JP4584948B2 - Color image forming method and color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming method and a color image forming apparatus used in a digital image forming apparatus such as a digital copying machine, a laser printer, and a facsimile machine, a display device, and the like.

  Conventionally, a color image forming method and a color image forming apparatus form a full color image by superimposing pixels of respective colors. Further, among image forming apparatuses having a halftone processing function, those having an intermediate processing technique are described in Patent Documents 1 to 6, and the like.

  These are mainly for the purpose of improving the reproducibility of the highlight part of the image. The image data is subjected to pulse width modulation and dither processing weighted with 2 dots in the main scanning direction to reduce the image highlight part. The optical reproduction beam diameter and the pixel interval in the main scanning direction are defined for this purpose.

  Patent Document 7 describes a semiconductor laser drive circuit that modulates a semiconductor laser using a modulation method that combines a pulse width modulation method and a power modulation method based on image data. In Patent Document 8, a semiconductor laser is modulated by a modulation method combining a pulse width modulation method and a power modulation method based on image data, and the phase of the modulation pulse is set to the center in the center mode and to the right in the right mode, and to the left. An image forming apparatus that is shifted to the left in the mode is described.

  Patent Document 9 discloses a laser multi-tone optical writing device that performs optical writing by performing laser light modulation using a combination of a pulse width modulation method and a power modulation method based on image data. The thing which attaches the phase of is described. Patent Document 10 describes an image forming apparatus that refers to density data of two adjacent dots and converts the reference data to generate density from specific dots.

  Patent Document 11 describes an image forming apparatus that refers to density data of adjacent two dots, performs density weighting and PWM modulation according to the reference result, and repeats this in the main scanning direction. Japanese Patent Application Laid-Open No. 2004-228688 describes document information including means for performing one-dot multi-tone light writing of read image data and means for performing multi-tone light writing for each dot of read image data and area gradation using a plurality of dots. Alternatively, an image forming apparatus that switches according to an image spatial frequency or a density difference between dots is described.

  Patent Document 13 describes an image forming apparatus that switches the line direction to the main scanning direction / sub-scanning direction according to the direction and size of the original and the image density. Patent Document 14 describes an image forming apparatus that refers to density data of two adjacent dots and generates a density on the higher density side of the two dots based on the reference result.

  Patent Document 15 describes an image forming apparatus that performs line-type optical writing (representing gradation by a line image in a predetermined direction) and emphasizes an edge in a direction orthogonal to the line. Patent Document 16 describes an image forming method in which adjacent two dots of data are distributed and the dot formation start phase in the main scanning direction or the sub-scanning direction is periodically changed to form various checkered patterns. .

JP-A-7-254985 JP 7-254986 A JP-A-7-283944 JP-A-8-114965 JP-A-8-125863 JP 7-254986 A JP-A-2-243363 JP-A-6-347852 Japanese Patent Laid-Open No. 3-1656 Japanese Patent Laid-Open No. 4-200075 Japanese Patent Laid-Open No. 4-200076 JP-A-4-200077 Japanese Patent Laid-Open No. 4-200078 JP-A-5-284339 JP-A-6-62248 Japanese Patent Application Laid-Open No. 5-292301

In image forming apparatuses and image forming methods that perform halftone processing, color unevenness occurs particularly in low-density areas and color reproducibility is poor, and skin colors and deep color tones that require delicate color tones are preferred. The reproducibility of the green color of natural plants is poor.
Further, in the color image forming apparatus and the color image forming method, pixels of each color are overlapped to form a full color image. Therefore, color unevenness occurs particularly in the low density portion, color reproducibility is poor, and graininess in the low density portion is low. Not good. Further, color turbidity occurs in the low density part to the medium density part due to the overlap between the multicolor dots.

Invention aims to provide a color image forming method particularly excellent in color reproducibility without color irregularity at a low density portion, and capable of realizing a superior color image formed on the graininess in a low density portion according to claim 1 And
An object of the present invention is to provide a color image forming method capable of reproducing a human skin color that requires a particularly delicate color tone with high quality.
An object of the present invention is to provide a color image forming method capable of reproducing the green color of a natural plant that is particularly preferred for deep color tone with high quality.
The invention according to claim 4 is to provide a color image forming method capable of reproducing both human skin color and natural plant green color with high quality.
The invention according to claim 5 is to provide a color image forming apparatus capable of realizing color image formation which is excellent in color reproducibility without color unevenness particularly in a low density portion and excellent in graininess in a low density portion. And
An object of the present invention is to provide a color image forming apparatus capable of reproducing a human skin color that requires a particularly delicate color tone with high quality.
According to claim 7 invention aims to provide a color image forming apparatus capable of particular reproduced green color natural image vegetation are preferred color tone having a deep high quality.
According to claim 8 invention aims to provide a color image forming apparatus capable of reproducing the green color both vegetation color and natural image of human skin quality.

In order to achieve the above object, the invention according to claim 1 refers to image data of a plurality of pixels, and distributes density data to specific positions of the plurality of pixels according to the reference result to generate a dot or line image. In the color image forming method to be formed, the position of the density generation pixel is changed in the main scanning direction according to the predetermined color information of the pixel data, and the adjacent pixel is combined with the predetermined color in the predetermined density portion. The image data of each color is shifted in the sub-scanning direction, and a predetermined different phase is added to the pixel for each color in the sub-scanning direction, and the position of the density generation pixel is set in the main scanning direction according to the color information of the data In order to change to this, a counter indicating the reading start position in the main scanning direction is used, and the reading start position in the main scanning direction is sequentially shifted for each color .

According to a second aspect of the present invention, in a color image forming method for forming an image by modulating a color image signal of multiple gradations, optical writing is performed by performing optical modulation including at least pulse width modulation by the image signal, and adjacent to each other. Adds image data of multiple pixels, time-divides the pixels, generates density from a specific direction of the specific pixel based on the added data, changes the density generation pixel in the main scanning direction, and responds to the color information of the data By changing the position of the density generation pixel in the main scanning direction, a phase for each color is added in the main scanning direction, and the cyan and yellow colors and the magenta and black colors overlap each other in the middle density portion. image to form the image data of each color by adding a predetermined different phases in the sub-scanning direction are shifted in the sub-scanning direction to the pixels of each color, density generated pixel according to the color information of the data To alter position in the main scanning direction, using the counter indicating the read start position in the main scanning direction, and wherein the sequentially shifting the reading start position in the main scanning direction for each color.

According to a third aspect of the present invention, in a color image forming method for forming an image by modulating a multi-tone color image signal, optical writing is performed by performing light modulation including at least pulse width modulation by the image signal, and adjacent to each other. Adds image data of multiple pixels, time-divides the pixels, generates density from a specific direction of the specific pixel based on the added data, changes the density generation pixel in the main scanning direction, and responds to the color information of the data By changing the position of the density generation pixel in the main scanning direction, a phase for each color is added in the main scanning direction, and the cyan and black colors and the magenta and yellow colors overlap each other in the middle density portion. image to form the image data of each color by adding a predetermined different phases in the sub-scanning direction are shifted in the sub-scanning direction to the pixels of each color, density generated pixel according to the color information of the data To alter position in the main scanning direction, using the counter indicating the read start position in the main scanning direction, and wherein the sequentially shifting the reading start position in the main scanning direction for each color.

According to a fourth aspect of the present invention, in the color image forming method for forming an image by modulating a multi-tone color image signal, optical writing is performed by performing optical modulation including at least pulse width modulation by the image signal, and adjacent to each other. Adds image data of multiple pixels, time-divides the pixels, generates density from a specific direction of the specific pixel based on the added data, changes the density generation pixel in the main scanning direction, and responds to the color information of the data By changing the position of the density generation pixel in the main scanning direction, a phase for each color is added in the main scanning direction, and the cyan and magenta colors and the yellow and black colors overlap each other in the middle density portion. to form, the image data of each color by adding a predetermined different phases in the sub-scanning direction are shifted in the sub-scanning direction to the pixels of each color, the density generating pixels in accordance with the color information of the data To change the location in the main scanning direction, using the counter indicating the read start position in the main scanning direction, and wherein the sequentially shifting the reading start position in the main scanning direction for each color.

According to a fifth aspect of the present invention, there is provided a color image forming apparatus that refers to image data of a plurality of pixels and distributes density data to specific positions of the plurality of pixels according to the reference result to form a dot or line image. Means for changing the position of the density generation pixel in the main scanning direction according to the predetermined color information of the pixel data and forming an image so as to combine adjacent pixels for the predetermined color in a predetermined density portion; Means for shifting the image data in the sub-scanning direction and adding predetermined different phases to the pixels for each color in the sub-scanning direction, and the position of the density generating pixel in the main scanning direction in accordance with the color information of the data The changing means has a counter indicating the reading start position in the main scanning direction, and has a function of sequentially shifting the reading start position in the main scanning direction for each color .

According to a sixth aspect of the present invention, in the color image forming apparatus for forming an image by modulating a multi-tone color image signal, an optical writing means for performing optical writing by performing optical modulation including at least pulse width modulation by the image signal Means for adding image data of a plurality of adjacent pixels, means for generating a density from a predetermined direction of a specific pixel by time-division between the pixels, and changing the density generating pixel in the main scanning direction And a phase for each color is added in the main scanning direction by changing the position of the density generating pixel in the main scanning direction according to the color information of the data. Means for forming a line image in which the colors of black overlap each other, and the image data of each color is shifted in the sub-scanning direction, and the pixels for each color are different from each other by a predetermined amount in the sub-scanning direction. Means for adding a phase, and means for changing the position of the density generation pixel in the main scanning direction in accordance with the color information of the data has a counter indicating the reading start position in the main scanning direction, and sequentially for each color. This has a function of shifting the reading start position in the main scanning direction .

According to a seventh aspect of the present invention, in a color image forming apparatus for forming an image by modulating a multi-tone color image signal, an optical writing means for performing optical writing by performing optical modulation including at least pulse width modulation by the image signal Means for adding image data of a plurality of adjacent pixels, means for generating a density from a predetermined direction of a specific pixel by time-division between the pixels, and changing the density generating pixel in the main scanning direction And a phase for each color is added in the main scanning direction by changing the position of the density generating pixel in the main scanning direction according to the color information of the data, and between the cyan and black colors, magenta Means for forming a line image in which the colors of yellow overlap each other, and the image data of each color are shifted in the sub-scanning direction, and the pixels for each color are different from each other by a predetermined amount in the sub-scanning direction. Means for adding a phase, and means for changing the position of the density generation pixel in the main scanning direction in accordance with the color information of the data has a counter indicating the reading start position in the main scanning direction, and sequentially for each color. This has a function of shifting the reading start position in the main scanning direction .

According to an eighth aspect of the present invention, in a color image forming apparatus that forms an image by modulating a multi-tone color image signal, the optical writing means performs optical writing by performing optical modulation including at least pulse width modulation by the image signal. Means for adding image data of a plurality of adjacent pixels, means for generating a density from a predetermined direction of a specific pixel by time-division between the pixels, and changing the density generating pixel in the main scanning direction And a phase for each color is added in the main scanning direction by changing the position of the density generating pixel in the main scanning direction according to the color information of the data, and cyan and magenta colors, yellow and Means for forming a line-shaped image in which the black colors overlap each other, and shifting the image data of each color in the sub-scanning direction to a pixel of each color having a predetermined different position in the sub-scanning direction And means for adding, the means for changing the position of the density generation pixels in the main scanning direction in accordance with the color information data has a counter indicating the read start position in the main scanning direction, sequentially primarily for each color This has a function of shifting the reading start position in the scanning direction .

According to the first aspect of the present invention, it is possible to realize color image formation that is excellent in color reproducibility without color unevenness particularly in the low density portion and excellent in graininess in the low density portion. In addition, according to the inventions according to claims 1 to 10, compared to the case of overprinting all colors, paper white portions are not formed, and the transfer conditions of each color are more even. It is possible to form an image with excellent color reproducibility, less roughness, and excellent graininess, and the present invention can be easily achieved.
According to the second aspect of the present invention, it is possible to reproduce the skin color of a person who requires a particularly delicate color tone with high quality.

According to the invention which concerns on Claim 3, the green color of the plant of the natural painting in which the deep color tone is liked especially can be reproduced with high quality.
According to the invention which concerns on Claim 4, both the color of a human skin and the green color of a natural plant can be reproduced with high quality .

According to the fifth aspect of the present invention, it is possible to realize color image formation that is excellent in color reproducibility without color unevenness especially in the low density portion and excellent in graininess in the low density portion.
According to the invention which concerns on Claim 6 , the color of the skin of the person for whom especially delicate color tone is requested | required can be reproduced with high quality.

According to the invention which concerns on Claim 7 , the green color of the plant of the natural picture in which the deep color tone is liked especially can be reproduced with high quality.
According to the invention which concerns on Claim 8 , both the color of a human skin and the green color of the natural plant can be reproduced with high quality.

FIG. 7 shows an outline of one reference embodiment of the present invention. The first reference embodiment is a form of a color image forming apparatus comprising a digital Tarukara copier. First, image formation of the first reference form will be described. In FIG. 7, reference numeral 100 denotes a laser printer as an image forming unit, 200 denotes an automatic document feeder (hereinafter referred to as ADF), 300 denotes an operation board, 400 denotes an image scanner as an image reading unit, and 500 denotes an external sensor.

  In the image scanner 400, a moving body on which an illumination lamp 402 disposed below a contact glass 401 serving as a document table is mounted is mechanically moved at a constant speed in the horizontal direction (sub-scanning direction) in the figure. An image reading unit that reads an image of a document on the glass 401. The light emitted from the illumination lamp 402 illuminates the document placed on the contact glass 401, and the reflected light, that is, the light image of the document passes through the mirrors 403 to 405 and the lens 406 as color separation means. Is incident on the dichroic prism 410.

  The dichroic prism 410 divides incident light into light of three colors of red (hereinafter referred to as R), green (hereinafter referred to as G), and blue (hereinafter referred to as B) according to the wavelength. The split three-color light is incident on an image sensor composed of a different one-dimensional charge coupled device (CCD) and photoelectrically converted, and the original image is R, G, B for each line in the main scanning direction. Each color component is color-separated and read simultaneously. Similar to the image scanner 400, the external sensor 500 is built in a handy type scanner composed of a CCD that can simultaneously detect R, G, and B color components of an original image.

  The ADF 200 is disposed above the image scanner 400, and a large number of documents are placed on the document placing table 210. During the document feeding operation, the rotating calling roller 212 feeds the document on the document placing table 210, and the separation roller 213 separates only the uppermost document. This document is conveyed onto the contact glass 401 of the image scanner 400 by the pull-out roller 217 and the conveyance belt 216, and stops at a predetermined reading position.

  When the image scanner 400 finishes reading the image of the original on the contact glass 401, the original on the contact glass 401 is discharged by the transport belt 216, and the next original is sent to the reading position as described above. A document presence / absence sensor 211, which is an optical sensor for detecting whether or not a document is placed on the document placement table 210, is installed in front of the calling roller 212, and between the separation roller 213 and the pull-out roller 217. A document leading edge sensor 214 that is an optical sensor for detecting the leading edge and the size of the document is provided.

  The document leading edge sensor 214 is composed of a plurality of sensors arranged at different positions in the main scanning direction, and detects the document size in the main scanning direction, that is, the document width, by combining the detection states of these sensors. Can do. In addition, a pulse generator that outputs a pulse corresponding to the rotation amount is provided in a paper feed motor (not shown), and the control device of the ADF 200 measures the time during which the original passes through the original leading edge sensor 214, thereby performing sub-scanning. The document size in the direction, that is, the length of the document is detected. The calling roller 212 and the separation roller 213 are driven by a paper feed motor (not shown), and the pull-out roller 217 and the transport belt 216 are driven by a transport motor (not shown). A registration sensor 215 made up of an optical sensor is disposed downstream of the pull-out roller 217 and detects a document.

