JP5380361B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method for preventing a decrease in visibility due to misregistration.

  In recent years, as one of image forming methods represented by an electrophotographic printer, photosensitive drums for four colors of black, yellow, magenta, and cyan are arranged in a row and formed (developed) on each photosensitive drum. There is known a color printer that realizes full-color printing by sequentially transferring and synthesizing toner images (plate images) of respective colors onto an intermediate transfer member or a transfer material.

In such a color printer, a so-called misregistration in which the position of the plate image is shifted may occur in the synthesis process (for example, development, transfer, fixing, etc.).
When misregistration occurs, color misregistration occurs in the output image, so visibility is extremely reduced.
For example, in the case of an image in which a graphic of a certain color and a graphic of another color are in contact with each other to form a boundary, a paper ground color (paper white) may appear in the vicinity of the boundary (hereinafter referred to as “white blank” as appropriate). ").

Therefore, in order to prevent plate misalignment that causes white spots, registration correction is generally performed to mechanically adjust the position of the plate.
However, according to resist correction, mechanical problems in each process such as development, transfer, and fixing (for example, the rotation speed of gears, rollers, belts, etc. is not necessarily uniform, the distance fluctuates due to the influence of vibration, Furthermore, there is a problem that the dot formation position shifts even within the same color plate due to the problem that the paper feed amount does not match on the left and right and the paper is skewed and shaken.

In addition, there is a problem in that the boundary is conspicuous by the period that is synchronized with the period of speed unevenness of the rotating body or is made higher.
That is, even if each hardware mechanism is adjusted so that the leading position of each plate is accurately aligned, the effect of registration correction may be ineffective due to subsequent plate misalignment.

For such a problem, so-called trapping by software control is performed (see Patent Documents 1 and 2).
According to the trapping process, one or both of the colors of the plate image are expanded or the colors approximating these are interpolated for the area where white spots are predicted to occur, so that the plate images are synthesized. The white spots can be made inconspicuous.
For example, if a boundary between figures is detected, it is determined whether trapping is performed on the neighboring pixels of the detected boundary, and if it is determined that trapping is to be performed, which color of the plate is detected for the neighboring pixels Is determined, and processing for correcting the original plate image is performed according to the determination.
According to such trapping, processing is performed regardless of whether or not misregistration occurs, so that even if white spots occur, the visual influence can be suppressed.

JP 2007-36699 A Japanese Patent Laid-Open No. 2003-223311

However, since such trapping is performed uniformly, the boundary is made conspicuous if no white spots occur.
Further, depending on the direction of misregistration, pixel overlap may appear in the boundary instead of white spots, and the boundary is further emphasized by trapping such a boundary.
Furthermore, the same problem occurs when trapping according to the degree of white spot or pixel overlap is not performed.

  Moreover, in order to avoid these problems, the occurrence of misregistration and its location are predicted, and when misregistration is predicted to occur, white spots may occur due to misregistration, or pixel overlap may occur. It is necessary to identify the occurrence of this, and the processing and control related to trapping are more complex than necessary, such as measuring the width of white spots and overlapping pixels and performing trapping according to the width. Therefore, it was lacking in practicality.

  The present invention has been made in view of the above problems. By performing trapping at an appropriate interval along the boundary between images formed by each plate image, white spots and pixels caused by plate misalignment are generated. It is an object of the present invention to provide an image forming apparatus and an image forming method capable of preventing a reduction in visibility caused by conventional trapping that has been performed as a countermeasure for such a problem.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a color separation processing unit that divides an input image into predetermined colors to form a plate image of each color, an object included in one plate image, and another plate. A boundary extraction processing unit that extracts a boundary with an object included in the image; a boundary line processing processing unit that performs a replacement process of replacing color values of pixels facing through the boundary in the plate image having the boundary; and the replacement A combined output unit that combines and outputs the processed plate image.

  The image forming method of the present invention also includes a step of dividing an input image into predetermined colors to form plate images of respective colors, and a boundary between an object included in one plate image and an object included in another plate image. A step of performing an exchange process for exchanging color values of pixels facing through the boundary in the plate image having the boundary, and a step of synthesizing and outputting the plate image subjected to the exchange process. As a method having

  According to the image forming apparatus and the image forming method of the present invention, not only a decrease in visibility caused by misregistration but also the visibility caused by the conventional trapping that has been performed to solve these problems. Decline can be prevented.

