JP6079274B2 - Image processing apparatus, image processing method, and image forming apparatus - Google Patents

Description

  The present invention relates to an image processing apparatus and an image processing method, and an image forming apparatus such as a printer, a copying machine, or a digital multifunction machine that forms a monochrome image or a color image by an electrophotographic method using the image processed image data.

In order to output image data created by an information processing device such as a computer as a hard copy, as an image forming device such as a printer that forms an image on a recording medium such as paper, an electrophotographic method, an inkjet method, a thermal transfer method, etc. There are various types.
Among them, the electrophotographic method can form a high-quality image at high speed, and is most suitable for an image forming apparatus for high-speed and high-quality applications.

  In the electrophotographic image forming apparatus, a photosensitive member is exposed to light such as laser light modulated and controlled according to image data to form an electrostatic latent image, which is developed with toner to be visualized, and the paper To form an image. At that time, due to the characteristics of optical elements such as lenses and mirrors through which light such as laser light passes and the inclination in assembling the apparatus, the scanning line is inclined with respect to the paper transport direction (sub-scanning direction) Bending may occur. As a result, in the case of a color image in which an image is formed with a plurality of colors, a shift between colors occurs and is perceived as a color shift.

In order to correct the inclination and bending of the main scanning line, the image data is divided into a plurality of areas in the main scanning direction, and the image data is sub-scanned in a direction opposite to the direction in which the inclination is generated in advance for each area. Techniques for shifting in the direction are already known.
When a multi-tone image is formed by such an image forming apparatus, generally, a multi-tone image data is generated by performing a dither process on the multi-tone image data. A pseudo multi-tone image is formed by the image data.

  For example, in Patent Document 1, in such an electrophotographic image forming apparatus, image data subjected to dither processing is divided into a plurality of areas in the main scanning direction, and the image data is divided into sub-scanning directions for each area. A technique relating to a process of correcting the skew (tilt) by shifting to the above is disclosed.

Here, the image data is divided into a plurality of areas in the main scanning direction, and the image data is shifted in the sub-scanning direction for each area, thereby correcting the skew and the bending in the main scanning direction of the formed image. The principle will be described with reference to FIG.
FIG. 11A schematically shows pseudo-halftone image data for one line without shift.
If an image is formed on the photoconductor using this optical data as it is, an “unshifted image plane image” shown in FIG.

  This is an image formed on the image surface of the photosensitive member or on the paper that is finally output. The characteristics of the optical system such as a lens and a mirror that transmit and reflect the beam emitted from the light source, and the assembly process Such bends and tilts occur depending on the tilt of the device generated in the above. When an image is formed by superimposing toner images of a plurality of colors, color deviation occurs between colors due to this bending or inclination, and the image quality is impaired.

Therefore, as shown in FIG. 11C, the image data is shifted in the direction opposite to the direction in which the inclination is generated in advance in the sub-scanning direction for each region in the main scanning direction.
In this example, the “non-shifted image screen image” shown in (b) has an upward slope from region 1 to region 3 and a downward slope from region 3 to region 4. Therefore, the image data is shifted downward from the region 1 toward the region 3, and the region 4 is shifted upward with respect to the region 3. The amount to be shifted at this time is the minimum unit of the image data in the sub-scanning direction, that is, one line that is the minimum unit that can be exposed by the laser beam.

By doing so, as shown in “image image after shift” in FIG. 11D, even if the optical system or the like is bent or tilted, it is bent in the sub-scanning direction on the image surface of the photoreceptor or on the paper. A toner image without inclination can be formed.
Normally, reading and writing image data from a memory storing image data is performed for each line. However, when image data is shifted to correct bending or tilting, data that has been shifted in the sub-scanning direction is changed by changing the line of the image read from the memory for each area divided in the main scanning direction. Output. As the image data to be shifted is smaller than the multi-valued multi-tone image data, the size of the handled data becomes smaller when the pseudo multi-valued image data reduced by dither processing is used. Can be reduced.

In the dither method, multi-value image data for forming a dark and light image can be converted into low-value image data such as binary (black and white) to form a pseudo multi-tone image. It is a technique to do. Therefore, multi-valued input image data is divided for each pixel area of a specific size (M × N) and binarized through a sub-matrix called a dither matrix composed of different threshold values of M × N. For example, if a 4 × 4 dither matrix is used, 17 (N ² +1) gradations can be expressed.

  However, as described above, in the method in which image data is shifted by one line in the sub-scanning direction for each region in the main scanning direction, linear noise in the sub-scanning direction (hereinafter, “streaks”) is added to the image at the boundary of the shifting region. )) And other abnormalities may occur. This will be described with reference to FIGS.

Figure 12 shows an example of an enlarged image 3 of halftone image 2 and a part of the single color is formed on the sheet 1. In order to reproduce a halftone image with binary dots, the halftone image data is subjected to a dither process using a dither matrix, for example, white and black dots in a staggered pattern as shown in the enlarged image 3 Suppose that a pseudo-halftone toner image in which are alternately arranged is formed.
In this image, the position in the sub-scanning direction is inclined upward as the main scanning line (the arrangement of pixels in the main scanning direction) moves to the right in FIG.