  The laser printer 100 reproduces an image using the photosensitive drum 1. Around the photosensitive drum 1, a unit for performing a series of electrophotographic processes, that is, a charging charger 5 as a charging unit, an optical writing unit 3, a developing unit 4, a transfer drum 2, a cleaning unit 6, and the like are arranged. Yes. The optical writing unit 3 includes a semiconductor laser (laser diode: hereinafter referred to as LD) (not shown), and laser light emitted from the LD is deflected and scanned in the main scanning direction by a rotating polygon mirror 3b as deflection scanning means. An image is formed on the surface of the photosensitive drum 1 through 3c, the mirror 3d and the lens 3e. The rotary polygon mirror 3b is driven to rotate at a constant speed at a high speed by a polygon motor 3a.

  The image control unit (not shown) controls the LD drive signal so that the light emission timing of the LD driven by the multi-tone image signal is synchronized with the laser beam deflection scanning of the rotary polygon mirror 3b, that is, the photosensitive drum 1 The light emission of the LD is controlled so that the upper side is scanned in the main scanning direction with a laser beam from a predetermined optical writing start position. The photosensitive drum 1 is previously charged uniformly at a high potential by corona discharge by a charging charger 5 serving as a charging unit, and then exposed to a laser beam from an optical writing unit 3 serving as an optical writing unit to be electrostatic latent image. Is formed. The electrostatic latent image on the photosensitive drum 1 is visualized by a developing unit 4 as developing means.

  For example, the developing unit 4 visualizes the electrostatic latent image on the photosensitive drum 1 into an image of each color of magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), yellow (hereinafter referred to as Y), and black (hereinafter referred to as Bk). 4 sets of developing devices 4M, 4C, 4Y, and 4Bk are provided. One of the developing devices 4M, 4C, 4Y, and 4Bk is selectively energized to perform the developing operation, and the electrostatic latent image on the photosensitive drum 1 is one of the colors of M, C, Y, and Bk. The toner image is visualized.

  On the other hand, the transfer paper stored in a paper feed cassette 11 as a paper feed device is fed out by a paper feed roller 12 and sent to the surface of the transfer drum 2 at a timing by a registration roller 13. It is attracted and moved as the transfer drum 2 rotates. The toner image on the photosensitive drum 1 is transferred onto a transfer sheet on the transfer drum 2 by a transfer charger 7 as a transfer unit.

  In the monochromatic copy mode, a monochromatic image forming process is performed, and the LD of the optical writing unit 3 is modulated by the monochromatic image signal to form the monochromatic toner image on the photosensitive drum 1. After the image is transferred to the transfer paper, the transfer paper is separated from the transfer drum 2. The transfer paper is fixed with a toner image by a fixing device 9 and discharged onto a paper discharge tray 10. In the case of the full color mode, an image forming process of each color for sequentially forming Bk, M, C, and Y images on the photosensitive drum 1 is sequentially performed, and the images are sequentially formed on the photosensitive drum 1. The Bk, M, C, and Y color images are transferred onto one transfer sheet in a superimposed manner.

  In this case, first, the LD of the optical writing unit 3 is modulated by the Bk image signal to form a Bk toner image on the photosensitive drum 1, and this Bk toner image is transferred to the transfer paper on the transfer drum 2. Without separating the transfer paper from the transfer drum 2, the LD of the optical writing unit 3 is modulated by the M image signal to form an M toner image on the photosensitive drum 1, and this M toner image is transferred to the transfer drum 2. The image is transferred onto the transfer paper so as to overlap the Bk toner image.

  Further, the LD of the optical writing unit 3 is modulated by the C image signal to form a C toner image on the photosensitive drum 1, and this C toner image is transferred onto the transfer paper on the transfer drum 2 with a Bk toner image, an M toner image, and the like. After being transferred in a superimposed manner, the LD of the optical writing unit 3 is modulated with a Y image signal to form a Y toner image on the photosensitive drum 1, and this Y toner image is transferred onto the transfer paper on the transfer drum 2 as a Bk toner image, A full color image is formed by transferring the M toner image and the C toner image in an overlapping manner. When the transfer of the toner images of Bk, M, C, and Y is completed, the transfer paper on the transfer drum 2 is separated from the transfer drum 2 by the separation charger 8 and discharged after the toner image is fixed by the fixing device 9. It is discharged to the tray 10.

Having described the image forming operation of this preferred embodiment, as a color image forming apparatus according to the present invention is not limited to the above configuration, using an intermediate transfer member such as an intermediate transfer belt instead of the transfer drum 2, Bk, M A system in which toner images of four colors C, Y are formed on a photosensitive drum for each color, and are sequentially superimposed and transferred onto an intermediate transfer member, and then the toner images are transferred collectively from the intermediate transfer member to transfer paper. And so on.

Next, a description is given of an image processing of the present reference embodiment.
Figure 1 shows an image processing unit as an image processing unit of the present reference embodiment. Operation control of the entire reference embodiment is controlled by the system controller 50 constituted by a microcomputer. The synchronization control circuit 60 generates a clock pulse that serves as a reference for control timing, and inputs and outputs various synchronization signals for synchronizing signals between the units. The main scanning synchronization signal that is the basis of the scanning timing in this reference embodiment is synchronized with the scanning start timing of the laser beam by the rotation of the rotary polygon mirror 3b of the laser printer 100.

  The image scanner 400 performs A / D conversion on R, G, and B color image signals obtained by reading a document and outputs the image signals as 8-bit color image information. This image information is output to the laser printer 100 after undergoing various processes in the image processing unit. The image processing unit includes a scanner γ correction unit 71, an RGB smoothing filter 72, a color correction unit 73, an under color removal (UCR) / UCA unit 74, a selector 75, an edge enhancement filter 76, a printer γ correction unit 77, and a gradation processing unit. 78, an image area separation unit 79, and an ACS unit 80.

  The scanner γ correction unit 71 converts the linear reflectance R, G, B color image signals from the image scanner 400 into density linear R, G, B color image signals. The RGB smoothing filter 72 performs a smoothing process on the R, G, B color image signals from the scanner γ correction unit 71 in order to suppress moire due to halftone originals. The color correction unit 73 converts the image signals of R, G, and B colors into image signals of Y, M, and C colors that are complementary colors of those colors.

  The UCR / UCA unit 74 combines the Y, M, and C color image signals input from the color correction unit 73, extracts the Bk component included in the combined image signal, and outputs it as a Bk signal. The Bk component is removed from the remaining color image signal, and the YMC component is added. The selector 75 selects and outputs any one of the image signals of each color Y, M, C, Bk input from the UCR / UCA unit 74 in accordance with an instruction from the system controller 50.

  The edge enhancement filter 76 emphasizes the edge information of the character part or the picture part with respect to the image signals of each color Y, M, C, Bk from the selector 75. The printer γ correction unit 77 sets a curve according to the printer characteristics, and performs correction including gradation processing on the image signals of each color Y, M, C, and Bk from the edge enhancement filter 76.

The gradation processing unit 78 multi-values the 8-bit Y, M, C, and Bk image signals input from the printer γ correction unit 77. In general, the gradation processing unit 78 often performs dither processing or the like on image signals of Y, M, C, and Bk colors. The image signal is output. The halftone processing described later in this reference embodiment is executed by the gradation processing unit 78.

  The R, G, B color image signals from the scanner γ correction unit 71 are sent to the image area separation unit 79 and the ACS unit 80. The image area separation unit 79 determines whether the image is a character part or a picture part based on the R, G, and B color image signals from the scanner γ correction unit 71 and whether the image is a chromatic color. It has a determination function for determining whether it is an achromatic color, and sends the determination result to a predetermined processing block in units of pixels. This processing block switches processing according to the determination result of the image area separation unit 79.

  The ACS unit 80 determines whether the document set on the scanner 200 is a monochrome document or a color document based on the R, G, and B color image signals from the scanner γ correction unit 71, and the determination result is the Bk version. It is sent to the system controller 50 at the end of scanning. Based on the determination result of the ACS unit 80, the system controller 50 causes the scanner 200 to perform the remaining three scans if the original set on the scanner 200 is a color original, and if the original set on the scanner 200 is a monochrome original. The scanner 200 terminates the operation in one scan. The parameters of the image processing blocks 71 to 80 of the image processing unit are all set by the CPU of the system controller 50. Further, the system controller 50 controls the image forming operation of the laser printer 100 including the LD multi-level optical writing operation.

Next, a description will be given LD multi-level modulation of the reference embodiment.
There are a pulse width modulation (PWM) method and a light intensity modulation (PM) method as LD multi-value modulation methods for performing 1-dot multi-value output. FIGS. 3A and 3B show light waveforms and dot patterns in one example of the light intensity modulation method and one example of the pulse width modulation method. Hereinafter, these modulation methods will be described.

(1) Light intensity modulation method In order to realize halftone recording (halftone image formation) using an intermediate exposure region, stabilization of the image forming process is an important requirement. The process is demanding. However, the light intensity modulation method makes LD control modulation simple. That is, the light intensity modulation method is a method of performing optical writing by changing the light output level itself as shown in FIG. 3A, and each dot pattern is a pattern as shown on the upper side of FIG. Is output. In this method, the control modulation unit of the LD can be configured simply and compactly, but since the halftone image is reproduced using the intermediate exposure region, the image forming process is stabilized such as the stabilization of the developing bias. The demand for is getting stricter.

(2) Pulse Width Modulation Method As shown in FIG. 3B, the pulse width modulation method has a binary light output level, but performs light writing by changing the light emission time, that is, the pulse width. Each dot pattern is output in a pattern as shown on the upper side of FIG. Since this method is basically binary light writing, the use of the intermediate exposure region is less than that of the light intensity modulation method, and the intermediate exposure region can be further reduced by combining adjacent dots. As a result, the demand for the image forming process can be reduced.

  However, in the pulse width modulation method, in order to realize 8 bits per dot by setting the pulse width, several tens of nsec. The time width must be divided into 256, high-speed and high-precision LD modulation is required, and the LD modulation portion becomes complicated. That is, in the light intensity modulation method, the demand for stabilization of the image forming process becomes severe, and in the pulse width modulation method, the configuration of the LD modulation unit becomes complicated.

Therefore, in this preferred embodiment employs a pulse width intensity mixing modulation scheme that combines the pulse width modulation (PWM) method and the light intensity modulation (PM) method in consideration of the above points.
(3) Pulse Width Intensity Mixed Modulation Method FIG. 4 shows left mode and right mode optical output waveforms and dot patterns in an example of the pulse width intensity mixed modulation method. This pulse width intensity mixed modulation method is based on pulse width modulation, and the transition between the pulse width and the pulse width is interpolated by light intensity modulation as shown in FIGS. 4A and 4B. A modulation degree equivalent to 8 bits (2 8 = 256 gradations) can be obtained by setting 8 values and setting values of light intensity modulation as 32 values.

  In this method, since the number of stages of pulse width modulation is small, the pulse width can be set digitally, the pulse width can be easily set, and pulse position control can be easily realized. That is, FIGS. 4A, 4B and 5A, 5B show the right mode light output waveform and the dot pattern that generate the optical writing pulse from the right end position of one dot, and the light from the left end of one dot. 2 shows a light output waveform and a dot pattern in a left mode for generating a write pulse. These control the phase of the optical writing pulse so that the exposure pulse is generated from the trailing edge and the leading edge, respectively, and as a result, the dot generation position can be controlled. Further, as shown in FIG. 5C, a central mode in which an optical writing pulse is generated in both directions from the central position of one dot can be selected.

Next, an example of a pulse width modulation (PWM) and LD driving method multilevel optical writing method according to a pulse width intensity mixing modulation method employing light intensity modulation (PM) of Embodiment. In this LD driving method, an LD light emission pattern for one pixel is temporally 2 ^ m steps with a resolution of a pixel clock width of 1/2 ^ m (2 ^ m means 2 to the power of m). Since the light emission power is divided into 2 ^ (n−m) steps with a light emission power resolution of 1/2 ^ (nm), and 2 ^ n gradations are expressed by the combination of both, The division accuracy of both the light emission time and the light emission power of the LD is relaxed, and multi-gradation can be easily realized.

For 8-bit digital image signal of Embodiment, a pulse width modulated (PWM) and 8 (= 2 ^ m = 23 ) steps as m = 3, the light intensity modulating (PM) 32 (= 2 ^ (n In the case of -m) = 25) stage, 2 ^ n = 28 = 256 types of light emission patterns can be formed by the combination of the two, and 256-level LD multi-level modulation becomes possible. An arbitrary light emission pattern can also be obtained by changing a signal generated and output by an LD timing generation circuit, a power setting circuit, or the like. Note that the multi-level optical writing type LD driving circuit and device can be configured using the prior application by the present applicant, for example, those described in Patent Documents 7 to 9, and the like.

Next, regarding phase control (position control) of pulse width modulation, it is shown in FIGS. 5A to 5C according to the mode (right mode / left mode / center mode) set by the phase (position) control logic. In this way, the dot position is controlled to the right, center, and left by controlling the phase of the pulse of the pulse width modulation. In addition to this function, this reference embodiment also has a fraction processing function as shown in FIGS.

  In the fraction processing function, when two continuous pixels in the main scanning direction are output together (added), the light intensity modulation time is normally generated at two places as indicated by the hatched portion in FIG. The operation of collecting these in one place is performed. This is realized on the basis of adding data with a small fraction to data with a large fraction (a value other than the maximum value). While the fractional part is not maximized, all data of the fractional part is added to the fractional part, and when the fractional part is maximized, the remainder is distributed to the fractional part to obtain the light intensity. Modulate. By having the fraction processing function in this way, the pulse width setting step can be made sufficiently smaller than the optical writing beam diameter.

  6A to 6C schematically show the dot image and light output waveform in the above operation, FIG. 6A shows the dot image before correction, and FIG. 6B shows the light output before and after correction. The waveform, FIG. 6C, is a dot image after correction. In the data of two adjacent pixels (pixels), when the light intensity does not become the maximum, the part where the light intensity does not become the maximum is compared between adjacent ones, the smaller one is added to the larger one, and the remainder is made smaller. To do.

Next, a description will be given of the control circuit for adding the phase control of the image data in the present reference embodiment.
In this reference embodiment, the gradation processing unit 78 determines whether the image data from the printer γ correction unit 77 is chromatic color data (here, image data of each color of Y, M, and C) or achromatic color data (Bk image data). The chromatic color data is processed in the chromatic color flow as described later, and the achromatic color data is processed in the achromatic color flow as described later.

In this reference embodiment, in the gradation processing of image data, image data of 2 dots adjacent in the main scanning direction or the sub-scanning direction, or 4 dots adjacent in the main scanning direction and the sub-scanning direction is added, and the addition result Based on the above, dots are reproduced in order from a specific pixel set in advance. At that time, adjacent specific pixels are combined using the right phase / left phase of the specific pixels. In this reference embodiment, the gradation processing unit 78 performs processing as described below is adopted one of the six schemes 1-6. Hereinafter, the systems 1 to 6 will be described in detail.

  FIG. 2 shows a control circuit as a control means for performing addition of data of adjacent pixels in an image, discrimination and distribution of the addition data, and dot phase control. The control circuit shown in FIG. 2 is a control circuit used in method 6 for adding up to 2 dots in the main scanning direction and 2 dots in the sub-scanning direction. This control circuit is provided for each color, and converts the image data of each color of Y, M, C, Bk, which is 8-bit 256 gradation image data input from the printer γ correction section 77 to the gradation processing section 78, for each color. The process is as follows.

  The 8-bit 256-gradation image data A input from the printer γ correction unit 77 to the gradation processing unit 78 is sequentially latched one dot at a time by the latch circuit 602 made up of DF / F. The image data B is delayed by one. Each 8-bit data A and B of 2 dots adjacent in the main scanning direction is input to an adding circuit 604 serving as a calculating means (adding means). The image data A is delayed by one line by the line memory 601 to become image data C, and is sequentially latched by one dot by the latch circuit 603 composed of DF / F, thereby being delayed by one dot. Image data D.

