JPH0583531A - Color image forming device - Google Patents

Abstract

PURPOSE:To improve the sharpness of images formed from a color scanner, computer graphics or font data, etc., without changing the tone. CONSTITUTION:Image density data from an image density data storage circuit 210 are read by a read circuit 220, an attention picture element is divided into small picture elements by a reference wave phase deciding circuit 240 and select circuits 250A-250C, the center of gravity in the density is calculated after executing an RF processing for the density of each small picture element so as to distribute the density of the attention picture element corresponding to the distribution of the adjacent picture density data containing the attention picture element, specified triangular waves are selected from this center of gravity in the density as reference waves deferring phases and in the case of generating a recording position demodulating signal by modulating source image density signals in respective colors with triangular wave signals selected by a modulation circuit 260 after an image discriminating circuit 231 discriminates a character area and a half tone area, recording position modulation is executed for all the color components in the case of the character area or only for the black component in the case of the half tone area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to perform high image quality recording by reflecting the distribution of adjacent pixels on the density distribution of recording pixels of interest. After dividing the image data for one pixel into m × n (horizontal × vertical) small pixels in consideration of the data of adjacent pixels,
The center of gravity is obtained for each row, the phase of the reference wave is displaced according to this center of gravity, and the dot recording consisting of n small scanning lines is performed by the modulation signal obtained by modulating the density data of the pixel by this reference wave signal And a color image forming apparatus for performing halftone reproduction. The recording device is intended for use as a printer device or a display device.

[0002]

2. Description of the Related Art In the field of electrophotographic image forming apparatus, a document image is read by a scanner as an image signal, and the image signal is subjected to gradation correction, A / D conversion, and shading correction to obtain image density data. A halftone reproduced digital image is obtained by modulating with a wave signal.

An image signal obtained by reading a document image with a scanner has an edge portion of the image read as a halftone density due to an aperture of a solid-state image pickup device incorporated in the scanner. When a latent image is formed on the photoconductor using the image density data obtained from this image signal, the recording pixels corresponding to the edge portion of the latent image are averagely recorded in the recording pixels when the density is intermediate. As a result, the sharpness of the image is reduced and the image is recorded. Conventionally, it has been known that the image signal is subjected to MTF correction by sharpening with a differential filter, a Laplacian filter or the like. However, this means that only the edges of the image are emphasized, and the uniformity of the halftone image is relatively reduced.

On the other hand, even if an interpolated character or figure is created from CG or font data, there is a similar problem. That is, when the edge portion is smoothly interpolated by the intermediate density with the interpolation data, the recording pixel corresponding to the edge portion is recorded as the average density in the pixel, so that the resolution of the recorded image is reduced.

[0005]

For the above reasons, it has been necessary to carry out an intermediate density process which effectively works at the image edge portion.

Further, in the color image forming apparatus, when the intermediate density processing is performed for each color, there is a problem that the color tone is changed or characters are unclear.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a color image forming apparatus which improves the resolution of an image made from a scanner, CG, font data, etc., and performs high quality image recording.

[0008]

SUMMARY OF THE INVENTION The above object is to provide a color image forming apparatus for performing high-density pixel recording by using density data of small pixels in a pixel of interest determined corresponding to density data of pixels adjacent to the pixel of interest. In the case where the pixel of interest is discriminated as an image, and when it is discriminated as a halftone region by this image discrimination, only the achromatic color component is subjected to recording position modulation from the density distribution of the adjacent pixels and discriminated as a character region. Is provided by means for performing the recording position modulation for all color components.

[0009]

EXAMPLE A color image forming apparatus which is an example of the present invention
The configuration of 400 will be described. FIG. 4 is a perspective view showing a schematic configuration of the image forming apparatus of this embodiment.

The color image forming apparatus 400 differentially amplifies an analog image density signal and a reference wave signal obtained by D / A converting digital image density data from a computer or a scanner after uniformly charging a photoconductor. The dot-shaped electrostatic latent image is formed by the spot light whose pulse width is modulated based on the obtained modulation signal, and this is inversely developed with toner to form a dot-shaped toner image. The development process is repeated to form a color toner image on the photoconductor, the color toner image is transferred onto a recording paper, separated from the photoconductor, and fixed to obtain a color image.