In order to correct the inclination of the main scanning line of this image, the image data forming the image shown in FIG. 12 is divided into two in the main scanning direction, and the image data in the right region is 1 in the sub scanning direction. FIG. 13 shows an image formed when the line is shifted in the direction indicated by the arrow A.
As can be seen from the enlarged image, on the left side and the right side of the boundary (indicated by a broken line) 4 between the area a where the image data is not shifted and the shifted area b, each formed dot corresponds to one line in the sub-scanning direction. It is off.
As a result, dots that were not originally adjacent to each other are adjacent to each other, and only the boundary position of the adjacent region is darker than the surrounding density. This is a density difference perceived by the user's eyes, and streaks 5 appear in the halftone image 2. The streak 5 is easily noticeable when a halftone image is formed in a wide area as in the example shown in FIG.

As described above, in order to prevent the occurrence of “streaks” in the halftone image by correcting the inclination of the main scanning line of the image, for example, in the image forming apparatus described in Patent Document 1 described above, As shown in FIG.
That is, when the target pixel to be corrected in the skew-corrected image data is at the division position in the main scanning direction, the densities of the target pixel and the surrounding pixels are detected. Then, the occurrence of density deviation is detected based on the detected density, the shift direction by skew correction, and a predetermined pattern. As a result, when the occurrence of density deviation is detected, density correction is performed based on the detected density deviation to compensate for differences in output areas of a plurality of pixels near the division position.

However, in order to perform such density correction, in order to detect the density of the target pixel and surrounding pixels, detect the occurrence of density shift, and perform density correction of a plurality of pixels in the vicinity of the division position, It is necessary to add a function by a circuit or program for performing complicated processing.
If such a circuit or function is added, the cost is considerably increased, and there is a problem that it cannot be implemented in an inexpensive image forming apparatus.

  The present invention has been made in view of such a background. When a halftone image is formed from pseudo multi-value image data, the inclination and bending of the main scanning line are corrected, and the “streaks” can be very easily achieved. It aims at making it possible to suppress generation | occurrence | production of ".

In order to achieve the above object, the present invention divides pseudo multi-value image data generated by performing dither processing on multi-tone image data for each predetermined area in the main scanning direction, and In an image processing apparatus that shifts and outputs image data in a sub-scanning direction orthogonal to the main scanning direction, and corrects the inclination and bending of the main scanning line of the formed image.
Input means for inputting information specifying the type of dither matrix used in the dither processing, and the image data in the sub-scanning direction according to the type of dither matrix specified by the information input by the input means. Shift amount changing means for changing the shift amount to be shifted.

  According to the present invention, when a halftone image is formed using pseudo-multi-value image data, the inclination and bending of the main scanning line can be corrected and the occurrence of “streaks” can be suppressed very easily.

It is a block diagram which shows the structure of one Embodiment of the image processing apparatus by this invention. It is a figure explaining the example of the dither matrix which selects 2 line shift. FIG. 3 is a diagram for explaining the reason why “streaks” do not occur due to a two-line shift in the example shown in FIG. 2. It is a figure explaining the example of the dither matrix which selects 3 line shift. It is a figure explaining the example of the dither matrix which selects 1 line shift. FIG. 3 is a diagram illustrating a halftone image in which toner images of two colors of cyan and magenta formed on a sheet are superimposed and an enlarged image thereof. FIG. 7 is a diagram showing the enlarged image in FIG. 6 in more detail with the area expanded. It is a figure for demonstrating that generation | occurrence | production of color unevenness can be suppressed by shifting cyan image data by 2 lines. 1 is a diagram showing a schematic configuration of a mechanism unit of an embodiment of an image forming apparatus according to the present invention. It is a figure which shows the figure which looked at a part of optical apparatus 102 in FIG. 9 from the arrow A direction with an image processing apparatus etc. FIG. It is a figure for demonstrating the principle which correct | amends the skew and the curvature of the main scanning direction of an image. FIG. 4 is a diagram illustrating an example of a monochrome halftone image formed on a sheet and a part of the enlarged image. An image formed when the image data forming the image shown in FIG. 12 is divided into two in the main scanning direction, and the image data in the region on the right side is shifted in the sub scanning direction in the direction of arrow A by one line; It is a figure which shows the example of the one part enlarged image.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
[Embodiments of Image Processing Apparatus and Image Processing Method]
First, an embodiment of an image processing apparatus according to the present invention will be described.
FIG. 1 is a block diagram showing a configuration of an embodiment of the image processing apparatus. The image processing apparatus 10 shown in FIG. 1 includes a controller 11 and a writing control unit 12. The image processing apparatus 10 executes the image processing method according to the present invention.

