JP2010141395A - Print controller, printing device, and print control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a print controller, a printing device and a print control program, capable of appropriately expressing the minimum density in an output image. <P>SOLUTION: In the case of using a change dither matrix 143 generated in a PC 10 of this first embodiment, the number of ON dots when a shading level is "1" becomes equal to the corresponding density level of a selected dither determination patch 52. Thus, for the object image data of the shading level "1", the output image of the same density as the selected dither determination patch 52 is printed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to processing for printing, and more particularly to a technique for generating output image data using a dither matrix.

  A dither method is known as a method for reproducing the density of an image with a printer (see Patent Document 1). In the dither method, multi-value image data is compared by comparing the tone value of each pixel included in the multi-value image data (for example, the tone value represented by 256 tones) and the threshold value of each element of the dither matrix. Is a processing (binarization processing) method for generating binary image data indicating ON / OFF (formation / non-formation) of dots. Specifically, when the gradation value of the pixel is equal to or greater than the corresponding threshold value, the dot is set to be formed. When the gradation value of each pixel is less than the corresponding threshold value, the dot is set. It is set not to be formed. The printer forms dots on the recording paper based on the binary image data, so that an image in which the density is expressed by the frequency of dot appearance can be printed on the recording paper.

Patent Document 2 describes that a pattern printed by a printer is color-measured and a dither matrix is designed so as to have a desired density characteristic based on the color measurement result.
JP-A-10-271334 JP-A-11-177823 JP 2001-322313 A Japanese Unexamined Patent Publication No. 7-221984 JP 2000-309116 A JP 11-41464 A

  However, even if the optimal dither matrix is designed at the development stage so that the gradation of the target image can be properly reproduced, the characteristics of the individual equipment used by the user are the same as the characteristics of the equipment used at the development stage. In addition, the usage environment changes in various ways. For this reason, the dot can be easily fixed. And in the part where dots are arranged alone or in a very small number (part where light color is reproduced), the ease of fixing is particularly unstable, so the influence of variations due to individual differences and environmental changes is not affected. It is easy to receive, and it tends to cause problems such as being too dark, too thin, or completely invisible.

  FIG. 17 is a diagram for explaining how an image is affected by the difference in ease of dot fixing when a light image is printed in a conventional printer. As shown in FIG. 17, when the dots are harder to fix than normal, the image is printed so thin that it is hardly visible, whereas when the dots are more likely to fix than normal, The image that you want to print lightly is printed darkly.

  The present invention has been made to solve the above-described problems, and an object thereof is to appropriately express the minimum density in an output image.

  In order to achieve this object, a first device of the present invention is a print control device that converts target image data representing a target image into output image data representing an output image, and causes the printing unit to print the output image. And a patch printing control unit that causes the printing unit to print a plurality of types of patches having different densities, and a selection unit that selects any one of the plurality of types of patches printed by the printing unit; A change means for generating a changed dither matrix in which at least a part of a threshold group included in a reference dither matrix prepared in advance is changed, and the target image data is converted into the output image data using the changed dither matrix Dithering means, and the changing means is a case where the gray level of each pixel included in the target image data is a minimum value excluding 0 The density of the output image printed by the printing unit based on the output image data obtained by converting the target image data using the conversion dither matrix is equal to the density of the selected patch. Further, at least a part of the threshold value group included in the reference dither matrix is changed to generate the changed dither matrix.

  In the above apparatus, when each pixel included in the target image data has the minimum value, the modified dither matrix is generated using the reference dither matrix so that the density of the output image becomes equal to the density of the selected patch. Is done. Then, output image data is generated using the modified dither matrix. For this reason, the minimum density can be appropriately expressed in the output image printed by the printing unit.

  In the above apparatus, the plurality of types of patches correspond to different shade levels, and the density of each patch is the target image data in which each pixel has the corresponding shade level as the reference dither. It is equal to the density of the output image represented by the output image data obtained by comparing with the matrix threshold value group, and the changing means is less than the gray level corresponding to the selected patch in the threshold value group of the reference dither matrix. Minimum threshold setting means for generating a minimum threshold setting dither matrix in which the threshold value is changed to the minimum threshold value in the threshold group included in the reference dither matrix, and the changing means is based on the minimum threshold setting dither matrix. Preferably, the modified dither matrix is generated.

  According to the above apparatus, the threshold value below the gray level corresponding to the selected patch in the threshold group of the reference dither matrix is changed to the minimum threshold value, so that the minimum density is the same as that of the selected patch. It is possible to print at a moderate density.

  In the above apparatus, the changing unit further changes the threshold other than the minimum threshold included in the minimum threshold setting dither matrix so that each threshold included in the changed dither matrix is continuous. It is preferable to include a threshold adjustment unit that generates a modified dither matrix.

  According to the above apparatus, the continuous change in the gray level included in the target image data can be reproduced as a smooth gradation in the output image. Therefore, it is possible to suppress the occurrence of an unnatural gradation jump (gradation jump) in the output image.

  In the above apparatus, the threshold adjustment unit further includes a threshold other than the minimum threshold included in the minimum threshold setting dither matrix larger than the minimum threshold and included in the minimum threshold setting dither matrix. Preferably, the modified dither matrix is generated by changing the threshold value so that it is smaller than the next smallest threshold value.

  According to the above apparatus, the difference between the minimum density printed by the printing unit and the next lowest density (second lowest density) can be suppressed from being noticeable in the output image.

  In the above apparatus, the threshold adjustment unit further includes a density change rate in a halftone area when the modified dither matrix is used, and the density change rate indicating a change in density of the output image with respect to a change in density level. Changing the threshold other than the minimum threshold of the minimum threshold setting dither matrix so as to be equal to the density change rate in the halftone region when the reference dither matrix is used. Is preferably generated.

  According to the above apparatus, in the halftone region, it is possible to reproduce the light and shade in the output image at the same density change rate as when the reference dither matrix is used.

  In the above apparatus, the threshold adjustment means is a first type of change dither matrix as the change dither matrix, and the density change rate in a low gradation region when the first type of change dither matrix is used. However, it is preferable to generate the first type of changed dither matrix that is set to be smaller than the density change rate in the low gradation region when the reference dither matrix is used.

  According to the above apparatus, when a change dither matrix is used, a sudden change in the density change rate that may occur in a region other than the halftone region is absorbed in a low gradation region where the change in the density change rate is relatively inconspicuous. Can do.

  In the above apparatus, the threshold adjustment means is a second type of change dither matrix as the change dither matrix, and the density change rate in a high gradation region when the second type of change dither matrix is used. It is preferable to generate the second type of changed dither matrix set so as to be smaller than the density change rate in the high gradation region when the reference dither matrix is used.

  According to the above-described apparatus, when a change dither matrix is used, a rapid change in density change rate that may occur in a region other than the halftone region can be absorbed in a high gradation region where the change in density change rate is relatively inconspicuous. it can.