The color image forming apparatus 400 includes a drum-shaped photoconductor (hereinafter, simply referred to as a photoconductor) 401 which rotates in the arrow direction.
A scorotron charger 402 that applies a uniform charge onto the photoconductor 401, a scanning optical system 430, yellow, magenta,
It comprises developing devices 441 to 444 loaded with cyan and black toners, a transfer device 462 composed of a scorotron charger, a separator 463, a fixing roller 464, a cleaning device 470, and a static eliminator 474.

The photosensitive member 401 used in this embodiment is a photosensitive member having a high γ characteristic, and a concrete configuration example thereof is shown in FIG.

As shown in FIG. 12, the photoconductor 401 comprises a conductive support 401A, an intermediate layer 401B and a photoconductive layer 401C. The thickness of the photosensitive layer 401C is about 5 to 100 μm, preferably 10
~ 50 μm. As the photoconductor 401, a drum-shaped conductive support 401A made of aluminum having a diameter of 150 mm is used.
0.1μm thick with ethylene-vinyl acetate copolymer on top
Intermediate layer 401B is formed, and a film thickness of 35μ is formed on the intermediate layer 401B.
The photosensitive layer 401C of m is provided.

As the conductive support 401A, a drum of aluminum, steel, copper or the like having a diameter of about 150 mm is used. In addition to this, paper, a belt-shaped material obtained by laminating or vapor-depositing a metal layer on a plastic film, or an electric electrode. It may be a metal belt such as a nickel belt made by the Chu method. Further, the intermediate layer 401B withstands a high charge of ± 500 to ± 2000 V as a photoconductor, for example, in the case of positive charge, it blocks injection from the conductive support IC of the electron and obtains excellent light attenuation characteristics due to avalanche phenomenon. As described above, it is desirable that the intermediate layer 401B has hole mobility, and therefore, for example, Japanese Patent Application No. 61-1889 previously proposed by the applicant of the present invention for the intermediate layer 401B.
It is preferable to add 10% by weight or less of the positively chargeable charge transport material described in the specification of No. 75.

As the intermediate layer 401B, for example, the following resins which are usually used in a photosensitive layer for electrophotography can be used.

(1) Vinyl-based polymers such as polyvinyl alcohol (poval), polyvinyl methyl ether, polyvinyl ethyl ether, etc. (2) Polyvinylamine, poly-N-
Vinyl imidazole, polyvinyl pyridine (quaternary salt),
Nitrogen-containing vinyl polymers such as polyvinylpyrrolidone and vinylpyrrolidone-vinyl acetate copolymer, (3) polyether polymers such as polyethylene oxide, polyethylene glycol and polypropylene glycol, (4) polyacrylic acid and its salts, polyacrylamide, poly-β -
Acrylic acid polymers such as hydroxyethyl acrylate, (5) polymethacrylic acid and its salts, polymethacrylamide, methacrylic acid polymers such as polyhydroxypropylmethacrylate, (6) methyl cellulose, ethyl cellulose, carboxymethyl cellulose,
Ether fibrin-based polymers such as hydroxyethyl cellulose and hydroxypropylmethyl cellulose, (7) polyethyleneimine-based polymers such as polyethyleneimine,
(8) Polyalanine, polyserine, poly-L-glutamic acid, poly- (hydroxyethyl) -L-glutamine, poly-
δ-carboxymethyl-L-cysteine, polyproline,
Polyamino acids such as lysine-tyrosine copolymer, glutamic acid-lysine-alanine copolymer, silk fibroin, casein, etc. (9) Starch acetate, hydroxyethyl ethyl starch, starch acetate, hydroxyethyl starch, amine starch, phosphate starch and other starch and Derivatives thereof, (10) Polymers that are soluble in a mixed solvent of water and alcohol, such as polyamide, soluble nylon and methoxymethyl nylon (8 type nylon).

The photosensitive layer 401C basically comprises a phthalocyanine fine particle having a diameter of 0.1 to 1 μm, which is made of a photoconductive pigment, an antioxidant and a binder resin, without using a charge transport material together, and a solvent for the binder resin. It is formed by mixing and dispersing to prepare a coating solution, coating the coating solution on the intermediate layer, drying and optionally heat treatment.

