JP5448600B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that obtains an image by transferring each color component toner image of at least one color onto a recording material by an electrophotographic method or an electrostatic recording method, such as a copying machine or a laser beam printer. Can be embodied.

  Conventionally, image forming apparatuses having various configurations have been used. Here, description will be made mainly using an image forming apparatus as shown in FIG.

  In the image forming apparatus as shown in FIG. 1, the photosensitive drum 4 is rotationally driven at a predetermined angular velocity, and the surface of the photosensitive drum is uniformly charged by the charger 8. Next, an electrostatic latent image according to the image data is formed on the photosensitive member by exposing and scanning the laser beam with an exposure device that is ON / OFF controlled according to the image data, and developed and visualized by the developing unit 3. . The visualized toner image is transferred onto the intermediate transfer member 5 that is rotationally driven while being pressed against the photosensitive drum 4 with a predetermined pressing force. Thereafter, the image is transferred to the recording material 6 fed from the paper feeding unit, and discharged to the outside through a fixing process by the fixing device 7.

  In recent years, such an electrophotographic image forming apparatus has been widely used in a market targeting office use, graphic use, printing, and the like. Especially, in the market such as office and SOHO, compared with image forming apparatuses that employ other methods. High-speed and image-independent image formation has become popular. However, the electrophotographic image forming apparatus has a problem that the apparatus itself is more expensive than other image forming apparatuses. One of the main factors is adjustment during assembly of a laser scanner that is often used as an exposure means.

  FIG. 4 shows a schematic diagram of a laser scanner which is a typical exposure means.

  The laser L is reflected by the rotary polygon mirror 42 installed on the rotary polygon mirror motor 41, passes through the optical system f-θ lens 43 such that the linear velocity is constant on the exposure surface, is reflected by the reflection mirror 44, and It reaches the photosensitive drum 4.

  When such a laser optical system is used, for example, the writing position of the scanning line exposed on the photosensitive drum 4 is shifted due to mechanical accuracy or an assembly error such as an assembly error during assembly installation, the magnification is distorted, the inclination or the curvature The problem is that it has distortions such as distortion. Of these, the correction of the writing position and magnification has conventionally been performed by detecting an error and electrically correcting it, but such electrical correction is difficult for the inclination and distortion of the scanning line. For this reason, conventionally, correction using expensive optical components is performed so as to prevent such inclination and distortion. For this reason, an apparatus having an expensive configuration is required, and further, the number of man-hours by precise fine adjustment is increased during assembly, resulting in an increase in production cost.

  The following proposals have been made for these issues.

  That is, registration detection means are provided at a plurality of positions in at least three locations in the main scanning direction, and distortions such as inclination and curvature in the main scanning direction are calculated from the results of the plurality of registration detection means, and calculated. The image data is changed so as to correct distortion such as inclination and curvature in the main scanning direction. Here, similarly for the correction of one pixel or less in the sub-scanning direction, the writing position in the sub-scanning direction is detected from the detection result by the registration detecting means, and the image data is changed so as to correct the detected sub-scanning writing position. .

  By forming an image of the image data changed by the above configuration, it is possible to correct the position of the scanning line tilt, distortion, etc. without using expensive optical components or through a precise adjustment process, and it is inexpensive and has high image quality. An image forming apparatus can be provided. (See Patent Document 1)

JP 2004-170755 A (page 13, FIG. 1)

  However, in the case of the configuration shown in Patent Document 1, the registration pattern is detected by the registration detection unit provided in the main scanning direction, and correction is performed based on the detection result. Therefore, at least 3 in the main scanning direction. It is necessary to provide a plurality of registration detecting means at more than one place, and there is a problem that the cost of the apparatus itself is greatly increased.

  Furthermore, the image data is corrected based on the correction position in the main scanning direction calculated according to the scanning line inclination / distortion from the detection result of the registration pattern. However, there is a problem that correction cannot always be optimally performed because of the occurrence of roughness at the correction position in the main scanning direction.

