JP7183057B2 - Image processing device, image processing method, program - Google Patents

Description

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

A dither method is known as a quantization method when recording an image using the pseudo-gradation method. The dithering method uses a threshold matrix in which thresholds associated with individual pixels are arranged, compares these thresholds with pixel values indicated by image data, and determines dot printing or non-printing for each pixel. How to decide.

Patent Document 1 describes a method of avoiding excessive dot overlap and improving dispersibility by considering the arrangement of dots of other colors when performing quantization using a threshold matrix. Specifically, when quantizing for each color using a distributed threshold matrix, by shifting the threshold based on the previously determined dot arrangement of the color, dots between colors are exclusively determined. do.

International publication number WO2002/005545

However, in the method described in Patent Document 1, if dots are formed so that different colors are mutually exclusive in an area where pixel values change sharply, such as an edge portion of an image, dots of a color with a higher priority are formed on the edge. It's easy to focus on one part. As a result, dots of low-priority colors are arranged around the edge portion, which may cause deterioration of sharpness and local coloring.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to appropriately control the degree of overlap of dots between colors according to the characteristics of the image when quantizing images of different colors.

To solve the above-described problems, the present invention provides an image processing apparatus for determining the arrangement of dots for each of a plurality of types of colorants using a threshold matrix based on images corresponding to each of the plurality of colorants. acquiring means for acquiring an output value of a pixel of interest corresponding to a first color for which dot arrangement has been determined among the plurality of types of color materials; an output value of the pixel of interest corresponding to the first color; for controlling the degree of exclusion of dots in the pixel of interest for a second color, among the plurality of types of color materials, for which dot arrangement has not been determined, based on the pixel value of the pixel of interest in the first color; calculating means for calculating an exclusive control value; and determining an output value of the pixel of interest corresponding to the second color based on the pixel value of the pixel of interest in the second color, the exclusive control value, and the threshold matrix. It is characterized by having decision means.

According to the present invention, it is possible to appropriately control the degree of overlap of dots between colors 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 image processing steps 3 is a block diagram for explaining a software configuration; FIG. Flowchart for explaining steps of quantization processing A diagram showing an example of the threshold matrix 409 A diagram showing an example of a processing area A diagram showing an example of gradation data Ik, Ic, and Im A diagram showing an example of quantization processing for K ink Diagram showing the process of quantization of C ink 3 is a block diagram for explaining a software configuration; FIG. Flowchart for explaining steps of quantization processing A diagram showing an example of dividing the processing target area Diagram showing a specific example of quantization processing A diagram showing an example of quantization processing for K ink A diagram showing an example of quantization processing for C ink. A diagram showing an example of quantization processing for M ink A diagram showing an example of quantization processing for Y ink. Diagram showing results of inter-color exclusion processing and suppression processing

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. Note that the configurations shown in the following embodiments are merely examples, and the present invention is not necessarily limited to the illustrated configurations.

<First Embodiment>
1A and 1B are schematic diagrams of a printing apparatus 100 and a printing head 102 used in this embodiment. The printing apparatus 100 used in this embodiment is a serial type inkjet printing apparatus. In the drawing, the x direction indicates the main scanning direction of the print head, the y direction indicates the conveying direction of the print medium S, and the z direction indicates the ejection direction of the coloring material (ink). As shown in FIG. 1B, in the print head 102, nozzle arrays for ejecting cyan (C), magenta (M), yellow (Y), and black (K) inks are arranged in parallel in the x direction. It is 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 is movable along a carriage shaft 107 in ±x directions. While the carriage 103 is moving in the ±x direction, the print head 102 ejects ink from the ejection openings 101 according to print data, thereby printing an image for one band on the print medium S. FIG. A flat platen platen 105 is arranged at a position facing the ejection port surface of the recording head 102 . The platen 105 supports the print medium S in the area printed by the print head 102 from the back surface, and keeps the distance between the ejection port surface of the print head 102 and the print medium S constant.

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

FIG. 2 is a block diagram for explaining the configuration of control in this embodiment. The image processing apparatus 200 includes a host PC or the like, and a CPU 201 executes various processes according to a program held in an HDD 203, which is a nonvolatile storage, while using a RAM 202, which is a volatile storage, as a work area. For example, the CPU 201 generates print data that can be printed by the printing apparatus 100 according to commands received from the user via the keyboard/mouse I/F 205 and programs held in the HDD 303 , and outputs the print data to the printing apparatus 100 . Information received from the recording apparatus 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 apparatus 100, the CPU 211 executes various processes while using the RAM 212, which is a volatile storage unit, as a work area according to a program held in a ROM 213, which is a nonvolatile storage unit. Further, the printing apparatus 100 includes an image processing accelerator 216 for performing high-speed image processing and a head controller 215 for controlling the printing head 102 . The image processing accelerator 216 is hardware capable of executing image processing faster than the CPU 211 . The image processing accelerator 216 is activated when the CPU 211 writes parameters and data necessary for image processing to a predetermined address in the RAM 212. After reading the parameters and data, the image processing accelerator 216 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 .

