JP2011019185A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which suitably handles striped density unevenness generated in a sub-scanning direction, when an image is formed by scanning an optical beam from a light source.SOLUTION: The image forming device includes: an image forming unit which forms an image on an image carrier by repeating exposure for scanning in a main scan direction according to image data for exposure on the image carrier which moves or rotates in the sub-scanning direction perpendicular to the main scan direction, and by visualizing the image and transferring it to recording paper; and an image processing unit which increases/decreases, to the image data for exposure, a pixel value in a correction pixel range in the main scan direction, for every image data for exposure in the range of the main scan direction. In the increasing/decreasing the pixel value, the correction pixel range and the correction amount corresponding to the pixel value of each pixel as the pixel to be corrected in the range of the main scan direction are defined.

Description

  The present invention relates to an image forming apparatus capable of forming an image in a state in which density unevenness occurring in the recording paper conveyance direction during image formation is taken into consideration.

  In an electrophotographic image forming apparatus, a rotating photosensitive drum or photosensitive belt image carrier is exposed with a laser beam in a direction (main scanning direction) perpendicular to the moving direction (sub-scanning direction) by rotation. Forming an electrostatic latent image, developing the electrostatic latent image to form a toner image on the image carrier, transferring the formed toner image directly or indirectly onto the recording paper, and further applying heat or pressure The toner image is fixed on the recording paper to form an image.

  In this image formation, a laser beam from a laser light source is used as scanning light by a rotating polygon mirror, and an optical system such as an fθ lens or a cylindrical lens is used, so that the main scanning direction on the image carrier is increased. The scanning speed is made uniform.

  By the way, even if there is no problem in the image data, streak-like density unevenness extending in the sub-scanning direction occurs for a specific pixel in the main scanning direction due to problems on the image forming apparatus side such as a defect or deterioration of the optical system. There is.

  This state is shown in FIG. 12 and FIG. Assume that when image formation is performed with image data corresponding to a shading chart as shown in FIG. 13, a chart having streaky density unevenness as shown in FIG. 12 is actually output. Here, a black stripe in which a black stripe having a high density in the sub-scanning direction can be seen and a white stripe in which a white stripe having a low density in the sub-scanning direction can be seen.

  Here, even when the black stripe or the white stripe is the same pixel position in the main scanning direction, if the density to be formed is different, the white portion (low density portion) is not noticeable, and the medium density portion is noticeable. The density shift is not uniform.

  For image unevenness correction in the image forming apparatus, proposals for efficient processing have been made in Patent Document 1 and Patent Document 2 below.

JP 2007-59990 JP 2003-112442 A

  In Patent Document 1 described above, a test pattern output by the apparatus itself is read by a scanner attached to the apparatus, and an image including unevenness is read to determine whether correction is possible. The main scanning direction is divided into a plurality of areas, and the gradation correction LUT prepared in each area is rewritten to suppress streaks and density unevenness.

  In this case, since the resolution of the position to be corrected is in the LUT unit divided into a plurality of parts in the main scanning direction, fine and precise correction in pixel units cannot be performed. For this reason, there is a case where correction is insufficient or excessive with respect to the width in the main scanning direction, and as a result, white stripes and black stripes may be generated. Since the LUT is used, the correction value at each position is constant.

  For this reason, as shown in FIG. 12, the inventors of the present application have found that even if the pixel position is the same in the main scanning direction, the appearance of unevenness changes if the pixel density is different. It was. For this reason, it has been found that this kind of density unevenness cannot be eliminated by the technique of the above cited reference 1.

  Although it is conceivable to perform image processing on the entire image data in units of one dot, this takes time and causes a new problem that the productivity of image formation is reduced.

  In the above Patent Document 2, in an image forming apparatus (LED printer) using an LED array in which a plurality of LED elements corresponding to pixels are arranged in the main scanning direction, the exposure amount of each LED element according to a plurality of halftone modes. Is used to correct streaky density unevenness.

