JP6504773B2 - IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD, AND PROGRAM - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program for an image forming apparatus that provides a printed material with high in-plane density uniformity.

  As an apparatus for forming an image on a recording medium (hereinafter, also referred to as “paper” or “paper”), there is an electrophotographic image forming apparatus (hereinafter, also referred to as “electrophotographic printer”). In an electrophotographic printer, a photosensitive drum is exposed to light such as a laser according to an image signal input to the printer to form an electrostatic latent image. Next, a toner, which is a coloring material, is developed on the electrostatic latent image to form a visible image. Thereafter, the toner developed on the photosensitive member is generally primarily transferred to an intermediate transfer belt (hereinafter also referred to as "intermediate transfer member"), and secondarily transferred from the intermediate transfer member to a recording medium. An image is formed by fixing the toner on the recording medium by heating and pressurizing the transferred toner.

  In recent years, using an exposure apparatus (hereinafter, also referred to as "light emitting element array" or "laser array") in which a plurality of light emitting elements are arranged in an array, the width of the array on the photosensitive drum is obtained by one main scan. Adoption of a multi-beam exposure method for accelerating the speed of exposure processing is progressing by performing latent image formation.

  In the above-described multi-beam exposure method, it is possible to realize high-speed image formation, but the exposure amount (hereinafter also referred to as “emission amount”) changes depending on switching of light emission / non-light emission of adjacent light emitting elements. There is a problem of so-called crosstalk.

  The aforementioned crosstalk problem will be described with reference to FIGS. FIG. 1 shows a binary image after halftone processing (hereinafter, also referred to as “halftone processing”) which is quantization processing on a multi-valued image. The gray hatched pixels in FIG. 1 are pixels that are dot on (hereinafter also referred to as “on pixels”), and are pixels that are exposed by the exposure device. In addition, white pixels are pixels in which dots are off, and are pixels that are not exposed by the exposure device (hereinafter, also referred to as “off pixels”). Note that a set of dot-on pixels after halftone processing is generally called a halftone dot. The direction indicated by the arrow in the main scanning direction in FIG. 1 is the main scanning direction of the laser. Pixels at the same vertical pixel position are exposed by the same element in the laser array. The exposure apparatus causes the element to emit light at the timing when the dot is on in synchronization with the scanning of the laser array. Here, elements for exposing the vertical pixel positions L1, L2, L3, and L4 are LD1, LD2, LD3, and LD4.

  FIG. 2 is a graph showing the exposure intensity with respect to the laser scanning position. FIG. 2A shows the exposure intensity of the element LD2 that exposes the vertical pixel position L2. FIG. 2B shows the exposure intensity of the element LD3 that exposes the vertical pixel position L3. In FIG. 2A, exposure is performed at horizontal pixel positions C3, C4 at which the dots are turned on at the vertical pixel position L2, and at horizontal pixel positions C2, C3, C4 where the dots are turned on at the vertical pixel position L3 in FIG. There is a rise in strength. The solid line in FIG. 2B indicates the change in exposure intensity when there is no crosstalk, and the dotted line indicates the change in exposure intensity when there is crosstalk. As shown in FIG. 2A, the element LD2 does not emit light at the horizontal pixel position C2, but starts emitting light at the horizontal pixel position C3. Under the influence of the emission of light from the element LD2 at the vertical pixel position L2, as can be seen from the dotted line in FIG. 2B, the exposure intensity temporarily increases compared to the case where there is no crosstalk at the horizontal pixel position C3. A phenomenon called overshoot occurs. As a result, at the horizontal pixel position C3, the exposure amount becomes larger than that of the other ON pixels. Depending on the type of exposure apparatus, the phenomenon of undershoot that is opposite to overshoot may occur, and the exposure amount may be smaller at a certain horizontal pixel position than the other ON pixels.

  As a technique for solving the above-mentioned problems, there is a technique of shaping a light waveform to be outputted by providing a circuit for intentionally generating an overshoot and controlling an overshoot amount according to the position of the element (Patent Document 1) ). Further, there is disclosed a technique for variably controlling the laser power of the isolated dot so that the exposure energy of the isolated dot is equal to the exposure energy of the continuous dot (Patent Document 2). Furthermore, in order to improve the reproducibility of isolated dots, a calibration method is also disclosed in which the laser power is determined by measuring the density of a chart formed with different laser power for each light emitting element (Patent Document 3) ).

Unexamined-Japanese-Patent No. 2003-266763 Unexamined-Japanese-Patent No. 2002-292929 JP, 2008-134326, A

  However, in the multi-beam exposure method, a halftone dot (i.e., a halftone dot formed by two main scans) located at the junction between one main scan and the next main scan of the laser array There is a problem that the shape and the density are different from those of halftone dots formed by the main scanning. This problem will be described with reference to FIGS.