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

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

USB, IEEE1394, LAN, or the like can be used 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 .

FIG. 3 is a flowchart for explaining image processing steps executed by the CPU 201 of the image processing apparatus 200 when a print command is issued. This processing is executed by the CPU 201 using the RAM 202 as a work area according to the program stored in the HDD 203 . Hereinafter, each step in the flowchart will be denoted as "S".

When this process is started, the CPU 201 first acquires image data created by an application program or the like and develops it in the RAM 202 . In this embodiment, it is assumed that image data having 8-bit (256 gradation levels) pixel values indicating the brightness of each of red (R), green (G), and blue (B) is acquired for each pixel. Image data composed of pixels having pixel values of a plurality of components such as R, G, and B is hereinafter referred to as RGB data using the components.

In S<b>301 , the CPU 201 executes color correction processing on the image data developed in the RAM 202 . Color correction processing is processing for converting image data representing a standardized color space such as sRGB into image data associated with a color space printable by the printing apparatus 100 . Specifically, the CPU 201 refers to a pre-stored RGB three-dimensional lookup table, converts RGB data having 8-bit (256 gradation) pixel values to R data having 8-bit (256 gradation) pixel values. Convert to 'G'B' data.

In S302, the CPU 201 executes color conversion processing on the R'G'B' data generated in S301. Color conversion processing converts R′G′B′ data representing luminance information into respective densities of K, C, M, and Y corresponding to colors of color materials (hereinafter referred to as ink colors) used by the printing apparatus 100. This is a process for converting into data representing information. Specifically, the CPU 201 refers to a prerecorded three-dimensional lookup table, and converts 8-bit (256 gradation) R′G′B′ data of each pixel into 8-bit (256 gradation) KCMY Convert to data. Data corresponding to each ink color that has undergone color conversion processing is collectively referred to as KCMY data.

In S303, the CPU 201 performs quantization processing on the KCMY data generated in S302. The quantization process will be described in detail later, but this quantization process converts 8-bit (256 gradation) KCMY data into 1-bit K'C'M'Y' data. In this embodiment, the K'C'M'Y' data is binary data that designates dot printing (1) or non-printing (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 printing apparatus 100 as printing data. This completes the processing.

The CPU 211 of the printing apparatus 100 that has received the print data develops 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 printed on the printing medium according to the printing data developed in the RAM 212 . 3 are processed in the ink jet recording system of the present embodiment, but it is difficult to distinguish which process is performed by the host PC 200 and which process and thereafter is performed by the printer 100. Can be set arbitrarily. For example, in the case where the host PC 200 performs up to quantization, the quantized data may be transferred to the printer 100 . Also, depending on the performance of the printer 100, it is possible to directly receive multi-valued RGB image data and perform all the steps from S300 to S304.

FIG. 4 is a block diagram for explaining the 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 in S302 is input to the area selection unit 401 for each ink color. Data for each ink color that constitutes the KCMY data is hereinafter 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).

A pixel selection unit 401 sets one pixel as a target pixel from 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 target pixel is set, the pixel selection unit 401 outputs the gradation values of the target pixel corresponding to the 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 color to be processed from among the first to fourth colors, and selects a color to be processed corresponding to 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 for executing the quantization process.

A threshold processing unit 403 executes quantization processing for each pixel using a threshold matrix 409 stored in memory in advance. FIG. 6 is a diagram showing part of the threshold matrix 409 used in this embodiment. A plurality of threshold values having different values are randomly arranged in the threshold matrix 409 so as to correspond to each pixel. By associating the threshold matrix 409 with the image to be processed in a tiled manner, each pixel in the image is associated with any threshold. Also, the threshold processing unit 403 uses the same threshold matrix 409 in association with similar positions for the gradation data of each color of CMYK.

The exclusion processing unit 404 controls the threshold corresponding to the color to be processed next so that 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 corresponding to the target pixel each time the threshold processing unit 403 quantizes the tone value of the target pixel.

A contrast calculation unit 405 calculates a contrast value that is correlated with the degree of contrast in a region near the pixel of interest. The contrast is high when there is a large difference in gradation value in neighboring areas, and the contrast is low when there is little difference in gradation value. The exclusion control unit 406 controls the degree of exclusion effect by the exclusion processing unit 404 .

A quantized data generation unit 407 generates quantized data printable by the printing apparatus 100 based on the dot arrangement data generated by the threshold processing unit 403, and outputs the quantized data to the printing apparatus 100 as print data. The quantized data of each color referred to here corresponds to the K'C'M'Y' data described in the flow chart 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. Each block described above is substantially a functional unit on software executed by the CPU 201 shown in FIG. In the following description, it is assumed that the dot size is a single dot size, and that 1-bit quantization data indicating dot ON/OFF for each pixel is generated for each of CMYK.

FIG. 5 is a flowchart for explaining processing steps executed by the CPU 201 using each block shown in FIG. 4 in the quantization processing of S303. The quantization process performed in this embodiment will be described in detail below according to the flowchart shown in FIG. 5 with reference to FIGS. 6 and 7(a) to (k).

