JP2001053979A - Color image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate irregular color which is caused at a low gray scale part and to improve color reproducibility by changing the position of gray scale generating pixels according to the color information of the image data when a line-like image is formed by distributing gray scale data to a prescribed position among a plurality of pixels by referring to the image data on these pixels. SOLUTION: A gradation processing part 78 of an image processing unit of this color image forming device multilevels the image signals of 8-bit Y, M, C and K colors which are received from a printer γcorrection part 77. The part 78 also functions as a means which changes the position of the density generating pixels according to the color information of the image data as the halftone processing. Thereby a paper white part can be eliminated more satisfactorily at a low density part compared with a case where all colors are overprinted and a more equal transfer condition is secured among colors. Thus, it is possible to obtain a color image which has no irregular color at a low gray scale part in particular to attain excellent color reproducibility and which excels in the graininess with reduced roughness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color image forming method and a color image forming apparatus used for a digital image forming apparatus such as a digital copying machine, a laser printer, a facsimile machine, and a display device.

[0002]

2. Description of the Related Art Conventionally, a color image forming method and a color image forming apparatus form a full-color image by superposing pixels of each color. Some image forming apparatuses having a halftone processing function have an intermediate processing technique.
Japanese Patent No. 254985, Japanese Patent Application Laid-Open No. 7-254986,
JP-A-7-283941, JP-A-8-11496
No. 5, JP-A-8-125863, JP-A-7-128
No. 2,549,862.

[0003] These are mainly intended to improve the reproducibility of the highlight part of the image, and perform pulse width modulation of the image data and perform dither processing weighted by two dots in the main scanning direction to perform image highlighting. Is stabilized with a low line frequency reproduction,
In addition, the optical writing beam diameter in the main scanning direction and the pixel interval are defined.

Japanese Patent Application Laid-Open No. 2-243363 discloses a semiconductor laser drive circuit that modulates a semiconductor laser by a modulation method combining a pulse width modulation method and a power modulation method with image data. JP-A-6-3
No. 47852 discloses that a semiconductor laser is modulated by a modulation method that combines a pulse width modulation method and a power modulation method with image data, and the phase of the modulated pulse is centered in a center mode, shifted rightward in a right mode, and shifted leftward in a right mode. An image forming apparatus that is shifted leftward in a mode is described.

Japanese Patent Application Laid-Open No. 3-1656 discloses a multi-gradation optical writing apparatus for a laser which performs optical modulation of a laser by a combination of a pulse width modulation method and a power modulation method with image data to perform optical writing. There is described an image forming dot having a predetermined phase. Japanese Patent Laying-Open No. 4-200075 describes an image forming apparatus that refers to density data of two adjacent dots, converts the reference data, and generates density from specific dots.

Japanese Patent Application Laid-Open No. 4-200076 describes an image forming apparatus which refers to density data of two adjacent dots, performs density weighting and PWM modulation based on the reference result, and repeats these in the main scanning direction. I have. JP-A-4-
Japanese Patent Application Laid-Open No. 200077 discloses a means for performing one-dot multi-tone light writing of read image data and a means for performing multi-tone light writing for each dot of read image data and performing area gradation with a plurality of dots in document information. Alternatively, an image forming apparatus in which switching is performed based on an image spatial frequency or a density difference between dots is described.

Japanese Patent Application Laid-Open No. Hei 4-200078 discloses that the direction of the line is determined by the direction and size of the original and the image density in the main scanning direction.
An image forming apparatus that switches in the sub-scanning direction is described. Japanese Unexamined Patent Publication No. Hei 5-284339 discloses that the density data of two adjacent dots is referred to,
An image forming apparatus that generates a density on a side of a dot having a high density among dots is described.

Japanese Patent Application Laid-Open No. 6-62248 discloses an image forming apparatus which performs line-type optical writing (expresses gradation by a line image in a predetermined direction) and emphasizes edges in a direction perpendicular to the line. ing. Japanese Patent Application Laid-Open No. 5-292301 discloses an image forming method in which data of two adjacent dots is distributed, and a dot formation start phase in the main scanning direction or the sub-scanning direction is periodically changed to form various checkered patterns. Has been described.

[0009]

In an image forming apparatus and an image forming method for performing halftone processing, color unevenness occurs particularly in a low-density portion, resulting in poor color reproducibility, and for human skin requiring a fine color tone. Poor reproducibility of green color of vegetation in natural paintings where colors and deep colors are preferred. Further, in the color image forming apparatus and the color image forming method, since a full-color image is formed by superimposing pixels of each color, color unevenness occurs particularly in a low-density part, resulting in poor color reproducibility, and graininess in a low-density part is poor. Not good. Further, due to the overlap between the multicolor dots, color turbidity occurs in the low density portion to the middle density portion.

The invention according to claim 1 provides a color image forming method capable of realizing a color image having excellent color reproducibility without color unevenness particularly in a low density portion and excellent granularity in a low density portion. The purpose is to: It is an object of the present invention to provide a color image forming method capable of reproducing a high quality human skin color requiring a particularly delicate color tone. An object of the invention according to claim 3 is to provide a color image forming method capable of reproducing a green color of a vegetation of a natural picture, in which a deep color tone is particularly preferred, with high quality.
It is an object of the invention according to claim 4 to provide a color image forming method capable of reproducing both the color of human skin and the green color of vegetation of a natural image with high quality. The invention according to claim 5 is
An object of the present invention is to provide a color image forming method capable of easily achieving the inventions according to claims 1 to 4. An object of the invention according to claim 6 is to provide a color image forming apparatus capable of achieving color image formation 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 invention according to claim 7 is to provide a color image forming apparatus capable of reproducing a human skin color requiring a particularly subtle color tone with high quality. An object of the invention according to claim 8 is to provide a color image forming apparatus capable of reproducing a green color of a vegetation of a natural image with a particularly preferable deep color tone with high quality. An object of the invention according to claim 9 is to provide a color image forming apparatus capable of reproducing both the color of human skin and the green color of vegetation of a natural image with high quality. The invention according to claim 10 is the invention according to claims 6 to
An object of the present invention is to provide a color image forming apparatus capable of easily achieving the invention according to No. 9.

[0011] It is an object of the present invention to provide a color image forming method which is excellent in color reproducibility without color unevenness particularly in a low density portion and excellent in graininess in a low density portion. An object of the invention according to claim 12 is to provide a color image forming method which is excellent in color reproducibility without color unevenness particularly in a low density portion and excellent in graininess in a low density portion.

An object of the present invention is to provide a color image forming method capable of maximally avoiding overlap between multicolor dots and having excellent color reproducibility and granularity in a low density portion. And A further object of the present invention is to provide a color image forming method capable of high-quality color reproduction without color turbidity in a low density portion to a medium density portion.

It is another object of the present invention to provide a color image forming method capable of reproducing high quality colors without color turbidity in a low density portion to a middle density portion. The invention according to claim 16 is a color image forming apparatus which is excellent in color reproducibility and granularity in a low-density portion and can reproduce a basic image of a diagonal line which is comfortable to human eyes with high quality. The aim is to provide a method.

A further object of the present invention is to provide a color image forming method capable of forming a color image which is comfortable to human eyes and excellent in color reproducibility and granularity in a medium density portion. And An object of the invention according to claim 18 is to provide a color image forming apparatus which is excellent in color reproducibility without color unevenness particularly in a low density portion and excellent in graininess in a low density portion.

An object of the present invention is to provide a color image forming apparatus which is excellent in color reproducibility without color unevenness particularly in a low density portion and excellent in graininess in a low density portion. It is an object of the present invention to provide a color image forming apparatus capable of avoiding overlap between multicolor dots to a maximum extent and having excellent color reproducibility and granularity in a low density portion.

A still further object of the present invention is to provide a color image forming apparatus capable of reproducing high quality colors without color turbidity in a low density portion to a middle density portion. It is an object of the invention according to claim 22 to provide a color image forming apparatus capable of performing high-quality color reproduction without color turbidity in a low density portion to a middle density portion.

The invention according to claim 23 is excellent in color reproducibility and granularity in a low-density portion, and can reproduce a basic image of a diagonal line which is comfortable for human eyes with high quality. It is an object to provide a color image forming apparatus. An object of the invention according to claim 24 is to provide a color image forming apparatus capable of realizing a color image formation which is comfortable to human eyes and excellent in color reproducibility and granularity in a medium density portion.

A further object of the present invention is to provide a color image forming method capable of realizing high-quality color reproduction. It is an object of the invention according to claim 26 to provide a color image forming method excellent in color reproducibility and granularity in a low density portion. It is an object of the invention according to claim 27 to provide a color image forming method more suitable for the characteristics of image data.

An object of the invention according to claim 28 is to provide a color image forming method capable of producing high-quality color without forming a paper white portion and without color turbidity. Claim 29
An object of the present invention is to provide a color image forming method capable of outputting in a desired processing mode. A color image forming method according to claim 30, wherein a user can recognize a property of image data and execute processing in an optimum processing mode for image data without manually selecting a processing mode. The purpose is to provide.

A further object of the present invention is to provide a color image forming method capable of effectively selecting / switching a processing mode based on a feature amount. It is an object of the invention according to claim 32 to provide a color image forming method capable of executing processing in an optimal mode for each block having different feature values even in the same output image.

An object of the invention according to claim 33 is to provide a color image forming apparatus capable of realizing high-quality color reproduction. It is another object of the present invention to provide a color image forming apparatus which is excellent in color reproducibility and granularity in a low density portion. It is an object of the invention according to claim 35 to provide a color image forming apparatus more suitable for the characteristics of image data.

An object of a thirty-sixth aspect of the present invention is to provide a color image forming apparatus which does not form a paper white portion and has no color turbidity and capable of high-quality color reproduction. Claim 37
An object of the present invention is to provide a color image forming apparatus capable of outputting in a desired processing mode. The color image forming apparatus according to claim 38, wherein the user can recognize the nature of the image data and execute processing in an optimal processing mode for the image data without manually selecting a processing mode. The purpose is to provide.

An object of the invention according to claim 39 is to provide a color image forming apparatus capable of effectively selecting / switching a processing mode based on a feature amount. It is an object of the invention according to claim 40 to provide a color image forming apparatus capable of executing processing in an optimal mode for each block having a different feature amount even in the same output image.

[0024]

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 a specific position among the plurality of pixels based on a result of the reference. In the color image forming method for forming a dot or line image, the position of the density generating pixel is changed according to the color information of the data.

According to a second 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 including at least pulse width modulation is performed by the image signal to perform optical writing. Add the image data of a plurality of adjacent pixels, time-division between the pixels, generate a density from a predetermined direction of a specific pixel by the added data, change the density generation pixel in the main scanning direction, and change the color of the data. By changing the position of the density generating pixel in the main scanning direction according to the information, a phase for each color is added in the main scanning direction, and the colors of cyan and yellow, and the colors of magenta and black are respectively changed in the middle density portion. It is characterized in that overlapping linear images are formed.

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 including at least pulse width modulation is performed by the image signal to perform optical writing. Add the image data of a plurality of adjacent pixels, time-division between the pixels, generate a density from a predetermined direction of a specific pixel by the added data, change the density generation pixel in the main scanning direction, and change the color of the data. By changing the position of the density generating pixel in the main scanning direction according to the information, a phase for each color is added in the main scanning direction, and the colors of cyan and black, and the colors of magenta and yellow are respectively changed in the medium density portion. It is characterized in that overlapping linear images are formed.

According to a fourth aspect of the present invention, in a color image forming method for forming an image by modulating a multi-gradation color image signal, optical writing including at least pulse width modulation is performed by the image signal to perform optical writing. Add the image data of a plurality of adjacent pixels, time-division between the pixels, generate a density from a predetermined direction of a specific pixel by the added data, change the density generation pixel in the main scanning direction, and change the color of the data. By changing the position of the density generating pixel in the main scanning direction according to the information, a phase for each color is added in the main scanning direction, and cyan and magenta colors and yellow and black colors overlap in the middle density portion, respectively. It is characterized in that a line-shaped image is formed.

According to a fifth aspect of the present invention, in the color image forming method according to any one of the first to fourth aspects, the position of the density generating pixel is changed in the main scanning direction according to the color information of the data. A reading start position in the main scanning direction is sequentially shifted for each color by using a counter indicating a reading start position in the main scanning direction.

According to a sixth aspect of the present invention, there is provided a color image forming a dot or line image by referring to image data of a plurality of pixels and distributing density data to a specific position of the plurality of pixels based on the reference result. In the forming apparatus, there is provided means for changing the position of the density generating pixel according to the color information of the data.

According to a seventh aspect of the present invention, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, optical writing including at least pulse width modulation by the image signal is performed. A light writing unit, a unit for adding image data of a plurality of adjacent pixels, a unit for time-division between pixels to generate a density from a predetermined direction of a specific pixel by the added data, and Means for changing the color in the main scanning direction, and adding a phase for each color in the main scanning direction by changing the position of the density generating pixel in the main scanning direction in accordance with the color information of the data. For forming a linear image in which the colors of magenta and black overlap each other.

According to an eighth aspect of the present invention, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, optical writing including at least pulse width modulation by the image signal is performed. A light writing unit, a unit for adding image data of a plurality of adjacent pixels, a unit for time-division between pixels to generate a density from a predetermined direction of a specific pixel by the added data, and Means for changing the color in the main scanning direction, and adding a phase for each color in the main scanning direction by changing the position of the density generating pixel in the main scanning direction in accordance with the color information of the data. And a means for forming a linear image in which the colors of magenta and yellow overlap each other.

According to a ninth aspect of the present invention, in a color image forming apparatus which forms an image by modulating a multi-gradation color image signal, optical writing is performed by performing light modulation including at least pulse width modulation by the image signal. A light writing unit, a unit for adding image data of a plurality of adjacent pixels, a unit for time-division between pixels to generate a density from a predetermined direction of a specific pixel based on the added data, and a main scan for the density generation pixel Means for changing the color in the main scanning direction by adding the phase for each color in the main scanning direction by changing the position of the density generating pixel in the main scanning direction in accordance with the color information of the data. And means for forming a linear image in which the colors of yellow and black overlap each other.

According to a tenth aspect of the present invention, in the color image forming apparatus according to any one of the sixth to ninth aspects, the means for changing the position of the density generating pixel in the main scanning direction in accordance with the color information of the data includes: It has a counter that indicates 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 an eleventh aspect of the present invention, in a color image forming method for forming an image by modulating a multi-tone color image signal, image data of a plurality of adjacent pixels are added.
A 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 or the sub scanning direction, and the position of the density generation pixel is changed in the sub scanning direction according to the color information of the data. In this way, a phase for each color is added in the main scanning direction, and a vertical line image is formed by at least two different colors of isolated dots in the low density portion.

According to a twelfth aspect of the present invention, in a color image forming method for forming an image by modulating a multi-tone color image signal, image data of a plurality of adjacent pixels are added.
Based on the added data, a density is generated from a predetermined direction of the specific pixel, the density generation pixel is changed in the main scanning direction or the sub-scanning direction, and the position of the density generation pixel is changed in the sub-scanning direction according to the color information of the data. In this manner, a phase for each color is added in the main scanning direction, and an image having a vertical parallel line shape is formed by isolated dots of cyan, magenta, yellow or cyan, magenta, yellow, and black in a low density portion.

According to a thirteenth aspect of the present invention, in a color image forming method for forming an image by modulating a multi-tone color image signal, image data of a plurality of adjacent pixels are added.
A density is generated from a predetermined direction of a specific pixel by the added data, the density generation pixel is changed in the main scanning direction or the sub scanning direction, and the position of the density generation pixel is changed in the main scanning direction or the sub scanning direction according to the color information of the data. In the main scanning direction and the sub-scanning direction by changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction according to the color information of the data. A staggered dot arrangement is formed by isolated dots of cyan, magenta, yellow, and black.

According to a fourteenth aspect of the present invention, there is provided a color image forming method for referencing image data of a plurality of pixels, distributing density data to a specific position of the pixel based on a result of the reference, and forming a dot or line image. The position of the density generating pixel is changed according to the chromatic / achromatic information of the data.

According to a fifteenth aspect of the present invention, in a color image forming method for forming an image by modulating a multi-tone color image signal, image data of a plurality of adjacent pixels are added.
Based on the added data, density is generated from a specific direction of a specific pixel, the density generating pixel is changed in the main scanning direction or the sub-scanning direction, and the position of the density generating pixel is changed in the main scanning direction or the sub-scanning direction according to the color information of the data. Direction, the position of the density generating pixel is changed in the main scanning direction or the sub-scanning direction according to the color information of the data, and the position of the density generating pixel is changed in the main scanning direction according to the color information of the data. It is characterized by adding a phase for each chromatic / achromatic color in the main scanning direction, and forming a linear dot arrangement in which cyan, magenta, and yellow do not overlap with black in the low density portion to the middle density portion.

According to a sixteenth aspect of the present invention, in the color image forming method according to the fourth aspect, the position of the density generating pixel is changed in the main scanning direction and the sub-scanning direction in accordance with the color information of the data, thereby achieving the main scanning. Color / sub-scan direction
A phase is added for each achromatic color, and in a low density portion, an oblique line-shaped dot arrangement is formed by three-color superimposed isolated dots of cyan, magenta, and yellow and black isolated dots.

According to a seventeenth aspect of the present invention, in the color image forming method according to the fourth aspect, the position of the density generating pixel is changed in the main scanning direction and the sub-scanning direction in accordance with the color information of the data, thereby achieving main scanning. Color / sub-scan direction
A phase is added for each achromatic color, and in a middle density portion, dots are grown so as to be arranged in a 2 × 2 dot shape by three-color superimposed dots of cyan, magenta, and yellow and black dots. I do.

According to an eighteenth aspect of the present invention, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, means for adding image data of a plurality of adjacent pixels, and this means for adding Means for generating density from a predetermined direction of a specific pixel based on the obtained data, and means for changing the density generation pixel to the main scanning direction or 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, a phase for each color is added in the main scanning direction, and at least two or more different isolated dots in the low-density portion form a vertical line. Is formed.

According to a nineteenth aspect of the present invention, there is provided a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, a means for adding image data of a plurality of adjacent pixels, and the means for adding the image data. Means for generating density from a predetermined direction of a specific pixel based on the obtained data, and means for changing the density generation pixel to the main scanning direction or 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, a phase for each color is added in the sub-scanning direction, and cyan, magenta, yellow or cyan, magenta, yellow, black Is used to form an image in the shape of a vertical line.

