JP2010060670A - Image forming apparatus, image forming method, image forming program and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, an image forming method, an image forming program and a recording medium by which a color dot image can be formed in high quality based on color digital pixel data. <P>SOLUTION: A digital copying machine 1 carries out a feature detection for a target pixel based on an arrangement state for a state value in a window for a prescribed pixel by converting color multi-value pixel data to gray scale pixel data by a gray scale image processing section 1310G and then converting to three state values which are no-color, maximum color and halftone. In addition, color image formation is carried out by carrying out feature detection by converting inputted multi-value pixel data to the tri-state value in respective channel image processing sections 1310Ca to Cn, then determining a reference look up table for a reference subject from a plurality of reference look up tables based on the color feature detection result in the same pixel position as the pixel position in which the prescribed feature is detected in the gray scale and the gray scale feature detection result and making the data value in the reference look up table as the multi-value pixel data for output. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, an image forming method, an image forming program, and a recording medium, and more specifically, a color dot image formed by an electrophotographic system based on digital image data such as a laser printer, a digital copying apparatus, a facsimile apparatus, etc. The present invention relates to an image forming apparatus, an image forming method, an image forming program, and a recording medium that improve image quality.

  An electrophotographic image forming apparatus such as a laser printer, a digital copying apparatus, a facsimile apparatus, or a composite apparatus has an image forming unit that shapes a beam bundle from a light source such as a laser diode with a collimator lens or the like, a polygon mirror, etc. Thus, deflection scanning in the main scanning direction is performed on a uniformly charged surface to be scanned such as a photoconductor rotated in the sub-scanning direction, and an electrostatic latent image is formed on the surface to be scanned. The image forming unit develops the latent image formed on the surface to be scanned by applying a toner by a developing process and developing the toner image on a recording medium (paper, sheet-like member, hereinafter simply referred to as paper). By transferring and fixing the toner image on the paper, an output image is formed.

  As described above, in an electrophotographic image forming apparatus, a beam bundle is irradiated to a position corresponding to a portion of an input image on which toner is placed (hereinafter referred to as a toner loading portion as appropriate) as an image forming unit. A negative / positive (N / P) process is generally used in which an electrostatic latent image is formed, and toner is supplied to the electrostatic latent image for development, but the beam when the beam bundle reaches the scanned surface. Depending on the diameter and development conditions, the toner volume state is different, and even if the input image data is the same, the output image is different.

  For example, when an image of a vertical line of one main scanning pixel is output, even if beam irradiation is performed for a period corresponding to one pixel, the beam diameter or the like varies depending on the model of the image forming apparatus, the lot, and the solids of the image forming apparatus. Due to the different development conditions, the vertical lines of the output image to be formed have different thicknesses. Even when the main scanning 1 pixel (vertical) line and the sub-scanning 1 pixel (horizontal) line are output on the same sheet, the vertical line and the horizontal line have different thicknesses depending on the beam diameter and development conditions. Sometimes. In particular, in the so-called grandchild copy in which a sheet copied by a copying apparatus is used again as a document, the above phenomenon appears greatly.

  The phenomenon in which the thickness of the line is different from that of the original image is not only the image portion line on which black or color toner is placed, but also on the background line of the paper on which the toner is not placed. Different, it may get thinner or thicker.

  The above problems are not limited to the case of forming a black and white image using black toner as the toner, and the same problem occurs when a color image is formed using color toner. In the case of forming a color image, an electrostatic latent image is sequentially formed by irradiating a beam bundle onto a portion of the surface to be scanned where the toner of the corresponding color is placed for each color to form the electrostatic image. The toner of the color corresponding to the latent image is placed, and the toner images of the respective colors are sequentially superimposed and transferred onto the paper to form a color toner image on the paper.

  Conventionally, as a conventional technique for solving such a problem, a vertical line having a width of 1 dot is formed based on a pattern of multivalued image data of a target pixel of input image data and peripheral pixels adjacent in the main scanning direction. A technique has been proposed in which an image is formed by detecting and reducing the vertical line printing dots to make the vertical line thinner (see Patent Document 1).

  And in this prior art, the determination process of the pattern of the input multi-value 2-bit data is performed by the hardware configuration, and this multi-value data is described only in the case of 2 bits. No explanation is given for the case of (four values) or more.

JP 2001-063134 A

  However, in the prior art described in the above publication, since image formation is performed by thinning the vertical lines, it is necessary to improve the image quality. In other words, the image output by the electrophotographic image forming process may not only make the vertical line thick, but also make it thin. In such a case, the conventional technique cannot make the vertical line thick. In order to improve the image quality, there is a need for improvement.

  In the prior art described in the above publication, the input image data is indicated as multi-value data. However, in the specification, only two bits (four values) are determined for the image pattern. The hardware configuration to be shown is shown. Therefore, when this conventional technique is applied to image data having a larger number of bits, there is a problem that the hardware configuration becomes enormous in size and becomes complicated and expensive.

  Further, in the image forming apparatus, when the vertical line is not a single color but a color, an image is formed by the number of laser beams corresponding to the color plate. Even if the misalignment is corrected, the vertical line may become thinner or thicker for each color. In this case, it is necessary to make adjustments by thickening processing and thinning processing for each color plate, but depending on the combination of the color of the vertical line and the color of the background, such a feature of the vertical line may not be seen. For example, if the background is not a white background but is colored (for example, yellow) and the vertical line is orange (a combination of magenta and yellow), even if a vertical line is detected in the magenta color plate, Yellow is on the vertical line and background, so you cannot find the characteristics of the vertical line. Further, when the background is magenta and a cyan vertical line, the vertical line is detected in the cyan color plate, but on the contrary, the feature of the white vertical line is detected in the magenta color plate. As described above, in a color image, image characteristics between channels (color plates) are different. Therefore, if thinning processing or thickening processing is performed uniformly, the color plate composition changes and the color changes. The problem occurs. There is a demand for a technique that appropriately solves the problems peculiar to thinning processing and thickening processing in the case of such a color image.

  Therefore, the present invention appropriately applies thickening processing for thickening vertical lines and thinning processing for thinning the input multivalued pixel data of color regardless of the amount of information of the input multivalued pixel data of color. An object is to provide an image forming apparatus, an image forming method, an image forming program, and a recording medium.

  In order to achieve the above object, the present invention converts color multivalued pixel data into grayscale pixel data, and converts the grayscale pixel data into at least three state values of colorless, maximum color, and halftone. The edge of the pixel of interest, the isolated line, etc. based on the arrangement state of the state values of the pixel in a pixel window composed of a predetermined number of adjacent pixels centered on the pixel of interest of the converted grayscale pixel data Detection, and for each color, the input multi-value pixel data is converted into at least three state values of colorless, maximum color, and halftone based on the colorless threshold and the maximum color threshold. The state in which the center pixel of the state value array having a predetermined characteristic detected for the grayscale pixel data in the state value array of the pixel in the pixel window is the target pixel Based on the arrangement, features such as edges and isolated lines of the target pixel are detected, and for each color, the target pixel of the input multi-valued pixel data and the color of a predetermined number of adjacent pixels centered on the target pixel Among a plurality of reference lookup tables in which data values of output multi-value pixel data are registered in correspondence with the state value array of the pixel in the pixel window in which the state value converted by the state conversion process is stored. A reference lookup table to be referred to is determined based on the feature detection result in the grayscale feature detection and the feature detection result in the color feature detection, and the data value of the input multi-value pixel data is determined as the reference lookup. Switching to the data value of the reference lookup table determined in the table determination processing step to form the color image as the output multi-value pixel data It is characterized.

  Further, the present invention provides a thinning reference lookup table in which data values for thinning processing for thinning the dot image of the pixel of interest forming the image in the main scanning direction are registered in the reference lookup table. No thickening reference lookup table in which data values for thickening processing for thickening the pixel of interest are registered, and no processing for converting the pixel of interest of the input multivalued pixel data into the output multivalued pixel data as it is It is also possible to have a reference lookup table for non-processing in which data values are registered.

  Further, according to the present invention, in the determination of the reference lookup table for each color, when the feature detected by the gray scale feature detection matches the feature detected by the color feature detection of the color, or both features are predetermined. A reference look-up table for thinning processing that thins the dot image of the pixel of interest forming the image in the main scanning direction or a reference look for thickening processing that thickens the pixel of interest when they are complementary. It may be characterized by selecting an uptable.

  Further, according to the present invention, the reference look-up table for each color uses the pixel of interest of the input multi-value pixel data as it is regardless of the feature detection result of the gray scale feature detection and the color feature detection. A through state as data can be set.

  Further, according to the present invention, in the reference lookup table, in the thinning process for thinning the dot image of the target pixel forming the image in the main scanning direction or the thickening process for thickening the target pixel, A pixel data value corresponding to the thinning process or the thickening process may be used, and a pixel data value of an additional pixel to be added to a pixel position adjacent to the target pixel may be registered.

  Further, the present invention may be characterized in that the pixel window is a pixel window including three or more pixels in the main scanning direction and one or more pixels in the sub scanning direction.

  According to the present invention, regardless of the amount of information of color input multivalued pixel data, the thickening process for thickening vertical lines and the thinning process for thinning are appropriately performed on the input multivalued pixel data of color. Image quality can be improved easily and inexpensively.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, since the Example described below is a suitable Example of this invention, various technically preferable restrictions are attached | subjected, However, The range of this invention is unduly limited by the following description. However, not all the configurations described in the present embodiment are essential constituent elements of the present invention.

  1 to 23 are diagrams showing an embodiment of an image forming apparatus, an image forming method, an image forming program, and a recording medium according to the present invention. FIG. 1 shows an image forming apparatus, an image forming method, and an image according to the present invention. 1 is a schematic front view of a configuration of a digital copying apparatus 1 to which an embodiment of a forming program and a recording medium is applied.

  1, the digital copying apparatus 1 has a configuration in which a paper feeding unit 100, a printer unit 200, and a scanner unit 300 are sequentially stacked. On the scanner unit 300, an automatic document feeder (hereinafter referred to as ADF). .) 400 is mounted.