  In addition, the image data is corrected based on the correction position in the main scanning direction calculated according to the inclination and distortion of the scanning line. However, pseudo halftone processing having a tissue structure such as dither is performed. If there is a problem, a phase shift of the tissue structure occurs at the correction position. In order to correct this phase shift, a technique has also been proposed in which smoothing processing is performed at the same time on the phase-shifted area. In addition, there are problems such as density steps and moire due to phase differences caused by different correction positions for each color.

The image forming apparatus of the present invention includes a photosensitive member, a rotating polygon mirror that deflects the light beam so that the light beam scans the photosensitive member, and the light beam deflected by the rotating polygon mirror to the photosensitive member. An image forming apparatus having an optical member for guiding the image forming unit corresponding to a plurality of colors, and half of dither processing or error diffusion processing for image data corresponding to each of the plurality of colors An image for each of a plurality of areas corresponding to each of the plurality of colors in the scanning direction of the light beam in order to perform tone processing and correct image distortion due to curvature of a scanning line of the light beam that scans the photoconductor Image data processing for shifting the image data in the rotational direction of the photoconductor, and image data smoothing processing for smoothing the image subjected to the image data processing is executed. Possible data processing means, and control means for controlling the image forming means based on image data processed by the data processing means, wherein the data processing means comprises at least one color of the plurality of colors The error diffusion processing and the image data processing are performed on the image data of the plurality of colors, the smoothing processing is not performed, the error diffusion processing and the image data processing are performed among the plurality of colors, and the smoothing is performed. The dither process, the image data process, and the smoothing process are performed on image data of at least one color other than a color that is not subjected to the process .

  According to the present invention, it is possible to provide an inexpensive and favorable image forming apparatus without performing correction by an expensive optical component or precise fine adjustment at the time of assembly with respect to inclination or distortion of a scanning line of an optical system. Can do.

FIG. The structure sectional view of an example. The flowchart regarding the image signal processing part in an Example. Schematic diagram of a conventional laser optical system. Schematic diagram of the laser optical system of the example The flowchart of an Example. The schematic diagram which shows a scanning line profile. The flowchart which calculates 1st correction data. Schematic which shows 1st correction | amendment. Schematic which shows 2nd correction | amendment. The figure of the pulse width table used in the Example. The image figure of the correction | amendment of an Example. The figure of the pseudo halftone process which has a general organizational structure. The figure of the pseudo halftone area | region by 1st correction | amendment and 2nd correction | amendment. The figure of the pseudo halftone area | region by 1st correction | amendment. The figure of the pseudo halftone process which does not have an organizational structure. The figure of the pseudo halftone area | region by 1st correction | amendment. The figure of the relationship between a halftone process and the granularity with respect to the brightness of a toner. The block diagram which shows the structure of an Example.

[Example]
FIG. 2 is a cross-sectional view showing the image forming apparatus 100 in the present embodiment.

  First, the reader unit A will be described.

  The document 101 placed on the document table glass 102 is imaged on the CCD sensor 105 through the optical system 104 irradiated by the light source 103. The CCD sensor 105 generates red, green, and blue component signals for each line sensor by a group of red, green, and blue CCD line sensors arranged in three rows. These reading optical system units scan the document in the direction of the arrow to convert the document into an electric signal data string for each line.

  Further, an abutting member 107 that abuts the position of the original to prevent the original from being placed obliquely on the original platen glass 102, and a CCD sensor 105 for determining the white level of the CCD sensor 105 on the original table glass surface. A reference white plate 106 for performing shading in the thrust direction is disposed.

  The image signal obtained by the CCD sensor 105 is subjected to image processing by the reader image processing unit 108, then sent to the printer unit B, and image processing is performed by the printer control unit 109.

  Next, the image processing unit 108 will be described with reference to FIG.

