JP4221666B2 - Image processing apparatus, image forming apparatus, image forming method, and program thereof - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image by performing screen processing.

For example, Patent Document 1 discloses a color image forming apparatus that corrects the image width in the main scanning direction by adding pixels.
JP 2001-005245 A

  The present invention has been made from the background described above, and it is a first object of the present invention to provide an image forming apparatus that performs image formation while suppressing the occurrence of image defects associated with screen processing. It is a second object of the present invention to provide an image forming process for forming an image while suppressing the occurrence of image defects due to addition or deletion of pixels for the purpose of correcting the image width and the like and screen processing. And

[Image processing device]
In order to achieve the above object, an image processing apparatus according to the present invention is a screen processing means for performing screen processing on an input image so as to form each output pattern having a size corresponding to the gradation of the input image in each screen unit area. And control means for controlling the screen processing means so that the arrangement position of the output pattern in at least one screen unit area is different from the arrangement position of the output pattern in other screen unit areas.

  Preferably, the control means controls the screen processing means so as to change the arrangement position of the output pattern in the screen unit areas adjacent in at least one direction.

  Preferably, the image processing device further includes pixel operation means for adding or deleting regularly arranged pixels to the input image, and the control means is arranged for the arrangement direction of the pixels added or deleted by the pixel operation means. The screen processing means is controlled so that the arrangement positions of the output patterns in the screen unit areas adjacent to each other are different.

  The image processing apparatus according to the present invention further includes a screen processing unit that performs screen processing on the input image based on a predetermined threshold matrix, and the screen processing unit includes screen units adjacent to each other in at least one direction. Different regions have different threshold matrices.

  Preferably, the screen processing unit forms output patterns adjacent to each other in the main scanning direction and the sub-scanning direction of the output image based on different threshold matrices.

  Preferably, the screen processing unit applies a plurality of threshold matrixes having different growth shapes, growth start positions, or barycentric positions of output patterns to be formed.

[Image forming apparatus]
In addition, an image forming apparatus according to the present invention includes a screen processing unit that performs screen processing on an input image so as to form each output pattern having a size corresponding to the gradation of the input image in each screen unit area, and at least one screen. Based on the control means for controlling the screen processing means so that the arrangement position of the output pattern in the unit area is different from the arrangement position of the output pattern in the other screen unit areas, and on the input image screen-processed by the screen processing means And image forming means for forming an image on a recording medium.

[Image forming method]
In the image forming method according to the present invention, different threshold matrixes are applied to screen unit areas adjacent to each other in at least one direction, screen processing is performed on the image data of the input image, and the screen processing is performed. An image is formed from the obtained image data.

[program]
The program according to the present invention includes a step of applying screen processing to image data of an input image by applying different threshold matrixes to screen unit areas adjacent to each other in at least one direction, and the screen processing is performed. And causing the computer to execute an image forming step from the obtained image data.

  According to the image forming apparatus of the present invention, it is possible to perform image formation while suppressing the occurrence of image defects due to screen processing.

[Printer]
First, the printer apparatus 10 to which the present invention is applied will be described.
FIG. 1 is a diagram illustrating a configuration of a tandem type printer device (image forming apparatus) 10.
As shown in FIG. 1, the printer device 10 includes an image reading unit 12, an image forming unit 14, an intermediate transfer belt 16, a paper tray 17, a paper conveyance path 18, a fixing device 19, and an image processing device 20. The printer device 10 has a function as a full-color copying machine using the image reading device 12 and a function as a facsimile in addition to a printer function for printing image data received from a personal computer (not shown). It may be a multifunction machine.

First, the outline of the printer apparatus 10 will be described. An image reading apparatus 12 and an image processing apparatus 20 are disposed above the printer apparatus 10 and function as image data input means. The image reading device 12 reads an image displayed on the document 30 and outputs it to the image processing device 20. The image processing apparatus 20 performs gradation correction and resolution correction on image data input from the image reading apparatus 12 or image data input from a personal computer (not shown) via a network line such as a LAN. And the like, and output to the image forming unit 14.
Below the image reading device 12, a plurality of image forming units 14 are arranged corresponding to the colors constituting the color image. In this example, the first image forming unit 14K, the second image forming unit 14Y, and the third image forming corresponding to each color of black (K), yellow (Y), magenta (M), and cyan (C). The unit 14M and the fourth image forming unit 14C are arranged horizontally along the intermediate transfer belt 16 with a certain interval. The intermediate transfer belt 16 rotates as an intermediate transfer member in the direction of an arrow A in the figure, and these four image forming units 14K, 14Y, 14M, and 14C are configured based on the image data input from the image processing apparatus 20. The toner images are sequentially formed and transferred (primary transfer) to the intermediate transfer belt 16 at a timing at which the plurality of toner images are superimposed on each other. The order of the colors of the image forming units 14K, 14Y, 14M, and 14C is not limited to the order of black (K), yellow (Y), magenta (M), and cyan (C). ), Magenta (M), cyan (C), black (K), and the like.

  The sheet conveyance path 18 is disposed below the intermediate transfer belt 16. The recording paper 32 supplied from the paper tray 17 is transported on the paper transport path 18, and the toner images of each color transferred onto the intermediate transfer belt 16 are collectively transferred (secondary transfer). The transferred toner image is fixed by the fixing unit 37 and discharged to the outside along the arrow B.

Next, each configuration of the printer device 10 will be described in more detail.
As shown in FIG. 1, the image reading unit 12 includes a platen glass 124 on which a document 30 is placed, a platen cover 122 that presses the document 30 onto the platen glass 124, and a document 30 placed on the platen glass 124. And an image reading device 130 for reading an image. The image reading apparatus 130 illuminates the original 30 placed on the platen glass 124 with a light source 132 and converts a reflected light image from the original 30 into a full rate mirror 134, a first half rate mirror 135, and a second half half. Scanning exposure is performed on an image reading element 138 made of a CCD or the like through a reduction optical system including a rate mirror 136 and an imaging lens 137, and the color material reflected light image of the document 30 is transferred to predetermined dots by the image reading element 138. It is configured to read at a density (for example, 16 dots / mm).

