JP2007235609A - Image forming apparatus and its image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the deviation of pixel operation positions when image processing is performed for correcting scale factor deviation to an image to which screen processing is completed, and to prevent the generation of image quality defects. <P>SOLUTION: A correction value setting part 33 provided at a controller 30 of an image forming apparatus calculates a correction value for correcting the registration deviation of the image. Based on the correction value, a pixel operation position arrangement setting part of an image correction part 34 sets the arrangement of pixel operation positions to and from which pixels are inserted or deleted. Then, a pixel operation position distribution processing part of the image correction part 34 calculates a ratio between pixel operation areas where the pixel operation positions exist and pixel non-operation areas where the pixel operation positions do not exist based on the set arrangement of the pixel operation positions and shifts the pixel operation positions based on the ratio between the pixel scanning areas and the pixel non-operation areas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine, and more particularly to an image forming apparatus that performs registration control.

  In an image forming apparatus such as a printer or a copying machine, when a recording medium such as a sheet is conveyed in an inclined or distorted state with respect to an image forming unit, an image is displayed on the recording medium according to the inclination or distortion. It will be formed out of alignment. Similarly, the image forming position (alignment) shifts with respect to the recording medium due to an attachment error of the image forming unit itself. Therefore, conventionally, shift control (registration control) for correcting such image shift has been performed.

  Further, as a general image forming apparatus for color image output that is widely used today, for example, image forming provided for each color of black (K), yellow (Y), magenta (M), and cyan (C). There is a so-called tandem-type image forming apparatus in which a portion is arranged so as to face a transfer target (a transfer belt as an intermediate transfer member or a sheet as a recording material). In this tandem type image forming apparatus, images of different colors formed in the respective image forming units are sequentially transferred and multiplexed on a moving transfer object to form a color image.

  In this tandem type image forming apparatus, an image formed for each color is overlapped to form a color image. Therefore, an error of each mounting position of the image forming unit, a peripheral speed error of each image forming unit, and an exposure position with respect to the transfer target In some cases, color misregistration may occur in the formed image due to a difference in linear velocity, a change in linear velocity of a transfer target, or the like. Therefore, in this type of image forming apparatus, it is indispensable to measure these color misregistration amounts and perform color misregistration control (color registration control) for suppressing the occurrence of color misregistration. In addition to the tandem type image forming apparatus as described above, for example, in a cycle method in which a color image is formed by rotating a plurality of image carriers or a so-called ink jet method image forming apparatus, color misregistration or the like is prevented. Have similar problems.

  Such image misregistration (including color registration control) (hereinafter, this type of misregistration is referred to as registration misalignment) includes scan line tilt (skew), curvature (bow), There are variations in magnification. As conventional techniques for correcting these registration errors, correction is performed by a mechanism in a mechanism system or an optical system, or correction is performed by image processing that deforms original image data in accordance with the direction or amount of registration error. There are various technologies such as those. Since mechanical correction by a mechanism system or an optical system requires very high accuracy, correction by image processing can reduce cost and convenience for fine correction.

  Among the registration deviations described above, deviations caused by magnification fluctuations (hereinafter, this registration deviation is particularly referred to as magnification deviation), particularly magnification deviations (main scanning magnification deviations) appearing in the main scanning direction, are ROS (Raster Output Scanner) for each color. ) And the photosensitive member, the positional deviation is caused by the difference in the width of the image forming unit on the photosensitive member in the main scanning direction for each color. As a method of correcting the main scanning magnification deviation, there is a conventional technique for correcting the main scanning magnification deviation by making the video clock frequency variable independently for each color (for example, see Patent Document 1). In addition, there is a conventional technique that electronically corrects a main scanning magnification shift by appropriately inserting or deleting (thinning out) pixels from image data (see, for example, Patent Document 2). Further, in the conventional technique for inserting or deleting pixels from image data, there is a technique for determining a position at which a pixel is inserted or deleted in accordance with the characteristics of a screen pattern applied to an image by screen processing (for example, Patent Documents). 3).

  As in the prior art described in Patent Documents 2 and 3, when performing correction by image processing, it is not necessary to provide dedicated hardware (for example, in the technique described in Patent Document 1, the exposure device performs correction of Therefore, it is necessary to provide dedicated hardware for the image, that is, an image clock generator for an image signal), and it is possible to suppress an increase in device scale and cost. However, when pixel insertion or deletion (thinning) is appropriately performed on the image data, a defect may occur in the image depending on how the pixel is inserted or deleted (position or pattern).

FIGS. 10A and 10B are diagrams showing how pixels are inserted into image data by correcting the main scanning magnification deviation. In the example shown in FIGS. 10A and 10B, three pixels are inserted per scanning line in the main scanning direction. FIG. 10A shows a pixel insertion position, and FIG. 10B shows a state where a pixel is inserted to the right of the position shown in FIG. 10A. Yes.
In the example shown in the figure, the number of pixels in the main scanning direction of the image data is 57. Therefore, as shown in the figure, inserting (or deleting) pixels at an appropriate interval does not significantly affect the image. In addition, the main scanning magnification can be corrected.

