JPH04226481A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device having the improvement of the sharpness of an image produced by a color scanner, a CG, font data, etc., but not having irregularities in scanning. CONSTITUTION:For generating a modulation signal that image density data from an image density data storage circuit 210 is modulated with a reference wave signal, a circuit 241 for detecting edges in all directions with respect to the image density data, a selecting circuit 243 selectively outputting the image density data based on the result of the detection, plural modulating circuits 260 modulating the image density data with plural reference waves, and a selecting circuit 245 synthesizing the modulation signal from the above- mentioned plural modulating circuits, are provided. Therefore, the image forming device for improving the sharpness of the image is obtained.

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 that reproduces halftones by recording dots using a modulation signal modulated by a reference wave signal, and particularly relates to an image forming apparatus that modulates image density data.

0002

2. Description of the Related Art In the field of image forming apparatuses using electrophotography, a scanner reads an original image as an image signal, and refers to image density data obtained by subjecting the image signal to gradation correction, A/D conversion, and shading correction. A digital image with halftone reproduction is obtained by modulating it with a wave signal.

[0003] When an image signal of a document image is read by a scanner, the edge portion of the image is read as a halftone density due to the aperture of a solid-state image sensing device built into the scanner. When forming a latent image on a photoconductor using 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 if the density is intermediate. As a result, the image will be recorded with reduced sharpness. This cannot be addressed even by adding MTF correction or the like to the image signal.

On the other hand, C. Similar problems arise even when interpolated characters and figures are created from G or font data. In other words, if the edge portion is smoothly interpolated with intermediate density using interpolation data, the recording pixel corresponding to the edge portion will be recorded as an average density in the pixel, and if recorded, the resolution will be lowered. For this reason, intermediate density processing is required at the edge portions of the image. As a conventional technique for solving this problem, U. S. P4,
847,641 are known. This is applied to a bitmap-developed binary image. That is, a matching table is used to determine the distribution of adjacent pixels for the image edge portion of interest, and the image density and position of the edge portion pixel of interest are redistributed.

[0005] However, when handling high-quality images, the image data becomes a multivalued image, and unlike the case of the above-mentioned binary image, (1) intermediate density information is present in the pixel of interest; ■There are problems in that the amount of information in the matching table becomes enormous, increasing costs and making high-speed processing difficult.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an image forming apparatus that efficiently handles multivalued image data and obtains high-quality images.
The object of the present invention is to improve the sharpness of images created from scanners, CG, font data, etc., and to provide an image forming apparatus with high sharpness without scanning unevenness.

[0007]

[Means for Solving the Problems] The above object is to provide an image forming apparatus that forms an image on an image forming body by oscillating a plurality of lasers using a modulation signal obtained by modulating image density data with a reference wave signal. An image forming apparatus comprising: an image density distribution detection circuit; and a combination modulation means for selectively combining a laser and a reference wave having a phase different from the image density data based on the detection result to modulate the image density. achieved.

Furthermore, in an image forming apparatus that forms an image on an image forming body by oscillating a plurality of lasers modulated by image density data, the number of light emitting elements of the laser is equal to the number of scans per pixel in the main scanning direction. This is achieved by an image forming apparatus characterized by the corresponding characteristics.

[0009]

Embodiment The configuration of an image forming apparatus 1000 according to this embodiment will be explained.

FIG. 5(a) is a perspective view showing the schematic structure of the image forming apparatus of this embodiment.

The color image forming apparatus 1000 uniformly charges a drum-shaped photoreceptor 1 as an image forming member, and then converts digital image density data from a computer or scanner into dot-like static light using pulse-width modulated or intensity-modulated spot light. An electrostatic latent image is formed, this is reversely developed with toner to form a dot-like toner image, and the above-mentioned charging, exposure and development steps are repeated to form a color toner image on the photoreceptor 1, and the color toner image is is transferred, separated, and fixed to obtain a color image.

The image forming apparatus 1000 includes a drum-shaped photoreceptor (hereinafter simply referred to as photoreceptor) 1 that rotates in the direction of the arrow.
, a scorotron charger 2 that applies a uniform charge to the photoreceptor 1, a scanning optical system 30, developing devices 41 to 44 loaded with yellow, magenta, cyan, and black toners, a cleaning device 3, etc. .

The configuration of each part will be explained below.

The scanning optical system 30 causes a semiconductor laser array 31 to oscillate with a modulation signal modulated with image density data from a page memory (not shown), and deflects this laser light with a polygon mirror 34 rotating at a predetermined speed. , an f-theta lens 35 and cylindrical lenses 33 and 36 scan the top surface of the photoconductor 1, which is uniformly charged, into a fine spot. A semiconductor laser array 31 is provided as a coherent light source, and a collimator lens is used as a light emitting optical system. 32, a polygon mirror 34 and an fθ lens 35 are provided as a deflection optical system, and cylindrical lenses 33 and 36 are provided as a surface tilt correction optical system using the polygon mirror 34.
is provided.