  The adjacent 2-dot 8-bit data C and D of the previous line in the main scanning direction are input to the adder circuit 604. The addition circuit 604 adds 4-dot data A, B, C, D adjacent in the main scanning direction and the sub-scanning direction, adds 2-dot data A, B adjacent in the main scanning direction, and is adjacent in the sub-scanning direction. Two-dot data A and C are added. The comparison / distribution / phase control circuit 605 compares the addition result of the 4-dot data A, B, C, D of the addition circuit 604 with the threshold value 1 of the data that saturates the dots, and the 4-dot data A, B, C , D, the added value of the 2-dot data A and B in the main scanning direction, and the added value of the 2-dot data A and C in the sub-scanning direction, and the concentrated data is concentrated according to an algorithm described later. Distribute as follows.

Further, the comparison / distribution / phase control circuit 605 toggles the 2-bit optical writing phase signal to toggle by the pixel clock frequency division signal CLOCK. In this preferred embodiment, the addition of the data of the adjacent pixels in the image, the addition result of the determination and distribution (allocation), and a control circuit that performs dot phase control has been a hardware as shown in FIG. 2, as described below In addition, it is possible to realize addition of data of adjacent pixels of the image, discrimination and distribution (distribution) of the addition result, and dot phase control even by processing by software.

FIG. 8 shows the state of data transition by 4-dot addition and 2-dot addition by the above processing. In the method 6, as shown in FIG. 8A, in the low density portion of the image, the addition value by the addition circuit 604 of the data d1 to d4 of 2 dots adjacent in the main scanning direction and 2 dots adjacent in the sub scanning direction is obtained. Since the value is smaller than the threshold value 1, the added value is used as data for the dot D1. Also, as shown in FIG. 8B, in the middle and high density portion of the image, the addition value by the addition circuit 604 of the two-dot data d1, d2 adjacent in the main scanning direction is greater than or equal to the threshold value 1, so The saturation value of the data of D1 is set, and the remainder is set as the data of dot D2.
(A) Method of adding image data of 2 dots adjacent in the sub-scanning direction (1/2 pulse division method: methods 1, 2, 3)
In the methods 1 to 3, the 1-dot size is set as shown in FIG. 9A, the 1-pixel size (minimum density unit) is set as 2-dot size as shown in FIG. In FIG. 10, a dot formation matrix as shown in FIG. 10 is set, and light writing pulses are sequentially generated in accordance with the addition value from the control circuit from a small value of the dot formation matrix to mix the pulse width intensity of the image data. Modulation is performed by the modulation method.

  At this time, the gradation processing unit 78 divides (assigns) the pulse into half pulses within one dot, and next time when the PWM pulse becomes full (50% duty) according to the added value within one dot. Moving to a larger number in the dot formation matrix, pulses are similarly generated within the next one dot. At this time, the gradation processing unit 78 switches the right phase / left phase (right mode / left mode) of the pulse by using even-numbered dots EVEN / odd-numbered dots ODD (hereinafter abbreviated as E / O) in the main scanning direction. The phase is controlled and pulses are combined in the same direction of the numerical values of the dot formation matrix. The gradation processing unit 78 performs gradation processing of image data using a light writing density generation algorithm expressed by the following equation. Here, in the following equations, d1 and d2 are image data (8-bit data) before processing of two dots adjacent in the sub-scanning direction, and D1 and D2 are after processing of two dots adjacent in the sub-scanning direction. Image data (8-bit data).

When 0 ≦ d1 + d2 ≦ 127 D1 = d1 + d2, D2 = 0
When 128≤d1 + d2≤254, D1 = 127, D2 = d1 + d2-127
When 255≤d1 + d2≤382 D1 = d1 + d2-127, D2 = 127
When 383 ≦ d1 + d2 ≦ 510 D1 = 255, D2 = d1 + d2-255
The 8-bit data after this processing is used as an LD optical write signal in the laser printer 100. Hereinafter, methods 1 to 3 will be described in detail.

First, the method 1 will be described in detail. In the method 1, the comparison / distribution / phase control circuit 605 of the control circuit shown in FIG. A control circuit configured to output only the added value as it is is used. The gradation processing unit 78 performs gradation processing of image data with the following dot formation algorithm.
1) The density of two dots adjacent in the sub-scanning direction is added by adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604.
2) Pulses are sequentially generated as optical writing signals (optical writing pulses) from 1 of the dot formation matrix.
3) The right / left phase of the PWM pulse (light writing pulse) is switched by E / O in the main scanning direction by the light writing phase signal from the control circuit, and the light writing pulse is combined in the same direction of the numerical values of the dot formation matrix.
4) The pulse is divided into half pulses within one dot, and when this pulse becomes full (50% duty) in accordance with the added value within one dot, a PWM pulse with the next number in the dot formation matrix is generated. .

  The dot formation matrix shown in FIG. 10 is expressed in the minimum density unit as shown in FIG. 11, and the gradation processing unit 78 generates a pulse in the right phase for the dot D1 and in the left phase for the dot D1 ′. A pulse combined with one portion of the formation matrix is generated in accordance with the density addition value (addition value of image data A and C (d1, d2) from the control circuit). In the same manner, the gradation processing unit 78 generates pulses in the second and subsequent portions of the dot formation matrix in accordance with the density addition values (addition values of the image data A and C (d1, d2) from the control circuit). To go.

Next, details of dot formation by the method 1 will be described with reference to FIGS.
(1) Density ~ 1/8 (2 isolated dots)
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/8, the gradation processing unit 78, as shown in FIG. An odd pixel in the main scanning direction is right-aligned by an optical writing phase signal from the control circuit, an even-numbered pixel is left-aligned, and a pulse combined with one portion of the dot formation matrix is added to the density addition value (image data A, C (d1, d2) added value). Here, the pulse width corresponding to the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is based on the pulse width intensity mixed modulation method of the image data as described above. This is the pulse width of the modulated pulse.
(2) Density ~ 1/4 (2 isolated dots)
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/8 to 1/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the 1 part of the dot formation matrix reaches 50% duty (added value of the image data A, C (d1, d2) from the control circuit). Increase according to. Here, the pulse width is increased in accordance with the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit). The pulse width is increased as described above. This means that the pulse width of the pulse modulated by the width intensity mixed modulation method is increased.
(3) Concentration ~ 3/8 (300 lines and 10,000 lines)
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/4 to 3/8, the gradation processing unit 78 is shown in FIG. As described above, the pulse combined with the second portion of the dot formation matrix in the same phase as the first portion of the dot formation matrix is added to the density (the added value of the image data A, C (d1, d2) from the control circuit). It is generated with the pulse width according to.
(4) Concentration to 1/2 (300 lines and 10,000 lines)
When the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is 3/8 to 1/2, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the second part of the dot formation matrix reaches 50% duty (added value of the image data A, C (d1, d2) from the control circuit). Increase according to.
(5) Concentration-5/8
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/2 to 5/8, the gradation processing unit 78 is shown in FIG. In this way, the dot width of the dot formation matrix 3 is increased so that the pulse width of one portion of the dot formation matrix is increased according to the density addition value (addition value of the image data A, C (d1, d2) from the control circuit) A pulse coupled to the portion of is generated.
(6) Concentration-3/4
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 5/8 to 3/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the third part of the dot formation matrix reaches 50% duty (added value of the image data A, C (d1, d2) from the control circuit). Increase according to.
(7) Concentration-7/8
When the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is 3/4 to 7/8, the gradation processing unit 78 is shown in FIG. Thus, the dot width of the dot formation matrix is increased so that the pulse width of the two portions of the dot formation matrix is increased in accordance with the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit). A pulse coupled to the portion 4 is generated.
(8) Concentration ~ 1/1
When the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is 7/8 to 1/1, the gradation processing unit 78 is the 4 part of the dot formation matrix. The pulse width is increased in accordance with the added value of density (added value of image data A, C (d1, d2) from the control circuit) until the pulse combined with DU reaches 50% duty of FULL.

  The gradation processing unit 78 repeats such gradation processing of image data in the main scanning direction and in the sub scanning direction. In this case, the gradation processing unit 78 sequentially generates write pulses for each line. The writing pulse generated in this method 1 is output as an optical writing signal to the optical writing unit 3 of the printer 100, and the LD in the optical writing unit 3 outputs the optical writing signals (color writing signals () from the gradation processing unit 78 as described above. The image signal is sequentially modulated by the LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color.

  In this method 1, the highlight portion of the image can be regularly reproduced with isolated dots, 300 lines (600 dpi) can be obtained in the medium density portion, and the gradation is linear with the growth type of isolated dots and vertical lines. , Increase potential concentration and saturation area to ensure stability and strong banding.

Next, method 2 will be described.
In method 2, the dot formation matrix is in phase in the sub-scanning direction with respect to method 1, and the spatial frequency of the highlight and high density portions of the image is increased. In method 2, the control circuit shown in FIG. 2 is configured such that the comparison / distribution / phase control circuit 605 outputs only the added value of the 2-dot data A and C adjacent in the sub-scanning direction from the adder circuit 604 as it is. A circuit is used. The gradation processing unit 78 performs gradation processing of image data with the following dot formation algorithm.
1) The density of two dots adjacent in the sub-scanning direction is added by adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604.
2) Sequentially generate pulses as optical writing pulses from 1 of the dot formation matrix. 3) The right / left phase of the PWM pulse (light writing pulse) is switched by E / O in the main scanning direction by the light writing phase signal from the control circuit, and the light writing pulse is combined in the same direction of the numerical values of the dot formation matrix.
4) The pulse is divided into half pulses within one dot, and when this pulse becomes full (50% duty) within one dot, the PWM pulse of the next number in the dot formation matrix is generated.

  FIG. 14 shows a dot formation matrix used in method 2. When this dot formation matrix is expressed in the minimum density unit, it is as shown in FIG. 15, and the gradation processing unit 78 generates a pulse in the right phase in the dot D1 and in the left phase in the dot D1 ′. The pulse combined with the portion 1 is generated according to the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit). In the same manner, the gradation processing unit 78 generates pulses in the second and subsequent portions of the dot formation matrix in accordance with the density addition values (addition values of the image data A and C (d1, d2) from the control circuit). To go.

Next, details of dot formation by method 2 will be described.
(1) Density ~ 1/8 (one isolated dot)
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/8, the gradation processing unit 78, as shown in FIG. An odd pixel in the main scanning direction is right-aligned by an optical writing phase signal from the control circuit, and an even-numbered pixel is left-aligned. C (d1, d2) added value).
(2) Density ~ 1/4 (one isolated dot)
When the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is 1/8 to 1/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with one portion of the dot formation matrix reaches 50% duty (added value of image data A, C (d1, d2) from the control circuit). Increase according to.
(3) Concentration ~ 3/8 (300 lines and 10,000 lines)
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/4 to 3/8, the gradation processing unit 78 is shown in FIG. As described above, the pulse combined with the second portion of the dot formation matrix in the same phase as the first portion of the dot formation matrix is added to the density (the added value of the image data A, C (d1, d2) from the control circuit). It is generated with the pulse width according to.
(4) Concentration to 1/2 (300 lines and 10,000 lines)
When the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is 3/8 to 1/2, the gradation processing unit 78 is shown in FIG. In this way, the pulse width is added until the pulse combined with the second part of the dot formation matrix reaches 50% duty of FULL, and the pulse is added to the density addition value (image data A, C (d1, d2) from the control circuit) Value).
(5) Concentration-5/8
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/2 to 5/8, the gradation processing unit 78 is shown in FIG. Thus, the pulse combined with the 3 part of the dot formation matrix is added with the density (image data A, C (d1, d2 from the control circuit) so as to increase the pulse width of the 1 part of the dot formation matrix. ) With a pulse width corresponding to the added value).
(6) Concentration-3/4
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 5/8 to 3/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the third part of the dot formation matrix reaches 50% duty (added value of the image data A, C (d1, d2) from the control circuit). Increase according to.
(7) Concentration-7/8
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 3/4 to 7/8, the gradation processing unit 78 is shown in FIG. Thus, the dot width of the dot formation matrix is increased so that the pulse width of the two portions of the dot formation matrix is increased in accordance with the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit). A pulse coupled to the portion 4 is generated.
(8) Concentration ~ 1/1
When the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is 7/8 to 1/1, the gradation processing unit 78 is the 4 part of the dot formation matrix. The pulse width is increased in accordance with the added value of density (added value of image data A, C (d1, d2) from the control circuit) until the pulse combined with DU reaches 50% duty of FULL.

The gradation processing unit 78 repeats such gradation processing of image data in the main scanning direction and in the sub scanning direction. In this case, the gradation processing unit 78 sequentially generates write pulses for each line. The writing pulse generated by this method 2 is output as an optical writing signal to the optical writing unit 3 of the printer 100, and the LD in the optical writing unit 3 outputs the optical writing signals (( The image signal is sequentially modulated by the LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color.
In this method 2, compared with the method 1, the highlight portion is dispersed in one isolated dot and is not easily visible, the dot size of the missing (white background) is small in the high density portion, and the character cracking is less noticeable.

Next, method 3 will be described.
In the method 3, the density reproduction dots of the dot formation matrix are dispersed as compared with the method 2, and the spatial frequency of the high density portion is made high (character cracking is inconspicuous). In the method 3, the control circuit shown in FIG. 2 is configured such that the comparison / distribution / phase control circuit 605 outputs only the added value of the 2-dot data A and C adjacent in the sub-scanning direction from the adder circuit 604 as it is. A circuit is used. The gradation processing unit 78 performs gradation processing of image data with the following dot formation algorithm.
1) The density of two dots adjacent in the sub-scanning direction is added by adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604.
2) Sequentially generate pulses as optical writing pulses from 1 of the dot formation matrix.
3) The right / left phase of the PWM pulse is switched by E / O in the main scanning direction by the optical writing phase signal from the control circuit, and the optical writing pulses are combined in the same direction of the numerical values of the dot formation matrix.
4) The pulse is divided into half pulses within one dot, and when this pulse becomes full (50% duty) according to the added value within one dot, the PWM pulse of the next number in the dot formation matrix (optical writing) Pulse).

  FIG. 18 shows a dot formation matrix used in Method 3. When this dot formation matrix is expressed in the minimum density unit, it is as shown in FIG. 19, and the gradation processing unit 78 generates pulses in the right phase for the dot D1 and in the left phase for the dot D1 ″. 18 is generated in accordance with the added value of density (added value of image data A and C (d1, d2) from the control circuit) connected to the portion 1 in Fig. 18. The gradation processing unit 78 Similarly, pulses are generated in the second and subsequent portions of the dot formation matrix in accordance with the density addition values (addition values of image data A and C (d1, d2) from the control circuit).

Next, details of dot formation by method 3 will be described.
The density range from (1) density to 1/8 (one isolated dot) to (4) density to 1/2 (300 lines and 10,000 lines) is the same as method 2.
(5) Concentration-5/8
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/2 to 5/8, the gradation processing unit 78 is shown in FIG. As described above, the dot formation matrix is configured so that the pulse widths of the first and second portions of the dot formation matrix are increased in accordance with the density addition values (addition values of the image data A and C (d1, d2) from the control circuit). A pulse is generated that is coupled to the third part.
(6) Concentration-3/4
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 5/8 to 3/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width combined with the 3 part of the dot formation matrix is added to the pulse width until the FULL reaches 50% duty (added value of the image data A, C (d1, d2) from the control circuit). Increase according to.
(7) Concentration-7/8
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 3/4 to 7/8, the gradation processing unit 78 uses 1 and 2 of the dot formation matrix. The pulse combined with the 4 part of the dot formation matrix is generated so as to increase the pulse width of the part according to the added value of density (added value of the image data A, C (d1, d2) from the control circuit). Let
(8) Concentration ~ 1/1
When the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit) is 7/8 to 1/1, the gradation processing unit 78 is the 4 part of the dot formation matrix. The pulse width is increased in accordance with the added value of density (added value of image data A, C (d1, d2) from the control circuit) until the pulse combined with DU reaches 50% duty of FULL.

