JP2006020181A - Image processor, image forming apparatus, image forming method and program therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which suppresses occurrence of image defects resulting from screen processing and color misalignment correction to perform image formation. <P>SOLUTION: The image forming apparatus 10 determines an amount of operation pixels in consideration of periods of a screen pattern. Specifically, the image forming apparatus 10, when the periods (including periods of natural number multiples) of the screen pattern and periods (including periods of natural number multiples) of the operation pixels coincide within a predetermined range, changes the periods of the operation pixels, makes the periods asynchronous with the periods of the screen pattern by changing the amount of operation pixels and suppresses the image defect such as gradation stripes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that corrects the size or position of an image by adding or deleting pixels.

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 in light of the above-described background, and an object thereof is to provide an image forming apparatus that suppresses a decrease in image quality caused by image correction.

[Image processing device]
In order to achieve the above object, an image processing apparatus according to the present invention is generated by a screen processing unit that performs screen processing on an input image, a positional deviation amount of an output image, and screen processing by the screen processing unit. The operation pixel amount determination means for determining the amount of pixels to be changed for the input image based on the period of the input image, and the pixel for the input image according to the amount of pixels determined by the operation pixel amount determination means. And a pixel operation means that periodically changes.

  Preferably, the change is addition or deletion of a pixel, the scanning pixel amount determination unit determines an amount of a pixel to be added to or deleted from the input image, and the pixel operation unit determines the determined pixel. Pixels are periodically added to or deleted from the input image by the amount of.

  Preferably, the operation pixel amount determination unit is configured to change the amount of pixels to be changed so that a cycle generated by the screen processing and a cycle of pixels changed by the pixel operation unit are not synchronized within a predetermined range. To decide.

  Preferably, the input image is a color image made up of a plurality of color component images, and the operation pixel amount determination means includes a positional deviation amount of the output image and a cycle generated by screen processing for each color component image. Based on the above, the amount of pixels to be changed for each color component image is determined.

  Preferably, the operation pixel amount determination unit determines a reference pixel amount to be changed based on a positional deviation amount of the output image, and determines a pixel amount different from the reference pixel amount for any one color component image. In this case, the amount of pixels to be changed with respect to the other color component images is determined so that the relative positions or sizes of the color component images and the other color component images substantially coincide with each other.

  Preferably, the operation pixel amount determining means determines the amount of pixels to be changed for each color component image according to the priority order set in advance for the plurality of color component images.

  Preferably, priorities are set in advance for the screens to be applied by the screen processing means, and the operation pixel amount determining means is configured to select a screen to be applied when a plurality of screens are applied to the input image. The amount of pixels to be changed is determined according to the priority order.

  Preferably, the operation pixel amount determination unit prohibits the change of the pixel with respect to the input image by setting the amount of the pixel to be changed to 0 when the input image is composed of one color component image.

[Image forming apparatus]
The image forming apparatus according to the present invention is based on a screen processing unit that performs screen processing on an input image, a positional deviation amount of the output image, and a cycle generated by the screen processing by the screen processing unit. The operation pixel amount determination means for determining the amount of pixels to be changed for the input image, and the pixels are periodically changed with respect to the input image in accordance with the pixel amount determined by the operation pixel amount determination means. And an image forming unit that forms an image on a recording medium based on the input image in which the pixel is changed by the pixel operating unit.

[Image processing method]
In addition, the image processing method according to the present invention performs screen processing on the input image, and the pixel to be changed for the input image based on the positional deviation amount of the output image and the period generated by the screen processing. And the pixels are periodically changed for this input image in accordance with the determined pixel amount.

[program]
In addition, the program according to the present invention provides a pixel to be changed for an input image based on the step of performing screen processing on the input image, the positional deviation amount of the output image, and the period generated by the screen processing. And causing the computer to execute a step of periodically changing the pixels of the input image according to the determined amount of pixels.

  According to the image forming apparatus of the present invention, the size or position of an image can be corrected while maintaining the image quality.

[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.
Further, 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 (hereinafter referred to as color misregistration), and the toner image deviates from a predetermined position of the intermediate transfer belt 16. This causes a problem that the position of the image on the recording paper 32 is shifted (hereinafter referred to as “page shift”). The misregistration is a general concept including color misregistration and page misregistration.