  However, as shown in FIGS. 10 (a) and 10 (b), when pixels are inserted at the same location in each scanning line, the inserted pixels are aligned in the sub-scanning direction, so that they are macroscopic on the image. In some cases, a striking streak-like image quality defect (hereinafter, simply referred to as “defect”) that is visually noticeable occurs. Therefore, by setting the pixel insertion position to be offset for each main scanning line, or by making the pixel insertion interval irregular, the inserted pixels are not aligned and the defect visibility is improved. It was done to reduce.

FIGS. 11A and 11B show the pixel insertion position (FIG. 11A) and the state in which the pixel is inserted when the pixel insertion position is offset for each main scanning line (FIG. 11B). )).
In the example shown in FIGS. 11A and 11B, the width of 7 scan lines (that is, the length of 7 pixels) is used as a pattern period, and the pixel insertion position is shifted by 1 pixel for each scan line. Every pattern is repeated. Thus, the arrangement of the inserted pixels is prevented from being a straight line having a certain length or more.

  By the way, in today's image forming apparatuses, an area gradation method is often used as a standard method for expressing a multi-gradation image. For example, an output image is first expressed as a multi-valued image having a resolution of 600 dpi, 8 bits (256 gradations) + Tag (4 bits), and subjected to screen processing to obtain a binary value with a resolution of 2400 dpi, 1 bit (2 gradations). Convert to image. That is, the gradation of one dot in a multi-value image is expressed by a set of binary 16 dots. In the screen processing, a regular screen pattern is formed for each part of the image according to the gradation to be expressed in that part.

Japanese Patent Publication No. 6-57040 JP 2001-5245 A JP 2003-274143 A

  As described above, in the image forming apparatus, the registration error including the magnification error is corrected by image processing that inserts or deletes pixels in the image. In addition, in order to suppress defects caused by image processing for correction, an effort has been made to offset the pixel insertion position and deletion position (hereinafter collectively referred to as pixel operation position) for each main scanning line. It has been broken.

  However, even when the pixel operation position is offset, if the screen processing by the above-described area gradation method or the like is performed on the image, the characteristics (period and angle) of the screen pattern and the pixel operation position In some cases, the image may have a defect due to synchronization. Even when the pixel insertion interval is irregular, there is a problem that the defect visibility is not necessarily reduced due to the irregularity.

  FIG. 12 is a diagram illustrating a state in which the characteristics of the screen pattern and the pixel operation position are synchronized. In FIG. 12, the direction in which the dots constituting the dot pattern, which is a screen pattern, are arranged (angle with respect to the main scanning direction) matches the direction in which the pixel operation positions are arranged (angle with respect to the main scanning direction). In addition, the repetition cycle of each dot in the sub-scanning direction and the repetition cycle in the sub-scanning direction of the arrangement of pixel operation positions are the same. In such a case, even if the pixel operation position is offset, the screen pattern and the pixel insertion or deletion pattern interfere with each other, causing a streak defect in the image.

  In the prior art described in Patent Document 3, the visibility of defects is reduced even when screen processing is performed by determining the pixel operation position according to the characteristics of the screen pattern applied to the image by screen processing. be able to. However, in this prior art, there is a detecting means for detecting the image characteristic of the screen pattern and a means for creating a parameter for determining the pixel operation position so that the pixel insertion or deletion pattern is not synchronized with the detected image characteristic. Since it is necessary to provide the image forming apparatus, there is a problem that the system configuration becomes complicated and the cost increases.

Even if the pixel operation position is not synchronized with the screen shape, if there is a bias in the pixel value at the pixel operation position, there are areas where pixels are inserted or deleted, and areas where they are not. It will cause a defect.
FIG. 13 is a diagram schematically illustrating a screen pattern and a pixel operation position when there is a bias in the pixel value at the pixel operation position, and defects caused thereby.
Referring to FIG. 13A, macroscopically, a pixel operation area where a pixel is inserted or deleted and a pixel non-operation area where a pixel is not inserted or deleted alternately along the main scanning direction. You can see that it appears. Therefore, as shown in FIG. 13B, a region having a high gradation density and a region having a thin gradation appear. Note that when a pixel is inserted, a region with a high gradation density corresponds to a pixel operation region, and when a pixel is deleted, a region with a high gradation density corresponds to a non-pixel operation region. It will be.

  This defect is likely to be visually recognized when the width of the region where the pixel operation point does not exist is increased to some extent. If the screen is known, it is possible to appropriately set the parameter for determining the pixel operation position to suppress the bias, but in this case, the parameter must be selected according to the type of the screen pattern. Don't be. However, when different types of screen patterns are used for a plurality of objects in one image, it is difficult to switch parameters according to the types of screen patterns due to hardware limitations. Therefore, it is necessary to deal with a plurality of types of screens with one parameter, and it is difficult to select an appropriate parameter. In addition, a defect may occur regardless of which parameter is selected.

  In the above description, the case where pixels are inserted or deleted mainly as correction of the main scanning magnification has been described. However, in addition to correction of the main scanning magnification, pixels are inserted or deleted entirely or partially in the image data. Thus, the same problem occurs when correction for deforming an image into a desired shape or size (for example, magnification correction in the sub-scanning direction or keystone correction) is performed.

  The present invention has been made in order to solve the technical problems as described above, and an object of the present invention is to perform image processing for correcting a magnification shift on a screen-processed image. In this case, the bias of the pixel operation position is suppressed, and the occurrence of image quality defects is prevented.