The gradation processing unit 78 repeats such gradation processing of image data in the main scanning direction and in the sub scanning direction. In this case, the gradation processing unit 78 sequentially generates write pulses for each line. The writing pulse generated in this method 3 is output as an optical writing signal to the optical writing unit 3 of the printer 100, and the LD in the optical writing unit 3 outputs the optical writing signals (( The image signal is sequentially modulated by the LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color.
In Method 3, as compared with Method 2, the omission (white background) is dispersed in a staggered manner in the high density portion, and character cracking is less noticeable.
(B) Method of adding image data of 2 dots adjacent in the sub-scanning direction (1/4 pulse division method: Method 4)
In method 4, when pulse 2 reaches 50% duty in the same dot formation matrix as in method 3, it shifts to pulse 3 in the dot formation matrix, making character cracking in the middle density portion inconspicuous. .
In method 4, as in method 3, one dot size is set as shown in FIG. 9A, and one pixel size (minimum density unit) is set as two dots as shown in FIG. The processing unit 78 sequentially generates pulses in accordance with the added values of the image data A and C (d1, d2) from the control circuit in ascending order of the numerical values of the dot formation matrix as shown in FIG. Modulation is performed by the pulse width intensity mixed modulation method.

  At this time, the gradation processing unit 78 divides the pulse into ½ or ¼ pulses within one dot, and the dot formation matrix when the pulse becomes 50% duty or 25% duty depending on the added value. Next, the next higher number is generated and the next pulse is generated in the same manner. At this time, the gradation processing unit 78 controls the phase of the pulse by switching the right phase / left phase (right mode / left mode) of the pulse by E / O in the main scanning direction, and the direction in which the numerical values of the dot formation matrix are the same. Combine the pulses with. The gradation processing unit 78 performs gradation processing of image data using an optical writing density generation algorithm expressed by the following equation.

When 0 ≦ d1 + d2 ≦ 127 D1 = d1 + d2, D2 = 0
When 128 ≦ d1 + d2 ≦ 190 D1 = 127, D2 = d1 + d2-127
When 191 ≦ d1 + d2 ≦ 254, D1 = d1 + d2-63, D2 = 63
When 255 ≦ d1 + d2 ≦ 318 D1 = 191, D2 = d1 + d2-191
When 319 ≦ d1 + d2 ≦ 382, D1 = d1 + d2-127, D2 = 127
When 383 ≦ d1 + d2 ≦ 510 D1 = 255, D2 = d1 + d2-255
Hereinafter, the method 4 will be described in detail. In the method 4, the comparison / distribution / phase control circuit 605 in the control circuit shown in FIG. A control circuit configured to output only the added value is used as it is. The gradation processing unit 78 performs gradation processing of image data with the following dot formation algorithm.
1) The density of two dots adjacent in the sub-scanning direction is added by adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604.
2) Sequentially generate pulses as optical writing pulses from 1 of the dot formation matrix.
3) The right / left phase of the PWM pulse is switched by E / O in the main scanning direction by the writing phase signal from the control circuit, and the optical writing pulses are combined in the same direction of the numerical values of the dot formation matrix.
4) Divide the pulse into half pulses or quarter pulses within one dot, and when this pulse reaches 50% duty or 25% duty within one dot, the next number in the dot formation matrix PWM pulses are generated.

  In the method 4, when the dot formation matrix shown in FIG. 21 is expressed in the minimum density unit, it is as shown in FIG. 22, and the gradation processing unit 78 applies the pulse in the right phase for the dot D1 and in the left phase for the dot D1 ″. In the same manner as in the method 3, a pulse combined with the portion 1 of the dot formation matrix is generated according to the added value of density (added value of image data A and C (d1, d2) from the control circuit). In the same manner, the gradation processing unit 78 generates pulses in the second and subsequent portions of the dot formation matrix in accordance with the density addition value (the addition value of the image data A and C (d1, d2) from the control circuit). I will let you.

Next, details of dot formation by method 4 will be described.
The density range from (1) density to 1/8 (one isolated dot) to (3) density to 3/8 (300 lines and 10,000 lines) is the same as method 3.
(4) Concentration to 1/2
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 3/8 to 1/2, the gradation processing unit 78 is shown in FIG. Thus, when the pulse combined with the second part of the dot formation matrix reaches 25% duty, it shifts to 3 of the dot formation matrix, and the pulse combined with the third part of the dot formation matrix becomes a dot at 25% duty. The pulse width is increased in accordance with the added value of density (added value of image data A and C (d1, d2) from the control circuit) until it becomes 75% by combining with 1 part of the formation matrix. If the arrangement of the matrix in the highlight portion is arranged in a staggered pattern (if 1 and 2 are exchanged in the dot formation matrix), the arrangement of 3 and 4 in the dot formation matrix will be alternated, and character cracking will be more random than in method 3. It can be made inconspicuous.
(5) Concentration-5/8
When the density addition value (addition value of the image data A and C (d1, d2) from the control circuit) is 1/2 to 5/8, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is increased in accordance with the added value of density (the added value of image data A and C (d1, d2) from the control circuit) until the 2 part of the dot formation matrix reaches 50% duty of FULL. Let
(6) Concentration to 3/4 and after are the same as in method 3.

The gradation processing unit 78 repeats such gradation processing of image data in the main scanning direction and in the sub scanning direction. In this case, the gradation processing unit 78 sequentially generates write pulses for each line. The writing pulse generated in this method 4 is output to the optical writing unit 3 of the printer 100 as an optical writing signal, and the LD in the optical writing unit 3 outputs the optical writing signal (( The image signal is sequentially modulated by the LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color.
In this method 4, as compared with the method 2, the omission (white background) is dispersed in a staggered manner in the high density portion, and the character cracking is less noticeable.
(C) Method of adding image data of 2 dots adjacent in the main scanning direction (1/2 pulse division method: Method 5)
In Method 5, a 2 × 1 matrix of continuous pixels in the main scanning direction is set as the minimum pixel, and the highlight portion is reproduced with staggered dots. In system 5, the comparison / distribution / phase control circuit 605 in the control circuit shown in FIG. 2 outputs only the addition value of the two-dot data A and B adjacent in the main scanning direction from the addition circuit 604 as it is. The control circuit is used.

  In Method 5, one dot size is set as shown in FIG. 24A, and one pixel size (minimum density unit) is set as two dots as shown in FIG. When the dot formation matrix as shown in FIG. 25 is expressed in the minimum density unit, it is as shown in FIG. 26. The gradation processing unit 78 sets the dot formation matrix as shown in FIG. The optical writing pulses are sequentially generated in accordance with the added value of the image data A and B (d1, d2) from the control circuit, and the image data is modulated by the pulse width intensity mixed modulation method.

  At this time, the gradation processing unit 78 divides the pulse into half pulses within one dot, and this pulse is full (50% duty) according to the added value of the image data A and B (d1, d2) from the control circuit. At that point, the next highest number in the dot formation matrix is entered and the next pulse is generated in the same manner. At this time, the gradation processing unit 78 controls the phase of the pulse by switching the right phase / left phase (right mode / left mode) of the pulse by E / O in the main scanning direction, and the direction in which the numerical values of the dot formation matrix are the same. Combine the pulses with. The gradation processing unit 78 performs gradation processing of image data using a light writing density generation algorithm expressed by the following equation.

When 0 ≦ d1 + d2 ≦ 127 D1 = d1 + d2, D2 = 0
When 128 ≦ d1 + d2 ≦ 254 D1 = 127, D2 = d1 + d2-127
When 255 ≦ d1 + d2 ≦ 382 D1 = d1 + d2-127, D2 = 127
When 383 ≦ d1 + d2 ≦ 510 D1 = 255, D2 = d1 + d2-255
Hereinafter, the method 5 will be specifically described. The gradation processing unit 78 performs image data processing using the following dot formation algorithm.
1) The density of two dots adjacent in the main scanning direction is added by adding two dots of data A and B adjacent in the main scanning direction by the adding circuit 604.
2) Sequentially generate pulses as optical writing pulses from 1 of the dot formation matrix.
3) The right / left phase of the PWM pulse (light writing pulse) is switched by E / O in the main scanning direction by the light writing phase signal from the control circuit, each pixel is formed from the outside, and the same direction of the numerical values of the dot formation matrix Combine the optical writing pulse with.
4) The pulse is divided into half pulses within one dot, and when this pulse reaches 50% duty according to the added value of image data A and B (d1, d2) from the control circuit within one dot, dot formation is performed. A PWM pulse of the next number in the matrix is generated.

  The dot formation matrix as shown in FIG. 25 is expressed in the minimum density unit as shown in FIG. 26, and the gradation processing unit 78 generates a pulse in the right phase for the dot D1 and in the left phase for the dot D1 ′. Then, a pulse combined with one portion of the dot formation matrix is generated according to the density addition value (the addition value of the image data A and B (d1, d2) from the control circuit). In the same manner, the gradation processing unit 78 generates pulses in the second and subsequent portions of the dot formation matrix in accordance with the density addition values (addition values of the image data A and B (d1, d2) from the control circuit). To go.

Next, details of dot formation by the method 5 will be described.
(1) Density ~ 1/8 (one isolated dot)
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is up to 1/8, the gradation processing unit 78, as shown in FIG. Odd pixels in the main scanning direction are right-justified, even pixels are left-justified, and a pulse combined with one portion of the dot formation matrix is added to density (added values of image data A and B (d1, d2) from the control circuit) ) With a pulse width according to
(2) Density ~ 1/4 (one isolated dot)
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 1/8 to 1/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with one portion of the dot formation matrix reaches 50% duty (added value of image data A, B (d1, d2) from the control circuit). Increase according to.
(3) Concentration ~ 3/8 (300 lines and 10,000 lines)
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 1/4 to 3/8, the gradation processing unit 78 is shown in FIG. As described above, a pulse combined from the outside of the pixel to the second portion of the dot formation matrix is generated with a pulse width corresponding to the added value of density (added value of image data A and B (d1, d2) from the control circuit). .
(4) Concentration to 1/2 (300 lines and 10,000 lines)
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 3/8 to 1/2, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the second part of the dot formation matrix reaches 50% duty (added value of the image data A and B (d1, d2) from the control circuit). Increase according to.
(5) Concentration-5/8
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 1/2 to 5/8, the gradation processing unit 78 is shown in FIG. Thus, the dot width of the dot formation matrix 3 is increased so that the pulse width of the portion 1 of the dot formation matrix is increased according to the density addition value (addition value of the image data A and B (d1, d2) from the control circuit). A pulse coupled to the portion of is generated.
(6) Concentration-3/4
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 5/8 to 3/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the third part of the dot formation matrix reaches 50% duty (added value of the image data A and B (d1, d2) from the control circuit). Increase according to.
(7) Concentration-7/8
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 3/4 to 7/8, the gradation processing unit 78 is shown in FIG. Thus, the dot width of the dot formation matrix 4 is increased so that the pulse width of the 2 portion of the dot formation matrix is increased in accordance with the density addition value (the addition value of the image data A and B (d1, d2) from the control circuit). A pulse coupled to the portion of is generated.
(8) Concentration ~ 1/1
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 7/8 to 1/1, the gradation processing unit 78 is the 4 part of the dot formation matrix. The pulse width is increased in accordance with the added value of density (added value of image data A and B (d1, d2) from the control circuit) until the pulse combined with the voltage reaches 50% duty of FULL.

  The gradation processing unit 78 repeats such gradation processing of image data in the main scanning direction and in the sub scanning direction. In this case, the gradation processing unit 78 sequentially generates write pulses for each line. The writing pulse generated in this method 5 is output to the optical writing unit 3 of the printer 100 as an optical writing signal, and the LD in the optical writing unit 3 outputs the optical writing signal ((1) of each color from the gradation processing unit 78 as described above). The image signal is sequentially modulated by the LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color.

In this method 5, the highlight portion can be regularly reproduced with staggered isolated dots, 300 lines (600 dpi) can be obtained in the medium density portion, and the gradation is linear with a growth type of isolated dots and vertical lines. Therefore, the potential concentration and saturation region can be increased to ensure stability and strong against banding.
(D) A method of adding 4-dot image data adjacent in the main scanning direction and the sub-scanning direction (1/2 pulse division method: method 6)
In method 6, image data for four dots adjacent in the main scanning direction and sub-scanning direction is added in a highlight portion having a density of ¼ or less, and the subsequent highlight portion, middle portion, and shadow portion are in the main scanning direction. 2 dot image data adjacent to each other is added. FIG. 43 shows the processing flow of method 6.

(A) When the density is ¼ or less One dot size is as shown in FIG. 29A, and one pixel size (minimum density unit) is four dots as shown in FIG. 29B. In method 6, the control circuit shown in FIG. 2 is used. The comparison / distribution / phase control circuit 605 compares the addition result of the 4-dot data A, B, C, D (d1, d2, d3, d4) of the addition circuit 604 with the threshold value 1 of the data that saturates the dots, The added value of the four dot data A, B, C, D is switched and output. The gradation processing section 78 sets a dot formation matrix as shown in FIG. 30 and sequentially adds pulses to density addition values (image data A, B, C from the control circuit) from the smaller numerical values of the dot formation matrix. , D (added value of d1, d2, d3, d4)).

  At this time, the gradation processing unit 78 divides the pulse into half pulses within one dot, and this pulse is an added value of density (image data A, B, C, D (d1, d2, d3, d4 from the control circuit). ), When the dot becomes full (50% duty) according to the added value), the dot formation matrix moves to the same number or the next larger number, and the next pulse is generated in the same manner. At this time, the gradation processing unit 78 controls the phase of the pulse by switching the right phase / left phase (right mode / left mode) of the pulse by E / O in the main scanning direction, and the direction in which the numerical values of the dot formation matrix are the same. Combine the pulses with.

  When the dot formation matrix as shown in FIG. 30 is expressed in the minimum density unit, it is as shown in FIG. 31, and the gradation processing unit 78 generates a pulse in the left phase in the dot D1 and in the right phase in the dot D1 ′. Then, a pulse combined with one portion of the dot formation matrix is generated according to the density addition values (addition values of the image data A, B, C, D (d1, d2, d3, d4) from the control circuit). To go. In the same manner, the gradation processing unit 78 performs 2 of the dot formation matrix according to the density addition values (addition values of the image data A, B, C, D (d1, d2, d3, d4) from the control circuit). Pulses are generated in the subsequent parts.

The gradation processing unit 78 performs gradation processing of image data using a light writing density generation algorithm expressed by the following equation.
When 0 ≦ d1 + d2 + d3 + d4 ≦ 127 D1 = d1 + d2 + d3 + d4
D2 = D3 = D4 = 0
When 128 ≦ d1 + d2 + d3 + d4 ≦ 254, D1 = 127,
D2 = d1 + d2 + d3 + d4-127,
D3 = D4 = 0
Here, d1, d2, d3, and d4 are 4-dot image data (8-bit data) adjacent in the main scanning direction and sub-scanning direction before processing, and D1, D2, D3, and D4 are main scanning after processing. This is 4-dot image data (8-bit data) adjacent in the direction and the sub-scanning direction. The 8-bit data after this processing is used as an optical writing signal for the laser printer 100.

(A) When the density is ¼ or more One dot size is as shown in FIG. 29A, and one pixel size (minimum density unit) is two dots as shown in FIG. The comparison / distribution / phase control circuit 605 compares the addition result of the 4-dot data A, B, C, D (d1, d2, d3, d4) of the addition circuit 604 with the threshold value 1 of the data that saturates the dots, The added value of the 2-dot data A and B (d1, d2) is switched and output.

  The dot formation matrix shown in FIG. 30 is expressed in the minimum density unit as shown in FIG. 33. The gradation processing unit 78 generates pulses in the left phase for the dot D1 and in the right phase for the dot D1 ′. A pulse combined with the second part of the formation matrix is generated with a pulse width corresponding to the added value of density (added value of image data A and B (d1, d2) from the control circuit). In the same manner, the gradation processing unit 78 generates pulses for the three portions of the dot formation matrix in accordance with the density addition values (image data A and B (d1, d2) from the control circuit). Go.

The gradation processing unit 78 performs gradation processing of image data using a light writing density generation algorithm expressed by the following equation.
When d1 + d2 + d3 + d4 = 254 in the one-pixel size expression shown in FIG. 29B, D1 = D2 = 127. Therefore, when replaced with the one-pixel size expression shown in FIG. 33, when d1 + d2 = 127, D1 = 127. , D2 = 0, and thereafter
When 128≤d1 + d2≤254, D1 = d1 + d2-127, D2 = 127
When 255≤d1 + d2≤382 D1 = d1 + d2-127, D2 = 127
When 383 ≦ d1 + d2 ≦ 510 D1 = 255, D2 = d1 + d2−255
It is.