The scanning optical system 30 includes an index detection circuit (not shown), and detects the surface position of the polygon mirror 34 rotating at a predetermined speed based on the index signal from the index sensor 39, and detects the period in the main scanning direction. In this way, optical scanning is performed using a modulated digital image density signal, which will be described later, using a raster scanning method.

The semiconductor laser array 31 has semiconductor lasers 31a to 31c arranged on a substrate at intervals of, for example, 0.1 mm. The semiconductor laser array 31 is made of GaAlA.
The maximum output is 5mW, and the light efficiency is 25%.
The divergence angle is 8 to 16 degrees in the direction parallel to the joint surfaces and 20 to 36 degrees in the direction perpendicular to the joint surfaces. Further, since the color toner images are sequentially superimposed on the photoreceptor 1, exposure with light of a wavelength that is less absorbed by the colored toner is preferable, and the wavelength of the beam in this case is 800 nm.

FIG. 7 is a sectional view showing a specific example of the structure of a high γ photoreceptor preferably used in the present image forming apparatus.

The main structure of the high γ photoreceptor of this embodiment will be explained below. As shown in FIG. 7, the photoreceptor 1 includes a conductive support 1A, an intermediate layer 1B, and a photosensitive layer 1C. The thickness of the photosensitive layer 1C is about 5 to 100 μm, preferably 10 to 50 μm. The photoreceptor 1 uses a drum-shaped conductive support 1A made of aluminum with a diameter of 150 mm, and an intermediate layer 1B with a thickness of 0.1 μm made of ethylene-vinyl acetate copolymer is formed on the support 1A. A photosensitive layer 1C with a film thickness of 35 μm is provided on 1B.

As the conductive support 1A, a drum with a diameter of about 150 mm made of aluminum, steel, copper, etc. is used, but it is also possible to use a belt-like material made of paper, a plastic film laminated or vapor-deposited with a metal layer, or a drum made of aluminum, steel, copper, etc. It may also be a metal belt such as a nickel belt made by the chewing method. In addition, the intermediate layer 1B can withstand high charging of ±500 to ±2000V as a photoreceptor, and for example, in the case of positive charging, it blocks injection of electrons from the conductive support 1A and provides excellent light attenuation characteristics due to the avalanche phenomenon. It is desirable that the intermediate layer 1B has hole mobility so that the
It is preferable to add 10% by weight or less of the positively charged charge transport material described in Japanese Patent No. 1-188975. As the intermediate layer 1B, the following resins, which are usually used in photosensitive layers for electrophotography, can be used.

(1) Vinyl polymers such as polyvinyl alcohol (Poval), polyvinyl methyl ether, polyvinylethyl ether, etc. (2) Polyvinylamine, poly N-vinylimidazole, polyvinylpyridine (quaternary salt), polyvinylpyrrolidone, vinylpyrrolidone- Nitrogen-containing vinyl polymers such as vinyl acetate copolymers (3) Polyether polymers such as polyethylene oxide, polyethylene glycol, and polypropylene glycol (4) Acrylics such as polyacrylic acid and its salts, polyacrylamide, and polyβ-hydroxyethyl acrylate Acid-based polymers (5) Methacrylic acid-based polymers such as polymethacrylic acid and its salts, polymethacrylamide, polyhydroxypropyl methacrylate (6) Methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose,
Ether cellulose polymers such as hydroxypropyl methylcellulose (7) Polyethyleneimine polymers such as polyethyleneimine (8) Polyalanine, polyserine, poly L-glutamic acid, poly(hydroxyethyl)-L-glutamine, poly-δ-carboxymethyl - Polyamino acids such as L-cysteine, polyproline, lysine-tyrosine copolymer, glutamic acid-lysine-alanine copolymer, silk fibroin, casein, etc. (9) Starches such as starch acetate, hydroxyethyl starch, amine starch, phosphate starch, etc. Derivatives (10) Polyamides such as soluble nylon, methoxymethyl nylon (type 8 nylon), etc., which are soluble in a mixed solvent of water and alcohol, photosensitive layer 1C, are basically photosensitive without the use of a charge transport substance. 0. made of conductive pigment.
A coating solution is prepared by mixing and dispersing phthalocyanine particles with a diameter of 1 to 1 μm, an antioxidant, and a binder resin using a solvent for the binder resin. It is formed by applying it to the intermediate layer, drying it, and subjecting it to heat treatment if necessary.

[0021] When a photoconductive material and a charge transport substance are used together, a photoconductive pigment and one of the photoconductive pigments may be used together.
The photosensitive layer is composed of a small amount of a charge transport material of 1/5 or less, preferably 1/1000 to 1/10 (weight ratio), and is dispersed in a photoconductive material, an antioxidant, and a binder resin.