  The printer unit (color image forming unit) 200 includes four process cartridges 210Y, 210C, 210M for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). The image forming unit 210 includes 210K, an optical writing unit 230, an intermediate transfer unit 240, a secondary transfer unit 250, a registration roller pair 260, a belt fixing type fixing unit 270, a sheet reversing unit 280, and the like.

  As will be described later, the optical writing unit 230 converts the surface of the photosensitive member 211Y, 211C, 211M, 211K of the process cartridges 210Y, 210C, 210M, 210K of each color into a laser beam bundle modulated based on the image data of each color. To form an electrostatic latent image of each color image on the photoconductors 211Y, 211C, 211M, and 211K.

  The process cartridges 210Y, 210C, 210M, and 210K include drum-shaped photoconductors 211Y, 211C, 211M, and 211K, chargers 212Y, 212C, 212M, and 212K, developing devices 213Y, 213C, 213M, and 213K, and numbers Although not attached, each has a drum cleaning device, a static eliminator, and the like.

  The chargers 212Y, 212C, 212M, and 212K uniformly charge the drum surface by sliding a charging roller to which an AC voltage is applied against the photoreceptors 211Y, 211C, 211M, and 211K. The chargers 212Y, 212C, 212M, and 212K may be in contact with other members such as a charging brush in place of the charging roller, and are not limited to those of the contact charging type. A contact charging type scorotron charger may be used.

  The surfaces of the photoconductors 211Y, 211C, 211M, and 211K that have been subjected to the charging process are irradiated with laser beam bundles that are modulated and deflected based on the image data of the respective colors by the optical writing unit 230, respectively. Electrostatic latent images for the respective colors are formed on the drum surfaces of 211C, 211M, and 211K, respectively.

  The process cartridges 210Y, 210C, 210M, and 210K supply the respective color toners from the developing units 213Y, 213C, 213M, and 213K to the photoconductors 211Y, 211C, 211M, and 211K of the respective colors on which the electrostatic latent images are formed. The electrostatic latent image is developed to form toner images of respective colors.

  The photoconductors 211Y, 211C, 211M, and 211K that are the surfaces to be scanned are, for example, drum-like ones in which a base tube made of aluminum or the like is coated with a photosensitive layer made of an organic photosensitive material that exhibits photosensitivity. However, it is not limited to a drum shape, and may be a belt shape.

  In the process cartridges 210Y, 210C, 210M, and 210K, toner images formed on the photoreceptors 211Y, 211C, 211M, and 211K are intermediately transferred to an intermediate transfer belt 241 described later, and the photoreceptors 211Y, 211C, and 211M after intermediate transfer are performed. The transfer residual toner remaining on the surface of 211K is cleaned by a drum cleaning device.

  The photoconductors 211Y, 211C, 211M, and 211K cleaned by the drum cleaning device are neutralized by a static eliminator (number omitted) as they rotate, are uniformly charged by the charger, return to the initial state, and again. It is used for image formation.

  In the intermediate transfer unit 240, an intermediate transfer belt 241 is stretched around a plurality of stretching rollers (not shown) and a secondary transfer backup roller 242, and the photoreceptors 211Y, 211C, Intermediate transfer bias rollers (number omitted) are disposed at positions facing 211M and 211K, respectively.

  In FIG. 3, the intermediate transfer belt 241 is tensioned by ten rollers including the tension roller described above, and at least one tension driven by a belt drive motor (not shown) that is driven and controlled. As the roller rotates, it is rotated endlessly in the clockwise direction indicated by the arrow in FIG. That is, the intermediate transfer belt 241 is stretched over four intermediate transfer bias rollers, a stretching roller, and a secondary transfer backup roller 242, and an intermediate transfer bias is applied to each intermediate transfer bias roller from a power source (not shown). As a result, the toner images on the photoconductors 211Y, 211C, 211M, and 211K are sequentially transferred by superimposing and transferring the toner images of the multiple (four colors in FIG. 1), and the color toner images are transferred onto the intermediate transfer belt 241. Transcribed. The color toner image superimposed and transferred onto the intermediate transfer belt 241 is secondarily transferred onto a transfer sheet (not shown) at a secondary transfer nip described later, and is transferred onto the surface of the intermediate transfer belt 241 after passing through the secondary transfer nip. The residual transfer residual toner is cleaned by a belt cleaning device (not shown) that sandwiches the belt between the left side tension roller in FIG.

  A secondary transfer unit 250 is disposed below the intermediate transfer unit 240, and the paper transfer belt 251 is stretched by two stretching rollers 252 in the secondary transfer unit 250. The paper transport belt 251 is rotated endlessly counterclockwise in FIG. 1 in accordance with the rotational drive of at least one of the stretching rollers 252 and is disposed on the right side of the two stretching rollers 252 in the drawing. One of the stretched rollers 252 is in a state where the intermediate transfer belt 241 and the paper transport belt 251 are sandwiched between the secondary transfer backup roller 242 of the intermediate transfer unit 240. By this sandwiching, a secondary transfer nip is formed in which the intermediate transfer belt 241 of the intermediate transfer unit 240 and the paper transport belt 251 of the secondary transfer unit 250 are in contact with each other.

  A secondary transfer bias having a polarity opposite to that of the toner is applied to the stretching roller 252 on the secondary transfer backup roller 242 side by a power source (not shown), and the secondary transfer bias is applied to the secondary transfer nip. A secondary transfer electric field for electrostatically moving the color toner image on the intermediate transfer belt 241 from the intermediate transfer belt 241 side toward the stretching roller 252 side on the secondary transfer backup roller 242 side is formed. A transfer paper (recording medium) is sent to the secondary transfer nip so as to be synchronized with the color toner image on the intermediate transfer belt 241 by the registration roller pair 260, and the secondary transfer is performed on the transfer paper sent to the secondary transfer nip. A color toner image affected by the electric field and nip pressure is secondarily transferred. Instead of the secondary transfer method in which the secondary transfer bias is applied to the stretching roller 252 on the secondary transfer backup roller 242 side, a charger for charging the transfer paper in a non-contact manner may be provided.

  A registration roller pair 260 is disposed on the upstream side of the secondary transfer nip in the moving direction of the intermediate transfer belt 241. Between the registration roller pair 260, a sheet feeding unit 100, which will be described later, is connected to the printer unit 200. Then, transfer paper (recording medium) is conveyed. On the other hand, in the intermediate transfer unit 240, the color toner image formed on the intermediate transfer belt 241 enters the secondary transfer nip as the intermediate transfer belt 241 rotates endlessly. The registration roller pair 260 feeds out the transfer paper sandwiched between the rollers at a timing when the transfer paper is brought into close contact with the color toner image at the secondary transfer nip, and the color toner image on the intermediate transfer belt 17 is timingd at the secondary transfer nip. The transfer sheet is brought into close contact with the adjusted transfer sheet and is secondarily transferred onto the transfer sheet to form a full-color image on the white transfer sheet. The transfer paper on which the full-color image is formed in this way exits the secondary transfer nip as the paper transport belt 251 moves endlessly, and then is sent from the paper transport belt 251 to the fixing unit 270. The registration roller pair 260 may be grounded, or a bias may be applied to remove paper dust received from the transfer paper. Further, the bias is not limited to the DC bias, but may be a bias in which the DC bias is superimposed on the AC bias.

  The fixing unit 270 moves the fixing belt 271 endlessly while being stretched by the heating roller 272 and the driven roller 273, and the pressure roller 274 is pressed against the heating roller 272 that forms a fixing nip with the fixing belt 271 interposed therebetween. ing. The fixing unit 270 has a heat source (not shown) inside the heating roller 272. The fixing belt 271 is heated by the heat generated by the heat source, and the heated fixing belt 271 holds the transfer paper sandwiched in the fixing nip. While being conveyed, the color toner image is fixed to the transfer paper by heating.

  In the paper feeding unit 100, paper cassettes 102 are stored in multiple stages in a paper bank 101, and each of the paper feeding cassettes 102 can store a plurality of transfer papers having different paper sizes and paper types. Each paper feed cassette 102 is provided with a feed roller 103 that feeds transfer paper in the paper feed cassette 102 and a separation roller 104 that feeds the transfer paper sent by the paper feed roller 103 one by one. In addition, the paper feed unit 100 is provided with a paper feed path 105 and a transport roller 106 for transporting transfer paper fed from each paper feed cassette 102 to the printer unit 200. The paper feed unit 100 starts the paper feed operation almost simultaneously with the start of the document reading operation, and one of the paper feed rollers 103 is selectively rotated, so that the paper feed cassettes 102 housed in multiple stages in the paper bank 101 are fed. The transfer paper is sent out from one. The paper feeding unit 100 separates the fed transfer paper one by one by the separation roller 104 and enters the paper feeding path 105, and then feeds the transfer paper to the paper feeding path 203 in the printer unit 200 by the transport roller 106. .

  Further, the digital copying apparatus 1 is provided with a manual feed tray 204 on the side surface of the printer unit 200, and a paper feed roller 205 and a separation roller 206 for separating and feeding the transfer paper on the manual feed tray 204 one by one. Is provided.

  Then, when the manual feed tray 204 is selected, the digital copying apparatus 1 rotates the paper feed roller 205 to feed the transfer paper on the manual feed tray 204 and separates the paper one by one by the separation roller 206. Paper is fed to the 200 manual paper feed path 207.

  The digital copying apparatus 1 conveys the transfer paper fed to the paper feed path 203 or the manual paper feed path 207 in the printer unit 200 via the pair of registration rollers 260 and the secondary transfer nip, so that the color toner image Is secondarily transferred, the toner image is fixed by the fixing unit 270, and then discharged outside the apparatus.

  Then, the transfer paper that has passed through the fixing unit 270 is discharged out of the apparatus via the pair of discharge rollers 201 in FIG. 1 and stacked on the stack unit 209 or disposed below the fixing unit 270. It is sent to the paper reversing unit 280.

  The sheet reversing unit 280 reverses the transferred transfer sheet upside down, and then again enters the secondary transfer nip where the intermediate transfer belt 241 of the intermediate transfer unit 240 and the paper transport belt 251 of the secondary transfer unit 250 come into contact with each other. Then, the color toner image is secondarily transferred to the other surface (back surface), and is discharged to the outside after passing through the fixing unit 270. Whether the transfer paper is sent from the fixing unit 270 to the paper discharge roller pair 201 or the paper reversing unit 280 is determined by switching the paper conveyance path by the switching claw 202.