  When a print job is input, the controller 11 expands the print data of the print job into page-unit image data as in the conventional general controller. Then, dither processing (also referred to as halftone processing) for generating pseudo multi-value image data is performed by reducing the value of the multi-tone image data using a dither matrix (binarization in this example). Along with the generated pseudo multi-value image data, information for specifying the type of the dither matrix used for the dither processing for the multi-tone image data is sent to the write control unit 12.

In this example, as information for specifying the type of the dither matrix, mode information such as a character mode or a photo mode and resolution information such as 600 dpi or 1200 dpi are sent to the writing control unit 12. In this image processing apparatus 10, the type of dither matrix used can be uniquely specified by such information, but information such as an identification code indicating the type of dither matrix used directly is transmitted. You may do it.
In this embodiment, the controller 11 has a function of a dither processing unit that performs dither processing on multi-tone image data to generate pseudo multi-value image data.

The write control unit 12 includes a memory 13 such as an SRAM (Static Random Access Memory), a shift control unit 14 that is an image data shift unit, and a ROM (Read Only Memory) 15.
The pseudo multi-value image data (binary data) sent from the controller 11 to the write control unit 12 is temporarily stored in the memory 13. Then, the image data is sequentially read out to the shift control unit 14 and subjected to some image processing and speed adjustment, and then the shift processing for correcting the inclination and the bending of the main scanning line is performed, and the LD It is sent to the lighting control unit 20.

The LD lighting control unit 20 controls turning on / off of a laser diode (LD) as a light source according to binary data constituting each pixel of image data. With the laser light, an optical device described later exposes the photosensitive drum and writes an image.
Inside the writing control unit 12, as described above, processing other than the processing for correcting the inclination and bending of the main scanning line by the shift of the image data is also performed, but the description thereof is omitted.
Reading of the image data sent from the controller 11 and stored in the memory 13 is performed for each line to be written. In order to correct the inclination and the bending of the main scanning line, the image data is corrected as described with reference to FIG. It is different when performing the shift.

  In that case, the image data for each page is divided into a plurality of areas in the main scanning direction, and the data that the image is shifted in the sub-scanning direction is output by changing the line of the image read from the memory for each area. To do. The processing is performed by the shift control unit 14 which is an image data shift unit, and the reading of the image data from the memory 13 is controlled according to the shift amount for each divided area.

Since the state of the inclination or bending of the main scanning line in the image formed according to the image data is determined by the characteristics of the optical system such as the lens and mirror constituting the optical device, the inclination of the device generated in the assembly process, etc. Measurement can be made in advance for each device. Based on the measurement data, the division position and the shift direction of the image data for correcting the inclination or the curvature in the main scanning direction can be set in advance.
Conventionally, the shift amount of the image data has always been one line which is the minimum unit of the image data in the sub-scanning direction, that is, the minimum unit that can be exposed by the laser beam.

However, the shift control unit 14 in this embodiment determines the amount by which the image data is shifted for each divided area, that is, the number of lines, according to the type of dither matrix used in the dither processing of the multi-tone image data in the controller 11. change.
In this example, since the type of dither matrix to be used is determined by the mode information and resolution information input from the controller 11, the shift control unit 14 inputs information for specifying the type of the dither matrix. Then, the shift control unit 14 reads the number of lines to be shifted from the ROM 15 according to the type of dither matrix specified by the input information. Then, the shift amount is changed so as to shift the number of lines.
The ROM 15 is a storage unit that stores in advance the dither matrix type and the number of lines to be shifted in association with each other.

Therefore, in this embodiment, the shift control unit 14 and the ROM 15 which is a storage unit constitute a shift amount changing unit. Then, the shift control unit 14 sequentially reads out the pseudo multi-value image data from the memory 13, divides it into predetermined areas in the main scanning direction, shifts the image data in the sub-scanning direction for each area, and outputs it. And a means for correcting the inclination and bending of a normal main scanning line.
The shift control unit 14 further includes input means for inputting information specifying the type of the dither matrix used for the dither processing from the controller 11. Further, the shift control unit 14 and the shift amount changing means by the ROM 15 as the storage means shift the image data in the sub-scanning direction in accordance with the type of dither matrix specified by the information input by the input means. Change the amount.

Since the dither processing means (halftone processing means) in the controller 11 knows what kind of dither matrix is used, the controller 11 directly sends information such as an identification code indicating the type of the dither matrix. You can also In this case, the shift control unit 14 can input information indicating the type of the dither matrix, and immediately obtain line number information that is a shift amount from the ROM 15.
Alternatively, if the correspondence relationship between the type of dither matrix and the number of lines to be shifted is also stored in the controller 11, the number-of-lines information that is the shift amount can be sent directly from the controller 11 to the shift control unit 14. In that case, the ROM 15 becomes unnecessary.

