JP5812960B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus, image data with multiple gradations (for example, 256 gradations) is converted into image data with the same number of gradations (for example, 16 gradations) as that of the print engine by gradation processing such as screen processing. The print engine performs printing based on the image data.

  In general, in an image forming apparatus adopting an electrophotographic method, due to the edge effect, a fine line or character drawn at a high density is printed more than usual (that is, more than the amount required for the density specified by image data). Toner is consumed.

  In order to suppress an increase in toner consumption due to such an edge effect, for example, in an image forming apparatus, for example, the density of a pixel of interest and its surrounding pixels for image data of 256 gradations that is the same as the number of gradations of a print engine. An edge is detected based on the difference, and the density in the vicinity of the detected edge is corrected (see, for example, Patent Document 1).

JP 2009-118378 A

  However, in the above-described image forming apparatus, the edge detection process is performed on image data having a large number of gradations, so that the circuit scale for the edge detection process becomes large.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain an image forming apparatus that appropriately performs density correction of an edge portion with a small circuit scale.

  In order to solve the above problems, the present invention is configured as follows.

An image forming apparatus according to the present invention includes a gradation processing unit that generates first gradation image data from original image data by gradation processing, and gradation based on first gradation image data corresponding to the original image data. Data correction that corrects the value of the first gradation image data for the pattern matching unit that detects edges by pattern matching and the pixels belonging to the edges detected by the pattern matching unit in the second gradation image data with a small number If there is no pixel whose first gradation image data value is a halftone value in the peripheral pixel region having a predetermined shape for the pixel belonging to the edge and the pixel belonging to the edge, the data belonging to the edge When the first gradation image data after correction by the correction unit is output and there is a pixel whose first gradation image data value is a halftone value, it belongs to that edge For iodine, and a data output section for outputting a value of the first gray level image data as it is.

  As a result, the edge detection is performed with the second gradation image data having a smaller number of gradations than the first gradation image data, so that the density correction of the edge portion is appropriately performed with a small circuit scale.

Further , when an edge is detected by pattern matching at a place that is not a character or a thin line, density correction is not performed.

An image forming apparatus according to the present invention includes a gradation processing unit that generates first gradation image data from original image data by gradation processing, and first gradation image data corresponding to the original image data. In the second gradation image data with a small number of gradations, the value of the first gradation image data is corrected for the pattern matching unit that detects edges by pattern matching and the pixels that belong to the edges detected by the pattern matching unit. A data correction unit, and the data correction unit includes a pixel having a halftone value in the first gradation image data value in a peripheral pixel region having a predetermined shape for the pixel belonging to the edge described above. If the value of the first gradation image data for the pixel belonging to the edge is corrected and there is a pixel whose value of the first gradation image data is a halftone value, the edge For the pixels belonging, the value of the first gray level image data, the value of the first gray level image data is corrected with a small correction amount than when the pixel is the value of the halftone is not present.

An image forming apparatus according to the present invention includes a gradation processing unit that generates first gradation image data from original image data by gradation processing, and first gradation image data corresponding to the original image data. In the second gradation image data with a small number of gradations, the value of the first gradation image data is corrected for the pattern matching unit that detects edges by pattern matching and the pixels that belong to the edges detected by the pattern matching unit. The second gradation image data is image data obtained by binarizing the original image data or the first gradation image data, and the data correction part is in the main scanning direction or the sub-scanning direction. The correction amount of the value of the first gradation image data is changed according to the number of consecutive dots from the edge.

  Thereby, density correction is performed with a correction amount suitable for the strength of the edge effect.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the pattern matching unit identifies the number of consecutive dots by pattern matching.

  Thus, edge detection and correction amount selection are performed together, so that edge detection and correction amount selection are performed in a short time.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the image forming apparatus includes a photosensitive member, an exposure device that makes light incident on the photosensitive member to form an electrostatic latent image, a developing device that develops the electrostatic latent image with toner, and a first gradation image. And an exposure control unit that controls the light amount of the exposure apparatus based on the data.

  According to the present invention, the density correction of the edge portion is appropriately performed with a small circuit scale in the image forming apparatus.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image processing apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration example of the exposure apparatus and peripheral circuits in FIG. FIG. 3 is a block diagram showing the configuration of the image processing unit in FIG. FIG. 4 is a diagram illustrating an example of pixel value patterns detected by the pattern matching unit in FIG. 3. FIG. 5 is a diagram illustrating determination by the halftone determination unit in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image processing apparatus according to an embodiment of the present invention. This image processing apparatus is an image forming apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, or a multifunction machine.