According to a twentieth aspect of the present invention, in a color image forming apparatus for forming an image by modulating a multi-tone color 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 based on the obtained data, means for changing the density generation pixel in the main scanning direction or the sub-scanning direction, and changing the position of the density generation pixel in the main scanning direction or Means for changing in the sub-scanning direction, and adding a phase for each color in the main scanning direction and the sub-scanning direction by changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction according to the color information of the data. And cyan, magenta,
A staggered dot arrangement is formed by yellow and black isolated dots.

According to a twenty-first aspect of the present invention, there is provided a color image forming apparatus which refers to image data of a plurality of pixels, distributes density data to specific positions of the pixels based on the reference result, and forms a dot or line image. It is provided with means for changing the position of the density generating pixel according to the chromatic / achromatic information of the data.

According to a twenty-second aspect of the present invention, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, a means for adding image data of a plurality of adjacent pixels, Means for generating a density from a specific direction of a specific pixel based on the obtained data, means for changing the density generation pixel in the main scanning direction or the sub-scanning direction, and setting the position of the density generation pixel in the main scanning direction or Means for changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction in accordance with the color information of the data; By changing to the main scanning direction, a phase for each chromatic / achromatic color is added in the main scanning direction, and cyan, magenta, and yellow overlap with black in the low-density part to the middle-density part. And forms a free linear dot arrangement.

According to a twenty-third aspect of the present invention, in the color image forming apparatus of the eleventh aspect, there is provided means for changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction in accordance with the color information of the data. Means for adding a phase for each chromatic / achromatic color in the main scanning direction and the sub-scanning direction. Is formed.

According to a twenty-fourth aspect of the present invention, in the color image forming apparatus of the eleventh aspect, there is provided means for changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction in accordance with the color information of the data. Means, a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction, and a dot of 2 × 2 is formed by a three-color superimposed dot of cyan, magenta and yellow and a black dot in the medium density portion. It is grown so as to be arranged in a dot shape.

According to a twenty-fifth aspect of the present invention, there is provided a color image forming method for forming an image by modulating a multi-gradation color image signal, wherein image data of a plurality of adjacent pixels are added.
A density is generated from a predetermined direction of a specific pixel by the added image data, the density generation pixel is changed in the main scanning direction or the sub-scanning direction, and the position of the density generation pixel is changed in the main scanning direction according to the color information of the image data. Alternatively, the phase of each color is added in the main scanning direction or the sub-scanning direction by 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 by changing the position of the density generating pixel. In a color image forming method for forming a linear image in which two colors overlap each other in a medium density portion, an option is provided for selecting a combination of the two colors based on color information of the image, and the option is switched. In this way, a line image in which two colors overlap each other in the middle density portion is switched.

According to a twenty-sixth aspect of the present invention, in the color image forming method according to the twenty-fifth aspect, a staggered dot arrangement is formed by isolated dots of cyan, magenta, yellow, and black in the low density portion. .

According to a twenty-seventh aspect of the present invention, in the color image forming method according to the twenty-fifth or twenty-sixth aspect, the positions of the density generating pixels are the same for all colors regardless of the color information of the image data. It is characterized in that an option for forming an overlapping image is added, and this option and the option are switched.

The invention according to claim 28 is the invention according to claims 25 and 2
28. The color image forming method according to 6 or 27, wherein a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction according to the chromatic / achromatic color information of the image data, and cyan and magenta are added in the middle density portion. And yellow have the option of a linear dot arrangement that does not overlap with black,
It is characterized by switching between this option and the option.

The invention according to claim 29 is the invention according to claims 25 to 2.
8. The color image forming method according to any one of items 8, wherein the options are switched and executed according to a user's selection through an interface.

The invention according to claim 30 is the invention according to claims 25 to 2.
8. The color image forming method according to any one of items 8, wherein a feature amount is automatically extracted from the image data, and the options are automatically switched based on the extracted data.

According to a thirty-first aspect of the present invention, in the color image forming method according to the thirty-first aspect, when the characteristic amount is extracted from the image data, the magnitude of the ratio of the green image signal from the image data is used as the characteristic amount. Features.

According to a thirty-second aspect, in the color image forming method according to the thirty-first or thirty-first aspect, a feature amount is automatically extracted from the image data, and the image data is divided into a plurality of blocks for each feature based on the extracted data. The selection is switched for each block.

According to a thirty-third aspect of the present invention, there is provided a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, comprising: means for adding image data of a plurality of adjacent pixels; Means for generating a density from a predetermined direction of a specific pixel based on the image data added in the step, means for changing the density generation pixel in the main scanning direction or the sub-scanning direction, and setting the position of the density generation pixel according to the color information of the image data. Means for changing in the main scanning direction or the sub-scanning direction, and changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction in accordance with the color information of the image data and changing the phase for each color in the main scanning direction or the sub-scanning direction. Means for forming a line-shaped image in which colors of two colors overlap each other in the middle density portion by adding Based provided the option to select a color combination of the two colors, the color between the two colors in the middle density part by switching this choice are those having a switching means for switching a line-shaped image overlapping each.

According to a thirty-fourth aspect, in the color image forming apparatus according to the thirty-third aspect, the staggered dot arrangement is formed by the isolated dots of cyan, magenta, yellow, and black in the low density portion.

According to a thirty-fifth aspect of the present invention, in the color image forming apparatus according to the thirty-third or thirty-fourth aspect, the positions of the density generating pixels are the same for all colors irrespective of the color information of the image data. An option for forming an overlapping image is added, and the option and the option are switched by the switching unit.

The invention according to claim 36 is the invention according to claims 33 and 3
36. The color image forming apparatus according to 4 or 35, wherein a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction according to the chromatic / achromatic color information of the image data, and cyan and magenta are added in the middle density portion. And yellow have the option of a linear dot arrangement that does not overlap with black,
The options and the options are switched by the switching means.

The invention according to a thirty-seventh aspect has an interface for switching and executing the options in accordance with a user's selection.

The invention according to claim 38 is the invention according to claims 33 to 3
6. The color image forming apparatus as described in any one of 6. above, further comprising means for automatically extracting a feature amount from the image data and automatically switching the options based on the extracted data.

According to a thirty-ninth aspect of the present invention, in the color image forming apparatus according to the thirty-eighth aspect, the means for extracting the characteristic amount from the image data uses the magnitude of the ratio of the green image signal from the image data as the characteristic amount. is there.

According to a fortieth aspect of the present invention, in the color image forming apparatus according to the thirty-eighth or thirty-ninth aspect, the image data is divided into a plurality of blocks for each feature based on the extraction data of the means for automatically extracting the feature amount from the image data. It has means for separating, and switches the option for each block.

[0064]

FIG. 7 schematically shows an embodiment of the present invention. This first embodiment is described in claims 1, 2, 9,
This is an embodiment of the invention according to Claim 10, and is an embodiment of a color image forming apparatus including a digital color copying machine. First, the image formation according to the first embodiment will be described. FIG.
, 100 is a laser printer as an image forming unit,
200 is an automatic document feeder (hereinafter ADF), 30
0 is an operation board, 400 is an image scanner as an image reading unit, and 500 is an external sensor.

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

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

The ADF 200 is an image scanner 400
, And a large number of documents are placed on the document table 210. During the document feeding operation, the rotating call roller 212 feeds out the document on the document table 210, and the separation roller 213 separates only the uppermost document. This original is supplied to the pull-out roller 217 and the conveying belt 21.
6, the contact glass 4 of the image scanner 400
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 placing table 210 is provided in front of the calling roller 212. A document leading edge sensor 214, which is an optical sensor for detecting the leading edge and 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.
The original size in the main scanning direction, that is, the original width can be detected. Also, a pulse generator for outputting a pulse corresponding to the rotation amount is provided in a paper feed motor (not shown),
The control device of the ADF 200 detects the size of the original in the sub-scanning direction, that is, the length of the original, by measuring the time that the original passes through the original leading edge sensor 214. Note that the call 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 composed of an optical sensor is disposed downstream of the pull-out roller 217 and detects a document.

The laser printer 100 includes the photosensitive drum 1
Is used to reproduce the image. Around the photosensitive drum 1, units 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. I have. The optical writing unit 3 includes a semiconductor laser (laser diode: L
D), the laser light emitted from the LD is deflected and scanned in the main scanning direction by a rotating polygon mirror 3b as a deflection scanning means, passes through a lens 3c, a mirror 3d, and a lens 3e to form a photosensitive drum 1. It is imaged on the surface. The rotary polygon mirror 3b is driven to rotate at a constant high speed by the polygon motor 3a.

The image control unit (not shown) controls the drive signal of the LD 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. The light emission of the LD is controlled so that the laser beam is scanned in the main scanning direction on the body drum 1 from a predetermined optical writing start position. The photoreceptor drum 1 is uniformly charged to a high potential in advance by corona discharge by a charging charger 5 as a charging unit, and is then exposed to laser light from an optical writing unit 3 as an optical writing unit to form an electrostatic latent image. Is formed. The electrostatic latent image on the photosensitive drum 1 is visualized by a developing unit 4 as a developing unit.

The developing unit 4 converts the electrostatic latent images on the photosensitive drum 1, for example, into magenta (hereinafter M), cyan (hereinafter C), yellow (hereinafter Y) and black (hereinafter Bk) color images, respectively. Are provided with four sets of developing units 4M, 4C, 4Y, and 4Bk. Developing device 4
One of M, 4C, 4Y, and 4Bk is selectively energized to perform a developing operation, and the electrostatic latent image on the photosensitive drum 1 is a toner image of any one of the colors M, C, Y, and Bk. Is visualized.

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

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

In this case, first, the optical writing unit 3
Is modulated by the Bk image signal to form a Bk toner image on the photosensitive drum 1. After the Bk toner image is transferred onto the transfer paper on the transfer drum 2, the transfer paper is transferred to the transfer drum 2.
Of the optical writing unit 3 without being separated from the
Is modulated by the M image signal to form an M toner image on the photosensitive drum 1, and the M toner image is transferred onto the transfer paper on the transfer drum 2 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 to the transfer paper on the transfer drum 2 by B
After being superimposed and transferred on the k toner image and the M toner image, the LD of the optical writing unit 3 is modulated by the Y image signal to form a Y toner image on the photosensitive drum 1. Bk toner image, M toner image,
A full-color image is formed by being transferred so as to overlap with the C toner image. When the transfer of all 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 the fixing device 9
After the toner image is fixed in the discharge tray 10, the toner image is discharged to the discharge tray 10.

The image forming operation according to the present embodiment has been described above. However, the color image forming apparatus according to the present invention is not limited to the above configuration, and an intermediate transfer member such as an intermediate transfer belt may be used instead of the transfer drum 2. After forming the toner images of four colors Bk, M, C and Y on the photosensitive drum for each color and transferring the toner images sequentially on the intermediate transfer member, the toner images are collectively transferred from the intermediate transfer member to the transfer paper. A transfer method may be used.

Next, the image processing of this embodiment will be described. FIG. 1 shows an image processing unit as an image processing unit of the present embodiment. The operation control of the entire embodiment is performed by a system controller 5 composed of a microcomputer.
Controlled by 0. The synchronization control circuit 60 generates a clock pulse as a reference for control timing, and inputs and outputs various synchronization signals for synchronizing signals between units.
The main scanning synchronization signal based on the scanning timing in the present 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 image signals of R, G, and B colors obtained by reading a document and outputs 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 7,
2. Color correction unit 73, under color removal (UCR) / UCA unit 7
4, a selector 75, an edge enhancement filter 76, a printer γ correction unit 77, a gradation processing unit 78, an image area separation unit 79, and an ACS unit 80.

The scanner γ correction unit 71 converts the reflectance linear R, G, B color image signals from the image scanner 400 into density linear R, G, B color image signals. R
The GB smoothing filter 72 performs a smoothing process on the R, G, and B color image signals from the scanner γ correction unit 71 to suppress moire due to a halftone dot document. Color correction unit 73
Converts 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 a Bk component included in the combined image signal, and uses it as a Bk signal. At the same time, the Bk component is removed from the image signals of the remaining colors, and the YMC component is added. The selector 75 receives Y, M, C, and C input from the UCR / UCA unit 74 in accordance with an instruction from the system controller 50.
One of the image signals of each color Bk is selected and output.

The edge emphasis filter 76 has a selector 75
The edge information of the character portion or the picture portion is enhanced with respect to the image signals of the respective colors Y, M, C, and Bk. The printer γ correction unit 77 sets a curve according to the printer characteristics, and outputs Y, M, C,
Correction including gradation processing is performed on the image signals of each color Bk.

The gradation processing unit 78 includes a printer γ correction unit 77
The 8-bit Y, M, C, and Bk color image signals input from are converted to multi-values. The gradation processing unit 78 generally includes Y,
In many cases, dither processing or the like is performed on the image signals of each of the colors M, C, and Bk, and multi-valued image signals of each of the colors Y, M, C, and Bk are output to the laser printer 100. The halftone processing described later in the present embodiment is executed by the gradation processing unit 78.

Further, R, R from the scanner γ correction unit 71
The G and B color image signals are supplied to an image area separation unit 79 and an ACS unit 80.
Sent to The image area separating section 79 includes the scanner γ correcting section 7.
A determination function for determining whether an image is a character portion or a picture portion, and a determination function for determining whether an image is a chromatic color or an achromatic color, based on the R, G, and B color image signals from 1 The determination result is sent to a predetermined processing block in units of one pixel. This processing block includes an image area separation unit 79
The process is switched according to the result of the determination.

The ACS unit 80 determines whether the original set on the scanner 200 is a black-and-white original or a color original based on the R, G, and B color image signals from the scanner γ correction unit 71. Is sent to the system controller 50 at the end of the Bk version scan. If the document set on the scanner 200 is a color document, the system controller 50 causes the scanner 200 to perform the remaining three scans based on the determination result of the ACS unit 80.
If the original set in the scanner is a black-and-white original, the scanner 200
The operation is terminated by 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. Also, the system controller 50 controls the laser printer 10 including the LD multi-level optical writing operation.
0 is controlled.

Next, the LD multi-level modulation of the present embodiment will be described. A pulse width modulation (PWM) method and a light intensity modulation (P) method are used as LD multi-level modulation schemes for outputting one dot multi-level output.
M) method. FIGS. 3A and 3B show a light waveform and a dot pattern in an example of the light intensity modulation method and an example of the pulse width modulation method. Hereinafter, these modulation methods will be described.

Light intensity modulation method Halftone recording using halfway exposure area (halftone image formation)
In order to realize the above, stabilization of the image forming process is an important requirement, and the light intensity modulation method has strict requirements for the image forming process. However, in the light intensity modulation method, LD control modulation is simplified. That is, the light intensity modulation method is a method in which light writing is performed by changing the light output level itself as shown in FIG. 3A, and each dot pattern has a pattern as shown in the upper part of FIG. Is output. According to this method, the control and modulation section of the LD can be configured simply and compactly. Demands become more stringent.

Pulse Width Modulation Method In the pulse width modulation method, as shown in FIG. 3B, the light output level is binary, but the light emission time, that is, the pulse width is changed to perform light writing. And each dot pattern is output in a pattern as shown in the upper part of FIG. Since this method is basically binary light writing, the degree of use of the intermediate exposure area is lower than that of the light intensity modulation method, and the intermediate exposure area can be further reduced by combining adjacent dots. Becomes possible,
The requirement 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. Must be divided into 256 times, and high-speed and high-precision LD modulation is required, which complicates the LD modulation portion. That is, in the light intensity modulation method, the requirement for stabilizing the image forming process becomes strict, and in the pulse width modulation method, the configuration of the LD modulation unit becomes complicated.

Therefore, in the present embodiment, in consideration of the above points, the pulse width modulation (PWM) system and the light intensity modulation (PM)
It employs a pulse-width-intensity mixed-modulation method that combines this method and the other methods. FIG. 4 shows a light output waveform and a dot pattern in the left mode and the right mode in an example of the pulse width intensity mixed modulation method.
In this pulse width intensity mixed modulation system, the pulse width modulation is basically used, and the pulse width and the transition portion of the pulse width are shown in FIG.
As shown in (a) and (b), interpolation is performed by light intensity modulation. For example, when the pulse width setting value is 8 values and the light intensity modulation setting value is 32 values, the modulation degree equivalent to 8 bits (28 = 256 gradations) is obtained. Obtainable.

In this system, since the number of pulse width modulation stages is small, the pulse width can be digitally set, the pulse width can be easily set, and the pulse position control can be easily realized. That is, FIGS. 4A and 5B and FIGS. 5A and 5B
Shows a light output waveform and a dot pattern in the right mode in which an optical writing pulse is generated from the right end position of one dot, and a light output waveform and a dot pattern in the left mode in which an optical writing pulse is generated from the left end of one dot. These control the phase of the optical writing pulse so that the exposure pulse is generated from the rear end and the front end, respectively. As a result, the dot generation position can be controlled. Further, as shown in FIG. 5C, a central mode in which optical writing pulses are generated in both directions from the central position of one dot can be selected.

Next, a description will be given of an example of an LD driving method of a multi-level optical writing system based on a pulse width intensity mixed modulation system combining pulse width modulation (PWM) and light intensity modulation (PM) in the present embodiment. In this LD driving method, the light emission pattern of the LD for one pixel is set in 2m steps with a resolution of a pixel clock width of 1 / 2m (2m means 2m). And the light emission power is divided into 2 ＾ (nm) steps with a light emission power resolution of 1/2 ＾ (nm).
Since ＾ n gradations are expressed, the division accuracy of the light emission time and the light emission power of the LD is alleviated, and multi-gradation can be easily realized.

In the case of an 8-bit digital image signal in this embodiment, m = 3, pulse width modulation (PWM) is performed in 8 (= 2 ＾ m = 23) steps, and light intensity modulation (PM) is 32 (= 2). If the (＾ (n−m) = 25) stage is selected, 2 ＾ n = 28 = 256 types of light emission patterns can be formed by combining the two, and 256-level LD multi-level modulation can be performed. Also, an arbitrary light emission pattern can be obtained by changing a signal generated and output by a timing generation circuit or a power setting circuit of the LD. It should be noted that the multilevel optical writing type LD driving circuit and device are disclosed in the prior application by the present applicant, for example, Japanese Patent Application Laid-Open Nos.
It can be constructed by using those described in, for example, JP-A No. 1656, JP-A-6-347852 and the like.