  The image processing apparatus 20 performs predetermined image processing such as shading correction, document position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, and the like on the image data read by the image reading unit 12. Apply processing. The color material reflected light image of the document 30 read by the image reading unit 12 is, for example, document reflectance data of three colors of red (R), green (G), and blue (B) (each of 8 bits). By the image processing by the image processing device 20, the original color material gradation data (raster data) of four colors of yellow (Y), magenta (M), cyan (C), and black (K) (each 8 bits) is converted. The

The first image forming unit 14K, the second image forming unit 14Y, the third image forming unit 14M, and the fourth image forming unit 14C (image forming means) are arranged in parallel at regular intervals in the horizontal direction. The arrangement is almost the same except that the color of the image to be formed is different. Accordingly, the first image forming unit 14K will be described below. The configuration of each image forming unit 14 is distinguished by adding K, Y, M, or C.
The image forming unit 14K forms an electrostatic latent image by an optical scanning device 140K that scans a laser beam in accordance with image data input from the image processing device 20, and a laser beam scanned by the optical scanning device 140K. And an image forming apparatus 150K.

The optical scanning device 140K modulates the semiconductor laser 142K according to the black (K) image data, and emits the laser light LB (K) from the semiconductor laser 142K according to the image data. The laser beam LB (K) emitted from the semiconductor laser 142K is applied to the rotary polygon mirror 146K via the first reflection mirror 143K and the second reflection mirror 144K, and is deflected and scanned by the rotation polygon mirror 146K. The light is irradiated onto the photosensitive drum 152K of the image forming apparatus 150K through the second reflecting mirror 144K, the third reflecting mirror 148K, and the fourth reflecting mirror 149K.
The image forming apparatus 150K includes a photosensitive drum 152K as an image carrier that rotates at a predetermined rotational speed in the direction of arrow A, and primary charging as a charging unit that uniformly charges the surface of the photosensitive drum 152K. And a developing device 156K for developing the electrostatic latent image formed on the photosensitive drum 154K, and a cleaning device 158K. The photosensitive drum 152K is uniformly charged by the scorotron 154K, and an electrostatic latent image is formed by the laser beam LB (K) irradiated by the optical scanning device 140K. The electrostatic latent image formed on the photosensitive drum 152K is developed with black (K) toner by the developing device 156K and transferred to the intermediate transfer belt 16. Residual toner, paper dust, and the like adhering to the photosensitive drum 152K after the toner image transfer process are removed by the cleaning device 158K.
The other image forming units 14Y, 14M, and 14C also form yellow (Y), magenta (M), and cyan (C) toner images in the same manner as described above, and intermediately transfer the formed toner images of the respective colors. Transfer to belt 16.

The intermediate transfer belt 16 has a constant tension between the drive roll 164, the first idle roll 165, the steering roll 166, the second idle roll 167, the backup roll 168, and the third idle roll 169. The drive roll 164 is rotationally driven by a drive motor (not shown), and is circulated at a predetermined speed in the direction of arrow A. The intermediate transfer belt 16 is formed into an endless belt by, for example, forming a flexible synthetic resin film such as polyimide in a belt shape and connecting both ends of the synthetic resin film formed in a belt shape by welding or the like. It has been done.
The intermediate transfer belt 16 includes a first primary transfer roll 162K, a second primary transfer roll 162Y, a third primary transfer roll 162M, and a position facing the image forming units 14K, 14Y, 14M, and 14C, respectively. A fourth primary transfer roll 162C is provided, and the toner images of the respective colors formed on the photosensitive drums 152K, 152Y, 152M, and 152C are transferred onto the intermediate transfer belt 16 in a multiple manner by these primary transfer rolls 162. The The residual toner adhering to the intermediate transfer belt 16 is removed by a cleaning blade or brush of a belt cleaning device 189 provided downstream of the secondary transfer position.

In the paper transport path 18, a paper feed roller 181 for taking out the recording paper 32 from the paper tray 17, a first roller pair 182, a second roller pair 183 and a third roller pair 184 for paper transport, and a recording paper A registration roll 185 is provided which conveys 32 to the secondary transfer position at a predetermined timing.
In addition, a secondary transfer roll 185 that is in pressure contact with the backup roll 168 is disposed at the secondary transfer position on the paper transport path 18, and each color toner image transferred onto the intermediate transfer belt 16 is Secondary transfer is performed on the recording paper 32 by the pressing force and electrostatic force of the secondary transfer roll 185. The recording paper 32 onto which the toner image of each color is transferred is conveyed to the fixing device 19 by the first conveyance belt 186 and the second conveyance belt 187.
The fixing device 19 melts and fixes the toner to the recording paper 32 by performing heat treatment and pressure treatment on the recording paper 32 to which the toner images of the respective colors are transferred.

[Image misalignment]
Next, an image misalignment that occurs in the printer 10 will be described.

In the printer apparatus 10 illustrated in FIG. 1, as illustrated below, the toner transferred onto the intermediate transfer belt 16 by each image forming unit 14 due to various factors such as vibration during transportation or installation or temperature change in the apparatus. The position of the image varies. For example, when the toner images of the respective colors deviate from each other, so-called color misregistration occurs and a beautiful color image is not formed. Also, when the toner image deviates from the predetermined position of the intermediate transfer belt 16, the image on the recording paper 32 is shifted. The problem that the position shifts occurs.

FIG. 2 is a diagram for explaining misalignment in the main scanning direction.
As illustrated in FIG. 2A, in the image forming unit 14, when the photosensitive drum 152 is displaced in the laser light irradiation direction, the distance (optical path length) between the optical scanning device 140 and the photosensitive drum 152 is increased. fluctuate. In this case, the range on the photosensitive drum 152 scanned by the optical scanning device 140 varies from “scanning range A” to “scanning range B” as illustrated in FIG. A shift in magnification in the laser beam scanning direction or a shift in left and right magnification in the main scanning direction occurs.
Further, as illustrated in FIG. 2C, in the image forming unit 14, when the optical scanning device 140 and the photosensitive drum 152 are displaced in the main scanning direction, as illustrated in FIG. 2B, the main scanning direction. Margin deviation occurs.

