JP4253843B2 - Image forming apparatus, image forming method and program thereof - Google Patents

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 from the above-described background, and an object thereof is to provide an image forming apparatus capable of suppressing a decrease in image quality due to image correction.

[Image forming apparatus]
In order to achieve the above object, an image forming apparatus according to the present invention includes an image processing unit that performs different image processing on image data for each image region and a characteristic of each image processing that is different for each image region. A correction unit that performs correction processing on the image data that has been subjected to the image processing, and an image forming unit that forms an image from the image data that has been subjected to the correction processing.

  The image forming apparatus according to the present invention detects characteristics of the image processing for each image area based on data acquisition means for acquiring image data subjected to image processing and the image data subjected to the image processing. A characteristic detection unit, a correction unit that performs correction processing on the image data that has been subjected to the image processing according to the characteristics of the image processing detected by the characteristic detection unit, and an image from the image data that has been subjected to the correction processing. And image forming means for forming the image.

  Preferably, the correction means performs different correction processing for each image area in accordance with the characteristics of the image processing.

  Preferably, the characteristics of the image processing are attached to the image data, and the correction means applies the image processing to the image data subjected to the image processing based on the characteristics of the image processing attached to the image data. To perform correction processing.

  Preferably, the image processing is a screen processing, the correction processing is a pixel operation processing for adding or deleting regularly arranged pixels, and the correction means is in accordance with characteristics of the screen processing. An array selection unit that selects an array of pixels to be added or deleted, and a pixel operation unit that adds or deletes pixels in the array selected by the array selection unit.

  Preferably, the array selection means selects a pixel array having a different angle with respect to an array angle at which an interval between the arrayed screen patterns is equal to or less than a predetermined reference value among a plurality of array angles of the screen pattern. The pixel operation means adds or deletes a pixel in the pixel array selected by the array selection means.

  Preferably, the array selection unit selects a pixel array having an approximately intermediate angle between a plurality of array angles in which the interval between the arrayed screen patterns is equal to or less than a predetermined reference value.

  Preferably, the array selection means selects a pixel array whose period does not match within a range narrower than a reference value with respect to the period in which the screen pattern is arrayed, and the pixel operation means is selected by the array selection means Pixels are added or deleted in the pixel arrangement.

  Preferably, the array selection means selects a pixel array whose period does not coincide with the screen pattern array period within a range of 0.5 millimeters or less on the image formed on the recording medium.

  Preferably, the array selection means selects a pixel array whose periods in at least the main scanning direction or the sub-scanning direction do not match.

  Preferably, the arrangement selection means includes a number of pixels corresponding to an interval in the main scanning direction or sub-scanning direction of the screen pattern to be arranged, and a number of pixels corresponding to an interval in the main scanning direction or sub-scanning direction of the pixel arrangement. The pixel array is selected so that are mutually prime.

  Preferably, the arrangement selection unit selects an arrangement different from that in the case where the pixel is deleted when the pixel is added.

  Preferably, the array selection unit selects an array of pixels according to the number of pixels to be added or deleted.

  Preferably, the correction means includes parameter storage means for storing an array parameter for defining an array of pixels in association with the characteristics of the screen processing and the number of added pixels or the number of deleted pixels. Further, the array selection unit stores in the parameter storage unit according to the characteristics of the screen processing performed by the image processing unit and the number of pixels added or deleted by the pixel operation unit. The array parameter to be selected is selected as the array of the pixels, and the pixel operation unit adds or deletes pixels of the array defined by the array parameter selected by the array selection unit.

  Preferably, the pixel operation means adds and / or deletes pixels so as to change the size or position of the image in the main scanning direction.

  Preferably, the pixel operation means adds and / or deletes pixels so as to change the size or position of the image in the sub-scanning direction.

  The image forming apparatus according to the present invention includes an image processing unit that performs image processing on image data in accordance with characteristics of the subsequent correction processing, and the correction processing on the image data that has been subjected to the image processing. Correction means for performing, and image forming means for forming an image from the image data subjected to the correction processing.

  Preferably, the image processing is screen processing, the correction processing is pixel operation processing for adding or deleting regularly arranged pixels, and the image processing means is added or deleted in the correction processing. Screen processing is performed according to the arrangement of the pixels to be processed.

  Preferably, the image forming unit forms a multicolor image from a plurality of color image data, and the image processing unit performs the image processing on each of the plurality of color image data, and the correction unit. At least, correction processing is performed independently for each of the plurality of color image data subjected to the image processing.

Preferably, the array selection unit selects a pixel array in which pixels are arranged in a cycle that does not interfere with the screen processing.
Preferably, the array selection means selects a pixel array in which pixels are arranged at an angle that does not interfere with the screen processing.

[Image forming method]
The image forming method according to the present invention performs image processing different for each image area on the image data, and the image data subjected to the image processing according to the characteristics of the image processing different for each image area. Is corrected, and an image is formed from the corrected image data.

[program]
The program according to the present invention also includes a step of performing different image processing on image data for each image region, and image data that has been subjected to the image processing based on the characteristics of the image processing that are different for each image region. And performing a correction process and a step of forming an image from the corrected image data.

  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 are arranged and formed in parallel at a certain interval in the horizontal direction. The configuration is almost the same except that the color of the image 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 main scanning magnification deviation.
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.

FIG. 3 is a diagram for explaining a main scanning margin shift.
As illustrated in FIG. 3A, when the optical scanning device 140 and the photosensitive drum 152 are displaced in the main scanning direction in the image forming unit 14, a margin in the main scanning direction is illustrated as illustrated in FIG. Deviation occurs.

