JP5409552B2 - Image forming apparatus and image forming program - Google Patents

Description

  The present invention relates to an image apparatus and an image program that prevent data loss for a specific print pattern.

  In an image forming apparatus such as a color printer, image forming processing is performed by interpreting print data transmitted from a host computer.

  In such an image forming process, when an image forming process is performed on a specific print pattern, a mask pattern of input print data and a halftone pattern of an object or the like to which the mask pattern is applied (pixel validity or invalidity is checked) And a matrix pattern which is a pattern), is converted into image data, and is printed out.

  However, in the mask pattern, interference with the matrix pattern causes a moiré phenomenon that a plane in the four planes (CMYK) is not output at all, or appears to be an unintended striped pattern, and image reproducibility is remarkably high. May decrease.

  Further, depending on how the mask pattern and the matrix pattern are overlapped, an actually printed image may cause a different phenomenon from the input print data image.

  On the other hand, in the image forming apparatus described in Patent Document 1, conversion pattern data having the same density value is generated by rearranging the valid and invalid pixels of the matrix pattern, and the conversion pattern data is used for the synthesis to generate moire. Is prevented.

  In the printing apparatus described in Patent Document 2, a simulated matrix pattern is generated and compared with a mask pattern, and the appearance rate of pixels to be printed is calculated by this comparison. The appearance rate is increased by converting the data.

  However, those described in Patent Documents 1 and 2 are not sufficient measures against the appearance rate of halftone pixels after screen processing. In particular, in the case of monochromatic output, color loss or the like may still occur, and there is a problem in image reproducibility.

JP 2007-27826 A JP 2006-166328 A

  The problem to be solved by the present invention is that there is no sufficient measure for the appearance rate of halftone pixels after screen processing, and there is a problem in image reproducibility in the case of monochromatic output.

The present invention is an image forming apparatus that generates halftone dot image data composed of halftone dots for input image data in order to improve image reproducibility in the case of monochromatic output after screen processing, A color conversion processing unit that generates color conversion data by performing color space conversion processing by applying a color conversion table to the input image data, and a screen table for each pixel block of a predetermined size based on the color conversion data. A screen processing unit for generating the halftone image data, a single color check unit for determining whether the halftone image data is a single color output, and the halftone image when the halftone image data is a single color output. An appearance rate check unit that determines an appearance rate of halftone pixels in data, and a color conversion table that is applied to the color conversion processing unit when the appearance rate of the halftone pixels is equal to or less than a threshold value The color conversion processing unit regenerates color conversion data by applying the changed color conversion table, and the screen processing unit regenerates the regenerated color conversion. Based on the data, the halftone dot image data by the multi-color output having the same color as the single color output is regenerated, and the table instruction unit is controlled by the user through the operation panel unit and is stored in the storage unit. The main feature is that a color conversion table to be applied is selected from the conversion tables, and the change of the color conversion table is repeated until the appearance rate of the halftone pixels becomes larger than a threshold value .

  In the present invention, when the halftone image data after the screen processing is a single color output and the appearance rate of the halftone pixel is equal to or less than the threshold value, the halftone dot by the multicolor output of the same color as the single color output through the change of the color conversion table Image data can be regenerated. As a result, the image structure can be changed to increase the appearance rate of halftone pixels, and the image reproducibility can be improved.

1 is a block diagram of a control unit of an image forming apparatus (first embodiment). FIG. 6 is a flowchart of image forming processing (first embodiment). FIG. 10 is a block diagram of a control unit of the image forming apparatus (second embodiment). 10 is a flowchart of image forming processing (second embodiment). (A) is pattern data, (b) is foreground data, (c) is a mask pattern, (d) is background data, (e) is a conceptual diagram of a matrix pattern (Example 2). . (A) is a matrix pattern, (b) is a conversion matrix pattern, (c) is a conceptual diagram of the conversion matrix pattern after input value conversion (Example 2). 10 is a flowchart of image forming processing (third embodiment). FIG. 10 is a block diagram of a control unit of an image forming apparatus (Example 4).