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

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

In S503, the threshold processing unit 403 acquires the gradation value I(x, y) of the processing target color corresponding to the pixel of interest from among the gradation data obtained by the color separation processing (step S302 in FIG. 3). In the present embodiment, gradation data is described as 8-bit data in which a gradation value of 0 to 255 is stored for each pixel.

In S504, the threshold processing unit 403 acquires the threshold th used for quantization processing of the target pixel. A threshold corresponding to the pixel of interest (x, y) is denoted as threshold th(x, y).

Next, in step S505, the threshold processing unit 403 compares the gradation value I(x, y) with the threshold th(x, y) to determine an output value indicating dot ON/OFF in the pixel of interest. . More specifically, if I(x, y)>th(x, y), the process advances to S507, where the dot of the target pixel (x, y) is turned ON (output value=1). On the other hand, if I(x, y)≤th(x, y), the process advances to S506, where the dot of the target pixel (x, y) is turned OFF (output value=0).

Next, in S508, the exclusion processing unit 404 changes the threshold th(x, y) corresponding to the pixel of interest used for the subsequent color to be processed. More specifically, the threshold th(x, y) is changed to the threshold th'(x, y) so that dots of other colors are less likely to be placed in the pixel of interest (x, y) for which the dot is ON in S507. and update. In this embodiment, the exclusion processing unit 404 updates the threshold according to Equation (1).
th′=th(x, y)−I(x, y) (1)

When the maximum value 255 of the gradation data is added to the threshold th′ calculated here and used for the quantization process, the threshold th′ is larger than the original threshold th. Therefore, it becomes difficult for dots to be arranged in subsequent processes, and an exclusive effect is obtained. The exclusive control unit saves the new threshold th(x, y) in memory. It should be noted that the exclusive arrangement of dots between colors in the pixel of interest by updating the threshold will be described later.

Next, in step S509, the contrast calculation unit 405 calculates cumulative tone data S for each pixel included in a predetermined area centered on the pixel of interest. For example, assume that a pixel 701 is a pixel of interest in an input image 700 as shown in FIG. At this time, the contrast calculation unit 405 sets a block of 3×3 pixels centering on the target pixel 701 as a processing area. For example, when the pixel position is at the edge of the image, such as the pixel 702, and a processing area of 3×3 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, as cumulative gradation data S, the sum of the gradation value of the processed color and the gradation value I of the color to be processed in the pixel of interest.

For example, assume that K is the target color of the target pixel. In this embodiment, since the quantization order is K→C→M→Y, there is no processed color in the pixel of interest yet, and the cumulative gradation data S of each pixel in the processing area is the gradation value Ik of the K ink. becomes. When the target color is C ink, the sum of the processed color K ink gradation value Ik and the processing target color C ink gradation value Ic is accumulated for each pixel in the target pixel. It is calculated as gradation data S. Similarly, when the color to be processed in the pixel of interest is the 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 color to be processed in the pixel of interest is Y ink, the sum of the tone values Ik, Ic, Im, and Iy is calculated as cumulative tone data for each pixel in the processing area. FIG. 8 shows examples of gradation values Ik, Ic, and Im of K, C, and M inks of each pixel in the processing area. Here, if the color to be processed in the target pixel is the M ink, the cumulative tone data S of each pixel calculated in S509 will be the values shown in FIG. 8D.

Next, in step S510, the contrast calculation unit 405 calculates a contrast value cnt indicating the contrast within the processing area based on the accumulated tone 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, let max_S be the maximum value and min_S be the minimum value of the accumulated gradation data S of each pixel in the processing area.
cnt=(max_S−min_S)/(max_S+min_S) (2)

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

In S<b>511 , the exclusion control unit 406 performs processing for suppressing the intensity of exclusion processing for the pixel of interest based on the contrast cnt within the processing region corresponding to the pixel of interest. More specifically, the threshold th(x, y) corresponding to the pixel of interest is further updated such that the larger the contrast value cnt corresponding to the processing region (the higher the contrast), the more the threshold change in S508 is canceled out. do. In the present embodiment, the exclusive control unit 406 calculates a new threshold th'' using the following equation (3), and stores the threshold th'' in the memory as a threshold corresponding to the pixel of interest.
th″=th′(x, y)+I(x, y)×cnt (3)

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

Next, in S512, the exclusive control unit 406 determines whether or not the threshold th''(x, y) is smaller than zero. If the threshold th''(x, y) is smaller than 0, the process proceeds to S513. In S513, the exclusion control unit 406 adds the upper limit value i_max (here, 255) in the gradation data to the threshold th''(x, y) as a new threshold th''. Update the threshold. On the other hand, if the threshold th''(x, y) is 0 or more, skip S513 and proceed to S514.