  The scanner unit 300 includes a contact glass 301, a first traveling body 302 on which a light source and a first mirror are mounted, a second traveling body 303 on which a second mirror and a third mirror are mounted, an imaging lens 304, and a CCD (Charge Coupled Device). 305 and the like, and the first traveling body 302 and the second traveling body 303 are accommodated in the main body housing of the digital copying apparatus 1 below the contact glass 301 and are arranged in the sub-scanning direction (left-right direction in FIG. 1). It is arranged to be movable. The scanner unit 300 irradiates the original set on the contact glass 301 from the light source on the first traveling body 302 with the reading light while the first traveling body 302 and the second traveling body 303 move in the sub-scanning direction. The reflected light from the original of the reading light is reflected by the first mirror on the first traveling body 302 to the second mirror on the second traveling body 303, and the incident light is reflected on the second traveling body 303 by the second mirror. The light is reflected by the third mirror, and the incoming / outgoing light is reflected in the direction of the imaging lens 304 by the third mirror. The imaging lens 304 condenses incident light on the CCD 305, and the CCD 305 photoelectrically converts the incident light to read an image on the document.

  The ADF 400 includes a document table 401, a paper feed roller 402, a separation roller 403, a conveyance roller 404, a conveyance belt 405, a paper discharge roller 406, a paper discharge table 407, and the like. The digital copying apparatus 1 can open and close the contact glass 301. It is attached to the main body housing.

  When the ADF 400 is opened, the upper surface of the contact glass 301 is opened, and a book-type document or the like can be set on the contact glass 301. When the ADF 400 is closed with the document set on the contact glass 301, It functions as a pressing plate that presses the document onto the contact glass 301.

  When the ADF 400 is closed and a sheet-like document is set on the document table 401 and reading is instructed, the document on the document table 401 is sent out by the paper feed roller 402, and the separation roller 403 Separate the documents to be sent one by one. The ADF 400 conveys the originals separated and sent one by one to the conveyance belt 405 by the conveyance roller 404, and conveys and conveys the conveyed original document to the reading position on the contact glass 301. When the reading of the original at the reading position on the contact glass 301 by the scanner unit 300 is completed, the ADF 400 conveys the read original to the discharge roller 406 by the conveyance belt 405, and discharges the original by the conveyance roller 406. It is discharged onto the table 407.

  As shown in FIG. 2, the optical writing unit 230 includes an LD (Laser Diode) array 231, a collimating lens 232, an aperture 233, a cylindrical lens 234, a polygon mirror 235, a polygon as a laser beam bundle source. A WTL (barrel toroidal lens: lens for surface tilt correction) 236 for correcting the surface tilt of the mirror 235, a folding mirror 237, a dustproof glass 238, a synchronization detection sensor 239, and the like are provided, and the LD array 231 serves as each light source. Laser beams emitted from a plurality of LDs are applied to the photosensitive member 211 (the photosensitive member 211 represents the photosensitive members 211Y, 211C, 211M, and 211K). The optical writing unit 230 includes the optical scanning system shown in FIG. 2 corresponding to each color YMCK, and the LD array 231 for each color corresponds to the laser bundle modulated based on the image data of each color. Irradiate the photoconductors 211Y, 211C, 211M, and 211K. Note that the LD array 231 may be one in which LDs as a plurality of light emission sources are arranged side by side in the sub-scanning direction, for example.

  The laser beam emitted from the LD array 231 passes through the collimating lens 232, the aperture 233, and the cylindrical lens 234, is shaped into a laser beam having a predetermined shape, and is irradiated onto the polygon mirror 235. The polygon mirror 235 continuously rotates at a predetermined high speed, reflects (deflects) the incident laser beam toward the folding mirror 237, and repeatedly moves and scans in the main scanning direction (axial direction of the photosensitive drum 19). To do. The laser beam reflected by the polygon mirror 235 is subjected to surface tilt correction by the surface tilt correction lens 17, then enters the folding mirror 237, and the angle is changed by the folding mirror 237, so that the surface of the photoconductor 211 A spot image is formed with a predetermined beam diameter.

  The laser beam reflected by the polygon mirror 235 and immediately before main scanning on the photosensitive member 211 is a laser on the main scanning start point side outside the main scanning writing area (outside a predetermined main scanning width) on the surface of the photosensitive member 211. The laser beam is incident on a synchronization detection sensor 239 provided on the beam scan. The synchronization detection sensor 239 detects the incident laser beam, generates a synchronization detection signal, and outputs the synchronization detection signal to the writing control unit 1300.

  As shown in FIG. 3, the digital copying apparatus 1 has a circuit block configuration, and includes a read processing unit 1100 that performs data processing of the scanner unit 300, a write control that performs data processing of the image processing unit 1200, and the printer unit 200. A unit 1300, a memory 1400, a light source control unit 1500, and the like, and a control unit 1600 that controls the entire digital copying apparatus 1.

  The reading processing unit 1100 has a phenomenon that the reading data varies even though the analog image data obtained by photoelectric conversion of the CCD 305 is sampled, A / D (analog / digital) conversion processing, and a document having a uniform density are read. Processing such as shading correction to be corrected is performed and output to the image processing unit 1200. The image processing unit 1200 performs image quality correction processing such as image scaling processing, rotation processing, and edge processing, and then multi-value image data. It is converted into (for example, 4-bit 16 values) and output to the write control unit 1300.

  The control unit 1600 includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processing Unit), and the like. The CPU uses the RAM as a work memory based on a program in the ROM. Then, each part of the digital copying apparatus 1 is controlled to control the operation of the entire digital copying apparatus 1.

  The write control unit 1300 uses an application specific integrated circuit (ASIC), and includes a printer image processing unit 1310, a write DMAC (direct memory access controller) 1320, a read DMAC 1330, a light emission data generation unit 1340, and a pixel clock control. The unit 1350 and the like are functionally configured. As the ASIC configuration, not only the writing control unit 1300 but also the reading processing unit 1100 and the image processing unit 1200 may be configured by ASIC. In this case, each may be configured by different ASICs, One ASIC may be configured, and when the reading processing unit 1100, the image processing unit 1200, and the writing processing unit 1300 are configured by one ASIC, in executing each function, other function units are mutually connected. You can use it or use the hardware configuration.

  The printer image processing unit 1310 includes a gray scale image processing unit 1310G and a plurality of color plate (channel) image processing units 1310Ca to 1310Cn. The gray scale image processing unit 1310G includes a gray scale conversion unit 1311G and a three-state conversion. A unit 1312G, an image matrix edge determination unit 1313G, and the like. Each channel image processing unit 1310Ca to Cn includes a three-state conversion unit 1311Ca to Cn, an image matrix 1312Ca to Cn, a look-up table 1313Ca to Cn, a target pixel code output unit 1314Ca to Cn, and the like. The pixel clock control unit 1350 generates a pixel clock that is a processing operation timing of the image data in the write control unit 1300 and outputs the pixel clock to each necessary unit. The frequency of the pixel clock is a main scan whose cycle is one pixel. It coincides with the period. Note that the three-state conversion units 1311Ca to Cn, the image matrices 1312Ca to Cn, the look-up tables 1313Ca to Cn, and the target pixel code output units 1314Ca to Cn are equivalent to the number of LD arrays 231 that are optical writing light sources. Although the number of color plates and the number of channels are not necessarily the same, different sub-scanning image data of one color plate are emitted by using a plurality of light sources (LD array 231). In this case, image data of different color plates can be appropriately set according to the case where a single light source (LD array 231) is used to emit a laser beam.

  The multi-valued image data (input multi-valued pixel data) output from the image processing unit 1200 includes the grayscale conversion unit 1311G of the grayscale image processing unit 1310G and the three-state conversion units 1311Ca to Cn of the image processing units 1310Ca to 1310Cn of each channel. Is input.

  The gray scale conversion unit (gray scale conversion unit) 1311G of the gray scale image processing unit 1310G converts the input multi-valued image data to gray scale and outputs it to the three state conversion unit 1312G to output the three state conversion unit (gray scale state conversion). Means) 1312G converts the input multi-valued image data into “white”, “black”, “halftone” based on the white threshold (colorless threshold) and the black threshold (maximum color threshold) set by the control unit 1600. Are output to the image matrix edge determination unit 1313G. The image matrix edge determination unit (grayscale feature detection unit) 1313G grasps data of the target pixel and adjacent pixels, and determines image features such as whether the target pixel is an edge portion, an isolated line, or the like (feature determination). The feature discrimination results are output to the image matrices 1312Ca to Cn of the channel image processing units 1310Ca to Cn.

  The three-state conversion units (color state conversion units) 1311Ca to Cn of the channel image processing units 1310Ca to 13n are input based on a white threshold value (colorless threshold value) and a black threshold value (maximum color threshold value) set by the control unit 1600. The multi-valued image data is distributed into three state values of “white”, “black”, and “halftone” and output to the respective image matrices 1312Ca to Cn. That is, the three-state converters 1311Ca to Cn convert, for example, multi-value image data having a 4-bit 16-value (0 to 15) density value into 2-bit 4-value data. When the input multi-valued image data is 4-bit 16-value, the three-state converters 1311Ca to Cn are image data in which the toner loading amount increases as the data value increases. It is assumed that the colorless threshold value (hereinafter referred to as the white threshold value for simplicity of description) is “1” and the maximum color threshold value (hereinafter referred to as “simplification”) for which the toner loading amount is in the maximum state. , Black threshold value) is “14”, when the input multi-valued image data has a data value of “14” or more, the pixel is determined to be the maximum color pixel (black pixel), and When converted to black state values (maximum color state values) and output to the image matrices 1312Ca to Cn, and the input multi-value image data has a data value of “1” or less, the pixel is a colorless pixel ( White pixel) and white It converted to state value (no color states values), and outputs the image matrix 1312Ca～Cn. Further, when the input multi-valued image data has a data value between “2” and “13”, the three-state conversion units 1311Ca to 13n determine that the input is a halftone, and change the halftone state value to the halftone state value. The image is converted and output to the image matrices 1312Ca to Cn. In the following description, a non-colored pixel (a pixel having no toner stacking amount) is appropriately referred to as a white pixel, a non-colored pixel is referred to as white, and a maximum color pixel (a pixel having a large toner stacking amount) is appropriately black. Although the pixel and the maximum color are black, unless otherwise specified, the white pixel means no color pixel, the white means no color, the black pixel means the maximum color pixel, and the black means the maximum color.