  The goal of improving image reproducibility in the case of single-color output after screen processing was realized by regenerating halftone image data with multiple color outputs of the same color as the single-color output by changing the color conversion table.

[Control Unit of Image Forming Apparatus]
FIG. 1 is a block diagram illustrating a control unit of the image forming apparatus according to the first exemplary embodiment of the present invention.

  The image forming apparatus 1 is composed of a digital multifunction peripheral such as a color printer, for example, and has at least a print output function. The image forming apparatus 1 includes a control unit 2 configured with a computer.

  The control unit 2 is a control element such as a CPU (Central Process Unit) that executes a software program stored in a storage unit (not shown) such as a ROM to perform various controls and operations. The control unit 2 includes a PDL interpretation unit 3, an output adjustment unit 4, and a determination unit 5 by executing an image forming program that is a software program.

  The PDL interpretation unit 3 interprets a command of PDL data (page description language data) as input print data transmitted from an external input device such as a computer.

  The output adjustment unit 4 includes a color conversion processing unit 6, a gamma correction unit 7, a screen processing unit 8, and a table instruction unit 9, and performs processing on PDL data and the like sent from the PDL interpretation unit 3.

  The color conversion processing unit 6 performs color conversion processing on input image data based on interpretation of PDL data. In this color conversion processing unit 6, the color space of the image data is changed from red (R), green (G), and blue (B) to cyan (C), magenta (M), and color space in the image forming apparatus 1. Color conversion data is generated by performing color conversion to yellow (Y) and black (K). This color conversion processing is performed using a color conversion table as a cLUT (Color Look-Up Table) stored in the storage unit.

  The gamma correction unit 7 converts characteristics such as luminance and density of the color conversion data. This conversion is performed using a gamma correction curve that is a density conversion function to generate gamma correction data.

  The screen processing unit 8 performs screen processing on the gamma correction data. The screen processing generates halftone image data composed of halftone pixels using a screen table for each pixel block of a predetermined size based on the gamma correction data.

  The table instruction unit 9 instructs the color conversion processing unit 6 to change the color conversion table to be applied in response to a change request from the appearance rate check unit 11 described later.

  The halftone image data sent from the output adjustment unit 4 is printed out by the print output unit and printed on paper or the like.

  When the output adjustment unit 4 performs output adjustment, the determination unit 5 determines whether or not the halftone image data in the screen processing unit 8 is pattern data and is a single color, and determines the appearance rate of pixels to be printed. I do. In this embodiment, a single color check unit 10 and an appearance rate check unit 11 are provided.

  The single color check unit 10 determines whether or not the halftone image data after the screen processing is a single color output.

  The appearance rate check unit 11 determines the appearance rate of halftone pixels when the halftone image data is a single color. At the time of determination, the appearance rate is calculated and compared with a predetermined threshold value. The threshold value can be arbitrarily set so as to ensure desired image reproducibility.

When the appearance rate is lower than the threshold, the appearance rate check unit 11 issues a color conversion table change request to the table instruction unit 9. In response to the change request, the table instruction unit 9 instructs to change the color conversion table applied to the color conversion processing unit 6 as described above.
[Image formation processing]
FIG. 2 is a flowchart of the image forming process according to the first embodiment of the present invention.

  In the image forming apparatus 1, when PDL data is input, the image forming process is sequentially performed from step S 1 in FIG. 2.

  In step S1, a “PDL interpretation” process is executed. In this process, the PDL interpretation unit 3 sequentially interprets the input PDL data commands. Thereby, the process proceeds to step S2.

  In step S2, “color conversion processing” is executed as the color conversion processing procedure. In this process, the color conversion processing unit 6 performs color conversion on the input image data by PDL interpretation, and generates color conversion data having a color space of CMYK. Thereby, the process proceeds to step S3.