  In this case, streaky density unevenness due to variations in LED elements in the LED printer can be dealt with, but an image forming apparatus such as a laser printer that scans a laser beam from a laser beam to form an image is completely dealt with. I can't.

  The present invention solves the above-described problems, and is an image forming apparatus that can appropriately cope with streaky density unevenness that occurs in the sub-scanning direction when an image is formed by scanning a light beam from a light source. It aims at realizing.

The present invention for solving the above-described problems is as follows.
(1) According to the first aspect of the present invention, the exposure for scanning in the main scanning direction according to the image data for exposure is repeatedly performed on the image carrier that moves or rotates in the sub scanning direction orthogonal to the main scanning direction. An image forming unit that forms an image on the image carrier, visualizes the image and transfers the image onto a recording sheet, and correction pixels in the main scanning direction with respect to the exposure image data. An image processing unit that performs pixel value increase / decrease processing for increasing / decreasing the pixel value in the range for each exposure image data in the range in the main scanning direction. In the pixel value increase / decrease processing, correction is performed in the main scanning direction range The image forming apparatus is characterized in that the correction pixel range and a correction amount corresponding to a pixel value of each pixel are determined as pixels.

  (2) In the invention according to claim 2, when the image processing unit obtains a correction amount according to a pixel value of each pixel as the pixel value increase / decrease process, an average of each pixel and its surrounding pixels The image forming apparatus according to claim 1, wherein the correction amount of each pixel is calculated based on the value.

  (3) In the invention according to claim 3, in the correction pixel range in the pixel value increase / decrease processing, a correction center pixel range in which correction is performed with a predetermined correction amount according to a pixel value, and the correction center pixel range and correction unnecessary. 3. The image forming apparatus according to claim 1, further comprising: a correction peripheral pixel range in which a correction amount varies with a pixel in accordance with a position.

  (4) In the invention according to claim 4, the image processing unit performs processing so that the absolute value of the correction amount decreases as the correction peripheral pixel range approaches the correction unnecessary pixel in the correction peripheral pixel range. The image forming apparatus according to claim 4, wherein:

  (5) The invention according to claim 5 stores an operation unit that receives an input of setting of the correction pixel range and the correction amount, and a memory that stores the correction pixel range and the correction amount input from the operation unit. A pixel value that increases or decreases a pixel value by a predetermined correction amount in the correction pixel range in the main scanning direction according to the correction pixel range and the correction amount stored in the storage unit. The image forming apparatus according to claim 1, wherein an increase / decrease process is performed.

According to the above invention, the following effects can be obtained.
(1) In the invention of the image forming apparatus according to the first aspect, the exposure for scanning in the main scanning direction according to the image data for exposure is performed on the image carrier that moves or rotates in the sub scanning direction orthogonal to the main scanning direction. When the image is formed by forming the image on the image carrier and transferring it to a recording sheet by repeating the above, the pixel value is increased or decreased within the correction pixel range in the main scanning direction. The pixel value increase / decrease process is performed by the image processing unit for each image data in the range in the main scanning direction based on the correction pixel range and the correction amount corresponding to the pixel value.

  Accordingly, correction can be performed in units of pixels within a necessary range, and appropriate correction can be performed according to the density of each pixel. Further, since processing is performed for each data in the main scanning direction, high-speed processing is possible. As a result, it is possible to realize an image forming apparatus that can appropriately cope with streaky density unevenness that occurs in the sub-scanning direction when image formation is performed by scanning a light beam from a light source.

  (2) In the invention of the image forming apparatus according to claim 2, when the image processing unit obtains the correction amount according to the pixel value of each pixel as the pixel value increase / decrease process, the individual pixels and the surrounding pixels are determined. The correction amount of each pixel is calculated based on the average value.

  As a result, only white (lowest value) and black (highest value) exist for each pixel, as in screen processing, and halftones are displayed with dots and lines that make up a certain range of screen. In addition, the pixel value increasing / decreasing process for increasing / decreasing the pixel value can be appropriately executed according to the pixel value to be displayed.