In this embodiment, since the color toner image is superimposed on the photoreceptor, a photoreceptor having spectral sensitivity on the long wavelength side is required so that the beam from the scanning optical system does not block the color toner image.

The light attenuation characteristics of the high γ photoreceptor of this example will be explained below.

FIG. 6 is a schematic diagram showing the characteristics of a high γ photoreceptor. In the figure, V1 is the charged potential (V), V0 is the initial potential before exposure (V), and L1 is the amount of laser beam irradiation required for the initial potential V0 to attenuate to 4/5 (μJ/cm2).
), L2 represents the amount of laser beam irradiation (μJ/cm2) required for the initial potential V0 to attenuate to 1/5.

[0025] The preferred range of L2/L1 is 1.0≦L2.
/L1≦1.5.

In this embodiment, V1=1000 (V), V0
=950(V), L2/L1=1.2. Further, the potential of the photoreceptor in the exposed area is 10V.

The photosensitivity at the position corresponding to the middle period of exposure, where the optical attenuation curve attenuates the initial potential (V0) to 1/2, is expressed as E.
1/2 and the photosensitivity at a position corresponding to the initial stage of exposure when the initial potential (V0) is attenuated to 9/10 is E9/10, (E1/2)/(E9/10)≧2 Preferably. A photoconductive semiconductor is selected that provides the relationship (E1/2)/(E9/10)≧5. Note that here, the photosensitivity is defined as the absolute value of the amount of potential drop with respect to the minute exposure amount.

In the optical attenuation curve of the photoreceptor 1, as shown in FIG. 6, the absolute value of the differential coefficient of the potential characteristic, which is photosensitivity, is small when the amount of light is small, and attenuates steeply as the amount of light increases. Specifically, as shown in FIG. 6, the light attenuation curve exhibits a light attenuation characteristic that is almost flat for a short period of time L1 during the initial period of exposure, but the sensitivity characteristics are poor and the light attenuation characteristics remain almost unchanged from the middle period of exposure L1 to L2. This results in ultra-high sensitivity and ultra-high γ characteristics that descend almost linearly. Specifically, photoreceptor 1 is +500 to +20
It is thought that high gamma characteristics are obtained by utilizing the avalanche phenomenon under high charging of 00V. In other words, 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 light attenuation is reliably suppressed, resulting in an extremely rapid avalanche in the middle stage of exposure. It is understood that a phenomenon occurs.

FIG. 4 is a schematic diagram when a latent image is formed using a modulation signal from the image processing apparatus of this embodiment.

The image forming apparatus 1000 of this embodiment expresses gradation by changing the area of dots. Further, as described above, in an image signal created by a computer or read by a scanner, when an edge portion with a high image density falls on a read pixel, the signal at the corresponding pixel becomes similar to the intermediate density in a uniform image. If the same reference wave is used without adopting a select circuit with edge detection in all directions, recording at the edge will be formed in isolation at the center of the pixel, as shown by the dotted line, as shown in Figure 4. become. Therefore, the image forming apparatus 1000 is capable of forming a dot-like latent image on the photoreceptor 1 by shaking it in all directions by shaking it in the main scanning direction and the sub-scanning direction. As a result, points at the edge portion are recorded on the photoreceptor 1 closer to the edge in all directions including the main/sub-scanning directions. In this way, the resolution at the edge portion of the electrostatic latent image is improved.

FIG. 1 is a block diagram showing an embodiment of an image processing circuit employed in the image forming apparatus of this embodiment, and FIG. 2 is a block diagram showing a modulation circuit of this embodiment.

The image processing circuit of this embodiment is a circuit that constitutes a driving circuit of a scanning optical system, and is a circuit that constitutes a driving circuit of a scanning optical system.
00, a modulation signal generation circuit, and a raster scanning circuit. The image data processing circuit 100 is a circuit that interpolates and outputs edge portions of font data, and includes an input circuit 110 made up of a computer, and a font data generation circuit 120.
, a font data storage circuit 130 , and an interpolation data generation circuit 140 , and sends the character code signal, size code signal, position code signal, and color code signal from the input circuit 110 to the font data generation circuit 120 . Font data generation circuit 120 selects an address signal from four types of input signals and sends it to font data storage circuit 130. Font data storage circuit 130 sends font data corresponding to one character corresponding to the address signal to font data generation circuit 120. Font data generation circuit 120 sends font data to data generation circuit 140, which interpolates the font data. Interpolation data generation circuit 1
Reference numeral 40 interpolates jaggedness or jumps in the image density data occurring at the edge portions of the font data using an intermediate density, and sends the interpolated image density data to the image density data storage circuit 210 consisting of a frame memory. Also, regarding the generated color, depending on the color code,
The corresponding colors are converted into density data of each Y, M, C, and BK. In this way, the font is bit map developed in each frame memory with each color having the same shape but different density ratios.