1 is an external view illustrating an external appearance of a multifunction peripheral according to a first embodiment of the present invention. 3 is a flowchart showing a schematic process of image processing performed by the multifunction peripheral according to the first embodiment of the present invention. It is the functional block diagram which showed the structure of the control part which concerns on 1st embodiment of this invention. It is the functional block diagram which showed the structure of the boundary extraction process part which concerns on 1st embodiment of this invention. It is the 1st figure which showed the specific example (before process) of the exchange process of 1st embodiment of this invention. It is the 2nd figure which showed the specific example (before process) of the exchange process of 1st embodiment of this invention. It is the 3rd figure which showed the specific example (before process) of the exchange process of 1st embodiment of this invention. It is the 4th figure showing the example (before processing) of exchange processing of a first embodiment of the present invention. It is the 5th figure showing the example (before processing) of exchange processing of a first embodiment of the present invention. It is the 1st figure which showed the specific example (after process) of the exchange process of 1st embodiment of this invention. It is the 2nd figure which showed the specific example (after process) of the exchange process of 1st embodiment of this invention. It is the 3rd figure which showed the specific example (after process) of the exchange process of 1st embodiment of this invention. It is the 4th figure which showed the specific example (after process) of the exchange process of 1st embodiment of this invention. It is the 5th figure showing the example (after processing) of exchange processing of a first embodiment of the present invention. It is the 1st figure which showed the specific example (after process) of the exchange process of 2nd embodiment of this invention. It is the 2nd figure which showed the specific example (after process) of the exchange process of 2nd embodiment of this invention. It is the 3rd figure which showed the specific example (after process) of the exchange process of 2nd embodiment of this invention. It is the 4th figure showing the example (after processing) of exchange processing of a second embodiment of the present invention. It is the 5th figure which showed the specific example (after process) of the exchange process of 2nd embodiment of this invention. It is the functional block diagram which showed the structure of the control part which concerns on 3rd embodiment of this invention. It is the functional block diagram which showed the structure of the misregistration amount measurement part which concerns on 3rd embodiment of this invention. It is an example of the chart figure used in this embodiment. It is the functional block diagram which showed the structure of the suppression amount calculating part which concerns on this embodiment. It is the figure which showed the specific example (after process) of the exchange process of 3rd embodiment of this invention. It is the functional block diagram which showed the structure of the control part which concerns on 4th embodiment of this invention. It is the functional block diagram which showed the structure of the auxiliary | assistant determination part which concerns on this embodiment. It is the 1st figure which showed the specific example (after process) of the exchange process of 4th embodiment of this invention. It is the 2nd figure which showed the specific example (after process) of the exchange process of 4th embodiment of this invention. It is the 3rd figure which showed the specific example (after process) of the exchange process of 4th embodiment of this invention. It is the 4th figure showing the example (after processing) of exchange processing of a 4th embodiment of the present invention. It is the 5th figure which showed the example (after process) of the exchange process of 4th embodiment of this invention. It is the 6th figure showing the example (after processing) of exchange processing of a 4th embodiment of the present invention. It is the 7th figure which showed the specific example (after process) of the exchange process of 4th embodiment of this invention. It is the 8th figure which showed the specific example (after process) of the exchange process of 4th embodiment of this invention. It is the 9th figure which showed the specific example (after process) of the exchange process of 4th embodiment of this invention. It is the 1st figure which showed the specific example (after process) of the exchange process of 5th embodiment of this invention. It is the 2nd figure which showed the specific example (after process) of the exchange process of 5th embodiment of this invention. It is the 3rd figure which showed the specific example (after process) of the exchange process of 5th embodiment of this invention. It is the 4th figure showing the example (after processing) of exchange processing of a 5th embodiment of the present invention. It is the 5th figure which showed the specific example (after process) of the exchange process of 5th embodiment of this invention. It is the 6th figure showing the example (after processing) of exchange processing of a 5th embodiment of the present invention. It is the 7th figure which showed the specific example (after process) of the exchange process of 5th embodiment of this invention. It is the 8th figure which showed the specific example (after process) of the exchange process of 5th embodiment of this invention. It is the 9th figure which showed the specific example (after process) of the exchange process of 5th embodiment of this invention. It is the functional block diagram which showed the structure of the control part which concerns on 6th embodiment of this invention. It is the functional block diagram which showed the structure of the boundary extraction process part which concerns on 6th embodiment of this invention. It is the functional block diagram which showed the structure of the auxiliary | assistant determination part which concerns on 6th embodiment of this invention. It is the functional block diagram which showed the structure of the auxiliary | assistant determination part which concerns on 7th embodiment of this invention.

Hereinafter, a configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.
The image forming apparatus according to the present embodiment is, for example, a multifunction machine 10 having a color printing function and a color printing function, and includes a control element such as a CPU (Central Process Unit) and a chip set, and a ROM (Read Only Memory). And a computer constituted by a RAM (Random Access Memory) or the like. The CPU is an arithmetic processing device that executes a program. The ROM is a non-volatile memory that stores programs and data in advance. The RAM is a memory that temporarily stores the program and data when the program is executed and uses it as a work area. The program stored in the ROM is read by the control means of the CPU, thereby causing the computer to perform predetermined processing.

  As described above, by cooperation between the program and the computer, for example, the controller 11 performs separation processing, boundary extraction processing, boundary line processing processing, and the like as functional components in the computer of the multifunction machine 10. Can be made. Further, as a hardware function, for example, the print engine 7 can cause the print processing of the image data subjected to each of the above processes to be executed.

<First embodiment>
FIG. 1 is an external view showing the external appearance of a multifunction machine having a color printing function and a color copying function as a first embodiment of the image forming apparatus of the present invention.
FIG. 2 is a flowchart showing a schematic process of image processing performed by the multifunction peripheral according to the present embodiment.

As shown in FIG. 2, first, the MFP 1 of the present embodiment performs preprocessing (hereinafter referred to as image information separation preprocessing) prior to image information separation processing performed in a later step ( S1).
As image information separation pre-processing when copying is performed, for example, when the document A is placed on the document feed tray 1 and a copy execution operation is performed by the user, the document A is transferred by the roller group 2 to the document transport unit. A process of conveying the document into the main body 3 and discharging it to the document discharge tray 4 is performed.
Then, the scanner unit 5 performs reading processing of the document A in the process. Specifically, the conveyed document A is exposed by an exposure lamp 51, and the reflected light is reduced and imaged by an image sensor 54 through a mirror group 52 and a condenser lens 53, and electronically processed through a photoelectric conversion process. The correct image data.

  Further, as image information separation preprocessing when printing is performed, for example, when a print execution operation is performed from the personal computer 20 or the like connected to the multifunction device 10, the print transmitted to the multifunction device 10 is performed. Data is received via an external interface 6 such as a USB interface or a LAN interface, and electronic image data is obtained through predetermined image processing.

Next, the control unit 11 performs a separation process (hereinafter referred to as an image information separation process) on the image data acquired through the image information separation pre-process (S2).
In the image information separation processing, for example, a plurality of electronic plate images are formed by dividing image data acquired via the scanner unit 5 and the external interface 6 for each toner color.
In the case of the present embodiment, image data of cyan, magenta, yellow, and black plate images is acquired by this image information separation preprocessing.
The image data of each plate image is output to the print engine 7 through various processes in the control unit 11.

The print engine (composite output unit) 7 performs development processing for each color corresponding to each plate image of cyan (C), magenta (M), yellow (Y), and black (K) (S3). For convenience of explanation, the display of the magenta printing unit 70M and the cyan printing unit 70C is omitted in FIG.
Specifically, in each printing unit 70, the charging unit 71 uniformly charges the surface of the photosensitive drum 74 based on the image data of the plate image, and the exposure unit 72 uses the plate on the surface of the photosensitive drum 74. An electrostatic latent image corresponding to the image is formed, and the developing unit 73 releases a toner to form a plate image with a toner image based on the electrostatic latent image on the surface of the photosensitive drum 74.

Next, a process of combining the plate images through the transfer process is performed (S4).
Specifically, the toner image formed on the surface of the photosensitive drum 74 is sequentially transferred onto the transfer belt 75 for each color printing unit 70, and is transferred onto the paper P fed from the paper cassette 8 or the manual feed tray 9. The plate images are combined on the same paper P by batch transfer.