FIG. 4 is a diagram for explaining skew deviation.
As illustrated in FIG. 4A, in the image forming unit 14, the rotating shaft of the photosensitive drum 152 may be inclined with respect to the rotating shaft of the intermediate transfer belt 16. In such a case, as illustrated in FIG. 4B, the toner image transferred from the photosensitive drum 152 to the intermediate transfer belt 16 is inclined, so that the image is transferred between the photosensitive drum 152 and the image transferred from the other photosensitive drum 152. So-called skew deviation occurs.

FIG. 5 is a diagram for explaining the sub-scan margin deviation.
Originally, the photosensitive drums 152 are arranged at predetermined intervals, but as illustrated in FIG. 5A, 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.

FIG. 6 is a diagram for explaining misregistration due to sub-scanning cycle fluctuations.
In the image forming unit 14, as illustrated in FIG. 6A, the relative speed between the photosensitive drum 152 and the intermediate transfer belt 16 corresponding to each color may periodically vary. FIG. 6B is a graph in which the vertical axis represents the speed fluctuation amount of the photosensitive drum 152M and the photosensitive drum 152C, and the horizontal axis represents time. FIG. 6C is a graph in which the vertical axis represents the difference between the speed fluctuation amount of the photosensitive drum 152M and the speed fluctuation amount of the photosensitive drum 152C, and the horizontal axis represents time. If the speed variation amount is the same among the image forming units 14 of the respective colors, the toner images of the respective colors overlap each other. However, if the speed variation amount is different between the image forming units 14, a positional shift occurs in the sub-scanning direction. And color misregistration occurs. As shown in FIG. 6C, the color misregistration periodically occurs according to the difference in the speed fluctuation amount.

FIG. 7 is a diagram for explaining misregistration due to main scanning cycle fluctuations.
As illustrated in FIG. 7A, the intermediate transfer belt 16 may meander in the main scanning direction. As described above, when the intermediate transfer belt 16 is periodically displaced in the main scanning direction, the intermediate transfer belt 16 is simultaneously displaced in the same direction with respect to the photosensitive drum 152M and the photosensitive drum 152C. Since 152M transfers the toner image at a timing earlier than that of the photosensitive drum 152C, as illustrated in FIG. 7B, the M color toner image and the C color toner image exhibit different positional fluctuations. Therefore, as illustrated in FIG. 7C, periodic color misregistration in the main scanning direction occurs.

  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. 8 is a diagram for explaining correction of misalignment in the printer apparatus 10.
As illustrated in FIG. 8A, when the printer device 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. 8B, the corrected image data is obtained by correcting the reverse 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.

[Pixel array]
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. 9 is a diagram illustrating an additional position (that is, an operation position) of pixel data in an image.
9A illustrates the binarized image data 700, and FIG. 9B illustrates the corrected image data 710 in which the image data 700 is enlarged 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. 9B, when pixels are simply added to the same position on the main scanning line, they are visually noticeable.
Therefore, as illustrated in FIG. 9C, the image processing apparatus 20 in 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 operation pixel angle) and the arrangement period of the additional pixels (hereinafter, the operation pixel period) will be described as pixel arrangement parameters. This arrangement period is a period 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. 9, the case where pixels are 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 pixels at the predetermined arrangement position. May be. Also in this case, as in the case illustrated in FIG. 9B, if 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.

FIG. 10 is a diagram illustrating a periodic structure incorporated in an image by screen processing.
When binarizing multivalued image data, the image processing apparatus 20 performs screen processing having screen characteristics as exemplified in FIG. 10A or FIG. Enable. The image processing apparatus 20 of this example compares a dither matrix associated with image attributes (such as a photographic image, a graphic image, and a character image) with each pixel value of the rasterized multi-valued image data to obtain a multi-value. The value image data is binarized.
FIG. 10A illustrates a dot type screen. A dot type screen is composed of “a plurality of points” arranged at a predetermined angle (screen angle) and period (screen period). FIG. 10B illustrates a line type screen. A line type screen is composed of “a plurality of lines” arranged at a predetermined screen angle and screen period.
Therefore, when the image processing device 20 performs the screen processing and the pixel operation processing in series, the periodic structure incorporated by the screen processing interferes with the operation pixel periodically added or deleted by the positional deviation correction. Image defects such as moire may appear. For example, when the interval between the screens and the interval between the pixel arrays to be added or deleted are matched or very close to each other, they may interfere with each other and become visually noticeable as an image defect.

  Therefore, the image processing apparatus 20 determines an arrangement of operation pixels that does not cause an image defect according to the screen characteristics (screen angle, screen period, number of screen lines, or screen type). Specifically, the image processing apparatus 20 determines the arrangement of the operation pixels so that the screen angle and the screen period differ from the pixel operation angle and the pixel operation period by a predetermined value or more, and prevents the occurrence of image defects such as moire. . More specifically, the image processing apparatus 20 does not match a primary to tertiary screen angle (described later) and an operation pixel angle and has a range equal to or smaller than a reference value on the print image (for example, on the print image The array parameters are determined so that the screen period (main scanning direction and sub-scanning direction) and the operation pixel period (main scanning direction and sub-scanning direction) do not coincide with each other in a range of 0.5 mm or less. Since the screen angle needs to be selected so as not to interfere with the screen used for the image data of other colors, the image processing apparatus 20 changes the array parameter and switches the operation pixel array according to the screen. Is preferred.