  (3) In the invention of the image forming apparatus according to claim 3, the correction pixel range in the pixel value increase / decrease process includes a correction center pixel range in which correction is performed with a predetermined correction amount according to the pixel value, a correction center pixel range, and correction. A correction peripheral pixel range in which the correction amount changes depending on the position between the unnecessary pixels and stripes generated in the sub-scanning direction when image formation is performed by scanning the light beam from the light source. Therefore, it is possible to realize an image forming apparatus that can appropriately cope with uneven density.

  (4) In the invention of the image forming apparatus according to claim 4, the image processing section performs processing so that the absolute value of the correction amount becomes smaller as the correction peripheral pixel range approaches the correction unnecessary pixel in the correction peripheral pixel range. Therefore, it is possible to realize an image forming apparatus that can appropriately cope with streaky density unevenness that occurs in the sub-scanning direction when an image is formed by scanning a light beam from a light source.

  (5) In the image forming apparatus according to claim 5, the correction pixel range and the correction amount input from the operation unit are stored in the storage unit, and the image processing unit includes the correction pixel range stored in the storage unit. In accordance with the correction amount, pixel value increase / decrease processing is performed to increase / decrease the pixel value by a predetermined correction amount in the correction pixel range in the main scanning direction, and sub-scanning is performed when the light beam from the light source is scanned to form an image. It is possible to realize an image forming apparatus that can appropriately cope with streaky density unevenness generated in the direction.

It is a block diagram which shows the structure of embodiment of this invention. It is a block diagram which shows the structure of embodiment of this invention. It is a flowchart which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows operation | movement of embodiment of this invention. It is explanatory drawing which shows density | concentration unevenness. It is explanatory drawing which shows a chart.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments (embodiments) for carrying out an image forming apparatus of the present invention will be described below in detail with reference to the drawings.
[Configuration of Image Forming Apparatus 100]
Here, the configuration of the image forming apparatus 100 according to the first embodiment will be described in detail based on FIG. 1 (block diagram) and FIG. 2 (perspective view).

  The image forming apparatus 100 of this embodiment can be applied to various types of image forming apparatuses. Here, a multifunction peripheral (MFP) having functions of a scanner, a copier, a printer, and a facsimile machine is used. The description will be continued with a specific example of the image forming apparatus.

Also, description of general portions that are known as the image forming apparatus 100 and are not directly related to the characteristic operation and control of the present embodiment is omitted.
The image forming apparatus 100 according to the present embodiment is broadly divided into a storage unit 104 that stores various setting values, an operation display unit 105 that receives input of operations from a user and displays various messages, and performs image processing on image data. A main body processing unit 110 that performs various processes such as performing image processing, a scanner 120 that reads a document to generate image data, and an image forming unit 130 that forms an image using the image processed image data.

  Here, the main body processing unit 110 includes a control unit 101 configured by a CPU or the like that controls each unit, an image processing unit 111 that performs various image processing, and an image memory 112 that is used during image processing. Yes.

  The image processing unit 111 includes an image data conversion unit 111A and a pixel value increase / decrease processing unit 111B. Here, the image data conversion unit 111A performs various data conversions (RGB → YMCK conversion, gamma correction, screen, etc.) necessary for exposure in the image forming unit 130 while buffering input image data in the image memory 112. Processing, PWM conversion, etc.). Further, the pixel value increase / decrease process 111B performs pixel processing within the correction pixel range in the main scanning direction while buffering the image data (exposure image data) subjected to various data conversion by the image data conversion unit 111A in the image memory 112. A pixel value increasing / decreasing process for increasing / decreasing is performed.

  The scanner 120 is an image input unit such as a scanner that reads an image from a document and inputs image data. A scanner 120 that reads an image from a document and obtains image data includes a scanning light source unit, a scanning mirror unit, an imaging lens, and a CCD image sensor.