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 respective photosensitive drums 152 are arranged at a predetermined interval, 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 means that the pixels are arranged according to a predetermined rule, and the image processing apparatus 20 in the present embodiment periodically arranges pixels at positions according to the predetermined rule as will be described below. Add or 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.
When binarizing multi-valued image data, the image processing device 20 compares a threshold parameter (threshold matrix) (not shown) with a pixel value (multi-value) of an input image to generate a binary screen pattern. Generate. The gradation (density) of the image is expressed by the ratio of the screen pattern in the screen unit area according to the area gradation method.

FIG. 6 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, the screen pattern is arranged with a substantially uniform period and angle, as illustrated in FIGS. 6A and 6B. In addition, when pixel operation processing is performed in order to correct misalignment, as illustrated in FIG. 6B, pixels are added to a range corresponding to the misalignment correction amount (hereinafter, 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. 6C, an image defect may occur due to a density change occurring in the pixel operation range. For example, the screen pattern illustrated in FIG. 6A has a halftone density of 20%, 20 pixels out 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 pixel, a minute density change occurs. In this example, the density change illustrated in FIG. 6C occurs due to the vertical arrangement of the additional pixel positions with a constant period interval. That is, in this example, as shown in FIG. 6B, 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. The density difference between the density of the area where no pixel is added and the area where the pixel is added (pixel operation range) is very small, but the cycle of the screen pattern and the cycle of the operation pixel are within the predetermined range. (For example, when the periods coincide within a range of 0.7 mm or less on the printed material), the image defect becomes apparent. In particular, there is no problem when the output resolution of a printer or the like is not so high, but in recent years, the image defect has become apparent and has become a problem as the output resolution of the printer or the like has improved. Note that the period of the screen pattern and the period of the operation pixel are synchronized with any period of the screen pattern (including a period that is a natural number multiple of the minimum period) and any period of the operation pixel (the natural period of the minimum period). (Including several times the period).

In FIG. 6, a case where a pixel is added has been described as a specific example, but the same applies to a 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 determines the operation pixel amount in consideration of the cycle of the screen pattern. Specifically, when the cycle of the screen pattern and the cycle of the operation pixel are synchronized within a predetermined range, the image processing apparatus 20 changes the cycle of the operation pixel by changing the operation pixel amount. Do not synchronize within the predetermined range with the pattern period.

[Functional configuration of image processing apparatus]
Next, the functional configuration of the image processing apparatus 20 will be described.
FIG. 7 is a diagram illustrating the functional configuration of the image processing apparatus 20 that implements the image processing method according to the present invention.
As shown in FIG. 7, the image processing apparatus 20 includes a screen processing unit 210, a screen setting unit 220, a misregistration detection unit 230, a correction amount setting unit 240, a pixel operation unit 250, and an output interface unit (output I / F unit). 260.
The screen processing unit 210 is a processing block to which multi-valued image data is input. The screen processing unit 210 performs screen processing having screen characteristics (angle and period) that hardly interfere with each other on the image data of each color. The digitized image data of each color is output to the pixel operation unit 250.
The screen processing unit 210 applies multi-valued image data by applying a screen selected according to the image attribute of each image area when image data having a plurality of image areas is input in one page. Is binarized.

The screen setting unit 220 sets screen parameters that define the cycle (number of lines), angle, and shape of the screen for the screen processing unit 210. Specifically, the screen setting unit 220 sets screen parameters according to the image attributes (photo image, character image, or CG image) of the input image data.
Note that when there are a plurality of image areas having different image attributes in one page, the screen setting unit 220 may switch the screen parameter for each image area.

  The misregistration detection unit 230 detects the misregistration amount of each color toner image based on, for example, a test pattern formed on the intermediate transfer belt 16 (FIG. 1), and sets the detected misregistration amount as a correction amount. 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 amount setting unit 240 adds or deletes the amount of pixels added or deleted by the pixel operation unit 250 based on the positional deviation amount detected by the positional deviation detection unit 230 and the screen period set by the screen setting unit 220. (Hereinafter, the operation pixel amount) is set. Specifically, the correction amount setting unit 240 is based on the positional deviation amount detected by the positional deviation detection unit 230 so as to cancel the positional deviation caused by each image forming unit 14 (FIG. 1). An operation pixel amount (that is, the number of operation pixels) and an operation direction (that is, an enlargement or reduction direction) are determined, and the cycle of the operation pixel and the cycle of the screen pattern corresponding to the determined operation pixel amount are within a predetermined range. In this case, the final operation pixel amount is determined by correcting the reference operation pixel amount.