  Thereafter, the fixing unit 76 heats and pressurizes the paper P to fix the color image on the paper P (S5). Then, the paper P on which the fixing process has been performed is discharged, and the user can obtain a printed material of the original reproduced by copying or printing.

Here, the image information separation process will be described in detail with reference to FIG.
FIG. 3 is a functional block diagram illustrating a configuration of a control unit that performs image information separation processing.
As shown in FIG. 3, the control unit 11 of the present embodiment includes a separation processing unit 111, a boundary extraction processing unit 112, a boundary line processing unit 113, a gamma correction processing unit 114, and a screening processing unit 115. Is provided.

The color separation processing unit 111 separates the input image according to the ink color of the toner ink and forms a plate image of each color.
For example, the color separation processing unit 111 converts RGB color system image data acquired through the scanner unit 5 into CMYK color system image data through a color conversion table that is stored in advance. Then, the color separation processing unit 111 acquires four plate images by separating or extracting cyan, magenta, yellow, and black image data from the CMYK color system image data.

Further, the color separation processing unit 111 can perform the same processing on image data based on print data received from the personal computer 20 to obtain cyan, magenta, yellow, and black plate images.
By this separation processing, each image data is decomposed into pixels based on the machine-specific resolution.

The boundary extraction processing unit 112 extracts a boundary between an object included in one plate image and an object included in another plate image for all combinations of the plate images.
In other words, in the case of this embodiment, 1) cyan-magenta, 2) cyan-yellow, 3) cyan-black, 4) magenta-yellow, 5) magenta-black, and 6) yellow-black 6-color plate images. A boundary extraction process is performed for the combination.

FIG. 4 is a functional block diagram showing the configuration of the boundary extraction processing unit.
As shown in FIG. 4, the boundary extraction processing unit 112 extracts a rising edge detection unit 1121 and a falling edge in order to extract an edge or an edge of an object such as a figure, a character, or a symbol for each plate image (ch). A detection unit 1122 and a misregistration interference occurrence location prediction unit 1123 are provided.
The rising edge detection unit 1121 and the falling edge detection unit 1122 measure the color value and density of each pixel included in the plate image, and the rising edge and the rising edge based on the amount of change in the color value and density of the target pixel and its surrounding pixels. The falling edge is detected and each coordinate is specified.

For example, the rising edge detection unit 1121 measures the density difference between the nth pixel and the (n + 1) th pixel in the horizontal direction of the plate image, and if the density difference is positive, the pixel is determined to be a rising edge and coordinates If the density difference is negative, the falling edge detection unit 1122 determines that the pixel is a falling edge and specifies the coordinates. Further, a pixel whose density difference is 0 (zero) or less than a preset specified value can be determined as a non-edge.
Note that a non-edge means either a flat part where there is no change in density or color value or a part where there is little change in density or color value (a gradation in which density or color value does not change suddenly but changes slowly). Show.

By the way, the problem of noise mixing in each step of image processing can be effectively prevented by providing an insensitive area for the edge determination. For example, a pixel whose absolute value of the density change amount in each pixel exceeds a predetermined threshold is detected as an edge. Can be prevented from detecting.
In this embodiment, for the sake of simplicity, only the horizontal direction of the image has been described. Similarly, the rising edge, the falling edge, and the non-edge are also detected in the vertical direction based on a change in the color value or density of the pixel. can do.
Further, the edge detection method is not limited to the above-described method, and other known methods may be used.

  The plate misalignment occurrence location prediction unit 1123 has a boundary portion that is generated when a rising edge or a falling edge specified in a certain plate image matches or approaches a rising edge or a falling edge specified in another plate image. This is extracted by predicting a place where misregistration is likely to occur.

For example, when a cyan plate image and a magenta plate image are targeted, the misregistration interference occurrence location prediction unit 1123 binarizes the edge coordinates in the cyan plate image and the edge coordinates in the magenta plate image, respectively, and performs logic processing. When "1 (on)" is output to the product circuit (AND circuit) (when edge pixels overlap), this coordinate is extracted as the boundary. Further, the misregistration interference occurrence location prediction unit 1123 binarizes the values obtained by adding ± 1 to the edge coordinates in the cyan plate image and the edge coordinates in the magenta plate image, and inputs the binarized values to the AND circuit. Are output (when edge pixels are in contact with each other), the coordinates can be extracted as the boundary.
The boundary extraction processing unit 112 outputs the boundary coordinates thus extracted to the boundary line processing unit 113.

The boundary line processing unit 113 receives the coordinates of the boundary output from the boundary extraction processing unit 112, performs an exchange process for replacing the color value of each pixel facing through the boundary as a trapping, and performs for each plate image A processed image is formed.
In particular, the boundary line processing unit 113 according to the present embodiment performs such exchange processing alternately for pixels arranged along the boundary for each plate image having the boundary, and has the boundary. This is performed for pixels arranged at the same position along the boundary in each plate image.
Hereinafter, a specific example of the exchange process of the present embodiment will be described with reference to FIGS.

  FIGS. 5A to 5I are diagrams illustrating examples of composite images of two plate images. In the figure, the display coordinates (p, q) represent the displacement of the plate image due to plate misalignment. Specifically, it indicates the number of horizontal displacement pixels (+ is rightward and-is leftward) of the edge of each plate image when the center in the horizontal direction is the reference coordinate (0, 0). Yes, (p) is the number of displacement pixels of the edge of the plate image object (hereinafter referred to as plate image 1) shown on the left, and (q) is the plate image object (hereinafter referred to as plate image) shown on the right. This shows the number of pixels displaced at the edge of the image 2). Also, in the figure, the plate image 1 is schematically shown as black, the plate image 2 as ash, the overlap of pixels as a black circle, and the white as a white background.

  5A to 5C are composite images in which white spots are generated between the plate image 1 and the plate image 2 due to plate misalignment, and FIGS. 5D to 5F are plates. The composite image in which pixel overlap occurs between the plate image 1 and the plate image 2 due to the shift, FIGS. 5G to 5I, no plate shift occurs, or the direction and width of the plate shift. Indicates a composite image in which white spots and pixel overlap do not occur.