When the photoconductive material and the charge transport substance are used in combination, the photoconductive pigment and 1 of the photoconductive pigment are used.
/ 5 or less, preferably 1/1000 to 1/10 (weight ratio) of a small amount of a charge transport substance, and dispersed in a photoconductive material, an antioxidant and a binder resin to form a photosensitive layer. By using such a high-γ photoconductor, a sharp latent image can be formed despite the spread of the beam diameter, and recording with high resolution can be effectively performed.

In this embodiment, the color toner image is transferred to the photosensitive member 401.
Since they are superposed on each other, a photosensitive member having infrared spectral sensitivity and an infrared semiconductor laser are used so that the beam from the scanning optical system is not blocked by the color toner image.

Next, the light attenuation characteristics of the high γ photoconductor used in this embodiment will be described.

FIG. 11 is a graph showing the characteristics of the high γ photoconductor. In the figure, V ₁ is a charging potential (V), V ₀ is an initial potential (V) before exposure, and L ₁ is a laser beam irradiation light amount (μJ / cm) required for the initial potential V ₀ to be attenuated to 4/5. ² ) and L ₂ represent the irradiation light amount (μJ / cm ² ) of the laser beam required for the initial potential V ₀ to be attenuated to ⅕.

The preferred range of L ₂ / L ₁ is _{1.0 <L 2 / L 1 ≦} 1.5.

In this embodiment, V ₁ = 1000 (V), V ₀ = 950
(V), L ₂ / L ₁ = 1.2. Also, the photoconductor potential in the exposed area is 1
It is 0V.

The photosensitivity at the position corresponding to the mid-exposure period when the light attenuation curve attenuates the initial potential (V ₀ ) to 1/2 is E1 /
2, and the photosensitivity at the position corresponding to the initial exposure stage where the initial potential (V ₀ ) is attenuated to 9/10 is E9 / 10, (E1 / 2) / (E9 / 10) ≧ 2 is preferable. , (E1 / 2) / (E9 / 10) ≧ 5 is selected as the photoconductive semiconductor. Here, the photosensitivity is defined by the absolute value of the potential decrease amount with respect to the minute exposure amount.

In the light attenuation curve of the photoconductor 401, as shown in FIG. 11, the absolute value of the differential coefficient of the potential characteristic, which is the photosensitivity, is small when the amount of light is small, and increases sharply as the amount of light increases. Specifically, as shown in Fig. 11, the light attenuation curve shows a nearly flat light attenuation characteristic in the early stage of exposure because of poor sensitivity characteristic for a short period of time. The sensitivity becomes an ultra-high γ characteristic that drops almost linearly. It is considered that the photoreceptor 401 specifically obtains a high γ characteristic by utilizing the avalanche phenomenon under the high charge of +500 to + 2000V. That is, the carriers generated on the surface of the photoconductive pigment in the initial stage of exposure are effectively trapped in the interface layer between the pigment and the coating resin, and the light attenuation is surely suppressed. It is understood that an avalanche phenomenon occurs.

Next, the color image forming apparatus of the present invention will be described. In this color image forming apparatus, one pixel of interest in the image density data is formed by m × n (horizontal × vertical) small pixels. Replacing the distribution of density data of adjacent pixels including the target pixel with the distribution of m × n small pixels in one pixel, and distributing the data of the target pixel multiplied by a constant P according to the distribution. Based on the image density data of the small pixels obtained by the above, the phase of the reference wave of each row of the small pixels is displaced to displace the writing position of the dots of the n rows to perform image formation. Displacement of the dot writing position is referred to as recording position modulation. Further, the process of converting the pixel of interest into image density data of small pixels obtained by dividing the target pixel into m × n is referred to as a resolution improving process (RE process). High density recording can be performed by this RE processing. In this case, the high-γ photoconductor is particularly effective for forming a latent image in response to the reference wave accurately.

FIG. 5A is a plan view showing the above target pixel as m5 and adjacent pixels including the target pixel m5 as m1 to m9 when the target pixel m5 is divided into 3 × 3.
(b) is an enlarged view showing a case where each small portion when the target pixel m5 is divided into 3 × 3 small pixels is represented by s1 to s9. m1-m9 and s1-s9 shall also represent the density | concentration of the part.

The RE process will be described in detail.
Taking the case of dividing 5 into 3 × 3 small pixels as an example, the density of the small pixel si is determined by the following equation.

