JP2000350027A - Method and device for forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for forming an image which is superior in an image stability, by which the image is formed to be an isolated dot shape in an image low density part and the image of superior appearance is obtained by referring to image data of a plurality of pixels, distributing density data to the specified position of each pixel by means of a reference result and forming the image where dots are arrayed. SOLUTION: A gradation processing part 78 conducts turning the image signal of each 8-bit color into multi-values, that is, Y, M, C or Bk which is inputted from a printer γ correcting part 77. The part 78 often executes a dither processing or the like concerning the images signals of the respective colors Y, M, C and Bk, and a laser printer 100 outputs the multi-valued image signal of each color Y, M, C or Bk. That is, the gradation processing part 78 for referring to image data of a plurality of pixels and distributing density data to the specified position of the pixel by the reference result is provide. As a result, the image where the dots are arrayed is formed so that the one which is excellent in appearance is obtained through a simple operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, some image forming apparatuses perform halftone processing such as dither processing using a matrix of 2 (main scanning direction) × 1 (sub scanning direction). Further, as an image forming apparatus having a halftone processing function, those having an intermediate processing technique are disclosed in Japanese Patent Application Laid-Open Nos. 7-254985 and 7-2.
54986, JP-A-7-283941, JP-A-8-114965, JP-A-8-125863
And Japanese Patent Application Laid-Open No. 7-254986.

The one having an intermediate processing technique called "highest" is mainly intended to improve the reproducibility of a highlight portion of an image, and image data is subjected to pulse width modulation and weighted by two dots in the main scanning direction. A dither process is performed to stabilize the image highlight portion with a low number of lines, and for this purpose, a light writing beam diameter and a pixel interval in the main scanning direction 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.
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 are referred to, and
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, dither processing using a conventionally used 2 (main scanning direction) × 1 (sub scanning direction) matrix is known. In some cases, the image density may not be preserved, and this appears as a color change particularly in color image formation. Further, if a data line of one dot line or less is applied to the side where the density of the 2 × 1 matrix is not generated, the line may be thinned or lost. This phenomenon tends to be promoted when the conversion of the density reduction of the image data is performed by the γ correction before the image data dither processing means.

Further, in an electrophotographic image forming apparatus and an image forming method, it is necessary to concentrate low-density portions of an image on a specific portion and reproduce the image stably. Consideration must be given to the resulting banding. Further, in an electrophotographic image forming apparatus and an image forming method capable of multi-value writing, when an image is formed as it is with image data read from a document, the potential distribution on the photosensitive member becomes flat, and the image forming is very difficult. It becomes unstable. In particular, in the image low-density portion, the potential on the photoreceptor becomes an intermediate potential and the granularity is poor, and the density tends to fluctuate.

An object of the present invention is to provide an image forming method which is capable of forming an image in an isolated dot shape in an image low-density portion and obtaining a beautiful image in appearance, and which is excellent in image stability. And It is another object of the present invention to provide an image forming method which can form an image in a line shape in a middle and high density portion and can obtain a beautiful image, and has excellent image stability.

Another object of the present invention is to provide an image forming method which does not change the density or the color in forming a color image. According to a fourth aspect of the present invention, the arrangement of dots can be made inconspicuous in an image low-density portion where dots are arranged at a low period, and the dots are combined as the image density increases to increase the density based on a line. It is an object of the present invention to provide an image forming method which can perform smooth gradation expression.

It is another object of the present invention to provide an image forming method capable of forming an image in which the texture of dots arranged in a low-density portion of an image or combined dots is inconspicuous. It is another object of the present invention to provide an image forming method capable of suppressing banding and stably reproducing an image low density portion.

Another object of the present invention is to provide an image forming method capable of forming a high quality image. An object of the invention according to claim 8 is to provide an image forming method capable of forming a stable image suitable for an electrophotographic system. It is an object of the present invention to provide an image forming apparatus which can form an image in an isolated dot shape in an image low-density portion and obtain a beautiful image, and has excellent image stability.

An object of the present invention is to provide an image forming apparatus which is capable of forming an image in a line pattern in a middle and high density part, and which can obtain an image which is beautiful in appearance, and which is excellent in image stability. I do. An object of the invention according to claim 11 is to provide an image forming apparatus in which there is no change in density or color.

According to a twelfth aspect of the present invention, the arrangement of dots can be made inconspicuous in a low-density portion of an image in which dots are arranged at a low period. It is an object of the present invention to provide an image forming apparatus that can increase the number of images and can perform smooth gradation expression. A further object of the present invention is to provide an image forming apparatus capable of forming an image in which the texture of dots arranged in an image low-density portion or a combined dot is inconspicuous.

It is another object of the present invention to provide an image forming apparatus capable of suppressing banding and stably reproducing a low density portion of an image. Claim 15
It is an object of the present invention to provide an image forming apparatus capable of forming a high-quality image. A further object of the present invention is to provide an image forming apparatus capable of forming a stable image suitable for an electrophotographic system.

[0018]

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 of the pixel according to a result of the reference. An image in which dots are arranged is formed.

The invention according to a second aspect is characterized in that the image data of a plurality of pixels is referred to, density data is distributed to specific positions of the pixels based on the reference result, and a line image is formed.

According to a third aspect of the present invention, a density is generated from a first specific position of a first specific pixel based on image data of a plurality of adjacent pixels, and a second density is generated based on image data of a next plurality of adjacent pixels. A density is generated from a second specific position of the specific pixel, and a total sum of image data of a plurality of adjacent pixels is held.

According to a fourth aspect of the present invention, image data of a plurality of adjacent pixels is referred to, density data is distributed to specific positions of the plurality of adjacent pixels based on a result of the reference, and a low-density portion of an image maps dots. It is characterized in that the image is arranged uniformly in the vertical and horizontal directions, and as the image density increases, the dots are combined with the dots and arranged to form a linear image.

The invention according to claim 5 refers to image data of a plurality of adjacent pixels, and generates a density from a first specific position of the plurality of adjacent pixels based on a result of the reference.
Referring to the image data of the next adjacent pixels, and generating a density from a second specific position different from the first specific position of the next adjacent pixels according to the reference result;
The image low-density part is characterized by forming dots arranged at approximately 45 ° or a combined dot image.

The invention according to claim 6 refers to image data of a plurality of adjacent pixels, and generates a density from a first specific position of the plurality of adjacent pixels based on a result of the reference.
Referring to the image data of the next adjacent pixels, and generating a density from a second specific position different from the first specific position of the next adjacent pixels according to the reference result;
The low-density portions form dots or combined dots at approximately 45 °, and the lowest-density portions are arranged at intervals of three or more dots in the sub-scanning direction. The arrangement is such that the interval in the scanning direction is narrowed.

According to a seventh aspect of the present invention, there is provided an image forming method for referring to image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels based on the reference result. The low density portion is formed at an image spatial frequency of 200 lpi or more.

An eighth aspect of the present invention is an image forming method for referring to image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels based on the reference result. The low-density portion distributes image data of eight or more adjacent dots as image data of the plurality of adjacent pixels to a single position corresponding to a specific one dot as the specific position.

According to a ninth aspect of the present invention, there is provided a means for referring to image data of a plurality of pixels and distributing density data to a specific position of the pixel based on the reference result, thereby forming an image in which dots are arranged. is there.

According to a tenth aspect of the present invention, there is provided a means for referring to image data of a plurality of pixels and distributing density data to a specific position of the pixel based on a result of the reference to form a linear image.

According to an eleventh aspect of the present invention, a density is generated from a first specific position of a first specific pixel based on image data of a plurality of adjacent pixels, and a second density is generated based on image data of a next plurality of adjacent pixels. And a means for generating a density from a second specific position of the specific pixel and holding a total sum of image data of a plurality of adjacent pixels.

According to a twelfth aspect of the present invention, the image data of a plurality of adjacent pixels is referred to, density data is distributed to specific positions of the plurality of adjacent pixels based on the reference result, and the low-density portion of the image forms dots. Means are provided for arranging the dots uniformly in the vertical and horizontal directions and combining the dots with the dots as the image density increases to form a line image.

According to a thirteenth aspect of the present invention, image data of a plurality of adjacent pixels is referred to, a density is generated from a first specific position of the plurality of adjacent pixels based on a result of the reference, and a next plurality of pixels are generated. Means for generating image density from a second specific position different from the first specific position of the next plurality of adjacent pixels based on the reference result of the image data of the pixel of Is for forming an image in the form of dots arranged at approximately 45 ° or a combined dot.