Next, in S<b>514 , the ink color selection unit 402 determines whether quantization processing for all colors has been executed for the pixel of interest according to the quantization order 408 . If the quantization processing for all colors in the pixel of interest has been completed, the process proceeds to S515. If there is an unprocessed color, the process advances to S502 to select a color to be processed in the pixel of interest and continue quantization processing in the pixel of interest.

In S<b>515 , the quantized data creation unit 407 outputs the quantized value of each color of the pixel of interest to the RAM 212 . In S516, the pixel selection unit 401 determines whether quantization processing has been performed for all pixels of the input image. For example, when pixels are selected in order from the upper left, it is only necessary to determine whether or not the quantized data of the lower right pixel has been created. If the result of determination is that quantization processing has already been performed for all pixels of the input image, the quantization processing ends. If there is an uncreated pixel, the process returns to S501 to select a new pixel of interest and continue the quantization process.

A specific example of the quantization processing according to the present embodiment will be described below with reference to FIGS. 9 and 10. FIG. FIG. 9A shows gradation data of K ink in a partial area of the input image. A rectangle indicates one pixel, and each pixel stores a gradation value. FIG. 9(b) shows a threshold group corresponding to the partial area shown in FIG. 9(a). FIG. 9C shows the result of quantization processing for K ink. Pixels filled in black in FIG. 9C indicate that dots of K ink (hereinafter also simply referred to as K dots) are arranged (output value is 1). Since the K ink is the first color, the output value is 1 for pixels whose gradation value is greater than the corresponding threshold value. When the K ink quantization process is executed, at least part of the threshold corresponding to each pixel is updated by the processes of S508 to S514. FIG. 9(d) shows the threshold th' set by the equation (1) in S508. For pixels with a K ink output value of 0, the threshold is not changed, and the same threshold as that shown in FIG. 9B is retained. On the other hand, for pixels with a K ink output value of 1, a value obtained by subtracting the gradation value from the threshold is stored as the threshold th'. Here, an output value of 1 means that the gradation value of the pixel is greater than the threshold. Therefore, the pixel whose output value is 1 always has a negative value as the threshold value th'.

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

FIG. 9(f) shows the threshold 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 exclusive control, a value greater than the original threshold value 19 is adopted as a threshold value for pixels in which K dots are arranged and the contrast is low, such as the lower right pixel in the partial area. Also, in pixels where K dots are arranged and the contrast is low, such as the lower two pixels in the second row, a value smaller than the original threshold value is adopted, and the strength of the exclusion process is suppressed. In addition, for pixels where K dots are not arranged, such as the pixel on the upper right and the pixel on the second row of the second column, a value smaller than the original threshold value is adopted.

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

In this embodiment, each gradation value of the C ink shown in FIG. 10A is quantized using the threshold group after exclusive control shown in FIG. 9F instead of the threshold group shown in FIG. 9B. do. The result of quantization in this embodiment is shown in FIG. 10(d). FIG. 10(b) shows the result of quantization using the threshold group shown in FIG. 9(b) in order to explain the effect of this embodiment. FIG. 9C shows the result of quantization using the threshold th' after exclusion processing. Note that FIG. 10 shows that dots of C ink (hereinafter referred to as C dots) are arranged in the blackened pixels in the drawing.

From FIGS. 9(c) and 10(b), when the same threshold value group is used to quantize the gradation value of each color, C dots are formed in any pixels where K dots are formed. It can be seen that That is, if the same set of threshold values is used for different ink colors, the overlapping rate of dots of different colors will increase. 9(a) and 10(a) both have a line with a width of 1 pixel in the second column from the left. Especially when the characteristics of the gradation data are similar, the same threshold value group is used for the quantum calculation. Dot duplication rate tends to increase. However, when the printing apparatus 200 ejects ink onto the print medium based on the quantized data, overlapping dots and exposure of paper white are mixed in a flat area. As a result, the contrast is high even though the area is flat, and the graininess is deteriorated due to overlapping dots, and the image quality may be impaired. In the partial area shown in FIG. 10(b), the right three columns are flat areas, and there is a possibility that image quality deterioration may occur due to dot overlap. In addition, the increase in the number of overlapping dots increases the paper whiteness, and the desired density may not be achieved in some cases.

Here, quantization data shown in FIG. 10C is obtained by quantizing the gradation value of each pixel using the threshold value th′ after exclusion processing shown in FIG. 9D. As described above, due to the exclusion effect, i_max=255 is added to th' for quantization when the threshold th'<0. From FIGS. 9C and 10C, it can be seen that C dots are not formed in pixels where K dots are formed when the threshold th' after exclusion processing is used. That is, by changing the threshold in S508, dots of different colors are arranged mutually exclusive. By arranging such inter-color dots exclusively, deterioration of graininess can be suppressed in a flat area.