  The image processing apparatus of this embodiment has a tandem color developing apparatus. The color developing device includes photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black. The exposure apparatuses 2a to 2d are apparatuses that form electrostatic latent images by irradiating the photosensitive drums 1a to 1d with laser light. The exposure apparatuses 2a to 2d are laser scanning units having a laser diode that is a light source of laser light and optical elements (lens, mirror, polygon mirror, etc.) that guide the laser light to the photosensitive drums 1a to 1d.

  Further, around the photosensitive drums 1a to 1d, a charger such as a scorotron, a cleaning device, a static eliminator and the like are arranged. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the static eliminator neutralizes the photosensitive drums 1a to 1d after the primary transfer.

  Each of the developing devices 3a to 3d is mounted with a toner cartridge filled with toners of four colors of cyan, magenta, yellow and black, and the toner is supplied from the toner cartridge and constitutes a developer together with the carrier. The developing devices 3a to 3d form toner images by attaching the toner to the electrostatic latent images on the photosensitive drums 1a to 1d.

  The photosensitive drum 1a, the exposure device 2a, and the developing device 3a develop magenta, and the photosensitive drum 1b, the exposure device 2b, and the developing device 3b develop cyan, the photosensitive drum 1c, and the exposure device. Yellow development is performed by the device 2c and the developing device 3c, and black development is performed by the photosensitive drum 1d, the exposure device 2d, and the developing device 3d.

  The intermediate transfer belt 4 is an annular image carrier that contacts the photosensitive drums 1a to 1d and primarily transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 4 is stretched around the driving roller 5 and circulates in the direction from the contact position with the photosensitive drum 1d to the contact position with the photosensitive drum 1a by the driving force from the driving roller 5.

  The transfer roller 6 brings the conveyed paper into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 is a sensor used for toner density adjustment, and irradiates the intermediate transfer belt 4 with a light beam and detects the reflected light. When adjusting the toner density, the sensor 8 irradiates a predetermined region of the intermediate transfer belt 4 with a light beam, detects reflected light (measurement light) of the light beam, and outputs an electrical signal corresponding to the light amount.

  FIG. 2 is a diagram showing a configuration example of the exposure apparatus 2a and peripheral circuits in FIG. 2 exposes the photosensitive drum 1a to form an electrostatic latent image, and the exposure devices 2b to 2d for the photosensitive drums 1b to 1d have the same configuration.

  In FIG. 2, the exposure apparatus 2 a includes a laser diode 11, an optical system 12, a polygon mirror 13, an optical sensor 14, a driver circuit 15, an exposure control unit 16, and an image processing unit 17.

  The laser diode 11 is a light source that emits a laser beam. The optical system 12 is various lens groups disposed between the laser diode 11 and the polygon mirror 13 and / or between the polygon mirror 13 and the photosensitive drum 1a and the optical sensor 14. For the optical system 12, an fθ lens or the like is used.

  The polygon mirror 13 is an element having an axis perpendicular to the axis of the photosensitive drum 1a, a cross section perpendicular to the axis being a polygon, and a side surface being a mirror. The polygon mirror 13 rotates about its axis, and scans the light beam emitted from the laser diode 11 along the axial direction (main scanning direction) of the photosensitive drum 1a.

  The optical sensor 14 is a sensor that receives light scanned by the polygon mirror 13 to generate a main scanning synchronization signal. When light is incident, the optical sensor 14 induces an output voltage corresponding to the amount of light. The optical sensor 14 is disposed at a predetermined position on the line where light is scanned, and is used to detect the timing at which the light spot passes through the position.

  The driver circuit 15 causes the laser diode 11 to emit light according to the drive signal while synchronizing in the main scanning direction based on the main scanning synchronization signal of the optical sensor 14.

  Further, the exposure control unit 16 outputs a drive signal corresponding to the value of image data of a predetermined gradation from the image processing unit 17 to control the light amount of the exposure apparatus 2a. That is, the exposure control unit 16 controls the amount of light incident on the photosensitive drum 1a (the amount of light of each pixel).

  Further, the image processing unit 17 uses the same level as the gradation (here, 16 gradations) from which image data can be formed on the photosensitive drum 1a by the exposure device 2a from the image data of multiple gradations (here, 256 gradations). Tone image data is generated, and density correction is performed to suppress an increase in toner consumption due to the edge effect. Then, the image data after gradation conversion and density correction processing is supplied from the image processing unit 17 to the exposure control unit 16.

  FIG. 3 is a block diagram showing a configuration of the image processing unit 17 in FIG. Note that the image processing unit 17 illustrated in FIG. 3 is a circuit that processes image data for one color of four color toners.