According to a fourteenth aspect of the present invention, image data of a plurality of adjacent pixels is referred to, a density is generated from a first specific position of the plurality of adjacent pixels based on a result of the reference, and a next plurality of pixels are generated. Means for generating image density from a second specific position different from the first specific position of the next plurality of adjacent pixels based on the reference result of the image data of the pixel of Forms an image in the form of dots arranged at approximately 45 ° or a combined dot, the lowest density portions are arranged at intervals of 3 dots or more in the sub-scanning direction, and the dots are arranged in the sub-scanning direction as the image density increases. Are arranged to be narrow.

The invention according to claim 15 is an image forming apparatus comprising means for referring to image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels based on the result of the reference. The low-density part of the image is 20
It is formed at an image spatial frequency of 0 lpi or more.

[0033] The invention according to claim 16 is an image forming apparatus comprising means for referring to image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels based on the reference result. The image low-density portion distributes image data of eight or more adjacent dots as image data of the plurality of adjacent pixels to a single position corresponding to a specific one dot as the specific position.

[0034]

FIG. 7 schematically shows an embodiment of the present invention. This embodiment is an embodiment of the invention according to claims 1 to 16, and is an embodiment of a color image forming apparatus including a digital color copying machine. First, the image formation of this embodiment will be described. 7, reference numeral 100 denotes a laser printer which is an electrophotographic image forming unit;
Denotes an automatic document feeder (hereinafter referred to as ADF), 300 denotes an operation board, 400 denotes an image scanner as an image reading unit, and 500 denotes an external sensor.

In the image scanner 400, a moving body on which a lighting 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 the 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 composed of mutually different one-dimensional charge-coupled devices (CCD), and is photoelectrically converted. 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 many originals are stacked on the original mounting 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, and by combining the detection states of these sensors,
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 document in the sub-scanning direction, that is, the length of the document, by measuring the time that the document passes through the document 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, a light writing unit 3, a developing unit 4, a transfer drum 2, a cleaning unit 6, and the like as charging means are arranged. I have. The optical writing unit 3 includes a semiconductor laser (laser diode: L
D), the laser light emitted from this 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-gradation image signal is synchronized with the laser beam deflection scanning of the rotary polygon mirror 3b. The light emission of the LD is controlled such that the laser beam is scanned in the main scanning direction from the predetermined light writing start position on the body drum 1. The photoreceptor drum 1 is uniformly charged to a high potential in advance by corona discharge by a charging charger 5 as charging means, and is then exposed to laser light from a light writing unit 3 as light writing means 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 an electrostatic latent image on the photosensitive drum 1 into an image of each color of magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), yellow (hereinafter referred to as Y), and black (hereinafter referred to as Bk). Are provided with four sets of developing devices 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, fed 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 accompanying 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 with 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, and 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 superposed 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 sheet tray, the sheet is discharged to the sheet discharge tray 10.

The image forming operation of the present embodiment has been described above. However, the color image forming apparatus according to the present invention is not limited to the above-described 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 50 composed of a microcomputer.
Is controlled by 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 that is the basis of the scanning timing in the present embodiment is synchronized with the scanning start timing of the laser light by the rotation of the rotary polygon mirror 3b of the laser printer 100.

The image scanner 400 A / D converts the image signals of each color of R, G, and B obtained by reading the original and outputs them as 8-bit color image information. This image information is output to the laser printer 100 after undergoing various processes in the image processing unit. The image processing unit includes a scanner γ correction unit 71, an RGB smoothing filter 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 linear reflectance R, G, and B color image signals from the image scanner 400 into linear density R, G, and 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 U 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 emphasizing filter 76 includes 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,
The image signal of each color Bk is corrected including gradation processing.

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 the respective colors M, C, and Bk. The halftone processing described later in the present embodiment is executed by the gradation processing unit 78.

Further, R,
The G and B color image signals are supplied to an image area separating 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
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. Further, the system controller 50 controls the laser printer 10 including the LD multi-level light writing operation.
0 is controlled.

Next, the LD multi-level modulation of this embodiment will be described. Pulse width modulation (PWM) and light intensity modulation (PM) as LD multi-level modulation schemes that output 1 dot multi-level output
There is a method. FIGS. 3A and 3B show a light waveform and a dot pattern in an example of a light intensity modulation method and an example of a pulse width modulation method. Hereinafter, these modulation methods will be described.

Light intensity modulation method Half tone recording (half tone image formation) using an intermediate exposure area
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. 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 use of the intermediate exposure area is less 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) method and the light intensity modulation (PM)
It employs a pulse-width-intensity mixed-modulation method that combines this method and that. 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.
(A) Interpolation by light intensity modulation as shown in (b), for example, with a pulse width setting value of 8 values and a light intensity modulation setting value of 32 values, a modulation degree equivalent to 8 bits (2 ⁸ = 256 gradations) Can be obtained.

In this system, since the number of pulse width modulation stages is small, the pulse width can be set digitally, 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 a 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 a 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, an example of an LD driving method of a multi-level optical writing system by a pulse width intensity mixed modulation system combining pulse width modulation (PWM) and light intensity modulation (PM) in the present embodiment will be described. 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 the present embodiment, m = 3, pulse width modulation (PWM) is performed in 8 (= 2 ＾ m = 2 ³ ) steps, and light intensity modulation (PM) is 32 (= With 2 ＾ (nm) = 2 ⁵ ) stages, 2 組合 せ n = 2 ⁸ = 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.

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).

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.

FIG. 40 shows a part of the processing flow of the image processing unit in this embodiment. The image processing unit
A common γ correction is performed on the input image data, and a characteristic is determined based on the magnitude of a value (maximum level difference) obtained by subtracting the minimum value from the maximum value of the data in one block for the data after the γ conversion,
When each value is large, the edge degree is high (that is, resolution priority), when the value is small, the edge degree is low (that is, gradation and highlight reproduction priority). It is classified into three levels called levels. Then, the image processing unit performs halftone processing suitable for each of these three stages. The image processing unit performs one-dot multi-value processing for resolution priority and performs multi-value modulation of dot addition and concentration in a block unit for tone priority.

That is, the image processing unit performs common γ correction on the input image data, and
Four adjacent dots of 2 dots in the main scanning direction × 2 dots in the sub-scanning direction are read. The image processing unit adds the read density data of four adjacent dots. Then, if the addition result is 254 or less, the image processing unit sets the read density data of adjacent 2 dots × 2 dots as density data of one pixel (one block) (see the left flow in FIG. 40). When the addition result is 255 or more, the image processing unit thereafter sets the density data of two dots in the main scanning direction as density data of one pixel,
The read density data of adjacent 2 dots × 2 dots is distributed to two blocks (refer to the flow on the right side in FIG. 40).

Next, the image processing unit calculates the maximum value and the minimum value in the dot data in one block. next,
Here, the maximum value of the image processing unit is 32 (specified value).
In the following cases, the block gives priority to highlight reproduction, and performs halftone processing of multi-level modulation of dot addition / concentration in a block unit as described later. Next, the image processing unit calculates the difference between the previously calculated maximum value and minimum value (maximum level difference). If the difference is equal to or less than 96 (threshold 1), the block has a high edge degree, 1 for resolution priority
Perform dot multi-value processing.

If the maximum level difference is equal to or less than 48 (threshold 2), the image processing unit regards the block as a non-edge portion and gives priority to gradation, and performs multi-level dot addition / concentration within a block unit. Performs halftone processing for modulation. Here, if a method of performing addition and phase control, which will be described later, is adopted for multi-level modulation of dot addition / concentration, it is more effective in highlight reproduction and gradation. Here, for example, a method described later is adopted. If the maximum level difference is (48 <the above difference <96), the image processing unit regards the degree of edge as an intermediate level and performs density distribution, that is, dot concentration according to the degree of the edge. The dot concentration is
As shown in FIG. 41, the percentage of level concentration is reduced by disrespecting the maximum level difference.

In the present embodiment, since the gamma correction is first performed by the gamma characteristic having the common characteristic regardless of the type of the halftone processing, the characteristic is determined from the maximum level difference in the block after the gamma conversion. Is determined for the actual output data value, and a characteristic corresponding to the level can be more reliably extracted by each halftone.