[0094]

Next, regarding the phase control (position control) of the pulse width modulation, according to the mode (right mode / left mode / center mode) set by the phase (position) control logic, FIGS. ), 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, in the present embodiment, in addition to this function, FIG.
It also has a fraction processing function as shown in (a) to (c).

[0096] The fraction processing function is a function of two consecutive in the main scanning direction.
When the pixels are output collectively (by addition), the light intensity modulation time usually occurs at two places as shown by the hatched portion in FIG. 6B, but the operation of combining these into one place is performed. This is realized basically by adding data of a small fraction to data of a large fraction (a value other than the maximum value). As long as the fractional part does not reach the maximum, all the data of the fractional part is added to the fractional part, and the remainder when the fractional part becomes the maximum is distributed to the fractional part and the light intensity Perform modulation. By having the fraction processing function, the pulse width setting step can be made sufficiently small with respect to the optical writing beam diameter.

6A to 6C schematically show the dot image and the light output waveform in the above operation, FIG. 6A shows the dot image before correction, and FIG.
FIG. 6 shows the light output waveforms before and after the correction, and FIG. 6C shows the dot image after the correction. In the data of two adjacent pixels (pixels), if the light intensity does not reach the maximum, the portion where the light intensity does not reach the maximum is compared between adjacent pixels, the smaller one is added to the larger one, and the remainder is added to the smaller one. I do.

Next, a control circuit for performing addition of image data and phase control in this embodiment will be described. In this 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 of Y, M, and C) or achromatic color data (Bk image data). Is determined, the chromatic color data is processed in the chromatic color flow as described below, and the achromatic data is processed in the achromatic color flow as described later.

In this embodiment, in the gradation processing of image data, two adjacent pixels in the main scanning direction or the sub-scanning direction are used.
Dot or 4 adjacent in the main scanning direction and sub-scanning direction
Dot image data is added, and based on the addition result,
The dots are reproduced in order from a specific pixel set in advance. At this time, adjacent specific pixels are combined using the right phase / left phase of the specific pixel. In the present embodiment, the gradation processing unit 78 has six methods 1-6.
The processing described below is performed by adopting any one of the above. Less than,
These methods 1 to 6 will be specifically described in detail.

FIG. 2 shows a control circuit as control means for adding data of adjacent pixels in an image, determining and distributing the added data, and controlling dot phase. FIG.
Is a control circuit used in a system 6 that adds up to two dots in the main scanning direction and two dots in the sub-scanning direction at the maximum. This control circuit is provided for each color, and converts 8-bit 256-gradation image data of Y, M, C, and Bk color image data input from the printer γ correction unit 77 to the gradation processing unit 78 for each color. Is processed as follows.

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

Each 8-bit data C and D of two dots adjacent to the previous line in the main scanning direction is input to the addition circuit 604. The addition circuit 604 adds data A, B, C, and D of four dots adjacent in the main scanning direction and the sub-scanning direction, adds data A and B of two dots adjacent in the main scanning direction, and is adjacent to the sub-scanning direction. Data A and C of two dots are added. The comparison / distribution / phase control circuit 605 is provided by the adder circuit 604
The addition result of the dot data A, B, C, and D is compared with the threshold value 1 of the data at which the dot becomes saturated, and the addition value of the four dot data A, B, C, and D and the two dot data A in the main scanning direction are obtained. , B, 2-dot data A, C in the sub-scanning direction
Are switched so as to concentrate the data according to an algorithm described later.

The comparison / distribution / phase control circuit 605
Switches the 2-bit optical writing phase signal to toggle according to the frequency-divided signal CLOCK of the pixel clock. In the present embodiment, the control circuit that performs the addition of the data of the adjacent pixels in the image, the determination and distribution (distribution) of the addition result, and the dot phase control is hardware as shown in FIG. 2, but will be described later. Furthermore, even by processing by software, addition of data of adjacent pixels of an image, determination and distribution (distribution) of the addition result, and dot phase control can be realized.

FIG. 8 shows a state of data transition by the addition of four dots and the addition of two dots by the above processing. Method 6
In the low density part of the image as shown in FIG.
Since the addition value of the data d1 to d4 of the two dots adjacent in the main scanning direction and the two dots adjacent in the sub-scanning direction by the addition circuit 604 is smaller than the threshold value 1, the addition value is represented by the dot D1.
Data. In the middle and high density portions of the image as shown in FIG. 8B, two dots of data d adjacent in the main scanning direction are used.
Since the sum of the 1 and d2 by the adder circuit 604 is equal to or greater than the threshold value 1, the sum is set to the saturation value of the data of the dot D1, and the rest is set to the data of the dot D2. (A) Method of adding image data of two dots adjacent in the sub-scanning direction (1/2 pulse division method: methods 1, 2, 3) In methods 1 to 3, one dot size is shown in FIG. FIG. 9 shows one pixel size (minimum density unit).
The gradation processing unit 7 has a two-dot size as shown in FIG.
At step 8, a dot forming matrix as shown in FIG. 10 is set, and light writing pulses are sequentially generated in accordance with the added value from the control circuit, starting from the place where the numerical value of the dot forming matrix is small, and the pulse width intensity of the image data is obtained. Modulation by the mixed modulation method is performed.

At this time, the gradation processing section 78 sets the pulse to 1
The pulse is divided (assigned) into half pulses within a dot, and the PWM pulse within one dot is full (50% duty) in accordance with the added value.
When ty) is reached, the process proceeds to the next larger number in the dot formation matrix, and a pulse is similarly generated within the next one dot. At this time, the gradation processing unit 78 determines the right phase / left phase (right mode / left mode) of the pulse with an even dot EVEN / odd dot ODD (hereinafter abbreviated as E / O) in the main scanning direction.
Is switched to control the phase of the pulse and combine the pulses in the same direction of the numerical value of the dot formation matrix. The gradation processing unit 78 performs gradation processing of image data by a density generation algorithm of optical writing expressed by the following equation. Here, in the following equation, d1 and d2 are image data (8-bit data) of two adjacent dots in the sub-scanning direction before processing, and
1 and D2 are image data (8-bit data) after processing two adjacent dots in the sub-scanning direction.

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 ≦ d1 + d2 ≦ 510 D1 = 255, D2 = d1 + d2−255 The 8-bit data after this processing is
And the optical write signal of LD. Hereinafter, method 1
3 will be specifically described.

First, the method 1 will be described specifically. In the method 1, the control circuit shown in FIG.
A control circuit is used in which the distribution / phase control circuit 605 outputs only the added value of the two-dot data A and C adjacent to each other in the sub-scanning direction from the addition circuit 604 as it is. The gradation processing section 78 performs gradation processing of image data by the following dot formation algorithm. 1) By adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604, the densities of two dots adjacent in the sub-scanning direction are added. 2) A pulse is sequentially generated as an optical write signal (optical write pulse) from one of the dot formation matrices. 3) The right / left of the PWM pulse (light writing pulse) in E / O in the main scanning direction by the light writing phase signal from the control circuit.
The left phase is switched, and the optical writing pulse is combined in the same direction of the numerical value of the dot formation matrix. 4) The pulse is divided into half pulses within one dot, and this pulse is full (50%
ty), a PWM pulse of the next number in the dot formation matrix is generated.

When the dot formation matrix shown in FIG. 10 is expressed in the minimum density unit, the result is as shown in FIG. 11, and the gradation processing section 78 generates a pulse in the right phase for the dot D1 and in a left phase for the dot D1 '. Then, a pulse combined with one portion of the dot forming matrix is generated according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). The gradation processing unit 78 performs the same operation in the same manner as described above for the added value of the density (image data A and C from the control circuit).
Pulses are generated in the second and subsequent portions of the dot formation matrix according to (addition value of (d1, d2)).

Next, the details of dot formation by the method 1 will be described with reference to FIGS. Density １ ／ (2 isolated dots) The gradation processing unit 78 determines that the sum of the densities (the sum of the image data A, C (d1, d2) from the control circuit) is １ ／. As shown in FIG. 12A, an odd pixel in the main scanning direction is right-justified by an optical writing phase signal from a control circuit,
Even-numbered pixels are left-aligned, and 1
Are generated with a pulse width corresponding to the sum of the densities (the sum of the image data A and C (d1, d2) from the control circuit). Here, the pulse width according to the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit) is defined by the pulse width intensity mixed modulation method of the image data as described above. This is the pulse width of the modulated pulse. Density: 1/4 (isolated 2 dots) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit) is 1/8 to 1/4.
In the case of (1), as shown in FIG. 12 (B), the pulse coupled to one portion of the dot formation matrix is FULL 5
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). Here, the pulse width is set to the sum of the densities (image data A, C (d1, d2) from the control circuit).
The expression “increase the pulse width” means increasing the pulse width to the pulse width of the pulse modulated by the pulse width intensity modulation method of the image data as described above. Density to ３ (300 lines per line) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) is １ ／ to ／.
In the case of, as shown in FIG. 12C, the pulse combined with the second part of the dot formation matrix in the same phase as the one part of the dot formation matrix is added to the density addition value (image data from the control circuit). A and C (added value of d1, d2)). Density １ ／ (300 lines per line) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit) is ８ to が.
In the case of (1), as shown in FIG. 12 (D), the pulse combined with the second portion of the dot formation matrix is 5 in FULL.
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). Density to ／ The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to ２〜 to ／.
In the case of (1), as shown in FIG. 13A, the pulse width of one portion of the dot formation matrix is determined by the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit).
3 of the dot forming matrix so as to increase according to
Generates a pulse coupled to the part. Density to 3/4 The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) is 5/8 to 3/4.
In the case of (3), as shown in FIG. 13 (B), the pulse combined with the portion 3 of the dot formation matrix is the FULL 5
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). Density to 7/8 The gradation processing unit 78 calculates the sum of the densities (the sum of the image data A and C (d1, d2) from the control circuit) from 3/4 to 7/8.
In the case of (1), as shown in FIG. 13C, the pulse width of the 2 portion of the dot formation matrix is determined by the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit).
A pulse is generated that is coupled to the four portions of the dot-forming matrix so as to increase in response to Density to 1/1 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to 7/8 to 1/1.
In the case of (1), the pulse width is added to the density (the image data A and C from the control circuit) until the pulse coupled to the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(Addition value of (d1, d2)).

The gradation processing section 78 repeats such gradation processing of image data in the main scanning direction and also in the sub-scanning direction. In this case, the gradation processing unit 78 sequentially generates the write pulse for each line. The write pulse generated by this method 1 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 (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 1, the highlight portion of the image can be reproduced regularly by isolated dots, 300 lines and 600 lines (600 dpi) can be obtained in the medium density portion, and the gradation of isolated dots and vertical lines can be obtained. Is linear, the potential concentration and the saturation region can be increased to ensure stability, and it is strong against banding.

Next, method 2 will be described. In the method 2, the spatial frequency of the highlight portion and the high density portion of the image is increased by making the dot forming matrix in-phase in the sub-scanning direction with respect to the method 1. In the method 2, the comparison / distribution / phase control circuit 605 in the control circuit shown in FIG.
04, two dot data A and C adjacent in the sub-scanning direction
A control circuit configured to directly output only the added value of is used. The gradation processing section 78 performs gradation processing of image data by the following dot formation algorithm. 1) By adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604, the densities of two dots adjacent in the sub-scanning direction are added. 2) Generate a pulse as an optical writing pulse sequentially from 1 in the dot formation matrix. 3) The right / left of the PWM pulse (light writing pulse) in E / O in the main scanning direction by the light writing phase signal from the control circuit.
The left phase is switched, and the optical writing pulse is combined in the same direction of the numerical value 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, a PWM pulse of the next number in the dot formation matrix is generated.

FIG. 14 shows a dot formation matrix used in the method 2. When this dot formation matrix is expressed in minimum density units, it becomes as shown in FIG.
A pulse is generated in the right phase for the dot D1 and in the left phase for the dot D1 ', and a pulse is generated in the dot forming matrix.
Are generated in accordance with the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). The gradation processing unit 78 performs the same operation in the same manner as described above for the density addition value (image data A, C (d1, d
A pulse is generated in the second and subsequent portions of the dot formation matrix in accordance with the (2) added value).

Next, details of the dot formation by the method 2 will be described. Density to 1/8 (isolated one dot) The gradation processing unit 78 determines that the sum of the densities (the sum of the image data A and C (d1, d2) from the control circuit) is up to 1/8. As shown in FIG. 16A, the odd pixels in the main scanning direction are right-justified by the optical writing phase signal from the control circuit,
Even-numbered pixels are left-aligned, and 1
Are generated with a pulse width corresponding to the sum of the densities (the sum of the image data A and C (d1, d2) from the control circuit). Density to 1/4 (isolated one dot) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) is 1/8 to 1/4.
In the case of (1), as shown in FIG. 16B, the pulse combined with one portion of the dot formation matrix
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). Density to ３ (300 lines per line) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) is １ ／ to ／.
In the case of (1), as shown in FIG. 16 (C), the pulse combined with the portion 2 of the dot formation matrix in the same phase as the portion 1 of the dot formation matrix is added to the density addition value (image data from the control circuit). A and C (added value of d1, d2)) are generated with a pulse width corresponding to the sum. Density １ ／ (300 lines per line) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit) is ８ to が.
In the case of (1), as shown in FIG. 16 (D), the pulse combined with the portion 2 of the dot formation matrix
Until the duty becomes 0%, the pulse width is increased according to the added value of the density of the pulse (the added value of the image data A and C (d1, d2) from the control circuit). Density to ／ The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to ２〜 to ／.
In the case of (1), as shown in FIG. 17A, the pulse combined with the third portion of the dot formation matrix is added to the density addition value (control value) so as to increase the pulse width of the first portion of the dot formation matrix. Image data A and C from the circuit
(Addition value of (d1, d2)). Density to 3/4 The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) is 5/8 to 3/4.
In the case of, as shown in FIG. 17B, the pulse combined with the portion 3 of the dot forming matrix
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). Density to 7/8 The gradation processing unit 78 calculates the sum of the densities (the sum of the image data A and C (d1, d2) from the control circuit) from 3/4 to 7/8.
In the case of (1), as shown in FIG. 17C, the width of the pulse of the 2 portion of the dot formation matrix is determined by the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit).
A pulse is generated that is coupled to the four portions of the dot-forming matrix so as to increase in response to Density to 1/1 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to 7/8 to 1/1.
In the case of (1), the pulse width is added to the density (the image data A and C from the control circuit) until the pulse coupled to the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(Addition value of (d1, d2)).

The gradation processing section 78 repeats such gradation processing of image data in the main scanning direction and also in the sub-scanning direction. In this case, the gradation processing unit 78 sequentially generates the write pulse for each line. The write pulse generated by the method 2 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 (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. This method 2
As compared with the method 1, the highlight portion is dispersed into one isolated dot and is hardly visible, and the dot size of a missing portion (white background) in the high density portion is small, and the character crack 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 increased (character cracks are not noticeable). In the method 3, in the control circuit shown in FIG. 2, the comparison / distribution / phase control circuit 605 outputs only the added value of the two-dot data A and C adjacent in the sub-scanning direction from the addition circuit 604 as it is. A circuit is used. The gradation processing section 78 performs gradation processing of image data by the following dot formation algorithm. 1) By adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604, the densities of two dots adjacent in the sub-scanning direction are added. 2) Generate a pulse as an optical writing pulse sequentially from 1 in the dot formation matrix. 3) The right / left phase of the PWM pulse is switched by E / O in the main scanning direction according to the optical writing phase signal from the control circuit, and the optical writing pulse is combined in the same direction of the numerical value of the dot formation matrix. 4) The pulse is divided into half pulses within one dot, and this pulse is full (50%
(ty), a PWM pulse (optical writing pulse) of the next number in the dot formation matrix is generated.

FIG. 18 shows a dot formation matrix used in the method 3. When this dot formation matrix is expressed in minimum density units, the result is as shown in FIG.
A pulse is generated in the right phase for the dot D1 and in the left phase for the dot D1 ″.
Are generated in accordance with the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). The gradation processing unit 78 performs the same operation in the same manner as described above for the density addition value (image data A, C (d1, d
A pulse is generated in the second and subsequent portions of the dot formation matrix in accordance with the (2) added value).

Next, the details of the dot formation by the method 3 will be described. Density-1/8 (isolated one dot) to density-1/2
In the density range up to (300 lines per line), it is the same as the method 2. Density to ／ The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to ２〜 to ／.
In the case of, as shown in FIG. 20A, the pulse widths of the portions 1 and 2 of the dot formation matrix are set to the sum of the densities (the sum of the image data A and C (d1, d2) from the control circuit). ) To generate a pulse coupled to the three parts of the dot-forming matrix in such a way as to increase accordingly. Density to 3/4 The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) is 5/8 to 3/4.
In the case of, as shown in FIG. 20 (B), the pulse combined with the portion 3 of the dot formation matrix is
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). Density to 7/8 The gradation processing unit 78 calculates the sum of the densities (the sum of the image data A and C (d1, d2) from the control circuit) from 3/4 to 7/8.
In the case of, the dot width is increased so that the pulse widths of the portions 1 and 2 of the dot formation matrix are increased in accordance with the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). A pulse is generated that is coupled to the four parts of the formation matrix. Density to 1/1 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to 7/8 to 1/1.
In the case of (1), the pulse width is added to the density (the image data A and C from the control circuit) until the pulse coupled to the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(Addition value of (d1, d2)).

The gradation processing section 78 repeats such gradation processing of image data in the main scanning direction and also in the sub-scanning direction. In this case, the gradation processing unit 78 sequentially generates the write pulse for each line. The write pulse generated by the method 3 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 (for each color) from the gradation processing unit 78 as described above. The image signal is sequentially modulated by an LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color. In the method 3, as compared with the method 2, missing portions (white background) are dispersed in a staggered manner in a high density portion, and character breakage is less noticeable. (B) A method of adding image data of two dots adjacent in the sub-scanning direction (1/4 pulse division method: method 4) In method 4, 50 pulses of 2 in the same dot formation matrix as method 3 When the duty reaches% duty, the pulse shifts to pulse 3 of the dot formation matrix, and character breakage in the middle density portion is made inconspicuous. In method 4, one dot size is set to a size as shown in FIG.
One pixel size (minimum density unit) is set to a two-dot size as shown in FIG. 9B, and the gradation processing unit 78 sequentially controls the pulse from the smaller value of the dot forming matrix as shown in FIG. Image data A, C (d1,
The data is generated according to the added value of d2), and the image data is modulated by the pulse width intensity mixed modulation method.