  The image processing unit 17 includes a gradation processing unit 31, a binarization processing unit 32, a pattern matching unit 33, a data correction unit 34, a halftone determination unit 35, and a data selection unit 36.

  The gradation processing unit 31 is a circuit that generates first gradation image data from original multi-gradation (256 gradations) image data (that is, 8-bit image data) by gradation processing such as screen processing. is there. In this embodiment, the first gradation image data is 16 gradations, that is, 4-bit image data.

  The binarization processing unit 32 is a circuit that generates second gradation image data having a smaller number of gradations than the first gradation image data from the first gradation image data. Here, the second gradation image data is two gradations, that is, 1-bit image data.

  The pattern matching unit 33 is a circuit that detects edges in the second gradation image data by pattern matching based on pixel value pattern data (not shown). Note that pixel value pattern data (not shown) is built in the image forming apparatus.

  In this embodiment, the pattern matching unit 33 detects the edge by pattern matching in the second gradation image data and specifies the number of consecutive dots from the edge in the main scanning direction or the sub scanning direction. Then, the pattern matching unit 33 supplies the data correction unit 34 and the data selection unit 36 with the position information of the pixel where the edge is detected and information indicating the number of consecutive dots from the edge in the main scanning direction or the sub scanning direction. .

  The data correction unit 34 is a circuit that corrects the value of the first gradation image data for the pixels belonging to the edge detected by the pattern matching unit 33.

  In this embodiment, the data correction unit 34 changes the correction amount of the value of the first gradation image data according to the number of consecutive dots from the edge in the main scanning direction or the sub-scanning direction.

  The halftone determination unit 35 determines that the value of the first gradation image data is a halftone value (for example, the first gradation image data is 4-bit data in the peripheral pixel region having a predetermined shape for the pixels belonging to the edge described above. In some cases, it is a circuit that determines whether or not a pixel of any one of 1 to 14) exists.

  The data selection unit 36 performs first gradation image data output from the gradation processing unit 31 and after correction by the data correction unit 34 according to the information from the pattern matching unit 33 and the determination result of the halftone determination unit 35. Is a circuit that outputs any one of the first gradation image data.

  Specifically, when the data selection unit 36 determines that the target pixel does not belong to the edge based on the information from the pattern matching unit 33, the data selection unit 36 outputs the first gradation image data from the gradation processing unit 31 as it is. When it is determined that the target pixel belongs to the edge based on the information from the pattern matching unit 33, the determination result by the halftone determination unit 35 indicates that the first tone image data in the peripheral pixel region of the predetermined shape for the target pixel When there is no pixel whose value is a halftone value, the first gradation image data after correction is output, and the result of determination by the halftone determination unit 35 is that the periphery of the predetermined shape for the target pixel When the pixel area indicates that there is a pixel whose first gradation image data has a halftone value, the first gradation image data from the gradation processing unit 31 is used as it is. To output.

  That is, the data selection unit 36 determines that the value of the first gradation image data is a halftone value in the peripheral pixel region having a predetermined shape for the pixel belonging to the edge according to the determination result by the halftone determination unit 35. If there is no pixel, the first gradation image data corrected by the data correction unit 34 is output for the pixel belonging to the edge, and the first gradation image data value is a halftone value. Is present, the value of the first gradation image data is output as it is for the pixels belonging to the edge. Note that the pixels belonging to the edge are specified from the position information supplied by the pattern matching unit 33.

  Next, the operation of the image forming apparatus will be described.

  The image processing unit 17 shown in FIG. 2 performs predetermined image processing (color conversion, image enhancement, smoothing, gamma) from print data described in PDL (Page Description Language), image data generated by scanning a document image, and the like. Multi-tone raster image data generated through the correction, etc. is received, image data of the number of gray levels of the exposure apparatus 2a is generated from the multi-tone raster image data, and supplied to the exposure control unit 16.

  The exposure control unit 16 generates a drive signal based on the image data and supplies it to the driver circuit 15. The driver circuit 15 causes the laser diode 15 to emit light according to the drive signal.

  In this embodiment, the image processing unit 17 operates as follows.

  The gradation processing unit 31 shown in FIG. 3 performs gradation processing (screen processing) on 8-bit raster image data, and the image data (first bit) of the number of gradations (4 bits in this case) of the exposure apparatus 2a. Gradation image data) is generated. Note that the gradation processing unit 31 sequentially designates the pixel of interest along the main scanning direction and the sub-scanning direction, and derives and outputs the value of the first gradation image data for the pixel of interest from the raster image data. .