  The luminance signal of the original image read by the CCD 301 is input to the A / D conversion unit 302 and converted into a digital signal. The digital luminance signal is sent to the shading unit 303, and shading correction is performed for unevenness in the amount of light due to variations in the sensitivity of each CCD element. By correcting the shading, the measurement reproducibility of the CCD is improved. The luminance signal corrected by the shading unit 303 is further subjected to LOG conversion by the LOG conversion unit 304. Subsequently, the LOG-converted signal is sent to the γLUT 305, and the image signal is generated by the γ-LUT 25 created so that the ideal density characteristic of the printer device matches the output image density characteristic processed according to the γ characteristic. Convert. The converted image signal is subjected to pseudo halftone processing by the halftone processing unit 310 and then transmitted to the printer unit 311 to form an image.

  Next, returning to FIG. 2 again, the printer unit B will be described.

  2 shows a tandem type image forming apparatus in which process cartridges 20Y, 20M, 20C, and 20K including a charging unit 8, a developing unit 3, a photosensitive drum 4, and a cleaning unit 9 are arranged. The charging means 8Y, 8M, 8C, and 8K included in the process cartridges 20Y to 20K are roller chargers. By applying a bias, the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K are uniformly negatively charged. Charge.

  The image data is converted into laser light via a laser driver and laser light sources 110Y, 110M, 110C, and 110K included in the printer image processing unit 109. The laser light is converted into polygon mirrors 1Y, 1M, 1C, and 1K, and mirrors 2Y, Each of the photosensitive drums 4Y to 4K reflected by 2M, 2C, and 2K and uniformly charged is irradiated. The photosensitive drums 4Y to 4K on which the latent images are formed by the scanning of the laser light rotate in the direction of the arrow A shown in the drawing.

  Reference numerals 3Y, 3M, 3C, and 3K denote developing means, each of which includes a yellow toner developing unit 3Y, a magenta toner developing unit 3M, a cyan toner developing unit 3C, and a black toner developing unit 3K for each of the process cartridges 20Y to 20K. . In this embodiment, a two-component developer including a magnetic carrier and a nonmagnetic toner is used as the developer.

  Here, taking the process cartridge 20Y as an example, the image forming process will be specifically described.

  The surface of the photosensitive drum 4Y of the process cartridge 20Y is uniformly charged by the charger 8Y (for example, −500 V in this embodiment). Next, exposure scanning is performed by exposure means that is ON / OFF controlled in accordance with the image data of the first color, and an electrostatic latent image of the first color (about −150 V in the present embodiment) is generated in the process cartridge. It is formed on a 20Y photosensitive drum 4Y. The electrostatic latent image of the first color is developed and visualized by a yellow developing device 3Y including yellow toner (-polarity) of the first color. The visualized first toner image is brought into pressure contact with the photosensitive drum 4Y with a predetermined pressing force, and is at a speed substantially equal to the peripheral speed of the photosensitive drum 4Y (in this embodiment, 273 mm / s 2) at the nip portion with respect to the intermediate transfer member 5 that is rotationally driven in the direction of arrow D, and is primarily transferred onto the intermediate transfer member 5.

  The toner remaining on the photosensitive drum 4Y without being transferred to the intermediate transfer member 5 in the primary transfer step is scraped off by a cleaning blade which is a cleaning means 9Y pressed against the photosensitive drum 4Y, and is disposed in a waste toner container (not shown). ).

  The same process as described above is performed for the other process cartridges 20M, 20C, and 20K, and toner images of different color toners are sequentially transferred and stacked on the intermediate transfer member 5 for each process cartridge. The recording material 6 is fed to the recording material 6 and is secondarily transferred to the recording material 6 and discharged to the outside through a fixing process by the fixing device 7 to be a full color print.

  Next, the outline of the laser optical system in the present embodiment will be described with reference to FIG.