On the other hand, in high-contrast areas, it may not be desirable to arrange dots of different colors in a mutually exclusive manner. For example, in the gradation data shown in FIGS. 9A and 10A, the gradation value in the second column from the left is larger than the gradation values in the other columns, forming a line of K+C. . However, when the printing apparatus 200 ejects ink onto the printing medium based on the quantized data of C ink shown in FIG. Regardless, there is no dot in which the K ink and the C ink overlap. As a result, since the K dots and C dots are dispersedly arranged, 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, in S511, processing is performed to control the degree of exclusion of dots between colors for each pixel based on the contrast. As for the threshold group after exclusive control, the quantized data of C ink obtained from the threshold matrix after exclusive control shown in FIG. 9(f) is shown in FIG. 10(d). 9(c) and 10(d), the K+C lines are reproduced by overlapping dots in the vicinity of the high-contrast K+C lines, while the C dots and K dots are mutually exclusive in the uniform area on the right side. I know there is.

In this way, in this embodiment, the inter-color exclusion process and the intensity of the exclusion process are controlled. In high-contrast areas, dots of different colors are controlled so that they tend to overlap, and in low-contrast areas, dots of different colors are controlled so that they are less likely to overlap. As a result, a high-quality image can be realized when dots of different colors are appropriately overlapped and printed on the printing medium.

Note that the processing area for calculating the contrast value cnt is not limited to 3 pixels×3 pixels. Further, the pixel of interest may not be the center, and the contrast cnt may be calculated in a 4×4 area with the pixel of interest at the upper left. Alternatively, instead of a continuous area, a houndstooth check or a processing area in which only pixels in odd or even columns are calculated may be used. Moreover, as a method of calculating the contrast value cnt, a method other than the calculation method by the expression (2) can be applied. For example, the contrast value cnt may be calculated based on the histogram of the accumulated tone data S. Specifically, the kurtosis may be calculated from a histogram in a predetermined area centered on the pixel of interest, and the contrast cnt may be determined to be higher as the kurtosis is smaller.

<Second embodiment>
In the first embodiment, the method of controlling the degree of exclusion of dots between colors in the method of using the same threshold matrix for the gradation data of each color has been described. In this embodiment, after calculating the number of dots using the average value in a predetermined area, the arrangement of the number of dots is determined, thereby controlling the degree of exclusion between different colors even if different threshold matrices are used. The method will be explained. Configurations similar to those of the first embodiment will be described using the same names, and detailed descriptions thereof will be omitted.

FIG. 11 is a block diagram for explaining the functional configuration in the quantization processing of this embodiment. A region selection unit 1101 divides the gradation data composed of a plurality of pixels into a plurality of unit regions, and sets one unit region among them as a processing target region. 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 an ink color to be processed for each region.

The memory stores a threshold matrix 1110 for each ink color. The dot history information 1111 stores output values of pixels of each color in the unit area. In other words, the dot history information 111 indicates the presence/absence of dots 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 output values of 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 by quantization processing into a binary value that designates dot printing (1) or non-printing (0) for each pixel. That is, the target number of dots can be rephrased as the number of pixels to be set to a value (here, 1) indicating printing by quantization among the pixels included in the processing target area.

The evaluation value setting unit 405 sets an 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 value group corresponding to the processing target area, and the dot history information. set. A detailed calculation method will be described later. A 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. A 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 using each block shown in FIG. 11 in the quantization processing of S303.

First, in S1200, the area selection unit 1101 sets one unit area from among the image areas to be printed as a processing target area. FIG. 13 is a conceptual diagram for explaining a method of setting the processing target area. The region selection unit 1101 divides the image 1300 to be printed into a plurality of unit regions of the same type, and sets one unit region among them as a processing target region. In this embodiment, the image area to be printed is divided into units of 4 pixels×4 pixels, and each 4 pixels×4 pixel area is treated as a unit area. Then, the plurality of unit areas are sequentially set as 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 this embodiment, they are set in order from the upper left of the figure in the +x direction, and when the processing of the farthest end is completed, the order is shifted to the adjacent stage in the +y direction. and

After the processing target area is set in S500, the ink color selection unit 1102 selects black (first color), cyan (second color), magenta (third color), and yellow based on the quantization order information 1108 in S1201. Set the color to be processed from (fourth color).

Next, in S1202, the dot number determination unit 1103 develops the gradation data of the processing target color of the processing target region in the memory among the gradation data obtained by the ink color separation processing (S302 in 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 area 1301 . In S1203, the target dot number determination unit 1103 acquires the threshold th(x, y) corresponding to each of the 16 pixels included in the processing target area from the threshold matrix 1110 of the processing target color. FIG. 14B is a diagram showing part of the threshold matrix of the color to be processed. The target dot number determination unit 1103 reads from the memory 16 thresholds at positions corresponding to the processing target area 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 tone data acquired in S1202 and the threshold value th(x, y) acquired in S1203. . Specifically, the average value obtained by dividing the sum SUM of the 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 where the average value > the threshold value is determined as a dot. number. Note that in this embodiment, the threshold th is obtained from a different threshold matrix for each color to be processed. For example, in the case of the processing target area shown in FIG. 14A, the target dot number determining unit 1103 first calculates an average value of 109.75 (=1756/16) of the gradation values of the processing target area. Next, by comparing the average value with each threshold value, the number of pixels where the average value>the threshold value=7 is calculated as the number of dots in the processing target area.

