data of M ink shown in FIG. 17I is obtained.

Further, FIG. 18 shows a process of quantization processing of the fourth color Y ink. However, the weight w3 for M ink is set to be 3=2. In this example, H_max=8, S_max=2040, and the number of dots=4. Therefore, the quantized data of the Y ink shown in FIG. 18I is obtained. By the above processing, quantized data of four colors of CMKY can be obtained.

Here, the effect of the exclusive control in this embodiment will be described. If the color to be processed is the second color or later, the exclusive control value H becomes a value based on the dot arrangement that has already been determined. For example, if the color to be processed is C ink, the exclusive control value H becomes a positive value for the pixels in which the K dots have been arranged, and it becomes difficult to arrange the dots. Specifically, FIG. 19A shows the dot arrangement when the number of dots=4 is arranged based on the evaluation value E before the exclusion process shown in FIG. Similarly, FIG. 19B shows the dot arrangement when the number of dots=4 is arranged based on the evaluation value E′ after the exclusive processing shown in FIG. As shown in FIG. 19A, in the dot arrangement based on the evaluation value E before the exclusion process, the dots are arranged even in the pixels in which the K ink has been arranged, and the arrangement is not exclusive between the colors. On the other hand, as shown in FIG. 19B, in the dot arrangement based on the evaluation value E′ after the exclusion process, the dots are arranged avoiding the pixels where the K ink is arranged. That is, an exclusive arrangement between different colors is obtained. In this way, the dot arrangement exclusive between different colors reduces dot overlap and excessive exposure of paper white. Particularly in the case of flat gradation data, it is possible to prevent the contrast from increasing in the local area, and to suppress the deterioration of graininess due to overlapping dots. Further, color turbidity due to overlapping of dots of different ink colors is suppressed, and the color developability is improved especially in a dark portion (high density portion).

However, in some cases, it is not desirable to arrange dots of different colors mutually exclusively, such as when the gradation data changes sharply in the processing target area. For example, on the grayscale data shown in FIGS. 15A to 18A, a CMYK four-color mixed line is formed in the second column from the left. However, in the dot arrangement using the evaluation value E′ after the exclusion processing shown in FIG. 19B, K and C do not overlap with each other, and the arrangement is exclusive. Therefore, there is a possibility that dots do not overlap the pixels where the four-color mixed line is to be formed and that the dots are not perceived as a mixed-color line. Alternatively, coloring other than mixed colors may occur locally.

On the other hand, in the dot arrangement based on the evaluation value E″ after the exclusive control processing shown in FIG. 16H, the C ink and the K ink overlap on the CMYK mixed line. Similarly, in the M ink and Y ink shown in FIGS. 17H and 18H, dots are arranged on the CMYK mixed line. That is, by arranging the dots according to the evaluation value E″ after the exclusion control processing, exclusion is suppressed in the region where the gradation data changes sharply, and a dot arrangement that allows overlapping is obtained. At this time, in the uniform area in the first column from the right on the gradation data, the dot arrangement based on the evaluation value E″ after the exclusive control processing provides an exclusive arrangement between different colors.

However, in the dot arrangement based on the evaluation value E before the exclusion processing shown in FIG. 16C, the K ink and the C ink overlap, and the arrangement is not exclusive between different colors. In this embodiment, if the gradation data I is flat, the cumulative gradation data S will also be flat. At this time, the absolute values of the evaluation values E′ and E″ change, but the relative magnitude relationship does not change. That is, in the flat gradation data area, the order in which the dots are arranged does not change between the evaluation values E′ and E″. Therefore, even if the exclusive control process using the cumulative gradation data S is performed, it is possible to obtain the dot arrangement in which the dots of different colors are exclusive in the area of the flat gradation data.