Depending on the type of dither matrix, it may be desirable to shift by a certain shift amount for one line as in the prior art. There is also a dither matrix in which “streaks” are unlikely to occur even with a conventional shift for each line. When dither processing is performed using the dither matrix, it is sufficient to shift only one line.
According to the embodiment of the present invention, when a halftone image is formed using pseudo multi-value image data, it is possible to correct the inclination and bending of the main scanning line and to suppress the occurrence of “streaks” very easily. Note that the occurrence of “streaks” is suppressed only by changing the shift amount for shifting the image data in the sub-scanning direction for each region in accordance with the type of the dither matrix used for the dither processing of the image data. Therefore, it can be realized with substantially the same configuration as the configuration of the image processing apparatus used for correcting the tilt by shifting the conventional image data.

In the embodiment shown in FIG. 1, the image processing apparatus 10 includes the controller 11 having the function of a dither processing unit. However, only the writing control unit 12 is an image processing apparatus, and the controller 11 is provided separately. You may provide in the apparatus side which produces | generates a print job. As an apparatus that generates a print job, there are an information processing apparatus such as a microcomputer, an image reading apparatus (image scanner) that reads an image of a document, and the like.

Here, the relationship between the type of the dither matrix used for the dither processing for generating the pseudo multi-value image data from the multi-tone image data and the shift amount of the image data will be described.
FIG. 2 is a diagram for explaining an example of a dither matrix for selecting 2-line shift.
This figure shows an example of dither processing (halftone processing) for converting 4-bit (16-value) multi-value image data into 1-bit (binary) low-value image data using the dither matrix DM1.
Actually, multi-valued image data of 8 bits (256 values) is converted into pseudo multi-valued image data which is 1-bit (binary), 2-bit ( 4-valued ), or 4-bit (16 values) small-valued image data. The number of bits is changed to make it easier.

The numerical value of each part of the dither matrix DM1 indicates a threshold value. When the input pixel is larger than this threshold value, it becomes a black pixel after decreasing the value, and when it is smaller, it becomes a white pixel.
FIG. 2A shows an example in which multi-valued image data having a density value of 2 for all pixels is converted into low-value (binary) image data by the dither matrix DM1. The repetitive period T in the sub-scanning direction (vertical direction in the figure) of the pixel pattern after conversion is 4 dots every other column and “all white without repetition”. Here, “dot” is the same as “pixel”.

(B) shows a case where multi-value image data having a density value of 4 in all pixels is converted into low-value (binary) image data by the dither matrix DM1. The repetitive period T in the sub-scanning direction of the pixel pattern after conversion is 2 dots every other column and “all white without repetition”.
(C) is a case where multi-valued image data having a density value of 8 for all pixels is converted into low-value (binary) image data by the dither matrix DM1. The repetition period T in the sub-scanning direction of the pixel pattern after conversion is 2 dots in each column.

(D) shows a case where multi-valued image data having a density value of 14 in all pixels is converted into low-value (binary) image data by the dither matrix DM1. The repetition period T in the sub-scanning direction of the pixel pattern after conversion is “full black without repetition” with 4 dots every other column.
Among these, in the case of (c) in which the repetition period T is the shortest and is 2 dots in all rows, “streaks” are likely to occur if one line is shifted.

That is, as shown in FIG. 3A, when the image data in the region b is shifted by one line in the sub-scanning direction (arrow direction) with respect to the image data in the region a, the boundary 4 between the region a and the region b. Since the black pixels are adjacent to each other on the left and right sides, a “streaks” occurs.
However, if the image data in the region b is shifted by 2 lines in the sub-scanning direction in the sub-scanning direction with respect to the image data in the region a, as shown in FIG. The left and right pixels on the boundary 4 are arranged in the same state before and after the shift. Therefore, “streaks” do not occur.

In this way, if the pixel pattern repetition period after the conversion is shifted by the number of lines corresponding to the minimum value, occurrence of “streaks” can be prevented.
Therefore, when dither processing is performed using the dither matrix DM1, the shift amount may be set to two lines.
As described above, “streaks” may occur in one line shift due to the arrangement of black pixels in the low-value image data. “Streak” is likely to occur when the density is medium. The reason is that the arrangement of black pixels that cause an abnormality frequently appears when the density is medium.

That is, among the cycles in the sub-scanning direction of the pixel pattern that can occur in the pseudo multi-value image data generated when the multi-value image data is dithered using a specific dither matrix to reduce the value, Check the number of lines corresponding to the minimum number of dots. Then, by shifting the number of lines, it is possible to prevent the occurrence of abnormal images such as “streaks”.
Accordingly, for each type of dither matrix, the number of lines to shift the number of lines corresponding to the minimum number of dots in the sub-scanning direction period of the pixel pattern that can occur in the image data after the dither processing described above. And correspondingly stored in the ROM 15.