FIG. 3 is a diagram for explaining a positional shift in the sub-scanning direction.
Originally, the photosensitive drums 152 are arranged at predetermined intervals, but as illustrated in FIG. 3A, they are displaced in the traveling direction (sub-scanning direction) of the intermediate transfer belt 16 due to vibration or the like. There is a case. In such a case, the transfer position of the toner image is also changed by the photosensitive drum 152 in accordance with the displacement of the photosensitive drum 152 in the sub-scanning direction. Therefore, as illustrated in FIG. The margin shift occurs.

There are various other misalignments. For example, a skew deviation is caused by a toner image transferred from the photosensitive drum 152 to the intermediate transfer belt 16 when the rotation axis of a certain photosensitive drum 152 is inclined with respect to the rotation axis of the intermediate transfer belt 16. Inclination occurs between the toner image transferred from the other photosensitive drum 152.
Further, the positional shift due to the sub-scanning cycle fluctuation is a speed between the image forming units 14 when the relative speed between the photosensitive drum 152 corresponding to each color and the intermediate transfer belt 16 fluctuates periodically. It occurs when the amount of fluctuation is different. The position shift due to the main scanning period fluctuation occurs when the intermediate transfer belt 16 meanders in the main scanning direction.
As described above, due to various factors, the magnification deviation in the main scanning direction, the magnification deviation between the left and right magnifications in the main scanning direction, the skew deviation, the sub scanning margin deviation, the main scanning margin deviation, the sub scanning period deviation, and the main scanning period deviation may occur. Arise. Since these misregistrations occur in combination in the same image forming process, the misregistrations are superimposed and appear on the recording paper 32 as color misregistrations.

FIG. 4 is a diagram for explaining correction of misalignment in the printer apparatus 10.
As illustrated in FIG. 4A, when the printer apparatus 10 outputs an image without correcting the positional deviation, the printer apparatus 10 prints an output image in which the plurality of positional deviations are integrated.
Therefore, the printer apparatus 10 generates and outputs corrected image data by causing the image processing apparatus 20 to add or delete pixels so as to cancel the positional deviation. As illustrated in FIG. 4B, the corrected image data is obtained by correcting the opposite phase with respect to the positional deviation by the printer device 10. For example, as illustrated in FIG. 2, when a magnification shift that enlarges in the main scanning direction occurs, the image processing apparatus 20 deletes some pixels from the image data by an amount corresponding to the enlargement magnification. Then, the image is reduced in the main scanning direction to generate corrected image data. The printer device 10 can obtain an output image in which the positional deviation is canceled by outputting the corrected image data to the image forming unit 14.
The image processing apparatus 20 generates corrected image data for each color image data, and outputs the corrected image data to the corresponding image forming units 14K, 14Y, 14M, and 14C.

Next, the arrangement of pixels added or deleted by the image processing apparatus 20 will be described. Here, the arrangement is to arrange in accordance with a predetermined rule, and the image processing apparatus 20 in the present embodiment adds or adds pixels to a position in accordance with a predetermined rule as described below. delete.
In the following description, pixel addition processing and deletion processing are collectively referred to as “pixel operation”, and pixels to be added or deleted are referred to as “operation pixels”.
FIG. 5 is a diagram illustrating an additional position (that is, an operation position) of pixel data in an image.
FIG. 5A illustrates the binarized image data 700, and FIG. 5B illustrates the corrected image data 710 obtained by enlarging the image data 700 in the main scanning direction. Thus, the image processing apparatus 20 can enlarge an image by adding pixels to each scan line and shifting subsequent pixels in the main scanning direction according to the addition of the pixels.
However, as illustrated in FIG. 5B, when pixels are simply added to the same position on the main scanning line, the image becomes visually noticeable.
Therefore, as illustrated in FIG. 5C, the image processing apparatus 20 according to the present embodiment changes the position of the operation pixel for each scan line at a predetermined angle and cycle. Note that the image processing apparatus 20 can determine the position of the additional pixel (that is, the arrangement of the additional pixel) according to various rules such as a periodic function. Hereinafter, the pixel operation angle) and the arrangement period of the additional pixels (hereinafter, pixel operation period) will be described as the pixel arrangement parameters. This pixel operation cycle is a cycle in the main scanning direction or the sub-scanning direction, and is expressed by the number of pixels. The array parameters are not limited to these angles and periods, and may be, for example, a period in a direction different from the main scanning direction or the sub-scanning direction, or a coefficient of a periodic function.

  In FIG. 5, the case where the pixel is added by the image processing device 20 has been described as a specific example. However, the image processing device 20 generates the corrected image data 710 by deleting the pixel at the predetermined array position. May be. Also in this case, as in the case illustrated in FIG. 5B, when a simple pixel is deleted from the same position on the main scanning line, a thin line overlaps the deleted position. This thin straight line disappears, and the amount of information in the image is significantly reduced. Therefore, the image processing apparatus 20 deletes the operation pixel at the position illustrated in FIG.

Next, screen processing will be described.
FIG. 6A illustrates a screen pattern having a uniform arrangement position in the screen unit region, and FIG. 6B illustrates a threshold parameter for forming this screen pattern.
When binarizing multi-valued image data, the threshold parameter (threshold matrix) illustrated in FIG. 6B is compared with the pixel value (multi-value) of the input image to obtain a binary screen pattern. Generated. The screen pattern (output pattern) is a print area in the screen unit area, and the gradation (density) of the image is expressed by the ratio of the screen pattern to the screen unit area. Further, the screen unit area is an area where each screen pattern is arranged, and is, for example, the smallest unit area that can be expressed independently by the area gradation method. The center of gravity of the screen pattern in this example is uniform in each screen unit area. The threshold parameter in this example corresponds to 32-gradation image data and is an example of a screen parameter. Here, the screen parameter is a coefficient that defines the screen processing, and is, for example, a numerical value that defines the arrangement position (center of gravity or growth start position) of the screen pattern or the growth shape of the screen pattern.