Next, a method for determining the pixel operation period and the pixel operation angle according to the screen characteristics will be described. First, a method for determining the operation pixel angle will be described.
FIG. 11 is a diagram illustrating a screen pattern in which no pixel operation is performed.
FIG. 12 is a diagram illustrating an image (screen pattern) when a pixel operation is performed on the screen pattern shown in FIG. A hatched portion in the figure corresponds to a screen pattern, and a black square corresponds to an operation pixel. Further, the vector shown in FIG. 11 indicates a position vector to a screen pattern adjacent to the reference pattern when one screen pattern is used as a reference pattern, and a set of vectors having the shortest distance is referred to as a primary vector. This primary vector corresponds to a basis vector. The secondary vector, the tertiary vector, and the like are expressed by a linear combination of base vectors (primary vectors), and the distance to the screen pattern becomes longer in the order of the secondary vector and the tertiary vector.

  Since the operation pixel (black square) in this example is a pixel added in the main scanning direction (the pixel value at the additional position is applied as it is), the screen pattern is also deformed according to the insertion of the operation pixel. Therefore, when the angle of the screen pattern and the operation pixel angle coincide (that is, when the relative difference between them is small), an image defect occurs. In particular, when the angle of pixel operation (addition or deletion) coincides with the primary vector or the secondary vector of the screen pattern, the image defect is easily noticeable. This is because the operation of the same pixel enters the same position in the cell unit area of the screen (area where each screen pattern is arranged), and the disturbance of the same pixel occurs periodically, resulting in streak-like from a macro viewpoint. This is because it becomes conspicuous as an image defect. Here, the fact that the screen angle and the operation pixel angle coincide with each other includes not only complete coincidence but also a case where the relative angle is small enough to cause an image defect. Therefore, the image processing apparatus 20 needs to select a pixel operation angle that does not match the screen angle (that is, the relative difference is large).

  Here, as illustrated in FIG. 11, the screen pattern formed by the screen processing is arranged at a regular position on the two-dimensional plane. Therefore, the screen pattern has periodicity in various directions. For example, in “primary vector a” in which the cycle of the screen pattern is the shortest, the angle of the screen pattern group is 45 degrees, and in “primary vector b”, the angle of the screen pattern group is 135 degrees. In “secondary vector a”, the angle of the screen pattern group is 0 degree, and in “secondary vector b”, the angle of the screen pattern group is 90 degrees. In the “third-order vector a”, the angle of the screen pattern group is 18.4 degrees. As described above, there are an infinite number of periodically arranged screen pattern groups (hereinafter referred to as array angles), and it is difficult to select pixel operation angles that do not match all these array angles.

  Therefore, the image processing apparatus 20 preferentially prevents an array angle (for example, the primary vector a and the primary vector b) having a short interval between the screen patterns from matching the operation pixel angle. Specifically, the image processing apparatus 20 selects a pixel operation angle that is different from at least the arrangement angle of the primary vector and the secondary vector. In addition to the primary vector and the secondary vector, depending on the number of lines and the angle of the screen, the image defect may be noticeable even when the tertiary vector of the screen matches the pixel operation angle. Therefore, more preferably, the image processing device 20 selects a pixel operation angle that is different from at least the arrangement angle of the primary vector, the secondary vector, and the tertiary vector. In other words, the image processing apparatus 20 selects an operation pixel angle that is a different angle with respect to an arrangement angle at which the interval between the screen patterns is equal to or smaller than a reference value (for example, equal to or smaller than a distance corresponding to a tertiary vector). In this example, the operation pixel angle (FIG. 12) of 11.3 degrees is selected so as to be positioned between the secondary vector a (0 degree) and the tertiary vector a (18.4 degrees) shown in FIG. Is done.

Next, a method for determining the pixel operation cycle will be described.
If the cycle of the screen pattern and the pixel operation cycle are synchronized in the main scanning direction or the sub-scanning direction, dots that change in the same shape in that cycle are connected, resulting in an image defect.
As illustrated in FIG. 12, the screen pattern has a period of 16 pixels in the main scanning direction and 16 pixels in the sub-scanning direction. The screen pattern also has a period (32 pixel period, 48 pixel period, etc.) corresponding to a multiple of 16 pixels.
Similarly, the pixel operation cycle of this example also has a cycle (5 pixel cycle, 10 pixel cycle, etc.) corresponding to a multiple of 5 pixels in the main scanning direction, and a cycle corresponding to a multiple of 7 pixels in the sub-scanning direction. (7 pixel period, 14 pixel period, etc.).
Therefore, the cycle of the screen pattern and the pixel operation cycle are always synchronized with at least the least common multiple of each cycle. However, if the period in which the screen pattern and the pixel operation period are synchronized is relatively long, it is not noticeable to human eyes.
Therefore, the image processing apparatus 20 in the present embodiment selects the pixel operation period so that it does not coincide with the period of the screen pattern in a range narrower than the reference value in each of the main scanning direction and the sub-scanning direction. More specifically, the image processing apparatus 20 selects a pixel operation cycle that does not match the cycle of the screen pattern in the range of 0.5 millimeters or less on the printed image in the main scanning direction and the sub-scanning direction. More preferably, the image processing apparatus 20 selects a pixel operation cycle that does not match the cycle of the screen pattern in a range of 0.7 millimeters or less on the printed image. For example, when the screen pattern period (interval) in the main scanning direction is 16 pixels as illustrated in FIG. 12, the image processing apparatus 20 uses 5 pixels that are relatively prime to the 16 pixels. The pixel operation cycle in the scanning direction is selected. As described above, the image processing apparatus 20 selects a pixel operation cycle that is relatively prime with respect to the number of pixels corresponding to the screen pattern interval. In the example, the least common multiple 80) is increased.