  Each image matrix (color feature detection means, reference look-up table determination means) 1312Ca to Cn includes at least one pixel including a target pixel to be output in the sub-scanning direction, and the front and rear adjacent centering on the target pixel in the main scanning direction. A pixel window (matrix) of one line or more is generated with three or more pixels in the main scanning direction including three pixels, and the state values for each pixel from the three-state conversion units 1311Ca to Cn are arranged in the generated pixel window, Feature identification such as edge portion or isolated line is performed. The image matrices 1312Ca to Cn discriminate this feature using, for example, a matrix of 3 pixels × 1 line, as shown in FIG. 4, and include 6 edge features and 5 non-edge features (edgeless features). A total of eleven features are performed.

  In addition, the image matrix 1312Ca to Cn receives the feature determination result from the image matrix edge determination unit 1313G of the grayscale image processing unit 1310G, and the image matrix 1312Ca to Cn receives all of the grayscale image feature determination result and all of the same pixels. The thinning / thickening is determined based on the feature discrimination results of the image matrices 1312Ca to Cn of the channel image processing units 1310Ca to 13n, and the thinning / thickening of the reference lookup tables held by the lookup tables 1313Ca to 1313Cn is determined. A reference lookup table to be used in the thickening process is determined. Therefore, it is necessary to perform feature discrimination simultaneously on the same pixel of all channels. However, in the tandem type digital copying apparatus 1 in which the photoconductors 211Y, 211C, 211M, and 211K of the respective colors are arranged in parallel, the images of the respective colors are respectively formed on the photoconductors 211Y, 211C, 211M, and 211K by the optical writing unit 230. An electrostatic latent image is formed by irradiating a laser beam based on the data, and the toner image formed by developing the electrostatic latent image with toner is sequentially superimposed and transferred onto the conveyed intermediate transfer belt 241. In order to form a full-color image and transfer the full-color image on the intermediate transfer belt 241 to a transfer sheet, writing with a laser beam to the photoconductors 211Y, 211C, 211M, and 211K has a time difference between the color plates, In a state with a time difference, pixels at the same position cannot be obtained at the same time. Therefore, the digital copying apparatus 1 of the present embodiment inputs color image data with uniform pixel positions from the image processing unit 1200 to each of the image processing units 1310G and 1310Ca to Cn of the printer image processing unit 1310, and performs image processing. Image data obtained as a result of processing in the image processing units 1310Ca to Cn is temporarily placed on the memory 1400 by the writing DMAC 1320, and read from the memory 1400 by the reading DMAC 1330 at a timing delayed according to the writing timing of each plate. The data is transferred to the unit 1500.

  The look-up tables 1313Ca to Cn include the number of types of features (“front end black”, “front end white”, “rear end black”) detected using an image matrix as shown in FIGS. , “Rear edge white”, “Isolated black”, and “Isolated white”) and the channel were halftone, all white, all black, but no edge feature was detected, but the edge feature was not detected in another channel There are a total of seven reference look-up tables when there is no edge to be used when it is detected and execution of thinning / thickening processing is determined. The reference look-up table is shown in FIG. It is a table like this. The look-up tables 1313Ca to Cn are for setting density conversion values when density conversion is performed on the reference pixel density by thickening processing or thinning processing according to the detected feature. Is to set a density conversion value for obtaining a desired corrected image by performing uniform image processing. In addition, an enable / disable setting key for setting the validity / invalidity of the vertical thinning / thickening processing function of the digital copying apparatus 1 is provided in the operation display unit. When the thick line processing function is disabled, the functions of the lookup tables 1313Ca to Cn are disabled and the input pixel density value is output as it is. Furthermore, the look-up tables 1313Ca to Cn have a through mode, and when the through mode is set, the input pixel density value is output as it is. For example, when performing thickening processing, there are two methods for giving density to white / black / white (front white) or black / white / white (rear end white) intermediate pixels. If this is done, the look-up tables 1313Ca to Cn may be overweight, so that the reference look-up table for one side, for example, the front white is set to the through setting, and the effective parameter is set to the reference look-up table for the rear white. By setting, thickening processing is performed only for the trailing white.

  Further, the channel image processing units 1310Ca to Cn determine whether or not to perform thinning / thickening processing, perform grayscale feature discrimination and all channel feature discrimination, and then aggregate the feature discrimination results. This is performed based on an edge processing algorithm (see FIG. 6) described in detail.

  As the window generation method of the image matrices 1312Ca to Cn, an existing method can be used. For example, in the case of a pixel window of three pixels and one line, three lines of flip-flops are prepared and the pixel clock control unit 1350 A pixel window in which state values of three pixels in the main scanning direction, which are delayed pixel by pixel based on the pixel clock, is generated. As described above, the image matrices 1312Ca to Cn may construct a window of at least one pixel in the sub-scanning direction and three pixels in the main scanning direction, but the window size is one pixel in the sub-scanning direction and the main scanning direction. The size is not limited to three pixels, and may be larger than this size. In this case, a matrix used in the reading processing unit 1100, the image processing unit 1200, or the like, for example, a matrix for edge enhancement processing may be used in combination. Such combined use of processing functions with other processing is performed when the other processing units, for example, the image processing unit 1200, the reading processing unit 1100, and the writing control unit 1300 are constructed using one ASIC. Can be easily used together.

  The image matrices 1312Ca to Cn determine a reference lookup table of the lookup tables 1313Ca to Cn based on the arrangement state of the state values in the pixel window, and use the data values of the determined reference lookup table as a target pixel code output unit. Output to 1314Ca to Cn.

  The lookup tables 1313Ca to 1313Cn correspond to feature types including one edgeless reference lookup table associating the reference pixel density value and the density after conversion of the density value as shown in FIG. 5, for example. Seven are provided.

  Each of the channel image processing units 1310Ca to Cn acquires the density of the reference pixel (the preceding pixel, the succeeding pixel, or the target pixel) by the edge processing algorithm (see FIG. 6) using the image matrices 1312Ca to Cn, and the lookup table 1313Ca to When one of the seven reference lookup tables of Cn is determined, the pixel value output unit 1314Ca of the target pixel code output unit 1314Ca is configured to refer to the determined reference lookup table and use the converted density value corresponding to the reference pixel density as an output pixel value. Output to Cn.

  The target pixel code output units (output data generation means) 1314Ca to Cn switch the input image data from the image processing unit 1200 to the pixel values of the selected reference lookup table of the lookup tables 1313Ca to Cn, and output a large number The value is determined as value image data, and the determined multi-value pixel data is output to the write DMAC 1320.

  The write DMAC 1320 transfers and arranges the multi-value pixel data from the target pixel code output units 1314Ca to Cn of the channel image processing units 1310Ca to Cn to the memory 1400, and the read DMAC 1330 arranges the multi-value pixel data arranged in the memory 1400. Pixel data is read according to the writing timing of each plate and transferred to the light emission data generation unit 1340.

  The light emission data generation unit 1340 includes light emission data generation units 1340Ca to Cn corresponding to the respective channels, and each of the light emission data generation units 1340Ca to Cn receives corresponding pixel-of-interest code output units 1314Ca to Cn input from the read DMAC 1330. Based on the multi-value pixel data from the light source, a light source lighting signal for controlling on / off of the LD array 231 and a light source emission amount control signal for controlling the light amount are generated and output to the light source control unit 1500.

  The light source control unit 1500 includes channel light source control units 1500Ca to Cn for channels, and a light source lighting signal and a light source emission amount control signal are input from the corresponding light emission data generation units 1340Ca to 1340Cn, and these signals are received. Based on the above, the lighting / extinguishing of the LD array 231 is controlled and the amount of emitted light is controlled.

  The digital copying apparatus 1 includes a ROM, an EEPROM (Electrically Erasable and Programmable Read Only Memory), an EPROM, a flash memory, a flexible disk, a CD-ROM (Compact Disc Read Only Memory), a CD-RW (Compact Disc Rewritable), and a DVD. (Digital Video Disk), SD (Secure Digital) card, MO (Magneto-Optical Disc), etc., that is, a recording medium readable by a CPU of the control unit 1600 of the digital copying apparatus 1 An image forming program for executing the image forming method is read into the ROM or other memory of the control unit 1600 and introduced into the ASIC that constitutes the write control unit 1300, thereby efficiently controlling the line width of the color vertical lines, which will be described later. Constructed as a digital copying apparatus 1 that executes an image forming method that is performed properly and appropriately It has been. This image forming program is a computer-executable program written in a legacy programming language such as assembler, C, C ++, C #, Java (registered trademark) or an object-oriented programming language, and is stored in the recording medium. Can be distributed.

  Next, the operation of this embodiment will be described. The digital copying apparatus 1 according to the present exemplary embodiment performs image forming processing for appropriately determining the background color and vertical line color of a color image and appropriately adjusting the line width. In order to clarify the explanation, in the following explanation, the case where the number of channels is two, that is, the foreground channel Ca and the background channel Cb, will be described. However, the number of channels is not limited to two, but two. The above description may be applied to the case where the number of channels is more than two.

  That is, the digital copying apparatus 1 inputs analog color image data photoelectrically converted by the CCD 305 of the scanner unit 300 to the reading processing unit 1100, and the reading processing unit 1100 performs sampling processing, A / D conversion processing, shading correction processing, and the like. The above processing is performed and passed to the image processing unit 1200. The image processing unit 1200 of the scanner unit 30 performs image quality correction processing such as image scaling processing, rotation processing, and edge processing, and then converts the data into multi-value image data (for example, 4-bit 16 values), and prints the printer. To the write control unit 1300 of the unit 200. The write control unit 1300 is a light emission data generation unit 1340Ca to Cn, and from the multi-value image data from the image processing unit 1200, a light source lighting signal for controlling on / off of each color (each plate) LD array 231 and a light source light emission for controlling the light amount. The amount control signals are respectively generated and output to the light source control units 1500Ca to Cn of the corresponding channels of the light source control unit 1500, and the light source control units 1500Ca to Cn output the light emission data generation units 1340Ca to Cn of the write control unit 1300. Based on the light source lighting signal and the light source emission amount control signal, lighting / extinguishing of the LD array 231 is controlled and the amount of emitted light is controlled. In the digital copying apparatus 1, the printer unit 200 forms electrostatic latent images on the photoreceptors 211Y, 211C, 211M, and 211K by the LD array 231 that is controlled to be lit for each color (plate), and develops, transfers, and fixes. Thus, a color toner image is formed on the transfer paper.