At this time, the gradation processing section 78 sets the pulse to 1
In the dot, the pulse is divided into 1/2 or 1/4 pulse, and when the pulse becomes 50% duty or 25% duty according to the above-mentioned added value, the dot is shifted to the next largest number in the dot formation matrix, and the next pulse is similarly processed. To be generated. At this time, the gradation processing unit 78 outputs the right phase / pulse of the pulse in E / O in the main scanning direction.
The phase of the pulse is controlled by switching the left phase (right mode / left mode), and the pulse is combined in the same direction of the numerical value of the dot formation matrix. The gradation processing unit 78 performs gradation processing of image data by an algorithm of density generation of optical writing 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 = 63 255 When ≦ d1 + d2 ≦ 318 D1 = 191, D2 = d1 + d2−191 319 ≦ d1 + d2 ≦ 382 D1 = d1 + d2-127, D2 = 127 When 383 ≦ d1 + d2 ≦ 510 D1 = 255, D2 = d1 + d2-255 More specifically, in the method 4, in the control circuit shown in FIG. 2, the comparison / distribution / phase control circuit 605 uses the addition value of the data A and C of two adjacent dots in the sub-scanning direction from the addition circuit 604. A control circuit configured to output only the data as it is is used. Gradation processing unit 7
8 performs gradation processing of image data by the following dot formation algorithm. 1) By adding the data A and C of two dots adjacent in the sub-scanning direction by the adding circuit 604, the densities of two dots adjacent in the sub-scanning direction are added. 2) Generate a pulse as an optical writing pulse sequentially from 1 in the dot formation matrix. 3) The right / left phase of the PWM pulse is switched by E / O in the main scanning direction according to the write phase signal from the control circuit, and the optical write pulse is combined in the same direction of the numerical value of the dot formation matrix. 4) The pulse is divided into a half pulse or a 1/4 pulse within one dot, and when this pulse becomes 50% duty or 25% duty within one dot according to the added value, the next number of the dot formation matrix is obtained. Are generated.

In the method 4, when the dot formation matrix shown in FIG. 21 is expressed by the minimum density unit, the result is as shown in FIG. 22, and the gradation processing unit 78 has the right phase for the dot D1 and the left phase for the dot D1 ″. In the same manner as in the method 3, a pulse combined with one portion of the dot forming matrix is generated according to the added value of the density (the added value of the image data A, C (d1, d2) from the control circuit). The gradation processing unit 78 similarly performs the following processing on the second and subsequent portions of the dot formation matrix according to the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit). Generate pulses.

Next, the details of dot formation by the method 4 will be described. Density ~ 1/8 (isolated one dot) to density ~ 3/8
In the density range up to (300 lines per line), it is the same as the method 3. Density to 1/2 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to 3/8 to 1/2.
In the case of (3), as shown in FIG. 23 (A), when the pulse coupled to the portion 2 of the dot formation matrix becomes 25% duty, the process shifts to dot formation matrix 3 and the dot formation matrix 3 The pulse connected to the part is 2
The pulse width is added to the density value (added value of image data A, C (d1, d2) from the control circuit) until the pulse width becomes 75% by combining with the portion of the dot forming matrix at 5% duty.
Increase according to. If the arrangement of the matrix of the highlight part is arranged in a staggered manner (if 1 and 2 are exchanged in the dot formation matrix), the arrangement of the dots 3 and 4 of the dot formation matrix are alternately switched, and character breakage is caused by the method 3
It can be even more random and less noticeable. Density to ／ The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d1, d2) from the control circuit) to ２〜 to ／.
In the case of (2), as shown in FIG. 23 (B), the pulse width is changed to the sum of the densities (image data A and C (from the control circuit) until the portion 2 of the dot formation matrix becomes 50% duty of FULL. d1 and d2). The method after the concentration of ３ /／ is the same as the method 3.

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

In the method 5, one dot size is set as shown in FIG.
The size is as shown in FIG. 24A, and one pixel size (minimum density unit) is a two-dot size as shown in FIG. If the dot formation matrix as shown in FIG. 25 is expressed in the minimum density unit, it becomes as shown in FIG. 26. The gradation processing unit 78 sets the dot formation matrix as shown in FIG. The optical writing pulse is generated sequentially 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 modulation method.

At this time, the gradation processing section 78 sets the pulse to 1
The dot is divided into half pulses within the dot, and when this pulse becomes full (50% duty) in accordance with the added value of the image data A and B (d1, d2) from the control circuit, the next largest number in the dot formation matrix And the next pulse is similarly generated. At this time, the gradation processing unit 78 outputs E in the main scanning direction.
Right phase / left phase of pulse with / O (right mode / left mode)
Is switched to control the phase of the pulse and combine the pulses in the same direction of the numerical value of the dot formation matrix. The gradation processing unit 78 performs gradation processing of image data by a density generation algorithm of optical writing expressed by the following equation.

When 0 ≦ d1 + d2 ≦ 127 D1 = d1 + d2, D2 = 0 When 128 ≦ d1 + d2 ≦ 254 D1 = 127, D2 = d1 + d2-127 255 ≦ d1 + d2 ≦ 382 D1 = d1 + d2-127, D2 = 127 ≤ d1 + d2 ≤ 510 D1 = 255, D2 = d1 + d2-255 Hereinafter, the method 5 will be described in detail. 1) The density of two dots adjacent in the main scanning direction is added by adding data A and B of two dots adjacent in the main scanning direction by the addition circuit 604. 2) Generate a pulse as an optical writing pulse sequentially from 1 in the dot formation matrix. 3) The right / left of the PWM pulse (light writing pulse) in E / O in the main scanning direction by the light writing phase signal from the control circuit.
The left phase is switched, each pixel is formed from the outside, and optical writing pulses are combined in the same direction of the numerical value of the dot formation matrix. 4) The pulse is divided into half pulses within one dot, and the pulse is divided into image data A and B from the control circuit within one dot.
When the duty becomes 50% according to the added value of (d1, d2), a PWM pulse of the next number in the dot formation matrix is generated.

When the dot formation matrix as shown in FIG. 25 is expressed in the minimum density unit, the result is as shown in FIG. 26. The gradation processing unit 78 outputs the pulse in the right phase for the dot D1 and the left phase for the dot D1 '. Is generated, and a pulse combined with one portion of the dot formation matrix is generated according to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). The gradation processing unit 78 generates pulses in the second and subsequent portions of the dot formation matrix in the same manner according to the added value of the density (the added value 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. Density to 1/8 (isolated one dot) The gradation processing unit 78 determines that the sum of the densities (the sum of the image data A and B (d1, d2) from the control circuit) is up to 1/8. As shown in FIG. 27A, the odd pixels in the main scanning direction are right-justified, and the even pixels are left-justified, and the pulse combined with one portion of the dot formation matrix is added to the density (the image data A from the control circuit). , B (added value of d1, d2)). Density １ ／ (isolated one dot) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) is ８ to ４.
In the case of (1), as shown in FIG. 27 (B), the pulse combined with one portion of the dot formation matrix is 5% of FULL.
Until the duty becomes 0% duty, the pulse width is increased according to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). Density to ／ (300 lines per line) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) is １ ／ to ／.
In the case of, as shown in FIG. 27 (C), the pulses combined from the outside of the pixel to the two portions of the dot formation matrix are added to the density (the image data A, B (d
(1) The pulse width is generated according to (d2) added value). Density １ ／ (300 lines per line) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) is ／ to が.
In the case of, as shown in FIG. 27 (D), the pulse combined with the portion 2 of the dot formation matrix is 5% of FULL.
Until the duty becomes 0% duty, the pulse width is increased according to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). Density to 5/8 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) to ２〜 to ／.
In the case of, as shown in FIG. 28A, the pulse width of one portion of the dot formation matrix is added to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). The dot forming matrix 3
Generates a pulse coupled to the part. Density to 3/4 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) to 5/8 to 3/4.
In the case of (3), as shown in FIG. 28 (B), the pulse coupled to the portion 3 of the dot formation matrix is the FULL 5
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). Density to 7/8 The gradation processing unit 78 calculates the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) from 3/4 to 7/8.
In the case of (2), as shown in FIG. 28 (C), the pulse width of the portion 2 of the dot forming matrix is added to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). 4 of the dot formation matrix so as to increase
Generates a pulse coupled to the part. Density to 1/1 The gradation processing unit 78 calculates the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) from 7/8 to 1/1.
In the case of (1), the pulse width is changed to the sum of the densities (image data A and B from the control circuit) until the pulse coupled to the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(Addition value of (d1, d2)).

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

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

(A) When the density is 1/4 or less One dot size is the size as shown in FIG. 29A, and one pixel size (minimum density unit) is 4 dot size as shown in FIG. 29B. And In the method 6, the control circuit shown in FIG. 2 is used. Comparison / distribution / phase control circuit 60
5 is the 4-dot data A, B, C, D of the adding circuit 604.
The result of the addition of (d1, d2, d3, d4) is compared with the threshold value 1 of the data that saturates the dots, and the 4-dot data A,
The added value of B, C, and D is switched and output. The gradation processing unit 78 sets a dot formation matrix as shown in FIG. 30 and sequentially applies pulses to the density addition values (image data A, B, and C from the control circuit) in ascending order of the value of the dot formation matrix. , D (added value of d1, d2, d3, d4)).

At this time, the gradation processing unit 78 sets the pulse to 1
The dot is divided into half pulses, and this pulse is used as the added value of the density (image data A, B, C, D (d
1, (d2, d3, d4)) (50% du)
When ty) is reached, the process proceeds to the same or the next larger number in the dot formation matrix, and the next pulse is generated in the same manner. At this time, the gradation processing unit 78 controls the pulse phase by switching the right phase / left phase (right mode / left mode) of the pulse by E / O in the main scanning direction, and controls the phase of the pulse in the same direction of the numerical value of the dot formation matrix. To combine the pulses.

When the dot formation matrix as shown in FIG. 30 is expressed in minimum density units, it becomes as shown in FIG.
The gradation processing unit 78 generates a pulse in the left phase for the dot D1, and a pulse in the right phase for the dot D1 ', and applies the pulse combined with one portion of the dot formation matrix to the added value of density (image Data A, B, C, D (d
1, d2, d3, and d4). The gradation processing unit 78 performs the same operation in the same manner as described above for the density addition value (image data A, B, C, D (d1, d
The pulse is generated in the second and subsequent portions of the dot formation matrix in accordance with the sum of (2, d3, d4).

The gradation processing section 78 performs gradation processing of image data by an optical 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 = 4, d3 = 4 Is image data (8-bit data) of 4 dots adjacent in the main scanning direction and the sub-scanning direction before processing, and D1, D2, D3 and D4 are 4 dots image data in the main scanning direction and the sub-scanning direction after processing. (8-bit data). The 8-bit data after this processing is used as an optical writing signal of the laser printer 100.

(A) When the density is 1/4 or more One dot size is a size as shown in FIG. 29A, and one pixel size (minimum density unit) is a two dot size as shown in FIG. Comparison / distribution / phase control circuit 6
05 is the 4-dot data A, B, C,
The result of addition of D (d1, d2, d3, d4) is compared with the threshold value 1 of the data that saturates the dots, and the two-dot data A,
The added value of B (d1, d2) is switched and output.

When the dot formation matrix shown in FIG. 30 is expressed in the minimum density unit, it becomes as shown in FIG. 33. The gradation processing section 78 generates a pulse in the left phase for the dot D1 and in a right phase for the dot D1 '. Then, a pulse combined with the second portion of the dot formation matrix is generated with a pulse width corresponding to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). The gradation processing unit 78
In the same manner, pulses of the third portion of the dot formation matrix are generated in accordance with the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit).

The gradation processing section 78 performs gradation processing of image data by an optical writing density generation algorithm expressed by the following equation. When d1 + d2 + d3 + d4 = 254 in the representation of one pixel size shown in FIG. 29B, D1 = D2 = 127.
Therefore, if the expression of one pixel size shown in FIG. 33 is substituted, when d1 + d2 = 127, D1 = 127 and D2 =
D1 = d1 + d2≤127, D2 = 127 255≤d1 + d2≤382, D1 = d1 + d2-127, D2 = 127 383≤d1 + d2≤510, D1 = 255 D2 = d1 + d2-255.

Hereinafter, the method 6 will be specifically described. The gradation processing section 78 performs gradation processing of image data by the following dot formation algorithm. 1) The addition of the four dots A, B, C, and D adjacent in the main scanning direction and the sub-scanning direction or the two-dot data A and B adjacent in the main scanning direction by the addition circuit 604.
The density of four dots adjacent in the sub-scanning direction or the density of two dots adjacent in the main scanning direction is added. 2) Generate a pulse as an optical writing pulse sequentially from 1 in 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 applied in the same direction of the numerical value of the dot formation matrix. Join. 4) The pulse is divided into half pulses within one dot, and when this pulse becomes 50% duty within one dot, a PWM pulse (optical writing pulse) of the same number or the next number in the dot formation matrix is generated.

Next, details of dot formation by the method 6 will be described. (A) Density 1/4 or less -1: Density to 1/16 (isolated one dot) Addition value of density (image data A, B, C,
When D (addition value of d1, d2, d3, d4) is up to 1/16, the density data A, B, C, D (d
1, d2, d3, and d4) are added by an adder circuit 604 and output via a comparison / distribution / phase control circuit 605, and the gradation processing unit 78 outputs a signal from the upper pixel 1 as shown in FIG. The isolated dot from the portion is calculated by adding the density (image data A,
It is generated with a pulse width corresponding to B, C, D (the sum of d1, d2, d3, d4).

At this time, the gradation processing unit 78 determines that 0 ≦ d1 +
If d2 + d3 + d4≤127, D1 = d1 + d2 + d3 +
d4, D2 = D3 = D4 = 0, 128 ≦ d1 + d2 + d3
If + d4 ≦ 254, D1 = 127, D2 = d1 + d2 +
It is assumed that d3 + d4-127 and D3 = D4 = 0. -2: density to 1/8 (isolated one dot) density added value (added value of image data A, B, C, D (d1, d2, d3, d4) from comparison / distribution / phase control circuit 605) Is 1/16 to 1/8, the density data A, B, C, and D (d1, d2, d3, d4) of the surrounding four dots are added by the adding circuit 604, and the comparison / distribution / phase control circuit is added. 6
05, and the gradation processing unit 78 outputs the signal shown in FIG.
As shown in the figure, the upper part of the pixel is saturated (full 50% du
ty) until the pulse width is added to the density (image data A,
B, C, and D (addition values of d1, d2, d3, and d4)).

At this time, the gradation processing unit 78 determines that 0 ≦ d1 +
If d2 + d3 + d4≤127, D1 = d1 + d2 + d3 +
d4, D2 = D3 = D4 = 0, 128 ≦ d1 + d2 + d3
If + d4 ≦ 254, D1 = 127, D2 = d1 + d2 +
It is assumed that d3 + d4-127 and D3 = D4 = 0. -1: Density to 3/16 (2 isolated dots) Added value of density (added value of image data A, B, C, D (d1, d2, d3, d4) from 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 the comparison / distribution / phase control circuit 6
05, and the gradation processing unit 78 outputs the signal shown in FIG.
After the upper part of the pixel is saturated, a pulse is applied to the lower part of the pixel as shown in FIG.
The remaining dots are generated with a pulse width corresponding to B, C, and D (addition value of d1, d2, d3, d4).

At this time, the gradation processing section 78 determines that 0 ≦ d1 +
If d2 + d3 + d4≤127, D1 = d1 + d2 + d3 +
d4, D2 = D3 = D4 = 0, 128 ≦ d1 + d2 + d3
If + d4 ≦ 254, D1 = 127, D2 = d1 + d2 +
It is assumed that d3 + d4-127 and D3 = D4 = 0. -2: Density to 2/8 (isolated two dots) Addition value of density (addition value of image data A, B, C, D (d1, d2, d3, d4) from comparison / distribution / phase control circuit 605) Is 3/16 to 2/8, the density data A, B, C, and D (d1, d2, d3, d4) of the surrounding four dots are added by the addition circuit 604, and the comparison / distribution / phase control circuit 6
05, and the gradation processing unit 78 outputs FIG.
As shown in the figure, the lower part of the pixel is saturated (50% du
ty), the pulse width is increased to the sum of the densities (image data A, B, C, D (d from the comparison / distribution / phase control circuit 605).
1, d2, d3, d4).

At this time, the gradation processing unit 78 determines that 0 ≦ d1 +
If d2 + d3 + d4≤127, D1 = d1 + d2 + d3 +
d4, D2 = D3 = D4 = 0, 128 ≦ d1 + d2 + d3
If + d4 ≦ 254, D1 = 127, D2 = d1 + d2 +
It is assumed that d3 + d4-127 and D3 = D4 = 0.

(A) Density 1/4 or more Density to 3/8 (300 lines per line) The gradation processing section 78 adds the density addition value (image data A, B (d1, d2) from the control circuit). Value) is 1/4 to 3/8
In the case of (a), as shown in FIG. 35 (A), the pulse combined with the two parts from the outside of the pixel of the dot formation matrix is added to the density addition value (image data A, B (d
(1) The pulse width is generated according to (d2) added value). Density １ ／ (300 lines per line) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) is ／ to が.
In the case of, as shown in FIG. 35 (B), the pulse combined with the second portion of the dot formation matrix
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). Density to 5/8 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) to ２〜 to ／.
In the case of (1), as shown in FIG. 35 (C), the pulse width of one portion of the dot formation matrix is added to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). The dot forming matrix 3
Generates a pulse coupled to the part. Density to 3/4 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) to 5/8 to 3/4.
In the case of (3), as shown in FIG.
Until the duty becomes 0%, the pulse width is increased according to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). Density to 7/8 The gradation processing unit 78 calculates the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) from 3/4 to 7/8.
In the case of, as shown in FIG. 36, the pulse width of the portion 2 of the dot formation matrix is increased according to the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit). A pulse is generated that is coupled to the four portions of the dot-forming matrix. Density to 1/1 The gradation processing unit 78 calculates the added value of the density (the added value of the image data A and B (d1, d2) from the control circuit) from 7/8 to 1/1.
In the case of (1), the pulse width is changed to the sum of the densities (image data A and B from the control circuit) until the pulse coupled to the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(Addition value of (d1, d2)).