In this example, the period in which the screen pattern and the operation pixel are synchronized in the main scanning direction is 80 pixels, which corresponds to 0.85 millimeters (greater than 0.7 millimeters) on an image printed at 2400 dpi. Therefore, it does not stand out as an image defect. Furthermore, in this example, as illustrated in FIG. 12, the operation pixel range in the main scanning direction (range in which pixels are added or deleted) is 31 pixels, and a period of 80 pixels does not appear.
In the sub-scanning direction, the screen pattern (16 pixel cycle) and the operation pixel (7 pixel cycle) are synchronized with each other, 16 and 7 are relatively prime and 112 pixels (112 lines). These 112 lines correspond to 1.19 millimeters on an image printed at 2400 dpi and are not conspicuous as image defects because they exceed 0.7 millimeters.

  The pixel operation illustrated in FIG. 12 is to change the image width or image position in the main scanning direction by adding pixels for each line in the main scanning direction. The same applies when a pixel operation to be changed is performed. That is, the same effect is achieved by applying what is illustrated in FIG. 12 after being rotated by 90 degrees.

FIG. 13 is a diagram for explaining the method of determining the pixel operation angle in more detail. FIG. 13A illustrates a screen pattern different from that shown in FIGS. 11 and 12, and FIG. Shows a table of angle components (primary vector, secondary vector and tertiary vector) of this screen pattern.
As illustrated in FIG. 13A, the screen pattern of this example includes eight vectors from a vector 1 (V1) to a vector 8 (V8) as a primary vector to a tertiary vector (that is, pixel operation angle and (An angular component that is not matched). In these angle components, as shown in FIG. 13B, the area between the vector 2 (V2) and the vector 8 (V8) is the widest. Therefore, the image processing apparatus 20 selects a substantially intermediate angle between the vector 2 (V2) and the vector 8 (V8) as the pixel operation angle. That is, the image processing apparatus 20 has two arrangement angles having the largest relative angle among the primary vector, the secondary vector, and the tertiary vector of the screen pattern (the arrangement angle in which the interval between the screen patterns is narrower than the reference value). A substantially intermediate angle is selected as the pixel operation angle. As a result, the relative difference between the pixel operation angle and the array angle also increases, and image defects are less likely to occur.

FIG. 14A illustrates another screen pattern, and FIG. 14B shows a table of angle components of this screen pattern.
This screen pattern also has eight vectors from vector 1 (V1) to vector 8 (V8) as a primary vector, a secondary vector, and a tertiary vector, as illustrated in FIG. 14A. In these angle components, as shown in FIG. 14B, the space between vector 1 (V1) and vector 5 (V5) is the widest. Therefore, the image processing apparatus 20 selects an angle 61.8 degrees, which is substantially intermediate between the vector 1 (V1) and the vector 5 (V5), as the pixel operation angle for the screen pattern.

Next, a method for determining the pixel operation position according to the pixel operation cycle and the pixel operation angle determined as described above will be described.
FIG. 15 is a table showing pixel operation positions corresponding to the screen pattern illustrated in FIG.
FIG. 16 is a diagram showing the relationship between the operation pixel operated according to the table shown in FIG. 15 and the ideal pixel operation angle. Note that the arrows shown in FIG. 16 indicate ideal pixel operation angles.
In the screen pattern illustrated in FIG. 14, the area between the vector 1 (V1) and the vector 5 (V5) is the widest, and the image processing apparatus 20 is intermediate between the vector 1 (V1) and the vector 5 (V5). .8 degrees was selected as the ideal pixel manipulation angle.
However, since the pixel operation (addition or deletion of pixels) needs to be performed in units of one pixel in the main scanning direction and in units of one pixel (one line unit) in the sub-scanning direction, the image processing apparatus 20 is an ideal pixel. The operating angle (61.8 degrees) cannot be realized as it is. For example, when the image width is changed by one pixel in the main scanning direction at a pixel operation angle of 61.8 degrees, it is necessary to always operate one pixel for each line in the sub-scanning direction. In order to satisfy the pixel operation angle of 61.8 degrees, it is necessary to shift by −0.535 pixels for each line in the sub-scanning direction. However, since the image to be manipulated is rasterized data at a certain resolution, only pixel manipulation in units of one pixel can be performed (that is, it cannot be shifted by −0.535 pixels).
Therefore, the image processing apparatus 20 calculates an ideal pixel operation position (ideal value) for each line with an accuracy of 1 pixel or less in order to realize an ideal pixel operation angle as much as possible, and performs pixel operation on each line. By rounding the position (ideal value), the pixel operation position in units of one pixel is determined. The rounding process may be rounded off, rounded down or rounded up. That is, as shown in FIG. 15, the image processing apparatus 20 first calculates an ideal value (up to the third decimal place in this example) indicating the operation position (main scanning direction) for each line, and calculates the calculated ideal value. The pixel operation position (position in the main scanning direction) in each line (sub-scanning line) is determined by rounding down or rounding up or down. The pixel operation position calculated by rounding off the decimal point of the ideal value in this way substantially matches the ideal pixel operation angle as shown in FIG. Similarly, the pixel operation position calculated by rounding off the decimal point of the ideal value almost coincides with the ideal pixel operation angle as shown in FIG. 16B, and is calculated by rounding up the decimal point of the ideal value. As shown in FIG. 16C, the performed pixel operation position substantially coincides with an ideal pixel operation angle.