  In order to achieve this object, the present invention is realized as an image forming apparatus configured as follows. The apparatus includes a correction value setting unit that obtains a correction value for correcting image registration deviation, an array setting unit that sets an array of pixel operation positions to insert or delete pixels based on the correction value, Based on the array of the set pixel operation positions, the ratio between the pixel operation area where the pixel operation position exists and the pixel no operation area where there is no pixel operation position is obtained, and the ratio between this pixel operation area and the no pixel operation area And a distributed processing unit for shifting the pixel operation position.

  The present invention can be realized as an image processing method including the following steps by grasping in the category of the method. That is, the method includes a step of obtaining a correction value for correcting an image registration deviation, a step of setting an array of pixel operation positions for inserting or deleting pixels based on the correction value, and Based on the arrangement of the pixel operation positions, a ratio between the pixel operation area where the pixel operation position exists and the pixel non-operation area where the pixel operation position does not exist is obtained, and based on the ratio between the pixel operation area and the no-pixel operation area And a step of shifting the pixel operation position.

  More specifically, in the above image forming apparatus, the dispersion processing unit shifts the pixel operation position for each of a plurality of scanning lines. Alternatively, the offset amount of the pixel operation position between the nth (n is a natural number) scan line and the (n + 1) th scan line is an integral multiple of the length of the pixel operation position in the shift direction in the pixel operation region. Shift the pixel operation position.

  In the image forming apparatus, the arrangement setting unit sets the arrangement of the pixel operation positions based on the arrangement parameter set so that the pixel operation position is not synchronized with the screen pattern used in the screen processing in addition to the correction value. It can be set as the structure to do. In this case, the distributed processing unit can shift the pixel operation position by an array unit of the pixel operation position set based on the array parameter. Alternatively, the pixel operation position can be shifted in synchronization with the period of the array of pixel operation positions set based on the array parameter.

  According to the present invention configured as described above, it is possible to suppress the bias of the pixel operation position when the image processing for correcting the magnification shift is performed on the screen-processed image. For this reason, it is possible to prevent the occurrence of image quality defects.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied.
This image forming apparatus is a so-called tandem type digital color machine employing an electrophotographic system. As shown in FIG. 1, the image forming apparatus includes an image forming unit 10 that forms an image and an exposure that forms an electrostatic latent image on a photosensitive drum 11 of the image forming unit 10 as a printing function (printing function). The apparatus 13 includes a transfer belt 21 as an intermediate transfer member that superposes and carries a toner image carried on the photosensitive drum 11. The image forming unit 10 is provided corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, when it is necessary to distinguish between them, they are expressed as image forming units 10Y, 10M, 10C, and 10K. When they are not necessary to be distinguished, they are simply expressed as image forming units 10. A primary transfer roll 23 for carrying an image on the transfer belt 21 is provided inside the transfer belt 21 at a position facing the photosensitive drum 11 of each image forming unit 10. Further, a secondary transfer roll 24 and a counter roll 25 provided inside the transfer belt 21 are arranged at a so-called secondary transfer position where the toner image carried on the transfer belt 21 is transferred to a sheet. Furthermore, a paper feed cassette 27 for storing paper as a recording medium and a fixing device 28 for fixing the transferred paper are provided. In addition, the image forming apparatus includes a control device 30 that performs image processing for correcting registration misregistration, and a color misregistration sensor 40 that reads a color misregistration control pattern formed in a predetermined area of the transfer belt 21.

  The control device 30 generates an image signal such as a digital image signal of an image obtained from image data input means such as an image reading device (IIT: Image Input Terminal) or a pattern image for color misregistration control, and an exposure device. 13, writing on the transfer belt 21 is performed. The control device 30 acquires the detection result of the color misregistration control pattern from the color misregistration sensor 40, analyzes the amount of color misregistration based on the acquired information, and performs necessary correction. These functions in the control device 30 are realized by, for example, a program-controlled CPU (Central Processing Unit) or the like. The control device 30 includes a nonvolatile ROM (Read Only Memory) and a readable / writable RAM (Random Access Memory) as memories. The ROM stores a software program for controlling an image forming operation and color misregistration detection and correction operation executed by the controller, image information of a color misregistration control pattern, and the like. The RAM stores various types of information acquired as the image forming apparatus operates, such as various counter values, the number of job executions, and execution information (time information, etc.) of the previous color misregistration detection process.

  For each color exposure device 13, a digital image signal obtained from, for example, an image reading device (IIT) or an external personal computer device (PC) and converted by an image processing device (not shown) is a control device 30. Is supplied through. The color misregistration sensor 40 forms an image of a color misregistration control pattern (ladder-like toner patch, chevron patch) formed on the transfer belt 21 on a detector composed of a PD (Photo Diode) sensor or the like. This is a reflective sensor that outputs a pulse when the center of gravity line and the center line of the detector coincide. The color misregistration sensor 40 detects, for example, the downstream side of the most downstream image forming unit 10K in FIG. 1 in order to detect the relative color misregistration of the color misregistration control pattern due to the patches formed in each image forming unit 10. And two are arranged along the main scanning direction. For example, two infrared LEDs (wavelength 880 nm) are used for the light emitting unit of the color misregistration sensor 40, and the light emission amount of the two LEDs can be adjusted (for example, in two stages) in order to ensure stable pulse output. It is configured.