  FIG. 5 is a diagram showing a state in which the photosensitive drum 4 is exposed using a laser optical system having a general configuration. The laser L is reflected by the rotary polygon mirror 42 installed on the rotary polygon mirror motor 41, passes through the optical system f-θ lens 43 so that the linear velocity is constant on the exposure surface, is reflected by the reflection mirror 44, and is photosensitive. Reach drum 4. However, the scanning line of the laser optical system mounted without any adjustment is inherently inclined and distorted, and when exposed as it is, it is exposed as shown in FIG. The scanning line scans on the photosensitive drum 4 with the influence of the inherent inclination and distortion. Conventionally, in order to scan the exposure scanning line on the photosensitive drum 4 without causing such inclination and distortion, expensive optical components have been used during assembly of the laser optical system, or precise fine adjustment has been performed on the apparatus itself. .

  In this example, without using such expensive parts or performing precise fine adjustment, the inclination and distortion of the inherent scanning line of the laser optical system are canceled by the method shown below, which is inexpensive and good. Achieves image quality.

  FIG. 6 shows a flow of a configuration for correcting the tilt and distortion of the laser optical system in this embodiment.

  In step 61, the profile of the tilt or distortion of the laser optical system is measured. Next, the scanning line profile data measured in step 62 is stored. In step 63, the printer main body reads the stored scanning line profile data. Next, first correction data is calculated from the profile of the scanning line read in step 64. In step 65, the input image data is rearranged according to the first correction data (first correction). Further, in step 66, smoothing processing is performed on the image rearranged in step 65 based on the first correction data (second correction). In step 67, the image created in step 66 is transmitted to the printer.

  Each item of Step 61 to Step 66 will be described in detail according to the flow shown in FIG.

(Scan line profile measurement)
In step 61, the scanning line profile such as the inherent tilt and distortion of the laser optical system is measured in advance during assembly.

  As shown in FIG. 7, the position in the sub scanning direction at each division point when the scanning line is divided into n in the main scanning direction (n is at least 3 or more, here n = 10 as an example) is defined as a profile point. N pieces of profile point data are obtained for each unit of each laser optical system.

(Retention of profile point data)
The profile point data measured in step 61 is stored in a storage medium such as an EPROM stored in the laser optical system unit, or, as a simple configuration, the data is encrypted as a bar code or the like and laser optical It is memorized and held by taking the configuration attached to the system unit body.

(Reading profile point data)
In the case of the former configuration at step 62, the stored profile point data is read from the EPROM of the laser optical system unit to the image forming apparatus main body at the time of assembly. Further, in the case of the latter configuration of step 62, a configuration in which an operator reads barcode data encrypted by using an encryption reading device such as a barcode reader at the time of assembly and reflects it in the image forming apparatus main body. To do.

  Even if the customer replaces the laser optical system unit after shipment, the profile point data corresponding to the laser optical system unit replaced from the EPROM held in the unit after the unit replacement is imaged. This is a configuration that is read into the main body of the forming apparatus. In the latter configuration, the bar code attached to the unit to be replaced by the service person is read with a bar code reader, or the laser is also replaced in the same way The profile point data corresponding to the optical system unit is read into the image forming apparatus main body.

(Calculation of first correction data)
Based on the profile point data of the n scanning lines read from the laser optical system unit to the image forming apparatus main body in step 63, a first correction amount is calculated from the deviation amount from each point and the ideal coordinates.

  Here, the calculation flow of the first correction data will be described with reference to FIG.

  In step 81 of FIG. 8A, first, as shown in FIG. 8B, the scanning lines divided by n pieces of n profile point data are approximated over the entire main scanning area. Here, in the present embodiment, the approximation and the linear approximation between two points of the point adjacent to the own point are used. Next, in step 82, the main scanning write position is set as a reference point among the approximate points in the entire main scanning area obtained in step 81. In step 83, the approximate point is checked from the reference point in the main scanning direction. If the difference ΔV in the sub-scanning direction from the reference point exceeds one pixel, the main scanning position of that point (point A) is offset in step 84. Points. Next, at step 86, the A + 1 point is reset as a new reference point. By performing the above steps 83 to 86 over the entire main scanning, the coordinates (X pieces) of points for performing offset in units of one pixel in the sub-scanning direction for correcting the inclination and distortion of the scanning line are obtained ( FIG. 8 (c)). The thus obtained first correction point data for performing X offsets includes coordinate information and information on the offset amount from the reference line, and these are referred to as first correction data.