  The binarization processing unit 32 binarizes the 4-bit first gradation image data with a predetermined threshold and generates 1-bit second gradation image data. Here, if the value of the 4-bit first gradation image data is 0 (minimum value) for the pixel of interest, the binarization processing unit 32 sets the binarized value to 0 and sets the 4-bit first If the value of the one-tone image data is any one of 1 to 15, the value after binarization is set to 1.

  The pattern matching unit 33 performs pattern matching on the 1-bit second gradation image data.

  FIG. 4 is a diagram illustrating an example of a pattern of pixel values detected by the pattern matching unit 33 in FIG. In FIG. 4, a pixel with a central hatch is a target pixel, the value of the target pixel is 1, and a white pixel surrounded by a solid line adjacent to the target pixel is a pixel with pixel value = 0. The black pixel located in the direction from the pixel having the pixel value = 0 to the target pixel (that is, the main scanning direction or the sub scanning direction) is a pixel having the pixel value = 1.

  That is, pattern matching is performed on a pixel column including the target pixel arranged in one column along the main scanning direction or the sub-scanning direction. That is, pixels surrounded by a broken line in FIG. 4 are not related to pattern matching.

  By using the pixel value pattern as shown in FIG. 4, the pattern matching unit 33 detects the edge in the 1-bit second gradation image data, and the direction of the edge and the pixel value continuous from the edge. = 1 (the number of consecutive dots) is collectively detected.

  In the case of the pixel value pattern shown in FIG. 4, the pattern matching unit 33 detects an edge corresponding to any of 4 or more, 3 and 2 dot continuations, and the dot continuation number is 4 or more, 3 and 2. Information indicating which one is provided is supplied to the data correction unit 34. Further, the pattern matching unit 33 supplies the position information of the target pixel from which the edge is detected to the data correction unit 34 and the data selection unit 36.

  Further, when an edge is detected for the target pixel, the data correction unit 34 corrects the value of the 4-bit first gradation image data for the target pixel with a correction amount corresponding to the number of consecutive dots. At this time, the value of the first gradation image data may be decreased by a value corresponding to the number of consecutive dots, or the value of the first gradation image data is changed to a value corresponding to the number of consecutive dots. You may do it.

  On the other hand, the halftone determination unit 35 determines whether or not there is a halftone pixel around the target pixel in the first gradation image data, and supplies the determination result to the data selection unit 36.

  Then, based on the information from the pattern matching unit 33, the data selection unit 36 (a) outputs the first gradation image data from the gradation processing unit 31 as it is when it is determined that the target pixel does not belong to the edge. (B) When it is determined that the target pixel belongs to the edge, (b1) the determination result by the halftone determination unit 35 indicates that the value of the first gradation image data is halftone in the peripheral pixel region of the predetermined shape for the target pixel. Is output, the corrected first gradation image data is output, and (b2) the result of determination by the halftone determination unit 35 is a peripheral pixel having a predetermined shape for the target pixel. When the area indicates that there is a pixel whose first gradation image data has a halftone value, the first gradation image data from the gradation processing unit 31 is output as it is.

  FIG. 5 is a diagram for explaining determination by the halftone determination unit 35 in FIG. For example, as shown in FIG. 5A, the halftone determination unit 35 performs a halftone (first gradation image data level) in a 7 × 7 pixel peripheral region (excluding the target pixel) centered on the target pixel. When the key is 16, it is determined whether or not there is a pixel having a pixel value of 1 to 14.

  For example, when the target pixel is located at the edge of a character or the like as shown in FIG. 5B, it is determined that there is no halftone pixel in the peripheral region.

  On the other hand, for example, when the target pixel is located in the gradation image as shown in FIG. 5C, it is determined that a halftone pixel exists in the peripheral region.

  In any of these cases, as shown in FIG. 5D, the pattern matching unit 33 detects an edge with the number of consecutive dots = 2, but in the case shown in FIG. As the value of the first gradation image data for the target pixel, the value corrected by the data correction unit 34 is output. In the case shown in FIG. 5C, the data selection unit 36 displays the value for the target pixel. The value output from the gradation processing unit 31 is output as the value of the first gradation image data, not the value corrected by the data correction unit 34.

  As described above, according to the above embodiment, the gradation processing unit 31 generates the first gradation image data from the original image data by gradation processing, and the pattern matching unit 33 converts the original image data into the original image data. In the corresponding second gradation image data having a smaller number of gradations than the first gradation image data, an edge is detected by pattern matching. Further, the data correction unit 34 corrects the value of the first gradation image data for the pixels belonging to the edge detected by the pattern matching unit 33.