  In each of the four color image forming units 10Y, 10M, 10C, and 10K, various units for image formation are similarly formed around the photosensitive drum 11 that is an image carrier. That is, a charging device for charging the photosensitive drum 11, a developing device for developing a toner image on the photosensitive drum 11 exposed by the exposure device 13, and residual toner remaining on the photosensitive drum 11 after the transfer of the toner image to the transfer belt 21. Various units, such as a cleaner, are provided. The configuration of the image forming unit 10 is other than so-called regular colors such as yellow (Y), magenta (M), cyan (C), and black (K). It is also possible to provide a specific color image forming unit corresponding to a special drawing material such as a color. In addition to the four colors Y, M, C, and K described above, five or more colors including dark yellow can be used as regular colors. In the present embodiment, the axial direction of the photosensitive drum 11 that is an image carrier is the main scanning direction, and the moving direction by the rotation of the photosensitive drum 11 is the sub-scanning direction.

As the transfer belt 21, for example, a flexible synthetic resin film such as polyimide is formed in a belt shape, and both ends thereof are connected by means such as welding to form an endless belt. The transfer belt 21 is stretched by a driving roll and a backup roll in a loop shape that is at least partially straightened. Then, the four-color image forming units 10Y, 10M, 10C, and 10K and the opposing primary transfer rolls 23 are arranged at substantially regular intervals with respect to the substantially linear portion of the transfer belt 21. Yes. In the example shown in FIG. 1, a yellow image forming unit 10Y, a magenta image forming unit 10M, and a cyan image forming unit 10C are sequentially arranged from the upstream side to the downstream direction with respect to the moving direction of the transfer belt 21 during the transfer operation. , Black image forming units 10K are arranged. A color toner image is formed on the transfer belt 21 by sequentially superimposing the images of the respective colors formed by the image forming unit 10 on the belt according to the movement of the transfer belt 21. Then, the movement of the transfer belt 21 and the timing of sheet conveyance are matched, and the color toner image formed on the transfer belt 21 is transferred to the sheet at a position including the secondary transfer roll 24 and the opposing roll 25. Thereafter, the sheet on which the color toner image has been transferred is conveyed to the fixing device 28 where the color toner image is fixed on the sheet and discharged to a discharge tray provided outside the casing of the image forming apparatus. The
Although FIG. 1 shows an example of the configuration of an electrophotographic image forming apparatus, the present embodiment can be applied to various image forming apparatuses such as an ink jet system and a thermal system. is there.

  In the image forming apparatus configured as described above, the ROS (for Y) of each exposure apparatus 13 corresponding to the image forming units 10Y, 10M, 10C, and 10K that forms images of each color of Y, M, C, and K is formed. ROS, M ROS, C ROS, and K ROS) and the photoreceptor have different optical distances, the images formed on the photosensitive drums 11 of the respective colors have different widths in the main scanning direction. It becomes. For this reason, when the images of the respective colors are superimposed on the transfer belt 21, the main scanning magnification shift occurs in the images of the respective colors. Therefore, under the control of the control device 30, the pixels are appropriately inserted into or deleted from the images formed by the image forming units 10Y, 10M, 10C, and 10K for the respective colors to correct the main scanning magnification. Hereinafter, the function of the control device 30 and the correction for the magnification deviation according to the present embodiment will be described in detail by taking as an example the case where the correction is performed for the main scanning magnification deviation.

FIG. 2 is a diagram illustrating a functional configuration of the control device 30 in the present embodiment.
Referring to FIG. 2, the control device 30 of the present embodiment includes a screen processing unit 31 that performs screen processing, a registration error detection unit 32, a correction value setting unit 33, and pixel insertion or correction for correction of registration error. An image correction unit 34 and a parameter storage unit 35 that perform deletion, and an output interface (I / F) 36 that sends an image corrected by the image correction unit 34 to an image forming unit (IOT) are provided. Among these configurations, the screen processing unit 31, the registration error detection unit 32, the correction value setting unit 33, and the image correction unit 34 are realized by a CPU controlled by a software program stored in the above-described nonvolatile ROM, for example. Is done. The parameter storage unit 35 is realized by the above-described ROM, for example, and stores parameters for calculating pixel operation positions, which will be described later.

  Data of an image to be printed is input to the control device 30 as a processing target. The input image includes multi-tone (multi-value) data and single-tone (binary) data. When the input image is multi-value data, the screen processing unit 31 performs screen processing on the input image for each of a specific color and a specific object (for example, a photograph, a character, or the like) to obtain an image. Convert to binary data. In addition, the screen processing unit 31 performs text / image separation (T / I separation) processing, and selects an appropriate screen pattern corresponding to the gradation expressed for each object. And the screen pattern selected from the memory | storage means (ROM etc. which are mounted in the control apparatus 30 mentioned above) which stored various screen patterns is read, and it uses for screen processing. The screen-processed image is sent to the image correction unit 34. If the input image is binary data, it is directly input to the image correction unit 34 without being subjected to screen processing by the screen processing unit 31.