FIGS. 6A to 6I are obtained by performing the replacement processing of the present embodiment on the synthesized images of FIGS. 5A to 5I.
For example, in the case of FIG. 5A, among the pixels of the column of x = 2 forming the edge of the plate image 1, the color value of the pixel arranged at y = 2, 4, 6 and the boundary of this edge (here In this case, the border line between the column of x = 2 and the column of x = 3 corresponds), and the color values of the pixels arranged at the opposing positions are exchanged. In addition, since this exchange process is performed for each plate image, the color values of the pixels that are colored and the pixels that are not colored are switched across the boundary.
A similar exchange process is performed for the plate image 2 as well. That is, among the pixels in the column of x = 4 forming the edge of the plate image 2, the color value of the pixel arranged at y = 2, 4, 6 (pixel arranged at the same position as the plate image 1), and this The color values of the pixels arranged at opposing positions across the edge boundary (here, the border line between the x = 4 column and the x = 3 column) are switched.

As a result, the image shown in FIG. 5A is processed into a mosaic as shown in FIG. 6A, and as a result, white spots can be made inconspicuous. The same applies to FIGS. 5B and 5C (see FIGS. 6B and 6C).
Further, as shown in FIGS. 6D to 6F, overlapping of pixels can be made inconspicuous in the images shown in FIGS. 5D to 5F.
In the present embodiment, for smooth processing, the replacement processing is performed uniformly regardless of whether or not misregistration occurs. For this reason, if the plate displacement does not occur (FIGS. 5 (g) to (i)), the visibility generally decreases significantly when the replacement process is performed. However, according to the exchange process of the present embodiment, as shown in FIGS. 6G to 6I, it is possible to make the boundary less noticeable than necessary.

The gamma correction processing unit 114 corrects the current input / output characteristics so as to approach the ideal (design) input / output characteristics, and the screening processing unit 115 uses a predetermined screen pattern to adjust the gradation and shading. Represents.
Therefore, the gamma correction processing unit 114 performs gamma correction and the screening processing unit 115 performs screen processing on the image data of the processed image formed by performing the above-described exchange processing by the boundary line processing processing unit 113.
Thereafter, in order to shift to the development process, the screen processing unit outputs the image data after the screen processing to the print engine 7.
The print engine 7 obtains an output of the printed matter through a development process, a transfer process, and a fixing process for the image data output from the screen processing unit.

As described above, according to the multifunction machine 10 according to the first embodiment of the present invention, as a countermeasure against misregistration, a boundary where misregistration can occur (that is, a boundary formed by objects of a plate image) is specified. The exchange process is performed by exchanging the color value of the edge pixel of the object related to the boundary with the color value of the pixel facing through the boundary.
In addition, this exchange process is alternately performed on pixels arranged along the boundary for each plate image, and for pixels arranged at the same position along the boundary in each plate image having the boundary. To do.
For this reason, not only can white spots and pixel overlap caused by misregistration be inconspicuous, but also borders caused by trapping that has been conventionally performed as a countermeasure for misregistration can be inconspicuous.

<Second embodiment>
Next, a multifunction machine according to the second embodiment of the present invention will be described.
The multifunction machine 10 of the present embodiment is characterized by the replacement process in the boundary line processing unit 113, and this part is different from the first embodiment described above.
Specifically, the boundary line processing unit 113 replaces the color values of the pixels facing each other through the boundary, similar to the first embodiment, but arranges the replacement process along the boundary. This is different from the first embodiment in that it is alternately performed on the pixels to be performed and is performed on the pixels arranged at different positions along the boundary in each plate image having the boundary.
Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted.
Hereinafter, an example of the exchange process of the present embodiment will be described with reference to FIGS. 5 and 7.

FIGS. 7A to 7I are obtained by performing the replacement processing of the present embodiment on the combined images of FIGS. 5A to 5I.
For example, in the case of FIG. 5A, among the pixels of the column of x = 2 forming the edge of the plate image 1, the color value of the pixel arranged at y = 1, 3, 5 and the boundary of this edge (here In this case, the border line between the column of x = 2 and the column of x = 3 corresponds), and the color values of the pixels arranged at the opposing positions are exchanged.
The same processing is performed for the plate image 2. That is, among the pixels in the column of x = 4 forming the edge of the plate image 2, the color values of the pixels arranged at y = 2, 4, 6 (pixels arranged at positions different from the plate image 1), and this The color values of the pixels facing each other across the boundary of the edge (here, the border line between the column of x = 4 and the column of x = 3 corresponds) are exchanged.

As a result, the image shown in FIG. 5A is processed into a mosaic as shown in FIG. 7A, and as a result, white spots can be made inconspicuous. The same applies to FIGS. 5B and 5C (see FIGS. 7B and 7C).
Further, as shown in FIGS. 7D to 7F, the overlapping of pixels can be made inconspicuous in the images shown in FIGS. 5D to 5F.
In the present embodiment, as in the first embodiment, the replacement process is uniformly performed regardless of whether or not misregistration occurs. For this reason, if the plate displacement does not occur (see FIGS. 5 (g) to (i)), generally, the visibility is significantly reduced. However, according to the present embodiment, as shown in FIGS. 7G to 7I, the boundary can be made inconspicuous more than necessary.

Furthermore, compared to FIG. 6, it is possible to prevent overlap of pixels and continuous occurrence of white pixels, which can contribute to improving visibility.
That is, the boundary line processing unit 113 according to the present embodiment can perform the same operation or effect as or more than that of the first embodiment while performing an exchange process by means different from the first embodiment.

<Third embodiment>
Next, a multifunction machine according to a third embodiment of the present invention will be described.
The MFP 10 according to the present embodiment has the same basic configuration as that of the first embodiment or the second embodiment described above, but measures the output result of the composite image (chart image) of the plate image to determine the amount of misregistration. This is characterized in that color value exchange processing is performed between pixels according to the obtained plate misalignment amount.

As shown in FIG. 8, the control unit 11 of the multifunction machine 10 according to the present embodiment is compared with the configuration (see FIG. 3) of the control unit 11 of the multifunction machine 10 according to the first embodiment or the second embodiment. A deviation amount measurement unit 120 and a suppression amount calculation unit 121 are further provided.
That is, based on the misregistration amount measured by the misregistration amount measurement unit 120, the suppression amount calculation unit 121 determines the pixel width (distance or distance range between pixels) according to the misregistration amount, and this is the boundary. By notifying the line processing processing unit 113, an exchange process corresponding to the amount of misregistration that can be predicted at the present time is performed.
Since other configurations are the same as those of the above-described embodiments, detailed description thereof is omitted.