In other words, in the present embodiment, the history information of the dots is referred to, and first, the evaluation value is corrected so that it is difficult to arrange the dots in the pixels in which the dots are arranged. Then, the dot arrangement evaluation value is further corrected so as to suppress the correction based on the contrast of the gradation data. By performing the processing in this manner, exclusion target dots including intercolors are dispersed and arranged based on the size of the threshold matrix in the region of low contrast, and the graininess can be improved. On the other hand, in a high-contrast region, it is possible to suppress dot exclusion based on the size of the gradation data and improve the reproducibility of the shape on the image data.

(Modification)
Although the value E is described as a real number in the above embodiment, it can be calculated as an 8-bit integer.

It is also possible to adjust the degree of exclusion in a flat area by multiplying the exclusion control value H and the cumulative gradation data S by a coefficient of 0 to 1. At this time, if 1 is used for the coefficient, the same result as the above-described embodiment can be obtained. On the other hand, the smaller the coefficient, the more the exclusion process in the flat area is suppressed, the number of dots overlapping between colors increases, and if 0 is used as the coefficient, the exclusion process is not performed even in the uniform area. For example, the coefficient for the exclusive value H and the gradation data S may be determined according to the registration deviation (relative positional deviation) between the colors assumed in the printer. Specifically, robustness against misregistration between colors is improved by making adjustments such as reducing the coefficient of a region in which relative displacement between colors is large and color unevenness is conspicuous.

Further, in a highlight portion having a small number of dots, the registration shift is hardly detected, so the coefficient may be controlled according to the brightness of the input image.

Further, the exclusion target color may be limited. That is, the above process is performed only on the exclusion target color, and the normal dither process is performed on the exclusion non-target color (or the coefficient is set to 0 for the exclusion non-target color).

In the above-described embodiment, the target number of dots is 16 or less in the unit area of 4 pixels×4 pixels. However, when a plurality of nozzle rows are held or when the same ink can be ejected by overlapping each pixel by scanning the same area a plurality of times, there are cases where more than 16 dots are arranged in the area. is there. For example, when ink can be ejected to each pixel up to twice, the gradation data, I_max may be set so that the gradation data I/I_max is normalized to 0 to 2. Then, th/th_max is normalized to 0 to 1, and the number of dots to be arranged in the area may be calculated using the normalized gradation data and the threshold. That is, first, dots are arranged one by one in pixels having I/I_max of 1 or more, and then, 1 is subtracted from I/I_max of the pixel in which the dots are arranged, and the remaining dots are arranged. At this time, the history information 1111 may hold the number of arranged dots 0 to 2 for each pixel.

Further, the print head may be able to form dots by changing the ejection amount. For example, the same processing can be performed when dots of three stages of large, medium and small can be formed. For example, a pixel in which one dot is arranged may be a small dot, a pixel in which two dots are arranged is a medium dot, and a pixel in which three dots are arranged may be a large dot.

Further, in the above-described embodiment, different threshold matrices for each ink color are used for calculating the number of dots and acquiring the dot arrangement order. However, it is also possible to use the same threshold matrix for all ink colors or multiple ink colors. Particularly in a flat region, the dot pattern is improved because the cumulative dot pattern of all ink colors is a pattern generated by a single threshold matrix. Further, by weighting the dots between the colors and performing the exclusive processing, the dots can be arranged in the order of the brightness of the dots including the overlapping of the dots. As a result, it is possible to reduce the contrast between dots and further improve the graininess.

Further, in the above-described embodiment, the exclusive control value H and the cumulative gradation data S are calculated by referring to all the dot arrangements of the colors processed before the color to be processed. However, the configuration may be such that exclusive control is performed only between some of the colors. In this case, the exclusive control value H and the cumulative gradation data S may be generated from the dot pattern of only the designated color by the means for designating the reference color. Further, when calculating the cumulative gradation data S of the target color, the gradation data of the target color may be added and calculated.