Hereinafter, the method 6 will be specifically described. The gradation processing unit 78 performs gradation processing of image data using the following dot formation algorithm.
1) Addition of 4 dots A, B, C, D adjacent in the main scanning direction and the sub scanning direction or 2 dot data A, B adjacent in the main scanning direction by the adding circuit 604, and the main sub scanning direction and the sub scanning direction The density of 4 dots adjacent to or the density of 2 dots adjacent in the main scanning direction is added.
2) Sequentially generate pulses as optical writing pulses from 1 of the dot formation matrix.
3) The right / left phase of the PWM pulse is switched by E / O in the main scanning direction by the optical writing phase signal from the control circuit, each pixel is formed from the outside, and the optical writing pulse is sent in the same direction of the numerical values of the dot formation matrix Join.
4) The pulse is divided into half pulses within one dot, and when this pulse reaches 50% duty within one dot, a PWM pulse (optical writing pulse) of the same number or the next number of the dot formation matrix is generated.

Next, details of dot formation by method 6 will be described.
(A) Density 1/4 or less (1) -1: Density to 1/16 (one isolated dot)
When the density addition value (addition value of image data A, B, C, D (d1, d2, d3, d4) from the control circuit) is 1/16, the density data A, B of the surrounding 4 dots , C, D (d 1, d 2, d 3, d 4) are added by the adder circuit 604 and output via the comparison / distribution / phase control circuit 605, and the gradation processing unit 78 is shown in FIG. 34 (A). An isolated dot is generated from one portion above the pixel with a pulse width corresponding to the added value of the density (added value of image data A, B, C, D (d1, d2, d3, d4)).

At this time, the gradation processing unit 78 sets D1 = d1 + d2 + d3 + d4 and D2 = D3 = D4 = 0 if 0 ≦ d1 + d2 + d3 + d4 ≦ 127, and D1 = 127, D2 = d1 + d2 + d3 + d4−127, D3 if 128 ≦ d1 + d2 + d3 + d4 ≦ 254. = D4 = 0.
(1) -2: Density to 1/8 (isolated 1 dot)
When the density addition value (addition value of the image data A, B, C, D (d1, d2, d3, d4) from the comparison / distribution / phase control circuit 605) is 1/16 to 1/8, The density data A, B, C, D (d1, d2, d3, d4) of the surrounding four dots are added by the adder circuit 604 and output through the comparison / distribution / phase control circuit 605, and the gradation processing unit 78 As shown in FIG. 34 (B), the pulse width is added to the density (image data A, B, C, D (d1, d2, d3, d4) until the portion 1 above the pixel is saturated (full 50% duty). ) Is increased according to the addition value).

At this time, the gradation processing unit 78 sets D1 = d1 + d2 + d3 + d4 and D2 = D3 = D4 = 0 if 0 ≦ d1 + d2 + d3 + d4 ≦ 127, and D1 = 127, D2 = d1 + d2 + d3 + d4−127, D3 if 128 ≦ d1 + d2 + d3 + d4 ≦ 254. = D4 = 0.
(2) -1: density to 3/16 (isolated 2 dots)
When the density addition value (addition value of the image data A, B, C, D (d1, d2, d3, d4) from the comparison / distribution / phase control circuit 605) is 1/8 to 3/16, The density data A, B, C, D (d1, d2, d3, d4) of the surrounding four dots are added by the adder circuit 604 and output through the comparison / distribution / phase control circuit 605, and the gradation processing unit 78 As shown in FIG. 34 (C), after the portion on the upper side of the pixel is saturated, a pulse is added to the portion on the lower side of the pixel (image data A, B, C, D (d1, d2, d3, The remaining dots are generated by generating a pulse width corresponding to the added value d4).

At this time, the gradation processing unit 78 sets D1 = d1 + d2 + d3 + d4 and D2 = D3 = D4 = 0 if 0 ≦ d1 + d2 + d3 + d4 ≦ 127, and D1 = 127, D2 = d1 + d2 + d3 + d4−127, D3 if 128 ≦ d1 + d2 + d3 + d4 ≦ 254. = D4 = 0.
(2) -2: density to 2/8 (isolated 2 dots)
When the density addition value (addition value of the image data A, B, C, D (d1, d2, d3, d4) from the comparison / distribution / phase control circuit 605) is 3/16 to 2/8, The density data A, B, C, D (d1, d2, d3, d4) of the surrounding four dots are added by the adding circuit 604 and output through the comparison / distribution / phase control circuit 605, and the gradation processing unit 78 As shown in FIG. 34 (D), the pulse width is added to the density value (image data A, B,... From the comparison / distribution / phase control circuit 605) until one portion below the pixel is saturated (full 50% duty). C, D (added values of d1, d2, d3, d4)).

  At this time, the gradation processing unit 78 sets D1 = d1 + d2 + d3 + d4 and D2 = D3 = D4 = 0 if 0 ≦ d1 + d2 + d3 + d4 ≦ 127, and D1 = 127, D2 = d1 + d2 + d3 + d4−127, D3 if 128 ≦ d1 + d2 + d3 + d4 ≦ 254. = D4 = 0.

(I) Concentration 1/4 or higher (3) Concentration to 3/8 (300 lines and 10,000 lines)
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 1/4 to 3/8, the gradation processing unit 78 is shown in FIG. As described above, the pulse combined with the two portions from the outside of the pixel of the dot formation matrix is generated with a pulse width corresponding to the added value of density (added value of image data A and B (d1, d2) from the control circuit). .
(4) Concentration to 1/2 (300 lines and 10,000 lines)
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 3/8 to 1/2, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the second part of the dot formation matrix reaches 50% duty (added value of the image data A and B (d1, d2) from the control circuit). Increase according to.
(5) Concentration-5/8
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 1/2 to 5/8, the gradation processing unit 78 is shown in FIG. Thus, the dot width of the dot formation matrix 3 is increased so that the pulse width of the portion 1 of the dot formation matrix is increased according to the density addition value (addition value of the image data A and B (d1, d2) from the control circuit). A pulse coupled to the portion of is generated.
(6) Concentration-3/4
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 5/8 to 3/4, the gradation processing unit 78 is shown in FIG. As described above, the pulse width is added to the pulse width until the pulse combined with the third portion of the dot formation matrix reaches 50% duty (added value of the image data A and B (d1, d2) from the control circuit). Increase according to.
(7) Concentration-7/8
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 3/4 to 7/8, the gradation processing unit 78, as shown in FIG. The 4th part of the dot formation matrix is increased so that the pulse width of the 2nd part of the dot formation matrix is increased in accordance with the density addition value (addition value of the image data A and B (d1, d2) from the control circuit). Generate a combined pulse.
(8) Concentration ~ 1/1
When the density addition value (addition value of the image data A and B (d1, d2) from the control circuit) is 7/8 to 1/1, the gradation processing unit 78 is the 4 part of the dot formation matrix. The pulse width is increased in accordance with the added value of density (added value of image data A and B (d1, d2) from the control circuit) until the pulse combined with the voltage reaches 50% duty of FULL.

  The gradation processing unit 78 repeats such gradation processing of image data in the main scanning direction and in the sub scanning direction. In this case, the gradation processing unit 78 sequentially generates write pulses for each line. The writing pulse generated in this method 6 is output as an optical writing signal to the optical writing unit 3 of the printer 100, and the LD in the optical writing unit 3 outputs the optical writing signals (color writing signals (for each color) from the gradation processing unit 78 as described above. The image signal is sequentially modulated by the LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color.

  In this method 6, compared with the method 5, the density of 4 dots is added in the highlight portion having a density of ¼ or less, and the isolated dots are arranged in a staggered manner, and the highlight portion having a density of ¼ or more is 2 in the highlight portion. Since the dots are arranged in a staggered pattern, the reproducibility of the highlight portion can be improved from a lower density.

In the first reference mode, for example, when the method 6 is adopted and the monochrome image density is 1/16, the pixel arrangement (Bk, M, C, Bk, M, C, Y) as shown in FIG. , rather than the entire color superimposition roots beating) to form a full color image superimposed Y each color pixel, adding a predetermined different phases to the pixels of each color as shown in FIG. 38, for example Bk, M, C, Y colors Is shifted by one dot at a time in the main scanning direction in the order of C → M → Y → K (Bk). FIG. 38 shows the arrangement of each color pixel when the density is ½.

In this way, the pixels for each color are arranged in a phase-separated manner so that the color turbidity mainly in the highlight portion is greater than when pixels of all Bk, M, C, and Y colors are overlapped at the same position.・ Can reduce color unevenness. Further, by shifting the image data of Bk, M, C, and Y colors one dot at a time in the main scanning direction in the order of C → M → Y → K (Bk), each color is printed at the time of overprinting all colors in the medium density portion. pixels what was arranged as shown in FIGS 35 (B), C pixels and Y pixels so that each color pixel in the reference embodiment is illustrated in FIG. 39, the pixel of the pixel and K of M Each line overlaps, and a line that does not overlap the M pixel and the Y pixel can be formed. Thus, since the M pixel and the Y pixel do not overlap, it is advantageous when reproducing the skin color of a person who requires a delicate color tone. 39 to 41 show the arrangement of each color pixel when the density is ½.

  By adding predetermined different phases to the pixels for each color, the position of the density generation pixel for each color is changed in the main scanning direction. In this way, the position of the density generation pixel for each color is changed in the main scanning direction. As means for this, a dot generation position shift circuit for each color is used which shifts the read position of the main scanning direction counter by one clock for each color.

  In this dot generation position shift circuit for each color, as shown in FIG. 44, the main scanning clock generation unit 611 receives the writing basic clock CLOCK in the main scanning direction, and receives the synchronization signal LSYNC as the start signal in the main scanning direction. A main scanning clock CLK in the image writing range in the main scanning direction is generated. The quaternary counter 612 repeatedly counts the main scanning clock CLK from the main scanning clock generator 611 from 1 to 4, and outputs a count value indicating the dot generation position as 2-bit data.

  The C plate counter 613 counts the 2-bit data from the quaternary counter 612, and the output of the C plate counter 613 is used to indicate the dot generation position for C plate writing. Further, 2-bit data from the quaternary counter 612 is sequentially delayed by one clock by the D flip-flops 614 to 616. The M plate counter 617 counts the 2-bit data from the D flip-flop 614, and the output of the M plate counter 617 is used to indicate the dot generation position for M plate writing.

  The Y plate counter 618 counts the 2-bit data from the D flip-flop 615, and the output of the Y plate counter 618 is used to indicate the dot generation position for Y plate writing. The K plate counter 619 counts 2-bit data from the D flip-flop 616, and the output of the Y plate counter 619 is used to indicate the dot generation position for K plate writing. The gradation processing unit 78 determines the dot generation position for each color based on the outputs of these counters 613 and 617 to 619, and forms dots whose positions are shifted in the order of Y, M, C, and K in the main scanning direction.

In the case where the dot generation positions are differently arranged in the main scanning direction, a ROM in which data is input in advance without using a counter is used, and reading is repeated in the order of 1, 4, 2, 3, etc. Dots are arranged in order. If a sub-scanning direction counter or a regular signal is used, the dot generation position for each color can be controlled also in the sub-scanning direction.
The gradation processing unit 78 temporarily stores image data of Bk, M, C, and Y colors sequentially input from the printer γ correction unit 77 in a buffer memory, reads the image data from the buffer memory, and performs gradation processing thereof. As described above.

  In this case, the main scanning direction counters 613 and 617 to 619 sequentially count the reading positions in the main scanning direction by counting the clocks as described above, and the sub scanning direction counter counts the other clocks to perform the sub scanning. The direction reading position is counted sequentially. The gradation processing unit 78 reads the image data from the address specified by the count values of the main scanning direction counters 613 and 617 to 619 and the count value of the sub scanning direction counter in the buffer memory.

  That is, the main scanning direction readout position is determined by the count values of the main scanning direction counters 613 and 617 to 619, and the sub scanning direction readout position is determined by the count value of the sub scanning direction counter. As shown in FIG. 42, the input clocks of the main scanning direction counters 613 and 617 to 619 are sequentially shifted by one clock for each color, and the reading start position of the image data of Bk, M, C, and Y is set to each color. The position of the density generation pixel is changed in the main scanning direction for each color by shifting by one dot in the main scanning direction every time.

In the first reference form, in the low density part, by adding adjacent 4 dots of image data and generating density from specific pixels, it is possible to combine adjacent dots to realize isolated dots, ensuring stability. it can. Furthermore, in a color image forming apparatus that refers to image data of a plurality of pixels (reading pixels: dots) and distributes density data to specific positions of the plurality of pixels based on the reference result to form a dot or line image. Since the gradation processing unit 78 is provided as a means for changing the position of the density generation pixel in accordance with the color information of the image data, a paper white part is not formed in the low density part compared with the case of overprinting all colors, Further, the transfer conditions of the respective colors are made more equal, and color image formation with excellent color reproducibility, low roughness, and excellent graininess can be realized, particularly without color unevenness in the low density portion.

The first reference mode is optical writing in which optical writing is performed by performing optical modulation including at least pulse width modulation by an image signal in a color image forming apparatus that modulates a multi-tone color image signal to form an image. A gradation processing unit 78 and a writing unit 3 as means, an adder circuit 604 as means for adding image data of a plurality of adjacent pixels, and a predetermined pixel of a specific pixel based on the added image data by time-sharing between pixels. A gradation processing unit 78 as a means for generating density from the direction, a gradation processing unit 78 as a means for changing the density generation pixel in the main scanning direction, and the position of the density generation pixel according to the color information of the image data By changing in the main scanning direction, a phase for each color is added in the main scanning direction, and a linear image in which the C and Y colors and the M and K colors overlap each other in the intermediate density portion. Since the gradation processing unit 78 is provided as a means for forming the data, when the line is formed by adding the data of a plurality of adjacent pixels in the low and medium density unit, two colors C, M, Y, and K are used. In other words, it is possible to realize a line that overlaps a plurality of colors, and it is possible to realize color image formation that reproduces the skin color of a person who requires a particularly delicate color tone with high quality.

In the second reference form of the present invention, in the first reference form, the Bk, M, C, Y color image data is shifted one dot at a time in the main scanning direction in the order of C → M → K → Y. It is said. In the dot generation position shifting circuit for each color, the gradation processing unit 78 sequentially shifts the clock input to the main scanning direction counter by one clock for each color, and images of Bk, M, C, and Y colors. The data is shifted by one dot in the main scanning direction in the order of C → M → K → Y, and the reading start position of the image data of each color Bk, M, C, Y is 1 dot in the main scanning direction for each color. The positions of the density generation pixels are changed in the main scanning direction for each color by shifting them.

Thus, the middle density part, those pixels of each color during full color superimposition roots beating was arranged as shown in FIGS 35 (B) is, the colors of the pixels in this reference embodiment is a C, as shown in FIG. 40 The pixel and the K pixel, the M pixel and the Y pixel overlap each other, and the C line and the Y pixel do not overlap each other. Since the C pixel and the Y pixel do not overlap in this way, it is advantageous when reproducing the green color of a plant in a natural image where a deep color tone is preferred.

According to the second referential embodiment, a color image forming apparatus for forming an image by modulating the multi-tone color image signal, the light for optical writing performed light modulation containing at least pulse width modulated by an image signal A gradation processing unit 78 and a writing unit 3 as writing means, an adding circuit 604 as means for adding image data of a plurality of adjacent pixels, and a predetermined pixel of a specific pixel based on the added data by time division between pixels. The gradation processing unit 78 as a means for generating density from the direction, the gradation processing unit 78 as a means for changing the density generation pixel in the main scanning direction, and the position of the density generation pixel according to the color information of the data. By changing in the scanning direction, a phase for each color is added in the main scanning direction, and a line image is formed in which the C and K colors and the M and Y colors overlap each other in the middle density portion. Since a gradation processing unit 78 as a means for the first reference embodiment and on achieving the substantially the same effect, high quality, especially the green color of the vegetation in the natural image tone is preferred that a deep It is possible to realize color image formation that reproduces easily.