The pixel operation unit 250 adds or deletes pixels from the input image input from the screen processing unit 210 in accordance with the operation pixel amount and the correction direction set by the correction amount setting unit 240, and outputs them to the output I / F unit 260. Output. In addition, when adding a pixel, the pixel operation unit 250 determines the pixel value of the additional pixel based on the pixel value of the peripheral pixel (for example, the pixel value of the leftmost pixel).
For example, when the main scanning magnification deviation illustrated in FIG. 2 occurs alone, the pixel operation unit 250 adds or deletes pixels so that the entire image area is enlarged or reduced in the main scanning direction.

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

FIG. 8 is a diagram for explaining a screen set for each image region.
As illustrated in FIG. 8A, image data (raster data) 700 input to the image processing apparatus 20 includes a first image area 702 composed of photographic images and a graphic image (created on a computer). A second image area 704 composed of a line image or the like, and a third image area 706 composed of a character image. That is, in this example, 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 (multivalued) illustrated in FIG. 8B in the main scanning direction and the sub-scanning direction, and the screen setting unit 220 includes tag data attached to each pixel data. Based on (additional data), it can be determined which image attribute each pixel corresponds to, and the screen parameter is determined based on the tag data.
In this example, a 200 lpi line-shaped screen is set in the first image area 702 including the photographic image, and a 150 lpi dot-shaped screen is set in the second image area 704 including the CG image. Then, a 300 lpi dot-shaped screen is set in the third image area 706 including the character image.
As described above, when a plurality of image areas having different image attributes are mixed in an image of one page, the screen setting unit 220 selects a combination of screen parameters (dither matrix) suitable for each image attribute. be able to.

FIG. 9 is a diagram illustrating a screen pattern formed by the screen processing unit 210. Note that the screen pattern illustrated in this figure corresponds to a pattern formed in a region having a uniform density (gradation).
As illustrated in FIG. 9A, when the screen processing unit 210 uses a 150 lpi dot-shaped screen, the formed screen pattern has a period of 80 pixels in the main scanning direction. Further, as illustrated in FIG. 9B, when the screen processing unit 210 uses a 200 lpi dot-shaped screen, the formed screen pattern has a period of 40 pixels in the main scanning direction. Similarly, as illustrated in FIG. 9C, when the screen processing unit 210 applies a 200 lpi line-shaped screen, the formed screen pattern has a period of 13 pixels in the main scanning direction, As illustrated in FIG. 9D, when the screen processing unit 210 applies a 300 lpi dot-shaped screen, the formed screen pattern has a cycle of 12 pixels in the main scanning direction.
Thus, the period of the screen pattern varies depending on the number of lines, the shape, and the direction of the screen. Further, the cycle of the screen pattern has not only the minimum cycle but also a cycle corresponding to a multiple thereof.
Therefore, the correction amount setting unit 240 determines the cycle of the screen pattern based on the number of lines, the shape, and the direction of the screen, and the determined cycle (including a multiple cycle) and the cycle of the operation pixel are predetermined. The operation pixel amount is determined so as not to coincide with each other in the range (for example, a range of 0.7 mm or less on the printed material).