  Further, the image processing apparatus 20 may select an approximate pattern corresponding to a desired angle as the image operation position instead of performing the rounding process as described above. The approximate pattern is a rule that defines a shift amount in units of pixels for each line close to a desired angle (in this example, −1 pixel for every two lines). In this case, the image processing apparatus 20 does not need to perform ideal value calculation and rounding processing, and thus the processing load can be reduced. For example, in this example, when one pixel is shifted every two lines, as shown in FIG. 16D, the actual pixel operation angle is 63.4 degrees, which is much larger than the ideal pixel operation angle of 61.8 degrees. There is no problem because it is not off. Furthermore, since the image processing apparatus 20 sets the pixel operation angle approximately in the middle of the vector 1 (V1) and the vector 5 (V5) having a large relative angle, an image defect is not caused by such an error. . In other words, the image processing device 20 determines the actual pixel operation position by setting the pixel operation angle between two vectors (primary vector to tertiary vector) having a large relative angle (truncation after the decimal point, The degree of freedom (allowable error range) can be increased when rounding or rounding up or applying an approximate pattern.

FIG. 17 is a diagram for explaining image data (raster data) 700 input to the image processing apparatus 20.
As illustrated in FIG. 17A, the image processing device 20 converts image data composed of a plurality of image areas into raster data 700 when input. The raster data 700 may include a plurality of image processing areas having different image attributes. The raster data 700 in this example is composed of a first image area 702 composed of a photographic image, a second image area 704 composed of a graphic image (such as a line drawing created on a computer), and a character image. Third image area 706. 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. 17B 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 is possible to determine which image attribute each pixel corresponds to.
Further, the image processing apparatus 20 refers to the tag data because image attributes (photo image, graphic image, character image, etc.) and screens (screen 200L, screen 150D, and screen 300D) are associated with each other. Thus, the screen can be switched according to the image attribute.

  As described above, when a plurality of image areas having different image attributes are mixed in one page image, screen processing is performed on the one page image using a plurality of screens. Needs to select an array of operation pixels that do not interfere with the plurality of screens. In addition, when the image processing device 20 cannot select an operation pixel array that does not interfere with all screens used in the same page, the image processing apparatus 20 may switch the operation pixel array in accordance with the image attribute of each image area. Good. The operation pixel is switched based on, for example, tag data illustrated in FIG.

  Further, the image processing apparatus 20 may not be able to specify image attributes (such as screen characteristics) when acquiring binary image data that has been subjected to screen processing in advance. In such a case, the image processing device 20 determines the characteristics (screen angle and screen cycle) of the screen processing applied to the image data based on the periodicity of the input image data, and according to the determination result. Then, an array parameter (that is, an array of operation pixels) may be selected.

FIG. 18 is a diagram illustrating the functional configuration of the image processing apparatus 20.
As shown in FIG. 18, the image processing apparatus 20 includes a screen processing unit 210, a periodic characteristic detection unit 220, a selection unit 230, a parameter setting unit 240, a parameter storage unit 250, a misregistration detection unit 260, a correction value setting unit 270, A position correction unit 280 and an output interface unit (output I / F unit) 290 are provided.
The screen processing unit 210 (image 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. 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 is binarized. The screen processing unit 210 outputs, to the parameter setting unit 240, screen characteristic information that specifies the screen angle and screen period of the screen applied for each image region. Note that the image processing unit may be any unit that performs image processing that incorporates periodicity into image data, for example, and the screen processing unit 210 is an example.

The periodic characteristic detection unit 220 (characteristic detection unit) is a processing block to which binary image data (for example, image data that has been subjected to screen processing in advance) is input, and the periodic characteristic (for example, input image data) , Screen characteristics, etc.), the detected periodic characteristics are output to the parameter setting unit 240, and the input image data is output to the selection unit 230. For example, the periodic characteristic detection unit 220 expands image data in the memory area, and calculates the number of screen lines, screens based on the periodicity of halftone image data in the main scanning direction and the sub-scanning direction, the phase change amount for each line, and the like. Calculate the angle or screen period.
The selection unit 230 selects the image data input from the screen processing unit 210 or the image data input from the periodic characteristic detection unit 220, and outputs the selected image data to the position correction unit 280.

The parameter setting unit 240 (array selection unit) determines the pixel array angle (operation pixel angle) and cycle (operation pixel angle) according to the screen characteristic information input from the screen processing unit 210 or the periodic characteristic input from the periodic characteristic detection unit 220. An array parameter that defines an operation pixel cycle) is set and output to the position correction unit 280. Specifically, the parameter setting unit 240 is configured such that the number of pixels corresponding to the screen pattern interval and the number of pixels corresponding to the pixel operation period are relatively prime in the main scanning direction and the sub-scanning direction, An array parameter is set so that the relative angle between the array angle from the vector to the tertiary vector and the pixel operation angle is as large as possible.
Note that the parameter setting unit 240 of this example refers to the parameter storage unit 250 to select the array parameter corresponding to the screen characteristic information or the periodic characteristic when setting the array parameter.
The parameter storage unit 250 stores the operation pixel angle and the operation pixel period values as array parameters in association with the screen characteristic information (screen angle and screen period) or the period characteristic. Further, even when the position of the operation pixel is the same, the situation of occurrence of image defects such as moire may be different between the case where the pixel is added and the case where the pixel is removed. This depends on the resolution of the printer device 10. For example, when the printer 10 capable of reproducing a thin line with high resolving power removes pixels, vertical moire tends to occur as an image defect in the operation pixel cycle.
Therefore, the parameter storage unit 250 may store the pixel operation angle and the pixel operation cycle in association with the screen characteristic information or the periodic characteristic and the operation content (that is, whether to add or delete a pixel). As a result, the printer apparatus 10 can apply array parameters having different values when the image width is expanded (pixel addition) and when the image width is reduced (pixel deletion), thereby suppressing the occurrence of image defects.