In the third reference embodiment of the present invention, the in the first reference embodiment, Bk, M, C, method of shifting by one dot image data of Y each color in the main scanning direction in the order of C → Y → M → K It is said. In the dot generation position shifting circuit for each color, the gradation processing unit 78 sequentially shifts the clock input to the main scanning direction counter by one clock for each color, and images of Bk, M, C, and Y colors. The data is shifted by one dot in the main scanning direction in the order of C → Y → M → K, and the read start position of the image data of each color Bk, M, C, Y is 1 dot in the main scanning direction for each color. The position of the density generation pixel is changed in the main scanning direction for each color by shifting it.

As a result, in the intermediate density portion, when all colors are overlaid, the pixels of each color are arranged as shown in FIG. 35B, but in this reference embodiment, the pixels of each color are C as shown in FIG. Pixels and M pixels, Y pixels and K pixels overlap each other, and a C line and Y pixel, and M and Y pixels do not overlap each other. In this way, the C pixel and the Y pixel, and the M pixel and the Y pixel do not overlap with each other in a natural image where reproduction of the skin color of a person who requires a delicate color tone and a deep color tone are preferred. This is advantageous when reproducing the green color of plants.

According to the third reference embodiment, in the color image forming apparatus for forming an image by modulating the multi-tone color image signal, the light for optical writing performed light modulation containing at least pulse width modulated by an image signal A gradation processing unit 78 and a writing unit 3 as writing means, an adding circuit 604 as means for adding image data of a plurality of adjacent pixels, and a predetermined pixel of a specific pixel based on the added data by time division between pixels. A gradation processing unit 78 as a means for generating density from the direction, a gradation processing unit 78 as a means for changing the density generation pixel in the main scanning direction, and the position of the density generation pixel according to the color information of the image data By changing in the main scanning direction, a phase for each color is added in the main scanning direction to form a line image in which the C and M colors and the Y and K colors overlap each other in the middle density portion. Since a gradation processing unit 78 as a means for, in the first reference embodiment and on achieving the substantially the same effect, the green color both vegetation color and natural image of human skin quality It is possible to realize color image formation that reproduces easily. Also, since Y is relatively invisible, pairing with K, which is relatively visible, improves the color reproducibility of the entire image.

Further, according to the first to third reference embodiments, the gradation processing unit 78 as means for changing the position of the density generation pixel in the main scanning direction according to the color information of the image data is the main scanning. Since it has a function of sequentially shifting the reading start position in the main scanning direction for each color, the invention according to claims 1 to 4 and 5 to 8 can be easily achieved. It becomes possible.

The first embodiment of the present invention is different from the first reference embodiment in the following points. In the first embodiment, when, for example, the method 6 is adopted in the first reference embodiment, the gradation processing unit 78 performs the processing flow shown in FIG. 43 as described above, and the monochrome image density is 1. In the case of / 16, not the pixel arrangement of Bk, M, C, and Y colors as shown in FIG. 37 (all-color overprinting that forms a full-color image by overlapping pixels of Bk, M, C, and Y colors), A system is adopted in which image data of each color of M, C, and Y is shifted in the sub-scanning direction, and predetermined different phases are added to the pixels for each color in the sub-scanning direction.

  In the dot generation position shift circuit for each color, the gradation processing unit 78 shifts the clock input to the sub-scanning direction counter by one pixel at a time for each color sequentially, so that each of the Bk, M, C, and Y colors. The image data is shifted by one pixel in the sub-scanning direction as shown in FIG. FIG. 45 shows the arrangement of each color pixel when the density is 1/16.

  Therefore, by forming a vertical line-shaped image, compared to the case of all-color overprinting in which each pixel of Bk, M, C, and Y is overlaid at the same position, a paper white portion is not formed. The transfer conditions of each color become more equal, and an image having excellent color reproducibility without color unevenness, little roughness, and excellent graininess can be formed particularly in a low density portion.

  By adding predetermined different phases to the pixels for each color, the position of the density generation pixel for each color is changed in the main scanning direction. In this way, the position of the density generation pixel for each color is changed in the main scanning direction. As the phase adding means, a dot generation position shifting circuit for each color as shown in FIG. 44 for shifting the reading position of the main scanning direction counter by one clock for each color is used.

  In the case where the dot generation positions are differently arranged in the main scanning direction, a ROM in which data is input in advance without using a counter is used, and reading is repeated in the order of 1, 4, 2, 3, etc. Dots are arranged in order. It is also possible to control the dot generation position for each color in the sub-scanning direction using a regular signal.

According to the first embodiment, in a color image forming apparatus that modulates a multi-tone color image signal to form an image, an adding circuit 604 as means for adding image data of a plurality of adjacent pixels; A gradation processing unit 78 as means for generating a density from a predetermined direction of a specific pixel by the data added by the means, and a gradation processing unit 78 as means for changing the density generation pixel in the main scanning direction or the sub-scanning direction The phase of each color is added in the sub-scanning direction by changing the position of the density generation pixel in the sub-scanning direction according to the color information of the data, and the vertical dots are formed by at least two different isolated dots in the low-density portion. Since a line-shaped image is formed, by adding the data of four adjacent pixels in the low density portion and generating the density from the appropriate direction of the specific pixel by the added value The contact pixels can be combined to realize isolated dots, and the stability can be secured. In addition, by adding a phase difference for each of at least two different colors in the sub-scanning direction, each color in the low density portion can be obtained. Images with vertical lines can be formed with isolated dots, and paper white areas are not formed more than when overprinting all colors, and the transfer conditions for each color are more even. It is possible to achieve a color image with excellent color reproducibility, little roughness, and excellent graininess.

Further, according to the first embodiment, in a color image forming apparatus that modulates a multi-tone color image signal to form an image, an adder circuit 604 as means for adding image data of a plurality of adjacent pixels. A gradation processing unit 78 as a means for generating density from a predetermined direction of a specific pixel by the data added by the means, and a gradation processing unit as a means for changing the density generation pixel in the main scanning direction or the sub-scanning direction 78, and by adding the phase for each color in the sub-scanning direction by changing the position of the density generating pixel in the sub-scanning direction according to the color information of the data, C, M, Y, K in the low density part Since a vertical line-shaped image is formed by isolated dots, the low density area is adjacent by adding the data of four adjacent pixels and generating the density from the appropriate direction of the specific pixel by the added value. The elements can be combined to realize isolated dots, and the stability can be secured. In addition, by adding the phase difference for each color of Bk, M, C, and Y in the sub-scanning direction, Images with vertical lines can be formed with isolated dots, and paper white areas are not formed more than when overprinting all colors, and the transfer conditions for each color are more even. Therefore, it is possible to realize color image formation with excellent color reproducibility, little roughness, and excellent graininess. In the first embodiment, a full-color image may be formed by pixels of M, C, and Y colors excluding Bk pixels.

In the second embodiment of the present invention, for example, method 6 is adopted in the first embodiment, and each color of Bk, M, C, and Y as shown in FIG. 37 when the monochrome image density is 1/16. This is not the pixel arrangement (all-color overprinting that forms a full-color image by overlapping pixels of each color Bk, M, C, and Y), but mainly the color turbidity and color unevenness in the highlight portion than in the case of all-color overstrike. As means for reducing, the image data of each color is shifted for each color in both the main scanning direction and the sub-scanning direction, and the pixels for each color are shifted to Bk, M, C, Y in both the main scanning direction and the sub-scanning direction. This is a method of adding a predetermined different phase for each color.

  In the dot generation position shifting circuit for each color, the gradation processing unit 78 sequentially shifts the clock input to the main scanning direction counter for each color, and sequentially shifts the clock input to the sub-scanning direction counter for each color. By shifting, the read image data of Bk, M, C, and Y colors are shifted so that the arrangement of pixels of Bk, M, C, and Y colors is staggered as shown in FIG. After adding predetermined different phases for each color of Bk, M, C, and Y to the image data of each color of C and Y, the gradation processing is performed as described above. FIG. 46 shows the arrangement of each color pixel when the density is 1/16. As a result, overlapping of different color pixels can be avoided as much as possible, and color image formation with excellent color reproducibility, low roughness, and excellent graininess can be realized, especially in low density areas with no color unevenness. .

According to the second embodiment, in a color image forming apparatus that modulates a multi-tone color image signal to form an image, an adder circuit 604 as means for adding image data of a plurality of adjacent pixels; A gradation processing unit 78 as means for generating a density from a predetermined direction of a specific pixel by the data added by the means, and a gradation processing unit 78 as means for changing the density generation pixel in the main scanning direction or the sub-scanning direction A gradation processing unit 78 as means for changing the position of the density generation pixel in the main scanning direction or the sub-scanning direction according to the color information of the data, and the position of the density generation pixel according to the color information of the data By changing between the scanning direction and the sub-scanning direction, a phase for each color is added in the main scanning direction and the sub-scanning direction, and a staggered dot arrangement is formed by C, M, Y, and K isolated dots in the low density portion. Therefore, in the low density part, by adding the data of four adjacent pixels and generating the density from the appropriate direction of the specific pixel by the added value, the adjacent pixels can be combined to realize isolated dots, and stability is improved. In addition to providing the effect of securing the vertical line shape by the isolated dots of each color in the low density area by adding the phase difference for each color of C, M, Y, K in both the main scanning direction and the sub-scanning direction. An image can be formed, and compared with the case of overprinting all colors, a white paper portion is not formed even in a low density portion, and a staggered dot arrangement is made by using C, M, Y, and K isolated dots as in this embodiment. By forming the color image, overlap between different color pixels can be avoided to the maximum, and color images with excellent color reproducibility, low graininess, and graininess can be achieved, especially in low density areas. it can.

In the third embodiment of the present invention, for example, method 6 is adopted in the first embodiment, and when the monochrome image density is 1/16, Bk, M, C, Y as shown in FIG. Rather than the pixel arrangement of each color (all-color overprinting that forms a full-color image by overlapping pixels of Bk, M, C, and Y colors), color turbidity and color unevenness mainly in the highlight portion than in the case of all-color overstrikes As a means for reducing this, the image data is shifted in the main scanning direction so that the phases of the chromatic image data and the achromatic color image data are different from each other, and the chromatic and achromatic pixels are present in the main scanning direction. A predetermined phase that is different between chromatic and achromatic colors is added.

  The gradation processing unit 78 determines whether the image data from the printer γ correction unit 77 is chromatic color data (here, Y, M, and C color image data) or achromatic color data (Bk image data). Chromatic color data / achromatic color data discrimination function and phase addition means for adding a predetermined phase different between the chromatic color and the achromatic color in the main scanning direction to each pixel of the chromatic color and the achromatic color. This phase adding means shifts the clock input to the main scanning direction counter between the chromatic color image data and the achromatic color image data according to the discrimination result of the chromatic color / achromatic color data discrimination function.

  The gradation processing unit 78 has a function of discriminating between chromatic color data and achromatic color data by phase adding means between chromatic (M, C, Y) image data and achromatic color (Bk) image data read from the buffer memory. As shown in FIG. 47, the chromatic color 3C (M, C, Y) pixel and the achromatic color K pixel are shifted so as not to overlap each other in the main scanning direction and the sub-scanning direction according to the determination result. A predetermined phase different between the chromatic color and the achromatic color is added to the image data and the achromatic image data. FIG. 47 shows the arrangement of each color pixel when the density is 1/16.

  As a result, a line-shaped image in which the chromatic color (M, C, Y) pixels and the achromatic color K pixel do not overlap each other is formed. On the line formed from the low density part to the middle density part without forming the white paper part, as shown in FIG. 48, the chromatic color 3C (M, C, Y) pixels and the achromatic color K pixels are mutually connected. Therefore, it is possible to realize color image formation that does not overlap with each other and is free from color turbidity and enables high-quality color reproduction.

According to the third embodiment, in a color image forming apparatus that refers to image data of a plurality of pixels, distributes density data to specific positions of the pixels according to the reference result, and forms a dot or line image. depending on the chromatic / achromatic color information than with a gradation processing unit 78 as a means for changing the position of the density generation pixel, chromatic color pixels and achromatic color that overlaps no dot arrangement and the pixel of As a result, it is possible to realize a color image formation that does not produce a paper white portion even in a low-density portion, and has no color turbidity and enables high-quality color reproduction, as compared to when all colors are overprinted.

In addition, according to the third embodiment, in a color image forming apparatus that modulates a multi-tone color image signal to form an image, an adding circuit 604 as means for adding image data of a plurality of adjacent pixels; The gradation processing unit 78 as means for generating the density of the specific pixel from the predetermined direction by the data added by the means, and the gradation processing unit 78 as means for changing the density generation pixel in the main scanning direction or the sub-scanning direction. And a gradation processing unit 78 as means for changing the position of the density generation pixel in the main scanning direction or the sub-scanning direction according to the data color information, and the position of the density generation pixel according to the data color information. And a gradation processing unit 78 as a means for changing in the sub-scanning direction or the sub-scanning direction, and changing the position of the density generation pixel in the main scanning direction according to the color information of the data. Adding color / achromatic another phase, of forming a dot arrangement C and M and Y that no line-shaped overlapping with K in the low density portion to the medium density portion, chromatic color of the pixel and achromatic By forming a dot arrangement that does not overlap with other pixels, compared to when all colors are overlaid, white paper is not produced even in low density areas, and chromatic and achromatic pixel data in particular. Are separated from each other on the line formed from the low density part to the middle density part, so that the chromatic color pixels and the achromatic color pixels do not overlap each other, and there is no color turbidity. Reproducible color image formation can be realized.

In the fourth embodiment of the present invention, in the third embodiment, as a means for reducing color turbidity and color unevenness mainly in the highlight portion, compared to the case of overprinting all colors, a phase adding means is used. The image data is shifted so that the phase of the chromatic color image data and the achromatic color image data in the main scanning direction are different from each other, and the chromatic color and the achromatic color pixel are changed to the chromatic color and the achromatic color in the main scanning direction. A method of adding different predetermined phases, and further shifting the image data so that the phase is different between the chromatic image data and the achromatic image data in the sub-scanning direction, and each pixel of chromatic color and achromatic color A predetermined different phase is added between the chromatic color and the achromatic color in the sub-scanning direction. The phase adding means shifts the clock input to the main scanning direction counter between the chromatic image data and the achromatic image data, and shifts the clock input to the sub scanning direction counter to the chromatic image data and the achromatic image. It is something that shifts with the data.

  The gradation processing unit 78 uses the phase addition means to convert the chromatic color (M, C, Y) image data and the achromatic color (K) image data according to the discrimination result of the chromatic color / achromatic color data discrimination function. As shown in FIG. 49, in the low density portion, the main scanning direction and the sub-scanning direction are formed so as to form an oblique line-like dot arrangement by the isolated dots of the three-color overlap 3C of C, M, and Y and the K isolated dots. By shifting to, the chromatic color image data and the achromatic color image data are added with different predetermined phases, and the position of the density generation pixel is changed in the main scanning direction and the sub scanning direction according to the color information of the data. To do. FIG. 49 shows the arrangement of each color pixel when the density is 1/16.

  In this case, the gradation processing unit 78 uses the phase difference of two dots in the main scanning direction as shown in FIG. 49, for example, for chromatic (M, C, Y) image data and achromatic (K) image data. In addition, the phase adding means shifts in the main scanning direction and the sub-scanning direction according to the determination result of the chromatic color / achromatic color data determination function so as to have a phase difference of one dot in the sub-scanning direction. Therefore, when the density is 1/4, as shown in FIG. 50, an oblique line-like dot arrangement is formed by the three-color overlapping 3C dots of C, M, and Y and the K dots, and in the middle density portion, C , M, Y three-color overlap 3C dots and K dots grow so as to be arranged in a 2 × 2 dot shape.