FIG. 10 is a diagram for explaining a correction amount setting method by the correction amount setting unit 240.
As illustrated in FIG. 10, first, the correction amount setting unit 240 cancels out the misregistration amount based on the misregistration amount detected by the misregistration detection unit 230 (the misregistration amount regarding each color component image). The reference correction amount to be calculated is calculated, and it is determined for each color component whether or not the cycle of the operation pixel and the cycle of the screen pattern corresponding to the calculated reference correction amount are synchronized within a predetermined range. In this example, a specific example is a case where an image in which 28062 pixels are arranged in the main scanning direction is printed at 2400 dpi.
Then, when it is determined that any one of the color components is synchronized, the correction amount setting unit 240 changes the reference correction amount for the color component. It is desirable that the change amount of the reference correction amount is approximately half of the minimum screen period to be applied. For example, when the screen illustrated in FIG. 9A and the screen illustrated in FIG. 9D are applied, the reference correction amount is changed by 6 pixels which is half of 12 pixels.
In this example, in order to correct the misregistration, it is necessary to enlarge the black color component image by 0.25% in the main scanning direction, and the operation pixel cycle (cycle of added pixels) is 400 pixels. Become. Therefore, this operation pixel period and the period of the screen (150 lpi or 200 lpi dot shape) are synchronized. Therefore, the correction amount setting unit 240 of this example calculates the fixed correction amount (406) by adding 6 pixels (half of the 300 dpi screen period) to the reference correction amount (400).
Since the black reference correction amount (operation pixel amount) is 70.2 pixels (28062/400) and the final correction amount (final operation pixel amount) is 69.1 (28062/406), the operation pixel The rate of change of quantity is
(28062 + 69.1) / (28062 + 70.2) = 0.99996
And becomes -0.004%.

  In addition, when the correction amount different from the reference correction amount is set as the fixed correction amount for any one color component, the correction amount setting unit 240 also corrects the reference correction for other color components in order to prevent color misregistration. Change the amount. The change amount for the other color components may be any amount that can prevent color misregistration, and the correction amount setting unit 240 in this example has the same ratio as the change amount for black (a pixel group in the main scanning direction). The reference correction amount of other color components is changed to a definite correction amount by the ratio of the changed pixel amount to the whole). That is, since the correction amount setting unit 240 decreases the operation pixel amount in the main scanning direction by 0.004% for black, the operation pixel amount in the main scanning direction by 0.004% for other color components. Decrease.

When the screen period and the operation pixel period are synchronized with respect to a plurality of color components, the correction amount setting unit 240 selects one of the color components based on the priority order set in advance for each color component. The reference correction amount related to is changed with priority. This priority order is preferably determined based on the conspicuousness of the image defect caused by the synchronization of the screen period and the operation pixel period. The order is black, cyan, magenta, and yellow. Note that cyan and magenta may have the same priority because image defects are equally noticeable.
In this example, when the operation pixel amount different from the reference correction amount is set as the definite correction amount for black (Black), the correction amount setting unit 240 sets the cycle of the operation pixel in other color component images (cyan etc.). Even if the period of the screen is synchronized, since the priority of black is higher than that of other colors, the change in the operation pixel amount made for black is given priority. As a result, the image defect is resolved in preference to the conspicuous color of the image defect, so that the image quality when viewed as a color image is improved.

[Print processing]
Next, the printing operation of the printer apparatus 10 will be described.
FIG. 11 is a flowchart for explaining the first printing operation (S10) of the printer apparatus 10.
As shown in FIG. 11, in step 100 (S100), the image processing apparatus 20 (FIGS. 1 and 7) 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 105 (S105), 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. 7).
The misregistration detection unit 230 detects the misregistration amount based on the test pattern toner image and outputs the misregistration amount to the correction amount setting unit 240.
In step 110 (S110), the correction amount 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. It is determined as a reference correction amount.

  In step 115 (S115), the screen setting unit 220 determines the number, angle, and shape of the screen to be applied to each color component image based on the tag data (FIG. 8) included in the image data of the input image. Then, the screen parameters of the determined screen are output to the screen processing unit 210. The screen setting unit 220 may determine the image attribute of the image area by analyzing the image data of the input image, and may determine the number of lines, the angle, and the shape of the screen according to the determined image attribute. .

In step 120 (S120), the correction amount setting unit 240 determines the cycle of the screen pattern in the main scanning direction and the sub-scanning direction based on the screen line number, angle, and shape set for each color component image by the screen setting unit 220. And the calculated screen pattern period (including a period that is a multiple of the minimum period) and the period of the operation pixel corresponding to the reference correction amount (including the period that is a multiple of the minimum period) are within a predetermined range. It is determined for each color component whether or not they match (that is, whether or not to synchronize) in the range of 0.5 mm or less on the output medium.
When it is determined that the period of the screen pattern and the period of the operation pixel are synchronized for any one of the color components, the correction amount setting unit 240 proceeds to the process of S125 and determines that none of the color components is synchronized. In this case, the calculated reference correction amount is directly output to the pixel operation unit 250, and the process proceeds to S130.