  In the above apparatus, the conversion means for converting the input image data into the target image data, and the input image data is high-intensity image data including many high-luminance pixels, or low and including many low-luminance pixels. And determining means for determining whether the image data is luminance image data, wherein the threshold value adjusting means is obtained by converting the high luminance image data by the converting means when the input image data is high luminance image data. As the modified dither matrix for converting target image data into the output image data, the first type of modified dither matrix is generated, and the input image data is low luminance image data, the low luminance image The modified dither matrix for converting target image data obtained by converting data by the conversion means into the output image data Then, a second type of the changed dither matrix is generated, and the first type of changed dither matrix has the density change rate in a high gradation region when the first type of changed dither matrix is used. It is set to be smaller than the density change rate in the high gradation region when the dither matrix is used, and the second type of changed dither matrix is a low gradation when the second type of changed dither matrix is used. It is preferable that the density change rate in the region is set to be smaller than the density change rate in the low gradation region when the reference dither matrix is used.

  According to the above apparatus, target image data obtained by converting high-luminance image data is converted into output image data using the first type of dither matrix. Then, a rapid change in density change rate that can occur in a region other than the halftone region when the first type dither matrix is used can be absorbed in the high gradation region. Since the high luminance image data corresponds to a bright image including many high luminance pixels, the change in the density change rate in the high gradation region (that is, the dark color region) is relatively inconspicuous.

  Similarly, target image data obtained by converting low-luminance image data is converted into output image data using a second type of dither matrix. Then, a rapid change in density change rate that can occur in a region other than the halftone region when the second type dither matrix is used can be absorbed in the low gradation region. Since the low-luminance image data corresponds to a dark image including many low-luminance pixels, the change in the density change rate in the low gradation region (that is, the light color region) is relatively inconspicuous.

  In the above apparatus, it is preferable that the selection unit selects a patch designated by a user from the plurality of types of patches.

  According to the above apparatus, an output image in which the minimum density is expressed by an appropriate density designated by the user can be printed on the printing unit.

  A second apparatus of the present invention is a print control apparatus, and includes the print control apparatus according to any one of the above and the printing unit.

  The present invention can be realized in various modes such as a print control apparatus, a print apparatus including the print control apparatus, a print control method, a computer program for controlling the print control apparatus, and a recording medium for recording the computer program. .

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electrical configuration of a personal computer 10 (hereinafter referred to as a PC 10), which is a first embodiment of a print control apparatus of the present invention, and a printer 40 connected to the PC 10. As shown in FIG. The PC 10 of the present embodiment is particularly configured to allow the printer 40 to print an output image in which the minimum density is appropriately expressed. The PC 10 corresponds to an example of a computer in the present invention.

  As shown in FIG. 1, the PC 10 mainly includes a CPU 11, a ROM 12, a RAM 13, a hard disk drive 14 (hereinafter referred to as an HDD 14), an interface 16, an input device 17, and a display device 18, which are connected via a bus line 20. Are connected to each other.

  The CPU 11 controls each unit connected by the bus line 20 according to fixed values and programs stored in the ROM 12, RAM 13, and HDD 14. The ROM 12 is a memory in which a program for controlling the operation of the PC 10 is stored, and the RAM 13 is a readable / writable memory for temporarily storing data necessary for the processing of the CPU 11.

  The HDD 14 is a hard disk drive, and the HDD 14 stores a printer driver 141, a reference dither matrix 142, a change dither matrix 143, and patch data 144, which are examples of the print control program of the present invention. The print data generation process executed according to the printer driver 141 will be described later.

  The input device 17 is for inputting a user instruction, and includes, for example, a keyboard and a mouse. The display device 18 is composed of, for example, a CRT display or a liquid crystal display, and visually displays various processing contents and input data.

  The PC 10 configured as described above converts the target image data representing the target image into output image data in the bitmap format using the change dither matrix 143, and the printer 40 (an example of a printing unit in the present invention) as print data. To output the output image represented by the output image data to the printer 40.

  On the other hand, the printer 40 is configured by a laser printer and includes a control unit 50 that controls the operation of the printer 40. The control unit 50 stores a CPU 41 that is an arithmetic device, a ROM 42 that stores various control programs and data executed by the CPU 41, and print data and control signals input from the PC 10 connected to the printer 40. And a RAM 43 which is a memory for performing the above. The CPU 41, the ROM 42, and the RAM 43 are connected to each other via a bus line 44. The bus line 44 is connected to an ASIC (Application Specific Integrated Circuit) 45 that is an integrated circuit.

  Further, the control unit 50 is connected to an interface 46 for connecting the printer 40 and an external device so as to be communicable, an image forming unit 47, a scanner unit 48, and a paper transport unit 49.

  The image forming unit 47 is provided with a photosensitive drum, a charger that uniformly charges the surface of the photosensitive drum, and a developing cartridge that contains toner. The image forming unit 47 of the printer 40 of the present embodiment is configured to be detachable with four developing cartridges containing toners of C (cyan), M (magenta), Y (yellow), and K (black). The printer 40 is configured as a color laser printer that can form an output image with four colors of C, M, Y, and K.

  When print data is supplied from the PC 10 via the interface 46, the printer 40 uses the charger to turn on and off the laser according to the output image data in the bitmap format included in the print data. Thus, the surface of the photosensitive drum positively charged is scanned, and the electric charge on the surface of the photosensitive drum is partially removed to form a minute spot. Then, an electrostatic latent image corresponding to the output image to be printed on the recording paper (recording medium) is formed by attaching positively charged toner to the site from which the charge has been removed. Then, the toner is transferred to a recording sheet conveyed by the sheet conveying unit 49 and fixed, whereby an output image can be printed.

  The PC 10 according to the present embodiment generates a modified dither matrix 143 in which at least a part of the threshold value group included in the reference dither matrix 142 is changed, and converts the target image data into output image data using the changed dither matrix 143. Thus, the printer 40 is configured to allow the printer 40 to print an output image in which the minimum density is appropriately expressed.

  First, the dither matrix will be described with reference to FIGS. FIG. 2A is a diagram illustrating an example of the reference dither matrix 142. As shown in FIG. 2A, the reference dither matrix 142 has a data structure in which, for example, one threshold value is stored in each of 16 × 16 cells (elements). As shown in FIG. 2A, each threshold value of the dither matrix is an integer.

  In general dither processing, the reference dither matrix 142 is superimposed on 16 × 16 pixels of the target image data composed of the light and dark levels of each color of C, M, Y, and K, and corresponds to the light and dark levels of each pixel. The threshold value is compared, and if the gray level is equal to or higher than the threshold value, it is converted to 1 (represents dot on), and if it is less than the threshold value, it is converted to 0 (dot off). When the 16 × 16 pixel processing is completed, the reference dither matrix 142 is sequentially moved to the next 16 × 16 pixel position, and the same processing is repeated. As a result, for example, target image data including a gray level of 256 gradations is converted into output image data represented by binary values.

  As shown in FIG. 2A, 256 cells (elements) of the reference dither matrix 142 are each assigned one threshold value from 1 to 254, and two threshold values 255 are assigned. Yes. Therefore, in the target image data, when the gray level of 16 × 16 pixels is 1, in the output image data, only one pixel out of 256 pixels is dot-on. On the other hand, when the gray level of 16 × 16 pixels is 255 in the target image data, the dot is turned on for all 255 pixels in the output image data. Therefore, if the dots are ideally fixed, the dot application frequency and the gray level are approximately proportional, and the gradation can be reproduced smoothly in the output image.