  FIG. 3 is a schematic view showing the correspondence between the element numbers of the laser array and the halftone image in each main scan. In the multi-beam exposure method, in order to obtain high resolution even for a laser array in which it is difficult to densify the light emitting elements, as shown in FIG. 4, they are often arranged obliquely with respect to the main scanning direction. The description will be made using a laser array disposed perpendicular to the main scanning direction as shown in FIG. An image 301 is a halftone dot image composed of a plurality of halftone dots. The gray hatched pixel in each pixel in FIG. 3 is a dot-on pixel. The laser array 302 is a laser array in which 32 elements are arranged. The halftone dots 303 are exposed by the 26th and 27th elements of the laser array 302, and the exposure is completed only by the Nth main scan. On the other hand, in the halftone dot 304, the upper 32 pixels of the laser array 302 are exposed in the N-th main scan, and the lower 1 pixel in the (N + 1) -th main scan is exposed Is exposed. At this time, since the halftone dot 303 causes crosstalk due to the light emission of the adjacent element as described above, the exposure intensity distribution similar to that of the dotted line in FIG. become. On the other hand, since the halftone dot 304 is formed by two main scans, it is not affected by the light emission of the adjacent element, so the lower three pixels constituting the halftone dot 304 are indicated by the solid line in FIG. It becomes exposure intensity distribution similar to. That is, the sum of the exposure to the halftone dot 304 is smaller than the sum of the exposure to the halftone dot 303, which causes the shape of the halftone dot to be smaller and the density to be thinner. Since this phenomenon occurs periodically in units of the width of the laser array, streak unevenness called banding and moire due to interference with the screen occur.

  The prior art mentioned above does not consider the halftone dots located at the seam of the laser array. Using the prior art described above, the exposure amount between the halftone dots (dots formed by two main scans) at the seam of the laser array and the halftone dots formed by one main scan In the case of performing correction so as to eliminate the difference, there is a problem that it is necessary to specially provide a dedicated circuit for laser power correction. In addition, even if the influence of crosstalk is suppressed using other methods, banding and moire will occur unless the output light waveform such as overshoot and undershoot is suppressed to a negligible error.

  The present invention has been made in view of the above problems. An object of the present invention is to suppress banding and moire in a multi-beam exposure type electrophotographic image forming apparatus.

The present invention is an image processing apparatus for an image forming apparatus for forming a latent image on an image carrier by a light emitting element array composed of a plurality of light emitting elements, and exposure of a target dot is one time of the light emitting element array. Based on the result of the determination by the determination means and the light emission information. And control means for controlling an exposure amount to the noted halftone dot , wherein the light emission information is for each dot in the halftone dot for the halftone dot whose exposure is completed by one main scan of the light emitting element array. Light emission information of a light emitting element adjacent to the light emitting element to be exposed .

  According to the present invention, it is possible to suppress the occurrence of banding and moire in a multi-beam exposure type electrophotographic image forming apparatus.

A diagram showing a binary image after halftone processing Graph showing exposure intensity against laser scanning position A schematic diagram showing the correspondence between the element number of the laser array and the dot image in each main scan A schematic view of a laser array disposed obliquely to the main scanning direction in the multi-beam exposure method Block diagram showing the functional configuration of the image forming apparatus It is a structural example of the image formation part of the 1 drum type electrophotographic recording system. Flow chart showing the flow of processing for calculating the exposure correction amount Graph showing pulse signal to laser scanning position for explaining exposure correction Flow chart showing the flow of processing for calculating the exposure correction amount Graph showing pulse signal to laser scanning position for explaining exposure correction Block diagram showing the functional configuration of the image forming apparatus Block diagram showing the functional configuration of the image forming apparatus

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

Example 1
(Functional configuration)
FIG. 5 is a block diagram showing the functional configuration of the image forming apparatus according to this embodiment. As shown in FIG. 5, the image forming apparatus includes an image input unit 501, a color conversion processing unit 502, a color separation processing unit 503, a quantization processing unit 504, a PWM processing unit 505, and an image forming unit 506. Equipped with PWM is an abbreviation for pulse width modulation. The image forming apparatus also includes a color separation LUT (look-up table) storage unit 507, an exposure correction amount calculation unit 508, and a laser array information storage unit 509. In this embodiment, the image forming apparatus includes an image input unit 501, a color conversion processing unit 502, a color separation processing unit 503, a quantization processing unit 504, and an image processing for executing image processing such as a PWM processing unit 505. The case where the image forming unit 506 is built in will be described as an example. However, for example, an image processing apparatus including an image input unit 501, a color conversion processing unit 502, a color separation processing unit 503, a quantization processing unit 504, and a PWM processing unit 505 may function as an external device. Alternatively, the processing from the image input unit 501 to the quantization processing unit 504 is executed by an external device such as a PC, and the PWM processing unit 505, the exposure correction amount calculation unit 508, the laser array information storage unit 509, the image forming unit 506 It may be incorporated in the image forming apparatus. At that time, the exposure correction amount calculation unit 508 and the laser array information storage unit 509 can be configured as one image processing apparatus and can be made independent of the other configurations. PC is an abbreviation of personal computer.

  An image to be printed is input to the image input unit 501.

