JPH05177882A - Image forming method - Google Patents

Abstract

PURPOSE:To improve a sharpness of an image formed by a scanner, a CG, font data, or the like by a method wherein data obtained by multivaluing an outline font is stored in a memory. CONSTITUTION:An image data processing circuit 100, which is a circuit for outputting multivalued font data, is composed of a personal computer 110, a font data generation circuit 120, and a processing circuit 130. The computer 110 issues code signals of character, size, position, and color to the circuit 120. The circuit 120 selects an address signal in accordance with the aforesaid four kinds of signals and transmits font data to the circuit 130 through the computer 110. The circuit 130 issues the font data to an image density data storage circuit 210 serving as a memory means for a frame memory. Additionally, in accordance with a color code, corresponding colors are converted to density data of yellow, magenta, cyan, and black. In this manner, a font for every color is developed to a multivalued bit map of the same shape in a different density ratio in each frame memory.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for specially processing image data and scanning one pixel with a plurality of laser beams to reproduce an image with high density and excellent sharpness.

[0002]

2. Description of the Related Art In the field of electrophotographic image forming apparatuses, 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. 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. This cannot be dealt with by adding MTF correction or the like to the image signal.

Further, 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.
Therefore, intermediate density processing is required at the image edge portion.

In addition, the conventional font data is often developed into a binary bit map as shown in FIG. 16, the ends of the characters are not smooth, and especially when the magnification is changed, jaggedness appears when enlarged. There was a problem that the characters would be cut off when reduced.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus which improves the sharpness of an image made from a scanner, CG, font data and the like.

[0007]

The above object is to provide an image forming apparatus having a memory means for storing image data,
The outline font is multivalued as intermediate density information and developed as a bit map in the memory means, and the writing position of the output pixel is calculated from this bit map, and the recording position modulation is performed in the main scanning direction based on the calculation result. It is achieved by an image forming method characterized by forming a latent image of dots formed by the above method.

Further, it is a preferable embodiment that the recording position modulation in the main scanning direction is performed by selecting a reference wave.

[0009]

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

The image forming apparatus 400 compares the analog image density signal obtained by D / A converting the digital image density data from the computer or the scanner after uniformly charging the photoconductor and the reference wave signal, and compares the analog image density signal with the reference wave signal. A dot-shaped electrostatic latent image (this is referred to as a dot latent image) is formed by spot light that is pulse-width-modulated or intensity-modulated based on a modulation signal obtained by digitizing or differentially amplifying it. The toner image is reversely developed with toner to form a dot-shaped toner image (this is referred to as a toner dot), the charging, exposing and developing steps are repeated to form a color toner image on the photoconductor 401, and this color toner image is transferred. Then, they are separated and fixed to obtain a color image.

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

In the scanning optical system 430 of this embodiment, a laser beam emitted from a semiconductor laser 431 having three light emitting portions, which will be described later, is collimated by a collimator lens 432 into a parallel beam. This laser beam is reflected and deflected by a rotary polygon mirror 434 that rotates at a constant speed, and a minute amount is formed on a peripheral surface of a photosensitive member 401, which is a drum-shaped photosensitive member uniformly charged, by an fθ lens 435 and cylindrical lenses 433 and 436. Image exposure is performed by scanning with a laser beam focused in a spot shape. Here, the fθ lens 435 is a correction lens for performing optical scanning at a constant speed, and the cylindrical lenses 433 and 436 are the rotary polygon mirror 43.
Correct the spot position variation due to the surface tilt of 4. 437 is a scanning mirror that reflects the laser beam, 438 is an index mirror, and 439 is an index sensor. The index signal from the index sensor 439 detects the start of scanning by the laser beam and the surface position of the rotary polygon mirror 434 that rotates at a predetermined speed to detect the period in the main scanning direction. As a result, the spot of the laser beam scans the photoconductor 401 in parallel with the drum axis.

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

As shown in FIG. 15, the photoconductor 401 comprises a conductive support 401A, an intermediate layer 401B and a photoconductive layer 401C. Photosensitive layer 40
The thickness of 1C is about 5 to 100 μm, preferably 10 to 50
μm. The photosensitive member 401 uses a drum-shaped conductive support 401A made of aluminum having a diameter of 150 mm, and an ethylene-vinyl acetate copolymer-made intermediate layer 401B having a thickness of 0.1 μm is formed on the support 401A. A photosensitive layer 401C having a film thickness of 35 μm is provided on 401B.