Si = (9 × m5 × P × mi / A) + (1−P) × m5 Here, i = 1, 2, ... 9 and P is a constant that should be called the intensity of RE processing. And a numerical value in the range of 0.1 to 0.9 is used. A is the sum of m1 to m9.

In the above equation, (9 × m5 × P × mi /
The term A) is obtained by dividing the product of the density of the target pixel m5 and P according to the ratio of the density of the adjacent pixels.
The term P) × m5 is obtained by evenly distributing the remaining densities of the target pixel m5 to the respective small pixels, which means that a blur factor is incorporated.

In FIG. 6, the target pixel m5 is divided into 3 × 3, and P
6A shows an example of the density distribution of adjacent pixels including the target pixel m5, and FIG. 6B shows P =
It is a figure which shows the density distribution in the attention pixel m5 calculated as 0.5.

Next, an example of dividing the target pixel m5 into 2 × 2 is shown in FIGS.

FIG. 7A is a diagram showing an example in which the target pixel m5 is divided into 2 × 2, and FIG. 7B is an example of adjacent pixels related to the small pixels s1 to s4 in the target pixel. It is a figure.

Calculation of the concentrations of s1, s2, s3, and s4 is given by
Is done according to.

[0035]

[Equation 1]

FIG. 8A is a diagram showing another example of the case where the target pixel m5 is divided into 2 × 2, and FIG. 8B shows the adjacent pixels related to the small pixels s1 to s4 in the target pixel. It is a figure which shows another example. The concentration calculation of s1, s2, s3, and s4 is performed according to equation 2.

[0037]

[Equation 2]

FIG. 1 is a block diagram showing an embodiment of an image processing circuit used in the color image forming apparatus of the present invention (an example in which a pixel of interest is divided into 3 × 3), and FIG. 3 is a block diagram showing the reference wave phase determination circuit of FIG. 3, and FIG. 3 is a block diagram showing the modulation circuit of the present embodiment.

The image processing circuit 1000 of this embodiment is a circuit which constitutes a drive circuit of a scanning optical system, and comprises an image data processing circuit 100, a modulation signal generating circuit 200 and a raster scanning circuit 300.

The image data processing circuit 100 is a circuit for interpolating and outputting the edge portion of the font data, and comprises an input circuit 110 and a font data generating circuit 12 which are composed of a computer.
0, font data storage circuit 130, interpolation data generation circuit 14
Consists of 0, the character code signal from the input circuit 110,
The size code signal, the position code signal and the color code signal are sent to the font data generating circuit 120. The fond data generation circuit 120 selects an address signal from four types of input signals and sends it to the font data storage circuit 130. The font data storage circuit 130 sends the font data corresponding to one character corresponding to the address signal to the font data generation circuit 120. Font data generation circuit 120
Sends the font data to the interpolation data generation circuit 140. The interpolation data generation circuit 140 interpolates jaggedness or jumps of the image density data generated at the edge portion of the font data using the intermediate density and sends the interpolated data to the image density data storage circuit 210 composed of a frame memory. As for the generated color, the corresponding color is converted into density data of each yellow (Y), magenta (M), cyan (C), and black (BK) according to the color code. In this way, the font is bitmap-developed in each frame memory in a state where each color has the same shape but different density ratios.

The modulation signal generation circuit 200 includes an image density data storage circuit 210, a read circuit 220, a latch circuit 230, an image discrimination circuit 231, an MTF correction circuit 232, a γ correction circuit 233, a reference wave phase determination circuit 240, and a selection circuit 250A. ~ 250C, modulation circuit 2
60A to 260C, a reference clock generation circuit 280, a triangular wave generation circuit 290, a delay circuit group 291 and the like.

The image density data storage circuit 210 is a normal page memory (hereinafter simply referred to as page memory 210), a RAM (random access memory) for storing in page units, and at least one page (for one screen). It has a capacity for storing corresponding multi-valued image density data. Further, if the device is adopted in a color printer, it is equipped with a page memory for storing image density signals corresponding to color components of a plurality of colors, for example, yellow, magenta, cyan and black.

The read circuit 220 reads continuous image density data in units of one scanning line in synchronization with the reference clock DCK ₀ by using the index signal as a trigger from the image density data storage circuit (page memory) 210, and the reference wave phase. It is sent to the decision circuit 240, the image discrimination circuit 231, and the MTF correction circuit 232.