(First correction)
Here, the configuration used in the first correction will be described with reference to FIG.

  (A) in FIG. 9 is a line buffer and is constituted by a RAM. In this embodiment, when the main scanning direction width is 297 mm and 600 dpi, correction data for about 7000 dots is written in the RAM. In this embodiment, the correction data is composed of, for example, 8 bits, and forms an offset line buffer 91 for the first correction with a signed binary number.

  FIG. 9B shows an offset line buffer 91 for the first correction.

In FIG. 9B, 92 is input image data, and 91 is an offset line buffer for the first correction. First, the coordinate information and offset amount information of the first correction data calculated in step 94 are read into the offset line buffer 91 for the first correction. That is, as shown in FIG. 9B, the offset amount Y _n is set with respect to the coordinate X _n of the first correction point, and the image data at the position where the number of sub-scanning lines with the number offset is corrected is extracted. The corrected bitmap data 93 subjected to the first correction is created by rearranging the data.

(Second correction)
The correction bitmap data rearranged by the first correction in step 65 is subjected to a smoothing process in the second correction.

  FIG. 10 is a configuration diagram used in the second correction.

  (A) in FIG. 10 is a line buffer and is constituted by a RAM. In this embodiment, when the main scanning direction width is 297 mm and 600 dpi, correction data for about 7000 dots is written in the RAM. In this embodiment, the smoothed data is composed of, for example, 8 bits, and constitutes a smoothing line buffer 101 for the second correction.

  FIG. 10B shows a second correction flow.

In step 101 of FIG. 10B, first, the bitmap data Img (x) of the main scanning coordinate x at the correction point X _n of the first correction data calculated in step 94 and the coordinate x one before in the main scanning direction are used. −1 bit map data Img (x−1) is compared. If Img (x) <Img (x−1), the region X _{n + 1} −X _n between the next correction point X _{n + 1} and the correction point X _n is calculated and smoothed in step 102. Region S is assumed. In step 103, if Img if was (x)> Img (x- 1), calculates the area X _n-1 -X _n of the previous correction points X _n-1 and the correction point X _n in step 104 The smoothing region S is obtained.

  Next, in step 105, a dot of less than one pixel is applied to the white data region (Img (x) = 0) adjacent to the correction point and the length | S | obtained in steps 102 and 104. Use to smooth. In this embodiment, a configuration is employed in which pixels are formed using 16-division PWM per pixel. That is, the smoothing process is performed using 16 levels of exposure corresponding to the pulse width.

  Here, in this embodiment, the input image signal value is configured to modulate the pulse width in accordance with a preset pulse width table as shown in FIG. If the sign of the smoothing section S obtained in steps 102 and 104 is positive, the pixel is in the forward order of the pulse width table. If the sign of the smoothing section S is negative, one pixel is in the reverse order of the pulse width table. Smoothing processing is performed by sequentially forming less than dots.

  The configuration of the smoothing line buffer 101 for the second correction used in the second correction is the same as the configuration of the offset line buffer 91 for the first correction used in the first correction. Therefore, in the present embodiment, it is described with another configuration for explanation, but in practice, the same line buffer can be used.

  FIG. 11 shows an image of the image correction so far.

  12A is an image diagram in which the first correction is performed. When the second correction is performed on the image in FIG. 12, the image shown in FIG. 12B is obtained. When the corrected image data of (b) is laser-exposed, a latent image is formed with an image as shown in (c), and when this latent image is formed, an image as shown in (d) is obtained as a result. It is done. The black triangles in the figure are the offset points where the first correction has been performed.

  By sequentially performing the first correction process and the second correction process as described above, the image data can be corrected based on the profile such as the inclination and distortion of the scanning line.