In step 125 (S125), the correction amount setting unit 240 corrects the reference correction amount of the color component determined that the cycle of the screen pattern and the cycle of the operation pixel are synchronized. Specifically, the correction amount setting unit 240 adds or subtracts approximately half of the minimum period of the screen applied to the color component image to the reference correction amount of the color component to determine the final correction amount. To do.
Next, the correction amount setting unit 240 corrects the reference correction amounts of the other color components at substantially the same rate as the correction of the reference correction amount of the color component, and determines the fixed correction amount. The definite correction amount determined for each color component is output to the pixel operation unit 250.
When the screen period and the operation pixel period are synchronized with respect to a plurality of color components, the correction amount setting unit 240 selects one of the color components based on the priority order set in advance for each color component. The reference correction amount related to is corrected with priority.

  In step 130 (S130), the screen processing unit 210 performs screen processing by applying the screen parameters set by the screen setting unit 220 to the input image data (input image). Note that the screen processing unit 210 performs screen processing by applying screens having different screen angles to each color component image of the input image so as not to interfere with each other.

In step 135 (S135), the pixel operation unit 250 adds or deletes pixels to each color component image according to the operation pixel amount and operation direction set by the correction amount setting unit 240. The image data with the added or deleted pixels is output to the output I / F unit 260.
In step 140 (S140), the output I / F unit 260 outputs each color component image in which pixels are added or deleted by the pixel operation unit 250 to each image forming unit 14 (FIG. 1).
Each image forming unit 14 forms a toner image of each color according to each color component image (binary data) 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 determines the pixel operation amount by considering not only the positional deviation amount but also the screen pattern cycle, so that the screen pattern cycle and the operation pixel cycle are determined. It is possible to suppress image defects (shading lines) that are manifested by synchronization.

[Modification]
Next, a modification of the above embodiment will be described. In the above embodiment, the printer apparatus 10 sets the priority order for each color component, and determines the final correction amount (final operation pixel amount) based on the set priority order. The fixed correction amount may be determined based on the priority order.
FIG. 12 is a diagram illustrating the priority order set for the screen.
As illustrated in FIG. 12, the correction amount setting unit 240 can preset priorities for screen types (number of lines, angles, and shapes), and a fixed correction amount according to the set priorities. To decide. Specifically, when a plurality of screens are applied to one color component image, the correction amount setting unit 240 sequentially selects the screen pattern cycle and the operation pixel cycle from these screens in descending order of priority. The fixed correction amount is determined by changing the reference correction amount so that and do not synchronize with each other within a predetermined range. The priority order for the screen is determined based on the image attribute of the input image or the frequency of use of each screen. The priority in this example is set so that the higher the frequency of use, the higher the priority. Specifically, a 200 lpi dot-shaped screen, a 150 lpi screen, a 200 lpi line-shaped screen, and a 300 lpi screen are used. The screen is in order.
For example, when the reference correction amount is corrected so that the 300 lpi screen cycle and the operation pixel cycle are asynchronous, the correction amount setting unit 240 uses the 200 lpi screen cycle and the operation pixel cycle. Are synchronized with each other, the correction of the reference correction amount for making the 300 lpi screen period and the operation pixel period asynchronous is prohibited. As a result, image defects are eliminated in preference to a screen having a high appearance frequency, so that the image quality when viewed as an entire image is improved.

In addition, when the input image is an image formed with a single color toner, the printer apparatus 10 may correct image misalignment (page misalignment) on the recording paper. Even if the input image is a single color, if the cycle of the screen of one color and the cycle of the operation pixel are synchronized, an image defect may occur. What is necessary is just to perform the process which makes the period of an operation pixel asynchronous.
When there is no need for page misalignment correction, the printer apparatus 10 prohibits pixel operations and suppresses image defects (light / dark streaks) that occur when the cycle of the screen and the cycle of the operation pixels are synchronized. Good.
FIG. 13 is a flowchart for explaining the second printing operation (S20) for switching the misregistration correction according to the color component of the input image.
As shown in FIG. 13, in step 200 (S200), the image processing apparatus 20 (FIGS. 1 and 7) acquires image data of an input image from a personal computer (not shown) or the image reading unit 12. Further, the image processing apparatus 20 converts the color space of the image data of the input image into a CMYK color space, and generates at least one color component image. For example, when the input image can be printed with one color toner, the image processing apparatus 20 needs to generate one color component image and print the input image by mixing two or more toners. In some cases, a plurality of color component images are generated.