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-like one in which a metal layer is laminated or vapor-deposited on a plastic film, or an electric wire is used. 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, and 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 preferable that the intermediate layer 401B has hole mobility, so that, for example, Japanese Patent Application No. 61-18897 previously proposed by the applicant of the present invention is used 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 No. 5. As the intermediate layer 401B,
Usually, for example, the following resins used for the photosensitive layer for electrophotography can be used.

(1) Polyvinyl alcohol (poval), polyvinyl methyl ether, polyvinyl ethyl ether and other vinyl polymers, (2) polyvinyl amine, poly-N
-Vinylimidazole, polyvinylpyridine (quaternary salt), polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer and other nitrogen-containing vinyl polymers, (3) polyethylene oxide, polyethylene glycol, polypropylene glycol and other polyether polymers, (4)
Acrylic acid-based polymers such as polyacrylic acid and its salts, polyacrylamide and poly-β-hydroxyethyl acrylate, (5) Polymethacrylic acid and its salts, methacrylic acid-based polymers such as polymethacrylamide and polyhydroxypropylmethacrylate Polymer, (6) ether cellulose polymer such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl 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 , Poly-amino acids such as lysine-tyrosine copolymer, glutamic acid-lysine-alanine copolymer, silk fibroin and casein, (9) starch acetate,
Starch and its derivatives such as hydroxyethyl ethyl starch, starch acetate, hydroxyethyl starch, amine starch, and phosphate starch, (10) Mixing water and alcohol such as polyamide soluble nylon and methoxymethyl nylon (8 type nylon) Polymer soluble in solvent.

The photosensitive layer 401C is basically composed of a phthalocyanine fine particle having a diameter of 0.1 to 1 μm, which is made of a photoconductive pigment, and an antioxidant and a binder resin, without using a charge transport material together, and a solvent of a 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. 14 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 when the initial potential (V ₀ ) is attenuated to 9/10 is E9 / 10, (E1 / 2) / (E9 / 10) ≧ 2 is preferable. A photoconductive semiconductor that gives a relationship of (E1 / 2) / (E9 / 10) ≧ 5 is selected. 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. 14, 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. 14, 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. Specifically, the photoconductor 401 is considered to obtain a high gamma 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 early 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.

In the present invention, it is preferable that the photoconductor has a high γ characteristic, but it is also possible to use a photoconductor in which the normal light amount and the potential decrease are in a proportional relationship.

Next, the image forming method used in the present invention will be described. In this image forming method, one pixel of the image density data of interest 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. This is a method of forming an image based on image density data of small pixels obtained by. This image density data processing will be referred to as resolution improving processing (RE processing). An image is formed by the pulse width modulated image signal obtained by combining the RE processed image density data and a fixed reference wave. In particular, a high-γ photoconductor is effective for forming a latent image by accurately responding to a reference wave.

Next, the RE processing will be described in detail. FIG. 6A is a diagram showing the above target pixel as m5, and the adjacent pixels including the target pixel m5 as m1 to m9 when the target pixel m5 is divided into 3 × 3, and FIG. Pixel m5
Is divided into 3 × 3 small pixels, each small part is divided by s1 to s9
It is an enlarged view showing the case represented by. m1-m9 and s1-
S9 also represents the density of that portion, and the density of the small pixel si is determined by the following equation.

Si = (9 × m5 × P × mi / A) + (1−P) × m5 where i = 1,2, ..., 9, and P is also the strength of RE processing. It is a power constant 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 / A)
The term is obtained by multiplying the density of the pixel of interest m5 by P, and is distributed in accordance with the density ratio of the adjacent pixel. (1-P)
The term xm5 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. 7, the pixel of interest m5 is divided into 3 × 3 pixels, and P
FIG. 7A shows an example of the density distribution of adjacent pixels including the target pixel m5, and FIG. 7B shows an example of the density distribution of the target pixel m5 calculated in the case of the above density distribution. It is a figure showing the density distribution of a small pixel.