  The image forming unit 130 moves or rotates the exposure scanned in the first direction (main scanning direction) according to the exposure image data in the second direction (sub-scanning direction) orthogonal to the first direction. The image is formed by transferring the visible image (toner image) formed on the image carrier onto the recording paper by repeating the process in FIG. 2, for example, as shown in FIG.

Here, the configuration of the writing unit forming the core of the image forming unit 130 using a laser beam will be described with reference to FIG.
Based on the exposure image data (PWM data) processed by the image processing unit 111, the laser diode (LD) 1300 emits light and generates a laser beam.

The laser beam from the LD 1300 passes through the collimator lens 1301 and the cylindrical lens 1302 and is then scanned in the main scanning direction by the polygon mirror 1303.
The laser beam scanned by the polygon mirror 1303 is adjusted so as to scan at a constant speed by the fθ lens 1304. Further, the data passes through the cylindrical lens 1305 and is written on the photosensitive drum 1320.

Then, the sub-scan is performed by rotating the image carrier 1320 while performing the main scan. That is, image formation for one page is performed by repeating main scanning in the sub-scanning direction.
A part of the laser beam scanned by the polygon mirror 1303 is guided to the index sensor 1306, and the timing is detected.

  In FIG. 2, only the configuration for one color is shown, but in the case of a color image forming apparatus, each unit is provided for each color of yellow Y, magenta M, cyan C, and black K as necessary. Has been.

  In an image forming apparatus that forms an image for one page by repeating such image formation in the main scanning direction in the sub-scanning direction, even if there is no problem in the image data, the optical system is defective or deteriorated. Due to problems on the image forming apparatus side, streaky density unevenness (see FIGS. 12 and 13) extending in the sub-scanning direction may occur for specific pixels in the main scanning direction.

[Operation of Image Forming Apparatus 100]
The operation of the image forming apparatus 100 will be described in detail below with reference to the flowchart of FIG.

In the following description, a value obtained by PWM conversion of 8-bit image data into 8-bit PWM data, for example, 0-255 is treated as a density.
[Operation (1)]
First, when the image forming apparatus 100 is turned on, the control unit 101 executes the following processing as a density unevenness correction setting mode before executing normal image formation. The density unevenness correction setting mode is desirably executed regularly or irregularly at regular intervals.

  First, when the image forming apparatus 100 operates in the density unevenness correction setting mode, the control unit 101 reads out calibration chart data as shown in FIG. 13 from the storage unit 104, and the image forming unit 130 puts it on the recording paper. It forms and outputs (step S101 in FIG. 3).

  Here, the calibration chart of FIG. 13 is a chart in which the pixel values (density) are uniform in the main scanning direction and change stepwise or smoothly so that the density ranges from white to black in the sub-scanning direction. is there. Here, a chart that changes from white to black in 10 steps is shown as an example. However, the chart is not limited to this example, and it is desirable to have a more detailed step. Further, although not shown, it is desirable that a scale indicating which density value, for example, a PWM value 0-255 corresponds to the density changing in the sub-scanning direction is attached. In this case, since the chart is from the right end to the left end in the main scanning direction, it is desirable to describe the density value at any position in the chart.

  It is desirable that a scale indicating the pixel position in the main scanning direction is attached for reading by the user. Here, a case where there are about 9000 pixels in the main scanning direction is illustrated.

  Then, the control unit 101 displays the correction instruction value input screen of FIG. 8 while displaying the meaning of the value to be input by the user on the help screen of FIG. Is received (step S102 in FIG. 3).

  If streaky density unevenness extending in the sub-scanning direction as shown in FIG. 12 exists in the chart output from the image forming apparatus 100, the user instructs the operation screen of FIG. A value is input (steps S102 and S103 in FIG. 3).

At this time, if there are a plurality of stripe-shaped density irregularities, they are distinguished by assigning numbers such as position # 1, position # 2,..., Position #n.
Here, as the stripe-shaped density unevenness in FIG. 12, the black stripe whose density is higher than the original value (or the surrounding area) in the sub-scanning direction is set to position # 1, and the original density (or the surrounding area) in the sub-scanning direction. ) Lower white stripe is treated as position # 2.