The latch circuit 230 is a circuit for latching the image density data only while the processing of the reference wave phase determination circuit 240 described later is being executed.

The reference clock generation circuit 280 is a pulse generation circuit, which generates a pulse signal having the same repetition period as the pixel clock and outputs it to the readout circuit 220, the triangular wave generation circuit 290, the delay circuit group 291, and the modulation circuits 260A to 260C. To do. For convenience, this clock is referred to as a reference clock DCK ₀ .

Reference numeral DCK ₀ indicates a triangular wave generation circuit 290.
Based on, the waveform shaping of the reference triangular wave φ ₀ which is the reference wave having the same period as the pixel clock is performed. Further, in the delay circuit group 291, a constant cycle (1/6 in this example) with respect to the reference clock DCK ₀
A plurality of clocks DCK ₁ to DCK having a phase difference are generated, and based on this, triangular waves φ _{1 to} φ ₄ which are reference waves having different phases (here, triangular waves φ ₁ , 2 delayed by 1/6 period)
The triangular wave φ ₂ delayed by / 6 cycle, the triangular wave φ ₃ advanced by 1/6 cycle, and the triangular wave φ ₄ advanced by 2/6 cycle are output.

The select circuits 250A to 250C have input sections for the triangular waves φ _{1 to} φ ₄ whose phases are out of phase with the reference triangular wave φ ₀ .
One of the triangular waves is selected by a selection signal from a reference wave phase determination circuit 240, which will be described later, and modulation circuits 260A to 260C are selected.
To the input terminal T of.

The modulation circuits 260A to 260C have the same circuit configuration as shown in FIG. 3, and are the same as the D / A conversion circuit 261, the comparator 262, and the reference triangular wave φ ₀ or a triangular wave whose phase is shifted by 1/6 cycle. Of the image data input through the latch circuit 230 to the reference clock D.
In this circuit, a D / A conversion circuit 261 performs D / A conversion in synchronism with CK _0, and the triangular wave input from the select circuits 250A to 250C is compared as a reference wave to obtain a pulse width modulation signal.

As shown in FIG. 2, the reference wave phase determination circuit 240 comprises a 1-line delay circuit 242, a 1-clock delay circuit 243, and an arithmetic processing circuit 241.
For the first image density data for one scan line for three scan lines of the image density data sent for each one scan line, a delay of two line scan time is set for the image data for one scan line in the middle. Delay 1 line scan time
(No delay is applied to the image data for the last scan line). Further, each image data has a 1-clock delay circuit 243.
Then, the image density data of all the pixels including the pixel of interest and adjacent to the pixel of interest are simultaneously sent to the arithmetic processing circuit 241 by delaying by two reference clocks or one reference clock.

In the arithmetic processing circuit 241, the RE processing is performed to obtain the density data of the small pixels. The density data of the small pixels obtained include the small scanning line including s1, s2, s3 ... In FIG. 5, the small scanning line including s4, s5, s6 ... And the s7, s8, s9. It is divided into small scanning lines that include the three small scanning lines of the small pixels and corresponds to one scanning line of the original pixel.

The arithmetic processing circuit 241 further performs an arithmetic operation for obtaining the center of gravity of the original density data in one pixel of each small scanning line, and outputs different selection signals from the output terminal OA as follows depending on the position of the center of gravity. Output to 250A-250C. That is, when the centroids of s1, s2, and s3 (first small scanning line) of the pixel m5 are near the center of s2, a signal for selecting the reference triangular wave φ ₀ having no phase displacement is sent to the centroid of s2.
When a signal for selecting a triangular wave phi ₁ delayed in phase by 1/6 cycle when in the vicinity of a boundary s1, when the center of gravity is located near the center of s1 selects a triangular wave phi ₂ delayed in phase by 2/6 cycle When the center of gravity is near the boundary between s2 and s3, a signal that selects a triangular wave φ ₃ whose phase is advanced by ⅙ cycle is selected, and when the center of gravity is near the center of s3, a triangular wave φ _{4 is} advanced by 2/6 cycle. Select signal 250A from output terminal OA
Output to. Similarly, from the output terminal OB, s4 of the pixel m5,
The triangular wave selection signal of the second small scanning line determined by the density centroid of s5, s6 is sent to the select circuit 250B, and the triangular wave of the third small scanning line determined by the density centroid of s7, s8, s9 of the pixel m5 from the output terminal OC. Select signal to select circuit 250
Output to C. FIG. 9 is a diagram showing an example of the relationship between the triangular waves having different phases and the pixel of interest.