  The color conversion processing unit 502 performs mapping processing for mapping from signal values (for example, RGB values or CMYK values) of an input image to a device-independent color space (for example, CIE L * a * b * or CIE XYZ). Do. Since the color reproduction range of the printer is generally narrower than the color reproduction range of the monitor, the color conversion processing unit 502 performs conversion processing for color compression into a color reproducible by the printer. This conversion process is performed based on, for example, a look-up table (LUT) in which the correspondence of L * a * b * values to RGB values is described. However, the present invention is not limited to the use of a LUT, and may be matrix operation.

  The color separation processing unit 503 is a signal value (for example, a CMYK value) of each color material color installed in the image forming apparatus from the value of the device-independent color space acquired by the conversion in the color conversion processing unit 502. Conversion processing to “color separation value” or “tone value”. The conversion method may be a known method and is not particularly limited. For example, by referring to a color separation LUT in which the correspondence between L * a * b * values and CMYK values is described stored in the color separation lookup table (LUT) storage unit 507, device-independent colors can be obtained. The values of space are converted into signal values of respective color materials.

  The quantization processing unit 504 performs quantization processing on the image data having the signal value of each color material color acquired by the conversion in the color separation processing unit 503. For example, it is assumed that the output of the color separation processing unit 503 is 600 dpi 8-bit (256 gradation) image data. This image data is divided by the quantization processing unit 504 by the main scanning resolution and the sub scanning resolution in the image forming unit 506, for example, 1 bit (two gradations) serving as on / off information for each pixel of 1200 dpi. It is converted into data to form so-called halftone dots.

  The details of the exposure correction amount calculation unit 508 will be described later, but the 1-bit image data acquired by quantization in the quantization processing unit 504 and the seam of the laser array stored in the laser array information storage unit 509. The exposure correction amount for the pixel of interest is calculated using the information on.

  The PWM processing unit 505 uses the pulse signal for exposure based on the 1-bit image data acquired by the quantization processing unit 504 and the exposure correction amount calculated by the exposure correction amount calculation unit 508. Perform pulse width modulation processing to control the width. The exposure signal data subjected to pulse width modulation processing by the PWM processing unit 505 is sent to the image forming unit 506.

(Configuration of image forming unit)
The image forming unit 506 will be described below with reference to FIG. FIG. 6 is a configuration example of the image forming unit 506 of a one-drum type electrophotographic recording method (also referred to as an electrophotographic method). As shown in FIG. 6, the image forming unit 506 includes a laser diode 6001, a polygon mirror 6002, a photosensitive drum 6003, an exposing unit 6004, a charging unit 6005, a developing unit 6006, and a photosensitive drum cleaner 6012. The image forming unit 506 further includes an intermediate transfer belt 6007, a primary transfer device 6008, and an intermediate transfer belt cleaner 6018. In the case of a single-drum type, a plurality of color developing devices 6006C (cyan), 6006M (magenta), 6006Y (yellow), 6006K (black), laser diode, polygon mirror, photosensitive drum, exposure unit, charger, primary transfer Share the photosensitive drum cleaner.

  The image forming unit 506 also includes a secondary transfer device 6009, a paper feed tray 6013 for setting the recording medium 6010, a registration roller 6014 for conveying the recording medium to the secondary transfer device at an appropriate timing, and a fixing device 6011. Equipped with In addition, the image forming unit 506 includes a sheet discharge roller 6015, a sheet discharge tray 6016, and a conveyance path 6017 through which the sheet is passed in duplex printing.

  The laser diode 6001 emits a laser beam based on the signal data for exposure generated by the PWM processing unit 505 described above. The emitted laser light passes through a polygon mirror 6002 and an fθ lens (not shown), and is exposed and scanned on a photosensitive drum 6003 which is an image carrier rotating in the direction of the arrow. Thus, an electrostatic latent image is formed on the photosensitive drum 6003.

  The photosensitive drum 6003 is uniformly discharged by the exposure unit 6004, and then uniformly charged by the charging unit 6005. Thereafter, in response to an exposure scan of laser light emitted from the laser diode 6001, an electrostatic latent image corresponding to binary image data is formed on the photosensitive drum 6003. Then, this electrostatic latent image is developed (visualized) as a visible image (toner image) by the toner supplied from the developing device 6006.

  The developed toner image is transferred by the action of the primary transfer device 6008 onto an intermediate transfer belt 6007 which is stretched between a plurality of rollers and endlessly driven.

  This operation is repeated while switching the developing devices 6006 C, 6006 M, 6007 Y, and 6006 K of the respective colors used in the developing device 6006 to form toner images of a plurality of colors sequentially transferred onto the intermediate transfer belt 6007.