Next, in S1205, the placement evaluation unit 1104 calculates an evaluation value E for evaluating the order of priority of dot placement for each of the 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 layout evaluation unit 1104 calculates the evaluation value E of each pixel based on the following equation (4).
E = I/I_max - th/th_max (4)

However, I is the gradation value of the target pixel, 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 it is for dots to be arranged. Also, th is a threshold corresponding to the pixel of interest, and th_max is the upper limit of the threshold. For example, if the threshold is 0 to 254, th_max=254. At this time, th/th_max is a real number from 0 to 1, and the larger the value, the harder it is to place dots.

Subsequently, in S1206, the exclusion 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 dot history information 1111 stores the output value of the processed K ink. Similarly, when the color to be processed is M, the dot history information 1111 contains the sum of the output value of K ink and the output value of C ink. The sum of the output values of is stored. Note that when the color to be processed is the K ink, there is no processed ink color, so the exclusion processing unit 1105 acquires nothing from the dot history information 1111 .

Next, in S<b>1207 , 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 using formulas (5) and (6).
E'=E-H/H_max (5)
However, H = Σ (wi × Di) (6)

H in Expression (5) is an exclusive control value calculated from history information, and is a real number indicating that the larger the value, the more difficult it is to place dots. In the present embodiment, the exclusive control value H is larger for pixels in which more dots of higher density are arranged.

Also, in the above equation (6), i is a number indicating the processing order of the color to be processed. For example, in this embodiment, the order of processing is K→C→M→Y, so if the color to be processed is K, i=1, and if it is C, i=2. Also, wi is a preset weight for the i-th ink color. In this embodiment, the higher the density of the 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, and w4=1. By determining the weight in this way, the exclusive control value H is calculated as a larger value as the dots with higher density are arranged.

Di indicates the number of dots of the i-th ink color. For example, when one dot of K ink is placed in the pixel of interest, D1=1. Also, Σ indicates the sum up to the (i−1)th. 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 exclusive control value H within the processing area. By dividing the exclusive control value H by H_max, the exclusive control value H within the processing area is normalized to 0-1. In addition, in Formula (5), when it is H_max=0, let E'=E. In other words, when the color to be processed is the first color, the evaluation value E is not corrected because no dots have been placed yet.

Next, in S1208, the exclusion control unit 1106 again corrects the evaluation value E' based on the cumulative grayscale data S for each pixel so as to cancel the correction effect of the evaluation value in step S1207. Specifically, the exclusive control unit 1106 calculates an evaluation value E″ after exclusive control of each pixel using the following equation (7).
E″=E′+S/S_max (7)
However, S = Σ (wi × Ii) (8)

Here, the cumulative gradation data S is a 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 accumulated tone data S of each pixel is zero. If the color to be processed is C ink, the product of the K ink gradation value Ik and the weight w1 for the K ink is obtained as cumulative gradation data S for each pixel. Similarly, if the color to be processed is M ink, Ik×w1+Ic×w2 is obtained for each pixel.

Note that S_max in Equation (7) indicates a theoretical upper limit value of the cumulative grayscale data S. For example, if w1=4 and the gradation data is 8-bit data that can take values from 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). Note that when S_max=0, E″=E′.

In the present embodiment, the weight wi of each ink in equations (6) and (8) is common, but it is also possible to use different weights for the same ink in each equation.

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

Next, in S<b>1210 , the dot placement unit 1107 updates the dot history information 1111 . Specifically, the output value of each pixel determined in S1209 is stored in the memory in association with the ink color. The stored dot history information is acquired as the dot history of the ink color processed in S1206 for the subsequent ink color.

Next, in S<b>1211 , the quantized data creation unit creates quantized data of the image from the output value for each unit area determined in S<b>1209 , and outputs it to the RAM 212 .

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

In S1213, the region selection unit 1101 determines whether quantization data has been created for all pixels of the input image. That is, all blocks divided into 4×4 pixels shown in FIG. 13 are selected as processing target areas, and it is determined whether or not quantization data has been created. For example, when blocks are selected in order from the upper left, it is only necessary to determine whether the processing area is the lower rightmost block. If the result of determination is that quantization data has already been created for all pixels of the input image, the quantization process ends. If there is an uncreated pixel, the process proceeds to S1200, selects a processing area, and continues the quantization process.

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

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

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

Further, FIG. 15(c) shows the evaluation value E calculated using the formula (3) in S1205. FIG. 15(d) 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 region. Therefore, as shown in FIG. 15E, the evaluation value E' after the exclusion process in S1207 is E'=E.

Similarly, the accumulated gradation data S shown in FIG. 15(f) is also S=0 for all pixels in the area, and the evaluation value E″ after the exclusive control process shown in FIG. 15(g) is E′ '=E. At this time, by arranging four dots (number of dots=4) in descending order of the evaluation value E″ shown in FIG. 15(g), the K ink dot arrangement shown in FIG. 15(h) is obtained. be done. Also, the quantized data shown in FIG. 15(i) is stored in the memory as the dot history information 1111 in association with the weight w1=4.