As described above with reference to FIG. 1, the registration error detection unit 32 acquires and analyzes the detection result of the color misregistration control pattern by the color misregistration sensor 40, and obtains the presence / absence of color misregistration and the amount of deviation.
The correction value setting unit 33 calculates a correction value required to cancel the color misregistration amount detected by the registration misregistration detection unit 32. For example, in the case of correction for a main scanning magnification shift, a value such as how many dots are inserted or deleted from a pixel row arranged in the main scanning direction is calculated.

  The image correction unit 34 inputs the image binarized by the screen processing unit 31 or the input image that was originally binary data, and performs image processing for correcting the magnification deviation. As shown in FIG. 2, the image correction unit 34 further shifts the set pixel operation position and disperses the pixel operation position array setting unit 341 that sets a pixel operation position at which a pixel is inserted or deleted from the image. A pixel operation position distribution processing unit 342.

  The pixel operation position array setting unit 341 sets an array of pixel operation positions based on the correction values calculated by the correction value setting unit 33 and the parameters stored in the parameter storage unit 35. When correcting the main scanning magnification shift by inserting or deleting pixels in the image data, the pixel operation position is set to minimize the influence on the original image (degradation of image quality due to image deformation). It is preferable to set an appropriate interval on each scanning line. For example, as shown in FIGS. 10 and 11, if the number of pixels in the main scanning direction in the image data is 57 pixels and 3 pixels are inserted per scanning line, 1 for every 19 (= 57/3) pixels. Pixel is inserted. Further, in order to prevent occurrence of a noticeable streak-like defect that can be visually recognized in the image after pixel insertion by arranging the inserted pixels adjacently and in a straight line, as shown in FIG. Based on the parameter for calculating the operation position, the pixel operation position of each main scanning line is offset.

  The parameters used here are parameters for offsetting the pixel operation positions to form a fixed array. Specifically, for example, an angle (hereinafter simply referred to as an angle) formed by a straight line connecting two pixel operation positions and a scanning direction (main scanning direction or sub-scanning direction) of image data, and an arrangement pattern of pixel operation positions Or a repetition period (hereinafter simply referred to as a cycle), or an offset value between two pixel operation positions (hereinafter simply referred to as an offset value) and a repetition period of an arrangement pattern of pixel operation positions. A pair can be used.

FIG. 3 is a diagram illustrating a configuration example of parameters when an angle and a cycle are used as parameters for calculating the pixel operation position.
Referring to the example shown in FIG. 3, the pixel operation positions are repeated in a pattern of pixel operation positions with a certain width (number of pixels) of scanning lines as a cycle. As an arrangement pattern of pixel operation positions in one cycle, the pixel operation positions are arranged so as to form an angle α with respect to the main scanning direction. The angle α is

tan α = 1 / offset value

It can be expressed as.

FIG. 4 is a diagram illustrating a configuration example of parameters when an offset value and a cycle are used as parameters for calculating the pixel operation position.
Referring to the example shown in FIG. 4, the pixel operation positions are repeated in a pattern of pixel operation positions with a certain width (number of pixels) of scanning lines as a cycle. As an arrangement pattern of the pixel operation positions in one cycle, the pixel operation positions are arranged by shifting by a certain amount (offset value) in the main scanning direction for each scanning line.

However, even if the pixel operation position is offset as described above, the pixel operation area and the non-pixel operation area are macroscopically divided depending on conditions such as the number of pixels to be inserted or deleted. In the screen-processed image, there may be a defect that an area corresponding to the pixel operation area and an area corresponding to the no-pixel operation area are visually recognized as a difference in gradation density.
Therefore, in this embodiment, the pixel operation positions set based on the above parameters are further shifted and dispersed, and the pixel non-operation area is reduced. By reducing the pixel non-operation area, it is possible to prevent the screen-processed portion of the image from having a macroscopic structure such that areas with different gradation densities are alternately viewed.

  The pixel operation position distribution processing unit 342 shifts the pixel operation position set by the pixel operation position array setting unit 341 based on the width of the pixel operation area and the width of the non-pixel operation area in the main scanning direction. The pixel operation position is shifted as much as possible over the entire area from a predetermined pixel operation area to the adjacent pixel operation area (that is, an area including one pixel operation area and one non-pixel operation area). This is done so that the positions are distributed. In addition, the pixel operation position after the dispersion is shifted so as to retain the characteristics of the pixel operation position array represented by the above parameters, that is, the angle and / or the periodic component. As a result, the pixel operation position after the shift is synchronized with the screen pattern, thereby preventing a new defect from occurring.

A specific pixel operation position distribution method in this embodiment will be described in detail.
For example, a method of shifting pixel operation positions may be a method of shifting for each main scanning line (that is, in units of individual pixel operation positions) and a method of shifting in units of pixel operation position arrays specified by parameters. It is done.

In the method of shifting for each main scanning line, for example, the sub-scanning direction position of the pixel operation position is n, the width in the main scanning direction (pixel operation area width) of the range taken by the pixel operation position is X ₁ , and the main operation in other areas The shift amount can be calculated by the following equation, where X ₂ is the width in the scanning direction (pixel non-operation area width).