On the other hand, the image discriminating circuit 231 discriminates whether the image is a character region or a halftone region, and when it is discriminated that it is a character region of a character or a line drawing, the reference wave is applied to all color components. A selection signal for outputting the triangular wave selected by the phase determination circuit 240 to the modulation circuits 260A to 260C is output to the selection circuits 250A to 250C, the MTF correction circuit 232 and the γ correction circuit 233 are inoperative, and the image density data remains unprocessed. The signals are sent to the modulation circuits 260A to 260C via the latch circuit 230. As a result, clear characters and edge portions with no change in color tone are reproduced. If it is determined that the area is a halftone area, a selection signal similar to that for the character area is output only for the achromatic color component, that is, black data, and for the other color components, the triangular wave selected by the reference wave phase determination circuit 240 is not output. No
Select circuit 2 for selecting signal that outputs only reference triangular wave φ ₀
Send to 50A-250C, MTF correction circuit 232, γ correction circuit 233
Operate. As a result, the image density data other than black read by the read circuit 220 is corrected by the MTF correction circuit 232 and the γ correction circuit 233, and then sent to the modulation circuits 260A to 260C via the latch circuit 230.

This makes it possible to form an image free from moire and color skipping in the halftone region, while producing the effect of giving sharpness and tightness to the image by the black image.

In the modulation circuits 260A to 260C, the triangular wave which is the selected reference wave is used to modulate the signal of the image density data inputted through the latch circuit 230 to generate a pulse width modulated signal. For 3 consecutive small scan lines in parallel (1 line of original image density data)
To the raster scanning circuit 300 as a unit.

Next, the operation of the modulation signal generation circuit 200 will be described.

FIGS. 10A to 10D are time charts showing signals at various parts of the modulation signal generating circuit when the recording position is modulated.

In FIG. 10, (a) shows the image density data read from the page memory 210 based on the reference clock DCK ₀ by using the index signal as a trigger and the D / A conversion circuit.
A part of the analog value converted by 261 is shown. The higher level shows a lighter density, and the lower level shows a darker density.

(B) shows a triangular wave which is a reference wave including the delayed ones which are sequentially output from the select circuit 250.

(C) shows the triangular wave (solid line) and the image density signal (dotted line) converted into the analog value, and shows the modulation operation in the modulation circuits 260A to 260C.

(D) shows a pulse width modulation signal generated by being compared by the comparator 262.

As a result of the above modulation signal generation, in the character area, the position of the small dot in the nth row in the pixel of interest moves to the position along the line direction of the original character or line drawing from the density data of the original adjacent pixel. As a result of position modulation, characters and images can be clearly reproduced. Further, the recording position modulation described above is performed only in the black component in order to prevent the change of the color tone in the halftone region, and is performed in the other color components by the triangular wave having no phase displacement.

Furthermore, by sequentially shifting the phase of the reference wave in the sub-scanning direction, dots corresponding to halftone dots with a screen angle can be formed. For example, the screen angle is 45 ° for the yellow component and 26.6 for the magenta component.
, -26.6 ° for the cyan component and 0 ° for the black component to improve the uniformity of color reproduction and prevent moire fringes from occurring.

Particularly, by setting the black component to 0 °, there is an advantage that the recording phase modulating means can be used as it is without changing.

The raster scanning circuit 300 includes a 2δ delay circuit 311 and
A δ delay circuit 312, laser drivers 301A to 301C, an index detection circuit (not shown), a polygon mirror driver and the like are provided.

The laser drivers 301A to 301C are modulation circuits 26.
A plurality of modulation signals from 0A to 260C (3 in this embodiment)
The semiconductor laser array 431 having (a) individual laser emission units 431A to 431C is oscillated, and a signal corresponding to the light amount of the beam from the semiconductor laser array 431 is fed back and driven so that the light amount becomes constant.

The index detection circuit detects the surface position of the rotary polygon mirror 434 that rotates at a predetermined speed by the index signal from the index sensor 439, and the image density signal modulated by the raster scanning method according to the cycle in the main scanning direction. Optical scanning is performed. Scan frequency 2204.72Hz
The effective print width is 297 mm or more, and the effective exposure width is 306 mm.
That is all.