If using a dither matrix DM1 performing dither processing shown in FIG. 2, the low concentration and the period when the high-density image data is four dots, period 2 dots when the image data of the medium concentration Therefore, the number of lines corresponding to 2 dots having a smaller period is set as the shift amount.
Since the period (shift amount) of this pixel pattern is uniquely determined when the dither matrix is determined, the shift amount information for each dither matrix may be held in the ROM 15 shown in FIG. Accordingly, it is possible to correct the inclination and the bending of the main scanning line with an optimum shift amount without detecting the period of the pixel pattern of the actual image data.

FIG. 4 is a diagram for explaining an example of a dither matrix for selecting the 3-line shift.
This figure shows a dither process (halftone process) that uses the dither matrix DM2 to convert 4-bit ( 16 values ) multi-valued image data into 1-bit (binary) low-value image data as in the example shown in FIG. An example is shown.
In this case, in the case of the low density image data shown in (a), the repetition cycle of the pixel pattern is 6 dots, and each of the medium density shown in (b) and (c) and the high density image shown in (d). In the case of data, the repetition cycle of the pixel pattern is 3 dots. Therefore, 3 lines corresponding to 3 dots having a smaller period are set as the shift amount.

FIG. 5 is a diagram for explaining an example of a dither matrix for selecting one line shift.
This figure shows a dither process (halftone process) that uses the dither matrix DM3 to convert 4-bit ( 16 values ) multi-valued image data into 1-bit (binary) low-value image data as in the example shown in FIG. An example is shown.

In this case, in the case of the low density image data shown in (a), the repetition cycle of the pixel pattern in the sub-scanning direction is 4 dots in some rows, but the black pixels are not continuous in the main scanning direction. Therefore, “streaks” do not occur even if one line is shifted. In the case of medium density image data shown in (b) and (c), black pixels or white pixels are continuous in the sub-scanning direction, and are not a repetitive pattern . Even in the case of the high density image data shown in (d), the pixel pattern repeat cycle is 4 dots in some rows, but black pixels are continuous in the sub-scanning direction in most rows, and the repeat pattern It is not. Even in such a case, “streaks” do not occur even if the line is shifted by one line.
Therefore, in this case, the shift amount may be one line corresponding to the minimum unit of the image data in the sub-scanning direction as in the conventional case.

When the pixel pattern repetition period in the sub-scanning direction is 4 dots or more, “streaks” are unlikely to occur even if the shift amount of image data is set to one line corresponding to the minimum unit.
Therefore, it is considered that the shift amount for shifting the image data in the sub-scanning direction may be changed between 1 line and 3 lines according to the type of the dither matrix used for the dither processing.
The correspondence between the type of dither matrix and the shift amount is, for example, repeated for each dither matrix type used in the image forming apparatus to be implemented, in particular, by forming and evaluating a medium density image with different shift amounts. Thus, the optimum shift amount can be determined.

In the above description, the case where the image data is data that forms a single color image has been described. However, the present invention is also effective when a color image is formed using image data of a plurality of colors, and will be described below. .
A main scanning line of an image to be formed when the above-described pseudo multi-value image data is pseudo multi-value multi-color image data generated by performing dither processing on multi-color multi-tone image data, respectively. The following problems may occur when the inclination and the curvature of the image are corrected.
That is, when only a part of the image data of multiple colors is divided into predetermined areas in the main scanning direction and shifted in the sub-scanning direction for each area, The color changes (hereinafter referred to as “color unevenness”).

An example of this will be described with reference to FIGS. FIG. 6 shows a halftone image 2 formed by superimposing cyan and magenta toner images formed on the paper 1 and an enlarged image 3 thereof. FIG. 7 is a diagram showing the enlarged image in more detail with the area expanded.
It is assumed that a cyan and magenta toner image as shown in the enlarged image is formed by performing dither processing (halftone processing) using a dither matrix in order to reproduce a halftone image with binary dots. . Depending on the dither processing, a dither matrix having the same shape for each color may be used to form a pixel pattern so that dots of each color overlap, and FIG. 6 is an example assuming such processing.

  In the example shown in FIG. 6, the main scanning line is inclined only in the cyan image, and the magenta image is not inclined, so that color misregistration occurs. In order to reduce the color misregistration, that is, to correct the inclination of cyan, only the cyan image data is divided into two in the main scanning direction, and the area on the right side of the boundary 4 is shifted by one line in the sub-scanning direction. .

By doing so, the color shift is reduced. However, as can be seen from the enlarged image 3 and FIG. 7 of FIG. 6, although cyan and magenta should originally form dots at the same position, cyan dots are formed on the right and left sides of the boundary 4 of the divided area. The position is shifted by one pixel (one line) in the sub-scanning direction. As a result, cyan and magenta dots overlap in the left area, but do not overlap in the right area, so the way in which cyan and magenta dots overlap changes, and this is perceived as uneven color.
Although the example of cyan and magenta has been described, the toner color is not limited to this, and the same can be said for any combination of colors.

In this case, it will be described with reference to FIG. 8 that the occurrence of color unevenness can be suppressed by shifting the cyan image data by two lines.
In the example shown in FIGS. 6 and 7, the color unevenness occurs when the cyan image data in the right region is 1 even though the pixel pattern of the cyan low-value image has a repetition period of 2 dots in the sub-scanning direction. This is due to the line shift.