The gradation processing section 78 repeats such gradation processing of image data in the main scanning direction and also in the sub-scanning direction. In this case, the gradation processing unit 78 sequentially generates the write pulse for each line. The write pulse generated by this method 6 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 (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 the method 6, compared with the method 5, the density 1
In a highlight portion of 以下 or less, the density of 4 dots is added, and the isolated dots are arranged in a staggered manner. In a highlight portion of a density of 1/4 or more, two dots are arranged in a staggered manner. The reproducibility of the highlight part can be improved.

In the first embodiment, for example, when the method 6 is adopted, when the image density of a single color is 1/16, the pixel arrangement (Bk, Mk) of each color Bk, M, C, and Y as shown in FIG. Instead of adding all the pixels of M, C, and Y to form a full-color image (overprinting all the colors), as shown in FIG.
The image data of each color of k, M, C, Y is converted into C → M → Y → K (B
The method of shifting by one dot in the main scanning direction in the order of k). FIG. 38 shows the arrangement of each color pixel when the density is 1/2.

As described above, the pixels for each color are separately arranged with a phase, so that the pixels of all colors Bk, M, C, and Y are mainly arranged in the highlight portion compared to the case where the pixels of all colors are overlapped at the same position. Can be reduced. Also, Bk,
Image data of each color of M, C, Y is converted into C → M → Y → K (Bk)
In the present embodiment, pixels of each color are arranged as shown in FIG. 35 (B) in the middle density portion when all the colors are overprinted by shifting one dot at a time in the main scanning direction in the following order. As shown in FIG. 39, the pixels of each color form a line in which the pixel of C and the pixel of Y and the pixel of M and the pixel of K overlap each other, and a line in which the pixel of M and the pixel of Y do not overlap can be formed. Since the M pixel and the Y pixel do not overlap in this way, 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 1/2.

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

In the dot generation position shifting circuit for each color, as shown in FIG.
Reference numeral 11 denotes a main scanning direction write basic clock CLOCK, and a synchronization signal LSY which is a main scanning direction start signal.
The NC generates a main scanning clock CLK in the image writing range in the main scanning direction. 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 a dot generation position as 2-bit data.

The C counter 613 is a quaternary counter 612.
Is counted, and the output of the C-plate counter 613 is used to indicate the dot generation position in the C-plate writing. The 2-bit data from the quaternary counter 612 is sequentially delayed by one clock by the D flip-flops 614 to 616. M version counter 61
Reference numeral 7 counts 2-bit data from the D flip-flop 614, and the output of the M-plate counter 617 is used as an indication of a dot generation position in M-plane writing.

The Y-plate counter 618 counts 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 writing in the Y-plate. 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 as an indication of a dot generation position in K-plate writing. The gradation processing unit 78 determines the dot generation position for each color based on the outputs of the 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 arranged differently in the main scanning direction, it is possible to use a ROM in which data is input in advance without using a counter and repeatedly read out data in the order of 1, 4, 2, 3, and the like. The dots are arranged in different orders.
Also, if a sub-scanning direction counter and regular signals are used,
The dot generation position for each color can also be controlled in the sub-scanning direction. The gradation processing unit 78 temporarily stores the image data of each color of Bk, M, C, and Y sequentially input from the printer γ correction unit 77 in a buffer memory, reads out the image data from the buffer memory, and executes the gradation processing. Is performed as described above.

In this case, the main scanning direction counters 613 and 6
17 to 619 sequentially count readout positions in the main scanning direction by counting clocks as described above, and the subscanning direction counter sequentially counts readout positions in the subscanning direction by counting another clock. . The gradation processing unit 78 reads out image data from an 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 reading position is determined by the count values of the main scanning direction counters 613 and 617 to 619, and the sub scanning direction reading position is determined by the count value of the sub scanning direction counter. Main scanning direction counter 61
The input clocks of 3, 617 to 619 are sequentially shifted by one clock for each color as shown in FIG.
The reading start position of the image data of each color of k, M, C, and Y is shifted by one dot in the main scanning direction for each color, and the position of the density generation pixel is changed in the main scanning direction for each color.

In the first embodiment, in the low density portion, adjacent four dots are added to generate image density from a specific pixel by adding the image data of the adjacent four dots. Nature can be secured. Further, referring to image data of a plurality of pixels (read pixels: dots),
In a color image forming apparatus that forms a dot or line image by distributing density data to a specific position among the plurality of pixels based on the reference result, the position of a density generating pixel is changed according to the color information of the image data. Since the tone processing section 78 is provided as a means, a paper white portion is not formed in a low-density portion as compared with the case of all-color overprinting, and the transfer conditions of each color are more even. It is possible to realize color image formation with no unevenness, excellent color reproducibility, little roughness, and excellent graininess.

In the first embodiment, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, optical writing including at least pulse width modulation is performed by the image signal to perform optical writing. The gradation processing unit 78 and the writing unit 3 serving as an optical writing unit, an addition circuit 604 serving as a unit for adding the image data of a plurality of adjacent pixels, and the image data specified by time division between the pixels. A gradation processing unit 78 as means for generating density from a predetermined direction of the pixel, a gradation processing unit 78 as means for changing the density generation pixel in the main scanning direction, and a density generation pixel according to color information of image data. By adding the phase for each color in the main scanning direction by changing the position in the main scanning direction,
Since a gradation processing unit 78 is provided as means for forming a linear image in which the colors C and Y and the colors M and K overlap each other in the middle density portion, a plurality of pixels adjacent to each other in the low density portion are provided. When the data is added to form a line, the four colors C, M, Y, and K can be divided into two to form a line in which a plurality of colors are superimposed, and a particularly delicate color tone is required. It is possible to realize color image formation that reproduces the color of the skin of a person to be performed with high quality.

The second embodiment of the present invention is described in claims 3 and 5,
This is one embodiment of the invention according to 8, 10. FIG. In the second embodiment, Bk,
The image data of each color of M, C, and Y is shifted one dot at a time in the main scanning direction in the order of C → M → K → Y. The gradation processing section 78 sequentially shifts the clock input to the main scanning direction counter by one clock for each color in the dot generation position shift circuit for each color, and sets
The image data of each color of k, M, C, Y 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 of Bk, M, C, Y Is shifted by one dot in the main scanning direction for each color to change the position of the density generation pixel in the main scanning direction for each color.

Thus, in the middle density portion, when all the colors are overprinted, the pixels of each color are arranged as shown in FIG. 35B, but in the present embodiment, the pixels of each color are arranged as shown in FIG. And C and K pixels, M pixel and Y
And the pixels of C and the pixels of Y can be formed as overlapping lines. Since the C pixel and the Y pixel do not overlap as described above, it is advantageous when reproducing the green color of the vegetation in a natural image in which a deep color tone is preferred.

According to the second embodiment, in a color image forming apparatus for forming an image by modulating a multi-tone color image signal, optical modulation including at least pulse width modulation is performed by the image signal to perform optical writing. The gradation processing unit 78 and the writing unit 3 as an optical writing unit for performing the above, an adding circuit 604 as a unit for adding the image data of a plurality of adjacent pixels, and time-division between the pixels to specify by the added data A gradation processing unit 78 as means for generating a density from a predetermined direction of the pixel, a gradation processing unit 78 as a means for changing the density generation pixel in the main scanning direction, and By changing the position in the main scanning direction, a phase for each color is added in the main scanning direction, and the C and K colors and the M and Y colors overlap each other in the middle density portion. Since the image processing apparatus includes the gradation processing unit 78 as a unit for forming an image, it has substantially the same effect as that of the first embodiment, and in addition, the green color of vegetation in a natural image in which a deep color tone is particularly preferred. Can be realized with high quality color image formation.

The third embodiment of the present invention relates to claims 4 and 5,
This is one embodiment of the invention according to 9 and 10. In the third embodiment, Bk,
The image data of 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. The gradation processing section 78 sequentially shifts the clock input to the main scanning direction counter by one clock for each color in the dot generation position shift circuit for each color, and sets
The image data of each color of k, M, C, Y is shifted by one dot in the main scanning direction in the order of C → Y → M → K, and the reading start position of the image data of each color of Bk, M, C, Y Is shifted by one dot in the main scanning direction for each color to change the position of the density generation pixel in the main scanning direction for each color.

Thus, in the middle density portion, when all the colors are overprinted, the pixels of each color are arranged as shown in FIG. 35B, but in this embodiment, the pixels of each color are arranged as shown in FIG. And C and M pixels, Y pixel and K
And the pixels of C and Y, and the pixels of M and Y do not overlap each other. Since the C pixel and the Y pixel and the M pixel and the Y pixel do not overlap as described above, the reproduction of the skin color of a person who requires a delicate color tone and the natural image in which a deep color tone is preferred. This is advantageous when reproducing the green color of vegetation.

According to the third embodiment, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, the image signal is subjected to light modulation including at least pulse width modulation to perform optical writing. The gradation processing unit 78 and the writing unit 3 as an optical writing unit for performing the operation, an adding circuit 604 as a unit for adding the image data of a plurality of adjacent pixels, and time-division between the pixels to specify by the added data A gradation processing unit 78 as means for generating density from a predetermined direction of the pixel, a gradation processing unit 78 as means for changing the density generation pixel in the main scanning direction, and a density generation pixel according to color information of image data. By adding the phase for each color in the main scanning direction by changing the position in the main scanning direction,
Since a gradation processing section 78 is provided as means for forming a line image in which the C and M colors and the Y and K colors overlap each other in the medium density portion, substantially the same as in the first embodiment. In addition to the effect, it is possible to realize color image formation that reproduces both the skin color of human beings and the green color of vegetation in a natural image with high quality. Further, since Y is relatively invisible and is paired with K, which is relatively noticeable, the color reproducibility of the entire image is improved.

According to the first to third embodiments, the gradation processing unit 78 as means for changing the position of the density generating pixel in the main scanning direction according to the color information of the image data is provided. A counter for indicating the read start position in the main scanning direction, and a function of sequentially shifting the read start position in the main scanning direction for each color. It is possible to do.

The fourth embodiment according to the present invention is characterized in that:
This is an embodiment of the invention according to 12, 18, and 19, and differs from the first embodiment in the following points. In the fourth embodiment, when, for example, the method 6 is employed in the first embodiment, as described above, the gradation processing unit 78 performs the processing flow shown in FIG. / 16, Bk, M, C, as shown in FIG.
Instead of the pixel arrangement of each Y color (all color superimposing to form a full-color image by superimposing pixels of Bk, M, C, and Y colors),
The image data of each color of Bk, M, C, and Y is shifted in the sub-scanning direction, and predetermined different phases are added to the pixels of each color in the sub-scanning direction.

The gradation processing section 78 sequentially shifts the clock input to the sub-scanning direction counter by one pixel for each color in the dot generation position shift circuit for each color, so that Bk, M, C , Y are shown in FIG.
As shown in (1), the image data is shifted by one pixel in the sub-scanning direction. FIG. 45 shows the arrangement of each color pixel when the density is 1/16.

Therefore, by forming an image in the shape of a vertical line, a paper white portion is formed more than when all the pixels of Bk, M, C, and Y are overprinted at the same position. In addition, the transfer conditions of each color become more equal, and an image having excellent color reproducibility without color unevenness, low roughness, and excellent graininess can be formed, particularly in a low density portion.

The position of the density generating pixel for each color is changed in the main scanning direction by adding a predetermined different phase to the pixel for each color. In this manner, the position of the density generating pixel for each color is changed to the main scanning direction. As the phase adding means for changing the direction, 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 arranged differently in the main scanning direction, a ROM in which data is input in advance without using a counter is read out repeatedly in the order of 1, 4, 2, 3, etc. , Dots are arranged in different orders.
In addition, the dot generation position for each color can be controlled in the sub-scanning direction using a regular signal.

According to the fourth embodiment, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, an adding circuit as means for adding image data of a plurality of adjacent pixels. 604, a gradation processing unit 78 as a means for generating a density from a predetermined direction of a specific pixel based on data added by this means, and a gradation processing as a means for changing a density generation pixel in the main scanning direction or the sub-scanning direction. And a unit 78 for changing the position of the density generating pixel in the sub-scanning direction in accordance with the color information of the data, thereby adding a phase for each color in the sub-scanning direction. Since a vertical line image is formed by dots, data of four adjacent pixels are added in a low density portion, and density is generated from an appropriate direction of a specific pixel based on the added value. Accordingly, adjacent pixels can be combined to realize an isolated dot, and the stability can be ensured. In addition, by adding a phase difference for at least two different colors in the sub-scanning direction, a low-density portion can be obtained. Since an isolated dot of each color can form a vertical line image, compared to the case of all colors overprinting, less white paper is created, and the transfer conditions of each color are more equal, especially in low density areas. A color image having excellent color reproducibility without color unevenness, less roughness, and excellent graininess can be realized.

Further, according to the fourth embodiment, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, the image data of a plurality of adjacent pixels is added. An adder circuit 604, a gradation processing unit 78 as a means for generating a density of a specific pixel from a predetermined direction based on the data added by this means, and a gradation as a means for changing the density generation pixel in the main scanning direction or the sub-scanning direction. And a tone processing unit 78, which adds a 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.
Since an image in the shape of a vertical line is formed by M, Y, and K isolated dots, the data of four adjacent pixels is added in the low density portion, and the density is generated from the appropriate direction of the specific pixel by the added value. In this way, adjacent pixels can be combined to realize an isolated dot, and the stability can be secured. In addition, by adding a phase difference for each of Bk, M, C, and Y in the sub-scanning direction, low density can be obtained. Can form a vertical line image with isolated dots of each color in the area, and compared to full color overprinting, it does not create more paper white area, and the transfer conditions of each color are more equal, so especially low density areas In this method, it is possible to realize a color image having excellent color reproducibility without color unevenness, low roughness, and excellent granularity. In the first embodiment, a full-color image may be formed by pixels of each color of M, C, and Y excluding the pixel of Bk.

According to another embodiment of the present invention,
0 is one embodiment of the present invention. In the fifth embodiment, in the fourth embodiment, for example, the method 6 is adopted. When the image density of a single color is 1/16, the Bk, M, C, and Y colors shown in FIG. Rather than pixel arrangement (all-color overprinting where pixels of Bk, M, C, and Y are overlapped to form a full-color image), color turbidity and color unevenness are mainly reduced in highlights compared to full-color overprinting. For this purpose, the image data of each color is shifted for each color in both the main scanning direction and the sub-scanning direction, and pixels for each color are shifted to Bk, M, C, Y in both the main scanning direction and the sub-scanning direction.
A predetermined different phase is added to each color.

The gradation processing section 78 sequentially shifts the clock input to the main scanning direction counter for each color in the dot generation position shifting circuit for each color, and shifts the clock input to the sub-scanning direction counter for each color. 46, the read image data of Bk, M, C, and Y is shifted so that the arrangement of the pixels of Bk, M, C, and Y is staggered as shown in FIG. , M, C,
After adding predetermined different phases for each of Bk, M, C, and Y to the image data of each of the Y colors, the gradation processing is performed as described above. FIG. 46 shows the arrangement of each color pixel when the density is 1/16. Thereby, overlapping of different color pixels can be avoided to the utmost, and especially in a low density portion, there is no color unevenness, excellent color reproducibility, and less roughness.
A color image with excellent graininess can be formed.

According to the fifth embodiment, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, an adding circuit as means for adding image data of a plurality of adjacent pixels. 604, a gradation processing unit 78 as a means for generating a density from a predetermined direction of a specific pixel based on the data added by this means, and a gradation processing as a 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 generating pixel in the main scanning direction or the sub-scanning direction according to the color information of the data. By changing the position between the main 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 the staggered dot arrangement by C, M, Y, K isolated dots in the low density portion. In the low-density part, adjacent pixels can be combined and an isolated dot can be realized by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel by the added value. In addition to the effect that stability can be secured, by adding a phase difference for each of C, M, Y, and K colors in both the main scanning direction and the sub-scanning direction, isolated dots of each color in the low-density portion cause vertical A line-shaped image can be formed, and compared to when all colors are overprinted, a white portion of the paper is not formed even in the low density portion. In particular, the staggered C, M, Y, K isolated dots as in the present embodiment. The overlapping of different color pixels can be avoided as much as possible by forming a dot arrangement in a shape of a circle. Particularly in low density areas, there is no color unevenness, excellent color reproducibility, less roughness, and excellent graininess. Can realize color images

Still another embodiment of the present invention is Claim 1
4, 15, 21, and 22 are embodiments of the invention according to the present invention.
In the sixth embodiment, for example, the method 6 is adopted in the fourth embodiment, and when the image density of a single color is 1/16, Bk, M,
Rather than pixel arrangement of each color of C and Y (all color superimposition where pixels of each color of Bk, M, C and Y are superimposed to form a full color image), color turbidity mainly in a highlight portion rather than at the time of full color superimposition As a means for reducing color unevenness, the image data is shifted in the main scanning direction so that the phases of the chromatic image data and the achromatic image data are different from each other, and the main scanning is performed on pixels of each chromatic color and achromatic color. In this method, a predetermined phase that is different between a chromatic color and an achromatic color is added in the direction.

The gradation processing section 78 is provided with a printer γ correction section 77.
Is chromatic color data (here, Y, M, C
Chromatic data / achromatic data discriminating function for discriminating whether the image data is image data of each color) or achromatic data (Bk image data); And a phase adding means for adding a predetermined phase that is different between an achromatic color and an achromatic color. This phase adding means shifts the clock input to the main scanning direction counter between the chromatic image data and the achromatic image data based on the result of the chromatic data / achromatic data determining function.

The gradation processing section 78 converts the chromatic (M, C, Y) image data and the achromatic (Bk) image data read from the buffer memory by the phase adding means into the chromatic / achromatic data. As shown in FIG. 47, pixels of chromatic color 3C (M, C, Y) and achromatic color K
Are shifted so as not to overlap with each other in the main scanning direction and the sub-scanning direction, so that a predetermined phase different between the chromatic image data and the achromatic image data is added to the chromatic 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 linear image in which the chromatic (M, C, Y) pixels and the achromatic K pixels do not overlap with each other is formed. In FIG. 48, a pixel of chromatic color 3C (M, C, Y) and a pixel of achromatic color K are formed on a line formed from a low density portion to a middle density portion as shown in FIG. Are not overlapped with each other, color turbidity is not generated, and color image formation capable of high-quality color reproduction can be realized.