Next, a control circuit for performing addition and phase control on image data in this embodiment will be described.
In the present embodiment, in gradation processing of image data, image data of two dots adjacent in the main scanning direction or the sub-scanning direction or image data of four dots adjacent in the main scanning direction and the sub-scanning direction are added, and the addition result is calculated. Based on this, the dots are reproduced sequentially from a predetermined specific pixel. 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 includes six methods 1 to 6 described below.
And the image data from the printer γ correction unit 77 is processed as described later.

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 the image data of each of Y, M, C, and Bk, which is the 8-bit 256-gradation 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). Further, the image data A is delayed by one line by the line memory 601 to become image data C, and is sequentially latched by one dot by one dot by the latch circuit 603 composed of DF / F, thereby being delayed by one dot. To become image data D.

The 8-bit data C and D of two dots adjacent to each other in the main scanning direction of the previous line are input to the adding circuit 604. The adding 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 in the sub-scanning direction. The addition of the two dot data A and C is performed. 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 that saturates the dot, and the addition value of the four dot data A, B, C, and D is compared with the two dot data A in the main scanning direction. , 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.

With the above processing, 4-dot addition and 2-dot addition
FIG. 8 shows a state of data transition due to data addition. Method 6
In the low density part of the image as shown in FIG.
Two dots adjacent in the main scanning direction and two dots adjacent in the sub-scanning direction
D of two dots₁~ D_FourBy the adder circuit 604
Since the calculated value is smaller than the threshold value 1, the added value is represented by a dot D ₁
Data. Also, as shown in FIG.
In the density portion, data d of two dots adjacent in the main scanning direction
₁, D_TwoIs greater than or equal to the threshold value 1
Therefore, the added value is represented by a dot D₁And the saturation value of the data
And the rest is dot D₁Data. (A) Add two-dot image data adjacent in the sub-scanning direction
Method (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.
8 sets the dot formation matrix as shown in FIG.
And sequentially from the smaller value of the dot formation matrix
Optical writing pulse according to the added value from the control circuit.
Generated by pulse width intensity mixed modulation of image data
Perform modulation.

At this time, the gradation processing section 78 sets the pulse to 1
In one dot, the pulse is divided (allocated) into half pulses, and in one dot, the PWM pulse becomes full (50% duty) according to 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 on image data by a density generation algorithm for optical writing expressed by the following equation. Here, in the following equation, d ₁ and d ₂ are image data (8-bit data) of two adjacent dots in the sub-scanning direction before processing.
D ₁ and D ₂ are image data (8-bit data) after processing two adjacent dots in the sub-scanning direction.

When 0 ≦ d ₁ + d ₂ ≦ 127, D ₁ = d ₁ + d ₂ ,
When D ₂ = 0 128 ≦ d ₁ + d ₂ ≦ 254 D ₁ = 127, D ₂
= D ₁ + d ₂ -127 When 255 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ −1
27, when D ₂ = 127 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₁
= D ₁ + d ₂ -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 specifically described. 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.

[0081] When the dot formation matrix shown in FIG. 10 to represent a minimum density unit is shown in Figure 11, the gradation processing unit 78, the right phase in the dot D _1, pulse the left phase in the dot D ₁ ' 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 C (d ₁ , d ₂ ) 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 (d ₁ , d ₂ )).

Next, details of dot formation by the method 1 will be described with reference to FIGS. Density to 1/8 (isolated 2 dots) The gradation processing unit 78 determines whether the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) is up to 1/8. 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
Is generated with a pulse width corresponding to the sum of the densities (the sum of the image data A and C (d ₁ , d ₂ ) 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 (d ₁ , d ₂ ) from the control circuit) is the pulse width intensity mixed modulation of the image data as described above. This is the pulse width of the pulse modulated by the method. Density １ ／ (isolated two dots) The gradation processing unit 78 determines that the added value of the density (the added value of the image data A, C (d ₁ , d ₂ ) from the control circuit) is ８ to 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% duty, the pulse width is increased according to the added value of the density (the added value of the image data A, C (d ₁ , d ₂ ) from the control circuit). In this case, the pulse width is set to the sum of the densities (image data A, C (d ₁ , d ₂ ) 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: が (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 (d ₁ , d ₂ ) from the control circuit) is １ ／ to 3 / 8
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, C (addition value of d ₁ , d ₂ )). 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 (d ₁ , d ₂ ) from the control circuit) is 3/8 to 1 / 2
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% duty, the pulse width is increased according to the added value of the density (the added value of the image data A, C (d ₁ , d ₂ ) 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 C (d ₁ , d ₂ ) from the control circuit) to ２〜 to ／.
In the case of (1), as shown in FIG. 13 (A), the pulse width of one portion of the dot formation matrix is determined by adding the density addition value (image data A, C (d ₁ , d ₂ ) from the control circuit). value)
3 of the dot forming matrix so as to increase according to
Generates a pulse combined with the part. Density to が The gradation processing unit 78 calculates the sum of the densities (the sum of the image data A and C (d ₁ , d ₂ ) from the control circuit) from ／ to ／.
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% duty, the pulse width is increased according to the added value of the density (the added value of the image data A, C (d ₁ , d ₂ ) from the control circuit). Density to 7/8 The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) is 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 adding the density addition value (image data A, C (d ₁ , d ₂ ) from the control circuit). value)
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 calculates the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) from 7/8 to 1/1.
In the case of (1), the pulse width is added to the added value of the density (image data A and C from the control circuit) until the pulse combined with the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(D ₁ , d ₂ ).

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 one line. The write pulse generated by the 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 isolated dots and vertical lines can be grown in gradation. Becomes 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 system 1, 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.
In the right phase in the dot D _1, it generates pulses in the left phase in the dot D ₁ ', dot formation matrix 1
Are generated in accordance with the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) 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, C (d ₁ ,
Pulses are generated in the second and subsequent portions of the dot formation matrix in accordance with (addition value of d ₂ )).

Next, details of the dot formation by the method 2 will be described. Concentration to 1/8 (isolated one dot) gradation processing unit 78, the sum of concentration when (image data A from the control circuit, C (d _1, the sum of d ₂₎₎ is up to 1/8 As shown in FIG. 16A, 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
Is generated with a pulse width corresponding to the sum of the densities (the sum of the image data A and C (d ₁ , d ₂ ) from the control circuit). Concentration to 1/4 (isolated one dot) gradation processing unit 78, the sum of concentration (image data A from the control circuit, C (d _1, d ₂ sum of)) is 1 / 8-1 / 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% duty, the pulse width is increased according to the added value of the density (the added value of the image data A, C (d ₁ , d ₂ ) from the control circuit). Density: が (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 (d ₁ , d ₂ ) from the control circuit) is １ ／ to 3 / 8
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, C (added value of d ₁ , d ₂ )). 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 (d ₁ , d ₂ ) from the control circuit) is 3/8 to 1 / 2
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% duty, the pulse width is increased in accordance with the added value of the density of the pulse (the added value of the image data A, C (d ₁ , d ₂ ) 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 C (d ₁ , d ₂ ) 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 (d ₁ , d ₂ )). Density to が The gradation processing unit 78 calculates the sum of the densities (the sum of the image data A and C (d ₁ , d ₂ ) from the control circuit) from ／ to ／.
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% duty, the pulse width is increased according to the added value of the density (the added value of the image data A, C (d ₁ , d ₂ ) from the control circuit). Density to 7/8 The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) is 3/4 to 7/8.
In the case of (1), as shown in FIG. 17 (C), the pulse width of the 2 portion of the dot formation matrix is determined by adding the density addition value (image data A, C (d ₁ , d ₂ ) from the control circuit). value)
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 calculates the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) from 7/8 to 1/1.
In the case of (1), the pulse width is added to the added value of the density (image data A and C from the control circuit) until the pulse combined with the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(D ₁ , d ₂ ).

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 one 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 system 1, the control circuit shown in FIG. 2 has a configuration in which the comparison / distribution / phase control circuit 605 outputs only the addition 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.
In the right phase in the dot D _1, 1 dot D to generate pulses in the left phase in ₁ ", similarly to scheme 2 Figure 18
Are generated in accordance with the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) 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, C (d ₁ ,
Pulses are generated in the second and subsequent portions of the dot formation matrix in accordance with (addition value of d ₂ )).