Therefore, by shifting the cyan image data in the right region by 2 lines corresponding to 2 dots in the repetition period of the pixel pattern in the sub-scanning direction, as shown in FIG. 8, the left and right sides of the boundary 4 of the divided region The cyan dot formation position becomes the same.
Therefore, since cyan and magenta dots overlap on the left and right sides of the boundary 4, color unevenness does not occur.
The minimum value of the repetition period in the sub-scanning direction of the pixel pattern that determines the optimum shift amount is uniquely determined by the type of dither matrix used for dither processing of the image data of the color to be shifted.

In this way, when only a part of the image data of multiple colors is shifted for each divided area, the shift amount of the image data is changed according to the type of the dither matrix used for the dither processing. By doing so, the occurrence of uneven color can be prevented.
When shifting the image data of all colors of the multi-color image data for each divided area, change the shift amount of each image data according to the type of the dither matrix used for the dither processing. It is possible to prevent the occurrence of “streaks” as in

  For this reason, the shift control unit 14, which is the image data shifting means shown in FIG. 1, generates pseudo multi-value image data that is generated by performing dither processing on multi-tone image data of a plurality of colors. In the case of image data of a plurality of values, it is preferable to have the following functions. One of them is to divide only a part of the plurality of color image data into predetermined areas in the main scanning direction and to sub-scanning direction orthogonal to the main scanning direction for each area. It is a function to shift to. The other is a function of changing the shift amount for shifting the image data of the color according to the type of the dither matrix used for the dither processing of the image data of the color.

[Embodiment of Image Forming Apparatus]
Next, an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS.
FIG. 9 is a diagram illustrating a schematic configuration of a mechanism unit of the image forming apparatus. FIG. 10 is a diagram showing a part of the optical device 102 in FIG. 9 as viewed from the direction indicated by the arrow A, together with the photosensitive drum and the image processing device 10 and the LD lighting control unit 20 described above with reference to FIG.
An image forming apparatus 100 shown in FIG. 9 includes the above-described image processing apparatus 10 according to the present invention, and is an image forming apparatus that forms an image by an electrophotographic method using image data processed by the image processing apparatus 10.

The image forming apparatus 100 of this embodiment is an electrophotographic tandem color printer, and includes an optical device 102, a color image forming unit 112, a transfer unit 122, and the like.
The color image forming unit 112 includes image forming process units (image forming units) 104, 106, 108, and 110 for magenta (M), cyan (C), yellow (Y), and black (K) colors. . The transfer unit 122 includes an endless intermediate transfer belt 114 and the like.

  Each image forming process unit 104, 106, 108, 110 of the color image forming unit 112 includes a photosensitive drum 104a, 106a, 108a, 110a, respectively. Around each of the photosensitive drums, chargers 104b, 106b, 108b, 110b, developing units 104c, 106c, 108c, 110c, primary transfer rollers 104d, 106d, 108d, 110d, and the like are arranged.

The optical device 102 is a multi-beam scanning device, and a laser beam emitted from a laser diode 206 (shown in FIG. 10) which is a semiconductor laser element is deflected by a polygon mirror 102c which is a deflector and is incident on an fθ lens 102b. ing. In this embodiment, the number of laser beams corresponding to the colors M, C, Y, and K is generated, and after passing through the fθ lens 102b, reflected by the reflecting mirror 102a.
Therefore, four laser diodes 206 are provided, the polygon mirror 102c is provided in two stages coaxially, and the fθ lens 102b is provided in two stages on both sides of the polygon mirror 102c.

  Each laser beam is shaped through the WTL lens 102d, then deflected again by the plurality of reflecting mirrors 102e, and emitted as four laser beams L used for exposure. The laser beams L are used to scan the scanned surfaces of the photosensitive drums 104a, 106a, 108a, and 110a of the image forming process units 104, 106, 108, and 110 (hereinafter also simply referred to as “surfaces”). Irradiation while scanning in the main scanning direction along the direction.

Since the irradiation of the laser beam L onto the surfaces of the photosensitive drums 104a, 106a, 108a, and 110a is performed using a plurality of optical elements as described above, timing synchronization is performed in the main scanning direction and the sub-scanning direction. .
The “main scanning direction” is defined as the scanning direction of the laser beam, and the “sub-scanning direction” is a direction orthogonal to the main scanning direction. In this image forming apparatus 100, the photosensitive drums 104a, 106a, 108a, 110a are It is defined as the direction of rotation, that is, the direction of movement of the surface.