FIG. 7 is a diagram illustrating a screen pattern when the pixel operation process and the screen process are performed. When the screen processing is performed by applying the threshold parameter as illustrated in FIG. 6, the screen pattern is arranged with a substantially uniform period and angle as illustrated in FIGS. 7A and 7B. . In addition, when pixel operation processing is performed in order to correct misalignment, as illustrated in FIG. 5C, pixels are added to a range corresponding to the misalignment correction amount (hereinafter referred to as pixel operation range). . The operation pixel (added pixel) in this example is obtained by directly applying the pixel value at the position to be added.
In this example, the screen angle and the pixel operation angle are made different so that the screen pattern and the operation pixel do not interfere with each other, and the screen pattern cycle (main scanning direction and sub-scanning direction) and the pixel operation cycle (main scanning direction) The scanning direction and the sub-scanning direction) are different. Therefore, the image defect caused by the interference between the screen pattern and the operation pixel (additional pixel) has not yet been visually recognized as a streak.

However, as shown in FIG. 7C, an image defect may occur due to a density change that occurs in the pixel operation range. For example, the screen pattern illustrated in FIG. 7A has a halftone density of 20%, 20 of 100 pixels are on (black) data, and the other are off (white) data. If the operation pixel to be added also maintains the ratio of on: off = 20: 80, the ratio of on and off does not change on the image after pixel addition, and the density does not change. However, depending on the relationship between the cycle of the screen pattern and the operation pixel cycle and the relationship between the arrangement angle of the screen pattern and the arrangement angle of the operation pixels, a minute density change occurs. In this example, the density change illustrated in FIG. 7C is generated by arranging the additional pixel positions in a vertical arrangement with a constant cycle interval. That is, in this example, as shown in FIG. 7B, screen patterns having the same cluster shape are arranged vertically, and the additional pixel positions arranged in the same direction and the screen pattern collide with each other. Deviation of off data occurs, causing density change. And even if the density difference between the density of the area where the pixel is not added and the area where the pixel is added (pixel operation range) is minute, it can be visually discerned. Further, since the pixel addition processing is periodically performed in the main scanning direction, density changes are also periodically generated at regular intervals, which makes it easier to discriminate.
Further, when the pixel operation position is determined in consideration of the on / off ratio of the image before and after the pixel addition, the density change does not occur, but the process becomes complicated.

In FIG. 7, the case where a pixel is added has been described as a specific example, but the same applies to the case where a pixel is deleted. That is, in the process of correcting the image width by deleting pixels in units of one pixel, depending on the screen and the deleted pixel position, the deviation of on (black) data and off (white) data of the pixel to be deleted occurs and the density change Occurs.
Further, the above density change occurs in the same way when a pixel operation is performed to correct the image width in the sub-scanning direction and when a pixel operation is performed to correct the image width in the main scanning direction.

  Therefore, the image processing apparatus 20 according to the embodiment of the present invention performs screen processing so that screen patterns adjacent in the arrangement direction of the operation pixels have different growth shapes, different growth start positions, or different barycentric positions. The image processing apparatus 20 performs screen processing so that screen patterns adjacent in at least one of the main scanning direction and the sub-scanning direction have different growth shapes, different growth start positions, or different barycentric positions.

FIG. 8 is a diagram for explaining the screen processing according to the present invention. FIG. 8A illustrates a screen pattern generated by this screen processing, and FIG. 8B and FIG. The threshold parameter (threshold matrix) applied by this screen process is illustrated. The screen pattern of this example corresponds to a 45 degree screen, and is periodically arranged in an array of 45 degrees.
As illustrated in FIG. 8A, the image processing apparatus 20 sets the screen pattern arrangement position (the relative position of the screen pattern to the screen unit area) in the screen unit area that is continuous in the main scanning direction and the sub-scanning direction. Make it different. In this example, there are two types of arrangement positions (center of gravity positions) of screen patterns formed in each screen unit area. That is, among these screen pattern arrangements, the first screen pattern a is arranged in the A column, and the second screen pattern b is arranged in the B column.
This is realized by applying different screen parameters (threshold matrixes) to adjacent regions in the main scanning direction and the sub-scanning direction. More specifically, the image processing apparatus 20 applies the threshold parameter a (first threshold matrix) illustrated in FIG. 8B to the pixel group divided by the screen unit area of the A column, and the B column. The threshold parameter b (second threshold matrix) illustrated in FIG. 8C is applied to the pixel group divided by the screen unit area. The screen pattern thus formed is a dot shape arranged at 45 degrees in the same manner as the screen pattern shown in FIG. 6A. However, the position of the dot shape in each screen unit area is very small. Will be different. Specifically, the arrangement position of the first screen pattern a in the screen unit area a is different from the arrangement position of the second screen pattern b in the screen unit area b. That is, the screen pattern a and the screen pattern b having different arrangement positions are adjacent to each other in the main scanning direction and the sub-scanning direction.
In this figure, the dot shape (screen pattern) having different arrangement positions in the screen unit area has been described as a specific example. However, the image processing apparatus 20 uses the dot (screen pattern) adjacent in the main scanning direction and the sub-scanning direction. The shape may be different.

FIG. 9 is a diagram for explaining the relationship between the operation pixel and the screen pattern when the screen processing (FIG. 8) according to the present invention is applied.
When the screen processing described with reference to FIG. 8 is performed, screen patterns adjacent in the main scanning direction and the sub-scanning direction are arranged at different positions as shown in FIG.
When a pixel operation is performed on an image that has been screen-processed in this way, the operation pixel (circled in the figure) that has been operated (added or deleted) is the pixel operation angle (FIG. 7B). ) Has an array angle (primary angle component) and an array angle (secondary angle component) in the direction of 90 degrees (sub-scanning direction).
As described above, the screen pattern array angle (sub-scanning direction) matches the operation pixel array angle (secondary angle component), but the screen patterns arrayed in the sub-scanning direction have different positions. Therefore, compared with the case illustrated in FIG. 7 (when the arrangement position in the screen unit area is uniform), the periodicity in which the operation pixel hits the ON pixel is disturbed. This reduces the occurrence of image defects due to density changes.