  In this way, since the C-, M-, and Y-color superimposing 3C dots and K dots form an oblique line-like dot arrangement, it is comfortable to the human eye and has color reproducibility and graininess in the low density portion. An excellent color image is formed. Furthermore, by growing so that the 3C color overlap 3C dots and K dots are arranged in a 2 × 2 dot shape over the middle density portion, the color is comfortable and colorable even in the middle density portion. A color image excellent in reproducibility and graininess is formed.

According to the fourth embodiment, in the third embodiment, the gradation processing unit 78 is provided as means for changing the position of the density generation pixel in the main scanning direction and the sub-scanning direction according to the color information of the data. By this means, a phase for each chromatic color / achromatic color is added in the main scanning direction and the sub-scanning direction, and the C, M, and Y three-color overlapping isolated dots and the K isolated dots are diagonally separated in the low density portion. Since the linear dot arrangement is formed, it is possible to reproduce a high-quality image of a diagonal line that is comfortable to human eyes and excellent in color reproducibility and graininess in a low density portion.

Further, according to the fourth embodiment, in the third embodiment, the gradation processing unit 78 as means for changing the position of the density generation pixel in the main scanning direction and the sub scanning direction according to the color information of the data. By this means, a phase for each chromatic color / achromatic color is added in the main scanning direction and the sub-scanning direction, and two dots are formed by the three-color overlapping dots of C, M, Y, and K dots in the middle density portion. Since it is grown so as to be arranged in a × 2 dot shape, it is possible to realize color image formation that is comfortable to human eyes and excellent in color reproducibility and graininess in the medium density portion.

Next, a fifth embodiment of the present invention will be described. As described above, in the first reference embodiment to third referential embodiment, the case of adopting the method 6, when the image density of a single color is 1/16 Bk as shown in FIG. 37, M, C, Y of respective colors Rather than the pixel arrangement (all-color overstrike that forms a full-color image by overlapping pixels of Bk, M, C, Y colors), a predetermined different phase is added to the pixels for each color, for example, Bk, M, C, The Y-color image data is shifted one dot at a time in the main scanning direction in the order of C → M → Y → K (Bk), C → M → K → Y, and C → Y → M → K. As described above, by arranging the pixels for each color in a phased manner, a line-shaped image in which the colors for each of the two colors overlap each other as shown in FIGS. 39 to 41 is formed in the intermediate density portion.

Here, as in the first reference embodiment, the image data of each color Bk, M, C, Y is shifted one dot at a time in the main scanning direction in the order of C → M → Y → K (Bk). In the density portion, when the image data of each color of Bk, M, C, and Y is overlapped in the main scanning direction, the pixel arrangement as shown in FIG. 35B is shown in FIG. 39 in the first reference form. Thus, C and Y, and M and K respectively become a line that overlaps, and a line that does not overlap M and Y can be formed. In this way, M and Y do not overlap on the line, which is advantageous in reproducing the skin color of a person who requires a delicate color tone.

Further, by shifting the image data of each color Bk, M, C, and Y in the main scanning direction one dot at a time in the order of C → M → K → Y as in the second reference form, , M, C, Y as was pixel arrangement shown in FIG. 35 (B) when the superimposed image data of each color in the main scanning direction, C and K as shown in FIG. 40 in the second referential embodiment , M and Y are each overlapped lines, and C and Y are not overlapped. Since C and Y do not overlap on the line as described above, it is advantageous in reproducing the green color of a plant in a natural picture where a deep color tone is preferred.

Further, as in the third reference embodiment, the Bk, M, C, and Y color image data are shifted one dot at a time in the main scanning direction in the order of C → Y → M → K. , M, C, as was a pixel arrangement shown in FIG. 35 (B) when superimposed image data of Y each color in the main scanning direction, the third C and M as shown in FIG 41 in the reference embodiment , Y and K overlap each other, and C and Y and M and Y do not overlap each other. In this way, C and M, Y and K do not overlap each other on the line, so that the reproduction of the skin color of people who require a subtle color tone and the green color of plants in natural paintings where a deep color tone is preferred. This is advantageous for color reproduction. In addition, the color reproducibility of the entire image is improved by pairing Y, which is relatively less noticeable, and K, which is relatively easily noticeable.

Therefore, in the fifth embodiment, the image data of each color Bk, M, C, and Y is shifted by one dot in the main scanning direction in the order of C → M → Y → K (Bk) in the first reference form. The first processing mode is performed, and the second processing mode is performed in which the image data of each color Bk, M, C, Y is shifted one dot at a time in the main scanning direction in the order of C → M → K → Y. By performing a third processing mode in which image data for each color of M, C, and Y is shifted one dot at a time in the main scanning direction in the order of C → Y → M → K, a predetermined different phase is applied to each color pixel. Append.

The gradation processing unit 78, the similar to the first reference embodiment executes the first processing mode, perform the second processing mode as in the second referential embodiment, the serial third referential embodiment The third processing mode is executed in the same manner as described above. The gradation processing unit 78 has first to third processing modes as options for selecting a combination of two colors based on the color information of the image data, and based on the color information of the image data. By switching and executing the first processing mode to the third processing mode, there is switching means for switching the line-shaped images in which the two colors overlap each other in the medium density portion. The switching means switches and executes the first processing mode to the third processing mode based on the color information of the image data.

According to the fifth embodiment, a color image forming apparatus that modulates a multi-tone color image signal to form an image, and an adding circuit 604 as means for adding image data of a plurality of adjacent pixels. And a gradation processing unit 78 as a means for generating a density from a predetermined direction of the specific pixel by the image data added by the means 604, and a gradation as a means for changing the density generation pixel in the main scanning direction or the sub-scanning direction. A processing unit 78; a gradation processing unit 78 as means for changing the position of the density generation pixel in the main scanning direction or the sub-scanning direction according to the color information of the image data; and the density generation pixel according to the color information of the image data. Is changed in the main scanning direction or the sub-scanning direction, and a phase for each color is added in the main scanning direction or the sub-scanning direction, so that the colors of the two colors overlap each other in the medium density portion. In a color image forming apparatus having a gradation processing unit 78 as means for forming a line-shaped image, an option is provided for selecting a combination of the two colors based on the color information of the image data, and this option is switched. Since the gradation processing unit 78 is provided as a switching means for switching the line-shaped images in which the two colors overlap each other in the medium density portion, the low density portion adds the data of four adjacent pixels and specifies the added value. By generating the density from the appropriate direction of the pixels, it is possible to combine adjacent pixels to achieve isolated dots and to ensure stability, and by adding a phase for each color, all colors Compared to overprinting, paper white areas are not produced even in low density areas, and the transfer conditions for each color are more even, so there is no color unevenness especially in low density areas. Excellent current property and less roughness can be realized an excellent color image graininess. Further, by providing an option for selecting a combination of two colors based on the color information of the image data and switching them, the line-shaped image in which the two colors overlap each other is switched in the medium density portion. For example, when switching to the option of selecting a combination of C and Y or M and K as the combination of each color, a line that does not overlap M and Y can be formed, and the skin color of a person who requires a particularly delicate color tone Can be reproduced with high quality. When switching to the option of selecting the combination of C and K and M and Y as the combination of colors for every two colors, a line that does not overlap C and Y can be formed, especially in a natural picture where a deep color tone is preferred The green color of plants can be reproduced with high quality. When switching to the option of selecting the combination of C and M and Y and K as the combination of colors for every two colors, it is possible to form lines that do not overlap C and Y and M and Y, respectively, and particularly delicate colors are required. Reproduction of the skin color of a person and the green color of plants in natural paintings where deep colors are preferred. In addition, the color reproducibility of the entire image is improved by pairing Y, which is relatively less noticeable, and K, which is relatively easy to notice. Furthermore, by switching these options based on the color information of the image data, it is possible to realize color image formation more suitable for the properties of the image data and to realize high-quality color reproduction.

Next, a sixth embodiment of the present invention will be described. As described above, in the second embodiment, the method 6 is adopted, and when the monochrome image density is 1/16, the pixel arrangement (Bk, M, Bk, M, C, Y) as shown in FIG. As a means for reducing color turbidity and color unevenness mainly in the highlight portion, rather than all color overstrike to form a full-color image by superimposing pixels of C, Y colors, The image data of each color is shifted for each color in both the main scanning direction and the sub-scanning direction, and the pixels for each color are different from each other in the Bk, M, C, and Y colors in both the main scanning direction and the sub-scanning direction. A phase is added.

  In particular, the Bk, M, C, and Y image data is shifted so that the arrangement of the Bk, M, C, and Y pixels is staggered as shown in FIG. A predetermined different phase for each color of Bk, M, C, and Y is added to the image data. As a result, overlapping of different color pixels can be avoided as much as possible, and color image formation with excellent color reproducibility, low roughness, and excellent graininess can be realized, especially in low density areas with no color unevenness. .

Therefore, in the sixth embodiment, in the fifth embodiment, the gradation processing unit 78 is input to the main scanning direction counter in the dot generation position shift circuit for each color, as in the second embodiment. The image data for each color Bk, M, C, and Y is converted to Bk, M, C, and Y by sequentially shifting the clock that is input for each color and sequentially shifting the clock that is input to the sub-scanning direction counter for each color. The pixels of each color are shifted in both the main scanning direction and the sub-scanning direction so that the arrangement of pixels is staggered, and image data of each Bk, M, C, Y color has a predetermined phase for each Bk, M, C, Y color. A fourth processing mode for adding different phases is provided as an option, and the first to fourth processing modes are switched and executed by the switching means based on the color information of the image data. In the sixth embodiment, as in the fifth embodiment, a line-shaped image in which two colors overlap each other is formed in the medium density portion (see FIGS. 39 to 41).

According to the sixth embodiment, in the fifth embodiment, the staggered dot arrangement is formed by cyan, magenta, yellow, and black isolated dots in the low density portion. By adding the pixel data and generating the density from the appropriate direction of the specific pixel by the added value, it is possible to combine adjacent pixels to realize isolated dots, and to achieve the effect of ensuring stability, By adding a phase for each color, compared to when all colors are overprinted, a white paper portion is not formed even in a low density portion, and in particular in a low density portion, staggered dots are formed by C, M, Y, K isolated dots. by forming the dot arrangement, since the overlap of different color dots can be avoided maximally, in addition to the effects of the fifth embodiment, in particular low density unevenness in color without color reproducibility in unit Excellent, and less roughness can achieve excellent color image forming graininess.

Next, a seventh embodiment of the present invention will be described. In the seventh embodiment, in the sixth embodiment, the gradation processing unit 78 uses the same clock input to the main scanning direction counter in the dot generation position shifting circuit for each color, and performs sub-scanning. By making the clock input to the direction counter the same for each color, the arrangement of the pixels of Bk, M, C, and Y is the same (see FIGS. 34 to 36). The fifth processing mode is provided as an option. The switching means switches between the first processing mode to the fifth processing mode based on the color information of the image data.

According to the seventh embodiment, in the sixth embodiment, the option of forming an image that overlaps the same position of all colors by making the positions of density generation pixels the same for all colors regardless of the color information of the image data. Since this option and the option are switched by the switching means, the low density portion adds adjacent four pixel data and generates the density from the appropriate direction of the specific pixel by the added value. In addition to being able to combine pixels to realize isolated dots and ensure stability, by making the positions of the density generation pixels of all colors the same, the resolution of edges of characters and line images can be improved. Even when required, a good edge output can be obtained without color misregistration, and color image formation more suitable for the properties of the image data can be realized.

Next, an eighth embodiment of the present invention will be described. In the above method 6, when the monochrome image density is 1/16, the pixel arrangement of each of the Bk, M, C, and Y colors is as shown in FIG. As a means for reducing color turbidity and color unevenness, a method in which different phases are added in the main scanning direction between chromatic and achromatic colors as shown in FIG.

Therefore, in the eighth embodiment, in the seventh embodiment, as shown in FIG. 51, the gradation processing unit 78 converts the image data into chromatic image data and achromatic image data in the main scanning direction. Each phase is shifted so that the phases are different, and a predetermined phase different in the main scanning direction is added to each pixel of chromatic and achromatic colors. A sixth processing mode is provided as an option for shifting the data phases so that they do not overlap and adding different predetermined phases in the sub-scanning direction to the chromatic and achromatic pixels.

  The gradation processing unit 78 determines whether the image data is chromatic color data (here, Y, M, or C color image data) or achromatic color data (Bk image data). A data discriminating function; and a phase adding means for adding predetermined phases different in the main scanning direction and the sub-scanning direction to each pixel of chromatic and achromatic colors. This phase adding means shifts the clock input to the main scanning direction counter between the chromatic color image data and the achromatic color image data, and shifts the clock input to the sub scanning direction counter to the chromatic color image data and the achromatic color data. It is shifted with the image data. The gradation processing unit 78 switches the first processing mode to the sixth processing mode based on the determination result of the chromatic color / achromatic color data determination function by the switching means, and executes the switched processing mode.

  Here, as shown in FIG. 51, by adding a phase difference to the main scanning direction and the sub-scanning direction for each chromatic color data / achromatic color data in the image data of each color, as shown in FIG. And Y three-color overlap 3C isolated dots and K isolated dots form an oblique line-like image, so that color that is comfortable to the human eye and excellent in color reproducibility and graininess in the low image density area An image can be formed. When the monochrome image density is 1/2, in the sixth processing mode, an image in the middle density portion is formed as shown in FIG. By adding the sixth processing mode as an option, color reproduction more suitable for the properties of the image data can be achieved.

According to the eighth embodiment, in the seventh embodiment, a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction according to the chromatic / achromatic information of the image data. In the middle density portion, C, M, and Y are added with the option of making a line-shaped dot arrangement that does not overlap with K, and this option and the option are switched by the switching means. By adding the values and generating the density from the appropriate direction of the specific pixel by the added value, it is possible to combine adjacent pixels to realize isolated dots, and to ensure the stability. A line-shaped dot in which C, M, and Y do not overlap K up to the middle density portion by adding a phase for each chromatic color / achromatic color in the main scanning direction and sub-scanning direction according to the chromatic / achromatic color information. Arrange By adding 択肢, than that in the entire color superimposition roots beating, without creating more paper white portion even in a low density area, and no color turbidity, it can realize high-quality color reproduction possible color image formation.

In the ninth embodiment and the tenth embodiment of the present invention, the sixth processing mode is added to the options in the fifth embodiment and the sixth embodiment, respectively, as in the eighth embodiment. As a result, color image formation more suitable for the nature of the image data can be realized.

Next, an eleventh embodiment of the present invention will be described. In the eleventh embodiment, in the eighth embodiment, the user can freely select a desired processing mode from the first processing mode to the fifth processing mode (hereinafter referred to as I / F). Is provided. As shown in FIG. 53, the I / F includes input keys 701 to 705 as selection means for selecting each of the first processing mode to the fifth processing mode, and the processing mode selected by the input keys 701 to 705. And an input key 706 for determining.

  The fifth processing mode that emphasizes resolution is selected by the input key 701, and the sixth processing mode for preventing color turbidity is selected by the input key 702. The second processing mode emphasizing green is selected by the input key 703, the first processing mode emphasizing skin color is selected by the input key 704, and one of the third processing mode and the sixth processing mode is the input key. Selected at 705. The gradation processing unit 78 executes the processing mode selected by the input keys 701 to 705 and determined by the input key 706 according to the input signals from the I / F input keys 701 to 706.

The twelfth to sixteenth embodiments are the same as the eleventh embodiment in the fifth to seventh embodiments, the ninth embodiment, and the tenth embodiment, respectively. An I / F for selecting each processing mode is provided, and the gradation processing unit 78 executes the selected processing mode.

According to the eleventh embodiment to the sixteenth embodiment, the fifth embodiment to the tenth embodiment have an interface that switches and executes the options according to the user's selection. By simply selecting the desired processing mode, it is possible to easily switch to that processing mode, and it is possible to output the processing mode desired by the user.

Next, a seventeenth embodiment of the present invention will be described. In the seventeenth embodiment, in the eighth embodiment, the color feature amount of the image data is automatically extracted, and an appropriate processing mode is automatically selected from each processing mode based on the extracted data. It is what you choose.