  For example, as shown in FIG. 7, correction start pixels (pixels in the main scanning direction where correction starts), step 1 (number of pixels in the correction peripheral pixel range), maximum correction amount width (number of pixels in the correction center pixel range) ), Step 2 (number of pixels in the correction peripheral pixel range), maximum correction amount (maximum correction amount), correction start density (density at which correction starts), correction gradient density (from correction start density to maximum correction amount) Is read from the output chart, and is input from the operation display unit 105 as a correction instruction value. Here, instead of the correction gradient density, the density that provides the maximum correction amount may be input.

  As for the maximum correction amount, a density B that does not need to be corrected is found, which appears to be equal to the density A ′ where the maximum density difference between the density A and the surrounding density A occurs. The density difference is the maximum correction amount.

  Here, at the density unevenness position # 1 (black stripe) in FIG. 12, it is necessary to perform pixel value increase / decrease processing for reducing the density of black stripes as shown in FIGS. Therefore, as indicated by position # 1 in FIG. 8, correction start pixel: 920, step 1:12, step 2:12, correction amount maximum width: 40, correction amount maximum value: -10, correction start density: 32, The user inputs a correction instruction value from the numeric keypad screen (lower left of the screen) of the operation display unit 105, such as correction gradient density: 16, and so on.

  Here, in the density unevenness position # 2 (white stripe) in FIG. 12, it is necessary to perform pixel value increase / decrease processing for increasing the density of the white stripe as shown in FIGS. Therefore, as shown in position # 2 of FIG. 8, correction start pixel: 7680, step 1:32, step 2:10, correction amount maximum width: 16, correction amount maximum value: 20, correction start density: 18, correction The user inputs a correction instruction value from the numeric keypad screen (lower left of the screen) of the operation display unit 105 such as the gradient density 105.

  In the example of FIG. 12, since density unevenness of 3 or more does not occur, OFF is set after position # 3 in FIG. 8, but if density unevenness exists, position # 3 and later are set. Is turned ON, and the user inputs a correction instruction value.

  When the user inputs “OK” on the correction instruction value input screen in FIG. 8, the control unit 101 assumes that the input of the correction instruction value has been completed (step S <b> 103 in FIG. 3) and inputs it via the operation display unit 105. A set value for pixel value increase / decrease processing is created from the corrected instruction value (step S104 in FIG. 3).

Here, the set value of the pixel value increase / decrease process is a data group in which correction amounts to be increased / decreased (added or subtracted) according to the density for each pixel included in the correction pixel range are summarized in a table format.
For example, FIG. 4 shows the maximum correction amount, and actually, the correction amount has an absolute value smaller than the maximum correction amount as shown in FIGS. 5 and 6 according to the density of each pixel. There is. That is, as shown in FIG. 9, even within the correction pixel range, the correction amount changes according to the density of the pixel. This state is prepared as a set value for pixel value increase / decrease processing.

  When obtaining the correction amount (FIGS. 5 and 6) according to the density (pixel value) of each pixel in the correction pixel range as described above, white (minimum value) is obtained for each pixel as in screen processing. If there is only black (highest value) and halftone shading is displayed with dots and lines that make up a range of screens, based on the average value of individual pixels and surrounding pixels, The correction amount of each pixel is calculated. And the control part 101 preserve | saves the setting value of this pixel value increase / decrease process in the memory | storage part 104 (step S105 in FIG. 3).

  In the above description, in the case of two positions as the stripe-shaped density unevenness, the correction amount is increased or decreased to the density unevenness with reference to a portion other than the unevenness. On the other hand, a method may be used in which the correction amount is increased / decreased for both the non-density unevenness and the density unevenness with reference to the vicinity of the intermediate value between the non-uniformity part and the density unevenness part. .