  In step S3, “gamma correction processing” is executed. In this process, the gamma correction unit 7 converts characteristics such as luminance and density of the color conversion data to generate gamma correction data. Thereby, the process proceeds to step S4.

  In step S4, “screen processing” is executed as a screen processing procedure. In this process, the screen processing unit 8 performs screen processing based on the gamma correction data to generate halftone image data including halftone pixels. Thereby, the process proceeds to step S5.

  In step S5, a “monochromatic output?” Process is executed as a monochromatic output check procedure. In this process, it is determined whether or not the halftone dot image data is a single color output. That is, when the halftone image data is a single color output, the process proceeds to step S6, and when it is not a single color output, the process proceeds to step S8 as a multi-color output with four colors of CMYK.

  In step S6, a determination process of “appearance rate is below threshold?” Is executed as an appearance rate check procedure. In this determination process, the appearance rate of halftone pixels in the halftone image data is calculated and compared with a threshold value. When the appearance rate is lower than the threshold value, the process proceeds to step S7, and when the appearance rate is higher than the threshold value, the process proceeds to step S8.

  In step S7, a “table instruction” process is executed as a table instruction procedure. In this process, the appearance rate check unit 11 issues a change request that is an instruction of the color conversion table to be applied to the table instruction unit 9. In response to the change request, the table instruction unit 9 instructs to change the color conversion table applied to the color conversion processing unit 6 as described above. Thereby, the image forming process returns to step S2.

  When returning from step S7 to step S2, the color conversion processing unit 6 regenerates color conversion data by applying the changed color conversion table. Next, after the “gamma correction process” in step S3, the process proceeds to step S4.

  In step S4, the screen processing unit 8 regenerates halftone dot image data based on a plurality of color outputs having the same color as the single color output based on the regenerated color conversion data. Thereafter, the processing after step S5 is executed in the same manner as described above.

In step S8, a “drawing start” process is executed. In this processing, the halftone image data is sent to the print output unit, and print output (drawing) on paper or the like is performed.
[Effect of Example 1]
In the image forming apparatus 1 of the present embodiment, a color conversion processing unit 6 that performs color space conversion processing by applying a color conversion table to input image data to generate color conversion data, and a predetermined size based on the color conversion data A screen processing unit 8 that generates halftone image data using a screen table for each pixel block, a single color check unit 10 that determines whether the halftone image data is a single color output, and a halftone image data that is a single color output. And an appearance rate check unit 11 that determines the appearance rate of halftone pixels in the halftone image data, and a color that is applied to the color conversion processing unit 6 when the appearance rate of halftone pixels is equal to or less than a threshold value. The color conversion processing unit 6 regenerates the color conversion data by applying the changed color conversion table, and the screen processing unit 8 regenerates the color conversion data. Regenerate the halftone image data by a plurality of colors output as a monochrome output the same color based on the converted data.

  Therefore, the image forming apparatus 1 determines that the image structure is difficult to output when the halftone image data after the screen processing is a single color output and the appearance rate of the halftone pixels is equal to or less than the threshold value, and performs color conversion. It is possible to regenerate halftone dot image data by single color output and multiple color output (composite output) of the same color through changing the table.

  As a result, in the image forming apparatus 1, the image structure can be changed to increase the appearance rate of halftone pixels, and the image reproducibility can be improved.

  FIG. 3 is a block diagram of the control unit of the image forming apparatus according to the second embodiment of the present invention. In the present embodiment, components corresponding to those in the first embodiment are denoted by the same reference numerals or the same reference numerals with an A, and redundant description is omitted.

  As illustrated in FIG. 3, in the image forming apparatus 1 </ b> A according to the second embodiment, the control unit 2 </ b> A includes a drawing processing unit 12 in addition to the configuration of the first embodiment.

  The drawing processing unit 12 includes a pattern processing unit 13, a pattern conversion unit 14, and an input value conversion unit 15.