Next, 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 5/8 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) to ２〜 to ／.
In the case of (1), as shown in FIG. 20A, the pulse widths of the portions 1 and 2 of the dot formation matrix are changed to the sum of the densities (the image data A, C (d ₁ , d ₂ ) from the control circuit). A pulse is generated that is coupled to the three parts of the dot forming matrix so as to increase the value in accordance with the sum. Density to が The gradation processing unit 78 calculates the sum of the densities (the sum of the image data A and C (d ₁ , d ₂ ) from the control circuit) from ／ to ／.
In the case of (1), as shown in FIG. 20 (B), the pulse combined with the portion 3 of the dot formation matrix is the FULL 5
Until the duty becomes 0% duty, the pulse width is increased in accordance with the added value of the density (the added value of the image data A, C (d ₁ , d ₂ ) from the control circuit). Density to 7/8 The gradation processing unit 78 determines that the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) is 3/4 to 7/8.
In the case of, the pulse widths of the portions 1 and 2 of the dot formation matrix are increased according to the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit). , Generate a pulse coupled to the four portions of the dot formation 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 C (d ₁ , d ₂ ) from the control circuit) from 7/8 to 1/1.
In the case of (1), the pulse width is added to the added value of the density (image data A and C from the control circuit) until the pulse combined with the portion 4 of the dot formation matrix becomes 50% duty of FULL.
(D ₁ , d ₂ ).

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 one 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 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 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 and C (d ₁ ,
The data is generated according to the sum of d ₂ ) 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
The pulse is divided into ２ or パ ル ス pulses within the dot, and when the pulse becomes 50% duty or 25% duty according to the above-mentioned added value, the pulse 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 /
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 ≦ d ₁ + d ₂ ≦ 127, D ₁ = d ₁ + d ₂ ,
When D ₂ = 0 128 ≦ d ₁ + d ₂ ≦ 190 D ₁ = 127, D ₂
= D ₁ + d ₂ -127 When 191 ≦ d ₁ + d ₂ ≦ 254 D ₁ = d ₁ + d ₂ -6
3, D ₂ = 63 Next, details of 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 5/8 The gradation processing unit 78 sets the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) to ２〜 to ／.
In the case of (1), as shown in FIG. 20A, the pulse widths of the portions 1 and 2 of the dot formation matrix are changed to the sum of the densities (the image data A, C (d ₁ , d ₂ ) from the control circuit). A pulse is generated that is coupled to the three parts of the dot forming matrix so as to increase the value in accordance with the sum. When the density is ４/4 255 ≦ d ₁ + d ₂ ≦ 318, D ₁ = 191, D ₂
= D ₁ + d ₂ −191 When 319 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ −1
27, D ₂ = 127 When 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₂
= D ₁ + d ₂ −255 Hereinafter, the method 4 will be specifically described. In the method 4, in the control circuit shown in FIG. 2, the comparison / distribution / phase control circuit 605 is adjacent to the addition circuit 604 in the sub-scanning direction. A control circuit configured to output only the added value of the two-dot data A and C as it is is used. The chromatic data processing unit 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.

[0095] In scheme 4, when representing a dot formation matrix shown in FIG. 21 with a minimum density unit is shown in Figure 22, chromatic data processing unit, in the right phase in the dot D _1, in the dot D ₁ " A pulse is generated in the left phase, and the pulse combined with one part of the dot forming matrix is added to the density in the same manner as in method 3 (addition value of image data A, C (d ₁ , d ₂ ) from the control circuit) The chromatic color data processing unit performs a dot formation matrix in accordance with the added value of the density (the added value of the image data A and C (d ₁ , d ₂ ) from the control circuit) in the same manner. The pulse is generated in the part after 2 of the above.

Next, details of the dot formation by the method 4 will be described.
I will tell. Density ~ 1/8 (isolated one dot) to density ~ 3/8
(Up to 300 lines per line)
is there. Density-1/2 The chromatic color data processing unit calculates the sum of the
Image data A, C (d ₁, D_Two) Is 3/8 to 1
In the case of / 2, as shown in FIG.
25% du pulse coupled to the second part of the matrix
Transition to dot formation matrix 3 when ty
And a pallet attached to the third part of the dot forming matrix.
Part of the dot formation matrix at 25% duty
Add the pulse width to the density until it becomes 75% by combining with
Value (image data A, C (d₁, D_Two)
Calculated value). In addition, the matrix
If the boxes are arranged in a staggered pattern (dot formation matrix
If you replace 1 and 2 in the
The positions of boxes 3 and 4 are switched alternately,
You can make it less noticeable more randomly than Method 3.
You. Density-5/8 The chromatic color data processing unit
Image data A, C (d ₁, D_Two) Is 1/2 to 5
In the case of / 8, as shown in FIG.
The second part of the matrix is 50% duty of FULL.
The pulse width until the added value of the density (the image from the control circuit)
Image data A, C (d₁, D_Two) Increases according to the added value)
Let 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 one line. The write pulse generated by the method 4 is output to the optical writing unit 3 of the printer 100 as an optical writing signal, and the LD in the optical writing unit 3 outputs the optical writing signal (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 the size of one pixel (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 minimum density units, it becomes as shown in FIG. 26. The chromatic data processing unit sets the dot formation matrix as shown in FIG. 25 and sets the numerical value of the dot formation matrix. , A light writing pulse is sequentially generated in accordance with the added value of the image data A and B (d ₁ , d ₂ ) from the control circuit, and the image data is modulated by the pulse width intensity mixed modulation method. .

At this time, the chromatic color data processing section divides the pulse into half pulses within one dot, and this pulse becomes a full pulse according to the added value of the image data A, B (d ₁ , d ₂ ) from the control circuit. At (50% duty), the process proceeds to the next larger number in the dot formation matrix, and the next pulse is generated in the same manner. At this time, the chromatic data processing unit controls the phase of the pulse by switching the right phase / left phase (right mode / left mode) of the pulse by E / O in the main scanning direction, and controls the phase of the pulse in the same direction of the numerical value of the dot formation matrix. To combine the pulses. The chromatic color data processing unit performs gradation processing of image data using a density generation algorithm for optical writing expressed by the following equation.

When 0 ≦ d ₁ + d ₂ ≦ 127, D ₁ = d ₁ + d ₂ ,
When D ₂ = 0 128 ≦ d ₁ + d ₂ ≦ 254 D ₁ = 127, D ₂
= D ₁ + d ₂ -127 When 255 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ −1
27, D ₂ = 127 When 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₂
= D ₁ + d ₂ −255 Hereinafter, the method 5 will be described in detail. The chromatic data processing unit processes image data by the following dot formation algorithm. 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 (d ₁ , d ₂ ), a PWM pulse of the next number in the dot formation matrix is generated.

[0102] When the dot formation matrix as shown in FIG. 25 to represent a minimum density unit is shown in Figure 26, chromatic data processing unit, in the right phase in the dot D _1, left phase in the dot D ₁ ' To generate a pulse, and combine the pulse combined with one portion of the dot formation matrix with the added value of the density (image data A, B (d ₁ , d ₂ ) from the control circuit)
). The chromatic color data processing unit similarly applies a pulse to 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 B (d ₁ , d ₂ ) from the control circuit). Generate.