According to the sixth embodiment, a color image forming apparatus which refers to image data of a plurality of pixels, distributes density data to specific positions of the pixels based on the reference result, and forms a dot or line image. In the above, since the tone processing section 78 as means for changing the position of the density generating pixel according to the chromatic / achromatic color information of the data is provided, the same effect as that of the invention according to claim 11 is obtained, and By forming a dot arrangement in which the chromatic pixels and the achromatic pixels do not overlap, compared to the case of all-color overprinting, less white paper is created even in low-density areas, and there is no color turbidity. It is possible to realize color image formation capable of high-quality color reproduction.

According to the sixth embodiment, in a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, addition as means for adding image data of a plurality of adjacent pixels is performed. A circuit 604, a gradation processing unit 78 as means for generating density from a predetermined direction of a specific pixel based on the data added by this means, and a gradation as 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 generating 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 generating pixel according to the color information of the data Is provided in the main scanning direction or the sub-scanning direction, and the position of the density generating pixel is changed in the main scanning direction according to the color information of the data. Chromatic / achromatic color different phases added to 査 direction, C, M and Y in the low density portion to the medium density portion K
Since the linear dot arrangement which does not overlap with the above is formed, the same effect as the invention according to claim 11 is obtained, and further, the dot arrangement where the chromatic pixels and the achromatic pixels do not overlap is formed. As a result, compared to the time of full-color overprinting, the white portion is not created even in the low-density portion, and in particular, the chromatic pixel data and the achromatic pixel data have different phases, so A chromatic pixel and an achromatic pixel do not overlap each other on a line formed over the middle density portion, and color image formation without color turbidity and capable of high-quality color reproduction can be realized.

Still another embodiment of the present invention is described in claim 1.
6, 17, 23, and 24 are embodiments of the invention.
In the seventh embodiment, as a means for reducing color turbidity and color unevenness mainly in a highlight portion in the sixth embodiment, an image is added by a phase adding means. Chromatic image data in the main scanning direction,
A method is adopted in which a predetermined phase that is different between the chromatic color and the achromatic color is added to each pixel of the chromatic color and the achromatic color in the main scanning direction by shifting the phase so that the phase differs from that of the achromatic color image data. In the sub-scanning direction, the chromatic image data and the achromatic image data are shifted so that the phases are different from each other. Add different phases. 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 data. It is shifted with the data.

The gradation processing section 78 has a chromatic color (M, C, Y)
And the achromatic color (K) image data by the phase adding means according to the determination result of the chromatic color data / achromatic color data determination function as shown in FIG.
The chromatic image data and the chromatic image data are shifted by shifting in the main scanning direction and the sub-scanning direction so that the M and Y three-color superimposed 3C isolated dots and the K isolated dots form an oblique parallel dot arrangement. A different predetermined phase is added to the achromatic image data, and the position of the density generating pixel is changed in the main scanning direction and the sub-scanning direction according to the color information of the data. FIG.
Reference numeral 9 denotes the arrangement of each color pixel when the density is 1/16.

In this case, the gradation processing section 78 converts the chromatic (M, C, Y) image data and the achromatic (K) image data by two dots in the main scanning direction as shown in FIG. The phase adding means shifts in the main scanning direction and the sub-scanning direction according to the determination result of the chromatic color data / achromatic color data determination function so as to have a phase difference of one dot in the sub-scanning direction and 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-shaped dot arrangement is formed by the dots of three colors 3C of C, M, and Y and the dots of K, and C is formed in the middle density portion. , M, Y 3C overlay 3C
Dot and K dot are grown so as to be arranged in a 2 × 2 dot shape.

As described above, since the C, M, and Y three-color superimposed 3C dots and the K dots form an oblique line-like dot arrangement, the low-density portion is comfortable for human eyes and has good color reproducibility. A color image excellent in graininess is formed. Further, the C, M, and Y three-color superimposed 3C dots and the K dots are grown so as to be arranged in a 2 × 2 dot shape over the middle density portion. A color image having excellent reproducibility and granularity is formed.

According to the seventh embodiment, in the sixth embodiment, a gradation processing section as means for changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction according to the color information of the data. 78, a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction.
Diagonal lines are formed by the isolated dots of the diagonal lines, so in low-density areas, high-quality diagonal lines that are comfortable for human eyes and have excellent color reproduction and granularity Can be reproduced.

Further, according to the seventh embodiment, in the sixth embodiment, the gradation processing as means for changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction according to the color information of the data. A unit 78 for adding a phase for each chromatic / achromatic color in the main scanning direction and the sub-scanning direction,
In the middle density part, the dots are grown so as to be arranged in a 2 × 2 dot shape by the dot of three colors of C, M and Y and the dot of K, so that it is comfortable for human eyes in the middle density part. Color image formation excellent in color reproducibility and granularity can be realized.

Next, an eighth embodiment of the present invention will be described. The eighth embodiment is an embodiment of the invention according to claims 25 and 33. As described above, in the first to third embodiments, when the method 6 is adopted, when the image density of a single color is 1/16, the Bk, M, C, and Y colors shown in FIG. Instead of a pixel arrangement (all-color superimposition for forming a full-color image by superimposing pixels of Bk, M, C, and Y), predetermined different phases are added to pixels of each color, for example, Bk, M, C, Y for each color image data →
M → Y → K (Bk), C → M → K → Y, C → Y → M → K
Are shifted one dot at a time in the main scanning direction in the order of.
As shown in FIG. 41, a line-shaped image in which colors of two colors overlap each other is formed.

Here, in particular, as in the first embodiment, B
The image data of each color of k, M, C, Y is converted into C → M → Y → K (B
By shifting one dot at a time in the main scanning direction in the order of k), when the image data of each color of Bk, M, C, and Y is superimposed in the main scanning direction in the middle density portion, as shown in FIG. In the first embodiment, although the pixel arrangement is used, a line is formed in which C and Y and M and K overlap each other as shown in FIG. 39, and a line in which M and Y do not overlap can be formed. Since M and Y do not overlap on the parallel line, it is advantageous when reproducing a skin color of a person who requires a delicate color tone.

Also, as in the second embodiment, Bk, M,
By shifting the image data of each color of C and Y by one dot in the main scanning direction in the order of C → M → K → Y, the image data of each color of Bk, M, C and Y is shifted in the main scanning direction in the middle density portion. In the second embodiment, C and K, M and Y overlap each other as shown in FIG. 40, and the pixels are arranged as shown in FIG.
Can be formed without overlapping. In this way, C
And Y do not overlap, which is advantageous when reproducing the green color of vegetation in a natural image where a deep color tone is preferred.

Further, as in the third embodiment, Bk,
By shifting the image data of each color of M, C, and Y by one dot in the main scanning direction in the order of C → Y → M → K, the image data of each color of Bk, M, C, and Y is The pixel arrangement as shown in FIG. 35 (B) when superimposed in the scanning direction is changed to a line in which C and M, and Y and K respectively overlap as shown in FIG.
And Y and M and Y can be formed without overlapping each other. Since C and M, and Y and K do not overlap each other on the parallel line, reproduction of human skin color requiring a subtle color tone and green color of a plant in a natural image 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 hard to see, and K, which is relatively easy to see.

Therefore, in the eighth embodiment, the image data of each color of Bk, M, C, and Y is different from the first embodiment in the order of C → M → Y → K (Bk) in the main scanning direction. A first processing mode for shifting dots by dot is performed, and Bk,
A second processing mode for shifting the image data of each color of M, C, and Y by one dot in the main scanning direction in the order of C → M → K → Y is performed, and the image data of each color of Bk, M, C, and Y is converted to C → Y
By performing a third processing mode of shifting one dot at a time in the main scanning direction in the order of → M → K, predetermined different phases are added to the pixels for each color.

The second gradation processing section 78 executes the first processing mode in the same manner as in the first embodiment, executes the second processing mode in the same manner as in the second embodiment, and executes the third processing mode. The third processing mode is executed in the same manner as in the embodiment. Further, 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. Switching means for switching between the first processing mode to the third processing mode and switching the line image in which the two colors overlap each other in the medium density portion is provided. This switching means performs the first switching based on the color information of the image data.
And the third to third processing modes.

According to the eighth embodiment, there is provided a color image forming apparatus for forming an image by modulating a multi-gradation color image signal, and serving as a means for adding image data of a plurality of adjacent pixels. An addition circuit 604, a gradation processing unit 78 as a means for generating a density of a specific pixel from a predetermined direction based on the image data added by the means 604, and a means for changing the density generation pixel in the main scanning direction or the sub-scanning direction And a tone processing unit 78 as means for changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction according to the color information of the image data. By changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction and adding a phase for each color in the main scanning direction or the sub-scanning direction, two colors in the middle density portion can be compared with each other. In the color image forming apparatus and a gradation processing unit 78 as a means for forming a linear image that overlaps Re respectively, based on said color information of the image data 2
An option for selecting a color combination for each color is provided, and the tone processing unit 78 is provided as switching means for switching this option to switch a line image in which two colors overlap each other in the medium density portion. In the density unit, by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel based on the added value, adjacent pixels can be combined, an isolated dot can be realized, and stability can be secured. In addition to the effect, by adding a phase for each color, compared to the time of full color overprinting, less white paper is created even in low density areas, and the transfer conditions of each color are more equal, so especially In the low-density portion, a color image with no color unevenness, excellent color reproducibility, little roughness, and excellent granularity can be realized. Further, by providing an option to select a combination of two colors based on the color information of the image data and switching the option, a line-shaped image in which the two colors overlap each other in the medium density portion is switched, so that two colors are switched. For example, when switching to an option of selecting a combination of C and Y or a combination of M and K as a color combination for each color, it is possible to form a line in which M and Y do not overlap. Can be reproduced with high quality. C as a combination of two colors
When switching to the option of selecting a combination of K, M and Y, C and Y can form a line without overlapping, and the green color of the vegetation in a natural image, in which a deep color tone is particularly preferred, is improved. Can be reproduced. C and M, Y and K as color combinations for every two colors
Switch to the option to select the combination of C and Y
And M and Y can form a line that does not overlap each other, and reproduces the skin color of a person who requires a particularly delicate color tone, and enhances the green color of the vegetation in natural images where a deep color tone is preferred. Can be reproduced. Moreover, by pairing the relatively invisible Y with the relatively invisible K,
The color reproducibility of the entire image is improved. Further, by switching these options based on the color information of the image data, it is possible to realize a color image formation more suitable for the characteristics of the image data, and to realize high-quality color reproduction.

Next, a ninth embodiment of the present invention will be described. This ninth embodiment is an embodiment of the invention according to claims 26 and 34. As described above, in the fifth embodiment, the method 6 is adopted, and the image density of a single color is reduced to 1 /
In the case of No. 16, the pixel arrangement of each color Bk, M, C, and Y is not the pixel arrangement shown in FIG. 37 (all-color superimposition in which the pixels of each color Bk, M, C, and Y are superimposed to form a full-color image). As a means for reducing color turbidity / unevenness mainly in a highlight portion than at the time of hitting, image data of each color is shifted for each color in both the main scanning direction and the sub-scanning direction to form a pixel for each color. B in both the main scanning direction and the sub-scanning direction
A predetermined different phase is added for each of the colors k, M, C, and Y.

In particular, the image data of each color of Bk, M, C, and Y is shifted so that the arrangement of pixels of each color of Bk, M, C, and Y is staggered as shown in FIG. , Y, and Y are given predetermined different phases for each of Bk, M, C, and Y colors. As a result, overlapping of different color pixels can be avoided to the utmost, and a color image can be formed with excellent color reproducibility without color unevenness, low roughness, and excellent graininess, especially in a low density portion. .

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

According to the ninth embodiment, in the eighth embodiment, the staggered dot arrangement is formed by the isolated dots of cyan, magenta, yellow, and black in the low density portion. By adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel based on the added value, adjacent pixels can be combined, an isolated dot can be realized, and the effect of securing stability can be obtained. By adding a phase for each color to the top, a paper white portion is not formed even in a low-density portion as compared with when all colors are overprinted, and C, M, Y, and K are particularly formed in a low-density portion.
By forming the staggered dot arrangement with the isolated dots, overlapping of dots of different colors can be avoided to the utmost. In addition to the effect of the eighth embodiment, in particular, there is no color unevenness in the low density portion. It is possible to realize a color image with excellent reproducibility, less roughness, and excellent graininess.

Next, a tenth embodiment of the present invention will be described. This tenth embodiment is defined in claims 27 and 35.
3 is an embodiment of the invention according to the present invention. In the tenth embodiment, in the ninth embodiment, the gradation processing unit 78
In the dot generation position shifting circuit for each color, the clock input to the main scanning direction counter is made the same,
By making the clock input to the sub-scanning 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 first to fifth processing modes are switched and executed by the switching means based on the color information of the image data.

According to the tenth embodiment, the ninth embodiment
In the embodiment, an option to form an image overlapping the same position in all colors by making the positions of the density generation pixels the same for all colors regardless of the color information of the image data is added, and this option and the options are switched by the switching means. Since the switching is performed, in the low-density part, adjacent pixels can be combined by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel based on the added value, thereby realizing an isolated dot.
In addition to the effect that stability can be ensured, color misregistration is achieved even when the resolution of edges of characters and line images is required by setting the positions of the density generation pixels of all colors to be the same. Thus, a good edge output can be obtained, and color image formation more suitable for the properties of image data can be realized. In another embodiment of the present invention, the invention according to claims 27 and 35 is described in the tenth aspect.
This is applied to the eighth embodiment as in the case of the eighth embodiment, and the same effects as in the eighth embodiment can be obtained.

Next, an eleventh embodiment of the present invention will be described. This eleventh embodiment is defined in claims 28 and 36.
3 is an embodiment of the invention according to the present invention. In the above method 6, when the image density of a single color is 1/16, the pixel arrangement of each of Bk, M, C, and Y is as shown in FIG. As a means for reducing the color turbidity / unevenness of the color, a method in which different phases are added to the chromatic color and the achromatic color in the main scanning direction as shown in FIG. 51 can be considered.

Therefore, in the eleventh embodiment, the first
0, the gradation processing unit 78 shifts the image data in the main scanning direction so that the phases of the chromatic image data and the achromatic image data are different from each other, as shown in FIG. And a predetermined phase different from each other in the main scanning direction are added to each pixel of the achromatic color, and the image data is shifted in the sub-scanning direction so that the phases of the chromatic image data and the achromatic image data do not overlap. A sixth processing mode in which predetermined phases different from each other in the sub-scanning direction are added to each pixel of chromatic and achromatic colors is provided as an option.

The gradation processing section 78 determines whether the image data is chromatic color data (here, image data of each color of Y, M, and C) or achromatic color data (Bk image data). It has an achromatic color data discriminating function, and a phase adding means for adding different predetermined phases to the chromatic and achromatic pixels in the main scanning direction and the sub-scanning direction, respectively. This 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 color image data. This is shifted from the image data. The gradation processing unit 78 switches between the first processing mode to the sixth processing mode based on the determination result of the chromatic color data / 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 image data of each color in the main scanning direction and the sub-scanning direction for each of the chromatic color data / achromatic color data, as shown in FIG. In order to form an oblique line-shaped image by the three-color superimposed 3C of C, M and Y, and the isolated dot of K, in a low image density portion, it is comfortable for human eyes and also has good color reproducibility and granularity. An excellent color image can be formed. When the monochromatic image density is で は, an image of a medium density portion is formed in the sixth processing mode as shown in FIG. By adding the sixth processing mode to options, color reproduction more suitable for the properties of image data can be performed.

According to the eleventh embodiment, the first
0, the chromatic / achromatic phase is added in the main scanning direction and the sub-scanning direction according to the chromatic / achromatic information of the image data, so that C, M and Y are K and K in the medium density portion. Since an option for a line-shaped dot arrangement that does not overlap is added, and this option and the option are switched by the switching means, data of four adjacent pixels are added in the low density portion, and the appropriate value of the specific pixel is determined by the added value. By generating density from different directions, adjacent pixels can be combined to realize isolated dots and stability can be ensured. In addition, in the main scanning direction according to chromatic / achromatic information of image data By adding a phase for each chromatic / achromatic color in the sub-scanning direction, and adding an option to arrange a line-shaped dot in which C, M and Y do not overlap with K up to the middle density portion, all colors are superimposed. Than when Chi, without creating more paper white portion even in a low density area, and no color turbidity, can realize high-quality color reproduction possible color image formation.

The twelfth embodiment and the thirteenth embodiment of the present invention are the same as the eighth embodiment and the ninth embodiment, respectively. This is similarly applied, and the same effects as in the eleventh embodiment can be obtained. Eleventh embodiment and the first
In the second embodiment, by adding the sixth processing mode as an option, it is possible to realize color image formation more suitable for the characteristics of image data.

Next, a fourteenth embodiment of the present invention will be described. The fourteenth embodiment is described in claims 29 and 37.
3 is an embodiment of the invention according to the present invention. In the fourteenth embodiment, in the eleventh embodiment, the user sets the first
Interface (hereinafter referred to as I / F) that allows the user to freely select a desired processing mode from the processing modes
Is provided. As shown in FIG. 53, the I / F includes input keys 701 to 705 as selection means for selecting the first to fifth processing modes, respectively, and a processing mode selected by the input keys 701 to 705. And an input key 706 for determining

A fifth processing mode emphasizing resolution is selected with an input key 701, and a sixth processing mode for preventing color turbidity is selected with an input key 702. The second processing mode emphasizing green is selected by an input key 703, the first processing mode emphasizing flesh color is selected by an input key 704, and one of the third processing mode and the sixth processing mode is an input key. 7
05 is selected. The gradation processing unit 78 receives the input signals from the input keys 701 to 706 of the I / F, and
The processing mode selected by 1 to 705 and determined by the input key 706 is executed.

The fifteenth to nineteenth embodiments are the embodiments of the present invention according to claims 29 and 37, and the eighth to tenth embodiments, the twelfth embodiment and the twelfth embodiment are described below. In the thirteenth embodiment, an I / F for selecting each processing mode in the same manner as in the fourteenth embodiment
And the gradation processing unit 78 executes the selected processing mode.

According to the fourteenth to nineteenth embodiments, in the eighth to thirteenth embodiments, the interface for switching and executing the option in accordance with the user's selection is provided. By simply selecting the processing mode desired by the user, the mode can be easily switched to that processing mode, and the processing mode desired by the user can be output.

Next, a twentieth embodiment of the present invention will be described. This twentieth embodiment is characterized in that:
3 is an embodiment of the invention according to the present invention. In the twentieth embodiment, a color feature of image data is automatically extracted in the eleventh embodiment, and based on the extracted data,
An appropriate processing mode is automatically selected from among the processing modes.