  On the other hand, the recording medium 6010 is conveyed from the paper feed tray 6013 to the registration roller 6014, and conveyed by the registration roller 6014 to the secondary transfer device 6009 at an appropriate timing. Then, the toner images of a plurality of colors transferred onto the intermediate transfer belt 6007 are transferred onto the conveyed recording medium 6010 by the secondary transfer device 6009. After transfer, the recording medium 6010 is conveyed and passes through the fixing device 6011. At this time, the fixing device 6011 fixes the toner image on the recording medium 6010 by performing a heating process and a pressure process. After that, when “no execution of double-sided printing” is set, the recording medium 6010 is discharged onto the discharge tray 6016 by the discharge roller 6015. On the other hand, when “execution of double-sided printing is set” is set, the rear end of the recording medium 6010 is chucked by the discharge roller 6015. Next, the recording medium 6010 is guided to the conveyance path 6017 by the reverse rotation of the paper discharge roller 6015, and conveyed to the registration roller 6014. The recording medium 6010 is again conveyed to the secondary transfer device 6009 by the registration roller 6014 at an appropriate timing, and after the transfer and fixing of the toner image of the second side (for back side) image is performed, Exhausted.

  The residual toner remaining on the photosensitive drum 6003 is scraped off by the photosensitive drum cleaner 6012 and collected. Further, after the recording medium 6010 is discharged, the residual toner remaining on the intermediate transfer belt 6007 is scraped off by an intermediate transfer belt cleaner 6018 configured by a blade or the like.

  In the above description, the one-drum type electrophotographic recording type image forming unit 506 is described as an example. However, the present embodiment is also applicable to an image forming apparatus adopting a tandem-type electrophotographic recording method in which each developing device of a plurality of colors has a mechanism, or another recording method.

(Exposure correction method)
The method of calculating the exposure correction amount executed by the exposure correction amount calculation unit 508 will be described in detail with reference to FIG. FIG. 7 is a flowchart showing a flow of processing for calculating the exposure correction amount according to the present embodiment. The following process is not shown in the figure but is performed for each halftone dot, and is repeated until the process is completed for all halftone dots constituting the halftone image.

  In step S701 (hereinafter, abbreviated as "S701". Other steps are similarly abbreviated.), The exposure correction amount calculation unit 508 determines that the halftone dot to be focused on (hereinafter, also referred to as "dot to be focused") is a laser array. It is determined whether or not it intersects with the joint of Information indicating which pixel the seam of the laser array (light emitting element array) is located in the sub-scanning direction is stored in the laser array information storage unit 509. The determination in step S701 is performed based on the position of the seam of the laser array and the position of the halftone dot formed by the quantization processing unit 504. If it is determined that the target halftone dot does not cross the seam of the laser array, the processing of this flow is completed. Therefore, in this case, the correction of the exposure amount to the noted halftone dot is not performed. If it is determined that the halftone dot of interest intersects the seam of the laser array, the process advances to step S702.

  In S702, the exposure correction amount calculation unit 508 acquires light emission information of the adjacent element for each pixel in the steady state halftone dot having the same shape as the shape of the target halftone dot. More specifically, considering that the halftone dot having the same shape as the shape of the halftone dot completes the exposure in one main scan, the light emission adjacent to the light emitting element that exposes each pixel in the halftone dot The light emission information of the element is acquired. In the present specification, a halftone dot whose exposure is completed in one main scan is referred to as a "steady-state halftone dot". The method of acquiring the light emission information of the adjacent element will be described by taking FIG. 1 described above as an example. Referring to FIG. 1, when the pixel (L2, C3) emits light, there is no switching of light emission / non-light emission in the upper pixel (L1, C3) and the lower pixel (L3, C3). When the pixel (L2, C4) emits light, there is no switching of light emission / non-light emission in the upper pixel (L1, C4) and the lower pixel (L3, C4). When the pixel (L3, C2) emits light, there is no switching of light emission / non-light emission in the upper pixel (L2, C2) and the lower pixel (L4, C2). When the pixel (L3, C3) emits light, the lower pixel (L4, C3) does not switch emission / non-emission, but the upper pixel (L2, C3) switches emission / non-emission. When the pixel (L3, C4) emits light, there is no switching of light emission / non-light emission in the upper pixel (L2, C4) and the lower pixel (L4, C4). As described above, by acquiring the light emission information of the adjacent element, the information that the target halftone dot is affected by crosstalk from only one pixel (L3, C3) in the steady state is acquired in S702.

  In S703, the exposure correction amount calculation unit 508 determines an exposure correction amount based on the information acquired in S702. For example, in halftone dot 303 in FIG. 3, the exposure amount increases due to the influence of crosstalk, but in halftone dot 304 in FIG. 3, there is a seam of the laser array between upper two pixels and lower three pixels. It is not affected by crosstalk and the exposure dose does not increase. The exposure correction amount can be calculated based on the crosstalk amount when the pixel of interest is affected by crosstalk from surrounding pixels and the information acquired in S702. Alternatively, as shown in FIG. 2B, the area difference between the part surrounded by the dotted line and the part surrounded by the solid line represents the difference in exposure amount due to the influence of crosstalk, so this area The difference may be determined as the exposure correction amount. Furthermore, the crosstalk amount corresponding to the shape of the halftone dot in the steady state is held in advance, and among the held crosstalk amounts, one corresponding to the shape of the halftone dot formed by the quantization processing unit 504 is selected. The amount of exposure correction may be determined by appropriately selecting. Here, although a small halftone dot having a vertical width of 2 pixels and a horizontal width of 3 pixels is described as an example, the present embodiment can also be applied to the case where the halftone dot is large.