  However, the dots are not always ideally fixed, and a light color gradation may not be suitably expressed. In particular, when the gray level of each pixel of the target image data is the minimum value (that is, 1) excluding 0, since one isolated dot is formed within 16 × 16 pixels, in other words, one dot Since no other dots are formed around the dot, dot fixation becomes unstable.

  Therefore, the PC 10 of the present embodiment first causes the printer 40 to print a plurality of types of dither determination patches 52 (see FIG. 6) having different densities, and allows the user to select them. Then, the PC 10 changes the threshold value of the reference dither matrix 142 so that the density of the selected dither determination patch 52 becomes the minimum density of the output image printed by the printer 40, and changes the dither matrix 143. (FIG. 3B) is generated. Then, the PC 10 performs dither processing using the changed dither matrix 143.

  First, an outline of the procedure for generating the modified dither matrix 143 will be described with reference to FIGS.

  FIG. 2B shows a dither in which “2” to “8” among the thresholds included in the reference dither matrix 142 are changed to “1” that is the minimum threshold in the threshold group included in the reference dither matrix 142. It is a figure which shows a matrix. For convenience of explanation, a dither matrix in which several threshold values are changed to the minimum threshold value “1” in the threshold value group of the reference dither matrix 142 is referred to as a “minimum threshold setting dither matrix”.

  In the minimum threshold value setting dither matrix shown in FIG. 2B, eight minimum threshold values “1” are arranged among 16 × 16 threshold values. Therefore, when the target image data whose gray level of each pixel is “1” is dithered using this minimum threshold value setting dither matrix, 8 dots in 16 × 16 pixels are turned on in the output image. . Therefore, when the target image data with the gray level of each pixel being “1” is dithered using the minimum threshold value setting dither matrix, the density is higher than when dithering is performed using the reference dither matrix 142. (Ie, dark) Here, the number of cells for which the minimum threshold value “1” is set is determined based on the dither determination patch 52 (see FIG. 6) designated by the user, and details will be described later.

  In the minimum threshold setting dither matrix shown in FIG. 2B, the next smallest threshold after the minimum threshold “1” is “9”, and the threshold is discontinuous (that is, a threshold jump occurs). ing). As a result, when the minimum threshold setting dither matrix is used, it is difficult to reproduce the difference in gradation between gray levels “1” and “8”.

  Therefore, the PC 10 of the first embodiment sets the next value of the minimum threshold “1” so that the threshold between the minimum threshold “1” and “8” included in the minimum threshold setting dither matrix is set. The threshold value is continuously reassigned from the threshold value “2”. In other words, a threshold value other than the threshold value “1” included in the threshold value group of the minimum threshold value setting dimatrix is greater than the minimum threshold value “1” and smaller than the minimum threshold value included in the minimum threshold value setting dither matrix. (That is, the second smallest threshold value) is changed to be smaller than “9”.

  In FIG. 3A, the threshold value is set between the minimum threshold value “1” included in the minimum threshold value setting dither matrix shown in FIG. 2B and the next smaller threshold value “9”. It is a figure which shows an example of the dither matrix which changed the threshold value. For convenience of explanation, the dither matrix shown in FIG. 3A is referred to as a gap correction dither matrix.

  In the gap correction dither matrix shown in FIG. 3A, threshold values are continuously set from “1” to “249”. However, since the number of thresholds that can be set is 256, a threshold value of 250 or more cannot be set, and a gray level of 250 or more cannot be reproduced.

  Therefore, next, the threshold value from “1” to “255” is re-allocated to change the threshold value of the gap correction dither matrix, and the changed dither matrix 143 is generated.

  FIG. 3B is a diagram illustrating an example of the change dither matrix 143. As shown in FIG. 3B, in the modified dither matrix 143, the threshold value is set continuously and the maximum threshold value is set to “255”. Specifically, two threshold values having the closest values are obtained by changing the other threshold values while leaving the minimum threshold value “1” set in the minimum threshold setting dither matrix (FIG. 2B) as it is. The threshold is changed so that the difference between the two values does not exceed a predetermined value. Therefore, by using this modified dither matrix 143 for the dither processing, the minimum density can be expressed appropriately, and unnatural gradation jump (gradation) is possible for the entire range of gray levels from 0 to 255. Occurrence of tone jump) can be suppressed. If the gray level is a value that can represent 256 gradations, the output image can be obtained by changing the threshold value so that the difference between the two threshold values having the closest value in the change dither matrix 143 is not 3 or more. The unnatural gradation jump in can be more reliably suppressed.

  In this embodiment, the change dither matrix 143 is generated for each color used in the printer. In FIG. 3B, the change dither matrix 143 is generated for one color among C, M, Y, and K. A dither matrix 143 is illustrated.

  FIG. 4 is a diagram showing output image data obtained by dither processing for each case where the gray level of each pixel constituting the target image data is “1” to “4”. 4A shows output image data obtained when the reference dither matrix 142 (FIG. 2A) is used, and FIG. 4B shows the changed dither matrix 143 (FIG. 3B). Output image data obtained when used is shown. In FIG. 4, each of the squares partitioned in a grid pattern represents a pixel constituting the output image data, and the colored squares are dot-on (that is, the color material is It represents a pixel that is fixed and forms a dot.

  As shown in FIG. 4A, when the reference dither matrix 142 (FIG. 2A) is used, the number of pixels that are dot-on among 16 × 16 pixels is equal to the gray level. On the other hand, as shown in FIG. 4B, in the changed dither matrix 143 (FIG. 3B), 8 pixels out of 16 × 16 pixels are dot-on with respect to the minimum gray level “1”. As the light and shade level increases from “1”, the number of pixels that are turned on increases. Therefore, if the changed dither matrix 143 is used, a light color can be printed at an appropriate density even if a color material such as toner is difficult to be fixed due to the characteristics of the printer or the usage environment of the printer. Also, as the density level increases, the number of dot-ons increases continuously, so that the change in gradation of the light portion is appropriately reproduced in the output image.

  FIG. 5 is a flowchart showing print data generation processing executed by the PC 10. This print data generation process is a process that is activated when the user instructs execution of printing, and is executed according to the printer driver 141 (see FIG. 1). In particular, in the present embodiment, when the user desires, a changed dither matrix 143 in which the threshold value of the reference dither matrix 142 is changed is generated, and dither processing is performed using the changed dither matrix 143.

  First, the CPU 11 determines whether or not the user has instructed to change the threshold value of the reference dither matrix 142 (S503). If the determination in S503 is affirmative (S503: Yes), the CPU 11 outputs the patch data 144 (see FIG. 1) to the printer 40, thereby causing the printer 40 to print the dither determination patch (S504).

  The dither determination patch will be described with reference to FIG. FIG. 6 is a diagram illustrating an example of a test sheet 50 that the PC 10 causes the printer 40 to print. As shown in FIG. 6, the test sheet 50 is printed with dither determination patches 52 having 12 different densities, for example, for each of the four colors C, M, Y, and K. The dither determination patch corresponds to an example of the patch according to the present invention.