FIG. 9 is a functional block diagram illustrating a configuration of the misregistration amount measurement unit.
As illustrated in FIG. 9, the plate misalignment measuring unit 120 includes a chart drawing unit 1201, a chart measuring unit 1202, and a plate misalignment calculating unit 1203.
Here, first, the chart drawing unit 1201 draws a misregistration measurement chart, the chart measurement unit 1202 measures this, and the misregistration amount calculation unit 1203 calculates the misregistration amount based on the measured value.

For example, the chart drawing unit 1201 forms a chart image as shown in FIG. 10 on a photosensitive drum or an intermediate transfer belt for each plate image, and the chart measurement unit 1202 measures the chart image with a reading sensor or the like. The misregistration amount calculation unit 1203 calculates the misregistration amount based on this measurement value. This figure is a chart image for measuring the amount of misregistration between the black plate image and the magenta plate image. For example, by reading the coincident part of the scale as in the caliper measurement method, The amount of deviation can be measured.
The plate misalignment amount can also be obtained by visually measuring the output of such a chart image on a printing paper or the like.

The plate misalignment measuring unit 120 outputs such a chart image according to the combination of the plate images, and calculates all the relative plate misalignment amounts between the plate images based on the output chart image.
The misregistration amount measurement unit 120 outputs the obtained misregistration amount to the suppression amount calculation unit 121.

FIG. 11 is a functional block diagram illustrating the configuration of the suppression amount calculation unit.
As illustrated in FIG. 11, the suppression amount calculation unit 121 includes a misregistration measurement value holding unit 1211, an interference degree prediction unit 1212, and a suppression amount calculation unit 1213.
The misregistration measurement value holding unit 1211 holds the misregistration amount input from the misregistration amount measurement unit 120 in a storage unit such as a memory.

The interference level prediction unit 1212 predicts the interference level based on the misregistration amount held by the misregistration measurement value holding unit 1211. The “interference level” is used as a reference for determining whether to execute or not to execute the replacement process depending on the degree of misregistration.
Specifically, a pixel whose amount of misregistration does not satisfy a predetermined reference value can be determined as having a low disturbance level and can be excluded from replacement processing.

Here, when the misregistration amount exceeds the reference value, the suppression amount calculation unit 1213 calculates the suppression amount based on the misregistration amount received from the misregistration amount measurement unit 120.
The suppression amount is the width of the replacement process (hereinafter referred to as a trap width) determined in accordance with the size of the misregistration. In this embodiment, when the misregistration is determined to be small, the trap amount is set. If the width is ± 1 pixel and it is determined that the plate displacement is large, the trap width is ± 2 pixels.
Therefore, the suppression amount calculation unit 1213 outputs the calculated suppression amount (± 1 pixel or ± 2 pixels) to the boundary line processing unit 113.

The boundary line processing unit 113 performs an exchange process based on the suppression amount output from the suppression amount calculation unit 121.
Hereinafter, an example of the exchange process of the present embodiment will be described with reference to FIGS. 5 and 12.

FIG. 12C shows the composite image of FIG. 5C subjected to the exchange process of this embodiment.
It is assumed that the suppression amount calculation unit 1213 calculates the suppression amount due to the mutual plate shift between the plate image 1 and the plate image 2 shown in FIG. 5C as ± 2 pixels.
In the present embodiment, when ± 2 pixel replacement processing is performed, the replacement processing for pixels arranged at ± 1 pixel from the boundary and the replacement processing for pixels arranged at ± 2 pixels from the boundary are performed by the length of the boundary. Alternate along the direction.

  For example, in the case of FIG. 5C, the color values of the pixels arranged at y = 2, 4, 6 among the pixels in the column of x = 2 forming the edge of the plate image 1 are the boundary of this edge ( Here, the color values of the pixels (ie, ± 1 pixel) facing each other across the border line between the column of x = 2 and the column of x = 3 are interchanged. Among the pixels in the column of x = 1 in contact with the edge of the plate image 1, the color values of the pixels arranged at y = 1, 3, 5 are the pixels facing across the edge boundary (that is, ±±). 2) color value.

  On the other hand, among the pixels in the column of x = 5 forming the edge of the plate image 2, the color values of the pixels arranged at y = 2, 4, 6 are the boundary of this edge (here, the column of x = 4 The color value of the pixel (that is, ± 1 pixel) facing each other across the border line with the column of x = 5 is replaced. In addition, among the pixels in the column of x = 6 in contact with the edge of the plate image 2, the color values of the pixels arranged at y = 1, 3, 5 are the pixels facing across the edge boundary (that is, ±±). 2) color value.

As a result, the image shown in FIG. 5C is processed into a mosaic as shown in FIG. 12A, and as a result, white spots for two pixels can be effectively made inconspicuous. This is clear even when compared with the above-described embodiments. For example, there are no continuous white pixels as compared with FIG. 6C according to the first embodiment, and white pixels are dispersed as compared with FIG. 7C according to the second embodiment. Can be further improved.
Similarly, the image shown in FIG. 5 (f) is processed into a mosaic shape as shown in FIG. 12 (b), and as a result, the overlap of two pixels can be made inconspicuous.

5A, 5 </ b> B, and FIGS. 5D to 5E, the suppression amount calculation unit 1213 sets the suppression amount due to mutual misregistration between the plate image 1 and the plate image 2 to ± 1. Calculate with pixels.
Therefore, the same replacement process as that in the first embodiment or the second embodiment is performed on the images in these drawings (see FIGS. 6 and 7).
5 (g) to (i), no plate misalignment has occurred, and the suppression amount calculation unit 1213 sets the suppression amount due to the mutual plate misalignment between the plate image 1 and the plate image 2 to 0 pixels. calculate. Therefore, in this case, the exchange process is not performed.

  As described above, the boundary line processing unit 113 according to the present embodiment can perform the same operation or effect as or more than that of the above-described embodiment, while performing the replacement process by means different from the above-described embodiment.

<Fourth embodiment>
Next, a multifunction machine according to a fourth embodiment of the present invention will be described.
The MFP 10 according to the present embodiment has the same basic configuration as that of the above-described embodiments, but is characterized in that execution control of exchange processing is performed using a predetermined random number.

As shown in FIG. 13, the control unit 11 of the multifunction machine 10 according to the present embodiment is different from the configuration of the control unit 11 according to the multifunction machine 10 of the first embodiment or the second embodiment (see FIG. 3). It further includes a determination unit 130A.
As illustrated in FIG. 14, the auxiliary determination unit 130 </ b> A includes a random number generation unit 1301 and an edge processing necessity determination unit 1302.