[Functional configuration of image processing apparatus]
FIG. 10 is a diagram illustrating the functional configuration of the image processing apparatus 20.
As shown in FIG. 10, the image processing apparatus 20 includes a screen processing unit 210, a parameter setting unit 220, a misregistration detection unit 230, a correction value setting unit 240, a position correction unit 250, and an output interface unit (output I / F unit). 260.
The screen processing unit 210 (screen processing means) is a processing block to which multi-valued image data is input, and performs screen processing having screen characteristics (angle and period) that hardly interfere with each other on the image data of each color. The image data of each color binarized by the screen processing is output to the selection unit 230. Further, the screen processing unit 210 applies screen processing to the input image by applying threshold parameters such that the gravity center positions (relative positions in the screen unit area) of the screen patterns adjacent in at least one direction are different. Specifically, the screen processing unit 210 performs the screen processing described with reference to FIG. 8 on the input image.
In addition, when image data having a plurality of image areas is input in one page, the screen processing unit 210 selects a screen according to the image attribute of each image area, and multi-values are selected on the selected screen. The image data may be binarized.

The parameter setting unit 220 (control unit) sets screen parameters for the screen processing unit 210. Specifically, the parameter setting unit 220 sets the two types of threshold parameters exemplified in FIGS. 8B and 8C in the screen processing unit 210. For example, the parameter setting unit 220 sets one dither matrix in which the threshold parameter a and the threshold parameter b illustrated in FIG. The screen processing unit 210 performs screen processing using the dither matrix set by the parameter setting unit 220.
The parameter setting unit 220 may switch the screen parameter according to the position correction (pixel operation) by the position correction unit 250. For example, the parameter setting unit 220 may set the screen parameters so that the arrangement positions of the screen patterns are different only in the arrangement direction of the operation pixels. Further, the parameter setting unit 220 applies the screen processing described with reference to FIG. 8 when the position correction (pixel operation) is performed by the position correction unit 250 and does not perform the position correction by the position correction unit 250. The screen parameters may be switched so that the screen processing described in 6 is applied.

  The misregistration detection unit 230 detects, for example, the misregistration amount of each color toner image based on a test pattern formed on the intermediate transfer belt 16 (FIG. 1), and sets the detected misregistration amount as a correction value. Output to the unit 240. That is, the positional deviation detection unit 230 detects in advance the positional deviation of the image described with reference to FIG. The misregistration detection unit 230 may predict the misregistration amount based on a change in environmental conditions of the printer device 10 (for example, if the temperature inside the device changes by 5 ° C., the magnification error may change by 100 μm. If measured in advance, the amount of misalignment can be predicted according to the temperature inside the apparatus).

  The correction value setting unit 240 corrects the correction amount (that is, the operation amount) for each color image so as to cancel out the positional shift by each image forming unit 14 (FIG. 1) according to the positional shift amount detected by the positional shift detection unit 230. The number of pixels) and the correction direction (that is, the direction of enlargement or reduction) are set, and the set correction amount and the like are output to the position correction unit 250.

The position correction unit 250 (pixel operation means) adds or deletes pixels from the input image input from the screen processing unit 210 according to the correction amount and the correction direction set by the correction value setting unit 240, and outputs I / F unit 260 for output. In addition, when adding a pixel, the position correction | amendment part 250 determines the pixel value of an additional pixel based on the pixel value (for example, pixel value of a right-left pixel) of a surrounding pixel.
For example, when the main scanning magnification deviation exemplified in FIG. 2 occurs alone, the position correction unit 250 adds or deletes pixels so that the entire image area is enlarged or reduced in the main scanning direction.
Note that the position correction unit 250 performs pixel operations by selecting an array of operation pixels that does not cause an image defect according to screen characteristics (screen angle, screen period, number of screen lines, or screen type). It is desirable. The position correction unit 250 is an example of image processing that incorporates periodicity into an input image, and may be other image processing means.

  The output I / F unit 260 outputs each color input image input from the position correction unit 250 to each image forming unit 14.

[Print processing]
Next, the print processing operation of the printer apparatus 10 will be described.
FIG. 11 is a flowchart for explaining the operation (S10) of the printer apparatus 10.
As shown in FIG. 11, in step 100 (S100), the image processing apparatus 20 (FIGS. 1 and 10) acquires image data of an input image from a personal computer (not shown) or the image reading unit 12. When the image data is input, the image processing apparatus 20 starts detecting the amount of displacement.

In step 102 (S102), the image processing apparatus 20 outputs the image data of the test pattern to each image forming unit 14 (FIG. 1), and each image forming unit 14 performs the test according to the input image data. A pattern toner image is formed on the intermediate transfer belt 16 (FIG. 1). A sensor (not shown) provided in the vicinity of the intermediate transfer belt 16 detects a test pattern toner image and outputs it to the misregistration detection unit 230 (FIG. 10).
The misregistration detection unit 230 detects the misregistration amount based on the test pattern toner image, and outputs the misregistration amount to the correction value setting unit 240.
In step 104 (S104), the correction value setting unit 240 (FIG. 10) sets the number of operation pixels and the operation direction so as to cancel out the positional deviation amount based on the positional deviation amount detected by the positional deviation detection unit 230. The determined number of operation pixels and the operation direction are output to the position correction unit 250 and the parameter setting unit 220.

  In step 106 (S106), the parameter setting unit 220 selects a screen parameter based on the number of operation pixels and the operation direction input from the correction value setting unit 240, and sends the selected screen parameter to the screen processing unit 210. Output. Specifically, the parameter setting unit 220 determines the width of the pixel operation range based on the number of operation pixels and the operation direction, and when the pixel operation range is wider than the reference width (including 0), FIG. When the dither matrix in which the threshold parameter a shown in B) and the threshold parameter b shown in FIG. 8C are combined is set in the screen processing unit 210 and the pixel operation range is narrower than the reference width, FIG. A dither matrix including the threshold parameters shown in (B) is set in the screen processing unit 210.

  In step 108 (S108), the screen processing unit 210 performs screen processing by applying the dither matrix set by the parameter setting unit 220 to the input image data (input image). The screen processing unit 210 performs screen processing on the input image data of each color by applying screens having different screen angles for each color so as not to interfere with each other.