For example, the misregistration detection unit 260 detects the misregistration amount of each color toner image based on the 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 270. That is, the positional deviation detection unit 260 detects in advance the positional deviation of the image described with reference to FIG. The misregistration detection unit 260 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 270 corrects the correction amount (that is, the operation amount) for the image of each color so as to cancel the positional shift by each image forming unit 14 (FIG. 1) according to the positional shift amount detected by the positional shift detector 260. The number of pixels) and the correction direction (that is, the direction of enlargement or reduction) are set, the set correction amount is output to the position correction unit 280, and the set correction direction is output to the parameter setting unit 240 To do. The parameter setting unit 240 identifies the operation content (whether to add or delete pixels) and the direction in which the operation pixels are arranged based on the set correction direction, and adjusts the array parameters according to these.

The position correction unit 280 (pixel operation means) is an image input from the selection unit 230 in accordance with the array parameter set by the parameter setting unit 240 and the correction amount and correction direction set by the correction value setting unit 270. Pixel data is added to or deleted from the data, and is output to the output I / F unit 290. In addition, when adding pixel data, the position correction | amendment part 280 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 illustrated in FIG. 2 occurs alone, the position correction unit 280 adds or deletes pixels so that the entire image area is enlarged or reduced in the main scanning direction, When a periodic shift occurs as illustrated in FIG. 6 or FIG. 7, the periodic shift of the image is canceled by adding or deleting pixels to a partial region of the image.
The output I / F unit 290 outputs the image data of each color input from the position correction unit 280 to each image forming unit 14.

[Print processing]
Next, the print processing operation of the printer apparatus 10 will be described.
FIG. 19 is a flowchart for explaining the operation (S10) of the printer apparatus 10.
As shown in FIG. 19, in step 100 (S <b> 100), the image processing device 20 (FIGS. 1 and 18) acquires image data from a personal computer (not shown) or the image reading unit 12. The image processing apparatus 20 outputs the input image data to the screen processing unit 210 (FIG. 18) when the input image data is multi-valued data, and the input image data when the input image data is binary data. It outputs to the periodic characteristic detection part 220 (FIG. 18).

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 260 (FIG. 18).
The misregistration detection unit 260 detects the misregistration amount based on the test pattern toner image and outputs it to the correction value setting unit 270.
In step 104 (S104), the correction value setting unit 270 (FIG. 18) 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 260. This is set and output to the position correction unit 280 and the parameter setting unit 240.

  In step 106 (S106), the image processing apparatus 20 determines whether the input image data is multi-value data or binary data. If the input image data is multi-value data, the process proceeds to S108. In other cases, the process proceeds to S116. Specifically, the selection unit 230 selects the image data input from the screen processing unit 210 or the periodic characteristic detection unit 220 and outputs the image data to the position correction unit 280.

In step 108 (S108), the screen processing unit 210 selects a screen for each color so as not to interfere with each other according to the image attribute of each image area of the input image data, and inputs using the selected screen. Screen processing is performed on the image data, and the image data is output to the position correction unit 280 via the selection unit 230.
Further, the screen processing unit 210 outputs screen characteristic information (screen angle, screen period, etc.) applied to the image data of each color to the parameter setting unit 240.

  In step 110 (110), the parameter setting unit 240 displays screen characteristic information (screen angle, screen period, etc.), correction amount (number of operation pixels), and correction direction (enlargement or reduction in the main scanning direction, or sub-scanning direction). The array parameter corresponding to (enlargement or reduction) is selected from the parameter storage unit 250, and the selected array parameter is output to the position correction unit 280.

In step 112 (S112), the position correction unit 280 is an operation set by the correction value setting unit 270 in a pixel array (operation pixel angle and operation pixel cycle) defined by the array parameters set by the parameter setting unit 240. Pixel data is added or deleted by the number of pixels. Image data whose size or position has been corrected by adding or deleting pixel data is output to the output I / F unit 290.
In step 114 (S114), the output I / F unit 290 outputs the image data of each color that has been corrected by the position correction unit 280 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 290 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.

When binary image data is input, in step 116 (S116), the periodic characteristic detection unit 220 detects the periodic characteristic of the input image data and uses the detected periodic characteristic as a parameter setting unit. Output to 240. In addition, the periodic characteristic detection unit 220 outputs the input image data to the position correction unit 280 via the selection unit 230.
In step 118 (S118), the parameter setting unit 240 selects an array parameter corresponding to the detected periodic characteristic, correction amount, and correction direction from the parameter storage unit 250, and selects the selected array parameter for the position correction unit 280. Output.

Next, the order of image processing (screen processing in this example) and pixel operation processing will be described.
FIG. 20 is a diagram illustrating the order of screen processing and misregistration correction processing. FIG. 20A illustrates an output image obtained by performing only screen processing and printing without misregistration. ) Illustrates the output image obtained by performing the positional deviation correction process (addition or deletion of pixels) after the screen processing, and (C) illustrates the positional deviation correction process (addition or deletion of pixels). An output image obtained by performing screen processing and printing later will be exemplified.
As shown in FIG. 20A, as described above, no correction is performed, and an output image obtained as a result of screen processing and printing may cause a positional deviation such as a skew deviation. .