Next, details of the dot formation by the method 5 will be described.
I will tell. Density ~ 1/8 (Isolated 1 dot) The chromatic color data processing unit
Image data A, B (d ₁, D_Two) Up to 1/8
In such a case, as shown in FIG.
Dot formation by aligning several pixels to the right and even pixels to the left
Add pulse combined with one part of matrix to density
Value (image data A, B (d₁, D_Two)
(Calculated value). Density to 1/4 (isolated one dot) The chromatic color data processing unit calculates
Image data A, B (d ₁, D_Two) Is 1/8 to 1
In the case of / 4, as shown in FIG.
The pulse coupled to one part of the matrix is FULL
The pulse width is added to the density until the 50% duty becomes
(Image data A, B (d₁, D_Two) Addition
Value). Density ~ 3/8 (300 lines per line) The chromatic color data processing unit
Image data A, B (d ₁, D_Two) Is 1/4 to 3
In the case of / 8, as shown in FIG.
Of the matrix connected to the two parts from the outside of the pixel of the matrix
Is added to the density (image data A and B from the control circuit).
(D₁, D_Two) With a pulse width corresponding to
You. Density １ ／ (300 lines per line) The chromatic color data processing unit
Image data A, B (d ₁, D_Two) Is 3/8 to 1
In the case of / 2, as shown in FIG.
The pulse coupled to the second part of the matrix is FULL
The pulse width is added to the density until the 50% duty becomes
(Image data A, B (d₁, D_Two) Addition
Value). Density-5/8 The chromatic color data processing unit
Image data A, B (d ₁, D_Two) Is 1/2 to 5
In the case of / 8, as shown in FIG.
The pulse width of one part of the matrix is the sum of the concentrations
(Image data A, B (d₁, D_Two) Addition
Value), the dot formation matrix
Generate a pulse coupled to the third part of the pulse. Density to 3/4 chromatic color data processing unit
Image data A, B (d ₁, D_Two) Is 5/8 to 3
In the case of / 4, as shown in FIG.
The pulse coupled to the third part of the matrix is FULL
The pulse width is added to the density until the 50% duty becomes
(Image data A, B (d₁, D_Two) Addition
Value). Density to 7/8 chromatic color data processing unit
Image data A, B (d ₁, D_Two) Is 3/4 to 7
In the case of / 8, as shown in FIG.
The pulse width of the second part of the matrix is added to the density
(Image data A, B (d₁, D_Two) Addition
Dot formation matrix so that it increases according to
Generate a pulse coupled to the fourth portion of the pulse. Density １ ／ 1/1 The chromatic color data processing unit
Image data A, B (d ₁, D_Two) Is 7/8 to 1
In the case of / 1, the dot formation matrix 4
Until the combined pulse becomes 50% duty of FULL
Add the pulse width to the density addition value (image data from the control circuit
A, B (d₁, D_Two)).

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 one 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 the LD driving unit, and multi-valued light writing of an image on the photosensitive drum 1 is sequentially performed for each color. In this method 5, the highlight portion can be regularly reproduced by staggered isolated dots, 300 lines per line (600 dpi) can be obtained in the middle density portion, and the gradation is linear with the growth type of isolated dots and vertical lines. The stability can be secured by increasing the potential concentration and the saturation region, and it is strong in 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.

(A) When the density is 1/4 or less One dot size is the size shown in FIG. 29A, and one pixel size (minimum density unit) is the four dot size 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 4-dot data A, B, C, D of the adder circuit 604.
The addition result of (d ₁ , d ₂ , d ₃ , d ₄ ) is compared with the threshold value 1 of the data that saturates the dots, and the above 4-dot data A,
The added value of B, C, and D is switched and output. The chromatic color data processing unit sets a dot formation matrix as shown in FIG. 30 and sequentially applies pulses in the order of smaller values of the dot formation matrix (addition values of density (image data A, B, C , D (d ₁ , d ₂ , d ₃ , d ₄ ))
Are generated with a pulse width corresponding to.

At this time, the chromatic data processing section divides the pulse into half pulses within one dot, and this pulse is used as the added value of the density (image data A, B, C, D from the control circuit).
(D ₁ , d ₂ , d ₃ , d ₄ ) according to the full (50
(% Duty), the same number in the dot formation matrix or the next larger number is formed, and the next pulse is generated in the same manner. At this time, the chromatic color data processing unit performs a right phase / left phase (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.

When the dot formation matrix as shown in FIG. 30 is expressed in minimum density units, it becomes as shown in FIG.
Chromatic data processing unit, the left phase in the dot D _1, generates pulses with the right phase in the dot D ₁ ', the sum of concentrations pulses attached to one portion of the dot formation matrix from (the control circuit Image data A, B,
C, D (added value of d ₁ , d ₂ , d ₃ , d ₄ )). The chromatic color data processing unit performs the same operation as described below for the added value of the density (image data A, B, C, D from the control circuit).
_{(D 1, d 2, d} 3, d 4) depending on the sum value) will generate a pulse 2 remainder of dot formation matrix.

The chromatic color data processing section performs gradation processing of image data by an optical writing density generation algorithm expressed by the following equation. When 0 ≦ d ₁ + d ₂ + d ₃ + d ₄ ≦ 127 D ₁ = d ₁
+ D ₂ + d ₃ + d ₄ , D ₂ = D ₃ = D ₄ = 0 When 128 ≦ d ₁ + d ₂ + d ₃ + d ₄ ≦ 254 D ₁ = 1
_{27, D 2 = d 1 +} d 2 + d 3 + d 4 -127, D 3 = D 4 =
0 Here, d ₁ , d ₂ , d ₃ , and d ₄ are image data (8-bit data) of four dots adjacent in the main scanning direction and the sub-scanning direction before processing, and D ₁ , D ₂ , D ₃ , D ₄ in the main scanning direction after processing is image data of four adjacent dots in the sub-scanning direction (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 the same as the size shown in FIG.
The size of one pixel (minimum density unit) is as shown in FIG.
2 dot size. Comparison / distribution / phase control circuit 6
05 is the 4-dot data A, B, C,
D (d₁, D_Two, D _Three, D_Four) To add dot saturation
Is compared with the threshold value 1 of the two-dot data A,
B (d₁, D_Two) Is switched and output.

[0109] When the dot formation matrix shown in FIG. 30 to represent a minimum density unit is shown in Figure 33, chromatic data processing unit, the left phase in the dot D _1, the pulse in the right phase in the dot D ₁ ' Is generated, and a pulse combined with the two portions 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 (d ₁ , d ₂ ) from the control circuit). Go. The chromatic data processing unit generates pulses for the three 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 (d ₁ , d ₂ ) from the control circuit). Let me do it.

The chromatic data processing unit performs gradation processing of image data by a density generation algorithm for optical writing expressed by the following equation. When d ₁ + d ₂ + d ₃ + d ₄ = 254 in the representation of one pixel size shown in FIG. 29B, D ₁ = D ₂ = 1
Since it is 27, by replacing the representation of a pixel size illustrated in FIG. 33, when _{d 1 + d 2 = 127,} D 1 = 127,
D ₂ = 0, and thereafter, when 128 ≦ d ₁ + d ₂ ≦ 254, D ₁ = d ₁ + d ₂ −1
27, when D ₂ = 127 255 ≦ d ₁ + d ₂ ≦ 382 D ₁ = d ₁ + d ₂ −1
27, D ₂ = 127 When 383 ≦ d ₁ + d ₂ ≦ 510 D ₁ = 255, D ₂ =
d ₁ + d ₂ -255.

Hereinafter, the method 6 will be specifically described. The chromatic data processing section 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, the 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 (added value of d ₁ , d ₂ , d ₃ , d ₄ )) is up to 1/16, the density data A, B, C, D (d
₁ , d ₂ , d ₃ , and d ₄ ) are added by an adder 604 and output via a comparison / distribution / phase control circuit 605, and the chromatic data processing unit outputs the upper pixel data as shown in FIG. Of 1
The isolated dot is generated with a pulse width corresponding to the added value of the density (the added value of the image data A, B, C, and D (d ₁ , d ₂ , d ₃ , d ₄ )).

At this time, the chromatic color data processing section sets 0 ≦ d
₁+ D_Two+ D_Three+ D_FourIf ≤127, D₁= D₁+ D_Two+ D_Three
+ D_Four, D_Two= D_Three= D_Four= 0 and 128 ≦ d₁+ D_Two+ D
_Three+ D_FourIf ≤254, D₁= 127, D_Two= D₁+ D_Two+
d_Three+ D_Four-127, D_Three= D _Four= 0. -2: Density to 1/8 (isolated one dot) Addition value of density (from comparison / distribution / phase control circuit 605)
Image data A, B, C, D (d₁, D_Two, D_Three, D_Four)
Calculated) is 1/16 to 1/8, the surrounding 4 dots
Density data A, B, C, D (d₁, D_Two, D_Three, D_Four)
Comparison / distribution / phase control circuit 6 which is added by the arithmetic circuit 604
05, and the chromatic data processing unit
As shown in (B), the upper part of the pixel is saturated (full 5).
Until the pulse width becomes 0% duty, add the pulse width to the density addition value (image data
A, B, C, D (d₁, D_Two, D_Three, D_Four)))
Increase accordingly.