  However, as described above, as a characteristic of the digital copying apparatus 1, even if the same input multi-value image data (pixel data) is used, there is a difference in the thickness between the vertical line and the horizontal line formed on the transfer paper. Deteriorates. For example, when a line is formed by turning on the LD array 231 in one pixel period in the main scanning direction, even if the LD array 231 is turned on for a period corresponding to one pixel and beam irradiation is performed, the transfer depends on the beam diameter and development conditions. The thickness of the line of the toner image formed on the paper is different from the ideal thickness of one pixel line. Further, as described above, when the vertical line is not a single color but a color, an image is formed by the number of laser beams from the LD array 231 corresponding to the color plate. Depending on the characteristics, even if the positional deviation for each color is corrected, the vertical line may become thinner or thicker for each color. In this case, it is necessary to make adjustments by thickening processing and thinning processing for each plate. However, depending on the combination of the color of the vertical line and the color of the background, such a feature of the vertical line may not be seen. As described above, in the color image, the image characteristics between the channels (plates) are different. Therefore, when the thinning process and the thickening process are uniformly performed, the color plate is mixed and the color changes. A problem occurs. It is necessary to appropriately solve problems peculiar to thinning processing and thickening processing in the case of such a color image.

  Therefore, the digital copying apparatus 1 according to the present embodiment performs edge processing using an algorithm as shown in FIG. 6 to perform feature determination in consideration of the background color and the vertical line color, and performs thinning processing, thickening processing, Control without processing. That is, the digital copying apparatus 1 detects the gray scale of the multi-valued image data and the features of the target pixel and adjacent pixels (edge feature and no edge feature) in each color (each channel), In the edge determination process for edge determination based on the feature, the reference lookup table of the lookup tables 1313Ca to Cn is determined according to the edge determination result to determine the output pixel density of the target pixel, and the processing speed is improved. In order to make the configuration simple and small-scale, the input multi-valued image data is converted into three states of white pixel, black pixel, and halftone pixel, and the target pixel in the three states is at least three pixels in the main scanning direction, The image state is determined from the array state of the state values in the pixel window of the image matrix 1312Ca to Cn of one pixel in the sub-scanning direction, Depending on another result, thick line processing or thin line processing or “no processing” is determined, the reference lookup table of the reference destination of the lookup tables 1313Ca to Cn is changed, the pixel value of the target pixel is determined, and the input multiple The value image data is corrected, and the light emission data generation unit 1340 generates a light source lighting signal and a light source emission amount control signal. In the present embodiment, as described above, two channels Ca and Cb (channel Ca is the foreground and channel Cb is the background) will be described, but the number of channel nests is not limited to two.

  That is, as shown in FIG. 6, the digital copying apparatus 1 receives multi-value image data from the image processing unit 1200 to the gray scale image processing unit 1310G of the write control unit 1300 and the image processing units 1310Ca and Cb of the channel Ca and channel Cb. When input (step S101), the grayscale image processing unit 1310 converts the input multivalued image data input from the image processing unit 1200 to grayscale by the grayscale conversion unit 1311G and outputs the grayscale to the three-state conversion unit 1312G. (Step S201) The three-state conversion unit 1312G is multi-value grayscaled by the grayscale conversion unit 1311g based on the white threshold (colorless threshold) and the black threshold (maximum color threshold) set by the control unit 1600. The image data is divided into three state values “white”, “black”, and “halftone”. And it outputs the over-di matrix edge judgment section 1313G. The image matrix edge determination unit 1313G grasps data of the target pixel and adjacent pixels in the pixel matrix of 3 pixels × 1 line, and determines whether the target pixel at the center of the pixel matrix is an edge portion, an isolated line, or the like. The feature of the image is discriminated (feature discrimination), and the feature discrimination result is output to the image matrices 1312Ca and Cb of the channel image processing units 1310Ca and Cb (step S202).

  Further, the image processing units 1310Ca and Cb of each channel are input based on the white threshold (colorless threshold) and the black threshold (maximum color threshold) set by the three-state conversion units 1311Ca and Cb from the control unit 1600. Multi-valued image data is distributed into three state values of “white”, “black”, and “halftone” and output to the respective image matrices 1312Ca and Cb. The image matrices 1312Ca and Cb generate a pixel window (matrix) of one pixel in the sub-scanning direction and three pixels in the main scanning direction, and array the state values for each pixel from the three-state conversion units 1311Ca to Cn in the generated pixel window. Then, it is determined whether or not there is a feature such as an edge portion or an isolated line (steps S301 and S401). When there is an edge feature in steps S301 and S401, the image matrices 1312Ca and Cb shift to the next determination as candidates for thinning / thickening processing. In the next determination, the features detected in two or more channels (currently, channel Ca and channel Cb) are the same features (normal edges) or complementary features (reverse edges) as the edge features of the grayscale image. It is determined whether there is any (steps S302 and S402). Here, complementary edges (reverse edges) are black and white (rear end black) with respect to white black and white (leading white), black and white (isolated white) with respect to black and white (isolated black), and black and white black (front end). Represents the inversion of each other's characteristics, such as black white and white (rear edge white) against black. As an actual image example, for example, when cyan characters / lines are arranged on a yellow background, the portion where the characters / lines are placed on the yellow plate is outlined, and conversely, cyan The background is white on the plate. The combinations of the relationships between the features are as shown in FIG. 7. In FIG. 7, double circles are the same edge (normal edge), single circles are the complementary edges (reverse edge), and x is the correlation. There is no edge. For example, in FIG. 7, when the gray scale is the leading white edge, the channel Ca or the channel Cb is the same edge (front edge) if it is the leading white edge, and the complementary edge (reverse edge) if it is the trailing black edge. If the leading edge is black, the trailing edge is white, isolated white, or isolated black, the edge has no correlation.

  In steps S302 and S402, when one or more channels Ca and Cb detect the same feature (positive edge) or a complementary feature (reverse edge) with the grayscale image, the channels Ca and Cb The image matrix 1312Ca and / or the image matrix 1312Cb checks whether the thinning / thickening processing (thinning processing) is set to invalid (no image correction) (steps S303 and S403), and the thinning / thickening processing is performed. When it is valid, it is checked whether the reference lookup table (LUT) of the target edge in the lookup tables 1313Ca and Cb is through (steps S304 and S404). In steps S304 and S404, when the reference look-up table (LUT) of the detected channels Ca and Cb having the same feature (positive edge) or the complementary feature (reverse edge) with the grayscale image is not through, the reference is made. A pixel determination process is performed, for example, a reference pixel determination table as shown in FIG. 8 is used to determine a reference pixel for pixel density conversion as a thinning / thickening process (steps S305 and S405). For example, the target edge reference look-up table (LUT) as shown in FIG. 5 is selected to perform density conversion of the pixel of interest (steps S306 and S406), and the converted pixel density is set as described above. The target pixel code output units 1314Ca and Cb are finally output to the light source control unit 1500 (steps S307 and S407).

  In this case, when positive edges are detected in the two channels Ca and Cb of the foreground and the background, the same processing is performed in the two channels, so that uniform thinning / thickening processing can be performed between the channels. it can. Further, in this case, since the color tables and the features are provided with the lookup tables 1313Ca and Cb, the difference in the degree of thinning / thickening processing can be controlled by the color plates.

  When a reverse edge is detected in any one of the channels Ca and Cb, processing corresponding to the positive edge side is performed regardless of the thinning / thickening settings of the channels Ca and Cb. That is, when the normal edge performs thickening processing, the reverse edge performs thinning processing, and the degree of thickening processing or thinning processing can be controlled by the density conversion values of the lookup tables 1313Ca and Cb.

  Therefore, when complementary features are detected, the reference pixels are the same, and the thinning and thickening are performed by adjusting to the opposite thinning and thickening processes to suppress color change. Processing can be performed.

  When features that are not in a complementary relationship (edges having no correlation in FIG. 7) are detected in steps S302 and S402, the image matrices 1312Ca and 1312Cb are thinned as part of a random image not composed of vertical and horizontal lines. It is determined that there is no thick line processing (thin line processing). By doing so, it is possible to prevent the random image from being unintentionally performed by performing the thinning process or the thickening process of the vertical line carelessly.

  When main edges or reverse edges are not detected in steps S302 and S402, or when thinning / thickening processing is disabled in steps S303 and S403, or in steps S304 and S404, When the edge lookup tables 1313Ca and Cb are set to “through”, the image matrices 1312Ca and Cb output the target pixel density value of the input multi-valued image data as an output pixel value as it is, and the process ends (step S308, S408).

  Hereinafter, in the case where the color vertical line becomes thick or thin according to the background color of the input multi-valued image and the vertical line color of the foreground, the digital copying apparatus 1 appropriately performs feature detection to make the thin line / thick line. The case of performing the digitization process will be specifically described sequentially. In the following description, as described above, the case where the number of channels is two will be described. However, the number of channels is not limited to two, and may be two or more. The same applies to the case where the number of channels is more than two.