S (n) = (n-INT {n / (INT {X ₂ / X ₁ } +1)} * (INT {X ₂ / X ₁ } +1)) * X ₁ (1)

According to the above equation (1), the shift amount with respect to the pixel operation position existing in the main scanning line (n + 1) is increased by X ₁ compared with the pixel operation position existing in the main scanning line n. When the shift amount becomes larger than the pixel non-operation area width, the initial value (shift amount 0) is restored. Note that the pixel non-operation area is not a pixel no-operation area because the pixel operation position is arranged after the pixel operation position is shifted. However, for convenience of explanation, the pixel no-operation area was a pixel no-operation area before the pixel operation position was shifted. The area is referred to as a pixel non-operation area even after the shift (the same applies in the following description).

FIG. 5 is a diagram illustrating a state in which the pixel operation positions are dispersed by using the method of shifting for each main scanning line using Expression (1). The pixel operation positions set by the pixel operation position array setting unit 341 as shown in FIG. 5A are shifted and dispersed by the pixel operation position distribution processing unit 342 as shown in FIG. 5B.
Referring to FIG. 5A, the pixel operation area width X ₁ and the pixel non-operation area width X ₂ have a relationship of X ₂ = 3X ₁ .
Referring to FIG. 5B, the pixel operation position shift amount S (0) in the uppermost stage (first main scanning line) is 0 (initial value), and the second pixel operation position shift amount S ( 1) is X ₁ corresponding to the pixel operation position array width indicated by the parameter, and the shift amount S (2) of the third-stage pixel operation position is 2 × X ₁ further shifted by X ₁ to the second-stage shift amount. Similarly, the shift amount S (3) of the pixel operation position in the fourth stage is 3 × X ₁ . Then, the shift amount S (4) of the pixels operating position of the fifth row, 4 × the results in the X _1, the shift amount is greater than the pixel unoperated region width, pixel operation position other pixel operation area after the shift Therefore, this shift is avoided and the shift amount is zero.

Regarding the method of shifting for each main scanning line, in addition to the basic method described with reference to FIG. 5, appropriate changes can be made in the embodiment.
FIG. 6 is a diagram showing a modification of the method of shifting for each main scanning line.
In the method of returning to 0 when the shift amount of the pixel operation position exceeds a certain value as described with reference to FIG. 5, the pixel operation position on the main scanning line where the shift amount has become 0 and the previous main operation line. The offset amount (difference in shift amount) from the pixel operation position in the scan line is larger than the offset amount between pixel operation positions in other adjacent main scan lines. In the example shown in FIG. 6A, each pixel operation position from the first stage to the fourth stage is opened by 9 pixels in the main scanning direction, but the shift amount returns to 0 at the fourth stage. The pixel operation position in the stage has an interval of 27 (= 3 × 9) pixels. The screen pattern may be greatly deformed due to the difference in the offset amount between the pixel operation positions.

  Therefore, as shown in FIG. 6B, when the shift amount calculated by the equation (1) becomes larger than the pixel non-operation area width, the shift amount is not returned to 0 but calculated. It is conceivable to reverse the sign of the value. In the illustrated example, the shift direction of the pixel operation position is opposite to the main scanning direction from the fifth stage to the seventh stage (that is, until it matches the position of the shift amount 0). By such an operation, the amount of offset between the pixel operation position in any main scanning line and the pixel operation position in another adjacent main scanning line becomes 9 pixels in the main scanning direction. Therefore, the screen pattern is not greatly deformed.

FIG. 7 is a diagram illustrating another modification of the method of shifting for each main scanning line.
In the basic method described with reference to FIG. 5, the period in the sub-scanning direction of the array of pixel operation positions set by the pixel operation position array setting unit 341 is synchronized with the period in which the shift amount returns to zero. There is no (the pixel operation position array is 7 pixels (that is, the pixel operation position appears at the same position in the main scanning direction every 7 main scanning lines), whereas the shift amount is once every 4 main scanning lines. , Return to 0). Therefore, referring to FIG. 5B, the pixel operation positions are adjacent to each other at the seventh and eighth stages, which are the boundary of the pixel operation position array, and the distribution is biased.

  In order to avoid this, as shown in FIG. 7, in addition to the basic method shown in FIG. 5, it is conceivable to reset the shift amount to 0 in synchronization with the period of the pixel operation position array. In the example shown in FIG. 7, the shift amount is zero for every seven main scanning lines in synchronization with the period of the pixel operation position array as the upper structure (see S (7) in the figure). As a subordinate structure, in each pixel operation position array, the shift amount at the fifth stage returns to 0 according to Expression (1) (see S (4) in the figure). By such an operation, the pixel operation positions are more evenly distributed in an area including one pixel operation area and one pixel non-operation area.

  Furthermore, in practice, the above modifications can be combined as appropriate. In each of the above examples, the shift amount is changed for each main scanning line. However, the shift amount may be changed for each of a plurality of main scanning lines. Further, according to Expression (1), the shift amount is set so that the offset amount of the pixel operation position for each main scanning line matches the pixel operation region width. However, this offset amount may be a multiple of the pixel operation region width. good. If it is ensured that the offset amount of the pixel operation position is at least a multiple of the pixel operation area width, an angle other than the angle represented by the parameter can be prevented from occurring in the array of the pixel operation positions after the shift.