At this time, the chromatic color data processing section sets 0 ≦ d
₁+ D_Two+ D_Three+ D_FourIf ≤127, D₁= D₁+ D_Two+ D_Three
+ D_Four, D_Two= D_Three= D_Four= 0 and 128 ≦ d₁+ D_Two+ D
_Three+ D_FourIf ≤254, D₁= 127, D_Two= D₁+ D_Two+
d_Three+ D_Four-127, D_Three= D _Four= 0. -1: density to 3/16 (isolated two dots) Addition value of density (from comparison / distribution / phase control circuit 605)
Image data A, B, C, D (d₁, D_Two, D_Three, D_Four)
Calculated) is 1/8 to 3/16, the surrounding 4 dots
Density data A, B, C, D (d₁, D_Two, D_Three, D_Four)
Comparison / distribution / phase control circuit 6 which is added by the arithmetic circuit 604
05, and the chromatic data processing unit
After the upper part of the pixel is saturated as shown in FIG.
A pulse is added to the lower part of the pixel at 1 (the image data
A, B, C, D (d₁, D_Two, D_Three, D_Four)))
Generate the remaining dots by generating them with the appropriate pulse width.
You.

At this time, the chromatic color data processing section sets 0 ≦ d
₁+ D_Two+ D_Three+ D_FourIf ≤127, D₁= D₁+ D_Two+ D_Three
+ D_Four, D_Two= D_Three= D_Four= 0 and 128 ≦ d₁+ D_Two+ D
_Three+ D_FourIf ≤254, D₁= 127, D₁= D₁+ D_Two+
d_Three+ D_Four-127, D_Three= D _Four= 0. -2: density to 2/8 (two isolated dots) Addition value of density (from comparison / distribution / phase control circuit 605)
Image data A, B, C, D (d₁, D_Two, D_Three, D_Four)
Calculated) is 3/16 to 2/8, the surrounding 4 dots
Density data A, B, C, D (d₁, D_Two, D_Three, D_Four)
Comparison / distribution / phase control circuit 6 which is added by the arithmetic circuit 604
05, and the chromatic data processing unit
As shown in (D), the lower part of the pixel is saturated (full 5).
Until the pulse width becomes 0% duty, add the pulse width to the added value
Image data A, B, C,
D (d₁, D_Two, D_Three, D_Four))
You.

The gradation processing unit 78 determines that the sum of the densities (the sum of the image data A and B (d ₁ , d ₂ ) from the control circuit) is 3
In the case of / 8 to ２, as shown in FIG.
Until the pulse coupled to the second part of the dot formation matrix becomes 50% duty of FULL, the pulse width is increased by the added value of density (image data A, B (d ₁ , d ₂ ) 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 B (d ₁ , d ₂ ) 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 forming matrix is calculated by adding the density value (addition value of image data A and B (d ₁ , d ₂ ) from the control circuit). 3) of the dot formation matrix so as to increase
Generates a pulse combined with the part. Concentration to 3/4 gradation processing unit 78, (the sum of the image data A from the control _{circuit, B (d 1, d 2} )) the sum of concentration of 5 / 8-3 / 4
In the case of (3), as shown in FIG. 35 (D), the pulse combined with the portion 3 of the dot formation matrix
Until the duty becomes 0%, the pulse width is increased in accordance with the added value of the density (the added value of the image data A and B (d ₁ , d ₂ ) 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 B (d ₁ , d ₂ ) from the control circuit) from 3/4 to 7/8.
In the case of, as shown in FIG. 36, the pulse width of the 2 portion of the dot formation matrix is determined according to the added value of the density (the added value of the image data A and B (d ₁ , d ₂ ) from the control circuit). To generate a pulse 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 (d ₁ , d ₂ ) 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, B
(D ₁ , d ₂ ).

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 one 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 to the method 5, the density of four dots is added in a highlight portion having a density of 1/4 or less, the isolated dots are arranged in a staggered manner, and in the highlight portion having a density of 1/4 or more, 2 dots are added. Since the dots are arranged in a staggered manner, the reproducibility of the highlight portion can be improved from a lower density.

In this embodiment, the gradation processing unit 78
Calculates the total value by adding the image data of two or four pixels adjacent to each other in the image low-density part, and distributes the total value to a specific position in the pixel based on the algorithm described above. This is combined in the form of dots at adjacent pixels.
(B), FIG. 16 (A) (B), FIG. 27 (A) (B), and FIG. 34 (A) (B), an image is formed in a shape in which isolated dots are dispersed. To obtain a uniform and beautiful image. Further, by concentrating the dot data at the specific position as described above, the stable area on the photosensitive member is increased, and the image stability is excellent. 12 (B), FIG. 16 (B), FIG. 27 (B), and FIG. 34 (B), the isolated dot data is the saturation density data for one dot, and a particularly stable state is secured.

As described above, this embodiment includes the gradation processing section 78 as means for referring to the image data of a plurality of pixels and distributing density data to a specific position of the pixel based on the reference result. Because it forms an array of images,
By a simple calculation, the image can be formed in the form of isolated dots in the image low density portion, and a beautiful image can be obtained.
In addition, since dot data is concentrated at a specific position, image stability is excellent.

In this embodiment, the gradation processing unit 78
Calculates the total value by adding the image data of four pixels or two pixels adjacent to each other in the middle and high density portions of the image,
The total value is distributed so as to be concentrated at a specific position in the pixel based on the above-described algorithm, and is combined in a dot shape with an adjacent pixel, so that a high density portion in the image is represented by FIG. In this manner, image formation is performed in a line. This means that the writing density is 600 dpi, and the number of lines is one in one line cycle, and an even and beautiful image can be obtained. In addition, by forming the line image by concentrating the dot data at the position on the straight line as described above, the stable potential area on the photosensitive member is increased, and the image stability is excellent. Furthermore, by forming the line-shaped image into a continuous line shape following the sub-scanning direction, banding due to a position change in the sub-scanning direction during image formation is less likely to occur.

As described above, this embodiment includes the gradation processing section 78 as a means for referencing the image data of a plurality of pixels and distributing density data to a specific position of the pixel based on the reference result. Since an image is formed, the image can be formed in a line pattern in a medium-high density portion with a line-like tone by a simple calculation, and a beautiful image can be obtained. Further, by concentrating the dot data at a specific position, the image stability becomes excellent. Further, by forming the line-shaped image into a continuous line shape following the sub-scanning direction, it is possible to reduce the occurrence of banding due to a position change in the sub-scanning direction during image formation.

In this embodiment, the gradation processing unit 78
Generates the density from a specific pixel by adding the image data of a plurality of adjacent pixels, and holds the total value of the image data of the plurality of adjacent pixels by adding and distributing the image data of the plurality of adjacent pixels. Image data can be rearranged in each dot in a state where the image is formed, and in an electrophotographic image forming system, particularly in a highlight portion, a stable image can be formed by concentrating the density on a specific dot, and also in the pixel. Can be maintained. Therefore, a reproduction shift due to a density shift of a minute portion in a pixel does not occur.

As described above, in this embodiment, the density is generated from the first specific position of the first specific pixel by the image data of the plurality of adjacent pixels, and the density is generated by the image data of the next plurality of adjacent pixels. Since a gradation processing unit 78 is provided as means for generating the density from the second specific position of the second specific pixel and holding the sum total of the image data of a plurality of adjacent pixels, the image density of the pixel is converted to the original data. Can be held at the same value as that of the above, without changing the density or changing the color especially in color image formation, and preventing the line from thinning or disappearing with data of one dot line or less. .

In this embodiment, the gradation processing unit 78
When the method 2 is used, image data is distributed to specific positions of a plurality of adjacent pixels as shown in FIGS. 16A and 16B, and dots are uniformly arranged in the vertical and horizontal directions in the image low density portion. And when the method 6 is used, FIGS.
As shown in (1), image data is distributed to specific positions of a plurality of adjacent pixels, and dots are arranged uniformly in the vertical and horizontal directions in the image low density portion. Then, as the image density increases, the dots are combined and rearranged as shown in FIGS. 34 (C) and (d). Further, as the image density increases, the dots are combined with the combined dots and arranged. FIG.
(C) As shown in (D) and FIGS. 35 (A) and (B), a linear image is formed. Therefore, as the image density increases, there is no change in the gradation such that the dot once generated disappears, and the line shifts to the line tone so as to combine the dots, and the density increases smoothly.