FIG. 54 shows a part of the processing flow of the gradation processing section 78 in the twentieth embodiment. Gradation processing unit 78
Extracts the feature amount (color feature amount) of the multi-valued image data from the printer γ correction unit 77 in step S1, and converts the image data from the feature amount into an edge portion of a character, a line image or the like in step S2. It is determined whether or not the image data requires image resolution. If the image data requires image resolution of an edge portion such as a character or a line image in step S3, the processing mode is determined in step S9. Is switched to the fifth processing mode as the resolution emphasis mode, and the fifth processing mode is executed.

If the image data is not image data requiring the resolution of an edge portion such as a character or a line image, the gradation processing unit 78 determines in step S3 that the image data has many achromatic colors from the above-described feature amounts. Determine if it is data,
If the image data is image data having 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. If the image data is not achromatic color image data, 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. In S5, it is determined from the histogram whether or not the image data has a large ratio of G image data. If the image data has a large ratio of G image data, the processing mode is changed to the second green mode ADAPT33 in step S11. And the second processing mode is executed.

If the ratio of the G image data to the image data is not large, the gradation processing unit 78 determines in step S6 whether or not the image data has many portions without G image data from the histogram. If there are many portions where the data does not include the G image data, the process is switched to the first processing mode as the skin color emphasizing mode ADAPT31 in step S12 to perform the first processing.
Execute the processing mode. If there is not a large portion of the image data without G image data, the gradation processing unit 78 switches the processing mode to the third processing mode ADAPT32 in step S7 and executes the third processing mode ADAPT32. Note that, in the subroutine of each processing mode, the gradation processing unit 78
Before performing the above-described actual halftone processing of image data in each processing mode, image processing such as filtering of image data and color correction is also performed.

The twenty-first to twenty-fifth embodiments of the present invention are the embodiments of the invention according to claims 30 and 38, and the eighth to tenth embodiments and the twelfth embodiment are described above.
In the embodiment and the thirteenth embodiment,
In the same manner as in the twentieth embodiment, a color feature amount of image data is automatically extracted, and based on the extracted data, an appropriate processing mode is automatically selected from each processing mode and executed. It was done.

According to the twentieth to twenty-fifth embodiments, in the eighth to thirteenth embodiments, a feature amount is automatically extracted from image data, and the feature amount is determined based on the extracted data. Since the gradation processing unit 78 is provided as means for automatically switching options, the user can recognize the nature of the image data and manually select a processing mode without performing the processing in the optimum processing mode for the image data. It can be implemented.

Next, a twenty-sixth embodiment of the present invention will be described. The twenty-sixth embodiment relates to claims 31 and 39
3 is an embodiment of the invention according to the present invention. FIG. 55 shows a part of the processing flow of the gradation processing unit 78 in the twenty-sixth embodiment.
In the twenty-sixth embodiment, in the twentieth embodiment, the gradation processing unit 78 executes steps S4 to S8, S11, and S12 by omitting steps S1 to S3, S9, and S10.
Note that, in the subroutine of each processing mode, the gradation processing unit 78 performs image processing such as filtering of image data and color correction before performing the actual halftone processing of the image data in each processing mode as described above. Has also gone.

According to the twenty-sixth embodiment, the second embodiment
In the zeroth embodiment, the means 78 for extracting a characteristic amount from image data sets the magnitude of the ratio of the green image signal from the image data as the characteristic amount. Selection / switching of the processing mode according to the amount can be performed.

Next, a twenty-seventh embodiment of the present invention will be described. The twenty-seventh embodiment has claims 32 and 40.
In the twenty-sixth embodiment, the image data is divided into a plurality of blocks according to the feature amount, and an appropriate processing mode is automatically selected from among a plurality of processing modes for each block. This is to make a selection. FIG. 56 shows a gradation processing unit 7 according to the twenty-seventh embodiment.
8 shows part of the processing flow of FIG. In the twenty-seventh embodiment,
In the twenty-sixth embodiment, the gradation processing unit 78 proceeds from step S4 to step S13, and determines a plurality of blocks based on a variation amount of G image data with respect to the image data from the printer γ correction unit 77, S5 ~ for each block
The processes in S7, S11, and S12 are performed, and it is determined in step S14 whether there is any unprocessed block. If there is an unprocessed block, the process returns to step SS5. Note that the gradation processing unit 78
In the subroutine of each processing mode, image processing such as filtering and color correction of image data is also performed before performing the above-described actual halftone processing of image data in each processing mode.

The twenty-eighth embodiment of the present invention is characterized in that
In the twenty-fifth embodiment, the image data is divided into a plurality of blocks according to the feature amount, and an appropriate one is automatically selected from among a plurality of processing modes for each block. The processing mode is selected. As in the case of the twenty-seventh embodiment, the gradation processing unit 78 proceeds from step S4 to step S13 and performs processing on the image data from the printer γ correction unit 77. A plurality of blocks are determined based on the variation amount of the G image data, and the processes of S5 to S7, S11, and S12 are performed for each block. If there is, return to step SS5.

According to the twenty-seventh embodiment and the twenty-eighth embodiment, in the twenty-sixth embodiment and the twenty-fifth embodiment, a gradation processing unit 78 as a means for automatically extracting a feature amount from image data. Has a gradation processing unit 78 as means for dividing image data into a plurality of blocks for each feature based on the extracted data, and switches the options for each block. Data can be processed in an appropriate processing mode for each block, and processing in an optimal mode can be performed for each block having a different feature amount even in the same output image (in the same recording medium).

[0222]

As described above, according to the first aspect of the present invention, a color having excellent color reproducibility without color unevenness particularly in a low-density portion and excellent granularity in a low-density portion is obtained by the above configuration. Image formation can be realized. According to the second aspect of the present invention, it is possible to reproduce a human skin color requiring a particularly subtle color tone with a high quality.

According to the third aspect of the present invention, the green color of the vegetation of a natural picture, in which a deep color tone is particularly preferred, can be reproduced with high quality. According to the fourth aspect of the present invention, both the color of the human skin and the green color of the vegetation of a natural picture can be reproduced with high quality by the above configuration. According to the fifth aspect of the present invention, with the above configuration, the inventions of the first to fourth aspects can be easily achieved.

According to the sixth aspect of the invention, with the above configuration, it is possible to realize a color image having excellent color reproducibility without color unevenness particularly in a low density portion and excellent granularity in a low density portion. According to the seventh aspect of the present invention, with the above-described configuration, it is possible to reproduce a human skin color requiring a particularly delicate color tone with high quality.

According to the eighth aspect of the present invention, the green color of the vegetation of a natural picture, in which a deep color tone is particularly preferred, can be reproduced with high quality. According to the ninth aspect of the present invention, with the above-described configuration, it is possible to reproduce both the color of the human skin and the green color of the vegetation of a natural image with high quality. According to the tenth aspect, with the above configuration, the inventions according to the sixth to ninth aspects can be easily achieved.

According to the eleventh aspect of the present invention, with the above structure, color unevenness is excellent without color unevenness particularly in a low density portion, and the granularity in a low density portion is excellent. According to the twelfth aspect of the present invention, with the above configuration, color unevenness is excellent without color unevenness particularly in a low-density part, and excellent in graininess in a low-density part.

According to the thirteenth aspect of the present invention, with the above configuration, overlapping between multicolor dots can be avoided to the utmost, and the color reproducibility and the granularity in a low density portion are excellent. According to the invention according to claim 14, with the above configuration,
It is possible to realize color image formation without color turbidity in the low density portion to the middle density portion and capable of high quality color reproduction. Claim 1
According to the fifth aspect of the invention, with the above-described configuration, it is possible to realize color image formation without color turbidity in the low density portion to the middle density portion and capable of high-quality color reproduction.

According to the sixteenth aspect of the present invention, with the above-described structure, not only the color reproducibility and the granularity in the low-density portion are excellent, but also the basic image of the oblique line which is comfortable for the human eyes can be displayed in high quality. Can be reproduced. According to the seventeenth aspect, with the above configuration, it is possible to realize a color image formation that is comfortable to human eyes and excellent in color reproducibility and granularity in the middle density portion.

According to the eighteenth aspect of the present invention, with the above structure, color unevenness is excellent without color unevenness particularly in a low density portion, and excellent in graininess in a low density portion. According to the nineteenth aspect of the invention, with the above configuration, color unevenness is excellent without color unevenness particularly in a low-density portion, and excellent in graininess in a low-density portion.

According to the twentieth aspect of the present invention, with the above configuration, overlapping between multicolor dots can be avoided to the utmost, and excellent color reproducibility and granularity in a low density portion are obtained. According to the invention according to claim 21, with the above configuration,
It is possible to realize color image formation without color turbidity in the low density portion to the middle density portion and capable of high quality color reproduction. Claim 2
According to the second aspect of the present invention, with the above configuration, it is possible to realize color image formation without color turbidity in the low density portion to the middle density portion and capable of high quality color reproduction.

According to the twenty-third aspect of the present invention, with the above-described structure, color reproducibility and granularity in a low-density portion are excellent, and a basic image of a diagonal parallel line which is comfortable to human eyes can be produced with high quality. Can be reproduced. According to the invention according to claim 24, with the above configuration, it is possible to realize a color image formation which is comfortable to human eyes and excellent in color reproducibility and granularity in the middle density portion.

According to the twenty-fifth aspect, in the low density portion, adjacent pixels can be combined by generating a density from an appropriate direction of a specific pixel by an addition value of data of four adjacent pixels, thereby forming an isolated dot. In addition to the effect of achieving stability and ensuring stability, by adding a phase for each color, compared to full color overprinting, less white paper is created even in low density areas, and each color Since the transfer conditions become more uniform, a color image with excellent color reproducibility without color unevenness, low roughness, and excellent graininess can be realized, especially in a low density portion. Further, since an option for selecting a combination of two colors is provided based on the color information of the image data and the selection is switched, a line image in which the two colors overlap each other in the medium density portion is switched.
And Y can form a line that does not overlap, and can reproduce the skin color of a person who requires a particularly delicate color tone with high quality. Also, a line that does not overlap C and Y can form a line that is particularly deep. You can reproduce the green color of the vegetation in the favorite natural painting with high quality,
C and Y, and M and Y can form a line without overlapping each other, and reproduce the skin color of a person who requires a particularly delicate color tone and the green color of the vegetation in a natural image where a deep color tone is preferred. This has the effect of being able to reproduce high quality. In addition, the color reproducibility of the entire image is improved by pairing the relatively invisible Y and the relatively easily visible K. Further, by switching these options based on the color information of the image data, it is possible to realize a color image formation more suitable for the characteristics of the image data, and to realize high-quality color reproduction.

According to the twenty-sixth aspect, in the low-density part, adjacent pixels are combined by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel by the added value. In addition to the effect that isolated dots can be realized and stability can be secured, by adding a phase for each color, paper white areas are not created even in low density areas compared to when all colors are overprinted. 26. The image forming method according to claim 25, wherein the staggered dot arrangement is formed by the isolated dots of cyan, magenta, yellow, and black, particularly in the low density portion, so that overlapping of the dots of different colors can be avoided as much as possible. In addition to the effects described above, it is possible to realize color image formation excellent in color reproducibility without color unevenness, low roughness, and excellent graininess, especially in a low density portion.

According to the twenty-seventh aspect, in the low-density part, adjacent pixels are combined by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel by the added value. In addition to the effect that isolated dots can be realized and stability can be secured, the resolution of edges of characters, line images, etc. is required by making the positions of the density generation pixels of all colors the same. Also in this case, a good edge output without color misregistration can be obtained, and color image formation more suitable for the properties of image data can be realized.

According to the twenty-eighth aspect, in the low-density part, adjacent pixels are combined by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel by the added value. In addition to the effect that isolated dots can be realized and stability can be secured, a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction according to the chromatic / achromatic color information of the image data. By adding an option to arrange line dots in which cyan, magenta, and yellow do not overlap with black up to the medium density area, paper white areas can be reduced even in low density areas compared to when all colors are overprinted. It is possible to realize color image formation that can be performed without color turbidity and that can reproduce high-quality colors.

According to the twenty-ninth aspect of the present invention, the user can easily switch to the desired processing mode only by selecting the desired processing mode, and can output the processing mode desired by the user.

[0237] According to the thirtieth aspect, it is possible to execute a process in an optimum processing mode for image data without a user recognizing the nature of the image data and manually selecting a processing mode. Become.

According to the thirty-first aspect, the third aspect is provided.
0, it is possible to effectively select / switch the processing mode based on the feature amount.

According to the invention of claim 32, claim 3
0, the image data can be processed in an appropriate processing mode for each block, and even in the same output image, the optimal mode processing can be performed for each block having a different feature amount. Will be possible.

According to the thirty-third aspect of the present invention, in the low-density portion, adjacent pixels can be combined by generating a density from an appropriate direction of a specific pixel based on an addition value of data of four adjacent pixels, thereby forming an isolated dot. In addition to the effect of achieving stability and ensuring stability, by adding a phase for each color, compared to full color overprinting, less white paper is created even in low density areas, and each color Since the transfer conditions become more uniform, a color image with excellent color reproducibility without color unevenness, low roughness, and excellent graininess can be realized, especially in a low density portion. Further, since an option for selecting a combination of two colors is provided based on the color information of the image data and the selection is switched, a line image in which the two colors overlap each other in the medium density portion is switched.
And Y can form a line that does not overlap, and can reproduce the skin color of a person who requires a particularly delicate color tone with high quality. Also, a line that does not overlap C and Y can form a line that is particularly deep. You can reproduce the green color of the vegetation in the favorite natural painting with high quality,
C and Y, and M and Y can form a line without overlapping each other, and reproduce the skin color of a person who requires a particularly delicate color tone and the green color of the vegetation in a natural image where a deep color tone is preferred. This has the effect of being able to reproduce high quality. In addition, the color reproducibility of the entire image is improved by pairing the relatively invisible Y and the relatively easily visible K. Further, by switching these options based on the color information of the image data, it is possible to realize a color image formation more suitable for the characteristics of the image data, and to realize high-quality color reproduction.

According to the thirty-fourth aspect, in the low-density part, adjacent pixels are combined by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel by the added value. In addition to the effect that isolated dots can be realized and stability can be secured, by adding a phase for each color, paper white areas are not created even in low density areas compared to when all colors are overprinted. 34. The image forming apparatus according to claim 33, wherein the staggered dot arrangement is formed by the isolated dots of cyan, magenta, yellow, and black, particularly in the low density portion, so that overlapping of dots of different colors can be avoided as much as possible. In addition to the effects described above, it is possible to realize color image formation excellent in color reproducibility without color unevenness, low roughness, and excellent graininess, especially in a low density portion.

According to the thirty-fifth aspect, in the low-density part, adjacent pixels are combined by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel based on the added value. In addition to the effect that isolated dots can be realized and stability can be secured, the resolution of edges of characters, line images, etc. is required by making the positions of the density generation pixels of all colors the same. Also in this case, a good edge output without color misregistration is obtained, and a color image formation more suitable for the properties of image data can be realized.

According to the thirty-sixth aspect, in the low density part, adjacent pixels are combined by adding data of four adjacent pixels and generating a density from an appropriate direction of a specific pixel by the added value. In addition to the effect that isolated dots can be realized and stability can be secured, a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction according to the chromatic / achromatic color information of the image data. By adding an option to arrange line dots in which cyan, magenta, and yellow do not overlap with black up to the medium density area, paper white areas can be reduced even in low density areas compared to when all colors are overprinted. It is possible to realize color image formation that can be performed without color turbidity and with high quality color reproduction.

According to the thirty-seventh aspect, it is possible to easily switch to a desired processing mode simply by selecting the desired processing mode by the user, and to output the processing mode desired by the user.

According to the thirty-eighth aspect of the present invention, it is possible for the user to recognize the nature of the image data and to execute the processing in the optimum processing mode for the image data without manually selecting the processing mode. Become.

According to the invention of claim 39, claim 3
In addition to the effects of the image forming apparatus described in Item 8, it is possible to effectively select / switch the processing mode based on the feature amount.

According to the fortieth aspect, the third aspect is provided.
In addition to the effects of the image forming apparatus described in Item 8, the image data can be processed in an appropriate processing mode for each block. Will be possible.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a control circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an image processing unit of the embodiment.

FIG. 3 is a diagram showing a light output waveform and a dot pattern of a light intensity modulation method and a pulse width modulation method.

FIG. 4 is a diagram showing an optical output waveform and a dot pattern of a pulse width intensity mixed modulation system used in the embodiment.

FIG. 5 is a diagram for explaining PWM pulse position control of the embodiment.

FIG. 6 is a diagram for explaining a fraction processing function of the embodiment.

FIG. 7 is a sectional view schematically showing the embodiment.

FIG. 8 is a diagram for explaining image data processing of the embodiment.

FIG. 9 is a diagram showing one dot size and one pixel size of methods 1 to 3 that can be adopted in the embodiment.

FIG. 10 is a diagram showing a dot formation matrix of a method 1 that can be adopted in the embodiment.

FIG. 11 is a diagram expressing the dot formation matrix in a minimum density unit.

FIG. 12 is a diagram showing a transition of dot formation in the method 1.

FIG. 13 is a diagram showing a transition of dot formation in the method 1.

FIG. 14 is a diagram showing a method 2 dot formation matrix that can be adopted in the embodiment.

FIG. 15 is a diagram expressing the dot formation matrix in a minimum density unit.

FIG. 16 is a diagram showing a transition of dot formation in the method 2;

FIG. 17 is a diagram showing a transition of dot formation in the method 2;

FIG. 18 is a diagram showing a dot formation matrix of a method 3 that can be adopted in the embodiment.

FIG. 19 is a diagram expressing the dot formation matrix in a minimum density unit.

FIG. 20 is a diagram showing the transition of dot formation in the above-mentioned method 3.

FIG. 21 is a diagram showing a method 4 dot formation matrix that can be adopted in the embodiment.

FIG. 22 is a diagram expressing the same dot formation matrix in minimum density units.

FIG. 23 is a diagram showing a transition of dot formation in the above method 4.

FIG. 24 is a diagram showing one dot size and one pixel size of a method 5 that can be adopted in the embodiment.

FIG. 25 is a diagram showing a dot formation matrix of the same method 5;

FIG. 26 is a diagram expressing the dot formation matrix in minimum density units.