<Thinning processing when the background is white and one vertical color is fat>
First, a thinning process for thinning a vertical line of one pixel when the main and sub resolutions are the same, the background is white, and one vertical line of the foreground color is thickened in the main scanning direction will be described with reference to FIG. Description will be made with reference to FIG. Now, the input multi-value pixel data is multi-value 4 bits, the white threshold value is “1”, and the black threshold value is “14”. The three-state conversion units 1312G, 1311Ca, and 1311Cb have the input multi-value pixel data “14”. ”Or more, the pixel is determined as a black pixel. If it is“ 1 ”or less, the pixel is determined as a white pixel, and pixels between“ 2 ”and“ 13 ”are determined as halftones.
In the gray scale image processing unit 1310G, the input multi-valued image data as shown in FIG. 9 is converted into gray scale by the gray scale conversion unit 1311G, and the state is converted into three states by the three state conversion unit 1312G. The image matrix edge determination unit 1313G performs matrix processing to perform edge determination. The density value (0, 15, 0) of the upper left matrix in FIG. 9 is characterized as isolated black. Further, in the image processing units 1310Ca and Cb of the channels Ca and Cb, the state conversion is performed by the three-state conversion units 1311Ca and Cb on the input multi-valued image data as shown in FIGS. 10 (a) and 11 (a). Edge determination is performed on the state values performed using the image matrices 1312Ca and Cb. The image matrix 1312Ca of the channel Ca uses the density value (0, 15, 0) at the same pixel position as that of isolated black in gray scale. Black is detected as a positive edge, but in the image matrix 1312Ca of the channel Cb, no edge feature is detected for the density value (0, 2, 0) at the same pixel position, and it is determined that there is no edge.

  When the edge processing of the algorithm shown in FIG. 6 is performed based on the feature detection result of the feature detection of the input multi-value image data by the three-state conversion units 1312G and 1311Ca and Cb of the gray scale and channels Ca and Cb. As described above, it is determined to perform the thinning process in both the channel Ca and the channel Cb, and the reference pixel is determined. Then, the image matrix 1312Ca of the channel Ca selects a reference lookup table corresponding to the isolated black of the lookup table 1313Ca, and uses the reference lookup table to set the reference pixel “15” to, for example, FIG. As shown in (b), it is converted to “11”. Further, the image matrix 1312Cb of the channel Cb selects a reference lookup table dedicated to no edge of the lookup table 1313Cb, and the reference pixel “2” is selected using the reference lookup table, for example, FIG. As shown in b), it is converted to “1”. Further, there is a density value (0, 13, 0) at another pixel position of the channel Cb (the middle right side of FIG. 11A), and this pixel position is as shown in FIGS. 9 and 10A. In addition, the feature is detected as isolated black in the gray scale G and the channel Ca. For this pixel position, the channel Ca image matrix 1312Ca selects the isolated black reference lookup table and converts the reference pixel “15” to “11” as shown in FIG. The Cb image matrix 1312Cb selects the isolated black reference lookup table and converts the reference pixel “13” to “10” as shown in FIG. 11B. Further, as shown in FIG. 10A, the channel Ca has characteristics other than isolated black, that is, the trailing white of the density value (15, 0, 0) and the leading white of the density value (0, 0, 15). In FIG. 10, the look-up table 1313Ca for these features is set to through, and the input pixel density value is output as it is.

  Therefore, the thinning / thickening processing is turned off, and in the edge processing shown in FIG. 6, it is determined that there is no edge for the corresponding part of the matrix, and the thinning / thickening processing is also suppressed for the channel Cb. The

  As a result, the density value of the black pixel at the center of isolated black, which is black and white (◯ ● ○), is converted into a small value according to the density value of the reference pixel, and the vertical line can be made thin.

<Thinning processing when the background is color solid and one vertical color is fat>
Next, thinning processing for thinning a vertical line of one pixel when the resolution is the same in the main and sub, the background is color solid, and one color vertical line is thick in the main scanning direction will be described with reference to FIGS. This will be described with reference to FIG. As described above, the input multi-value pixel data is multi-value 4 bits, the white threshold is “1”, and the black threshold is “14”.
In the grayscale image processing unit 1310G, when the three-state conversion unit 1312G performs state conversion on the input multivalued image data as shown in FIG. 12, the image matrix edge determination unit 1313G has two columns from the bottom in FIG. The density values (5, 15, 5) of the matrix in the three pixels at the left end of the eye are characterized as isolated black. In addition, in the image processing units 1310Ca and Cb of the channels Ca and Cb, the result of the state conversion performed by the three-state conversion units 1311Ca and Cb is a value as illustrated in FIGS. 13A and 14A. In this case, the image matrix 1312Ca of the channel Ca detects the positive edge of the density value (0, 15, 0) at the same pixel position as isolated black, but the input multivalue at the same pixel position is detected in the image matrix 1312Ca of the channel Cb. The density value (15, 15, 2) of the image data is determined as the rear end black.
However, as shown in FIG. 7, the rear end black in the channels Ca and Cb with respect to the isolated black of gray scale is an edge having no correlation which is neither a normal edge nor a reverse edge. In FIG. 13B, it is determined that there is no thinning / thickening processing. As shown in FIGS. 13B and 14B, for this pixel, the input pixel density values are output pixels as they are in all the channels Ca and Cb. Output as a value. That is, this pixel portion can be determined as a part of a random image that is not a vertical or horizontal line, and unnecessary thinning / thickening processing can be prevented.
In FIGS. 12 to 14, the pixel at the same pixel position is (0, 15) in the channel Ca with respect to the isolated black of the density value (7, 15, 7) in the upper left three pixels of the gray scale in FIG. , 0) and channel Cb are isolated white of (15, 2, 15), and from FIG. 7, the isolated black of channel Ca is the positive edge, and the isolated white of channel Cb is the isolated white of channel Cb. The reverse edge. Therefore, for the reference pixel, in channel Ca, the isolated black reference lookup table of lookup table 1313Ca is selected to convert reference pixel “15” to “11”, and in channel Cb, lookup table 1313Cb. The isolated white reference lookup table can be selected to convert the reference pixel “2” to “1” and output as an output pixel. As a result, when the background is a solid color and the line of one vertical color is thick, thinning processing can be performed appropriately.

<Thinning processing when the background is white and one vertical color is fat>
FIG. 15 to FIG. 17 show thickening processing for thickening a vertical line of one pixel when the resolution is the same in the main and sub, the background is white, and one vertical color line is thinned in the main scanning direction. This will be explained based on. Similarly to the above, the input multi-value pixel data is multi-value 4 bits, the white threshold is “1”, and the black threshold is “14”.

  Now, in the gray scale image processing unit 1310G, for the gray scale density values (0, 15, 0) of the input multivalued image data in the upper left of FIG. 15, the channel Ca in FIG. The pixel density value (0, 15, 0) at the pixel position is determined as an isolated point using the image matrix 1312Ca. However, the density value “15” of the reference pixel is the maximum value because the pixel density is 4 bits, and the thickening process cannot be performed any more. Furthermore, the lookup table 1313Ca cannot be set to through in order to enable the thickening process of isolated black with low density of other channels (channel Cb) at the same pixel position. In such a case, thickening processing can be performed by giving density to white at the center when white black and white (leading white) or black and white (rear white) continues. In this embodiment, FIG. As shown in (b), by setting the leading white look-up table to the through setting and the effective setting for the trailing white look-up table, the density is given to the white at the center of the black-and-white (the trailing white). Perform thick line processing. Therefore, the pixel density at the same pixel position in the channel Cb is (0, 2, 0) and no edge, but it is determined as isolated black in the channel Ca. Therefore, in the edge processing shown in FIG. The reference pixel is thickened. As described above, since the density value “15” of the reference pixel of the channel Ca is the maximum value, the converted value does not change, but the channel Cb selects the lookup table 1313Cb dedicated to no edge, As shown in FIG. 17B, for example, the density value is converted to “8”.

  In addition, for the rear end white pixel of (15, 0, 0) of the channel Ca shown in FIG. 16A, a reference lookup table corresponding to the rear end white of the lookup table 1313Ca is used with the reference pixel as the preceding pixel. As shown in FIG. 16B, the pixel density is converted from “0” to “4”. On the other hand, the pixel at the same pixel position in the channel Cb has a pixel density of (2, 0, 0) and is not a feature of the edge, but the channel Ca is white at the rear end, so thinning / thickening processing is effective. become. Therefore, the image matrix 1312Cb of the channel Cb selects the reference lookup table for no edge of the lookup table 1313Cb, and as shown in FIG. 17B, the density value “2” of the preceding pixel as the reference pixel. For example, a process of converting the value into a density value “8” is performed. Further, as shown in FIG. 17A, by setting the density value “2” in the reference lookup table of the lookup table 1313Cb as the density value after conversion of the reference pixel with respect to the preceding pixel density value “13”. As shown in FIG. 17B, a thickening process extending to adjacent pixels can be performed.

  In this way, when the line of one color vertical pixel in the color solid background becomes thick, it is possible to accurately recognize one color vertical pixel and perform thinning processing appropriately.

<Thinning processing when the background is white and the color vertical multiple pixel lines are thick>
Next, when the main and sub resolutions are the same, the background is white, and the vertical line of two pixels in the main scanning direction of color is thickened in the main scanning direction, the thinning process for thinning the vertical line of two pixels Will be described with reference to FIGS. As described above, the input multi-value pixel data is multi-value 4 bits, the white threshold is “1”, and the black threshold is “14”.
In the grayscale image processing unit 1310G, when the three-state conversion unit 1312G performs state conversion on the input multivalued image data as shown in FIG. 18, the image matrix edge determination unit 1313G displays the density value (0 , 15, 15) are distinguished from the front end black, and the density values (15, 15, 0) are determined to be the rear end black. Further, in the image processing unit 1310Ca of the channel Ca, when the result of the state conversion performed by the three-state conversion unit 1311Ca is a value as illustrated in FIG. 19A, the image matrix 1312Ca of the channel Ca includes the same pixel. A positive edge is detected with the position density value (0, 15, 15) as the leading edge black and the density value (15, 15, 0) as the trailing edge black, and as shown in FIG. The density value is reduced to, for example, (0, 12, 13), (12, 13, 0), and thinning processing is performed. On the other hand, in the image processing unit 1310Cb of the channel Cb, when the result of the state conversion performed by the three-state conversion unit 1311Cb is a value as illustrated in FIG. 20A, the image matrix 1312Cb is a matrix at the same pixel position. Density values (0, 2, 2) and density values (2, 2, 0) are determined to have no edge. According to the edge processing of FIG. 6, as shown in FIG. , (0, 1, 1), (1, 1, 0), and the thinning process is executed. That is, thinning is performed by reducing the density values on both sides of a vertical line composed of a plurality of pixels.