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

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

Furthermore, the evaluation value E′ after the exclusion process shown in FIG. 16(e) is calculated from the evaluation value E shown in FIG. 16(c) and the exclusion control value H normalized by H_max.

Similarly, from the K ink tone data shown in FIG. 15(a) and the weight w1=4 for the K ink, the cumulative tone data S of each pixel shown in FIG. 16(f) is calculated. Note that S_max=1020 from w1=4. Further, an evaluation value E″ after the exclusion control process shown in FIG. 16G is calculated from the evaluation value E′ after the exclusion process and the accumulated tone data S normalized by S_max.

At this time, by arranging four dots (the number of dots=4) in descending order of the evaluation value E″ shown in FIG. 16(g), the C ink dot arrangement shown in FIG. be done. Also, the quantized data shown in FIG. 16(i) is stored in the memory as the dot history information 1111 in association with the weight w2=2 for the C ink.

Similarly, FIG. 17 shows the quantization process for the third color M ink. 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. 17(i) is obtained.

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

Here, the effect of 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 already determined dot arrangement. For example, if the color to be processed is C ink, the exclusion control value H will be a positive value for pixels where K dots have already been placed, making it difficult for dots to be placed. 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. 16C. Similarly, FIG. 19(b) shows the dot arrangement when the number of dots=4 is arranged based on the evaluation value E′ after the exclusion process shown in FIG. 16(e). As shown in FIG. 19A, in the dot arrangement based on the evaluation value E before the exclusion process, dots are arranged even in the pixels where the K ink has already been arranged, and the colors are not arranged exclusively. On the other hand, as shown in FIG. 19B, in the dot arrangement based on the evaluation value E' after exclusion processing, the dots are arranged avoiding the pixels where the K ink is arranged. That is, an exclusive arrangement is obtained between different colors. By arranging dots exclusive among different colors in this way, overlapping of dots and excessive exposure of paper white are reduced. In particular, for flat gradation data, the increase in contrast in a local area is suppressed, and the deterioration of graininess due to overlapping dots is suppressed. In addition, color turbidity due to overlapping dots of different ink colors is suppressed, and color developability is improved particularly in dark areas (high-density areas).

However, in some cases, such as when the gradation data changes sharply in the processing target area, it is not preferable to arrange dots of different colors mutually exclusive. For example, on the gradation data shown in FIGS. 15(a) to 18(a), a CMYK four-color mixture line is formed in the second column from the left. However, in the dot arrangement using the evaluation value E' after the exclusion process shown in FIG. 19B, K and C do not overlap and are arranged to be excluded. Therefore, there is a possibility that dots will not be overlapped on pixels where a four-color mixed line is to be formed, and the line will not be 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 process shown in FIG. 16(h), the C ink and the K ink overlap on the CMYK mixed line. Similarly, the M ink and Y ink shown in FIGS. 17(h) and 18(h) also have dots arranged on the CMYK mixed line. That is, by arranging the dots according to the evaluation value E″ after the exclusion control process, the exclusion is suppressed in the area where the gradation data changes sharply, and the dot arrangement that allows the overlap is obtained. Also, at this time, in the uniform area in the first row from the right on the gradation data, in the dot arrangement based on the evaluation value E'' after the exclusive control process, the arrangement exclusive between the different colors is obtained.

However, in the dot arrangement based on the evaluation value E before the exclusion process 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 is also flat. At this time, although the absolute values of the evaluation values E′ and E″ change, the relative magnitude relationship does not change. That is, in a flat gradation data area, the order in which dots are arranged does not change between the evaluation values E′ and E″. Therefore, even if exclusive control processing is performed using the accumulated gradation data S, it is possible to obtain a dot arrangement in which dots of different colors are exclusive for areas of flat gradation data.

In other words, in the present embodiment, the dot history information is referenced, and the evaluation value is first corrected so that dots are less likely to be placed in pixels where dots are already placed. In addition, the dot arrangement evaluation value is further corrected based on the contrast of the gradation data so as to suppress the correction. By performing such processing, it is possible to disperse and arrange exclusion target dots including between colors based on the magnitude of the threshold matrix in low-contrast regions, thereby improving graininess. On the other hand, in high-contrast regions, dot exclusion is suppressed based on the magnitude of the gradation data, and the reproducibility of the shape on the image data can be improved.

(Modification)
In the above embodiment, the value E is explained as a real number, but it can also 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 accumulated grayscale data S by a coefficient of 0 to 1. FIG. At this time, using a coefficient of 1 can obtain the same result as the above example. On the other hand, the smaller the coefficient, the more suppressed the exclusion process in flat areas, and the more dots overlap between colors. For example, it is preferable to determine the coefficients for the exclusion value H and the gradation data S according to misregistration (relative misregistration) between colors assumed in the printer. Specifically, the robustness against color misregistration is improved by performing adjustments such as reducing coefficients in areas where relative positional misalignment between colors is large and color unevenness is conspicuous.