  The dither determination patches 52 correspond to different shade levels, and the corresponding shade levels are printed on the test sheet 50 as “patch numbers”. In the test sheet 50, since the patch number is printed for each column, the user visually recognizes the test sheet 50 and specifies the color and the patch number, so that each dither determination patch 52 printed in a matrix is displayed. Can be specified.

  The density of each dither determination patch 52 is printed at a density equivalent to that obtained when the target image data of each pixel having the corresponding gray level is compared with the threshold value group of the reference dither matrix 142 and dithered. In other words, each dither determination patch 52 indicates the print result based on the output image data when the dither processing is performed using the reference dither matrix 142 in the range of the gray level from “1” to “12”. For example, the C dither determination patch 52 corresponding to the patch number “1” is the output image data obtained by dithering the target image data having the C gray level “1” of each pixel with the reference dither matrix 142. In other words, a printing result based on (that is, data in which only one pixel is dot-on among 16 × 16 pixels) is shown.

  The PC 10 according to the first embodiment causes the user to designate a patch having a density that the user wants to associate with the gray level “1” from the dither determination patches 52. Then, the PC 10 is printed using the output image data obtained by converting the target image data using the conversion dither matrix 143 if the gray level of each pixel included in the target image is “1”. The modified dither matrix 143 is generated so that the density of the output image to be equalized with the density of the selected dither determination patch 52.

  Here, “the density of the output image is equal to the density of the selected dither determination patch 52” means “the color density of the output image is equal to that of the dither determination patch 52”. For example, it may be that the results measured by the colorimeter and digitized are equal, but other than that, it is formed in the unit area on the recording medium on which the output image is printed The number of dots formed may be equal, or the dot fixing area per unit area on the recording medium may be equal. Further, as in the present embodiment, when the printer 40 is configured to print a color output image using a plurality of color materials, the dither determination patch 52 is selected for each color. . Then, the modified dither matrix 143 is generated for each color so that the density of each color constituting the output image is equal to the density of the dither determination patch 52 selected for that color.

  Returning to FIG. Next, the CPU 11 selects the dither determination patch 52 specified by the patch number input by the user, that is, the dither determination patch 52 specified by the user, and stores the patch number in the RAM 13 (see FIG. 1). (S506).

  Next, the CPU 11 determines whether or not four color dither determination patches have been selected (S507). If the determination in S507 is negative (S507: No), the CPU 11 returns to S506 and repeats the process. On the other hand, if the determination in S507 is affirmative (S507: Yes), the CPU 11 executes a dither threshold value changing process (S510) and generates a changed dither matrix 143. The dither threshold value changing process (S510) will be described later.

  Next, the CPU 11 determines whether or not the change dither matrix 143 for four colors has been generated (S512). If the determination in S512 is negative (S512: No), the CPU 11 returns to S510 and repeats the process.

  When the determination of S512 is affirmed (S512: Yes) or when the determination of S503 is negative (S503: No), the CPU 11 determines the brightness of each color of R (red), G (green), and B (blue). Color conversion processing for converting RGB image data composed of values into target image data composed of shade levels of each color of C, M, Y, K using a three-dimensional lookup table prepared in advance (S513) )I do.

  Next, the CPU 11 executes dither processing to convert the target image data into output image data (S514). Specifically, when the determination in S503 is negative, the CPU 11 executes dither processing using the reference dither matrix 142. On the other hand, if the determination in S512 is affirmative, the CPU 11 executes dither processing using the changed dither matrix 143.

  Then, the CPU 11 ends the print data generation process, outputs the output image data obtained by this process to the printer 40 as print data, and causes the printer 40 to print the output image.

  FIG. 7 is a flowchart showing the dither threshold value changing process (S510) of FIG. First, the CPU 11 executes an input level 1 threshold value changing process (S702). In this input level 1 threshold value changing process (S702), the gap correction dither matrix (FIG. 3 (a)) is passed from the reference dither matrix 142 (FIG. 2 (a)) through the minimum threshold value setting dither matrix (FIG. 2 (b)). ) Is generated.

  FIG. 8 is a flowchart showing the input level 1 threshold value changing process (S702) of FIG. In the input level 1 threshold value changing process (S702), first, the CPU 11 reads the reference dither matrix 142 (FIG. 2A) into the RAM 13 (S800), and among the threshold value groups included in the reference dither matrix 142, the processing target. The threshold value corresponding to the dither determination patch 52 selected for the color is changed to “1” (corresponding to “the minimum threshold value in the threshold value group included in the reference dither matrix” in the present invention) (S801). . For example, when patch number 8 is designated, the threshold value of “8” or less is changed to “1”. By this process, a minimum threshold setting dither matrix (FIG. 2B) is generated.

  Next, the CPU 11 sets 2 to the variable “n” (S802). Next, the CPU 11 searches the threshold value group of the minimum threshold setting dither matrix (FIG. 2B) for the next smallest threshold value “1” (“9” in FIG. 2B), and finds the found value. The variable “Xmin” is set (S803).

  Next, the CPU 11 changes the value of the cell for which the threshold value of “Xmin” has been set to “n” (n = 2 in the present embodiment) (S804). Next, the CPU 11 adds 1 to “n” (S805), and adds 1 to “Xmin” (S806). Then, the CPU 11 determines whether “Xmin” is greater than 255 (S807). If the determination in S807 is negative (S807: No), the CPU 11 searches for a cell in which the threshold value of “Xmin” is set. (S808), the process returns to S804.

  If the determination in S807 is affirmed while the process is repeated in this manner (S807: Yes), the CPU 11 ends the input level 1 threshold value changing process (S702). A gap correction dither matrix (FIG. 3A) is generated by this input level 1 threshold value changing process (S702).

  Returning to FIG. In the processing after S704, the gap correction dither matrix (FIG. 3A) is included so that the threshold value included in the finally generated change dither matrix 143 is continuous between “2” and “255”. The changed dither matrix 143 is generated by changing a threshold other than the minimum threshold “1”.

  First, the CPU 11 searches for the maximum threshold value included in the gap correction dither matrix (FIG. 3A), and sets the found value to the variable “Smax” (S704). Next, the CPU 11 determines whether or not Smax ≠ 255 is established (S706). When Smax = 255 (S706: No), the gap correction dither matrix is stored in the HDD 14 (FIG. 1) as the color change dither matrix 143 to be processed (S708), and the process ends.

  On the other hand, if Smax ≠ 255 (S706: Yes), the CPU 11 obtains one threshold other than the minimum threshold “1” from the gap correction dither matrix (S710), and calculates (threshold / Smax × 255). . And CPU11 rounds off the calculation result, and changes the threshold acquired by the process of S710 to the result (S712). Next, the CPU 11 determines whether or not the processing has been completed for all threshold values except the minimum threshold value “1” (S714). If the determination in S714 is negative (S714: No), the process returns to S710 and is repeated.