[Operation (2)]
In a state where the correction instruction value based on the density unevenness generated in the chart as described above is input by the user and the control unit 101 has created the setting value for the pixel value increasing / decreasing process, the image forming apparatus 100 is as follows. The image forming operation is executed.

  In the image forming apparatus 100, when image data read by the scanner 120 or image data is input from an external device such as a PC (not shown), the control unit 101 stores the image data in the image memory 112. Thus, the image processing unit 111 executes various image processing necessary for image formation in the image forming unit 130.

  Here, first, while buffering image data in the image memory 112, the image data conversion unit 111A performs RGB → YMCK conversion processing, gamma correction processing as various data conversion necessary for exposure in the image forming unit 130. Then, screen processing, PWM conversion processing, and the like are performed (step S201 in FIG. 3) to convert them into PWM data that can be used for exposure in image formation. Note that if there is image data that has already undergone screen processing, the control unit 101 performs control so that screen processing is not performed repeatedly.

Here, the control unit 101 checks whether or not the setting value of the pixel value increase / decrease process is stored in the storage unit 104 in order to determine whether or not to perform density unevenness correction (step S202 in FIG. 3).
If the set value of the pixel value increase / decrease process is not stored in the storage unit 104, it is not necessary to correct the density unevenness (NO in step S202 in FIG. 3). Therefore, the control unit 101 performs the above image data conversion. The PWM data generated by the unit 111A is sent to the image forming unit 130, and control is performed so that an image is formed on the recording paper by image formation (exposure, development, transfer, fixing) (step S205 in FIG. 3).

In this image forming apparatus 100, PWM conversion and exposure are repeated for each image data in the main scanning direction (steps S201 to S205, S206, and S201 in FIG. 3).
On the other hand, if the set value of the pixel value increase / decrease process is stored in the storage unit 104, it is necessary to correct the density unevenness (YES in step S202 in FIG. 3). The PWM data generated by the data converter 111A is sent to the pixel value increase / decrease processor 111B.

  Then, the control unit 101 reads out the set value of the pixel value increase / decrease process from the storage unit 104 and passes it to the data conversion unit 111A (step S203 in FIG. 3). The pixel value increase / decrease processing unit 111B increases or decreases the pixel value in the correction pixel range in the main scanning direction while buffering the image data subjected to PWM conversion by the image data conversion unit 111A in the image memory 112. Processing is performed (step S204 in FIG. 3). In this case, as described with reference to FIG. 9, the correction amount changes according to the density of the pixel even within the correction pixel range.

  Here, if the correction instruction value is input based on the correction instruction value input screen of FIG. 8, the density of each pixel in the correction pixel range of 64 (12 + 40 + 12) pixels from 920 pixels to 983 pixels as position # 1. The pixel value increase / decrease process is executed with a correction amount that changes in accordance with (see FIG. 10A). The correction start density is 32, the correction gradient density is 16, and the maximum correction amount is -12 (see FIG. 10B).

  Similarly, if it is based on the correction instruction value input on the correction instruction value input screen of FIG. 8, the density of each pixel in the correction pixel range of 58 (32 + 10 + 16) pixels of 7680 to 7737 pixels as position # 2 The pixel value increase / decrease process is executed with a correction amount that changes in accordance with (see FIG. 11A). The correction start density is 18, the correction gradient density is 105, and the maximum correction amount is 20 (see FIG. 11B).

Here, a correction amount determined according to the density of the PWM data is added to or subtracted from the PWM data, and this process is a pixel value increase / decrease process.
Since the above processing is executed for each image data in the main scanning direction to be exposed, the processing does not require much time and can be executed during image processing for image formation in real time. Even in an image forming apparatus that simultaneously exposes a plurality of main scanning lines, it is only necessary to process image data in the main scanning direction such as 2, 4, 8, and 16 lines. Therefore, the amount of calculation is small compared to what is processed, and processing is possible in a short time.