The random number generation unit 1301 generates a random number using a known pseudo random number generation algorithm (random number generation means) such as referring to a pseudo random number table created so as to be uniformly distributed in a range of 0 to 1.
Specifically, the random number generation unit 1301 generates a random number using a single pseudorandom number generation algorithm for the pixels to be exchanged in all the plate images.

The edge processing necessity determination unit 1302 determines, for each target pixel, whether or not to perform the exchange processing based on the random number obtained via the random number generation unit 1301.
For example, when the value of the random number generated by the random number generation unit 1301 is 0.0 or more and less than 0.5, the edge processing necessity determination unit 1302 determines that the replacement process is performed, and when the value of the random number is 0.5 or more and less than 1.0, The edge processing unit determination unit 1302 determines that the replacement processing is not performed.
The edge processing necessity determination unit 1302 outputs a determination signal that can identify the determination result to the boundary line processing unit 113.

The boundary line processing unit 113 performs an exchange process on the target pixel in accordance with the determination signal input from the edge processing necessity determination unit 1302.
That is, the boundary line processing unit 113 performs the replacement process only when a determination signal indicating that the replacement process is to be performed is received. Further, the exchange process may not be performed when a determination signal indicating that the exchange process is not performed is received.
Since other configurations are the same as those of the above-described embodiments, detailed description thereof is omitted.

Hereinafter, an example of the exchange process of the present embodiment will be described with reference to FIGS. 5 and 15.
FIG. 15 shows the composite image of FIG. 5 subjected to the exchange processing of this embodiment.
For example, in the image of FIG. 5A, the random number generation unit 1301 uses the random number table to relate the pixels in the x = 2 column of the plate image 1 and the pixels in the x = 4 column of the plate image 2 to y = 1, 2, 3, 4, 5, 6,... As a result, it is assumed that values of 0.0 or more and less than 0.5 are assigned to y = 1, 3, 6, 9, 10.

For this reason, the edge processing necessity determination unit 1302 performs replacement processing on the pixels y = 1, 3, 6, 9, and 10 of the edge pixel (x = 2) of the plate image 1, and the edge pixel ( A determination signal indicating that the replacement processing is performed for the pixels of y = 1, 3, 6, 9, 10 in x = 4) is output to the boundary line processing unit 113.
As a result, as shown in FIG. 15A, an image that has been subjected to color expansion processing randomly at the boundary portion is formed.
FIGS. 15B to 15I are diagrams showing the results of performing the same exchange process for FIGS. 5B to 5I.
As shown in these drawings, white spots and pixel overlap occurring near the boundary can be made inconspicuous also by the exchange processing according to the present embodiment.

<Fifth embodiment>
Next, a multifunction machine according to a fifth embodiment of the present invention will be described.
The MFP 10 according to the present embodiment is substantially the same as that of the fourth embodiment, but in the same embodiment, one random number is shared for all the plate images, whereas in this embodiment, each plate image is respectively It is characterized in that it is determined whether or not a pixel is to be exchanged using an individual independent random number, and the exchange process is performed based on this determination.
Specifically, it has a random number generation algorithm corresponding to magenta, a random number generation algorithm corresponding to cyan, a random number generation algorithm corresponding to yellow, and a random number generation algorithm corresponding to black, and each version image , It is determined whether or not to perform the exchange process based on the random numbers generated by the respective random number generation algorithms.
In addition, since the structure of the control part 11 is the same as 4th embodiment, detailed description is abbreviate | omitted.

FIG. 16 is obtained by performing the exchange process of the present embodiment on the composite image of FIG.
For example, as illustrated in FIG. 5A, the random number generation unit 1301 uses the random number table of A, and y = 1, 2, 3, 4, 5, for pixels in the x = 2 column of the plate image 1. A process of assigning random numbers in the order of 6,. On the other hand, the random number generation unit 1301 similarly performs a process of assigning random numbers to the image of the x = 4 column of the plate image 2 using the B random number table. As a result, a value of 0.0 or more and less than 0.5 is assigned to y = 1, 3, 4, 7, 10, 11 of plate image 1, and 0.0 for y = 1, 2, 6, 9, 10 for plate image 2. It is assumed that a value less than 0.5 is assigned.

Therefore, the edge processing necessity determination unit 1302 performs an exchange process on the pixels of y = 1, 3, 4, 7, 10, and 11 of the edge pixel (x = 2) of the plate image 1 to obtain the edge of the plate image 2 A determination signal indicating that the replacement processing is performed on the pixels of pixels (x = 4) y = 1, 2, 6, 9, and 10 is output to the boundary line processing unit 113.
As a result, as shown in FIG. 16a, an image that has been randomly subjected to color expansion processing at the boundary portion is formed.
FIGS. 16B to 16I are diagrams showing the results of performing the replacement process in the same manner as FIGS. 5B to 5I.
Thus, even with the exchange processing according to the present embodiment, white spots and pixel overlap occurring near the boundary can be made inconspicuous.
Note that since random numbers are used independently, the occurrence of pixel overlap can be further suppressed compared to the fourth embodiment, and the boundary can be made more inconspicuous.

<Sixth embodiment>
Next, a multifunction machine according to the sixth embodiment of the present invention will be described.
As shown in FIG. 17, in the multifunction machine 10 of the present embodiment, the configuration of the control unit 11 is substantially the same as that of the fifth embodiment described above (see FIG. 13).
However, since the MFP 10 of the present embodiment has a small density difference between the pixels forming the boundary, pixels that can be determined not to deteriorate the visibility even if misregistration occurs are excluded from replacement processing. It has the feature in the point to do.
In other words, the image processing is facilitated by excluding the exchange processing with a small effect.

FIG. 18 is a functional block diagram showing the configuration of the boundary extraction processing unit.
As can be seen from comparison with FIG. 4, the boundary extraction processing unit 112 of this embodiment further includes an edge portion density difference information measurement unit 1124.
The edge portion density difference information measurement unit 1124 measures the pixel density difference between the rising edge portion and the falling edge portion detected by the rising edge detection portion 1121 or the falling edge detection portion 1122.
The edge density difference information measurement unit 1124 outputs the measured density difference information of the pixels of the edge part to the auxiliary determination unit 130B.
Other configurations are the same as those in FIG. Therefore, detailed description of other configurations is omitted.