Further, since the misregistration is hardly detected in a highlight portion with few dots, the coefficient may be controlled according to the lightness of the input image.

Also, the colors to be excluded may be limited. That is, the above processing is performed only for the colors to be excluded, and the normal dither processing is performed for the colors not to be excluded (or the coefficients are set to 0 for the colors not to be excluded).

Further, in the above-described embodiment, the target number of dots is 16 or less in a unit area of 4 pixels×4 pixels. However, when a plurality of nozzle rows are held, or when the same area can be scanned multiple times so that the same ink can be ejected onto each pixel, the number of dots exceeding 16 may be arranged in the area. be. For example, if ink can be ejected to each pixel up to twice, the gradation data I_max may be determined so that the gradation data I/I_max is normalized to 0-2. Then, th/th_max is normalized to 0 to 1, and the number of dots to be arranged in the area is calculated using the normalized gradation data and the threshold value. That is, first, one dot is placed in each pixel whose I/I_max is 1 or more, then 1 is subtracted from the I/I_max of the pixel where the dot is placed, and the remaining dots are placed. At this time, the history information 1111 may hold the number of arranged dots 0 to 2 for each pixel.

Also, there are cases where the print head can form dots by changing the ejection amount. For example, even when dots of three stages of large, medium and small can be formed, the same process can be performed. For example, a pixel in which one dot is arranged is a small dot, a pixel in which two dots are arranged is a medium dot, and a pixel in which three dots are arranged is a large dot.

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

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

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 the computer of the system or apparatus reads and executes the program. It can also be realized by processing to It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

403 threshold processing unit 404 exclusion processing unit 405 contrast calculation unit 406 exclusion control unit 407 quantized data creation unit

Claims (11)

An image processing device for determining dot arrangement for each of the plurality of types of colorants using a threshold matrix based on images corresponding to the plurality of colorants,
acquisition means for acquiring an output value of a pixel of interest corresponding to a first color for which dot arrangement has been determined among the plurality of types of color materials;
For a second color, among the plurality of types of color materials, for which dot arrangement has not been determined, 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 degree of exclusion of dots in the pixel of interest;
An image characterized by comprising determining means for determining an output value corresponding to the second color of the pixel of interest based on the pixel value of the pixel of interest in the second color, the exclusive control value, and the threshold matrix. processing equipment. If the output value of the pixel of interest corresponding to the first color indicates that a dot has been placed in the pixel of interest and the contrast is high in the vicinity of the pixel of interest, then the second The exclusion control value is calculated so that the degree of exclusion for a color indicates that a dot has been placed in the pixel of interest and is smaller than when the contrast is low in the vicinity of the pixel of interest. 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 calculation means excludes dots from the pixel of interest corresponding to the second color. 3. The image processing apparatus according to claim 1, wherein the image processing apparatus does not The calculating means further includes first correcting means for correcting the threshold value corresponding to the pixel of interest based on the output value of the pixel of interest corresponding to the first color;
corrected by the first correcting means using the exclusive control value corresponding to the pixel value of the target pixel in the first color and the pixel values of pixels in the vicinity of the target pixel in the first color Having a second correction means for further correcting the threshold,
4. The determining means uses the threshold corrected by the second correcting means to quantize the pixel value of the pixel of interest corresponding to the second color. 1. The image processing device according to item 1. 5. The first correcting means does not correct the threshold when the output value of the target pixel corresponding to the first color indicates that no dot is placed in the target pixel. The image processing device according to . 3. The first correction means corrects the threshold corresponding to the target pixel by subtracting the pixel value of the target pixel in the first color from the threshold corresponding to the target pixel. 6. The image processing device according to 4 or 5. Further, 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 the pixel in the vicinity of the target pixel in the first color. have the means
5. The image processing apparatus according to claim 4, wherein said second correction means calculates said exclusive control value according to said contrast value. moreover,
a target dot number determining means for calculating a target dot number for a predetermined area in the second color;
Based on the pixel value of each pixel included in the predetermined region of the second color and the threshold value group corresponding to the predetermined region in the threshold matrix, each pixel included in the predetermined region of the second color and evaluation value calculation means for calculating the evaluation value,
4. The image processing apparatus according to claim 1, wherein said determining means determines the output value of each pixel in said predetermined area based on said target number of dots and said evaluation value. . 9. The image processing apparatus according to claim 8, wherein said calculation means corrects the evaluation value of each pixel calculated by said evaluation value calculation means based on said exclusive control value. A program for causing a computer to function as the image processing apparatus according to any one of claims 1 to 9. An image processing method for determining the arrangement of dots for each of the plurality of types of colorants using a threshold matrix based on an image corresponding to each of the plurality of colorants, comprising:
obtaining an output value of a pixel of interest corresponding to a first color for which dot arrangement has been determined among the plurality of types of color materials;
For a second color, among the plurality of types of color materials, for which dot arrangement has not been determined, 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 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.

Images