  Then, the control unit 101 converts the PWM data into the PWM data by the image data conversion unit 111A as described above, further causes the pixel value increase / decrease processing unit 111B to perform the pixel value increase / decrease processing, and outputs the PWM data after the pixel value increase / decrease processing to the image forming unit. Control is performed so that an image is formed on the recording paper by image formation (exposure, development, transfer, fixing) (step S205 in FIG. 3).

  In this image forming apparatus 100, PWM conversion, pixel value increase / decrease processing, and exposure are repeated for each image data in the main scanning direction (steps S201, S203, S204, S205, S206, and S201 in FIG. 3).

  By the operation of the image forming apparatus 100 described above, correction can be performed in units of pixels within a necessary range, and appropriate correction can be performed according to the density of each pixel. Is possible. As a result, it is possible to realize an image forming apparatus that can appropriately cope with streaky density unevenness that occurs in the sub-scanning direction when image formation is performed by scanning a light beam from a light source.

[Other Embodiments]
In the above embodiment, the correction pixel range has been described as having Step 1 (the number of pixels in the correction peripheral pixel range) and Step 2 (the number of pixels in the correction peripheral pixel range). However, the present invention is not limited to this. is not. That is, the density unevenness may be such that the corrected peripheral pixel range does not exist on both sides of the maximum correction amount width, but only one side or both. In this case, “0” may be input as the correction instruction value for step 1 or step 2 described above.

  In the above embodiment, the correction pixel range includes step 1 (number of pixels in the correction peripheral pixel range), maximum correction amount width, and step 2 (number of pixels in the correction peripheral pixel range). Although described as correction, it is not limited to this. That is, the maximum correction amount width does not exist, and the triangular density unevenness and correction only in the correction peripheral pixel range may be used. In this case, “0” may be input as the correction instruction value for the above-described maximum correction amount width.

  In the above embodiment, the pixel value increase / decrease process is executed by adding or subtracting the correction amount determined according to the density of the PWM data to the PWM data. However, the present invention is not limited to this. Various changes that add or subtract correction amounts determined according to pixel values (signal values, luminance values, density values) of image data of various formats used for exposure in the image forming apparatus 100. Is possible.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 104 Memory | storage part 105 Operation display part 110 Main body process part 111 Image processing part 111A Data conversion part 111B Pixel value increase / decrease processing part 120 Scanner 130 Image formation part

Claims (5)

An image is formed on the image carrier by repeatedly performing exposure scanning in the main scanning direction according to the image data for exposure on the image carrier that moves or rotates in the sub-scanning direction orthogonal to the main scanning direction. An image forming unit that forms an image by forming a visible image and transferring it to a recording paper;
An image processing unit that performs pixel value increase / decrease processing for increasing / decreasing a pixel value in the correction pixel range in the main scanning direction for each exposure image data in the main scanning direction with respect to the image data for exposure;
With
In the pixel value increase / decrease process, the correction pixel range and the correction amount according to the pixel value of each pixel are determined as pixels to be corrected within the main scanning direction range.
An image forming apparatus. In the pixel value increase / decrease process, the image processing unit calculates the correction amount of each pixel based on the average value of each pixel and its surrounding pixels when obtaining the correction amount according to the pixel value of each pixel. calculate,
The image forming apparatus according to claim 1. The correction pixel range in the pixel value increase / decrease process is:
A correction center pixel range for performing correction with a predetermined correction amount according to the pixel value;
A correction peripheral pixel range in which a correction amount changes according to a position between the correction center pixel range and a correction unnecessary pixel;
Having
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image processing unit performs processing so that an absolute value of the correction amount decreases as the correction peripheral pixel range approaches the correction unnecessary pixel from the correction central pixel range.
The image forming apparatus according to claim 4. An operation unit that receives input of settings of the correction pixel range and the correction amount;
A storage unit that stores the correction pixel range and the correction amount input from the operation unit;
The image processing unit performs pixel value increase / decrease processing for increasing / decreasing a pixel value by a predetermined correction amount in the correction pixel range in the main scanning direction according to the correction pixel range and the correction amount stored in the storage unit,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.