  If the determination in S714 is affirmed while the processing is repeated in this way (S714: Yes), the CPU 11 stores the generated dither matrix in the HDD 14 as the changed dither matrix 143, and the dither threshold value changing process (S510). Exit.

  When the target image data is converted into output image data by the dither process (S514) using the changed dither matrix 143 generated by the dither threshold value change process (S510), the gray level of each pixel included in the target image data is temporarily assumed. If “1”, the density of the output image printed by the printer 40 is equal to the density of the selected dither determination patch 52. In other words, the minimum density of the output image printed by the printer is made equal to the density of the dither determination patch 52 selected based on the user's designation.

  Thus, according to the PC 10 of the first embodiment, the minimum density printed by the printer 40 can be dynamically changed, and an output image in which the minimum density is appropriately expressed is printed on the printer. Can be made.

  Further, according to the PC 10 of the present embodiment, the changed dither matrix 143 is generated by changing the thresholds other than the minimum threshold so that the thresholds included in the changed dither matrix 143 are continuous. In other words, compared with the minimum threshold setting dither matrix (FIG. 2B), in the modified dither matrix 143, the threshold value gradually increases from the minimum threshold value “1” to the maximum threshold value “255”. . If the target image data is converted into output image data using the change dither matrix 143 generated in this way, the continuous change in the gray level included in the target image data can be reproduced with the continuous density change. Can do.

  FIG. 9 is a graph showing changes in the number of ON dots in the output image data with respect to changes in the gray level of the target image data. FIGS. 9A and 9B are a reference dither matrix 142 and a modified dither matrix, respectively. 14 is a graph showing a case where dither processing is performed using 143. The graphs shown in FIGS. 9A and 9B both have a gray level on the x-axis, and on the y-axis, the dots that are turned on within 16 × 16 pixels as a value corresponding to the density of the output image. The number (number of ON dots) is taken.

  As shown in FIG. 9B, when the changed dither matrix 143 is used, the number of ON dots when the gray level is “1” becomes equal to the density level corresponding to the selected dither determination patch. An output image having the same density as that of the selected dither determination patch 52 can be printed on the target image data having the gray level “1”. That is, it is possible to cause the printer to print an output image in which the minimum density is expressed with an appropriate density designated by the user.

  Further, in the range larger than the light / dark level “1”, the number of ON dots continuously changes up to 255 which is the maximum value as in FIG. 9A. Therefore, an image is printed at a density (number of ON dots) corresponding to the gradation level, and an unnatural gradation jump (gradation jump) can be prevented from occurring in the output image.

  Next, a second embodiment will be described with reference to FIGS. In the dither threshold value changing process of the first embodiment, after setting the minimum threshold value “1”, the threshold values “2” to “255” are evenly allocated. In other words, as shown in FIG. 9, the slope θ ′ of the graph when the modified dither matrix 143 is used (FIG. 9B) is the same as that of the graph when the reference dither matrix 142 is used (FIG. 9A). It was gentler than the inclination θ. Therefore, when the changed dither matrix 143 is used, the density change rate (θ ′) indicating the change in the density of the output image with respect to the change in density level is smaller than the density change rate (θ) when the reference dither matrix 142 is used. Become.

  On the other hand, in the PC 10 of the second embodiment, the density change rate in the halftone region when the changed dither matrix 143 is used is equal to the density change rate (θ) when the reference dither matrix 142 is used. The modified dither matrix is generated. The changed dither matrix generated by the PC 10 of the second embodiment is referred to as a “light absorption change dither matrix 145”.

  The print data generation process executed in the second embodiment is the same as that of the first embodiment except that the dither process (S514) is executed using the light absorption type change dither matrix 145 instead of the change dither matrix 143. This is the same as the print data generation process in FIG.

  FIG. 10 is a flowchart showing a light absorption type dither threshold value changing process (S100) executed in the second embodiment. This light absorption type dither threshold value changing process (S100) is a process executed in place of the dither threshold value changing process (S510: FIG. 7) of the first embodiment.

  First, the CPU 11 reads the reference dither matrix 142 into the RAM 13 (S1001), and selects a threshold value equal to or lower than the gray level corresponding to the dither determination patch 52 selected for the color to be processed from the threshold group included in the reference dither matrix 142. The threshold value is changed to the minimum threshold value “1” (S1002). By this process, a minimum threshold setting dither matrix (FIG. 2B) is generated. Next, the CPU 11 sets 2 to the variable “Si” (S1004). Next, the CPU 11 sets “1 + Si” in the variable “n” (S1006).

  Next, the CPU 11 searches for the next smallest threshold value included in the minimum threshold value setting dither matrix (FIG. 2B), and sets the found value to the variable “Xmin” (S1008). Next, the CPU 11 changes the value of the cell for which the threshold value “Xmin” has been set to “n” (S1010). Next, the CPU 11 adds “Si” to “n” (S1012), and adds 1 to “Xmin” (S1014). Then, the CPU 11 determines whether “Xmin” is equal to n (S1016). If the determination in S1016 is negative (S1016: No), the CPU 11 searches for a cell in which the threshold of “Xmin” is set (S1018). ), The process returns to S1010.

  If the determination in S1016 is affirmed while the processing is repeated in this way (S1016: Yes), the CPU 11 sets the generated dither matrix in the HDD 14 (FIG. 1) as the light absorption type change dither matrix 145. This is stored, and the light absorption type dither threshold value changing process (S100) is terminated.

  FIG. 11 is a diagram illustrating an example of the light absorption type change dither matrix 145. As shown in FIG. 11, in the light absorption change dither matrix 145, for example, a threshold value “1” is set for eight cells, and between the minimum threshold values “1” and “15”, An even threshold is thinned out. The threshold values are stored in the same array as the reference dither matrix 142 (FIG. 2A) between the threshold values “16” and “255”.

  FIG. 12 is a graph showing the correspondence between the gray level and the number of ON dots. The upper row shows the range of the gray level from 0 to 255, and the lower row shows the range of the gray level from 0 to 25 in an enlarged manner. . In the graph shown in FIG. 12, the horizontal axis indicates the gray level, and the vertical axis indicates the number of dots that are turned on within 16 × 16 pixels (the number of ON dots) as a value corresponding to the density of the output image. Have taken. In FIG. 12, a broken line indicates an output result when dither processing is performed using the reference dither matrix 142, and a solid line indicates a case where dither processing is performed using the light absorption type change dither matrix 145 (FIG. 11). The output result is shown.

  As shown in FIG. 12, according to the light absorption type change dither matrix 145 (FIG. 11), a low gradation region having an intensity level of “1” to “13” (an example of the low gradation region of the present invention). ), The corresponding number of ON dots is higher than when the reference dither matrix 142 is used. In other words, when the light absorption type change dither matrix 145 (FIG. 11) is used, in the low gradation region where the light and dark levels are “1” to “13”, compared to the case where the reference dither matrix 142 is used. A dark output image is printed as a whole.

  On the other hand, as shown in FIG. 12, when the light absorption dither matrix 145 is used, the density (ON) of the output image with respect to the change of the light and shade level in the low gradation region where the light and shade levels are “1” to “13”. The threshold value of the light absorption type dither matrix 145 is set so that the density change rate indicating a change in the number of dots) is smaller than the density change rate in the low gradation region when the reference dither matrix 142 is used. Has been. In the present embodiment, “density change rate” means a value expressed as dy / dx, where dx is a change in density level and dy is a change in density of the output image.