FIG. 19 is a functional block diagram illustrating the configuration of the auxiliary determination unit.
As can be seen from comparison with FIG. 14, the auxiliary determination unit 130 </ b> B of the present embodiment further includes an edge density difference information holding unit 1303 and an interference degree prediction unit 1304.
Other configurations are the same as those in FIG. Therefore, detailed description of other configurations is omitted.

  The edge part density difference information holding unit 1303 holds the density difference information of the pixels in the edge part input from the edge part density difference information measuring unit 1124 in a storage unit such as a memory, and for example, a color whose color value is changed. A patch density measurement value is held, and a combination of combined images that can ensure a certain level of visibility when these color patches are superimposed and a density difference range in that case are specified and held in advance. Also, combinations of color patches and paper white that can ensure a certain level of visibility and the range of density difference in that case are specified and stored in advance.

Therefore, the boundary line processing unit 113 performs an exchange process on pixels whose density difference during actual image processing is included in the range of density differences held in the edge part density difference information holding unit 1124. By avoiding this, unnecessary processing can be omitted.
In the present embodiment, as described later, the execution determination of the exchange process is performed in association with the random number.

The disturbing degree predicting unit 1304 determines whether or not to perform the replacement process for the pixel based on the density difference information of the pixel in the edge portion held by the edge portion density difference information holding unit 1303. "Correction coefficient" is obtained.
The interference correction coefficient is a coefficient defined between 0 and 1. For example, if the image data is 8 bits and takes a value of 0 to 255, a value obtained by dividing the density difference by 255 may be used.

For example, assuming the time of maximum misregistration, a difference “virtual maximum color difference” between a value obtained by intentionally causing misregistration in advance and a measured value when no misregistration has occurred may be obtained. Predict the chromaticity difference when assuming that misregistration has occurred, and calculate the interference correction coefficient by dividing the color change "color difference" from the color when no misregistration has occurred by the "virtual maximum color difference" .
The disturbance degree prediction unit 1304 outputs the obtained disturbance degree correction coefficient to the edge processing necessity determination unit 1302.

The edge process necessity determination unit 1302 determines, for each target pixel, whether or not to perform the exchange process based on the random number and the interference correction coefficient.
Specifically, a multiplication value is obtained by multiplying the disturbance degree correction coefficient input from the disturbance degree prediction unit 1304 and the random number obtained by the random number generation unit 1301.
For example, when the multiplication value is 0.0 or more and less than 0.5, the edge processing necessity determination unit 1302 determines that the replacement process is performed on the pixel. When the multiplication value is 0.5 or more and less than 1.0, the edge processing unit The determination unit 1302 determines that the replacement process is not performed for the pixel.
The edge processing necessity determination unit 1302 outputs a determination signal that can identify the determination result to the boundary line processing unit 113.

The boundary line processing unit 113 performs an exchange process on the target pixel in accordance with the determination signal input from the edge processing necessity determination unit 1302.
That is, the boundary line processing unit 113 performs the replacement process only when a determination signal indicating that the replacement process is to be performed is received. Further, the exchange process may not be performed when a determination signal indicating that the exchange process is not performed is received.

As described above, according to the multifunction machine 10 of the present embodiment, it is possible to achieve operations and effects equivalent to or higher than those of the above-described embodiment while performing exchange processing by means different from those of the above-described embodiment.
For example, compared to the fourth embodiment and the fifth embodiment that determine whether or not an exchange process is necessary only with a random number, the color difference is added to the determination element. Image processing can be performed.

<Seventh embodiment>
Next, a multifunction machine according to a seventh embodiment of the present invention will be described.
The multifunction machine 10 according to the present embodiment has substantially the same configuration as that of the sixth embodiment described above. Specifically, it is the same as in the sixth embodiment in that it is determined whether or not it is an exchange processing target using the density difference of the target pixel and a random number. It has the characteristic in the point added as.

FIG. 20 is a functional block diagram illustrating a configuration of the auxiliary determination unit according to the present embodiment.
As can be seen from comparison with FIG. 19, the auxiliary determination unit 130 </ b> C of the present embodiment further includes a misregistration measurement value holding unit 1305.
Other configurations are the same as those in FIG. Therefore, detailed description of other configurations is omitted.

The misregistration measurement value holding unit 1305 holds the misregistration amount input from the misregistration amount measurement unit 120 (not shown) in a storage unit such as a memory.
For example, as described in the third embodiment, a chart image as shown in FIG. 10 is formed on a photosensitive drum or an intermediate transfer belt for each plate image, and the chart image is measured by a reading sensor or the like. The amount of misregistration calculated based on the measured value is held in advance.
Then, the interference degree prediction unit 1304 calculates an interference degree correction coefficient based on the density difference information held in the edge portion density difference information holding unit 1303 and the plate deviation amount held in the plate deviation measurement value holding unit 1305. Ask.

If the image data is 8 bits and takes a value of 0 to 255, the interference degree correction coefficient is obtained by dividing the obtained density difference by 255 to obtain the first coefficient for the density difference, and the maximum possible deviation amount is also obtained. The second coefficient for the misregistration amount is obtained by dividing by the value.
For example, assuming the maximum misregistration time, a “virtual maximum color difference” between a value obtained by intentionally causing misregistration in advance and a measured value when no misregistration has occurred is obtained, The first coefficient is calculated by predicting the chromaticity difference when it is assumed that a deviation has occurred and dividing the “color difference” when no deviation has occurred by the “virtual maximum color difference”.

In addition, assuming the time of maximum misregistration, the “virtual maximum misregistration amount” between the value obtained by intentionally causing misregistration in advance and the measured value when no misregistration has occurred is obtained and A second coefficient is calculated by predicting a misregistration amount when it is assumed that a possible misregistration has occurred and dividing the misregistration amount when no misregistration has occurred by the “virtual maximum misregistration amount”.
The interference level prediction unit 1304 outputs the first coefficient and the second coefficient related to the interference level correction coefficient to the edge processing necessity determination unit 1302.

The edge process necessity determination unit 1302 determines, for each target pixel, whether or not to perform the exchange process based on the random number and the interference correction coefficient.
Specifically, the multiplication value is obtained by multiplying the first coefficient and the second coefficient input from the interference degree prediction unit 1304 and the random number obtained by the random number generation unit 1301.
For example, when the multiplication value is 0.0 or more and less than 0.5, the edge processing necessity determination unit 1302 determines that the replacement process is performed on the pixel. When the multiplication value is 0.5 or more and less than 1.0, the edge processing unit The determination unit 1302 determines that the replacement process is not performed for the pixel.
The edge processing necessity determination unit 1302 outputs a determination signal that can identify the determination result to the boundary line processing unit 113.