FIG. 54 shows a part of the processing flow of the gradation processing unit 78 in the seventeenth embodiment. The gradation processing unit 78 extracts the feature amount (color feature amount) of the multi-value image data from the printer γ correction unit 77 in step S1, and in step S2, the image data is converted to a character, line image, or the like. In step S3, it is determined whether the image data is image data that requires resolution of the edge portion, such as a character or a line image. In step S9, the fifth processing mode is executed by switching the processing mode to the fifth processing mode as a resolution-oriented moat.

  If the image data is not image data that requires resolution of an edge portion such as a character or a line image, the gradation processing unit 78 is image data having many achromatic colors based on the feature amount in step S3. If the image data is image data with many achromatic colors, the processing mode is switched to the sixth processing mode as the color turbidity prevention mode in step S10, and the sixth processing mode is executed. Further, if the image data is image data that does not have many achromatic colors, the gradation processing unit 78 calculates a histogram of G (green) image data from the image data from the printer γ correction unit 77 in step S4, and step S4. In S5, it is determined whether or not the ratio of the image data of G is large from the histogram. If the ratio of the image data of G is large, the processing mode is set as the green-oriented mode ADAPT33 in step S11. The process mode is switched to the second process mode.

  If the ratio of image data with G image data is not large, the gradation processing unit 78 determines whether there are many portions without image data with G image data from the histogram in step S6. If there are many portions without image data, the first processing mode is executed by switching to the first processing mode as the skin color emphasis mode ADAPT31 in step S12. If there are not many portions where the image data is not G image data, the gradation processing unit 78 switches the processing mode to the third processing mode ADAPT32 and executes the third processing mode ADAPT32 in step S7. Note that the gradation processing unit 78 performs image processing such as image data filtering and color correction before executing the actual halftone processing of the image data in each processing mode in each processing mode subroutine. Is also going.

The eighteenth to twenty- second embodiments of the present invention are the same as the seventeenth embodiment in the fifth to seventh embodiments, the ninth embodiment, and the tenth embodiment, respectively. In the same manner as described above, the feature amount on the color of the image data is automatically extracted, and based on the extracted data, an appropriate processing mode is automatically selected and executed.

According to the seventeenth to twenty- second embodiments, feature values are automatically extracted from image data in the fifth to tenth embodiments, and the options are automatically selected based on the extracted data. Since the gradation processing unit 78 is provided as a means for switching automatically, the user can recognize the property of the image data and manually perform the processing in the optimum processing mode for the image data without manually selecting the processing mode. Is possible.

Next, a twenty- third embodiment of the present invention is described. FIG. 55 shows a part of the processing flow of the gradation processing unit 78 in the twenty- third embodiment. In the twenty- third embodiment, in the seventeenth embodiment, the gradation processing unit 78 omits steps S1 to S3, S9, and S10 and executes steps S4 to S8, S11, and S12. It should be noted that the gradation processing unit 78 performs image processing such as image data filtering and color correction before executing the actual halftone processing of the image data in each processing mode within the subroutine for each processing mode. Is also going.

According to an embodiment of the first 23, in embodiments of the seventeenth, the means 78 for extracting a feature value from the image data and feature quantity the magnitude of the ratio of the image signals of the green from the image data, the first 17 In addition to the effects of the embodiment, it is possible to effectively select / switch the processing mode by the feature amount.

Next, a twenty- fourth embodiment of the present invention is described. In the twenty- fourth embodiment, the image data is divided into a plurality of blocks according to the feature amount in the twenty- third embodiment, and an appropriate processing mode is automatically selected from a plurality of processing modes for each block. Is to do. FIG. 56 shows a part of the processing flow of the gradation processing unit 78 in the twenty-fourth embodiment. In the twenty- fourth embodiment, in the twenty- third embodiment, the gradation processing unit 78 proceeds from step S4 to step S13, and the image data from the printer γ correction unit 77 is changed according to the variation amount of the G image data. A plurality of blocks are determined, and the processes of S5 to S7, S11, and S12 are performed for each block. In step S14, it is determined whether there is an unprocessed block. If there is an unprocessed block, the process returns to step SS5. . It should be noted that the gradation processing unit 78 performs image processing such as image data filtering and color correction before executing the actual halftone processing of the image data in each processing mode within the subroutine for each processing mode. Is also going.

25th embodiment of the present invention, in the above embodiment 22, divided into a plurality of blocks by its characteristic quantity of image data, for each block, automatically correct processing mode from among a plurality of processing modes As in the twenty-fourth embodiment, the gradation processing unit 78 proceeds from step S4 to step S13, and the G processing is performed on the image data from the printer γ correction unit 77. A plurality of blocks are determined according to the fluctuation amount of the image data, the processing of S5 to S7, S11, and S12 is performed for each block, and it is determined whether there is an unprocessed block in step S14. Then, the process returns to step SS5.

According to the 24th embodiment and 28th embodiment of the embodiment and the twenty-second embodiment of the 23, the extracted data of the gradation processing unit 78 as a means for extracting automatically a feature from the image data In addition to the effects of the seventeenth embodiment, the gradation processing unit 78 is provided as means for dividing the image data into a plurality of blocks for each feature, and the options are switched for each block. It is possible to perform processing in an appropriate processing mode every time, and it is possible to perform processing in an optimum mode for each block having different feature amounts even in the same output image (in the same recording medium).

It is a block diagram which shows the control circuit in the 1st reference form of this invention. It is a block diagram which shows the image process part of the same reference form. It is a figure which shows the optical output waveform and dot pattern of a light intensity modulation system and a pulse width modulation system. It is a figure which shows the optical output waveform and dot pattern of the pulse width intensity | strength mixed modulation system used by the said reference form. It is a figure for demonstrating the PWM pulse position control of the said reference form. It is a figure for demonstrating the fraction processing function of the said reference form. It is sectional drawing which shows the outline of the said reference form. It is a figure for demonstrating the image data processing of the said reference form. It is a figure which shows 1 dot size and 1 pixel size of the systems 1-3 employable with the said reference form. It is a figure which shows the dot formation matrix of the system 1 employable with the said reference form. It is the figure which expressed the dot formation matrix in the minimum density unit. It is a figure which shows the transition of the dot formation of the said system 1. FIG. It is a figure which shows the transition of the dot formation of the said system 1. FIG. It is a figure which shows the dot formation matrix of the system 2 employable with the said reference form. It is the figure which expressed the dot formation matrix in the minimum density unit. It is a figure which shows the transition of the dot formation of the said system 2. FIG. It is a figure which shows the transition of the dot formation of the said system 2. FIG. It is a figure which shows the dot formation matrix of the system 3 employable with the said reference form. It is the figure which expressed the dot formation matrix in the minimum density unit. It is a figure which shows the transition of the dot formation of the said system 3. FIG. It is a figure which shows the dot formation matrix of the system 4 employable with the said reference form. It is the figure which expressed the dot formation matrix in the minimum density unit. It is a figure which shows the transition of the dot formation of the said system 4. FIG. It is a figure which shows 1 dot size and 1 pixel size of the system 5 employable with the said reference form. It is a figure which shows the dot formation matrix of the system 5. It is the figure which expressed the dot formation matrix in the minimum density unit. It is a figure which shows the transition of the dot formation of the said system 5. FIG. It is a figure which shows the transition of the dot formation of the said system 5. FIG. It is a figure which shows 1 pixel size in the highlight part of 1 dot size of the system 6 employable with the said reference form, and a density of 1/4 or less. It is a figure which shows the dot formation matrix of the method 6. FIG. 10 is a diagram expressing a dot formation matrix at a density of 1/4 or less in the same method 6 in a minimum density unit. It is a figure which shows 1 pixel size in the density 1/4 or more of the method 6. It is a figure expressing the dot formation matrix in the density of 1/4 or more of the same method 6 in the minimum density unit. It is a figure which shows the transition of the dot formation in the density | concentration 1/4 or less of the system 6. FIG. It is explanatory drawing of the dot formation in the density 1/4 or more of the same system 6. It is a figure which shows the dot formation state in the density | concentration 7/8 of the system 6. FIG. It is a figure for demonstrating the said reference form. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/16 of the said reference form. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/2 of the said reference form. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/2 of the 2nd reference form of this invention. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/2 of the 3rd reference form of this invention. It is a figure which shows the image data read-out position by the main scanning counter of the said reference form. It is a flowchart which shows the processing flow of the gradation process part in the said reference form. It is a block diagram which shows the dot generation position shift circuit for every color of the said reference form. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/16 of the 2nd Embodiment of this invention. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/16 of the 3rd reference form of this invention. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/16 of the 3rd Embodiment of this invention. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/4 of the embodiment. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/16 of the 4th Embodiment of this invention. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/4 of the embodiment. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/16 of the 8th Embodiment of this invention. It is a figure which shows arrangement | positioning of each color dot by the density | concentration 1/2 of the said 8th Embodiment. It is a top view which shows I / F of the 11th Embodiment of this invention. It is a flowchart which shows a part of processing flow of the gradation process part in the 17th Embodiment of this invention. It is a flowchart which shows a part of processing flow of the gradation process part in the 23rd Embodiment of this invention. It is a flowchart which shows a part of processing flow of the gradation process part in the 24th Embodiment of this invention.

Explanation of symbols

3 Writing Unit 78 Gradation Processing Circuit 100 Laser Printer 400 Image Scanner 601 Line Memory 602, 603 Latch Circuit 604 Adder Circuit 605 Comparison / Distribution / Phase Control Circuit

Claims (8)

In a color image forming method of referring to image data of a plurality of pixels and allocating density data to specific positions of the plurality of pixels according to the reference result to form a dot or line image, a predetermined color of the pixel data According to the information, the position of the density generation pixel is changed in the main scanning direction , an image is formed so as to combine adjacent pixels for the predetermined color in a predetermined density portion, and the image data of each color is shifted in the sub scanning direction. In order to add a predetermined different phase in the sub-scanning direction to the pixels for each color and change the position of the density generation pixel in the main scanning direction according to the color information of the data, the reading start position in the main scanning direction is indicated. A color image forming method, wherein a reading start position in a main scanning direction is sequentially shifted for each color using a counter . In a color image forming method that forms an image by modulating a multi-tone color image signal, optical writing is performed by performing optical modulation including at least pulse width modulation by the image signal, and image data of a plurality of adjacent pixels are added. Then, the pixels are time-divided and the density is generated from a predetermined direction of the specific pixel by the added data, the density generation pixel is changed in the main scanning direction, and the position of the density generation pixel is changed according to the color information of the data. By changing in the scanning direction, a phase for each color is added in the main scanning direction, and a line-shaped image is formed in which the cyan and yellow colors and the magenta and black colors overlap each other in the middle density portion. adding a predetermined different phases in the sub-scanning direction by shifting the data in the sub-scanning direction to the pixels of each color, varying the position of the density generation pixels in the main scanning direction in accordance with the color information of the data Color image forming method according to claim to, using a counter indicating the read start position in the main scanning direction, the sequentially shifting the reading start position in the main scanning direction for each color to. In a color image forming method that forms an image by modulating a multi-tone color image signal, optical writing is performed by performing optical modulation including at least pulse width modulation by the image signal, and image data of a plurality of adjacent pixels are added. Then, the pixels are time-divided and the density is generated from a predetermined direction of the specific pixel by the added data, the density generation pixel is changed in the main scanning direction, and the position of the density generation pixel is changed according to the color information of the data. By changing in the scanning direction, a phase for each color is added in the main scanning direction, and a line-shaped image is formed in which the cyan and black colors and the magenta and yellow colors overlap each other in the middle density portion. adding a predetermined different phases in the sub-scanning direction by shifting the data in the sub-scanning direction to the pixels of each color, varying the position of the density generation pixels in the main scanning direction in accordance with the color information of the data Color image forming method according to claim to, using a counter indicating the read start position in the main scanning direction, the sequentially shifting the reading start position in the main scanning direction for each color to. In a color image forming method that forms an image by modulating a multi-tone color image signal, optical writing is performed by performing optical modulation including at least pulse width modulation by the image signal, and image data of a plurality of adjacent pixels are added. Then, the pixels are time-divided and the density is generated from a predetermined direction of the specific pixel by the added data, the density generation pixel is changed in the main scanning direction, and the position of the density generation pixel is changed according to the color information of the data. By changing in the scanning direction, a phase for each color is added in the main scanning direction, and a linear image in which cyan and magenta colors and yellow and black colors overlap each other is formed in the middle density portion, and image data of each color was added a predetermined different phase in the sub-scanning direction are shifted in the sub-scanning direction to the pixels of each color, change the position of the density generation pixels in the main scanning direction in accordance with the color information of the data Runoni, using a counter indicating the read start position in the main scanning direction, a color image forming method characterized by shifting the sequential read start position in the main scanning direction for each color. In a color image forming apparatus that refers to image data of a plurality of pixels and distributes density data to specific positions of the plurality of pixels according to the reference result to form a dot or line image, a predetermined color of the pixel data Means for changing the position of the density generation pixel in the main scanning direction in accordance with the information and forming an image so as to combine adjacent pixels for the predetermined color in the predetermined density portion; and image data of each color in the sub-scanning direction Means for shifting and adding predetermined different phases to the pixels for each color in the sub-scanning direction, and means for changing the position of the density generating pixel in the main scanning direction in accordance with the color information of the data. A color image forming apparatus having a counter that indicates the read start position of the image, and having a function of sequentially shifting the read start position in the main scanning direction for each color. In a color image forming apparatus that modulates a multi-tone color image signal to form an image, an optical writing unit that performs optical writing by performing optical modulation including at least pulse width modulation by the image signal, and a plurality of adjacent pixels Means for adding image data; means for generating a density from a predetermined direction of a specific pixel by time-division between pixels; and means for changing the density generating pixel in the main scanning direction; and data color information Accordingly, the phase of each color is added in the main scanning direction by changing the position of the density generation pixel in the main scanning direction, and the cyan and yellow colors and the magenta and black colors overlap each other in the middle density portion. Means for forming a line-shaped image, and means for shifting image data of each color in the sub-scanning direction and adding a predetermined different phase in the sub-scanning direction to the pixels for each color. The means for changing the position of the density generation pixel in the main scanning direction according to the color information of the data has a counter indicating the reading start position in the main scanning direction, and sequentially reads out the reading start position in the main scanning direction for each color. A color image forming apparatus having a function of shifting In a color image forming apparatus that modulates a multi-tone color image signal to form an image, an optical writing unit that performs optical writing by performing optical modulation including at least pulse width modulation by the image signal, and a plurality of adjacent pixels Means for adding image data; means for generating a density from a predetermined direction of a specific pixel by time-division between pixels; and means for changing the density generating pixel in the main scanning direction; and data color information Accordingly, the phase of each color is added in the main scanning direction by changing the position of the density generating pixel in the main scanning direction, and the cyan and black colors and the magenta and yellow colors overlap each other in the middle density portion. Means for forming a line-shaped image, and means for shifting image data of each color in the sub-scanning direction and adding a predetermined different phase in the sub-scanning direction to the pixels for each color. The means for changing the position of the density generation pixel in the main scanning direction according to the color information of the data has a counter indicating the reading start position in the main scanning direction, and sequentially reads out the reading start position in the main scanning direction for each color. A color image forming apparatus having a function of shifting In a color image forming apparatus that modulates a multi-tone color image signal to form an image, an optical writing unit that performs optical writing by performing optical modulation including at least pulse width modulation by the image signal, and a plurality of adjacent pixels Means for adding image data; means for generating a density from a predetermined direction of a specific pixel by time-division between pixels; and means for changing the density generating pixel in the main scanning direction; and data color information Accordingly, the phase of each color is added in the main scanning direction by changing the position of the density generating pixel in the main scanning direction, and the cyan and magenta colors and the yellow and black colors overlap each other in the middle density portion. And a means for shifting the image data of each color in the sub-scanning direction and adding a predetermined different phase in the sub-scanning direction to the pixels for each color. , Means for changing the position of the density generation pixels in the main scanning direction in accordance with the color information data has a counter indicating the read start position in the main scanning direction, the sequentially read start position in the main scanning direction for each color color image type forming apparatus characterized by having a function of shifting.

Images