Next, a method for shifting the pixel operation position array as a unit will be described.
In this method, for example, the shift amount can be calculated by the following equation.

S (n) = (F (n) -INT {F (n) / (INT {X ₂ / X ₁ } +1)} * (INT {X ₂ / X ₁ } +1)) * X ₁ (2)
Where F (n) = INT {INT {n / Y}}

According to the above formula (2), the shape of the pixel operation position array indicated by the parameter is not changed, and the application position of the parameter is sequentially changed by X ₁ corresponding to the pixel operation position array width indicated by the parameter along the main scanning direction. Shifted. When the shift amount becomes larger than the pixel non-operation area width, the initial value (shift amount 0) is restored.

FIG. 8 is a diagram illustrating a state in which pixel operation positions are dispersed by using a method of shifting the pixel operation position array as a unit for the image illustrated in FIG. 5A using Expression (2).
Referring to FIG. 8, the pixel operation position array (in units of 7 pixels) set as shown in FIG. 5A by the pixel operation position array setting unit 341 is shifted by this array unit. That is, the shift amount Sa (0) of the pixel operation position included in the uppermost array (for seven main scanning lines) is 0, and the shift amount Sa (1) of the pixel operation position included in the second array is X. ₁ The shift amount Sa (2) of the pixel operation position included in the third row array is 2 × X ₁ , and the shift amount Sa (3) of the pixel operation position included in the fourth row array is 3 × X ₁ . It has become. Then, the shift amount of the pixel operation position in the array of fifth stage Sa (4) is 4 when resulting in the × X _1, the shift amount is greater than the pixel unoperated region width, pixel operating position after the shift is other Therefore, this shift is avoided and the shift amount is zero.

By offsetting the pixel operation positions by the width of the pixel operation area in units of the pixel operation position array, the pixel operation position arrays are continuous as shown in FIG. 8, and the pixel operation position is one pixel. In an area including the operation area and one pixel non-operation area, the pixels are evenly distributed.
Also in this method, similar to the method of shifting for each main scanning line described above, appropriate modifications can be made in the embodiment. For example, when the shift amount becomes larger than the pixel non-operation area width as in the example shown in FIG. 6, the sign of the calculated value of the shift amount is reversed instead of returning the shift amount to 0. May be. As a result, there is no difference in the offset amount between adjacent pixel operation position arrays, and the screen pattern can be prevented from being greatly deformed. In the above example, the shift amount of the pixel operation position is changed for each parameter period (that is, for each pixel operation position array). However, the pixel operation is performed for each multiple of the parameter period (for each of the plurality of pixel operation position arrays). It is also possible to change the shift amount of the position. Further, the change amount (offset amount) of the shift amount can be a multiple of the pixel operation area width.

  As described above, after further shifting the pixel operation position set by the predetermined parameter, the image correction unit 34 moves the pixel to the pixel operation position according to the correction value calculated by the correction value setting unit 33. Insert or delete pixel from pixel operation position. When a pixel is inserted at the pixel operation position, for example, the pixel at the pixel operation position or a pixel adjacent in the main scanning direction is copied and inserted. The image corrected by the pixel insertion or deletion is sent to the image forming unit via the output interface 36.

  Since the pixel operation position is distributed over substantially the entire image by the pixel operation position distribution processing unit 342, the width of the non-pixel operation area is reduced, and even if there is a difference in gradation density with the pixel operation area, the visual recognition Sex declines. Further, according to the above dispersion method, the characteristics of the pixel operation position array specified by the above parameters do not change. For this reason, after the pixel operation position is shifted, the pixel operation position after the shift is not synchronized with the screen pattern and a new defect does not occur. Therefore, the freedom of parameter design and selection is improved.

  In the above embodiment, when the structure of the screen pattern in the screen-processed image is known, the pixel operation position array setting unit 341 sets the pixel operation position using parameters according to the characteristics of the screen pattern. It was decided. However, when the structure of the screen pattern applied to the image is unknown (for example, when the image forming apparatus inputs an image that has already been subjected to screen processing as an output target image), the characteristics of the pixel operation position array Even if the characteristics of the screen pattern are partially synchronized, the visibility of the generated defect is reduced by sufficiently distributing the pixel operation positions.

  In this embodiment, the case of correcting the magnification shift in the main scanning direction due to the color registration shift has been described, but it goes without saying that the same method can be used for the magnification shift due to the shift in the alignment with respect to the sheet. Further, the present invention can be applied when correcting not only the magnification deviation in the main scanning direction but also the deviation in the sub scanning direction. Furthermore, the present embodiment can be similarly applied to various corrections that transform an image into a desired shape or size by inserting or deleting pixels entirely or partially in the image data. It is.