The boundary line processing unit 113 performs an exchange process on the target pixel in accordance with the determination signal input from the edge processing necessity determination unit 1302.
That is, the boundary line processing unit 113 performs the replacement process only when a determination signal indicating that the replacement process is to be performed is received. Further, the exchange process may not be performed when a determination signal indicating that the exchange process is not performed is received.

As described above, according to the multifunction machine 10 of the present embodiment, it is possible to achieve operations and effects equivalent to or higher than those of the above-described embodiment while performing exchange processing by means different from those of the above-described embodiment.
For example, compared to the sixth embodiment in which the necessity of the replacement process is determined using a random number and a color difference, since the amount of misregistration is added to the determination element, the case where the effect of the replacement process is small is further excluded. Image processing can be performed efficiently.

As described above, according to the image forming apparatus or the image forming method of the present invention, it is possible to effectively prevent a decrease in visibility caused by the replacement process itself as in the conventional art.
Specifically, by performing an exchange process at an appropriate interval along the boundary, it is possible not only to perform image processing so that white spots and overlapping of pixels are not conspicuous in the case of misregistration, Even if there is no misregistration, the boundary is made not to stand out more than necessary.

Further, the necessity and method of the replacement process are controlled by measuring the current misregistration amount.
Furthermore, by performing the exchange process at random in the longitudinal direction of the boundary, the image of the boundary can be expressed more naturally.
In addition, it is possible to realize smoothing of the entire image processing by configuring the target pixel corresponding to the density difference that does not require the replacement processing to be limited to the execution of the replacement processing.

The image forming apparatus according to the present invention has been described with reference to the preferred embodiment. However, the image forming apparatus according to the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. It goes without saying that implementation is possible.
For example, by combining the above-described embodiments, it is possible to realize a multi-function machine that achieves a plurality of or synergistic effects.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used for a copying machine that can perform a copying process or a printing process on a color document, a printing apparatus, or a multifunction machine having these functions.

10 MFP (image forming device)
DESCRIPTION OF SYMBOLS 11 Control part 111 Separation processing part 112 Boundary extraction processing part 113 Boundary line processing part 120 Printing displacement amount measurement part 121 Suppression amount calculation part 130 Auxiliary judgment part 1301 Random number generation part 1302 Edge processing necessity judgment part 1303 Edge part density difference Information holding unit 1304 Interference degree prediction unit 1305 Print displacement measurement value holding unit 20 Personal computer

Claims (11)

A color separation processing unit that divides an input image into predetermined colors and forms a plate image of each color;
A boundary extraction processing unit that extracts a boundary between an object included in one plate image and an object included in another plate image;
A boundary line processing unit for performing an exchange process for replacing the color values of pixels facing through the boundary in the plate image having the boundary;
A synthesis output unit that synthesizes and outputs the plate image subjected to the exchange processing ,
Furthermore, an independent random number generating unit corresponding to each plate image is individually provided, and the target pixel of the exchange processing of each plate image having the boundary is a random number generated by each random number generating unit corresponding to the plate image When equipped with a random number generator that is determined based on
The boundary line processing unit is:
An image forming apparatus that performs the replacement process on the target pixel determined by the random number generation unit for each plate image . The boundary line processing unit is:
The image forming apparatus according to claim 1, wherein the replacement process is performed on pixels arranged at the same position along the boundary in each plate image having the boundary. The boundary line processing unit is:
The image forming apparatus according to claim 1, wherein the replacement process is performed on pixels arranged at different positions along the boundary in each plate image having the boundary. A plate deviation amount measuring unit that measures the image output by the composite output unit and measures the deviation amount for each plate image,
The boundary line processing unit is:
The image forming apparatus according to claim 1, wherein execution control of the replacement process is performed according to the measured deviation amount. Based on the deviation amount measured by the plate deviation amount measurement unit, a suppression amount calculation unit for obtaining a distance range for performing the replacement process,
The boundary line processing unit is:
The image forming apparatus according to claim 4, wherein the replacement processing is performed on pixels that are opposed to each other through the boundary and are disposed to face each other within the distance range from the boundary. The suppression amount calculation unit specifies two or more distance numbers included in the distance range,
The boundary line processing unit is:
The exchange process performed on pixels arranged opposite to each other via a distance number from the boundary, and the exchange process performed on pixels arranged opposite to the boundary via another distance number The image forming apparatus according to claim 5, wherein the step is performed along the boundary. A color difference information holding unit for holding a color difference range specified based on a color difference between a color value related to a plate image and a predetermined color value;
The boundary line processing unit is:
The execution control of the replacement process for the target pixel is performed based on whether or not a color difference between a color value of a target pixel of the replacement process and a predetermined color value in each plate image is included in the range of the color difference. The image forming apparatus according to claim 1. The color difference information holding unit
Based on the color difference between the color value related to one plate image and the color value related to another plate image, the range of the color difference is retained,
The boundary line processing unit is:
Whether or not a difference between the color value of the target pixel of the replacement process in one plate image having the boundary and the color value of the target pixel of the replacement process in another plate image having the boundary is included in the range of the color difference The image forming apparatus according to claim 7, wherein execution control of the exchange process is performed depending on the type of the image. The random number generator is
Claims 1-8, characterized in that comprises one random number generation means, the target pixel of the replacement process of each plate image with the boundary, is determined based on the random numbers generated by said one random number generating means The image forming apparatus according to claim 1. The image forming apparatus according to claim 2 , wherein the replacement process is alternately performed on pixels arranged along the boundary. Dividing the input image into predetermined colors to form plate images of the respective colors;
Extracting a boundary between an object included in one plate image and an object included in another plate image;
Performing an exchange process for replacing color values of pixels facing through the boundary in the plate image having the boundary;
Synthesizing and outputting the plate image subjected to the exchange process , and
Further, an independent random number generation unit corresponding to each plate image is individually provided, and the target pixel of the exchange process of each plate image having the boundary is set to a random number generated by each random number generation unit corresponding to the plate image. Having a step to make a decision based on
The image forming method , wherein in the step of performing the replacement process, the replacement process is performed on the determined target pixel for each plate image .