  The PWM processing unit 505 converts the 1-bit image signal into a pulse signal for exposure based on the above-described exposure correction amount. FIG. 8 shows pulse signals for the laser scanning position. FIG. 8A is a pulse signal of the vertical pixel position L3 in the halftone dot shape of FIG. 1 when the exposure correction is not performed. FIG. 8B is a pulse signal of the vertical pixel position L3 in the halftone dot shape of FIG. 1 when the exposure correction is performed. In FIG. 8B, the halftone dot of interest is added by adding the exposure amount corresponding to the exposure variation due to the crosstalk that occurs when the halftone dot having the same shape as the halftone dot does not intersect the seam of the laser array. The exposure amount of That is, as can be seen from FIG. 8B, in order to increase the exposure amount corresponding to the exposure amount variation due to crosstalk at the horizontal pixel position C3, the pulse width at the horizontal pixel position C3 is wider than FIG. Do. Although the method of correcting the exposure amount by PWM control, which is pulse width modulation processing, has been described, the exposure amount may be corrected by PAM control, which is pulse amplitude modulation processing. PAM is an abbreviation of pulse amplitude modulation. FIG. 8C shows an example of exposure amount correction by PAM control. As shown in FIG. 8B, it can be seen that instead of widening the pulse width at the horizontal pixel position C3, the pulse amplitude is increased without changing the pulse width. On the other hand, in the case of a laser array having a characteristic that the exposure amount decreases due to the occurrence of an undershoot when the halftone dots do not intersect the seam of the laser array, the halftone dot of interest intersects the seam of the laser array If it is a halftone dot, the amount of exposure to the target halftone dot is reduced.

  As described above, by performing the exposure correction described above, a halftone dot formed by two main scans located at a junction between main scans of the laser array and a halftone dot formed by one main scan. By correcting the difference in the amount of exposure between them, the occurrence of banding and moire can be suppressed.

Example 2
In the first embodiment, the exposure amount between halftone dots located at the seam of the laser array is increased (or decreased) to provide exposure between the halftone dots located at the steady state and the halftone dots located at the seam of the laser array. The method of correcting to eliminate the difference in quantity has been described. However, conversely, the exposure of halftone dots not located at the seam of the laser array (that is, halftone dots in steady state) may be corrected. This method will be described with reference to FIGS. In addition, since the other structure is the same as that of Example 1, description is omitted.

  FIG. 9 is a flowchart showing a flow of processing for calculating the exposure correction amount according to the present embodiment. The following process is not shown in the figure but is performed for each halftone dot, and is repeated until the process is completed for all halftone dots constituting the halftone image.

  In S901, the exposure correction amount calculation unit 508 determines whether the halftone dot of interest intersects the seam of the laser array. Information indicating which pixel the seam of the laser array is positioned in the sub-scanning direction is stored in the laser array information storage unit 509. The determination in step S901 is performed based on the position of the seam of the laser array and the position of the halftone dot formed by the quantization processing unit 504. If it is determined that the target halftone dot intersects the seam of the laser array, the processing of this flow is completed. Therefore, in this case, the correction of the exposure amount to the noted halftone dot is not performed. If it is determined that the target halftone dot does not intersect the seam of the laser array, the process proceeds to step S902.

  In step S902, the exposure correction amount calculation unit 508 acquires light emission information of the adjacent element for each pixel in the target halftone dot from the shape of the target halftone dot. The target halftone dot to be processed in S902 is a steady-state halftone dot formed only by one main scan, which does not intersect the seam of the laser array (determined as NO in S901). The method of acquiring the light emission information of the adjacent element is the same as that of the first embodiment. For example, in S902, the information that the target halftone dot is affected by crosstalk from only one pixel (L3 and C3) in FIG. It is acquired.

  In S903, the exposure correction amount calculation unit 508 determines an exposure correction amount based on the information acquired in S902. For example, in halftone dot 303 in FIG. 3, the exposure amount increases due to the influence of crosstalk, but in halftone dot 304 in FIG. 3, there is a seam of the laser array between upper two pixels and lower three pixels. It is not affected by crosstalk and the exposure dose does not increase. The exposure correction amount can be calculated based on the crosstalk amount when the pixel of interest is affected by crosstalk from surrounding pixels and the information acquired in S702. Alternatively, as shown in FIG. 2B, the area difference between the part surrounded by the dotted line and the part surrounded by the solid line represents the difference in exposure amount due to the influence of crosstalk, so this area The difference may be determined as the exposure correction amount. Furthermore, the crosstalk amount corresponding to the shape of the halftone dot in the steady state is held in advance, and among the held crosstalk amounts, one corresponding to the shape of the halftone dot formed by the quantization processing unit 504 is selected. The amount of exposure correction may be determined by appropriately selecting.