  The pattern processing unit 13 creates pattern data of input print data as image data based on the interpretation result of the PDL interpretation unit 3A. The pattern data of the present embodiment is composed of foreground data that is a foreground pattern and background data that is a background color.

  In the pattern processing unit 13, a mask pattern corresponding to the foreground data interpreted by the PDL interpretation unit 3A and a halftone pattern corresponding to the background data of the intermediate color (a matrix pattern in which pixel validity / invalidity is a checkered pattern) Generate.

  The matrix pattern is for pseudo intermediate color processing, and is composed of “1” and “0” representing valid / invalid display of pixels. The effective pixels of the matrix pattern have a density according to an input value based on the interpretation result of the PDL interpretation unit 3A, and the input value is red (R), green which is a color space constituting the input print data. It is determined by (G) and blue (B).

  Therefore, the pattern processing unit 13 interprets the input print data, and implements a pattern processing procedure for determining a mask pattern and a matrix pattern to be combined with the mask pattern, the input value and the number of valid / invalid pixels. To do.

  The pattern conversion unit 14 generates a conversion matrix pattern in which the number of effective pixels is increased with respect to the matrix pattern generated by the pattern processing unit 13. In the present embodiment, conversion is performed in which all pixel displays are effective pixels (all displays).

  Therefore, the pattern conversion unit 14 realizes a pattern conversion procedure for generating a conversion matrix pattern in which the number of effective pixels of the matrix pattern is increased.

  The input value conversion unit 15 adjusts the density of the conversion matrix pattern. That is, the input value conversion unit 15 changes the input value of the conversion matrix pattern according to the increase in the number of pixels so that the density of the conversion matrix pattern becomes equal to the density of the matrix pattern generated by the pattern processing unit 13. Do. Thereby, the input value conversion matrix pattern data is generated.

  Therefore, the input value conversion unit 15 realizes an input value conversion procedure for changing the input value of the conversion matrix pattern according to the increase in the number of pixels so that the densities of the conversion matrix pattern and the matrix pattern are equal.

  FIG. 4 is a flowchart of the image forming process. In the flowchart of FIG. 4, steps S9 to 12 are newly added after step S1 of FIG. That is, in the flowchart of FIG. 4, after “PDL interpretation” in step S1, the processes in steps S9 to S12 are executed.

  In step S9, a “pattern data discrimination” process is executed. In this process, the presence / absence of pattern data is determined based on command interpretation by the PDL interpretation unit 3A. If the pattern data is determined from the PDL data, the process proceeds to step S10. If the pattern data is not determined, the process proceeds to step S2.

  In step S10, “pattern processing” is executed as a pattern processing procedure. In this process, a mask pattern and a matrix pattern are generated corresponding to the foreground data and the background data based on the PDL interpretation, and the process proceeds to step S11. A generation image of the mask pattern and the matrix pattern will be described later with reference to FIG.

  In step S11, a “pattern conversion” process is executed as a pattern conversion procedure. In this process, the pattern conversion unit 14 increases the number of effective pixels for the matrix pattern. In this embodiment, a conversion matrix pattern having all matrix patterns as effective pixels is generated, and the process proceeds to step S12. The pattern conversion image will be described later with reference to FIG.

  In step S12, an “input value conversion” process is executed as an input value conversion procedure. In this process, the input value converter 15 adjusts the density of the conversion matrix pattern. Thereby, the process proceeds to step S2. The image of density adjustment will be described later with reference to FIGS.

Thereafter, the processing after step S2 is repeated as in the first embodiment. In step S5, “pattern data and single color output?” Is executed, and in step S6, “pattern appearance rate is equal to or less than threshold?” Is executed.
[Generation of Mask Pattern Data and Matrix Pattern Data: Step S10]
FIG. 5 shows pattern processing in step S10 of FIG. 4, where (a) is pattern data, (b) is foreground data, (c) is mask pattern, (d) is background data, and (e) is a matrix pattern. FIG. FIG. 5 illustrates a case where checkered pattern data including background data of 50% red is input when the color space is RGB as a specific example.