  However, in a full-color image forming apparatus having a plurality of laser optical systems, the inclination and distortion of the scanning line for each color are different. Therefore, when the correction processing as described above is performed, the first correction is performed for each color. The distribution of the offset points is different, that is, the area where the second correction smoothing process is performed is also different for each color, and the probability of occurrence of adverse effects such as density steps in the correction area and color moire as the number of colors to be overlaid increases. Becomes higher.

  For example, in a halftone area of a full-color image, a pseudo halftone process having a systematic structure such as dither as shown in FIGS. 13A and 13B in order to place importance on gradation, graininess, and stability. Is generally used, but when the first correction and the second correction described above are performed on such a region, smoothing which is the second correction as shown in FIG. 14 depending on the density region. A case where a density step is generated by the processing can be considered. Such a density step is manifested by the fact that the correction area is different for each color when colors are superimposed when forming a full-color image rather than a single color. However, when the second correction process is not performed on such a pseudo-halftone area, the phase shift of the systematic structure of dither occurs, and the gradation becomes discontinuous, as shown in FIG. There is also a harmful effect that appears in the form of streaks. In FIG. 15, black triangles in the drawing indicate offset points by the first correction.

  In this embodiment, therefore, in addition to the first correction and the second correction, pseudo halftone processing having no texture structure is used in combination with at least one color.

  FIG. 16 shows an error diffusion process as an example of a pseudo halftone process having no organization structure. As shown in FIG. 16, in the error diffusion process, the discontinuous error is distributed to the adjacent pixels of the pixel of interest, and therefore there is no systematic structure compared to the dither process shown in FIG. There is. Therefore, even when the first correction is performed as shown in FIG. 17, the phase shift of the structure does not occur at the offset point (black triangle in the figure), and therefore the second correction need not be performed.

  However, as described above, when using pseudo halftone processing that does not have a systematic structure such as error diffusion processing, a structure in which dots grow systematically continuously with adjacent pixels, such as dither processing, is used. Therefore, when the dot reproduction is unstable, there is a problem that the gradation expression becomes unstable due to the influence. In addition, since the dots are irregularly arranged, there is a problem that the graininess is lowered particularly in the low and medium density regions. Here, the experiment result of the present inventor showing the relationship between the lightness L * of the color material and the granularity is shown. According to the experiments of the present inventor, a toner image formed when a maximum signal is inputted is a toner A having a lightness L * of 20, a toner B having L * = 50, a toner C having L * = 60, For the four types of toner D, which is L * = 70, granularity is measured by performing two types of pseudo halftone processing, dither processing having a structured structure and error diffusion processing having no structured structure. As a result, a result as shown in FIG. 18 was obtained. In FIG. 18, the vertical axis is an index indicating the granularity, and indicates that the granularity is lower as it goes up and the granularity is better as it goes down. According to this, the toners A and B having low brightness have a large difference in granularity between the dithering process and the error diffusion process, and the granularity is lowered when the error diffusion process having no systematic structure is used. I understand. On the other hand, it can be seen that toners C and D having high brightness have almost no difference in granularity due to pseudo halftone processing such as dither processing and error diffusion processing.

  For these reasons, in this embodiment, in order to suppress the adverse effects of the first correction and the second correction as much as possible, and to prevent the negative effects of normal image reproduction, an error diffusion process is performed for a color material with high brightness. Are used to perform pseudo halftone processing and only the first correction is performed, and for other color materials, pseudo halftone processing is performed using normal dither processing, and the first correction and the second correction are performed. It is set as the structure performed together. It is considered that the color material having a high lightness here is preferably a color having L * of 60 or more in the chromaticity of the maximum density from the experiment of the present inventors. For example, in the case of a general full-color image forming apparatus composed of four colors of cyan, magenta, yellow, and black, in this embodiment, only yellow is used for error diffusion processing.

  FIG. 19 shows a block diagram of the present embodiment.