  As a result, as shown in FIG. 12, in the region where the light and shade level is “14” or more, the output result when the light absorption type change dither matrix 145 is used and when the reference dither matrix 142 is used. The graphs showing match. In other words, a sudden change in the density change rate caused by increasing the number of the minimum threshold value “1” is absorbed in the low gradation region (region having a low gray level). As a result, the density change rate when using the light absorption type dither matrix 145 can be made equal in the case of using the light absorption type dither matrix 145 in the halftone area and the high gradation area. Accordingly, in the halftone area and the high gradation area, even a slight difference in light and shade level can be reproduced clearly to the same extent as when the reference dither matrix 142 is used.

  Note that the low gradation area means an area including the lowest gradation level when the area from the minimum value to the maximum value excluding 0 among the values that can express the gradation level is divided into three areas. The high gradation area means an area including the highest gray level among the above three areas, and the halftone area is a value that can express the gray level. This means an area excluding a low gradation area and a high gradation area. How to set the value that defines the boundary between the low gradation area, the halftone area, and the high gradation area can be changed according to circumstances. When the value that can express the light and shade level is from 0 to 255, for example, the region from the first predetermined value below 1 to 50 is set as the low gradation region, and the region from the second predetermined value to 255 above 201 Is preferably a high gradation region.

  According to the PC 10 of the second embodiment, when the light absorption change dither matrix 145 is used, a rapid change in the density change rate that can occur in a region other than the halftone region is relatively conspicuous. It can be absorbed in a difficult low gradation region.

  Next, a third embodiment will be described with reference to FIGS. In the PC 10 of the second embodiment, the change dither matrix (the light absorption type dither matrix 145) is set so that the density change rate (dy / dx) is slower than the reference dither matrix 142 in the low gradation region. Was generated. On the other hand, the PC 10 according to the third embodiment generates a modified dither matrix so that the density change rate (dy / dx) is slower than that of the reference dither matrix 142 in the high gradation region. Note that the modified dither matrix generated by the PC 10 of the third embodiment is referred to as a “dark part absorption type dither matrix 146”.

  The print data generation process executed in the third embodiment is the same as that in the first embodiment (FIG. 5) except that the dither process (S514) is executed using the dark part absorption type change dither matrix 146 instead of the change dither matrix 143. This is the same as the print data generation process 5).

  FIG. 13 is a flowchart showing the dark part absorption type dither threshold value changing process (S130) executed in the third embodiment. This dark part absorption type dither threshold value changing process (S130) is a process executed instead of the dither threshold value changing process (S510: FIG. 7) of the first embodiment.

  First, the CPU 11 executes an input level 1 threshold value changing process (S702). The input level 1 threshold value changing process (S702) is the same process as S702 in FIG. By this input level 1 threshold value changing process (S702), a gap correction dither matrix (FIG. 3A) is generated.

  Next, the CPU 11 sets “2” to the variable “Si” (S1302), sets “255” to the variable “n” (S1304), and sets “255” to the variable “L” (S1306). . Next, in the reference dither matrix 142 (FIG. 2A), the CPU 11 specifies a cell in which a threshold value of “L” (eg, 255) is stored (S1307), and corrects the gap for the specified cell. The threshold value (for example, 249) set in the dither matrix (FIG. 3A) is acquired, and the acquired threshold value is set to the variable “Ln” (S1308).

  Next, the CPU 11 determines whether “Ln” and “n” are equal (S1310). When the determination in S1310 is negative (S1310: No), the CPU 11 changes the value of the cell in which the threshold value of “L” has been set to “n” in the gap correction dither matrix (FIG. 3A). (S1312). Next, the CPU 11 subtracts “Si” from “n” (S1314), and subtracts 1 from “L” (S1316). Then, the CPU 11 returns to S1307 and repeats the process.

  If the determination in S1310 is affirmed while the processing is repeated in this manner (S1310: Yes), the CPU 11 stores the generated dither matrix in the HDD 14 (FIG. 1) as the dark part absorption type change dither matrix 146. In step S1318, the dark part absorption type dither threshold value changing process (S130) ends. By this dark part absorption type dither threshold value changing process (S130), a dark part absorption type change dither matrix 146 is generated.

  FIG. 14 is a diagram illustrating an example of the dark part absorption type change dither matrix 146. As shown in FIG. 14, in the dark part absorption type change dither matrix 146, the threshold value “1” is set for eight cells, and an even threshold value is set between the maximum threshold value “255” and “243”. Is thinned out. The threshold value is continuously set between the threshold values “2” and “242”.

  FIG. 15 is a graph showing the correspondence between the light / dark level and the number of ON dots, and corresponds to FIG. The upper part of FIG. 15 shows the range where the gray level is 0 to 255, and the lower part shows the range where the gray level is 225 to 255 in an enlarged manner. In FIG. 15, a broken line indicates a case where dither processing is performed using the reference dither matrix 142, and a solid line indicates a case where dither processing is performed using the dark part absorption type change dither matrix 146 shown in FIG. 14.

  As described above, in the dark part absorption type change dither matrix 146 (FIG. 14), the minimum threshold value “1” is set to, for example, 8 cells, and the threshold value “2” or higher is continuously set. Yes. Therefore, as shown in FIG. 15, the number of ON dots when the dark part absorption type change dither matrix 146 is used is higher as a whole than when the reference dither matrix 142 is used. In other words, when the dark part absorption type change dither matrix 146 is used, the entire output image is printed darker than when the reference dither matrix 142 is used.

  However, in a high gradation region (an example of the high gradation region of the present invention) having a light and shade level of “241” or more, the change rate of the number of ON dots when using the dark part absorption type change dither matrix 146 becomes gradual, and the light and shade level At 255, the number matches the number of ON dots when the reference dither matrix 142 is used. In other words, when the dark part absorption type change dither matrix 146 is used, the density change rate indicating the change in the number of ON dots with respect to the change in the light and shade level in the high gradation region is the high gradation region when the reference dither matrix 142 is used. The threshold value of the dark part absorption type change dither matrix 146 is set so as to be smaller than the density change rate. Therefore, a rapid change in the density change rate caused by increasing the number of the minimum threshold value “1” is absorbed in the high gradation area (area with a high density level). As a result, the density change rate when the dark part absorption type change dither matrix 146 is used can be made equal to the case where the reference dither matrix 142 is used in the low gradation region and the halftone region where the light and shade levels are low.

  According to the PC 10 of the third embodiment, when the dark part absorption type change dither matrix 146 is used, a sudden change in the density change rate that may occur in an area other than the halftone area is relatively conspicuous. It can be absorbed in a difficult high gradation region. Similarly to the second embodiment, in the halftone area, the density can be reproduced in the output image at the same density change rate as when the reference dither matrix 142 is used.