  In this way, when the background is white and the vertical line composed of a plurality of color pixels in the main scanning direction becomes thick, the color vertical line composed of the plurality of pixels in the main scanning direction is accurately recognized and thinned appropriately. Processing can be performed.

  In the thinning process when a plurality of vertical lines are thickened, it is not always necessary to thin both sides of the vertical lines, and one side may be thinned. When narrowing one side of the vertical line, processing is performed by setting either one of the two look-up tables for the white end and the black for the rear end to the through setting. Can do.

<Thinning processing when the background is color solid and the color vertical multiple pixel lines are thin>
Next, when the main and sub resolutions are the same, the background is color solid, and the vertical line of 2 pixels in the main scanning direction of color is thinned in the main scanning direction, the thickening process for thickening the vertical line of 2 pixels Will be described with reference to FIGS. As described above, the input multi-value pixel data is multi-value 4 bits, the white threshold is “1”, and the black threshold is “14”.
In the grayscale image processing unit 1310G, when the three-state conversion unit 1312G performs state conversion on the input multivalued image data as shown in FIG. 21, the image matrix edge determination unit 1313G displays the density value (2 of the matrix in FIG. 21). 2, 12) is the leading white, the density value (10, 5, 5) is the trailing white, the density value (15, 10, 5) is the trailing black, and the density value (5, 5, 15) is the leading white. Is determined. Further, in the image processing unit 1310Ca of the channel Ca, when the input multi-valued image data as shown in FIG. 22A is subjected to state conversion by the three-state conversion unit 1311Ca, the image matrix 1312Ca of the channel Ca has the above gray scale. The density value (0, 0, 12) at the same pixel position as the edge determination of the leading edge white (positive edge), density value (10, 0, 0), trailing white (positive edge), density value (15, 10 and 0) are detected as the rear end black and the density values (0, 0 and 15) are detected as the front end white, and as shown in FIG. 22B, thickening processing is performed using two pixels. On the other hand, in the image processing unit 1310Cb of the channel Cb, when the input multivalued image data as shown in FIG. 23A is subjected to state conversion by the three-state converting unit 1311Cb, the image matrix 1312Cb determines the grayscale edge. The density value (5, 5, 0) at the same pixel position is no edge, the density value (0, 10, 10) is the leading black (reverse edge), and the density value (0, 0, 10) is the trailing white (reverse) Edge) and density value (10, 10, 0) are determined to be rear end black (reverse edge), but thick line processing is executed as shown in FIG. 23B according to the edge processing of FIG. That is, thickening is performed by increasing density values on both sides of a vertical line composed of a plurality of pixels.

  In this way, when the background is color solid and the vertical line consisting of a plurality of color pixels in the main scanning direction becomes thin, the color vertical line consisting of the plurality of pixels in the main scanning direction is accurately recognized and appropriately thickened. Processing can be performed.

  As described above, the digital copying apparatus 1 according to the present embodiment converts color multi-value pixel data into grayscale pixel data, and converts the grayscale pixel data into at least three state values of colorless, maximum color, and halftone. And the edge of the pixel of interest, an isolated line, etc. based on the array state of the state value of the pixel in a pixel window composed of a predetermined number of adjacent pixels around the pixel of interest of the converted grayscale pixel data For each color, the input multi-value pixel data is converted into at least three state values of colorless, maximum color, and halftone based on the colorless threshold and the maximum color threshold. The central pixel of the state value array having a predetermined characteristic detected for the grayscale pixel data in the state value array of the pixel in the pixel window is set as the target pixel. Based on the state value array, features such as edges and isolated lines of the target pixel are detected, and for each color, the target pixel of the input multi-value pixel data and a predetermined number of adjacent pixels adjacent to the target pixel A plurality of reference lookup tables in which data values of output multi-value pixel data are registered in correspondence with the state value array of the pixel in the pixel window in which the state value converted by the color state conversion processing is stored A reference lookup table to be referred to is determined based on the feature detection result in the grayscale feature detection and the feature detection result in the color feature detection, and the data value of the input multivalued pixel data By switching to the data value of the reference lookup table determined in the reference lookup table determination processing step, the color image formation is performed as the output multi-value pixel data. Cormorant.

  Therefore, regardless of the amount of information of the color input multivalued pixel data, it is possible to appropriately perform a thickening process that thickens the vertical lines and a thinning process that thins the input multivalued pixel data of the color, Image quality can be improved easily and inexpensively.

  In the digital copying apparatus 1 according to the present embodiment, the lookup tables 1313Ca to Cn of the channel image processes 1310Ca to Cn use the reference lookup table to narrow the dot image of the target pixel to be imaged in the main scanning direction. Thinning reference lookup table in which data values for thinning processing are registered, reference lookup table for thickening in which data values for thickening processing for thickening the pixel of interest are registered, and input multivalued pixels There is a no-process reference lookup table in which data values for no processing are registered, in which the target pixel of data is used as output multi-value pixel data as it is.

  Therefore, by referring to the reference lookup table as appropriate based on the feature detection result of grayscale feature detection and the feature detection result of each color feature detection, thinning processing, thickening processing, and no processing can be performed easily and appropriately. And the image quality can be improved even more easily and inexpensively.

  Furthermore, the digital copying apparatus 1 according to the present embodiment determines the reference lookup table for each color when the feature detected by the gray scale feature detection matches the feature detected by the color feature detection of the color, or both A reference look-up table for thinning processing for thinning the dot image of the target pixel to form an image in the main scanning direction or a thickening processing for thickening the target pixel when the features have a predetermined complementary relationship. A reference lookup table is selected.

  Therefore, the thinning / thickening process can be performed with the color plate having an appropriate blending state, and the thinning / thickening process can be performed with the color being appropriate.

  Further, in the digital copying apparatus 1 according to the present embodiment, the reference lookup table for each color uses the target pixel of the input multivalued pixel data as it is regardless of the grayscale feature detection and the feature detection result of the color feature detection. A through state for pixel data can be set.

  Therefore, it is possible to appropriately prevent over-thinning and over-thinning in the thickening process and the thinning process, and to perform more appropriate thinning / thickening process.

  Further, in the digital copying apparatus 1 of the present embodiment, the reference lookup table sets the pixel of interest to the pixel data value corresponding to the thinning process or the thickening process in the thinning process or the thickening process, and the target pixel Pixel data values of additional pixels to be added to pixel positions adjacent to are registered.

  Therefore, even if the pixel value of the input image data is the maximum density value, it can be appropriately thickened, and can be thickened or thinned in a natural state using a plurality of adjacent pixels. More appropriate thinning / thickening processing can be performed.

  Further, the digital copying apparatus 1 of the present embodiment uses a pixel window composed of 3 pixels in the main scanning direction and 1 pixel or more in the sub-scanning direction as the pixel window.

  Therefore, a vertical line can be detected with a simple configuration, and thinning / thickening processing can be performed easily and appropriately.

  In the above description, when the thinning characteristics and weighting characteristics of the vertical line are different for each channel, it may be necessary to perform processing to make a specific channel thicker and other channels to be unprocessed or thinned. In such a case, the processing for a specific channel is turned off or independently, and the thinning / thickening setting is performed to control the thickening processing and thinning processing for each channel.

  In this way, thinning / thickening processing can be performed easily and appropriately.

  In the above description, in order to process the line width of the line, the image matrices 1312Ca to Cn having the size of 3 pixels for main scanning and 1 pixel for sub scanning are used. The image matrices 1312Ca to Cn may be used in combination with other image detection matrices used in the digital copying apparatus 1.

  In this way, for example, the edge of a line composed of a plurality of pixels as shown in FIGS. 18 to 23 is also appropriately identified, the reference lookup table is determined, and the line thinning / thickening processing is performed. Can be performed appropriately.

  The invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to that described in the above embodiments, and various modifications can be made without departing from the scope of the invention. It goes without saying that it is possible.

  The present invention can be used in an image forming apparatus, an image forming method, an image forming program, and a recording medium such as a copying apparatus, a composite apparatus, and a printer apparatus that correct a pixel configuration for forming a color image.

1 is a schematic front view of a digital copying apparatus to which an embodiment of the present invention is applied. The perspective view of the optical writing unit of FIG. FIG. 3 is a block diagram of a main part of a digital copying apparatus. The figure which shows an example of the characteristic extracted by the matrix of 3 pixels x 1 line. The figure which shows an example of a lookup table. The flowchart which shows edge processing. The figure which shows the combination of the relationship between characteristics. The figure which shows an example of a reference pixel determination table. Explanatory drawing of the characteristic determination of the gray scale in the thinning process in case the background is white and one color vertical line becomes fat. Explanatory drawing of the thinning process in channel Ca when a background is white and one color vertical line becomes fat. Explanatory drawing of the thinning process in the channel Cb when a background is white and one color vertical line becomes fat. Explanatory drawing of the gray scale characteristic discrimination | determination in the thinning process in case a background is color solid and one color vertical line becomes fat. Explanatory drawing of the thinning process in the channel Ca when a background is color solid and one color vertical line becomes fat. Explanatory drawing of the thinning process in the channel Cb when the background is color solid and one color vertical line becomes fat. Explanatory drawing of the characteristic determination of the gray scale in the thick line process when a background is white and one color vertical line is thin. Explanatory drawing of the thickening process in channel Ca when a background is white and one color vertical line is thin. Explanatory drawing of the thickening process in the channel Cb when a background is white and one color vertical line is thin. Explanatory drawing of the characteristic determination of the gray scale in the thinning process in case a background is white and a color vertical several pixel line becomes fat. Explanatory drawing of the thinning process in the channel Ca when a background is white and a color vertical several pixel line becomes fat. Explanatory drawing of the thinning process in the channel Cb when a background is white and a color vertical several pixel line becomes fat. Explanatory drawing of the gray scale characteristic discrimination | determination in the thick line process when a background is color solid and a color vertical several pixel line becomes thin. Explanatory drawing of the thickening process in the channel Ca when a background is color solid and a color vertical several pixel line will become thin. Explanatory drawing of the thickening process in the channel Cb when a background is color solid and a color vertical several pixel line becomes thin.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital copying apparatus 100 Paper feed part 101 Paper bank 102 Paper feed cassette 103 Paper feed roller 104 Separation roller 105 Paper feed path 106 Conveyance roller 200 Printer part 201 Paper discharge roller pair 202 Switching claw 203 Paper feed path 204 Manual feed tray 205 Paper feed Roller 206 Separating roller 207 Manual paper feed path 209 Stack unit 210 Image forming unit 210Y, 210C, 210M, 210K Process cartridge 211Y, 211C, 211M, 211K Photoconductor 212Y, 212C, 212M, 212K Charger 213Y, 213C, 213M, 213K Developer 230 Optical writing unit 231 LD array 232 Collimating lens 233 Aperture 234 Cylindrical lens 235 Polygon mirror 236 WTL
237 Folding mirror 238 Dust-proof glass 239 Synchronization detection sensor 240 Intermediate transfer unit 241 Intermediate transfer belt 242 Secondary transfer backup roller 250 Secondary transfer unit 251 Paper transport belt 252 Stretching roller 260 Registration roller pair 270 Fixing unit 271 Fixing belt 272 Heating roller 273 Follower roller 280 Paper reversing unit 300 Scanner unit 301 Contact glass 302 First traveling body 303 Second traveling body 304 Imaging lens 305 CCD
400 ADF
401 Document Plate 402 Paper Feed Roller 403 Separation Roller 404 Transport Roller 405 Transport Belt 406 Paper Discharge Roller 407 Paper Discharge Stand 1100 Read Processing Unit 1200 Image Processing Unit 1300 Write Control Unit 1310 Printer Image Processing Unit 1310G Gray Scale Image Processing Unit 1310Ca-Cn Channel image processing unit 1311G Gray scale conversion unit 1311Ca to Cn 3 state conversion unit 1312G 3 state conversion unit 1312Ca to Cn Image matrix 1313G Image matrix edge determination unit 1313Ca to Cn Look-up table 1314Ca to Cn Attention pixel code output unit 1320 Write DMAC
1330 Read DMAC
1340 Light emission data generation unit 1340Ca to Cn Channel light emission data generation unit 1350 Pixel clock control unit 1400 Memory 1500 Light source control unit 1600 Control unit