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

FIG. 8 (a) is a diagram showing an example in which the target pixel m5 is divided into 2 × 2, and FIG. 8 (b) is a small pixel s in the target pixel.
It is a figure which shows an example of the adjacent pixel related to 1-s4. s1,
The calculation of the concentrations of s2, s3, and s4 is performed according to Equation 1.

[0034]

[Equation 1]

FIG. 9 (a) is a diagram showing an example in which the target pixel m5 is similarly divided into 2 × 2, and FIG. 9 (b) is another pixel of the adjacent pixels related to the small pixels s1 to s4 in the target pixel. It is a figure which shows an example. The concentrations of s1, s2, s3, and s4 are calculated according to equation 2.

[0036]

[Equation 2]

FIG. 1 is a block diagram showing an embodiment of an image processing circuit used in the image forming apparatus of the present invention (an example in which a pixel of interest is divided into 3 × 3), and FIG. 2 shows this embodiment. FIG. 3 is a block diagram showing the RE processing circuit 240, and FIG. 3 is a block diagram showing the modulation circuits 260A to 260C of this 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 outputting multi-valued font data, and includes a personal computer 110, a font data generation circuit 120, and a processing circuit 130.
The personal computer 110 sends a character code signal, a size code signal, a position code signal and a color code signal to the font data generating circuit 120. The fond data generation circuit 120 selects an address signal from four types of input signals to select a personal computer.
The font data is sent to the processing circuit 130 via 110.
The processing circuit 130 sends the font data to the image density data storage circuit 210 which is a memory means including a frame memory. Regarding the generated colors, the corresponding colors are yellow (Y), magenta (M), and cyan according to the color code.
Convert to density data of (C) and black (BK). In this way, in the state where each color has the same shape and the density ratio is different, the font is subjected to multi-valued bit map expansion in each frame memory as shown in FIG. 10, for example.

The numbers in the figure represent density data of a specific color when "A" is expanded into 8 bits. Conventionally, binary expansion with 0 or 1 was performed. By developing it as multi-valued data, it can be handled without distinction from the information from the scanner in the image processing system. Then, the font data is such that image deterioration is prevented by RE processing, MTF correction, and the like.

The modulation signal generation circuit 200 includes an image density data storage circuit 210 which is a memory means, a read circuit 220, latch circuits 230A to 230C, an image discrimination circuit 231, an MTF correction circuit 232.
RE processing circuit 240, clock generation circuit 280, reference triangular wave generation circuit 290A, delay circuit group 290B, select circuits 250A to 250
C, modulation circuits 260A to 260C.

[0042] In the circuit clock generation circuit 280 for generating a reference clock pulse DCK _0, reference clock pulses DCK ₀ is read circuit 220 which outputs than this, the reference triangular wave generating circuit 290
A, delay circuit group 290B, select circuits 250A to 250C, modulation circuits 260A to 260C, and the like.

The reference triangular wave generation circuit 290A is a reference clock.
A circuit for generating a reference triangular wave phi ₀ no phase shift and DCK ₀ at the same period, the delay circuit group 290B is the reference triangular wave phi ₀ to example 1/3 cycle delay triangular wave phi ₁ and 2/3 cycle delay (i.e. This circuit generates a triangular wave φ _{2 (} advanced by 1/3 cycle). FIG. 3B is a diagram showing comparison among the triangular waves φ _{0 to} φ ₂ in the small scanning line.

Image density data storage circuit as memory means
210 is a normal page memory (hereinafter, simply page memory 210
Say. ), Which is a RAM (random access memory) that stores in page units, and at least one page (1
It has a capacity for storing multivalued image density data corresponding to a screen portion. Further, if it is an apparatus adopted for a color printer, it will have a page memory for storing image density signals corresponding to a plurality of color components, for example, yellow, magenta, cyan and black color components.

The reading circuit 220 uses the index signal as a trigger to synchronize the image density data for three consecutive scanning lines in units of one scanning line in synchronization with the reference clock DCK ₀ from the image density data storage circuit (page memory) 210. The data is read and sent to the RE processing circuit 240 and the image discrimination circuit 231.

The latch circuit 230 latches for the time required for the processing of the RE processing circuit 240 and sends it to the modulation circuits 260A to 260C.