In addition, as shown in FIG. 20C, screen processing is performed after the misalignment correction, and the output image obtained as a result of printing does not disturb the screen structure, thereby reducing interference between the misalignment correction processing and the screen. Is done.
However, in the case shown in FIG. 20C, since the positional deviation of the screen structure itself is not corrected, there is a possibility that the screen angle changes and the positional deviation remains in the output image.
In misalignment correction by adding or deleting pixels, slight changes are repeatedly added to the image as viewed from the whole. For this reason, from a minute structure such as a screen structure, the minute change may not be ignored, and the screen structure may be changed so as to appear at some interval.
In general, the resolution of an image before screen processing (for example, 600 dpi, 8 bits, continuous tone) is higher than the resolution of an image after screen processing (2400 dpi, 1 bit, binary (bin)). Is low, it is not suitable for the positional deviation correction in pixel units.
Therefore, the order of the positional deviation correction processing is optimally after screen processing as shown in FIG.

As described above, the printer device 10 according to the present embodiment can determine the arrangement of the operation pixels so as not to interfere with the regularity (periodicity) incorporated in the image by image processing such as screen processing. Image defects such as moire can be prevented.
In particular, the printer device 10 can easily select a realistic and effective pixel operation cycle so that the screen cycle does not coincide with the pixel operation cycle within a range of 0.5 mm or less in the printed image. can do. Further, the printer device 10 narrows down the arrangement angle of the screen to be evaluated when selecting the pixel operation angle from the primary vector to the tertiary vector of the screen, thereby realizing a realistic and effective pixel operation angle. Can be selected.

[Modification]
In the above-described embodiment, the printer device 10 determines the arrangement of the operation pixels according to the characteristics of the screen processing, but conversely, the screen may be selected according to the arrangement of the operation pixels. This is suitable, for example, in the printer device 10 in which only one arrangement parameter can be set.

In the above-described embodiment, the printer device 10 selects the operation pixel array according to the screen characteristics, the number of operation pixels, and the operation direction, but in addition to the number of pixels in the main scanning direction or the sub-scanning direction, An array of operation pixels (operation pixel angle and operation pixel cycle) may be determined.
FIG. 21 is a diagram illustrating the arrangement of operation pixels according to the number of pixels in the main scanning direction. (A) illustrates an array of operation pixels selected without considering the number of pixels in the main scanning direction, and (B) illustrates an array of operation pixels selected with the number of pixels in the main scanning direction taken into account. Illustrate.
As illustrated in FIG. 21A, operation areas in which pixels are added or deleted and non-operation areas in which no pixels are added or deleted appear alternately in the main scanning direction of the image. In these operation areas and non-operation areas, minute density changes periodically occur, and this becomes visible mainly as vertical moire.
Therefore, the parameter storage unit 250 (FIG. 18) stores an array parameter that minimizes the non-operation area in association with the number of pixels in the main scanning direction in addition to the screen characteristics, and the parameter setting unit 240 stores the screen characteristics. The array parameters are set according to the number of operation pixels, the operation direction, and the number of pixels in the main scanning direction. Accordingly, as illustrated in FIG. 21B, the position correction unit 280 can add or delete pixels so that the non-operation area is not conspicuous, and can suppress the occurrence of image defects. The array parameters (operation pixel angle and operation pixel cycle) that minimize the non-operation area are determined according to the number of pixels to be added or deleted in the main scanning direction and the number of pixels in the main scanning direction of the entire image. It can be set by changing the pixel angle or the operation pixel cycle. Further, although the main scanning direction has been described in the figure, the present invention can be similarly applied to the sub-scanning direction.

Further, in the printer device 10 in the above-described embodiment, the screen characteristic (number of lines, angle, and period) is specified by developing the image data by the periodic characteristic detection unit 220 provided therein, but the memory capacity required for the image expansion is small. Large, complicated and heavy processing load.
Therefore, the printer device 10 reads an output sample (test chart) printed on the recording paper 32 with an external detector (such as a scanner) and analyzes the read output sample to detect periodic characteristics. May be. Alternatively, a human may observe the output sample that has been test printed with a magnifying glass or the like, measure the periodic characteristics of the output sample, and input the sample to the printer device 10 via a UI device (not shown). Thereby, the processing load of the printer apparatus 10 is reduced.
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 main scanning magnification gap. It is a figure explaining main scanning margin shift. It is a figure explaining skew (skew) shift. It is a figure explaining a subscanning margin shift. It is a figure explaining the position shift by subscanning cycle fluctuation | variation. It is a figure explaining the position shift by a main scanning period fluctuation | variation. FIG. 4 is a diagram for explaining correction of misalignment in the printer device 10. It is a figure which shows the addition position or deletion position of the pixel data in an image. It is a figure which illustrates the periodic structure integrated in an image by screen processing. It is a figure which illustrates the screen pattern which has not performed pixel operation. It is a figure which illustrates the image at the time of performing pixel operation with respect to the screen pattern shown in FIG. It is a figure explaining the determination method of a pixel operation angle in detail, (A) illustrates a screen pattern, (B) is the angle component (a primary vector, a secondary vector, and a tertiary vector) of this screen pattern. ). (A) illustrates another screen pattern, and (B) is a diagram showing a table of angle components of this screen pattern. 15 is a table illustrating pixel operation positions corresponding to the screen pattern illustrated in FIG. 14. It is a figure which shows the relationship between the operation pixel operated according to the table | surface shown by FIG. 15, and an ideal pixel operation angle. 4 is a diagram for explaining image data (raster data) 700 input to the image processing apparatus 20. FIG. 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 explaining the order of a screen process and a position shift correction process. It is a figure explaining the operation pixel arrangement | sequence according to the number of pixels of a main scanning direction, and the number of operation pixels.