Claims (13)

  A color image forming means for forming a color dot image using a developer corresponding to the color based on color multi-value pixel data; a gray scale conversion means for converting input multi-value pixel data into gray scale pixel data; Grayscale state conversion means for converting the grayscale pixel data into at least three state values of colorless, maximum color, and halftone based on a predetermined colorless threshold and a predetermined maximum color threshold; and attention of the input multivalued pixel data The pixel of interest based on the array state of the state value of the pixel in the pixel window in which the state values converted by the grayscale state conversion means of a predetermined number of adjacent pixels adjacent to the pixel and the pixel of interest are stored Gray scale feature detection means for detecting features such as edges, isolated lines, etc., and the input multi-valued pixel data for each color, the colorless threshold value and the maximum value. Color state conversion means for converting at least three state values of colorless, maximum color, and halftone based on a color threshold, a target pixel of the input multi-value pixel data for each color, and a predetermined adjacent center around the target pixel A plurality of registered multivalued pixel data values corresponding to the state value array of the pixels in the pixel window in which the state values converted by the color state converting means of a number of adjacent pixels are stored A reference look-up table and the center of the state array at the same pixel position as the state value array having a predetermined feature detected by the grayscale feature detection means in the state value array of the pixel in the pixel window for each color Color feature detection means for detecting features such as edges and isolated lines of the pixel of interest using the pixel as the pixel of interest, and the gray scale characteristic of each pixel of interest for each color A reference lookup table determining unit for determining a reference lookup table to be referred to from a plurality of the reference lookup tables based on the feature detection result of the detection unit and the feature detection result of the color feature detection unit; and the input multi-value pixel Output data generation means for switching the data value of the data to the data value of the reference lookup table determined by the reference lookup table determination means and outputting the data value to the color image forming means as the output multi-value pixel data. An image forming apparatus.   The reference lookup table is a thinning reference lookup table in which data values for thinning processing for thinning the dot image of the pixel of interest formed by the image forming unit in the main scanning direction are registered. A thick line reference lookup table in which data values for thick line processing for thickening pixels are registered, and non-processed data in which the target pixel of the input multi-value pixel data is used as it is as the output multi-value pixel data. 2. The image forming apparatus according to claim 1, further comprising a reference lookup table for no processing in which values are registered.   The reference look-up table determining unit for each color is configured such that when the feature detected by the gray scale feature detecting unit matches the feature detected by the color feature detecting unit for the color, or both features are predetermined complementary. When there is a relationship, a reference look-up table for thinning processing that thins the dot image of the target pixel formed by the image forming unit in the main scanning direction or a reference look for thickening processing that thickens the target pixel The image forming apparatus according to claim 1, wherein an up table is selected.   The reference look-up table for each color is a through-through that uses the target pixel of the input multi-value pixel data as it is as the output multi-value pixel data, regardless of the feature detection results of the gray scale feature detection means and the color feature detection means. The image forming apparatus according to claim 1, wherein the state can be set.   The reference look-up table thins the target pixel in a thinning process for thinning a dot image of the target pixel formed by the image forming unit in a main scanning direction or a thickening process for thickening the target pixel. 5. The pixel data value of an additional pixel to be added to a pixel position adjacent to the target pixel is registered together with a pixel data value corresponding to the processing or the thickening processing. The image forming apparatus according to any one of the above.   2. The image forming apparatus according to claim 1, wherein the colorless threshold value and the maximum color threshold value of the gray scale state conversion unit and the color state conversion unit and / or data values of the reference lookup table can be set as appropriate. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the pixel window is a pixel window including three pixels in the main scanning direction and one pixel or more in the sub-scanning direction.   Color image formation processing step for forming a color dot image using a developer corresponding to the color based on multi-value pixel data of color, and gray scale conversion for converting input multi-value pixel data into gray scale pixel data A processing step, a grayscale state conversion processing step for converting the grayscale pixel data into at least three state values of colorlessness, maximum color, and halftone based on a predetermined colorless threshold and a predetermined maximum color threshold; An array state of the state value of the pixel in the pixel window in which the state value converted in the gray scale state conversion processing step of the target pixel of the value pixel data and a predetermined number of adjacent pixels adjacent to the target pixel is stored A gray scale feature detection processing step for detecting features such as edges and isolated lines of the target pixel based on A color state conversion processing step for converting the input multi-valued pixel data into at least three state values of colorless, maximum color, and halftone based on the colorless threshold and the maximum color threshold for each color; The edge of the target pixel based on the state value array having the center pixel of the state value array having the predetermined feature detected in the grayscale feature detection processing step in the state value array of the pixel in the window as the target pixel A color feature detection processing step for detecting features such as isolated lines, and a color state conversion processing step for a target pixel of the input multi-value pixel data and a predetermined number of adjacent pixels adjacent to the target pixel for each color A plurality of registered data values of the output multi-value pixel data in correspondence with the state value array of the pixel in the pixel window in which the state value converted in step S3 is stored. Reference lookup table determination processing for determining a reference lookup table to be referenced based on the feature detection result in the gray scale feature detection processing step and the feature detection result in the color feature detection processing step in the illumination lookup table And the color image forming processing step as the output multi-value pixel data by switching the data value of the input multi-value pixel data to the data value of the reference lookup table determined in the reference lookup table determination processing step. An image forming method comprising: an output data generation processing step for outputting to the apparatus.   In the image forming method, the reference lookup table has thinned data values for thinning processing in which the dot image of the pixel of interest formed in the image forming processing step is thinned in the main scanning direction. Reference lookup table, thick line reference lookup table in which data values for thickening processing to thicken the pixel of interest are registered, and the pixel of interest of the input multivalued pixel data as they are are the output multivalued pixels 9. The image forming method according to claim 8, further comprising a reference lookup table for no processing in which data values for no processing as data are registered.   In the reference lookup table determination processing step for each color, the feature detected in the gray scale feature detection processing step matches the feature detected in the color feature detection processing step for the color, or both features are When there is a predetermined complementary relationship, a reference lookup table for thinning processing that thins the dot image of the pixel of interest formed in the image forming processing step in the main scanning direction or the pixel of interest is fattened. 10. The image forming method according to claim 8, wherein a reference lookup table for thickening processing is selected.   In the image forming method, the reference look-up table for each color uses the target pixel of the input multi-value pixel data as it is regardless of the feature detection result in the gray scale feature detection processing step and the color feature detection processing step. 11. The image forming method according to claim 8, wherein a through setting as output multi-value pixel data can be set for each reference lookup table.   Color image forming processing for forming a color dot image using a developer corresponding to the color based on the color multi-value pixel data, and gray scale conversion for converting the input multi-value pixel data into gray scale pixel data Processing, grayscale state conversion processing for converting the grayscale pixel data into at least three state values of colorless, maximum color, and halftone based on a predetermined colorless threshold and a predetermined maximum color threshold; and the input multi-valued pixel Based on an array state of the state value of the pixel in the pixel window in which the state value converted by the grayscale state conversion process of the pixel of interest of the data and a predetermined number of adjacent pixels adjacent to the pixel of interest as the center is stored Grayscale feature detection processing for detecting features such as edges and isolated lines of the target pixel, and the input multi-valued pixel data for each color A color state conversion process for converting at least three state values of colorless, maximum color, and halftone based on the colorless threshold and the maximum color threshold; and the state value array of the pixels in the pixel window for each color Color feature detection processing for detecting features such as edges and isolated lines of the target pixel based on the state value array using the center pixel of the state value array having a predetermined feature detected by the grayscale feature detection processing as the target pixel And the pixel of interest in the input multi-valued pixel data for each color and the state value converted by the color state conversion processing of a predetermined number of adjacent pixels centered on the pixel of interest in the pixel window Among the plurality of reference lookup tables in which the data values of the output multi-value pixel data are registered in correspondence with the state value array of the pixel, the gray scale feature detection process A reference lookup table determination process for determining a reference lookup table to be referred to based on a feature detection result and a feature detection result in the color feature detection process; and a data value of the input multivalued pixel data as the reference lookup table An output data generation process for switching to the data value of the reference lookup table determined in the determination process and outputting the output multi-valued pixel data to the color image forming process. .   A computer-readable recording medium on which the image forming program according to claim 12 is recorded.

Images