  The PWM processing unit 505 converts the 1-bit image signal into a pulse signal for exposure based on the above-described exposure correction amount. FIG. 10 shows pulse signals for laser scanning positions. FIG. 10A is a pulse signal of the vertical pixel position L3 in the halftone dot shape of FIG. 1 when the exposure correction is not performed. FIG. 10B is a pulse signal of the vertical pixel position L3 in the halftone dot shape of FIG. 1 when the exposure correction is performed. In FIG. 10B, the exposure amount of the noted halftone dot is corrected so as to offset the exposure amount fluctuation due to the crosstalk in the noted halftone dot. That is, as can be seen from FIG. 10 (b), the pulse width at the horizontal pixel position C3 is narrowed from FIG. 10 (a) in order to reduce the exposure amount corresponding to the exposure amount fluctuation due to crosstalk at the horizontal pixel position C3. Do. Although the method of correcting the exposure amount by PWM control, which is pulse width modulation processing, has been described, the exposure amount may be corrected by PAM control, which is pulse amplitude modulation processing. FIG. 10 (c) shows an example of exposure amount correction by PAM control. It can be seen that instead of narrowing the pulse width at the horizontal pixel position C3 as shown in FIG. 10B, the pulse amplitude is reduced without changing the pulse width. Conversely, in the case of a laser array having a characteristic that the exposure amount decreases due to the occurrence of an undershoot when the halftone dots do not intersect the seam of the laser array, the halftone dot does not intersect the seam of the laser array If it is a halftone dot, the amount of exposure to the target halftone dot is increased.

  As described above, by performing the exposure correction described above, a halftone dot formed by two main scans located at a junction between main scans of the laser array and a halftone dot formed by one main scan. By correcting the difference in the amount of exposure between them, the occurrence of banding and moire can be suppressed.

[Example 3]
In the first and second embodiments, the method of correcting the exposure amount to the target halftone dot by PWM control or PAM control has been described, but in the present embodiment, a method of correcting the halftone dot shape by color separation processing will be described. In addition, since the other structure is the same as that of Example 1, description is omitted.

  FIG. 11 is a block diagram showing a functional configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 11, the image forming apparatus includes an image input unit 1101, a color conversion processing unit 1102, a color separation processing unit 1103, a quantization processing unit 1104, a PWM processing unit 1105, and an image forming unit 506. Equipped with The image forming apparatus also includes a color separation LUT storage unit 1106 and a laser array information storage unit 1107.

  An image to be printed is input to the image input unit 1101.

  The color conversion processing unit 1102 performs mapping processing for mapping from signal values (for example, RGB values or CMYK values) of an input image to a device-independent color space (for example, CIE L * a * b * or CIE XYZ). Do.

  The color separation processing unit 1103 generates signal values (for example, CMYK values) of the respective color materials installed in the image forming apparatus from the device-independent color space values acquired by the conversion in the color conversion processing unit 1102. Perform conversion processing to The conversion method may be a known method and is not particularly limited. For example, by referring to the color separation LUT in which the correspondence between L * a * b * values and the CMYK values is described stored in the color separation LUT storage unit 1106, it is possible to obtain device-independent values Converted to signal value. In this embodiment, in the color separation process, the color separation process is performed using the information on the seam of the laser array stored in the laser array information storage unit 1107. The laser array information storage unit 1107 stores information indicating which pixel in the sub-scanning direction the seam of the laser array is located. The color separation processing unit 1103 determines whether or not the pixel of interest contacts the junction of the laser array above the pixel, and as a result of the determination, the pixel of interest contacts the junction of the laser array above the pixel. A process of increasing the color separation value by a predetermined amount is performed. Further, as a result of the determination, when the pixel of interest does not contact the junction of the laser array above the pixel, the process is not performed. This assumes that the amount of exposure increases due to the occurrence of overshoot when the pixel of interest does not contact the junction of the laser array above the pixel.

  In contrast to the above, in the case of a laser array having a characteristic that the amount of exposure decreases due to the occurrence of an undershoot when the pixel of interest does not contact the junction of the laser array above the pixel, the color separation of the pixel of interest The value is reduced by a predetermined amount. In addition, when the pixel of interest does not contact the junction of the laser array, the color separation value may be corrected to coincide with the case where the pixel of interest contacts the junction of the laser array.

  The quantization processing unit 1104 performs quantization processing on image data having signal values of respective color material colors acquired by the conversion in the color separation processing unit 1103. The PWM processing unit 1105 performs pulse width modulation processing for controlling the width of the pulse signal for exposure based on the image data acquired by the quantization in the quantization processing unit 1104. The exposure signal data subjected to pulse width modulation processing in the PWM processing unit 1105 is sent to the image forming unit 506.

  By performing the color separation processing described above, the occurrence of banding and moire can be suppressed.

Example 4
In the third embodiment, the method of correcting the halftone shape by the color separation processing has been described. In this embodiment, a method of correcting the halftone dot shape by correcting the quantization processing result will be described. In addition, since the other structure is the same as that of Example 1, description is omitted.