In step 110 (110), the position correction unit 250 adds or deletes pixel data to the image data of the input image according to the number of operation pixels and the operation direction set by the correction value setting unit 240. Image data in which the size or position of the image is corrected by adding or deleting pixel data is output to the output I / F unit 260.
In step 112 (S112), the output I / F unit 260 outputs the image data of each color that has been corrected by the position correction unit 250 to cancel the positional deviation to each image forming unit 14 (FIG. 1).
Each image forming unit 14 forms a toner image of each color according to the image data (pulse signal) input from the output I / F unit 260 and transfers the toner image onto the intermediate transfer belt 16. The toner images of the respective colors superimposed on each other on the intermediate transfer belt 16 are secondarily transferred to the recording paper 32 conveyed through the paper conveyance path 18. The recording paper 32 onto which the toner image has been transferred is further transported to the fixing device 19, subjected to a fixing process, and discharged onto a paper discharge tray.

  Note that in this example, a positional deviation correction process (pixel operation process) is performed after the screen process. This is because when the screen processing is performed after the positional deviation correction process, the positional deviation of the screen pattern itself is not corrected, so the screen angle may change, and the positional deviation may remain in the output image. Since the resolution of the image before screen processing (for example, 600 dpi, 8 bits, continuous tone) is lower than the resolution of the image after screen processing (2400 dpi, 1 bit, binary), This is because it is not suitable for correction of positional deviation in pixel units.

  As described above, the printer device 10 according to the present embodiment makes the density generated by adding or deleting pixels in order to make the arrangement positions (relative positions with respect to the screen unit area) of the screen patterns adjacent in the arrangement direction of the operation pixels different. The occurrence of changes can be suppressed. In addition, it is expected that image defects such as banding caused by positional deviation and density change of an image visually recognized as horizontal stripes, or vertical stripes caused by cleaning of the photosensitive drum or intermediate transfer member or charging / transfer defects are also expected. it can.

[Modification 1]
Next, a first modification of the above embodiment will be described. In the above embodiment, the printer apparatus 10 has different screen pattern arrangement positions regardless of the image density (that is, the size of the screen pattern). However, the conspicuousness of image defects varies depending on the image density. Therefore, the printer device 10 according to this modification changes the arrangement position of the screen pattern according to the image density.

FIG. 12 is a diagram illustrating the third threshold parameter a ′ and the fourth threshold parameter b ′ applied in the first modification.
FIG. 13 is a diagram illustrating a screen pattern formed in the low density region by the third threshold parameter a ′ and the fourth threshold parameter b ′ illustrated in FIG.
FIG. 14 is a diagram illustrating a screen pattern formed in the middle density region by the third threshold parameter a ′ and the fourth threshold parameter b ′ illustrated in FIG.
Note that the low density region in this modification refers to a range where the image density (that is, the ratio of the screen pattern occupying the screen unit region) is less than 10%, and the medium density region is the image density of 10% or more. And the range which is 30% or less.

  The parameter setting unit 220 in this modification sets the threshold parameter a ′ and the threshold parameter b ′ illustrated in FIG. 12 in the screen processing unit 210. When the screen processing unit 210 applies the threshold parameter a ′ and the threshold parameter b ′ to perform screen processing on the low density image, a screen pattern as shown in FIG. 13 is formed. These screen patterns are arranged at uniform arrangement positions in the respective screen unit areas. That is, in the low-density image, the position of the screen pattern a in the A row formed based on the threshold parameter a ′ (that is, the relative position to the screen unit area) is the B row formed based on the threshold parameter b ′. Is the same as the position of the screen pattern b (that is, the position relative to the screen unit area).

In addition, when the screen processing unit 210 applies the threshold parameter a ′ and the threshold parameter b ′ to perform screen processing on the image in the middle density region, a screen pattern as shown in FIG. 14 is formed. These screen patterns are arranged at different positions in the respective screen unit areas as compared with screen patterns adjacent in the main scanning direction and the sub-scanning direction. That is, in the medium density image, the position of the screen pattern a in the A row formed based on the threshold parameter a ′ (that is, the relative position to the screen unit area) is the B row formed based on the threshold parameter b ′. Is different from the position of the screen pattern b (that is, the relative position to the screen unit area).
That is, the image processing apparatus 20 according to the present modification makes the screen pattern arrangement position uniform for low density image data, and the main scanning direction and sub-scanning direction for medium density image data. The arrangement positions of the screen patterns adjacent to each other are made different.

As described above, the printer device 10 according to the present modification reduces the image defect by changing the arrangement position of the adjacent screen patterns only in the middle density region where the image defect is conspicuous, and the screen in the low density region where the image defect is not conspicuous. Better image quality is achieved by equalizing the pattern placement positions.
Note that the threshold parameter a ′ and the threshold parameter b ′ illustrated in FIG. 12 have the same screen pattern arrangement position again in the high density region (that is, the density range of 30% or more). Therefore, the image output at this time is a 45 degree screen similar to that in FIG. 6 in a macro view, but the center of gravity position of the screen pattern is slightly different depending on the image density, and image defects caused by pixel operations are reduced. The density change is suppressed in a conspicuous density range, and the screen pattern is uniformly arranged in the other density ranges (low density range and high density range), so that it is possible to realize a uniform image quality.
Although FIG. 14 shows an example in which the gravity center position (arrangement position) of the screen pattern in the screen unit area differs depending on the density, the same effect can be obtained when the shape of the screen pattern is different.

[Modification 2]
Next, a description will be given of a screen process in which the center of gravity position of the screen pattern is different in the middle density region, but the center of gravity position of the screen pattern is substantially uniform in the high density region. Note that the high density area in this modification means a range in which the image density (that is, the ratio of the screen pattern occupying the screen unit area) exceeds 30%, and the density is higher than the density at which the dot-shaped screen pattern is connected to the adjacent screen pattern It is. That is, in the high density region, dot-shaped screen patterns are connected to adjacent screen patterns to form a line shape, and image defects due to pixel operations are less noticeable.