  As shown in FIG. 5, after pattern data (a) is input as PDL data, foreground data (b) and background data (d) are processed by interpretation of the command.

From the foreground data (b), a mask pattern (c) including a foreground pattern is generated. From the background data (d), a matrix pattern (e) in which the background color is represented by a pseudo intermediate color is generated. In the matrix pattern, the density is defined by the input value and the number of effective invalid pixels. In this embodiment, the input value is red: 200, and the valid / invalid pixels are arranged in a checkered pattern.
[Pattern Conversion and Input Value Conversion: Step S11, Step S12]
6 shows pattern conversion and input value conversion in step S11 of FIG. 4, where (a) is a matrix pattern, (b) is a conversion matrix pattern, and (c) is a concept of a conversion matrix pattern obtained by converting input values. FIG.

  As shown in FIG. 6, in the pattern conversion in step S <b> 11 of FIG. 4, the matrix pattern (a) generated as described above is converted into a conversion matrix pattern (b) in which all the effective pixels are used. The input value of this conversion matrix pattern (b) remains red: 200, and the density value is doubled.

  In the input value conversion in step S12 of FIG. 4, the input value of the conversion matrix pattern generated as described above is converted to adjust the density. In the conversion of the input value, the input value of the conversion matrix pattern is changed according to the increase in the number of pixels so that the densities of the matrix matrix and the conversion matrix pattern in FIGS. 6A and 6B are equal.

  This input value is calculated from the following mathematical formula (1).

(Input value calculation formula)

InputRGB ′: Input value to be converted of the conversion matrix pattern InputRGB: Input value when generating a matrix pattern by a command

  In this embodiment, since the number of effective pixels is doubled, the input value of the conversion matrix pattern (b) is half red: 100.

  As described above, the image forming apparatus 1 </ b> A according to the present embodiment can achieve the same functions and effects as those of the first embodiment.

  In addition, the image forming apparatus 1A interprets the input print data, determines a mask pattern and a matrix pattern to be synthesized with the mask pattern by specifying the density with the input value and the number of valid / invalid pixels as input image data. Part 13 is provided.

  Therefore, even if the input PDL data is pattern data, the appearance structure of halftone pixels can be increased by changing the image structure for monochromatic output, and the image reproducibility can be improved.

  In addition, the image forming apparatus 1A includes a pattern conversion unit 14 that generates a conversion matrix pattern to be combined with a mask pattern by increasing the number of effective pixels with respect to the determined matrix pattern, and the conversion matrix pattern and the pre-conversion (original) An input value conversion unit 15 is provided that changes the input value of the conversion matrix pattern according to the increase in the number of pixels so that the density with the matrix pattern becomes equal.

  Therefore, the image forming apparatus 1A can perform pattern processing and pattern conversion on the pattern data to form a converted matrix pattern in which the effective pixels of the matrix pattern are increased.

  As a result, in the image forming apparatus 1A, it is possible to reliably form an image of pattern data regardless of the way in which the mask pattern and the matrix pattern as input image data that is the premise of the screen processing overlap.

  In particular, in the image forming apparatus 1A of the present embodiment, all pixels on the matrix pattern are made effective pixels by pattern conversion processing, so that image formation can be reliably performed without losing pattern data such as a checkered pattern. it can.

  Therefore, in the image forming apparatus 1A, the pattern appearance rate after the screen processing can be increased, and the image reproducibility can be improved more reliably.

  Further, in the image forming apparatus 1A, by changing the input value of the conversion matrix pattern, the density of the conversion matrix pattern can be made equal to the density of the effective pixel and invalid pixel display of the original matrix pattern.

  Therefore, in the image forming apparatus 1A, even if a conversion matrix pattern is used, color reproducibility equivalent to that of the original matrix pattern can be ensured. Therefore, in this embodiment, it is possible to ensure color reproducibility while improving the appearance rate of objects and the like, and to improve image reproducibility more reliably.