  In step 205 (S205), the screen setting unit 220 determines the number, angle, and shape of the screen to be applied to each color component image based on the tag data (FIG. 8) included in the image data of the input image. Then, the screen parameters of the determined screen are output to the screen processing unit 210.

  In step 210 (S210), the image processing apparatus 20 determines whether the generated color component image is one or two or more, and if the generated color component image is one, The process proceeds to S250, and if there are two or more color component images generated, the process proceeds to S215.

In step 215 (S215), 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 a 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. 7).
The misregistration detection unit 230 detects the misregistration amount based on the test pattern toner image and outputs the misregistration amount to the correction amount setting unit 240.
In step 220 (S220), the correction amount 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. It is determined as a reference correction amount.

In step 225 (S225), the correction amount setting unit 240 determines the cycle of the screen pattern in the main scanning direction and the sub-scanning direction based on the screen line number, angle, and shape set for each color component image by the screen setting unit 220. And the calculated screen pattern period (including a period that is a multiple of the minimum period) and the period of the operation pixel corresponding to the reference correction amount (including the period that is a multiple of the minimum period) are within a predetermined range. It is determined for each color component whether or not they match (that is, whether or not to synchronize) in the range of 0.5 mm or less on the output medium.
When it is determined that the cycle of the screen pattern and the cycle of the operation pixel are synchronized with respect to any color component, the correction amount setting unit 240 proceeds to the process of S230 and is determined not to synchronize with any color component. In this case, the calculated reference correction amount is output as it is to the pixel operation unit 250, and the process proceeds to S235.

In step 230 (S230), the correction amount setting unit 240 corrects the reference correction amount of the color component determined that the cycle of the screen pattern and the cycle of the operation pixel are synchronized. Specifically, the correction amount setting unit 240 adds or subtracts approximately half of the minimum period of the screen applied to the color component image to the reference correction amount of the color component to determine the final correction amount. To do.
Next, the correction amount setting unit 240 corrects the reference correction amounts of the other color components at substantially the same rate as the correction of the reference correction amount of the color component, and determines the fixed correction amount. The definite correction amount determined for each color component is output to the pixel operation unit 250.
When the screen period and the operation pixel period are synchronized with respect to a plurality of color components, the correction amount setting unit 240 selects one of the color components based on the priority order set in advance for each color component. The reference correction amount related to is corrected with priority.

In step 235 (S235), the screen processing unit 210 performs screen processing by applying the screen parameters set by the screen setting unit 220 to each color component image of the input image data.
In step 240 (S240), the pixel operation unit 250 adds or deletes pixels to each color component image according to the operation pixel amount and operation direction set by the correction amount setting unit 240. The image data with the added or deleted pixels is output to the output I / F unit 260.

In step 245 (S245), the screen processing unit 210 performs screen processing by applying the screen parameters set by the screen setting unit 220 to the color component image of the input image data.
The correction amount setting unit 240 prohibits the addition and deletion of pixels by setting the operation pixel amount to 0, and the pixel operation unit 250 outputs the color component image input from the screen processing unit 210 as it is accordingly. Output to the I / F unit 260.
That is, the image processing apparatus 20 does not perform pixel operation for canceling the positional deviation when the input image data can be printed with one color toner.

In step 250 (S250), the output I / F unit 260 outputs the color component image input from the pixel operation unit 250 to each image forming unit 14 (FIG. 1).
Each image forming unit 14 forms a toner image of at least one color according to the color component image (binary data) input from the output I / F unit 260 and transfers the toner image onto the intermediate transfer belt 16. The toner image transferred onto the intermediate transfer belt 16 is 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.