The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. It can also be realized by the processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

403 Threshold processing unit 404 Exclusive processing unit 405 Contrast calculation unit 406 Exclusive control unit 407 Quantized data creation unit

Claims (11)

An image processing device for determining a dot arrangement for each of the plurality of types of color materials using a threshold matrix based on an image corresponding to each of the plurality of color materials,
An acquisition unit for acquiring the output value of the pixel of interest corresponding to the first color of which the dot arrangement is determined among the plurality of types of color materials;
For the second color of which the dot arrangement is not determined among the plurality of types of color materials based on the output value of the pixel of interest corresponding to the first color and the pixel value of the pixel of interest in the first color Calculating means for calculating an exclusion control value for controlling the exclusion degree of dots in the pixel of interest,
An image, characterized in that it has a determining means for determining an output value corresponding to the second color of the target pixel based on the pixel value of the target pixel in the second color, the exclusive control value, and the threshold matrix. Processing equipment. When the output value of the pixel of interest corresponding to the first color indicates that a dot is arranged in the pixel of interest and the contrast is high in the vicinity of the pixel of interest, the calculating unit determines the second value. It is characterized in that the exclusion control value is calculated so that the degree of exclusion for a color indicates that a dot has been arranged in the target pixel, and is smaller than that in the case where the contrast is low in the vicinity of the target pixel. The image processing apparatus according to claim 1. When the output value of the pixel of interest corresponding to the first color indicates that no dot is arranged in the pixel of interest, the calculating unit excludes dots for the pixel of interest corresponding to the second color. The image processing apparatus according to claim 1, wherein the image processing apparatus is not provided. The calculating unit further includes a first correcting unit that corrects a threshold value corresponding to the target pixel based on an output value of the target pixel corresponding to the first color.
The exclusion control value is corrected by the first correction unit using the exclusive control value according to the pixel value of the pixel of interest in the first color and the pixel value of the pixel in the vicinity of the pixel of interest in the first color. A second correction means for further correcting the threshold value,
4. The determination unit quantizes the pixel value of the pixel of interest corresponding to the second color using the threshold value corrected by the second correction unit. The image processing device according to one item. 5. The first correction unit does not correct the threshold when the output value of the target pixel corresponding to the first color indicates that no dot is arranged in the target pixel. The image processing device according to. The first correction unit corrects the threshold value corresponding to the target pixel by subtracting the pixel value of the target pixel in the first color from the threshold value corresponding to the target pixel. The image processing device according to 4 or 5. Further, a contrast calculation for calculating a contrast value indicating a contrast in the vicinity of the target pixel based on the pixel value of the target pixel in the first color and the pixel value of a pixel in the vicinity of the target pixel in the first color Have means,
The image processing apparatus according to claim 4, wherein the second correction unit calculates the exclusive control value according to the contrast value. further,
Target dot number determining means for calculating a target dot number for a predetermined area in the second color;
On the basis of the pixel value of each pixel included in the predetermined area of the second color and the threshold value group corresponding to the predetermined area of the threshold matrix, each pixel included in the predetermined area of the second color And an evaluation value calculation means for evaluating the evaluation value,
The image processing apparatus according to claim 1, wherein the determining unit determines an output value of each pixel in the predetermined area based on the target dot number and the evaluation value. .. 9. The image processing apparatus according to claim 8, wherein the calculation unit corrects the evaluation value of each pixel calculated by the evaluation value calculation unit based on the exclusive control value. A program for causing a computer to function as the image processing device according to claim 1. An image processing method for determining a dot arrangement for each of the plurality of types of color materials using a threshold matrix based on an image corresponding to each of the plurality of color materials,
Obtaining the output value of the pixel of interest corresponding to the first color of which the dot arrangement is determined among the plurality of types of color materials,
For the second color of which the dot arrangement is not determined among the plurality of types of color materials based on the output value of the pixel of interest corresponding to the first color and the pixel value of the pixel of interest in the first color Calculating an exclusion control value for controlling the degree of exclusion of dots in the pixel of interest,
An image processing method, wherein an output value corresponding to the second color of the pixel of interest is determined based on the pixel value of the pixel of interest in the second color, the exclusion control value, and the threshold matrix.

Images