FIG. 15 is a diagram illustrating the fifth threshold parameter a ″ and the sixth threshold parameter b ″ applied in the second modification.
FIG. 16 is a diagram illustrating a screen pattern formed in the middle density region by the fifth threshold parameter a ″ and the sixth threshold parameter b ″ illustrated in FIG. Note that the medium density region in this modification refers to a range in which the image density is 30% or less.
FIG. 17 is a diagram illustrating a screen pattern formed in the high density region by the fifth threshold parameter a ″ and the sixth threshold parameter b ″ illustrated in FIG.

When the threshold parameter a ″ and the threshold parameter b ″ are applied to the medium density input image, the dot-shaped screen patterns are arranged differently in each screen unit area, like the screen patterns shown in FIGS. Formed in position. Then, when the threshold parameter a ″ and the threshold parameter b ″ are applied to the high density area image, a line-shaped screen pattern is formed. The center-of-gravity position of the line-shaped screen pattern in this example is substantially the same in the A column formed based on the threshold parameter a ″ and the B column formed based on the threshold parameter b ″. That is, the image processing apparatus 20 in the second modification example changes the position of the screen pattern at the image density below the reference (that is, the growth start position of the screen pattern), and if the image density exceeds this reference, the screen pattern The shape, the position of the center of gravity (in the screen unit area), etc. are made substantially the same.
As a result, the density change is suppressed in a density region where image defects caused by pixel operations are conspicuous, and the screen pattern is uniformly arranged in other density regions, so that it is possible to realize a uniform image quality.
Although FIG. 17 shows an example in which the center of gravity position of the screen pattern is different in the middle density region, the same effect can be obtained when the growth shape (dot shape) of the screen pattern is different in the low density region. .

[Modification 3]
Next, a case where three types of screen parameters are applied will be described as a third modification.
FIG. 18 is a diagram illustrating a screen pattern formed by three types of screen parameters.
The image processing apparatus 20 in the third modification performs screen processing by applying three types of screen parameters to a continuous area. Specifically, as shown in FIG. 18, the screen processing unit 210 (FIG. 10) applies three different threshold parameters to the partial images corresponding to the A column, the B column, and the C column, respectively. Perform screen processing. As a result, a screen pattern a is formed in the A row, a screen pattern b is formed in the B row, and a screen pattern c is formed in the C row. The screen pattern a, the screen pattern b, and the screen pattern c have different centroid positions in the screen unit area. As a result, three screen patterns (screen pattern a, screen pattern b, and screen pattern c) that are continuous in the main scanning direction and the sub-scanning direction have different centroid positions in the screen unit area.
As a result, even when the arrangement angle of the screen pattern and the arrangement angle of the operation pixel coincide with each other, since the three consecutive screen patterns are arranged at different positions, the periodicity with which the operation pixel hits the ON pixel is improved. Disturbed and the occurrence of image defects due to density changes is suppressed.

[Other variations]
In the above embodiment, the screen processing with a screen angle of 45 degrees has been described as a specific example. However, the present invention is not limited to this, and the present invention can be similarly applied to other screen angles.
FIG. 19 is a diagram illustrating a screen pattern when the present invention is applied to a 26-degree screen.
FIG. 20 is a diagram illustrating the relationship between the screen pattern of the 26-degree screen and the operation pixels.
As shown in FIG. 19, when screen processing is performed with a screen angle of 26 degrees, the screen unit area is also set in the direction of 26 degrees. Further, the image processing apparatus 20 according to the present modification changes the shape (growth shape) of the screen patterns adjacent in the direction of the screen angle (26 degrees). As described above, the image processing apparatus 20 may suppress image defects caused by pixel operations by changing the shape of the screen pattern instead of changing the position of the center of gravity of the screen pattern in the screen unit area. That is, as shown in FIG. 20, even when the screen angle and the pixel operation angle are substantially the same, the shape of the screen pattern adjacent in the direction of the pixel operation angle is different from each other, so that the operation pixel corresponds to the on-pixel. The periodicity is disturbed and the occurrence of image defects is suppressed.
As described above, the image processing apparatus 20 can suppress image defects even when the screen angle and the pixel operation angle coincide with each other. Therefore, the degree of freedom in selecting the screen angle or the degree of freedom in selecting the pixel operation angle is increased. .
Note that the image processing apparatus 20 may vary the shape of the adjacent screen patterns (that is, the growth shape) according to the image density of the input image.

Further, the image processing apparatus 20 may change the combination of screen parameters to be applied (that is, the combination of threshold parameters) for each image area of the input image. Here, the image area is an area that is classified by the attributes (photo image, font image, CG image, etc.) of the object included in the input image. For example, in the image area corresponding to an image (CG image) by computer graphics, the image processing apparatus 20 uses the threshold parameter a ′ and the threshold parameter b ′ illustrated in FIG. 12 (screen for forming a screen pattern that grows in a dot shape). In the image region corresponding to the photographic image, the threshold parameter a ″ and the threshold parameter b ″ (screen parameters for forming a screen pattern that grows from a dot shape to a line shape) are applied.
Further, the image processing apparatus 20 uses a threshold as shown in FIG. 12 or FIG. 17 in an image region having a large number of gradations (that is, an image region to which a screen having a small number of lines is applied) like a photographic image or a CG image. Apply a combination of parameters (screen parameters that change the center of gravity of the screen pattern according to the image density), and use an image area with a small number of gradations (ie, a screen with a large number of lines) such as a font image In the (region), a combination of threshold parameters as shown in FIG. 8 (screen parameters that vary the center of gravity of the screen pattern regardless of the image density) may be applied.

FIG. 21 is a diagram for explaining image data (raster data) 700 input to the image processing apparatus 20.
As illustrated in FIG. 21A, the raster data 700 includes a first image area 702 composed of photographic images and a second image composed of graphic images (such as line drawings created on a computer). An area 704 and a third image area 706 composed of character images are included. That is, in the present embodiment, an image is a collection of images included in one page, and means, for example, a graphic image, a photographic image, a character image, or a combination thereof.
The raster data 700 is obtained by arranging pixel data (multi-value) illustrated in FIG. 21B in the main scanning direction and the sub-scanning direction. The image processing apparatus 20 uses tag data attached to each pixel data. Based on (additional data), it can be determined which image attribute each pixel corresponds to, and a combination of threshold parameters is determined based on the tag data.