As described above, this embodiment refers to the image data of a plurality of adjacent pixels, distributes the density data to specific positions of the plurality of adjacent pixels based on the reference result, Are arranged evenly in the horizontal and vertical directions,
As the image density increases, a gradation processing unit 78 as means for arranging dots in combination with the dots is provided to form a line-shaped image, so that the image low-density part arranges dots evenly in the vertical and horizontal directions, The low-density portion of the image in which dots are arranged at a low period makes the arrangement of the dots inconspicuous, and reduces the difference between the vertical and horizontal directions of the image, thereby reducing the difference depending on the image output direction and the viewing direction. Furthermore, as the image density increases, the dots are combined with the dots and the dots are positioned at four positions,
By forming a line-shaped image, as the image density increases, the density is increased based on the line so that dots are combined, so that there is no sense of incongruity due to changes in the texture of the image, the gradation expression is smooth, and the gradation is inverted. No such troubles occur.

In this embodiment, when the method 6 is used, isolated dots arranged in a 45 ° oblique direction as shown in FIG. 34A, or sub-scanning as shown in FIG. An image is formed by combining two dots in the direction. In particular, in a low density state as shown in FIG. 34A, there is no difference between the image forming direction in the vertical and horizontal directions. Further, the low-density portion becomes more conspicuous because the dots are discrete and have a low frequency, but the dot arrangement in the 45 ° direction is more difficult to recognize than the keynote in other directions.

As described above, in this embodiment, when the method 6 is used, the image data of a plurality of adjacent pixels is referred to, and the first result of the plurality of adjacent pixels is referred to based on the reference result.
The density is generated from the specific position of the pixel, and the image data of the next plurality of adjacent pixels are referred to. The reference result indicates that the second specific pixel is different from the first specific position of the next plurality of adjacent pixels.
The image low-density section forms dots arranged at approximately 45 ° or combined dot-shaped images, so that the area gradation of the image data can be reduced. When this is done, the dots and lines are arranged in the image low-density part at a low period. By arranging the dots arranged in the image low-density part or the combined dots at approximately 45 °, the dots arranged in the image low-density part are arranged. Alternatively, an image can be formed such that the texture of the combined dots is less noticeable.

In this embodiment, when the method 6 is used, as shown in FIGS. 34A and 34B, isolated dots having a high density are arranged at intervals of 3 dots in the sub-scanning direction. . When the density does not reach the saturation density of one dot, if an exposure beam (laser light emitted from the optical writing unit 3 to the photosensitive drum 1) is present adjacent to the sub-scanning direction, the exposure of the image forming system is performed. Banding is likely to occur due to beam pitch unevenness. Further, even when the density has reached the saturation density of one dot, banding is likely to occur if the density generation portion approaches in the sub-scanning direction.

FIG. 3 shows the mechanism of the banding occurrence.
7 to 39. FIG. 37 shows the exposure energy by the LD in the sub-scanning direction of the solid density portion due to the total exposure, and the latent image potential on the photoreceptor belt 1 is obtained from the total value thereof.
The latent image potential in this case has reached a saturation value, and FIG.
As shown in (B), the exposure amount is sufficiently higher than the visualization exposure amount. FIG. 38 shows the exposure energy of the low-density portion of the image and the potential of the latent image on the photosensitive belt 1. This is a state in which isolated dots having a concentrated concentration are arranged at intervals of three dots in the sub-scanning direction, as shown in FIG. In this state, dots are formed.

The exposure energy of the low-density portion of the image and the latent image potential on the photosensitive belt 1 shown in FIG. 39 are in a state where isolated dots are arranged at intervals of one dot in the sub-scanning direction.
Overlap of the foot of the exposure beam in the sub-scanning direction occurs, and a potential image peak on the latent image potential on the photosensitive belt 1 is generated between the exposure beams. In this state, if the interval between the exposure beams is reduced due to the uneven pitch of the exposure beam, banding that does not exist in the original data occurs at that portion.

In the state where isolated dots are arranged at intervals of one dot in the sub-scanning direction as shown in FIG. 38, even if the exposure amount of the dots is not saturated as shown in FIG. Since no overlapping occurs due to the uneven pitch of the exposure beam, banding does not occur. FIG.
When the dots are combined in the sub-scanning direction as the density increases as shown in FIGS. 4C and 4D, the preceding dot shown in FIG. 34B is in a sufficiently stable state. The potential of the latent image on the photoreceptor belt 1 is in a state in which another dot is combined with the stable dot portion.

In this case, the intermediate potential area of the latent image potential is reduced as compared with discrete formation of isolated dots not reaching the saturation light amount, and image formation is stabilized. Further, in the intermediate density portion, a linear image continues in the sub-scanning direction as shown in FIG. 35 (B), and even if the pitch unevenness of the exposure beam occurs, the line portion remains in the state shown in FIG. , And no banding occurs because the white portion is not exposed.

As described above, in this embodiment, when the method 6 is used, the image data of a plurality of adjacent pixels is referred to, and the first result of the plurality of adjacent pixels is referred to based on the reference result.
The density is generated from the specific position of the pixel, and the image data of the next plurality of adjacent pixels are referred to. The reference result indicates that the second specific pixel is different from the first specific position of the next plurality of adjacent pixels.
A low-density part forms dots or combined dot-shaped images arranged at approximately 45 °, and the lowest-density part is in the sub-scanning direction. Are arranged at intervals of 3 dots or more, and the dots are arranged so that the interval in the sub-scanning direction becomes narrower as the image density increases, so that the overlapping of the exposure beams in the sub-scanning direction when forming an image in a low density portion. And banding can be suppressed. Further, as the density increases, when the dots are combined in the sub-scanning direction, the preceding dots are in a sufficiently stable state, so that banding due to their overlap is unlikely to occur, and the intermediate potential area of the latent image is small. As a result, image formation becomes stable.

In this embodiment, when the method 6 is used, isolated dots arranged in the 45 ° direction as shown in FIGS. 34A and 34B in the low density portion of the image, or FIG. C) As shown in (D), an image is formed by combining two dots in the sub-scanning direction. FIG. 34A shows image data 1
The uniform portion of 5/255, and FIG.
255 shows a dot forming state of a uniform portion of 255. Also,
FIG. 35A shows a uniform portion of image data 47/255, and FIG.
FIG. 5B shows the dot formation state of the uniform portion of the image data 63/255.

At this time, the dots for image formation are arranged in the direction of 45 °, the distance between the oblique dots is 2√2 dots, and the number of lines by 600 dpi writing of this embodiment is 600 / (2√2). = 212 lpi (line / inc
h), and it is difficult to confirm at a relatively high image spatial frequency.
As shown in FIGS. 34 (C) and (D), even when two dots are combined in the sub-scanning direction, the image frequency is 212 lpi (lin).
e / inch). The medium density portion where the image data shown in FIG. 35 (B) is uniform data of 127/255 is formed by a line arrangement of a higher image spatial frequency of 600/2 = 300 lpi (line / inch), and is completely recognized. It will not be a level.

As described above, in the present embodiment, when the method 6 is used, the image data of a plurality of adjacent pixels is referred to, and the density data is stored at a specific position of the plurality of adjacent pixels based on the reference result. Gradation processing unit 7 as means for allocating
8 wherein the image low density portion is 20
Since the image is formed at an image spatial frequency of 0 lpi or more, the low-density portion of the image is difficult to be resolved by human eyes, so that a high-quality image can be formed. In the middle density part, 30
The line is formed with a line arrangement of 0 lpi (line / inch) and a higher image spatial frequency, and the level is not recognized at all.

In this embodiment, when the method 6 is used, an image is formed by isolated dots arranged in the 45 ° direction in the low density portion of the image as shown in FIGS. 34 (A) and 34 (B). . According to the image forming method of distributing density data to a specific position of a pixel as described above, in the image low-density portion, as shown in FIG. A dot is formed by concentrating data of a pixel to be formed on a portion corresponding to a specific one dot substantially at the center of the pixel.

Therefore, as shown in FIGS. 37 to 39, the amplitude of the potential distribution on the photosensitive drum 1 is large, and the stable potential region of the white portion or the toner-attached portion is increased. State, and the graininess is improved. Concentrating 8 dot data into 1 dot
Since the image data of 12.5% is output at the maximum density on the area of 12.5%, the image data can be reproduced well even in a low density portion of the image density of 12.5%.