  FIG. 12 is a block diagram showing the functional configuration of the image forming apparatus according to this embodiment. As shown in FIG. 12, the image forming apparatus includes an image input unit 1201, a color conversion processing unit 1202, a color separation processing unit 1203, a quantization processing unit 1204, a quantization correction unit 1205, and a PWM processing unit 1206. And an image forming unit 506. The image forming apparatus further includes a color separation LUT storage unit 1207, a quantization correction amount calculation unit 1208, and a laser array information storage unit 1209.

  An image to be printed is input to the image input unit 1201.

  The color conversion processing unit 1202 performs mapping processing for mapping from signal values (for example, RGB values or CMYK values) of an input image to a device-independent color space (for example, CIE L * a * b * or CIE XYZ). Do.

  The color separation processing unit 1203 generates signal values (for example, CMYK values) of the respective color materials installed in the image forming apparatus from the device-independent color space values acquired by the conversion in the color conversion processing unit 1202. Convert to The conversion method may be a known method and is not particularly limited. For example, by referring to the color separation LUT stored in the color separation LUT storage unit 1207 and in which the correspondence between L * a * b * values and CMYK values is described, the device-independent value to each color material color can be obtained. Converted to signal value.

  The quantization processing unit 1204 performs quantization processing on the image data having the signal value of each color material color acquired by the conversion in the color separation processing unit 1203. For example, it is assumed that the output of the color separation processing unit 1203 is 600 dpi 8 bit (256 gradations) image data. This image data is divided by the quantization processing unit 1204 into the main scanning resolution and the sub scanning resolution in the image forming unit 506, for example, 1 bit (two gradations) serving as on / off information for each pixel of 1200 dpi. It is converted into data to form so-called halftone dots.

  The quantization correction amount calculation unit 1208 uses the halftone dot image formed by the quantization processing unit 1204 and the information on the seam of the laser array stored in the laser array information storage unit 1209 to calculate the quantization result. The quantization correction amount necessary for correction is calculated for each halftone dot. The laser array information storage unit 1209 stores information indicating which pixel in the sub-scanning direction the seam of the laser array is located. The quantization correction amount calculation unit 1208 determines whether or not the focused halftone dot intersects with the seam of the laser array, and as a result of the determination, when the focused halftone dot intersects with the seam of the laser array, the intersecting grid Calculate the number of pixels to be increased for a point. This assumes that the amount of exposure increases due to the occurrence of overshoot when the target halftone dot does not intersect the seam of the laser array. The amount of exposure to the halftone dot is measured in advance by increasing the number of ON pixels of the halftone dot by one pixel, and the quantization correction amount calculation unit 1208 increases the number of pixels to be increased based on the overshoot amount. calculate. Alternatively, how much the exposure amount to the halftone dot is increased by increasing the ON pixel of the halftone dot by one pixel may be calculated based on the characteristics of the exposure element or the like instead of measuring it in advance. On the contrary, in the case of a laser array having a characteristic that the exposure amount decreases due to the occurrence of an undershoot when the halftone dots do not intersect the seam of the laser array, the halftone dot intersects the seam of the laser array When it is a point, the number of pixels to be reduced is calculated with respect to the intersecting halftone point. The number of pixels to be increased (or decreased) with respect to the target halftone dot, which is calculated by the quantization correction amount calculation unit, is referred to as a correction pixel number.

  The quantization correction unit 1205 corrects the quantization result in the quantization processing unit 1204 based on the quantization correction amount calculated by the quantization correction amount calculation unit 1208, that is, the number of correction pixels. In the above description, when the target halftone dot crosses the seam of the laser array, the dot shape is corrected by increasing (or decreasing) the number of pixels for the target halftone dot. However, if the focused halftone dot does not intersect the seam of the laser array, the number of pixels is reduced with respect to the focused halftone dot so that the exposure amount matches the case where the halftone dot intersects the seam of the laser array (or Correction may be performed by increasing the value. The PWM processing unit 1206 performs pulse width modulation processing for controlling the width of the pulse signal for exposure based on the 1-bit image data acquired by the correction in the quantization correction unit 1205. Exposure signal data subjected to pulse width modulation processing by the PWM processing unit 1206 is sent to the image forming unit 506.

  By performing the above-described quantization correction processing, the occurrence of banding and moire can be suppressed.

(Other embodiments)
The present invention is also realized by performing the following processing. That is, software (program) for realizing the functions of the above-described embodiment is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU or the like) of the system or apparatus reads the program. It is a process to execute.