The polygon mirror driver rotates the DC motor uniformly at a predetermined speed to rotate the rotary polygon mirror 434 at 16535.4 rpm.

As the semiconductor laser array 431, as shown in FIG. 13, an array in which three light emitting portions 431A to 431C are arranged at equal intervals is used. Normally, it is difficult to set the distance d between the light emitting portions to 20 μm or less. Therefore, as shown in FIG. 13, the axis passing through the centers of the light emitting portions 431A to 431C is parallel to the rotation axis of the rotary polygon mirror 434, and the main scanning Install at an angle to the direction. In this way, the semiconductor laser array 431
Laser beam s on the photoconductor 401
As shown in FIG. 14, a, sb, and sc can be vertically and closely scanned. However, for this reason, the positions of the laser spots sa, sb, and sc in the scanning direction shift with respect to the scanning direction. In order to correct this deviation, 2δ is provided between the modulation circuit 260A and the laser driver 301A.
A δ delay circuit 312 is inserted between the delay circuit 311 and the modulation circuit 260B and the laser driver 301B, and each laser is delayed by an appropriate amount to correct the deviation, and the laser spot sa emitted from the semiconductor laser array 431 is corrected. ,
sb and sc are sa ', sb', which are aligned perpendicular to the scanning direction.
It can be recorded as sc. When the RE process is performed by dividing the target pixel into 2 × 2 small pixels, a semiconductor laser array having two light emitting units is used.

Next, the image forming apparatus 400 shown in FIG.
The image forming process will be described.

First, the photoconductor 401 is uniformly charged by the scorotron charger 402. The electrostatic latent image corresponding to yellow is formed on the drum-shaped photoconductor 401 by the image density data storage circuit 210.
The laser beam modulated by the yellow data (8-bit digital density data) from the inside is formed by irradiation through the cylindrical lens 433, the rotary polygon mirror 434, the fθ lens 435, the cylindrical lens 436, and the reflection mirror 437. The electrostatic latent image corresponding to the yellow is developed by the first developing device 441, and the dot-shaped first toner image (yellow toner image) having extremely high sharpness is formed on the photoconductor 401.
Is formed. The first toner image is not transferred to the recording sheet, passes under the retracted cleaning device 470, and is charged again on the photoconductor 401 by the scorotron charger 402.

Then, the laser beam modulated by the magenta data (8-bit digital density data) is irradiated onto the photoconductor 401 to form an electrostatic latent image. This electrostatic latent image is developed by the second developing device 442 to form a second toner image (magenta toner image). The third developing device 443 sequentially develops in the same manner as described above,
The toner image (cyan toner image) of
A three-color toner image is sequentially formed on the upper surface. Finally, the fourth toner image (black toner image) is formed, and the photoconductor 401
A four-color toner image that is sequentially stacked on top is formed.

According to the image forming apparatus 400 of this embodiment, the photoconductor 401 has excellent high γ characteristics, and this excellent high γ characteristic is used for charging, exposing and developing a toner image many times. The latent image is stably formed even when the toner images are repeatedly formed over each other. That is, even if a laser beam is irradiated from above the toner image based on a digital signal, a dot-shaped electrostatic latent image with high fringes and high sharpness is formed, and as a result, a toner image with high sharpness can be obtained. You can

These four-color toner images are transferred by the operation of the transfer device 462 onto the recording paper supplied from the paper feeding device.

The recording paper carrying the transferred toner image is separated by a separator.
The sheet is separated from the photoconductor 401 by 463, is conveyed by a guide and a conveyance belt, is carried into a fixing roller 464, is heated and fixed, and is discharged to a discharge tray.

In this example, as a result of various experiments by changing the value of the coefficient P of RE processing, the value of P was 0.1 to 0.9.
Good images were obtained in the range of. However, when P is small, the sharpness of the character is insufficient, and when P is large, the edge portion of the character or the line drawing is overemphasized. Therefore, the preferable value range of P is 0.3 to 0.7. Was found to be in the range. As a result, when the manuscript is a character or a line drawing, the edge part appears clearly, and even small characters can be reproduced in detail. In addition, no adverse effects were observed even when the image had a halftone. This is because the method has a small effect on the value of P for a halftone image.