As shown in FIG. 2, the RE processing circuit 240 includes a 1-line delay circuit 242, a 1-clock delay circuit 243, and an arithmetic processing circuit 241, and the 1-line delay circuit 242 causes the scaling circuit 221 to scan one scan line. The image density data for the first one scanning line for the three scanning lines of the image density data sent one by one has a delay of two line scanning time and the intermediate one
The image data for one scanning line is delayed by one line scanning time (the image data for the last one scanning line is not delayed). Further, each image data is delayed by 2 reference clocks or 1 reference clock by the 1-clock delay circuit 243, and all the image density data of pixels including the target pixel and adjacent to the target pixel are simultaneously calculated by the arithmetic processing circuit 241.
To send to.

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 obtained small pixels are s1, s2,
It is divided into a small scan line including s3 ..., a small scan line including s4, s5, s6 ... and a small scan line including s7, s8, s9 ... Modulation circuit 2
At the same time as sending to 60A to 260B, the center of gravity of the density data in the pixel of interest is calculated, and a selection signal for selecting the reference wave of the phase corresponding to this center of gravity is sent to the select circuits 250A to 250C. That is, with respect to the small scanning lines of s1, s2, s3, ..., When the center of gravity of the density data is at s1, the triangular wave φ ₂ advanced by 1/3 period, and when the center of gravity is at s2, the reference triangular wave φ 2
_When the center of gravity is s3, a selection signal for selecting a triangular wave φ ₁ delayed by 1/3 period is sent to the select circuit 250A. The same selection signal is applied to the other small scan lines by the select circuit.
Send to 250B, A250C.

One of the original pixels is obtained by the above three small scanning lines.
This corresponds to scanning lines, and writing (recording) by image data of small scanning lines including s1, s2, s3 ... Is handled by the light emitting section 431A of the semiconductor laser array 431, which will be described later, and s4, s5, The light emitting unit 431B is in charge of writing by the image data of the small scanning line including s6 ..., and the light emitting unit 431C is writing by the image data of the small scanning line including s7, s8, s9 ...
Will be in charge.

The modulation circuits 260A to 260C are the same circuit 260 as shown in FIG. 3 (a), and the D / A conversion circuit 261, the comparator 262, the input terminal CK of the reference clock DCK ₀ , and the input of the image density data. It has a terminal D 1 and a reference wave input terminal T, and the image data of the small scanning line inputted through the latch circuits 230A to 230C is D / A converted by the D / A conversion circuit 261 and the selection circuit 250A to This is a circuit that obtains a pulse width modulation signal by comparing a triangular wave selected from the triangular waves φ ₀ , φ ₁ , and φ ₂ input from 250C as a reference wave.

On the other hand, the image discrimination circuit 231 discriminates whether the image is a character / halftone / halftone dot.

(A) If it is determined that the image is composed of characters and halftone dots, the MTF correction circuit 232 is disabled and the image data divided by the small scanning line output from the RE processing circuit 231 is output. Is directly sent to the modulation circuits 260A to 260C, and a selection signal for selecting a triangular wave having a phase corresponding to the center of gravity of the small scanning line is sent to the selection circuits 250A to 250C.

(B) When it is determined that the image is a halftone image, the MTF correction circuit 232 is operated to send the image data subjected to the MTF correction to the modulation circuits 260A to 260C.

In the case of (a), the modulation circuits 260A to 260C generate a modulation signal in which the image data of the RE-processed small scanning line which is not subjected to the MTF correction is pulse width modulated by the selected triangular wave, and In the case of (b), a modulation signal in which the MTF-corrected image data of the small scanning line is pulse-width modulated by the selected triangular wave is generated, and the modulation signal is supplied in parallel with three small scanning lines (the original image). One line of density data) is sent to the raster scanning circuit 300 as one unit.

FIGS. 5 (a) to 5 (d) are time charts showing signals at respective parts when the modulation signal is generated for each small scanning line in the case of (a).

In the figure, (a) shows a part of the image density data of the small scanning line read from the page memory 210 based on the reference clock DCK ₀ with the index signal as a trigger. The image density data is converted into an analog value by the D / A conversion circuit 261, and the higher level side shows a lighter density and the lower level side shows a darker density.