  As described above, when the input image can be printed with a single color toner, the printer device 10 according to the present modification prohibits the displacement correction by the pixel operation, and the cycle of the screen pattern and the cycle of the operation pixel are synchronized. Thus, it is possible to suppress image defects (shading lines) generated and to print an output image with high image quality.

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, a roll-shaped intermediate transfer member or a recording medium conveying member method, and 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.

1 is a diagram illustrating a configuration of a tandem type printer apparatus (image forming apparatus) 10. FIG. 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. 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 functional structure of the image processing apparatus 20 which implement | achieves the image processing method concerning this invention. It is a figure explaining the screen set for every image area. It is a figure which illustrates the screen pattern formed by the screen process part. It is a figure explaining the setting method of the correction amount by the correction amount setting part 240. FIG. 4 is a flowchart for explaining a first printing operation (S10) of the printer apparatus 10; It is a figure which illustrates the priority set about the screen. It is a flowchart explaining the 2nd printing operation (S20) which switches misalignment correction according to the color component of the inputted image.

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 ... Screen setting part 230 ... Misregistration detection part 240 ... Correction amount setting section 250 ... Pixel operation section 260 ... Output interface section

Claims (11)

Screen processing means for performing screen processing on the input image;
An operation pixel amount determination unit that determines an amount of pixels to be changed for the input image based on a positional deviation amount of the output image and a cycle generated by the screen processing by the screen processing unit;
An image processing apparatus comprising: a pixel operation unit that periodically changes pixels of the input image according to the amount of pixels determined by the operation pixel amount determination unit. The change is the addition or deletion of a pixel,
The scanning pixel amount determination means determines the amount of pixels to be added or deleted from the input image,
The image processing apparatus according to claim 1, wherein the pixel operation unit periodically adds or deletes pixels from the input image by a determined amount of pixels. The operation pixel amount determination unit determines an amount of a pixel to be changed so that a cycle generated by the screen processing and a cycle of the pixel changed by the pixel operation unit are not synchronized within a predetermined range. Item 8. The image processing apparatus according to Item 1. The input image is a color image composed of a plurality of color component images,
The operation pixel amount determination means determines the amount of pixels to be changed for each color component image based on the positional deviation amount of the output image and the period generated by screen processing for each color component image. The image processing apparatus according to claim 1 or 3. The operation pixel amount determination unit determines a reference pixel amount to be changed based on a positional deviation amount of the output image, and determines a pixel amount different from the reference pixel amount for any one color component image. The image according to claim 4, wherein an amount of a pixel to be changed with respect to another color component image is determined so that a relative position or size of the color component image and the other color component image substantially coincide with each other. Processing equipment. The image according to claim 4 or 5, wherein the operation pixel amount determination unit determines an amount of a pixel to be changed for each color component image according to a priority set in advance for a plurality of color component images. Processing equipment. Priorities are set in advance for the screens applied by the screen processing means,
The image processing according to claim 1, wherein when a plurality of screens are applied to the input image, the operation pixel amount determination unit determines an amount of pixels to be changed according to a priority order of the applied screens. apparatus. 2. The image according to claim 1, wherein when the input image is composed of one color component image, the operation pixel amount determination unit sets a pixel amount to be changed to 0 and prohibits the change of the pixel with respect to the input image. Processing equipment. Screen processing means for performing screen processing on the input image;
An operation pixel amount determination unit that determines an amount of pixels to be changed for the input image based on a positional deviation amount of the output image and a cycle generated by the screen processing by the screen processing unit;
Pixel operation means for periodically changing pixels with respect to the input image according to the amount of pixels determined by the operation pixel amount determination means;
An image forming apparatus comprising: an image forming unit that forms an image on a recording medium based on an input image in which pixels are changed by the pixel operating unit. Perform screen processing on the input image,
Based on the amount of positional deviation of the output image and the period generated by the screen processing, determine the amount of pixels to be changed for this input image,
An image processing method for periodically changing pixels of the input image according to the determined amount of pixels. Screen processing the input image;
Determining the amount of pixels to be changed for this input image based on the amount of displacement of the output image and the period generated by the screen processing;
A program that causes a computer to execute a step of periodically changing pixels of the input image in accordance with the determined amount of pixels.

Images