In the present invention, although P can be used as a constant value, it is preferable to change P according to the image (character area or halftone area). When the value in the case of the character area is P ₁ and the value in the case of the halftone area is P ₂ , it is preferable that P ₁ > P ₂ . That is, when the image is a character or the like, the value of P is large and is preferably 0.9 to 0.4, and when the image is halftone, the value of P is small and is 0.6 to 0.1.

The above-described flow of image data has been described as a laser printer which outputs data once stored in the page memory 210, but the present invention is not limited to this, and the color scanner 151, A / A instead of the image data processing circuit 100 is used. Instead of the image data processing circuit 150 composed of the D conversion circuit 152, the density conversion circuit 153, the masking UCR circuit 154 and the like, if a circuit for inputting image density data from the scanner and performing image processing is used, it may be a copy machine or the like. It can be applied to an image forming apparatus.

[0078]

As described above, the RE processing in which the target pixel is divided into small pixels and the density of each small pixel is distributed according to the distribution of the density data of the adjacent pixels including the target pixel. If the phase of the reference wave signal is selected from the processed image data, the recording position modulation signal is generated by modulating the density signal of the pixel of interest with this reference wave, and the image discrimination circuit performs image discrimination, Since the recording position modulation is performed for all color components and only the achromatic color component (black) is subjected to the recording position modulation in the halftone area, color image recording is performed. Therefore, it is possible to create a color image from a scanner, CG or font data. It was possible to provide an excellent color image forming apparatus capable of improving sharpness without causing a change in the color tone of the obtained color image.

Although the above method can be applied only to a single main scanning of the recording beam, the effect can be further improved by scanning one pixel with a plurality of recording beams and using a high γ photoconductor. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of an image processing circuit of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a block diagram showing an example of a reference wave phase determination circuit of the circuit of FIG.

FIG. 3 is a block diagram showing an example of a modulation circuit of the circuit of FIG.

FIG. 4 is a perspective view showing a schematic configuration of an example of an image forming apparatus of the present invention.

FIG. 5 is a diagram for explaining an RE process used for determining a reference wave phase.

FIG. 6 illustrates a pixel of interest for RE processing divided into 3 × 3 pixels, and P = 0.
FIG. 7 is a diagram showing an example of a case of setting 5.

FIG. 7 is a diagram showing an example of dividing a target pixel of RE processing into 2 × 2.

FIG. 8 is a diagram showing another example in the case where the target pixel indicated by RE is divided into 2 × 2.

FIG. 9 is a diagram for explaining a phase displacement of a reference wave.

FIG. 10 is a time chart showing signals of respective parts of the modulation signal generation circuit of the embodiment of FIG.

FIG. 11 is a graph showing characteristics of the high γ photoconductor used in this example.

FIG. 12 is a cross-sectional view showing a specific configuration example of a high γ photoconductor used in this example.

13 is a diagram showing a semiconductor laser array of the embodiment of FIG.

14 is a diagram showing a scanning locus of a laser spot by the semiconductor laser array of FIG.

[Explanation of symbols]

 100 Image data processing circuit 200 Modulation signal generation circuit 210 Image density data storage circuit (page memory) 220 Read circuit 230 Latch circuit 231 Image discrimination circuit 232 MTF correction circuit 233 γ correction circuit 240 Reference wave phase determination circuit 241 Arithmetic processing circuit 250A ~ 250C Select circuit 260A to 260C Modulation circuit 280 Reference clock generation circuit 290 Triangular wave generation circuit 291 Delay circuit group 300 Raster scanning circuit 400 Image forming device

Claims (2)

[Claims] 1. A color image forming apparatus for performing high-density pixel recording based on density distribution data within a pixel of interest determined corresponding to density data of a pixel adjacent to the pixel of interest, and means for discriminating the image of the pixel of interest. And a means for performing recording position modulation of only the achromatic color component from the density distribution of the adjacent pixels when the image is determined to be a halftone region. 2. A color image forming apparatus for performing high-density pixel recording based on density distribution data in a pixel of interest determined corresponding to density data of a pixel adjacent to the pixel of interest, and a means for discriminating the image of the pixel of interest. A color image forming apparatus, wherein when the image area is determined by the image determination, the recording position modulation is performed on all color components.