Each of the photosensitive drums 104a, 106a, 108a, and 110a includes a photoconductive layer including at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum.
Each of the photoconductive layers is charged with a surface charge applied by chargers 104b, 106b, 108b, and 110b constituted by a corotron, a scorotron, a charging roller, or the like.
The surface of the charged photoconductive layer of each of the photosensitive drums 104a, 106a, 108a, 110a that rotates counterclockwise in the figure is controlled by a laser beam L whose light emission is controlled according to the value of each pixel of the image data from the optical device 102. Exposure scanning is performed. Thereby, a two-dimensional electrostatic latent image is formed (image writing is performed).

  In this embodiment, formation of the electrostatic latent image and a toner image to be described later is started in the order of K, Y, C, and M. The order of forming the electrostatic latent image of each color and a toner image to be described later is as follows. This is not a limitation. Therefore, the arrangement order of the image forming process units 104, 106, 108, 110 for each color is not limited to the order shown.

The electrostatic latent images formed on the surfaces of the photosensitive drums 104a, 106a, 108a, and 110a are respectively developed by the developing units 104c, 106c, 108c, and 110c, and are K, Y, C, and M as developers of the respective colors. The toner is developed with each toner, and a toner image of each color is formed.
Each developing device 104c, 106c, 108c, 110c includes a developing sleeve, a developer supply roller, a regulating blade, and the like.

  The developed toner images of the respective colors are sequentially superimposed and transferred in the order of K, Y, C, and M on the intermediate transfer belt 114 moving in the arrow B direction in the primary transfer portion. In the primary transfer portion, the photosensitive drums 104a, 106a, 108a, and 110a face the primary transfer rollers 104d, 106d, 108d, and 110d, respectively, with the intermediate transfer belt 114 interposed therebetween. A transfer bias voltage is applied to the primary transfer rollers 104d, 106d, 108d, and 110d.

The intermediate transfer belt 114 is stretched around the conveyance rollers 114a, 114b, and 114c, and one of the intermediate transfer belts 114 is rotated in a direction indicated by an arrow B (referred to as rotation) by the conveyance rollers 114a or 114c, which are driving rollers. The intermediate transfer belt 114 carries a full-color toner image of K, Y, C, and M toner images that are sequentially transferred and superimposed on the surface of the intermediate transfer belt 114, and conveys the toner image to the secondary transfer unit.
The secondary transfer unit includes a secondary transfer belt 118 that is rotated in the direction indicated by arrow C by the transport rollers 118a and 118b. The conveyance roller 114b of the intermediate transfer belt 114 also functions as a secondary transfer counter roller.

  A sheet-like recording medium 124 (corresponding to the above-mentioned paper 1) such as transfer paper or a plastic sheet is supplied to the secondary transfer unit from a recording medium accommodating unit 128 such as a paper feed cassette by a conveying roller 126. Then, a secondary transfer bias is applied to the conveying roller 114 b that also functions as a secondary transfer counter roller, and the full-color toner image carried on the intermediate transfer belt 114 is held by suction on the secondary transfer belt 118. Transfer to the recording medium 124.

The recording medium 124 onto which the full-color toner image has been transferred is conveyed to the fixing device 120 by the rotation of the secondary transfer belt 118 in the direction of arrow C.
The fixing device 120 fixes the toner image on the recording medium 124 by sandwiching the recording medium 124 at the nip portion between the fixing roller 121 and the pressure roller 123 and conveying the recording medium 124 with the transferred toner image while heating and pressing. The recording medium 124 that has passed through the fixing device 120 is discharged to the outside of the image forming apparatus 100 as a printed matter 132.
After the toner image is transferred to the recording medium, the transfer residual toner is removed from the intermediate transfer belt 114 by a cleaning unit 116 including a cleaning blade to prepare for the next image forming process.

The optical device 102 shown in FIG. 10 deflects and scans the laser light from the laser diode 206 with the polygon mirror 102c, and exposes the surface of the photosensitive drum 104a with the laser beam L passing through the fθ lens 102b while performing main scanning. The polygon mirror 102c is rotationally driven at a peripheral speed of several thousand to several tens of thousands rpm by a polygon motor (not shown).
In order to detect the laser beam L at a predetermined position on the near side (outside the image area) from the writing start position of the main scanning, a reflection mirror 208 and a synchronization detection sensor 210 using an optical sensor such as a photodiode are provided. The writing start position of each main scan is controlled by the synchronization detection signal from the synchronization detection sensor 210.

In this optical device 102, four laser diodes 206 are provided for each color, and as shown in FIG. 9, the polygon mirror 102c is provided in two upper and lower stages (the stage is shared by laser beams for two colors). The four laser beams L can be deflected and scanned. Four fθ lenses 102b and four reflection mirrors 102a are also provided. A surface emitting laser (VCSEL) may be provided instead of the laser diode 206.
As shown in FIG. 9, the photosensitive drums 104a, 106a, 108a, and 110a are provided for the image forming process units 104, 106, 108, and 110 for the respective colors.