  Next, a fourth embodiment will be described with reference to FIG. The PC 10 of the fourth embodiment generates the light absorption dither matrix 145 depending on whether the input image data to be printed is high luminance image data or low luminance image data, or This is different from the other embodiments in that the generation of the dark part absorption type dither matrix 146 is switched.

  FIG. 16 is a flowchart illustrating print data generation processing executed by the PC 10 according to the fourth embodiment. This print data generation process is executed instead of the print data generation process (FIG. 5) of the first embodiment. Hereinafter, the same steps as those included in the print data generation process (FIG. 5) of the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.

  In the fourth embodiment, after selecting the dither determination patches for four colors by the processing from S504 to S507, the CPU 11 creates a luminance histogram of the input image data (S1602). The input image data is composed of RGB image data composed of luminance values of R (red), G (green), and B (blue) colors. In the present embodiment, a value calculated according to the following equation (1) is calculated as the luminance of each pixel, and a histogram is created.

Luminance = R luminance value × 0.29891 + G luminance value × 0.58661 + B luminance value × 0.11448 (1)

  Next, the CPU 11 determines whether the input image data is high-luminance image data including many high-luminance pixels or low-luminance image data including many low-luminance pixels (S1604). Specifically, referring to the luminance histogram, for example, the amount of high-brightness pixels (number of pixels) is compared with the amount of low-brightness pixels (number of pixels). If it is larger than the amount of low pixels, it is determined as high luminance image data. Note that an appropriate threshold value for distinguishing between high luminance and low luminance may be, for example, an average value (center value) of values that the luminance can take.

  If it is determined in step S1604 that the input image data is high-luminance image data, that is, if it is determined that the input image data is image data representing an overall bright image, the CPU 11 executes a dark-absorption dither threshold value changing process. (S1606). This process (S1606) is the same as the process (S130) of FIG. According to this processing (S1606), the dark part absorption type change dither matrix 146 (FIG. 14) is generated as the change dither matrix for converting the target image data obtained by converting the high luminance image data into the output image data. And stored in the HDD 14 (FIG. 1). The dark area absorption type changed dither matrix corresponds to an example of the first type of changed dither matrix in the present invention.

  Then, the CPU 11 determines whether or not the processing for four colors in the dark part absorption type dither threshold value changing process (S1606) has been completed (S1608), and when the determination in S1608 is negative (S1608: No), S1606. Return to and repeat the process.

  On the other hand, if it is determined in step S1604 that the input image data is low-luminance image data, that is, if it is determined that the input image data is image data representing a dark image as a whole, the CPU 11 changes the dither threshold value of the light absorption type. Processing is executed (S1610). Since this process (S1610) is the same as the process (S100) of FIG. 10, detailed description thereof is omitted. According to this processing (S1610), the light absorption type change dither matrix 145 (FIG. 11) is used as the change dither matrix for converting the target image data obtained by converting the low luminance image data into the output image data. Generated and stored in the HDD 14. The dark part absorption type change dither matrix 145 corresponds to an example of a second type of change dither matrix.

  Then, the CPU 11 determines whether or not the processing for four colors of the light absorption type dither threshold value changing process (S1610) has been completed (S1612), and when the determination of S1612 is negative (S1612: No), Returning to S1610, the processing is repeated.

  In this way, when either the dark part absorption type change dither matrix 146 or the light part absorption type change dither matrix 145 is generated for four colors and the determination in S1608 or S1612 is affirmative (S1608 or S1612: Yes), the CPU 11 executes a color conversion process for converting the input image data into the target image data according to a predetermined relationship (S1614), and outputs the target image data according to the change dither matrices 145 and 146 generated immediately before. A dither process (S1616) for conversion to an image is executed. That is, the target image data obtained by color-converting the high-luminance image data is converted into output image data using the dark area absorption type change dither matrix 146 generated in the processing of S1606, while the low-luminance image data Is converted into output image data using the light absorption type change dither matrix 145 generated in the processing of S1610.

  According to the fourth embodiment, target image data obtained by color-converting high-luminance image data is dithered using the dark part absorption type change dither matrix 146. As described with reference to FIG. 17, when the dark part absorption type change dither matrix 146 is used, the density change rate in the high gradation region (that is, the dark color region) is the case where the reference dither matrix 142 is used. Will be different. However, since the high luminance image data is bright image data including many high luminance pixels, the change in the density change rate in the high gradation region (that is, the dark color region corresponding to the low luminance) is relatively inconspicuous.

  Similarly, target image data obtained by color-converting low-luminance image data is dithered using a light absorption type change dither matrix 145. As described with reference to FIG. 13, when the light absorption type change dither matrix 145 is used, the density change rate in the low gradation region (that is, the light color region) is the case where the reference dither matrix 142 is used. Will be different. However, since the low-brightness image data is dark image data including many low-brightness pixels, the change in the density change rate in the low gradation region (that is, a light-colored region corresponding to high luminance) is relatively inconspicuous. .

  The CPU 11 that executes the steps S100, S130, S510, S1606, and S1610 corresponds to an example of a changing unit of the present invention, and executes the steps S706 to S714, S1004 to S1018, S1302 to S1316, S1606, and S1610. The CPU 11 corresponds to an example of threshold adjustment means. The CPU 11 that executes step S504 corresponds to an example of the patch printing control unit of the present invention, and the CPU 11 that executes step S506 corresponds to an example of a selection unit. Further, the CPU 11 that executes the steps S801 and S1002 corresponds to an example of the minimum threshold setting means of the present invention, and the CPU 11 that executes the steps S514 and S1616 corresponds to an example of a dither means. Further, the CPU 11 that executes the step of S1604 corresponds to an example of a determination unit of the present invention, and the CPU 11 that executes the step of S1614 corresponds to an example of a conversion unit.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be easily made without departing from the spirit of the present invention. Can be inferred.

  For example, in the present embodiment, the number of the minimum threshold value “1” is increased. However, when a plurality of minimum threshold values “1” are set in the reference dither matrix 142 in advance, the dither determination patch 52 with a lighter color is added. When the user designates, for example, the threshold value may be changed so as to decrease the number of minimum threshold values.

  In the above-described embodiment, the print data generation process (FIGS. 5 and 16) is executed by the PC 10, but may be executed by the control unit 50 of the printer 40 instead. In this case, the control unit 50 (see FIG. 1) corresponds to an example of a printing control apparatus of the present invention, the image forming unit 47 corresponds to an example of a printing unit, and the printer 40 corresponds to an example of a printing apparatus. The CPU 41 corresponds to an example of the computer of the present invention, and the program stored in the ROM 42 corresponds to an example of a print control program.

  In the above-described embodiment, the printer 40 is described as being configured by a laser printer. However, the present invention is applicable even when the printer 40 is a printer that employs a system other than a laser, such as an inkjet system.

  In the above embodiment, the threshold values of the minimum threshold setting dither matrix (FIG. 2B) are further changed to generate the changed dither matrices 143, 145, and 146. The modified dither matrix 143 may be configured to be used for dither processing. Even in this case, similarly to the above-described embodiment, the printer 40 can print an output image in which the minimum density is appropriately expressed.