As described above, in this embodiment, when the method 6 is used, the image data of a plurality of adjacent pixels is referred to, and the density data is stored at a specific position of the plurality of adjacent pixels based on the reference result. Gradation processing unit 7 as means for allocating
8. The image forming apparatus according to claim 1, wherein the image low-density portion distributes image data of eight or more adjacent dots as image data of the plurality of adjacent pixels to a single position corresponding to a specific one dot as the specific position. Therefore, a stable image suitable for the electrophotographic method can be formed. That is, since the amplitude of the potential distribution on the photoreceptor is large and the stable potential region in the white portion or the toner-attached portion is large, a very stable state is formed in image formation, and the graininess is improved. Concentrating 8 dot data into 1 dot
Since the image data of 12.5% is output at the maximum density on the area of 12.5%, the image data can be reproduced well even in a low density portion of the image density of 12.5%.

[0140]

As described above, according to the first aspect of the present invention, an image can be formed in the form of isolated dots in an image low-density portion, and a beautiful image can be obtained. Is excellent. According to the second aspect of the present invention, with the above-described configuration, an image can be formed in a line shape in the middle and high density portions, and a beautiful image can be obtained, and the image stability is excellent.

According to the third aspect of the present invention, with the above configuration, there is no change in density or color in forming a color image. According to the fourth aspect of the present invention, with the above configuration, the arrangement of the dots can be made inconspicuous in an image low-density portion where dots are arranged at a low period, and the dots are combined as the image density increases to achieve a line-based tone. The density can be increased, and a smooth gradation expression can be performed.

According to the fifth aspect of the present invention, an image can be formed in which the texture of the dots arranged in the low-density portion of the image or the combined dots is inconspicuous. According to the invention according to claim 6, with the above configuration,
Banding can be suppressed, and the low density portion of the image can be reproduced stably.

According to the seventh aspect of the present invention, a high quality image can be formed by the above configuration. Claim 8
According to the invention, a stable image suitable for an electrophotographic system can be formed by the above configuration. According to the ninth aspect of the present invention, with the above-described configuration, an image can be formed in the form of isolated dots in an image low-density portion, and a visually beautiful image can be obtained, and the image stability is excellent.

According to the tenth aspect of the present invention, with the above configuration, an image can be formed in a line shape in the middle and high density portions, and a beautiful image can be obtained, and the image stability is excellent. According to the eleventh aspect, there is no change in density or color due to the above configuration. According to the twelfth aspect of the present invention, with the above configuration, the arrangement of dots can be made inconspicuous in an image low-density portion in which dots are arranged at a low period, and the dots are combined as the image density increases to achieve a line tone. The density can be increased, and a smooth gradation expression can be performed.

According to the thirteenth aspect of the present invention, it is possible to form an image in which the texture of the dots arranged in the low-density portion of the image or the combined dots is inconspicuous. According to the fourteenth aspect of the invention, with the above-described configuration, banding can be suppressed, and a low-density portion of an image can be stably reproduced.

According to the fifteenth aspect of the present invention, a high quality image can be formed by the above configuration. According to the sixteenth aspect of the present invention, a stable image suitable for an electrophotographic system can be formed by the above configuration.

[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 for describing the embodiment.

FIG. 39 is a diagram for describing the embodiment.

FIG. 40 is a flowchart showing a part of the processing flow of the image processing unit in the embodiment.

FIG. 41 is a diagram for describing the embodiment.

[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 603 Comparison / Distribution / Phase Control Circuit

Continued on the front page F term (reference) 2C262 AA05 AA24 AA26 AA27 AB07 BB10 BB20 BB22 BB25 BB49 BC07 DA09 5C077 LL08 LL19 MP01 MP08 NN05 NN07 NN08 NN17 NN19 PP15 PP20 PP28 PP32 PP33 PP45 PP68 PQ04 TTQ06

Claims (16)

[Claims] 1. An image forming method, comprising the steps of: referring to 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 an image in which dots are arranged. 2. An image forming method, comprising the steps of: referring to 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 linear image. 3. A density is generated from a first specific position of a first specific pixel by image data of a plurality of adjacent pixels, and a second density of a second specific pixel is generated by image data of a next plurality of adjacent pixels. An image forming method for generating a density from a specific position, and holding a total sum of image data of a plurality of adjacent pixels. 4. A method of referring to image data of a plurality of adjacent pixels, allocating density data to specific positions of the plurality of adjacent pixels according to a result of the reference, and arranging dots uniformly in the vertical and horizontal directions in the image low density portion. And forming a linear image by combining the dots with the dots as the image density increases. 5. A method according to claim 1, further comprising: referring to image data of a plurality of adjacent pixels;
The density is generated from the specific position of the pixel, and the image data of the next plurality of adjacent pixels are referred to. The reference result indicates that the second specific pixel is different from the first specific position of the next plurality of adjacent pixels.
Density is generated from a specific position of the
An image forming method, wherein an image in the form of dots arranged at an angle or combined dots is formed. 6. A method of referring to image data of a plurality of adjacent pixels, and determining the first of the plurality of adjacent pixels based on a result of the reference.
The density is generated from the specific position of the pixel, and the image data of the next plurality of adjacent pixels are referred to. The reference result indicates that the second specific pixel is different from the first specific position of the next plurality of adjacent pixels.
Density is generated from a specific position of the
An image in the form of dots arranged in degrees or combined dots is formed, and the lowest density portion is arranged at intervals of 3 dots or more in the sub-scanning direction, and the intervals in the sub-scanning direction become narrower as the image density increases. An image forming method characterized in that the image forming method is arranged as follows. 7. An image forming method for referring to image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels according to a result of the reference, wherein the image low-density portion is 200 lpi or more. An image forming method, wherein the image is formed at the image spatial frequency. 8. An image forming method for referring to image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels based on a result of the reference. An image forming method comprising: allocating image data of 8 dots or more adjacent as image data of a plurality of pixels to a single position corresponding to a specific one dot as the specific position. 9. An image forming apparatus comprising: means for referring to image data of a plurality of pixels, and distributing density data to a specific position of the pixel based on a result of the reference, and forming an image in which dots are arranged. . 10. An image forming apparatus comprising: means for referring to image data of a plurality of pixels, and distributing density data to a specific position of the pixel based on a result of the reference, and forming a line image. 11. A density is generated from a first specific position of a first specific pixel by image data of a plurality of adjacent pixels,
Means for generating a density from the second specific position of the second specific pixel based on the image data of the next adjacent plurality of pixels, and holding a total sum of the image data of the plurality of adjacent pixels. Image forming device. 12. Reference is made to image data of a plurality of adjacent pixels, and density data is distributed to specific positions of the plurality of adjacent pixels based on a result of the reference. An image forming apparatus comprising: means for arranging dots in combination with the dots as the image density increases, thereby forming a linear image. 13. The image data of a plurality of adjacent pixels is referred to, and a first result of the plurality of adjacent pixels is referred to based on a result of the reference.
The density is generated from the specific position of the pixel, and the image data of the next plurality of adjacent pixels are referred to. The reference result indicates that the second specific pixel is different from the first specific position of the next plurality of adjacent pixels.
An image forming apparatus comprising means for generating a density from a specific position, and forming an image in the form of dots or combined dots arranged at approximately 45 ° in the image low-density portion. 14. A method of referring to image data of a plurality of adjacent pixels, and determining the first of the plurality of adjacent pixels based on a result of the reference.
The density is generated from the specific position of the pixel, and the image data of the next plurality of adjacent pixels are referred to. The reference result indicates that the second specific pixel is different from the first specific position of the next plurality of adjacent pixels.
Means for generating a density from a specific position, the image low-density portion forms an image of dots arranged at approximately 45 ° or a combined dot shape, and the lowest density portion has an interval of 3 dots or more in the sub-scanning direction. An image forming apparatus, wherein the dots are arranged so that the intervals in the sub-scanning direction become narrower as the image density increases. 15. An image forming apparatus comprising: means for referencing image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels based on a result of the reference. Is an image forming apparatus which forms at an image spatial frequency of 200 lpi or more. 16. An image forming apparatus comprising: means for referencing image data of a plurality of adjacent pixels and distributing density data to specific positions of the plurality of adjacent pixels based on a result of the reference. Wherein the image data of eight or more dots adjacent to each other as the image data of the plurality of adjacent pixels is distributed to a single position corresponding to a specific one dot as the specific position.