(B) shows a reference wave which has been subjected to RE processing in the RE processing circuit 240 and then selected according to the position of the center of gravity of the density data and input from the select circuits 250A to 250C to the T terminal of the modulation circuit 260.

(C) shows a triangular wave (solid line) which is a reference wave sequentially output from the select circuits 250A to 250C to the modulation circuits 260A to 260C and the analog-converted image density data (dashed-dotted line), and the modulation circuit The modulation operation at 260A to 260C is shown.

(D) shows a pulse width modulation signal generated by being compared by the comparator 262. The dotted line in the figure shows a modulation signal in which the recording position modulation is not performed in the case of modulation with the reference triangular wave φ ₀ .

As described above, the pulse width modulation accompanied by the recording position modulation in which the recording position in the main scanning direction is displaced by the modulation by the reference waves having different phases is performed. Further, the modulation signal divided for each small scanning line is the laser driver 30.
It is sent to each light emitting portion of the semiconductor laser array 431 having n light emitting portions via 1A to 301C. As a result, a latent image is formed for each small scanning line, so that the recording density in the sub-scanning direction is improved to nearly n times.

FIG. 11 is a diagram showing the structure of a character formed by the modulated signal which has been subjected to the RE processing in (a) above, and a small pixel portion shaded is a portion having density data. In this way, the recording position modulation is performed in the main and sub scanning directions based on the distribution of the density data, and in the shaded portion of the character or line drawing, the conventional 2
It will be reproduced much more clearly than the digitized data.

The raster scanning circuit 300 includes a laser driver 301.
A 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 260A.
A plurality of modulated signals from ~ 260C (three in this embodiment)
A semiconductor laser array 431 having a laser emitting section is oscillated, and a signal corresponding to the light quantity of the beam from the semiconductor laser array 431 is fed back and driven so that the light quantity 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 digital image density signal modulated by the raster scanning method at the cycle in the main scanning direction. Optical scanning is performed. Scan frequency 2204.7
2Hz, effective print width 297mm or more, effective exposure width 30
It is 6 mm or more.

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

As shown in FIG. 12, the semiconductor laser array 431 has n (n = 3 in this embodiment) light emitting portions 431A, 431B, 43.
Use 1C arranged in an array at equal intervals. Since it is usually difficult to set the interval of the light emitting parts to 0.1 mm or less, the rotary polygon mirror 43 is used as an axis passing through the centers of the light emitting parts 431A to 431C.
It is installed parallel to the rotation axis of 4 and inclined at a constant angle θ with respect to the main scanning direction. In this way, the laser spot of the laser beam on the photoconductor 401 by the semiconductor laser array 431 can be scanned vertically and closely. However, for this reason, the positions of the respective laser spots in the scanning direction deviate from the scanning direction. In order to correct this deviation, delay circuits 311 and 312 having a delay time of δ and 2δ are inserted between the modulation circuits 260B and 260C and the laser drivers 432B and 432C connected to the modulation circuits 260B and 260C, respectively, and the timing is obtained by delaying each by an appropriate amount. By the above, the above-mentioned deviation can be corrected, and the laser spots by the semiconductor laser array 431 can be recorded perpendicularly to the scanning direction.

For simplification of the description above, the case where three triangular waves whose reference wave phases are also different by 1/3 cycle are used has been described, but the reference wave phase is, for example, five or six phases which are different by 1/6 cycle. Of course, it is also possible to use seven triangular waves to perform finer recording position modulation.

Next, the image forming process of the image forming apparatus 400 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.
It is formed by irradiating a laser beam optically modulated with yellow data (8-bit digital density data) from the inside. The electrostatic latent image corresponding to yellow is developed by the first developing device 441, and a dot-shaped first toner image (yellow toner image) having extremely high sharpness is formed on the photoconductor 401. This first toner image passes under the cleaning device which is retracted without being transferred to the recording paper,
The scorotron charger 402 charges the surface 401 again. Then, the laser light is optically modulated by magenta data (8-bit digital density data), and the modulated laser light is irradiated on 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 to form a third toner image (cyan toner image), and a three-color toner image sequentially laminated on the photoconductor 401 is formed. Finally, a fourth toner image (black toner image) is formed, and a four-color toner image sequentially formed on the photoconductor 401 is formed.