Claims (16)

An image processing apparatus for an image forming apparatus for forming a latent image on an image carrier by a light emitting element array comprising a plurality of light emitting elements, comprising:
A determination unit that determines whether exposure to a target halftone dot is completed by one main scan of the light emitting element array;
Acquisition means for acquiring light emission information of adjacent light emitting elements of the light emitting element array;
Control means for controlling the exposure amount to the noted halftone dot on the basis of the result of the determination by the determination means and the light emission information ;
The light emission information is light emission information of a light emitting element adjacent to a light emitting element that exposes each pixel in the halftone dot, for a dot whose exposure is completed by one main scan of the light emitting element array. Image processing device. The image processing apparatus according to claim 1, wherein the halftone dot whose exposure is completed by one main scan of the light emitting element array has the same shape as the halftone dot to which attention is paid .   The image processing apparatus according to claim 1, wherein the light emission information is information indicating whether or not there is a switch between light emission regarding a light emitting element to be focused on and a light emitting element adjacent thereto, and non-light emission.   The image processing apparatus according to any one of claims 1 to 3, wherein information of exposure fluctuation due to crosstalk is obtained from the light emission information.   When the determination means determines that the exposure of the noted halftone dot is not completed by one main scan of the light emitting element array, the control means determines the exposure amount for the noted halftone dot as the halftone dot. The image processing apparatus according to any one of claims 1 to 4, wherein the amount of exposure is made larger or smaller than the amount of exposure when exposure is completed by one main scan of the light emitting element array.   When the determination means determines that the exposure of the noted halftone dot is completed by one main scan of the light emitting element array, the control means exposes the exposure amount for the noted halftone dot as the exposure of the halftone dot. The image processing apparatus according to any one of claims 1 to 4, wherein the amount of exposure is made larger or smaller than the amount of exposure not completed by one main scan of the light emitting element array.   The image processing apparatus according to any one of claims 1 to 6, wherein the control unit controls an exposure amount by pulse width modulation or pulse amplitude modulation.   The image processing apparatus according to any one of claims 1 to 6, wherein the control unit controls an exposure amount by correcting a gradation value by color separation processing.   The image processing apparatus according to any one of claims 1 to 6, wherein the control unit controls an exposure amount by correcting a quantization result. A built-in image processing apparatus according to any one of claims 1 to 9,
An electrophotographic image forming apparatus in which a latent image is formed on an image carrier by a light emitting element array comprising a plurality of light emitting elements. An image processing method for an image forming apparatus, wherein a latent image is formed on an image carrier by a light emitting element array comprising a plurality of light emitting elements, which is an image forming method.
A determination step of determining whether exposure to a target halftone dot is completed by one main scan of the light emitting element array;
Obtaining light emission information of adjacent light emitting elements of the light emitting element array;
A control step of controlling an exposure amount to the noted halftone dot based on the result of the determination in the determination step and the light emission information
Equipped with
The light emission information is light emission information of a light emitting element adjacent to a light emitting element that exposes each pixel in the halftone dot, for a dot whose exposure is completed by one main scan of the light emitting element array. Image processing method.   A program for causing a computer to execute the image processing method according to claim 11. An image processing apparatus for an image forming apparatus for forming a latent image on an image carrier by a light emitting element array comprising a plurality of light emitting elements, comprising:
A determination unit that determines whether exposure to a target halftone dot is completed by one main scan of the light emitting element array;
Acquisition means for acquiring light emission information of adjacent light emitting elements of the light emitting element array;
A control unit configured to control an exposure amount to the noted halftone dot based on the result of the determination by the determination unit and the light emission information;
When the determination means determines that the exposure of the noted halftone dot is not completed by one main scan of the light emitting element array, the control means determines the exposure amount for the noted halftone dot as the halftone dot. An image processing apparatus characterized in that the exposure amount is made larger or smaller than the exposure amount when the exposure is completed by one main scan of the light emitting element array. An image processing method for an image forming apparatus, wherein a latent image is formed on an image carrier by a light emitting element array comprising a plurality of light emitting elements, which is an image forming method.
A determination step of determining whether exposure to a target halftone dot is completed by one main scan of the light emitting element array;
Obtaining light emission information of adjacent light emitting elements of the light emitting element array;
And controlling the amount of exposure of the target halftone dot based on the result of the determination in the determination step and the light emission information.
In the determination step, when it is determined that the exposure of the noted halftone dot is not completed by one main scan of the light emitting element array, in the control step, the exposure amount for the noted halftone dot is the halftone dot An image processing method characterized in that the exposure amount is made larger or smaller than the exposure amount when the exposure of the light emitting element array is completed by one main scanning. The program for making a computer perform the image processing method of Claim 14. An image processing apparatus for an image forming apparatus for forming a latent image on an image carrier by a light emitting element array comprising a plurality of light emitting elements, comprising:
A determination unit that determines whether exposure to a target halftone dot is completed by one main scan of the light emitting element array;
Acquisition means for acquiring light emission information of adjacent light emitting elements of the light emitting element array;
A control unit that controls an exposure amount to the noted halftone dot based on the result of the determination by the determination unit and the light emission information;
Equipped with
When the determination means determines that the exposure of the noted halftone dot is completed by one main scan of the light emitting element array, the control means exposes the exposure amount for the noted halftone dot as the exposure of the halftone dot. The image processing apparatus is characterized in that the amount of exposure is larger or smaller than the amount of exposure not completed by one main scan of the light emitting element array.

Images