  In FIG. 19, among the input image signal 191, low brightness color signals of cyan, magenta, and black are dithered in the halftone processing circuit 192 as shown in (a), while yellow, which is a high brightness color signal, As shown in (b), the halftone processing circuit 192 performs error diffusion processing. Next, the first correction circuit 193 performs first correction processing according to the offset amount calculated from the scanning line profile for both the low lightness color signal (a) and the high lightness color signal (b). The first correction circuit 193 performs the first correction processing shown in FIGS. 8 and 9 in the same manner for the low lightness color signal (a) and the high lightness color signal (b). Thereafter, the low lightness color signal (a) is subjected to the second correction processing for the section of length | S | obtained in steps 102 and 104 as shown in FIGS. However, the high brightness color signal (b) does not pass through the second correction circuit 194 and does not perform the second correction. Thereafter, the low lightness color signal (a) subjected to the second correction process and the high lightness color signal (b) not subjected to the second correction process are synthesized again to become an output image signal 195, and an image is formed. .

  Here, an example of an image forming apparatus composed of four color materials of cyan, magenta, yellow, and black, which is often used in a general full-color image forming apparatus, has been described. However, in recent years, the above four colors have been added for the purpose of further subtracting image quality. In addition, a high-quality full-color image forming apparatus that forms an image by adding special colors such as light light cyan, light magenta, or gray has been proposed. Of course, the present embodiment can be easily applied in such a case. In this case, a light color such as light cyan, light magenta, and gray having high brightness is used as the error diffusion process in addition to the yellow.

  As described above, in this embodiment, the density step generated by performing the streak at the offset point generated by the first correction or the second correction for the pseudo halftone processing region where the colors are overlapped at the time of full-color image formation. In order to reduce the brightness, for example, pseudo-halftone processing having no systematic structure such as error diffusion processing is performed for high brightness colors, and only the first correction processing is performed and the second correction processing is performed. The configuration is not implemented. With this configuration, no streak generated by the first correction or a density step caused by the second correction does not occur in the high-brightness color pseudo-halftone processing region, so that it is possible to reduce image defects during full-color image formation. .

DESCRIPTION OF SYMBOLS 3 Developing device 4 Photosensitive drum 5 Intermediate transfer body 6 Recording material 7 Fixing device 8 Charger 9 Cleaner 20 Process cartridge 41 Rotating polygon mirror 42 Rotating polygon mirror 43 f-θ lens 44 Reflecting mirror 91 Offset line buffer 101 For smoothing Line buffer

Claims (4)

An image having a photoconductor, a rotary polygon mirror that deflects the light beam so that a light beam scans the photoconductor, and an optical member that guides the light beam deflected by the rotary polygon mirror to the photoconductor An image forming apparatus in which forming units are provided corresponding to a plurality of colors,
In order to correct the image distortion caused by the curve of the scanning line of the light beam that scans the photoconductor, and performs dither processing or error diffusion halftone processing on the image data corresponding to each of the plurality of colors Performing image data processing for shifting the image in the rotation direction of the photoconductor for each of the plurality of regions corresponding to the plurality of colors in the scanning direction of the light beam, and smoothing the image subjected to the image data processing Data processing means capable of executing smoothing processing of image data for
Control means for controlling the image forming means based on the image data processed by the data processing means,
The data processing means performs the error diffusion processing and the image data processing on image data of at least one color among the plurality of colors, and does not perform the smoothing processing, and among the plurality of colors Performing the error diffusion process and the image data process, and performing the dither process, the image data process, and the smoothing process on image data of at least one color other than the color for which the smoothing process is not performed. An image forming apparatus. 2. The image formation according to claim 1, wherein the data processing unit performs the error diffusion process on the image data having the highest brightness among the plurality of colors and does not perform the smoothing process. apparatus. The data processing means executes the error diffusion process on image data of a color having a lightness L * of a toner image formed when the image data has a maximum value, and does not execute the smoothing process. The image forming apparatus according to claim 1 , wherein the image forming apparatus is an image forming apparatus. Wherein the data processing means, an image forming apparatus according to any one of claims 1 to 3, wherein varying the amount of exposure by modulating the pulse width in accordance with the pulse width table set in advance.

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