  FIG. 7 is a flowchart of the image forming process according to the third embodiment of the present invention. Since the image forming apparatus of the present embodiment has the same configuration as the image forming apparatus 1A of the second embodiment, the same reference numerals as those of the second embodiment are used and redundant description is omitted.

  As illustrated in FIG. 7, the image forming apparatus 1 </ b> A according to the present embodiment performs image forming processing in which step S <b> 13 is newly added after step S <b> 6 in FIG. 4.

  That is, in the flowchart of FIG. 7, if the pattern data is not a single color in step S5, the process proceeds to step S13.

  In step S13, as in step S6, the determination process of “pattern appearance rate is equal to or less than threshold?” Is executed. Then, when the appearance rate is lower than the threshold, the process proceeds to step S12, and when the appearance rate is higher than the threshold, the process proceeds to step S8.

  When returning from step S13 to step S12, the input value of the conversion matrix pattern is changed again.

The reconversion of the input value is performed by the following equation (2).
(Input value calculation formula accompanying the change)

Input correction factor: α
(InputRGB '/ InputRGB'<α<InputRGB / InputRGB ')
InputRGB ′: Input value at the time of forming the conversion matrix pattern to be reconverted InputRGB: Input value at the time of generating the matrix pattern by the command After that, the processing after step S2 is repeated, and the appearance rate exceeds the threshold value at step S13. The process proceeds to step S8, where “drawing is started”.

  As described above, the image forming apparatus 1 </ b> A according to the present embodiment can achieve the same effects as those of the second embodiment.

  In addition, in this embodiment, when the pattern appearance rate falls below a predetermined threshold, the input correction coefficient α is multiplied to change the input value of the transformation matrix pattern again, and the pattern in the subsequent screen processing is changed. You can increase the appearance rate.

  Therefore, in this embodiment, the image reproducibility can be improved more reliably.

  FIG. 8 relates to a fourth embodiment of the present invention, and FIG. 8 is a block diagram of a control unit of the image forming apparatus 1.

  In the present embodiment, as shown in FIG. 8, the same reference numerals are assigned to the components corresponding to the first embodiment, and a duplicate description is omitted.

  The image forming apparatus 1B of this embodiment includes an operation panel unit 16 that is an input device for instruction operation, and a panel control unit 17 that controls the operation panel unit 16 in the control unit 2B.

  The operation panel unit 16 is an operation display element such as a touch panel that receives setting / selection operations such as various functions of the image forming apparatus 1B and sends the operation contents to the panel control unit 17 in the control unit 2B.

  By operating the operation panel unit 16, the table instruction unit 9 can be controlled via the panel control unit 17, and halftone dot image data of a plurality of colors can be formed by changing the color conversion table.

  Therefore, in this embodiment, in addition to the same effects as the above embodiment, the appearance rate can be raised based on the user's intention.

  The input device may be an external control device such as a PC connected to the image forming apparatus 1B via a network.

[Other]
As mentioned above, although the Example of this invention was described, this invention is not limited to this, A various change is possible.

  For example, in Embodiments 2 to 4 described above, pattern conversion is performed using all matrix patterns for the background color of the input print data as effective pixels. However, the effective pixel display may not be all.

  In the second to fourth embodiments, pattern conversion and input value conversion can also be performed as one piece. For image formation by combining a mask pattern corresponding to foreground data and a matrix pattern corresponding to background data, It is also possible to perform image formation by combining the mask pattern of the image mask with a matrix pattern corresponding to the foreground data and the background data.