FIGS. 9A to 9D are diagrams showing various aspects of magnification deviation in the main scanning direction and correction thereof. FIG. 9A shows the original image data, and FIGS. 9B to 9D show the output image when the correction is not performed and the image data deformed by the correction.
In the example of FIG. 9B, the output image is entirely reduced in the main scanning direction with respect to the original image data. Therefore, in order to cancel out this deformation, correction is performed to increase the size by inserting pixels throughout the main scanning direction.
In the example of FIG. 9C, the size of the output image in the main scanning direction is gradually reduced along the sub-scanning direction (direction from top to bottom). Therefore, in order to cancel this deformation, the size of the main scanning direction is enlarged by gradually increasing the number of inserted pixels per scanning line along the sub-scanning direction, and the correction is performed so as to deform into a trapezoid as a whole. Is done.
In the example of FIG. 9D, the left area of the output image is reduced in the main scanning direction, and the right area is enlarged in the main scanning direction (the overall size is the same as the original image data). Therefore, in order to cancel out this deformation, correction is performed in which the pixels in the left area of the image data are inserted to increase the size in the main scanning direction and the pixels in the right area are deleted to reduce the size in the main scanning direction. Is called.

1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. It is a figure which shows the function structure of the control apparatus in this embodiment. It is a figure which shows the structural example of the parameter in the case of using an angle and a period as a parameter for calculating a pixel operation position. It is a figure which shows the structural example of the parameter in the case of using an offset value and a period as a parameter for calculating a pixel operation position. It is a figure which shows a mode that the pixel operation position was disperse | distributed by the method of shifting for every main scanning line by this embodiment. It is a figure which shows the modification of the method of shifting for every main scanning line by this embodiment. It is a figure which shows the other modification of the method of shifting for every main scanning line by this embodiment. It is a figure which shows a mode that the pixel operation position was disperse | distributed by the method of shifting per pixel operation position arrangement | sequence by this embodiment. It is a figure which illustrates the aspect of main scanning magnification correction. It is a figure which shows a mode that a pixel is inserted in image data by correction | amendment of main scanning magnification deviation. It is a figure which shows a mode that the pixel insertion position and a mode that the pixel was inserted when the pixel insertion position was offset for every main scanning line. It is a figure which shows a mode that the characteristic of a screen pattern and a pixel operation position are synchronizing. It is the figure which represented typically the screen pattern and pixel operation position when the pixel value of a pixel operation position has bias | inclination, and the defect produced by this.

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 ... Control apparatus, 31 ... Screen processing part, 32 ... Registration deviation detection part, 33 ... Correction value setting part, 34 ... Image correction part, 35 ... Parameter storage part, 341 ... Pixel operation position arrangement | positioning setting part, 342 ... Pixel operation Position distribution processing unit

Claims (12)

A correction value setting unit for obtaining a correction value for correcting registration deviation of the image;
An array setting unit for setting an array of pixel operation positions for inserting or deleting pixels based on the correction value;
Based on the array of pixel operation positions or a parameter for setting the array of pixel operation positions, a ratio between a pixel operation area where the pixel operation position exists and a pixel non-operation area where the pixel operation position does not exist is obtained. An image forming apparatus comprising: a dispersion processing unit that shifts the pixel operation position based on a ratio between a pixel operation area and the non-pixel operation area.   The image forming apparatus according to claim 1, wherein the distributed processing unit shifts the pixel operation position for each of a plurality of lines.   In the dispersion processing unit, the offset amount of the pixel operation position between the nth (n is a natural number) line and the (n + 1) th line is an integral multiple of the length of the pixel operation position in the shift direction in the pixel operation region. The image forming apparatus according to claim 1, wherein the pixel operation position is shifted so that   The arrangement setting unit sets the arrangement of the pixel operation positions based on an arrangement parameter set so that the pixel operation positions are not synchronized with a screen pattern used in screen processing, in addition to the correction value. The image forming apparatus according to claim 1.   5. The image forming apparatus according to claim 4, wherein the distribution processing unit shifts the pixel operation position in units of an array of the pixel operation positions set by the array setting unit based on the array parameter. .   5. The dispersion processing unit shifts the pixel operation position in synchronization with an array cycle of the pixel operation position set based on the array parameter by the array setting unit. Image forming apparatus. An image processing method of an image forming apparatus for forming an image on a recording medium,
Obtaining a correction value for correcting image registration deviation;
Setting an array of pixel operation positions for inserting or deleting pixels based on the correction value; and
Based on the set array of the pixel operation positions, a ratio between the pixel operation area where the pixel operation position exists and the pixel non-operation area where the pixel operation position does not exist is obtained, and the pixel operation area and the pixel no operation And a step of shifting the pixel operation position based on a ratio to the region.   The image processing method according to claim 7, wherein in the step of shifting the pixel operation position, the pixel operation position is shifted for each of a plurality of lines.   In the step of shifting the pixel operation position, the offset amount of the pixel operation position between the nth (n is a natural number) line and the (n + 1) th line is the length in the shift direction of the pixel operation position in the pixel operation area. The image processing method according to claim 7, wherein the pixel operation position is shifted so as to be an integral multiple of the length.   In the step of setting the arrangement of the pixel operation positions, in addition to the correction value, the arrangement of the pixel operation positions is based on an arrangement parameter set so that the pixel operation position is not synchronized with a screen pattern used in screen processing. The image processing method according to claim 7, wherein the image processing method is set.   The image processing method according to claim 10, wherein in the step of shifting the pixel operation position, the pixel operation position is shifted in an array unit of the pixel operation position set based on the array parameter. .   The pixel operation position is shifted in the step of shifting the pixel operation position in synchronization with an array cycle of the pixel operation position set based on the array parameter. Image processing method.

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