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 ... Periodic characteristic detection part 230 ... Selection part 240 ··· Parameter setting unit 250 ··· Parameter storage unit 260 ··· Position shift detection unit 270 ··· Correction value setting unit 280 ··· Position correction unit 290 ··· Output interface unit

Claims (21)

Image processing means for performing different image processing on image data for each image area;
Correction means for performing pixel operation processing for adding or deleting regularly arranged pixels to the image data subjected to the image processing according to the characteristics of the image processing different for each image region;
An image forming apparatus comprising: an image forming unit that forms an image from the image data subjected to the pixel operation processing . Data acquisition means for acquiring image data subjected to image processing;
Characteristic detection means for detecting characteristics of the image processing for each image region based on the image data subjected to the image processing;
Correction means for performing pixel operation processing for adding or deleting regularly arranged pixels to the image data subjected to the image processing according to the image processing characteristics detected by the characteristic detection means;
An image forming apparatus comprising: an image forming unit configured to form an image from image data obtained by the pixel operation unit . The image forming apparatus according to claim 1, wherein the correction unit performs different pixel operation processing for each image area in accordance with characteristics of the image processing. The characteristics of the image processing are attached to the image data,
The image forming apparatus according to claim 1, wherein the correction unit performs pixel operation processing on the image data on which the image processing has been performed based on characteristics of the image processing attached to the image data. The image processing is screen processing,
The correction means includes
Array selection means for selecting an array of pixels to be added or deleted according to the characteristics of the screen processing;
The image forming apparatus according to claim 1, further comprising: a pixel operation unit that adds or deletes pixels in the array selected by the array selection unit. The array selection means selects a pixel array having a different angle with respect to an array angle in which an interval between the arrayed screen patterns is equal to or less than a predetermined reference value among a plurality of array angles of the screen pattern,
The image forming apparatus according to claim 5, wherein the pixel operation unit adds or deletes a pixel in the pixel array selected by the array selection unit. The image forming apparatus according to claim 6, wherein the array selection unit selects a pixel array having a substantially intermediate angle among a plurality of array angles in which an interval between the arrayed screen patterns is equal to or less than a predetermined reference value. The array selection unit selects a pixel array whose period does not match in a range narrower than a reference value with respect to the period in which the screen pattern is arrayed,
The image forming apparatus according to claim 5, wherein the pixel operation unit adds or deletes a pixel in the pixel array selected by the array selection unit. 9. The image forming apparatus according to claim 8, wherein the arrangement selection unit selects a pixel arrangement that does not coincide with an arrangement period of a screen pattern within a range of 0.5 mm or less on an image formed on a recording medium. 10. The image forming apparatus according to claim 8, wherein the array selection unit selects a pixel array whose periods in at least the main scanning direction or the sub-scanning direction do not match. The array selection means is configured such that the number of pixels corresponding to the interval in the main scanning direction or sub-scanning direction of the screen pattern to be arrayed and the number of pixels corresponding to the interval in the main scanning direction or sub-scanning direction of the pixel array are relatively prime. The image forming apparatus according to claim 5, wherein the pixel array is selected so as to be. The image forming apparatus according to claim 5, wherein the arrangement selection unit selects an arrangement different from the case where the pixel is deleted when the pixel is added. The image forming apparatus according to claim 5, wherein the array selection unit selects an array of pixels according to the number of pixels to be added or deleted. The correction means includes
Parameter storage means for storing an array parameter for defining the array of pixels in association with the characteristics of the screen processing and the number of added or deleted pixels;
The array selecting means stores array parameters stored in the parameter storage means according to the characteristics of the screen processing performed by the image processing means and the number of pixels added or deleted by the pixel operating means. As the array of pixels,
The image forming apparatus according to claim 5, wherein the pixel operation unit adds or deletes pixels in an array defined by an array parameter selected by the array selection unit. The image forming apparatus according to claim 5, wherein the pixel operation unit performs addition and deletion of pixels or any one of them so as to change the size or position of the image in the main scanning direction. The image forming apparatus according to claim 5, wherein the pixel operation unit performs addition and deletion of pixels or any one of them so as to change the size or position of the image in the sub-scanning direction. Image processing means for performing image processing on the image data according to the characteristics of the pixel operation processing in the subsequent stage;
Correction means for performing the pixel operation processing on the image data subjected to the image processing;
Have a image forming means for forming an image from the image data the pixel operation processing has been performed,
The pixel operation process is an image forming apparatus that adds or deletes regularly arranged pixels . The image processing is screen processing,
The image forming apparatus according to claim 17, wherein the image processing unit performs a screen process in accordance with an array of pixels added or deleted in the pixel operation process . The image forming means forms a multicolor image from a plurality of color image data,
The image processing means performs the image processing on each of the plurality of color image data,
The image forming apparatus according to claim 1, wherein the correction unit performs the pixel operation process independently for each of the plurality of color image data subjected to the image processing. Perform different image processing for each image area on the image data,
In accordance with the characteristics of the image processing that are different for each image region, pixel operation processing for adding or deleting regularly arranged pixels is performed on the image data subjected to the image processing ,
An image forming method for forming an image from the image data subjected to the pixel operation processing . Performing different image processing for each image area on the image data;
Performing pixel operation processing for adding or deleting regularly arranged pixels to the image data on which the image processing has been performed based on characteristics of the image processing that are different for each image region;
A program for causing a computer to execute the step of forming an image from the image data subjected to the pixel operation processing .

Images