FIG. 27 is a diagram showing a transition of dot formation of the method 5;

FIG. 28 is a diagram showing a transition of dot formation in the method 5;

FIG. 29 is a diagram showing one dot size of a method 6 that can be adopted in the embodiment and one pixel size in a highlight portion having a density of 1/4 or less.

FIG. 30 is a diagram showing a dot formation matrix of the same method 6.

FIG. 31 is a diagram showing a dot formation matrix at a density of 1/4 or less according to the same method 6 in a minimum density unit.

FIG. 32 is a diagram showing one pixel size at a density of 1/4 or more in the same method 6;

FIG. 33 is a diagram showing a dot formation matrix in a density of 1/4 or more in the same method 6 in a minimum density unit.

FIG. 34 is a diagram showing the transition of dot formation at a density of 1/4 or less in the same method 6.

FIG. 35 is an explanatory diagram of dot formation at a density of 1/4 or more in the same method 6.

FIG. 36 is a diagram showing a dot formation state at a density of 7/8 in the same method 6.

FIG. 37 is a diagram for describing the embodiment.

FIG. 38 is a diagram showing the arrangement of each color dot at a density of 1/16 in the embodiment.

FIG. 39 is a diagram illustrating an arrangement of dots of each color at a density of の in the embodiment.

FIG. 40 is a diagram illustrating an arrangement of dots of each color at half density according to another embodiment of the present invention.

FIG. 41 is a diagram illustrating an arrangement of color dots at a density of の according to another embodiment of the present invention.

FIG. 42 is a diagram showing image data readout positions by the main scanning counter of the embodiment.

FIG. 43 is a flowchart showing a processing flow of a gradation processing unit in the embodiment.

FIG. 44 is a block diagram showing a dot generation position shift circuit for each color according to the embodiment.

FIG. 45 is a diagram illustrating an arrangement of dots of each color at a density of 1/16 according to the fourth embodiment of the present invention.

FIG. 46 is a diagram illustrating an arrangement of color dots at a density of 1/16 according to another embodiment of the present invention.

FIG. 47 is a diagram showing an arrangement of color dots at a density of 1/16 according to another embodiment of the present invention.

FIG. 48 is a diagram showing the arrangement of each color dot at a density of １ ／ in the embodiment.

FIG. 49 is a diagram showing an arrangement of color dots at a density of 1/16 according to still another embodiment of the present invention.

FIG. 50 is a diagram showing an arrangement of dots of each color at a density of の of the embodiment.

FIG. 51 is a diagram illustrating an arrangement of dots of each color at a density of 1/16 according to the eleventh embodiment of the present invention.

FIG. 52 is a diagram illustrating an arrangement of dots of each color at a density of の in the eleventh embodiment.

FIG. 53 is a plan view showing an I / F of a fourteenth embodiment of the present invention.

FIG. 54 is a flowchart showing a part of a processing flow of a gradation processing unit according to a twentieth embodiment of the present invention.

FIG. 55 is a flowchart showing a part of a processing flow of a gradation processing unit in a twenty-sixth embodiment of the present invention.

FIG. 56 is a flowchart showing a part of a processing flow of a gradation processing unit in a twenty-seventh embodiment of the present 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 Addition circuit 605 Comparison / distribution / phase control circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 2C262 AA05 AA24 AA26 AA27 AB05 AB13 BB06 BB20 BB22 BB25 BB27 BB49 BC07 DA09 EA06 GA11 GA23 5C077 LL19 MP08 NN17 NP01 PP33 PP52 PP57 PQ08 PQ12 PQ17 TT06 5C03 LA03 PA02

Claims (40)

[Claims] 1. A color image forming method for forming a dot or line image by referring to image data of a plurality of pixels and distributing density data to a specific position among the plurality of pixels based on the reference result. A color image forming method, wherein the position of a density generating pixel is changed according to color information. 2. A color image forming method for forming an image by modulating a multi-gradation color image signal, performing optical writing including at least pulse width modulation by the image signal, performing optical writing, and forming a plurality of adjacent pixels. Add the image data of
The density is generated from a predetermined direction of a specific pixel by the data obtained by time-division between pixels, the density generating pixel is changed in the main scanning direction, and the position of the density generating pixel is changed in the main scanning direction according to the color information of the data. The color is characterized by adding a phase for each color in the main scanning direction by changing to a linear image in which cyan and yellow colors and magenta and black colors overlap each other in the middle density portion. Image forming method. 3. A color image forming method for forming an image by modulating a multi-gradation color image signal, wherein light writing including at least pulse width modulation is performed by the image signal to perform optical writing, and a plurality of adjacent pixels are formed. Add the image data of
The density is generated from a predetermined direction of a specific pixel by the data obtained by time-division between pixels, the density generating pixel is changed in the main scanning direction, and the position of the density generating pixel is changed in the main scanning direction according to the color information of the data. The color is characterized by adding a phase for each color in the main scanning direction by changing to a linear image in which cyan and black colors and magenta and yellow colors overlap each other in the middle density portion. Image forming method. 4. A color image forming method for forming an image by modulating a multi-gradation color image signal, performing optical writing including at least pulse width modulation by the image signal, performing optical writing, and forming a plurality of adjacent pixels. Add the image data of
The density is generated from a predetermined direction of a specific pixel by the data obtained by time-division between pixels, the density generating pixel is changed in the main scanning direction, and the position of the density generating pixel is changed in the main scanning direction according to the color information of the data. A color image is formed by adding a phase for each color in the main scanning direction by changing to a linear image in which cyan and magenta colors overlap each other and yellow and black colors overlap each other in the middle density portion. Forming method. 5. The method according to claim 1, wherein the position of the density generating pixel is changed in the main scanning direction in accordance with the color information of the data. A color image forming method, wherein a reading start position in the main scanning direction is sequentially shifted for each color by using a counter indicating a position. 6. A color image forming apparatus which refers to image data of a plurality of pixels and distributes density data to a specific position among the plurality of pixels based on the reference result to form a dot or line image. A color image forming apparatus comprising: means for changing a position of a density generation pixel according to color information. 7. A color image forming apparatus for forming an image by modulating a multi-gradation color image signal, comprising: an optical writing unit for performing optical writing including at least pulse width modulation by the image signal to perform optical writing; Means for adding image data of a plurality of pixels to be processed, means for time-division between pixels to generate a density from a predetermined direction of a specific pixel based on the added data, and means for changing a density-generated pixel in the main scanning direction. 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 according to the color information of the data, and the cyan and yellow colors
Means for forming a linear image in which the colors of magenta and black overlap each other. 8. A color image forming apparatus for forming an image by modulating a multi-gradation color image signal, comprising: an optical writing means for performing optical writing including at least pulse width modulation by the image signal to perform optical writing; Means for adding image data of a plurality of pixels to be processed, means for time-division between pixels to generate a density from a predetermined direction of a specific pixel based on the added data, and means for changing a density-generated pixel in the main scanning direction. 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 in accordance with the color information of the data, and the cyan and black colors in the middle density portion are added.
Means for forming a linear image in which the colors of magenta and yellow overlap each other. 9. A color image forming apparatus for forming an image by modulating a multi-gradation color image signal, comprising: an optical writing unit for performing optical writing including at least pulse width modulation by the image signal to perform optical writing; Means for adding image data of a plurality of pixels to be processed, means for time-division between pixels to generate a density from a predetermined direction of a specific pixel based on the added data, and means for changing a density-generated pixel in the main scanning direction. By changing the position of the density generation pixel in the main scanning direction according to the color information of the data, a phase for each color is added in the main scanning direction, and cyan and magenta colors
Means for forming a line image in which yellow and black colors overlap each other. 10. The color image forming apparatus according to claim 6, wherein the means for changing the position of the density generating pixel in the main scanning direction in accordance with the color information of the data starts reading in the main scanning direction. A color image forming apparatus comprising: a counter for indicating a position; and a function of sequentially shifting a reading start position in the main scanning direction for each color. 11. A color image forming method for forming an image by modulating a multi-tone color image signal, adding image data of a plurality of adjacent pixels, and using the added data, a density of a specific pixel from a predetermined direction. Is generated, the density generating pixel is changed in the main scanning direction or the sub-scanning direction, and the position of the density generating pixel is changed in the sub-scanning direction according to the color information of the data, thereby adding a phase for each color in the sub-scanning direction. And forming an image in the shape of a vertical line by using isolated dots of at least two different colors in the low density portion. 12. In a color image forming method for forming an image by modulating a multi-gradation color image signal, image data of a plurality of adjacent pixels are added, and a density of a specific pixel is determined from a predetermined direction based on the added data. Is generated, the density generating pixel is changed in the main scanning direction or the sub-scanning direction, and the position of the density generating pixel is changed in the sub-scanning direction according to the color information of the data, thereby adding a phase for each color in the sub-scanning direction. A color image forming method characterized by forming an image in the form of a vertical line by using cyan, magenta, yellow or isolated dots of cyan, magenta, yellow, and black in a low density portion. 13. A color image forming method for forming an image by modulating a multi-tone color image signal, adding image data of a plurality of adjacent pixels, and using the added data, a density of a specific pixel from a predetermined direction. Is generated, the density generation pixel is changed in the main scanning direction or the sub scanning direction, the position of the density generation pixel is changed in the main scanning direction or the sub scanning direction according to the color information of the data, and the density generation pixel is changed according to the color information of the data. By changing the position of the density generating pixel in the main scanning direction and the sub scanning direction, a phase for each color is added in the main scanning direction and the sub scanning direction,
A color image forming method comprising forming a staggered dot arrangement with isolated dots of cyan, magenta, yellow, and black in a low density portion. 14. A color image forming method for referencing image data of a plurality of pixels, distributing density data to a specific position of the pixel based on the reference result, and forming a dot or line image. A color image forming method, wherein the position of a density generating pixel is changed according to coloring information. 15. A color image forming method for forming an image by modulating a multi-tone color image signal, adding image data of a plurality of adjacent pixels, and using the added data, a density of a specific pixel from a predetermined direction. Is generated, the density generation pixel is changed in the main scanning direction or the sub scanning direction, the position of the density generation pixel is changed in the main scanning direction or the sub scanning direction according to the color information of the data, and the density generation pixel is changed according to the color information of the data. The position of the density generating pixel is changed in the main scanning direction or the sub-scanning direction, and the position of the density generating pixel is changed in the main scanning direction in accordance with the color information of the data. And forming a line-shaped dot arrangement in which cyan, magenta, and yellow do not overlap with black in a low-density part to a medium-density part. 16. The color image forming method according to claim 4, wherein the position of the density generating pixel is changed in the main scanning direction and the sub-scanning direction according to the color information of the data, so that the position of the density generating pixel is changed in the main scanning direction and the sub-scanning direction. A phase for each chromatic / achromatic color is added, and three levels of cyan, magenta, and yellow are added in the low density area.
A color image forming method, wherein an oblique line-shaped dot arrangement is formed by color-separated isolated dots and black isolated dots. 17. The color image forming method according to claim 4, wherein the position of the density generating pixel is changed in the main scanning direction and the sub-scanning direction according to the color information of the data, so that the position of the density generating pixel is changed in the main scanning direction and the sub-scanning direction. A phase for each chromatic / achromatic color is added, and three colors of cyan, magenta, and yellow are added in the middle density portion.
2 dots by overlapping dots and black dots
A color image forming method, wherein the image is grown so as to be arranged in a × 2 dot shape. 18. A color image forming apparatus for forming an image by modulating a multi-gradation color image signal, a means for adding image data of a plurality of adjacent pixels, and a data for a specific pixel based on the data added by the means. A means for generating a density from a predetermined direction, and a means for changing a density generation pixel in the main scanning direction or the sub-scanning direction, and by changing a position of the density generation pixel in the sub-scanning direction according to color information of data. A color image forming apparatus which adds a phase for each color in a sub-scanning direction and forms a vertical line image with at least two different colors of isolated dots in a low density portion. 19. A color image forming apparatus for modulating a multi-gradation color image signal to form an image, a means for adding image data of a plurality of adjacent pixels, and a data for a specific pixel based on the data added by the means. A means for generating a density from a predetermined direction, and a means for changing a density generation pixel in the main scanning direction or the sub-scanning direction, and by changing a position of the density generation pixel in the sub-scanning direction according to color information of data. A phase for each color is added in the sub-scanning direction, and cyan, magenta, yellow or cyan, magenta,
A color image forming apparatus for forming an image in the shape of a vertical line using isolated dots of yellow and black. 20. A color image forming apparatus for forming an image by modulating a multi-gradation color image signal, comprising: means for adding image data of a plurality of adjacent pixels; Means for generating density from a predetermined direction, means for changing the density generating pixel in the main scanning direction or the sub-scanning direction, and changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction according to the color information of the data Means for changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction in accordance with the color information of the data, thereby adding a phase for each color in the main scanning direction and the sub-scanning direction. A color image forming apparatus wherein a staggered dot arrangement is formed by cyan, magenta, yellow, and black isolated dots. 21. A color image forming apparatus which 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. A color image forming apparatus comprising means for changing a position of a density generating pixel according to coloring information. 22. A color image forming apparatus for forming an image by modulating a multi-gradation color image signal, a means for adding image data of a plurality of adjacent pixels, and a data for a specific pixel based on the data added by the means. Means for generating density from a predetermined direction, means for changing the density generating pixel in the main scanning direction or the sub-scanning direction, and changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction according to the color information of the data Means for changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction in accordance with the color information of the data, and changing the position of the density generating pixel in the main scanning direction in accordance with the color information of the data. In this way, chromatic / achromatic color phases are added in the main scanning direction, and cyan, magenta, and yellow do not overlap with black in the low-to-medium density areas. Color image forming apparatus, and forming a placement. 23. A color image forming apparatus according to claim 11, further comprising means for changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction in accordance with the color information of the data. And a phase for each chromatic / achromatic color is added in the sub-scanning direction, and an oblique line-shaped dot arrangement is formed by a three-color superimposed isolated dot of cyan, magenta, and yellow and a black isolated dot in a low density portion. A color image forming apparatus, comprising: 24. A color image forming apparatus according to claim 11, further comprising means for changing the position of the density generating pixel in the main scanning direction and the sub-scanning direction in accordance with the color information of the data. And a phase for each chromatic / achromatic color is added in the sub-scanning direction, and dots are arranged in a 2 × 2 dot shape by three-color superimposed dots of cyan, magenta, and yellow and black dots in the middle density portion. A color image forming apparatus characterized in that the color image forming apparatus is grown. 25. A color image forming method for forming an image by modulating a multi-tone color image signal, wherein image data of a plurality of adjacent pixels are added, and a predetermined pixel of a specific pixel is determined by the added image data. The density is generated in the main scanning direction or the sub-scanning direction.
Changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction according to the color information of the image data, and changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction according to the color information of the image data In the color image forming method of adding a phase for each color in the main scanning direction or the sub-scanning direction to form a linear image in which two colors overlap each other in the medium density portion,
A color image forming method comprising: providing an option for selecting a color combination for each color; and switching the option to switch a linear image in which two colors overlap each other in a medium density portion. 26. A color image forming method according to claim 25, wherein the staggered dot arrangement is formed by the cyan, magenta, yellow, and black isolated dots in the low density portion. 27. The color image forming method according to claim 25, wherein the density generating pixel positions are the same for all colors regardless of the color information of the image data to form an image overlapping the same position for all colors. And switching between this option and the option. 28. A color image forming method according to claim 25, wherein a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction according to chromatic / achromatic color information of the image data. A color image forming method characterized by adding an option of a line-shaped dot arrangement in which cyan, magenta, and yellow do not overlap with black in a medium density portion, and switching between the option and the option. 29. A color image forming method according to claim 25, wherein said options are switched and executed according to a user's selection by an interface. 30. A color image forming method according to claim 25, wherein a feature amount is automatically extracted from image data, and said options are automatically switched based on the extracted data. Color image forming method. 31. A color image forming method according to claim 30, wherein when extracting a characteristic amount from the image data, a magnitude of a ratio of a green image signal from the image data is set as a characteristic amount. Method. 32. A color image forming method according to claim 30, wherein a feature amount is automatically extracted from the image data, and the image data is divided into a plurality of blocks for each feature based on the extracted data. A color image forming method characterized by switching the options. 33. A color image forming apparatus for forming an image by modulating a multi-gradation color image signal, comprising: means for adding image data of a plurality of adjacent pixels; Means for generating density from a predetermined direction of a specific pixel; means for changing the density generating pixel in the main scanning direction or sub-scanning direction; and setting the position of the density generating pixel in the main scanning direction or sub-scanning according to the color information of the image data. Means for changing the position of the density generating pixel in the main scanning direction or the sub-scanning direction according to the color information of the image data and adding a phase for each color in the main scanning direction or the sub-scanning direction. Means for forming a line image in which two colors overlap each other in the density portion. Provided the option of selecting a combination, the color image forming apparatus characterized by comprising a switching means for switching a line-shaped image in which the color between the two colors overlap each at the middle density part by switching this option. 34. A color image forming apparatus according to claim 33, wherein a staggered dot arrangement is formed by the cyan, magenta, yellow, and black isolated dots in the low density portion. 35. The color image forming apparatus according to claim 33, wherein the positions of the density generating pixels are the same for all colors, regardless of the color information of the image data, to form an image overlapping the same position for all colors. A color image forming apparatus, wherein the option and the option are switched by the switching unit. 36. A color image forming apparatus according to claim 33, wherein a phase for each chromatic / achromatic color is added in the main scanning direction and the sub-scanning direction according to the chromatic / achromatic color information of the image data. A color image forming apparatus characterized in that, in the middle density portion, cyan, magenta and yellow have an option to arrange a linear dot arrangement that does not overlap with black, and this option and the option are switched by the switching means. 37. A color image forming apparatus according to claim 33, further comprising an interface for switching and executing said options in accordance with a user's selection. 38. A color image forming apparatus according to claim 33, further comprising means for automatically extracting a characteristic amount from the image data and automatically switching the options based on the extracted data. A color image forming apparatus. 39. A color image forming apparatus according to claim 38, wherein the means for extracting the characteristic amount from the image data sets the magnitude of the ratio of the green image signal from the image data as the characteristic amount. apparatus. 40. A color image forming apparatus according to claim 38, further comprising: means for dividing the image data into a plurality of blocks for each feature based on the extracted data of the means for automatically extracting a feature amount from the image data; A color image forming apparatus, wherein the options are switched for each block.