1 Image forming apparatus 3 PDL interpretation unit (determination unit)
6 color conversion processing unit 8 screen processing unit 9 table instruction unit 10 single color check unit
11 appearance rate check unit 13 pattern processing unit 14 pattern conversion unit 15 input value conversion unit 17 operation panel unit

Claims (8)

An image forming apparatus that generates halftone dot image data composed of halftone dots with respect to input image data, and prints it out.
A color conversion processing unit that performs color space conversion processing by applying a color conversion table to the input image data to generate color conversion data;
A screen processing unit that generates the halftone image data using a screen table for each pixel block of a predetermined size based on the color conversion data;
A monochrome check unit for determining whether the halftone image data is a monochrome output;
An appearance rate check unit for determining an appearance rate of halftone pixels in the halftone image data when the halftone image data is a single color output;
A table instructing unit for instructing a change of a color conversion table to be applied to the color conversion processing unit when the appearance rate of the halftone pixels is equal to or less than a threshold;
The color conversion processing unit regenerates color conversion data by applying the changed color conversion table;
The screen processing unit regenerates the halftone image data by a plurality of colors output to be the monochrome output the same color on the basis of the regenerated color conversion data,
The table instructing unit selects a color conversion table to be applied from color conversion tables controlled through an operation panel unit operated by a user and stored in a storage unit, and the appearance rate of the halftone pixels is lower than a threshold value. Repeat the change of the color conversion table until it becomes larger,
An image forming apparatus. The image forming apparatus according to claim 1,
A pattern processing unit that interprets the input print data and defines a mask pattern and a matrix pattern to be combined with the mask pattern by defining the density with the input value and the number of effective invalid pixels, as the input image data;
An image forming apparatus. The image forming apparatus according to claim 2,
A pattern conversion unit for generating a conversion matrix pattern to be combined with the mask pattern by increasing the number of effective pixels with respect to the determined matrix pattern;
An input value conversion unit that changes the input value of the conversion matrix pattern according to an increase in the number of pixels so that the densities of the conversion matrix pattern and the matrix pattern before conversion are equal;
An image forming apparatus comprising: The image forming apparatus according to any one of claims 1 to 3,
The table instruction unit changes the color conversion table in accordance with an input from an input device for instruction operation.
An image forming apparatus. An image forming program that generates halftone dot image data composed of halftone pixels for input image data, and prints it out.
A color conversion processing procedure for generating color conversion data by performing color space conversion processing by applying a color conversion table to the input image data;
A screen processing procedure for generating the halftone image data using a screen table for each pixel block of a predetermined size based on the color conversion data;
A monochrome output check procedure for determining whether the halftone image data is a monochrome output;
An appearance rate check procedure for determining an appearance rate of the halftone pixels when the halftone image data is a single color output;
Causing the computer to execute a table instruction procedure for instructing a change of a color conversion table to be applied to the color conversion processing unit when an appearance rate of the halftone pixels is equal to or less than a threshold;
The color conversion processing procedure regenerates color conversion data by applying the changed color conversion table,
The screen processing procedure generates halftone image data by a plurality of colors output to be the monochrome output the same color on the basis of the regenerated color conversion data,
In the table instruction procedure, the table instruction unit is controlled via an operation panel unit operated by a user, and a color conversion table to be applied is selected from the color conversion tables stored in the storage unit, and the halftone pixel appearance rate Repeat the change of the color conversion table until is greater than the threshold,
An image forming program. An image forming program according to claim 5,
The computer executes a pattern processing procedure for interpreting the input print data and determining the mask pattern, the input value and the number of effective invalid pixels as a density, and determining the matrix pattern synthesized with the mask pattern as the input image data. ,
An image forming program. An image forming program according to claim 6,
A pattern conversion procedure for generating a conversion matrix pattern to be combined with the mask pattern by increasing the number of effective pixels with respect to the determined matrix pattern;
Causing the computer to execute an input value conversion procedure for changing the input value of the conversion matrix pattern according to the increase in the number of pixels so that the densities of the conversion matrix pattern and the matrix pattern before conversion are equal.
An image forming program. An image forming program according to any one of claims 5 to 7,
The table instruction procedure changes the color conversion table in accordance with an input from an input device for instruction operation.
An image forming program.