  In the above embodiment, the dither determination patch 52 designated by the user is selected. However, when the printer 40 includes a sensor for density measurement, the printer 40 can acquire the measurement result of the sensor. In such a configuration, the dither determination patch 52 may be selected based on the measurement result of the sensor.

FIG. 2 is a block diagram illustrating an electrical configuration of the PC according to the first embodiment and a printer connected to the PC. (A) is a figure which shows an example of a reference | standard dither matrix, (b) is a figure which shows an example of a minimum threshold value setting dither matrix. (A) is a figure which shows an example of a gap correction dither matrix, (b) is a figure which shows an example of a change dither matrix. It is a figure which shows the output image data obtained by a dither process about each case where the lightness level of each pixel which comprises object image data is "1" to "4". 3 is a flowchart illustrating print data generation processing executed by the PC according to the first embodiment. It is a figure which shows an example of the test sheet which PC makes a printer print. It is a flowchart which shows a dither threshold value change process. It is a flowchart which shows an input level 1 threshold value change process. It is a graph which shows the change of the ON dot number of output image data with respect to the change of the shading level of object image data, (a) is a graph which shows the case where a dither process is performed using a reference | standard dither matrix, (b) is a change. It is a graph which shows the case where a dither process is carried out using a dither matrix. It is a flowchart which shows the light part absorption type dither threshold value change process performed with PC of 2nd Embodiment. It is a figure which shows an example of the light part absorption type change dither matrix. It is a graph which shows the correspondence of a light / dark level and the number of ON dots. It is a flowchart which shows the dither threshold value change process of the dark part absorption type performed with PC of 3rd Embodiment. It is a figure which shows an example of a change absorption dither matrix of a dark part absorption type. It is a graph which shows the correspondence of a light / dark level and the number of ON dots. It is a flowchart which shows the print data generation process performed with PC of 4th Embodiment. FIG. 10 is a diagram illustrating how an image is affected by a difference in ease of dot fixing when a light image is printed in a conventional printer.

Explanation of symbols

10 PC
40 Printer 52 Dither Determination Patch 141 Printer Driver 142 Reference Dither Matrix 143 Change Dither Matrix 145 Light Part Absorption Type Change Dither Matrix 146 Dark Part Absorption Type Change Dither Matrix

Claims (11)

A print control apparatus that converts target image data representing a target image into output image data representing an output image, and causes the printing unit to print the output image,
Patch printing control means for causing the printing unit to print a plurality of types of patches having different densities;
Selecting means for selecting any one of the plurality of types of patches printed by the printing unit;
Changing means for generating a changed dither matrix in which at least a part of a threshold group included in a reference dither matrix prepared in advance is changed;
Dither means for converting the target image data into the output image data using the modified dither matrix;
The changing means is the output obtained by converting the target image data using the conversion dither matrix when the gray level of each pixel included in the target image data is a minimum value excluding 0. Changing at least a part of the threshold group of the reference dither matrix so that the density of the output image printed by the printing unit based on image data is equal to the density of the selected patch; A print control apparatus that generates the modified dither matrix. The plurality of types of patches correspond to different shade levels, and the density of each patch is the target image data of each pixel having the corresponding shade level as a threshold group of the reference dither matrix. It is equal to the density of the output image represented by the output image data obtained by comparison,
The changing means is
A minimum threshold setting dither matrix is generated by changing a threshold level below the gray level corresponding to the selected patch from the threshold group included in the reference dither matrix to a minimum threshold among the threshold groups included in the reference dither matrix. A minimum threshold setting means for
The print control apparatus according to claim 1, wherein the change unit generates the change dither matrix based on the minimum threshold setting dither matrix. The changing means further includes:
Threshold adjustment means for generating the changed dither matrix by changing a threshold other than the minimum threshold included in the minimum threshold setting dither matrix so that each threshold included in the changed dither matrix is continuous. The print control apparatus according to claim 2. The threshold adjustment means further includes
Threshold values other than the minimum threshold value included in the minimum threshold value setting dither matrix are set to be larger than the minimum threshold value and smaller than the next smallest threshold value after the minimum threshold value included in the minimum threshold value setting dither matrix. The print control apparatus according to claim 3, wherein the change dither matrix is generated by changing to the following. The threshold adjustment means further includes
The density change rate in the halftone area when the changed dither matrix is used, and the density change rate indicating the change in density of the output image with respect to the change in the gray level is the halftone area when using the reference dither matrix 5. The changed dither matrix is generated by changing a threshold other than the minimum threshold of the minimum threshold setting dither matrix so as to be equal to the density change rate in a region. The printing control apparatus described. The threshold adjustment means includes
The change dither matrix is a first type of change dither matrix, and the density change rate in the low gradation region when the first type of change dither matrix is used, the case where the reference dither matrix is used. 6. The print control apparatus according to claim 5, wherein the first type of changed dither matrix set to be smaller than the density change rate in a low gradation region is generated. The threshold adjustment means includes
The modified dither matrix is a second type of modified dither matrix, and the density change rate in the high gradation region when the second type of modified dither matrix is used is the higher order when the reference dither matrix is used. 6. The print control apparatus according to claim 5, wherein the second type of change dither matrix set so as to be smaller than the density change rate in the tone area is generated. Conversion means for converting input image data into the target image data;
Determining means for determining whether the input image data is high-luminance image data including many high-luminance pixels or low-luminance image data including many low-luminance pixels;
The threshold adjustment means includes
When the input image data is high-luminance image data, the target image data obtained by converting the high-luminance image data by the conversion unit is used as the modified dither matrix for converting the output image data. Generate one kind of the modified dither matrix,
When the input image data is low-luminance image data, the target image data obtained by converting the low-luminance image data by the conversion unit is used as the modified dither matrix for converting the output image data. Generate two types of the modified dither matrix,
The first type of change dither matrix is such that the density change rate in the high gradation region when the first type change dither matrix is used is the density change in the high gradation region when the reference dither matrix is used. Set to be less than the rate,
The second type of change dither matrix is such that the density change rate in the low gradation region when the second type of change dither matrix is used is the same as that in the low gradation region when the reference dither matrix is used. The print control apparatus according to claim 5, wherein the print control apparatus is set to be smaller than the density change rate.   The print control apparatus according to claim 1, wherein the selection unit selects a patch designated by a user from the plurality of types of patches.   A printing apparatus comprising: the printing control apparatus according to claim 1; and the printing unit. A print control program for converting target image data representing a target image into output image data representing an output image, and causing the printing unit to print the output image,
Computer
Patch printing control means for causing the printing unit to print a plurality of types of patches having different densities;
Selecting means for selecting any one of the plurality of types of patches printed by the printing unit;
Changing means for generating a changed dither matrix in which at least a part of a threshold group included in a reference dither matrix prepared in advance is changed;
Using the modified dither matrix, the target image data is made to function as dither means for converting into the output image data,
The changing means is the output obtained by converting the target image data using the conversion dither matrix when the gray level of each pixel included in the target image data is a minimum value excluding 0. Changing at least a part of the threshold group of the reference dither matrix so that the density of the output image printed by the printing unit based on image data is equal to the density of the selected patch; A printing control program for generating the modified dither matrix.

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