  As described above, when a plurality of image areas having different image attributes are mixed in one page image, the image processing apparatus 20 can select a combination of threshold parameters suitable for each image attribute.

Further, the printer device 10 in the above embodiment is not limited to a type using a photoconductor and an intermediate transfer belt, but directly sensitizes each color toner image on a recording medium (paper) electrostatically attracted to the belt and conveyed. A method of transferring from a body or a method of forming a color image by repeating exposure and development on a photosensitive belt may be used.
Further, the exposure apparatus is not limited to the laser beam scanning apparatus, and may be exposure using an LED.
Further, an image forming apparatus of a type that directly prints on a sheet as represented by an ink jet type image forming apparatus may be used.

  In the above-described embodiment, the form in which the present invention is used for color misregistration correction has been described. Therefore, the printer apparatus 10 can apply the present invention when correcting the position of an image even when printing a monochrome image.

1 is a diagram illustrating a configuration of a printer device 10 according to the present invention. It is a figure explaining the position shift in the main scanning direction. It is a figure explaining the position shift in a subscanning direction. FIG. 4 is a diagram for explaining correction of misalignment in the printer device 10. It is a figure which shows the addition position (namely, operation position) of the pixel data in an image. (A) illustrates a screen pattern having a uniform arrangement position in the screen unit region, and (B) illustrates a threshold parameter for forming the screen pattern. It is a figure which illustrates a screen pattern at the time of pixel operation processing and screen processing being made. It is a figure explaining the screen processing concerning this invention, (A) illustrates the screen pattern produced | generated by this screen processing, (B) and (C) show the threshold parameter applied by this screen processing. Illustrate. It is a figure explaining the relationship between the operation pixel at the time of the screen processing (FIG. 8) concerning this invention being applied, and a screen pattern. 2 is a diagram illustrating a functional configuration of an image processing device 20. FIG. 6 is a flowchart for explaining an operation (S10) of the printer apparatus 10; It is a figure which illustrates 3rd threshold value parameter a 'and 4th threshold value parameter b' applied in the 1st modification. FIG. 13 is a diagram illustrating a screen pattern formed in a low density region by the third threshold parameter a ′ and the fourth threshold parameter b ′ illustrated in FIG. 12. FIG. 13 is a diagram illustrating a screen pattern formed in a medium density region by the third threshold parameter a ′ and the fourth threshold parameter b ′ illustrated in FIG. 12. It is a figure which illustrates the 5th threshold value parameter a "and the 6th threshold value parameter b" applied in the 2nd modification. FIG. 16 is a diagram exemplifying a screen pattern formed in a middle density region by the fifth threshold parameter a ″ and the sixth threshold parameter b ″ illustrated in FIG. 15. FIG. 16 is a diagram illustrating a screen pattern formed in a high density region by the fifth threshold parameter a ″ and the sixth threshold parameter b ″ illustrated in FIG. 15. It is a figure which illustrates the screen pattern formed by three types of screen parameters. It is a figure which illustrates the screen pattern at the time of applying this invention with respect to a 26 degree | times screen. It is a figure which shows the relationship between the screen pattern of a 26 degree | times screen, and an operation pixel. 4 is a diagram for explaining image data (raster data) 700 input to the image processing apparatus 20. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Printer apparatus 14 ... Image forming unit 16 ... Intermediate transfer belt 20 ... Image processing apparatus 210 ... Screen processing part 220 ... Parameter setting part 230 ... Misregistration detection part 240 ... Correction value setting section 250 ... Position correction section 260 ... Output interface section

Claims (6)

Pixel operation means for adding or deleting pixels from the input image;
A screen processing unit to perform the screen processing on the input image to form an output pattern corresponding to the gradation of the input image to each screen unit areas,
A growth shape in which the arrangement direction of the pixels added or deleted by the pixel operation means coincides with the arrangement direction of the output pattern, and the output pattern in at least one screen unit area is different from the output pattern in other screen unit areas An image processing apparatus comprising: control means for controlling the screen processing means so as to have different growth start positions or different barycentric positions . The control means has a plurality of different threshold matrices, and switches and applies the different threshold matrices.
  The image processing apparatus according to claim 1. Wherein the at least one output in the output patterns and other screen unit area in the screen unit region pattern is the output pattern adjacent each main scanning direction and the sub scanning direction of the output image is formed based on different threshold matrices each other the image processing apparatus according to claim 1 that. Pixel operation means for adding or deleting pixels from the input image;
A screen processing unit to perform the screen processing on the input image to form an output pattern corresponding to the gradation of the input image to each screen unit areas,
A growth shape in which the arrangement direction of the pixels added or deleted by the pixel operation means coincides with the arrangement direction of the output pattern, and the output pattern in at least one screen unit area is different from the output pattern in other screen unit areas Control means for controlling the screen processing means so as to have different growth start positions or different center-of-gravity positions ;
An image processing apparatus comprising: an image forming unit that forms an image on a recording medium based on an input image screen-processed by the screen processing unit. Pixels are added to or deleted from the input image, and the input image is subjected to screen processing so that an output pattern corresponding to the gradation of the input image is formed in each screen unit area. Is a threshold matrix such that the output pattern of the at least one screen unit region coincides with the arrangement direction of the output patterns and has a different growth shape, a different growth start position, or a different barycentric position from the output patterns in the other screen unit regions. To apply screen processing to the image data of the input image,
An image forming method for forming an image from the image data subjected to the screen processing. Adding or removing pixels from the input image;
Applying screen processing to the input image so as to form an output pattern corresponding to the gradation of the input image in each screen unit region;
The arrangement direction of the pixels added or deleted by the step of adding or deleting the pixels coincides with the arrangement direction of the output pattern, and an output pattern of at least one screen unit area is an output pattern in another screen unit area. Applying a threshold matrix so as to be different growth shapes, different growth start positions or different barycentric positions, and screen processing the image data of the input image;
A program for causing a computer to execute the step of forming an image from the image data subjected to the screen processing.

Images