According to the image forming apparatus 400 of the present embodiment, the photoconductor has excellent high gamma characteristics, and the excellent high gamma characteristics are used for charging, exposing and developing a toner image over a number of times. The latent image is stably formed even when the toner images are repeatedly overlapped and formed. 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 onto the recording paper supplied from the paper feeding device by the action of the transfer device 462.

The recording paper carrying the transferred toner image is separated from the photoconductor 401 by the separation electrode 463, conveyed by the guide and the conveyor belt, conveyed to the fixing roller 464, heated and fixed, and ejected to the paper ejection tray.

In this example, as a result of various experiments by changing the value of the coefficient P of the RE processing, the value of P was 0.1 to 0.9.
Good images were obtained in the range of, and excellent results were obtained particularly in the range of 0.4 to 0.5.

[0074]

As described above, since the data in which the outline font is multivalued is stored in the memory, it can be treated in the same manner as the density information inputted by the scanner. Also, divide the pixel of interest into small pixels,
The density of each small pixel is modulated by the reference wave selected from the center of gravity of the image data for each small scanning line that has undergone RE processing to distribute the density of the target pixel according to the distribution of the density data of adjacent pixels including the target pixel. By the image forming method in which a modulated signal is generated and the image is recorded by the semiconductor laser array driven by this modulated signal, recording position modulation is performed in the main both scanning directions, and in the sub scanning direction, n light emitting portions are spread. As a result of image recording, the sharpness of an image created from a scanner, CG, font data, etc. is improved, and when an original is a character or a line drawing, what was conventionally unclear at the edge part appears clearly. And even small letters can be reproduced in detail. Moreover, it does not appear jagged when enlarged, does not cut out characters when reduced, does not have any adverse effect even when it has halftones, and does not show moire fringes even when copying a document consisting of halftone dots. The image forming apparatus can be provided.

[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.

2 is a block diagram showing an example of an RE processing circuit of the circuit of FIG. 1. FIG.

3 (a) is a block diagram showing an example of a modulation circuit of the circuit of FIG. 1. FIG.

FIG. 3 (b) is a diagram showing a comparison of reference waves.

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

5 is a time chart showing signals of a small scanning line of the modulation signal generation circuit of the embodiment of FIG.

FIG. 6 is a diagram for explaining RE processing.

FIG. 7 is a diagram showing an example of a density distribution when RE processing is performed with m, n = 3 and P = 0.5.

FIG. 8 is a diagram showing an example of a density distribution when RE processing is performed with m, n = 2, and P = 0.5.

FIG. 9 is a diagram showing another example of the density distribution when RE processing is performed with m, n = 2, and P = 0.5.

FIG. 10 is a diagram showing a structure of a character formed by multi-valued data of the present invention.

FIG. 11 is a diagram showing a configuration of characters formed by the RE-processed modulated signal of the present invention.

12 is an enlarged view showing the semiconductor laser array of the embodiment of FIG.

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

FIG. 14 is a graph showing the characteristics of the high γ photoconductor used in this example.

FIG. 15 is a cross-sectional view showing a specific configuration example of a high-γ photoconductor used in this example.

FIG. 16 is a diagram showing a structure of a character formed by conventional binary data.

[Explanation of symbols]

 100 Image data processing circuit 200 Modulation signal generation circuit 210 Image density data storage circuit (page memory) 220 Readout circuit 230A to 230C Latch circuit 231 Image discrimination circuit 232 MTF correction circuit 240 RE processing circuit 241 Arithmetic processing circuit 250A to 250C Select circuit 260A ~ 260C Modulation circuit 280 Clock generation circuit 290A Reference triangular wave generation circuit 290B Delay circuit group 300 Raster scan circuit 301A ~ 301C Laser driver 311,312 Delay circuit 400 Image forming device 431 Semiconductor laser array

Claims (2)

[Claims] 1. An image forming apparatus having a memory means for storing image data, wherein an outline font is multi-valued as intermediate density information and developed into a bit map in the memory means, and then output pixels are output from the bit map. An image forming method characterized in that a writing position is calculated, and a dot latent image whose recording position is modulated in the main scanning direction is formed based on the calculation result. 2. The image forming method according to claim 1, wherein the recording position modulation in the main scanning direction is performed by selecting a reference wave.