Therefore, in the case of forming a color image, the LD lighting control unit 20 turns on the four laser diodes 206 for each color, respectively, for the image data of each color input from the writing control unit 12 of the image processing apparatus 10. Control is performed according to each pixel value.
When forming a black and white image, only the black image data is sent from the writing control unit 12 to the LD lighting control unit 20, and the LD lighting control unit 20 uses the black data for each pixel value of the image data. It is only necessary to control lighting of the laser diode 206. At this time, the laser diodes 206 for other colors are kept off, and the image forming process units 104, 106, 108 other than the black image forming process unit 110 are not operated.
The configuration and operation of the image processing apparatus 10 have been described above with reference to FIG.

  The image forming apparatus 100 according to this embodiment is a tandem type intermediate transfer type color printer, but may be a tandem type color printer that directly and directly transfers toner images of respective colors onto a recording medium. In addition, a color printer other than the tandem type or a monochrome printer may be used. Furthermore, the present invention can also be applied to image forming apparatuses such as copiers and facsimile machines other than printers, and digital multifunction peripherals having these functions.

The embodiments of the image processing apparatus, the image processing method, and the image forming apparatus according to the present invention have been described above. The specific configuration of each unit, the contents of processing, the data format, and the like have been described in the embodiments. It is not limited to.
In addition, the configuration of each embodiment described above can be added, changed, or partially omitted as appropriate, and can be implemented in any combination as long as there is no contradiction.

1: Paper 2: Halftone image 3: Enlarged image 4: Border 5: Line 10: Image processing device 11: Controller 12: Write control unit 13: Memory 14: Shift control unit 15: ROM 20: LD lighting control unit 100 : Image forming apparatus 102: Optical apparatus 102a, 102e : Reflecting mirror
102b: fθ lens 102c: polygon mirror 102d: WTL lens
104, 106, 108, 110: Image forming process section (image forming section)
104a, 106a, 108a, 110a: photosensitive drum
104b, 106b, 108b, 110b: charger
104c, 106c, 108c, 110c: Developer
104d, 106d, 108d, 110d: primary transfer roller
112: Color image forming unit 114: Intermediate transfer belt 116: Cleaning unit
118: Secondary transfer belt 120: Fixing device 122: Transfer section
124: Recording medium (paper) 128: Recording medium container 126: Conveying roller
132: Printed material 206: Laser diode L: Laser beam

JP 2010-217795 A

Claims (8)

The pseudo multi-valued image data generated by dithering the multi-gradation image data is divided into predetermined areas in the main scanning direction, and the image data is subordinately orthogonal to the main scanning direction in each area. In an image processing apparatus that shifts and outputs in the scanning direction and corrects the inclination and bending of the main scanning line of the formed image,
Input means for inputting information specifying the type of the dither matrix used in the dither processing, and the image data in the sub-scanning direction according to the type of dither matrix specified by the information input by the input means An image processing apparatus comprising: a shift amount changing unit that changes a shift amount to be shifted to. The image processing apparatus according to claim 1.
Dither processing means for performing dither processing on multi-tone image data to generate pseudo multi-value image data, and the dither processing means, together with the generated pseudo multi-value image data, the dither matrix used for the dither processing An image processing apparatus characterized in that information specifying the type of the image is sent to the input means.   The shift amount changing means shifts the shift amount for shifting the image data in the sub-scanning direction between 1 line and 3 lines according to the type of dither matrix specified by the information input by the input means. The image processing apparatus according to claim 1, wherein the image processing apparatus is changed.   The shift amount changing unit has a storage unit that stores the type of dither matrix and the number of lines to be shifted in correspondence with each other, and the number of lines to be shifted according to the specified type of dither matrix is stored in the storage unit. The image processing apparatus according to claim 1, wherein the shift amount is changed by reading.   For each type of dither matrix, the storage means is the minimum value among the periods in the sub-scanning direction of the pixel pattern that can occur in the pseudo multi-valued image data generated when dither processing is performed using the dither matrix. 5. The image processing apparatus according to claim 4, wherein the number of lines corresponding to the number of dots is stored in association with the number of lines to be shifted.   When the pseudo multi-value image data is pseudo multi-value multi-color image data generated by performing dither processing on multi-color multi-tone image data, respectively, the shift amount changing means Means for dividing only a part of color image data of color image data into predetermined areas in the main scanning direction, and shifting each area in a sub-scanning direction orthogonal to the main scanning direction; And means for changing a shift amount for shifting the image data of the color according to the type of the dither matrix used for the dither processing of the image data of the color. The image processing apparatus according to one item. The pseudo multi-valued image data generated by dithering the multi-gradation image data is divided into predetermined areas in the main scanning direction, and the image data is orthogonal to the main scanning direction for each area. An image processing method that shifts and outputs in the sub-scanning direction and corrects the inclination and bending of the main scanning line of the formed image,
An image processing method comprising: changing a shift amount for shifting the image data in the sub-scanning direction according to a type of a dither matrix used for the dither processing.   An image forming apparatus comprising the image processing apparatus according to claim 1, wherein an image is formed by an electrophotographic method using image data processed by the image processing apparatus.