  As a result, the edge detection is performed with the second gradation image data having a smaller number of gradations than the first gradation image data, so that the density correction of the edge portion is appropriately performed with a small circuit scale.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, the image forming apparatus according to the above embodiment is a color image forming apparatus, but a monochrome image forming apparatus can have the same configuration.

  In the above embodiment, the second gradation image data may be image data obtained by binarizing the original image data.

  In the above embodiment, the data correction unit 34 does not include a pixel whose first gradation image data value is a halftone value in the peripheral pixel region having a predetermined shape for the pixel belonging to the edge. In this case, the value of the first gradation image data for the pixel belonging to the edge is corrected, and if there is a pixel whose first gradation image data value is a halftone value, it belongs to the edge The value of the first gradation image data for the pixel may be corrected with a smaller correction amount than when there is no pixel in which the value of the first gradation image data is a halftone value. In this case, the determination result by the halftone determination unit 35 is supplied to the data correction unit 34, and the correction amount is changed according to the determination result. Then, the first gradation image data corrected by the data correction unit 34 is output to the exposure control unit 16.

  In the above-described embodiment, the binarization processing unit 32 sets the value after binarization to 1 if the value of the 4-bit first gradation image data is 15 (maximum value). If the value of the first gradation image data is any of 0 to 14, the value after binarization may be set to 0.

  In the embodiment described above, the correction amount by the data correction unit 34 may be changed according to the direction of the edge detected by the pattern matching unit 33. In this case, when the pixel value pattern shown in FIG. 4 is used, the information indicating the edge direction (any one of the four directions) and the number of consecutive dots (any one of 4 or more, 3, and 2) is 4 bits.

  In the above embodiment, the size and shape of the peripheral region to be determined by the halftone determination unit 35 may be changed according to the edge direction detected by the pattern matching unit 33.

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

1a to 1d photoconductor drum (example of photoconductor)
2a to 2d exposure apparatus 3a to 3d development apparatus 16 exposure control unit 31 gradation processing unit 33 pattern matching unit 34 data correction unit 36 data selection unit (an example of data output unit)

Claims (5)

A gradation processing unit that generates first gradation image data from original image data by gradation processing;
A pattern matching unit that detects edges by pattern matching in the second gradation image data having a smaller number of gradations than the first gradation image data, corresponding to the original image data;
A data correction unit for correcting the value of the first gradation image data for the pixels belonging to the edge detected by the pattern matching unit;
In the peripheral pixel region having a predetermined shape for the pixel belonging to the edge, when there is no pixel whose value of the first gradation image data is a halftone value, the data correction unit for the pixel belonging to the edge When the first gradation image data after the correction according to the above is output and there is a pixel in which the value of the first gradation image data is a halftone value, the pixel belonging to the edge is A data output unit for outputting the value of the toned image data as it is,
An image forming apparatus comprising: A gradation processing unit that generates first gradation image data from original image data by gradation processing;
A pattern matching unit that detects edges by pattern matching in the second gradation image data having a smaller number of gradations than the first gradation image data, corresponding to the original image data;
A data correction unit that corrects the value of the first gradation image data for pixels belonging to the edge detected by the pattern matching unit;
In the peripheral pixel region having a predetermined shape with respect to the pixel belonging to the edge, the data correction unit includes a pixel belonging to the edge when there is no pixel in which the value of the first gradation image data is a halftone value When the value of the first gradation image data is corrected and there is a pixel whose value of the first gradation image data is a halftone value, the first gradation image data value for the pixel belonging to the edge Correcting the value of one gradation image data with a smaller correction amount than when there is no pixel in which the value of the first gradation image data is a halftone value ;
Images forming device you characterized. A gradation processing unit that generates first gradation image data from original image data by gradation processing;
A pattern matching unit that detects edges by pattern matching in the second gradation image data having a smaller number of gradations than the first gradation image data, corresponding to the original image data;
A data correction unit that corrects the value of the first gradation image data for pixels belonging to the edge detected by the pattern matching unit;
The second gradation image data is image data obtained by binarizing the original image data or the first gradation image data,
The data correction unit changes a correction amount of the value of the first gradation image data in accordance with the number of consecutive dots from the edge in the main scanning direction or the sub-scanning direction;
Images forming device you characterized. The image forming apparatus according to claim 3 , wherein the pattern matching unit specifies the number of consecutive dots by the pattern matching. A photoreceptor,
An exposure apparatus for forming an electrostatic latent image by making light incident on the photoreceptor;
A developing device for developing the electrostatic latent image with toner;
An exposure control unit that controls a light amount of the exposure apparatus based on the first gradation image data;
The image forming apparatus according to any one of claims 1 to 4, characterized by further comprising a.

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