The image processing circuit of this embodiment is a circuit that drives the semiconductor laser array 31 using a modulation signal obtained by pulse width modulating image density data, and corresponds to, for example, a plurality of pixels adjacent in all vertical, horizontal, and diagonal directions. It has a function to detect the density gradient between pixel density data and to shift the imaging center of the beam formed on the photoreceptor 1 in the main/sub direction. circuit 24
1. Image discrimination circuit 242, selection circuits 243, 245
, modulation circuits 260A to 260C, a synthesis circuit 270, a reference clock generation circuit 280, a delay circuit group 282, and delay circuits 291 and 292.

The reference clock generation circuit 280 is a pulse signal generation circuit that generates a pulse signal having the same repetition period as the pixel clock, and for convenience, this clock is referred to as a reference clock DCK0.

The delay circuit group 282 uses the reference clock DCK
This is a circuit that generates a plurality of pixel clocks DCK1 and DCK2 having a phase difference of 1/n period from the reference clock DCK0.
Pixel clock DC whose phase is advanced by 1/3 period relative to
Generate K2.

Here, the image density data storage circuit 210 is a normal page memory (hereinafter simply referred to as page memory 210), and is a RAM (random access memory) that stores data in units of pages, and stores at least one page (one screen). It has a capacity to store multivalued image density data corresponding to Furthermore, if the device is to be used as a color printer, it will be equipped with a page memory capable of storing image density signals corresponding to color components of a plurality of colors, for example, yellow, magenta, cyan, and black.

The readout circuit 220 uses the index signal as a trigger to read out, for example, image density data of three adjacent scanning lines to the edge detection circuit 241 in all directions including the horizontal, vertical, and diagonal directions in synchronization with the reference clock DCK0. Image density data corresponding to the central scan line to be recorded among the three scan lines is sent to the latch circuit 230.

The latch circuit 230 is a circuit that latches image density data only while the omnidirectional edge detection circuit 241 is executing the process.

The omnidirectional edge detection circuit 241 sequentially detects image density data corresponding to a plurality of pixels adjacent in all directions, that is, vertically, horizontally, and diagonally, with respect to image density data in three scanning lines that are input in parallel. A difference is made, and a select signal corresponding to the difference result is read out from the built-in memory and sent to the select circuits 243 and 245. In other words, the omnidirectional edge detection circuit 241 detects data corresponding to an edge from three lines of adjacent image density data, and furthermore,
Detect edge orientation. Here, the direction of the edge is
In the image density data, there is a change from low density to high density, and the image forming apparatus 1000 of this embodiment
In this method, the latent image corresponding to the edge is formed by moving the recording device toward the side where the image density is higher.

According to the present invention, when information from the omnidirectional edge detection circuit 241 is used to select a reference wave, a good image can be obtained for character reproduction, but edge portions tend to be emphasized for halftone reproduction. was recognized. Therefore, it is more preferable to select a reference wave by combining image discrimination and edge detection information. The image discrimination circuit 242 indicated by the broken line in FIG. 1 indicates this.

The image discrimination circuit 242 determines whether the image is a character, a halftone, or a halftone dot, and when it is determined that the image is a character or a halftone dot, a reference wave is determined based on the edge detection judgment of the present invention described above. Select a combination with On the other hand, if it is determined that the tone is an intermediate tone, a combination with a reference wave written from the center of the pixel is selected. That is, in the embodiment shown in FIG. 1, image modulation is performed only by the modulation circuit 260A. It is preferable to prepare a plurality of line memories and perform the above image judgment and edge detection based on two-dimensional information. In this way, a more favorable image reproduction was obtained.

[0042] In addition to the present invention, as a circuit for combining image data and a reference wave, a circuit that selects from among a plurality of reference waves based on image discrimination and edge detection information, and then combines the selected reference wave and the image. It is also possible to have a configuration in which data is combined and modulated.

In the omnidirectional edge detection circuit 241, if the difference value is equal to or greater than the specific value α, “+1”
is output, and if it is less than -α, outputs "-1". Image data other than edges, i.e. differential value is from -α to +α
If it is between, the difference value is set to "0". The difference results obtained in this way are temporarily set in the main scanning direction (-1, 0
), (0, -1) in the sub-scanning direction, (0, -1) in the diagonal left direction, and (0, 0) in the diagonal right direction, then the movement in this combination is In this example, the position is read from a reference table in the ROM, and in this correspondence table, (+1, -1) is output for the combination of input data. As a result, the recording position is selectively moved by +1/3 in the main scanning direction, and the laser scanning downward in the sub-scanning direction is selected. Also, it is (0, -1) in the main scanning direction and (0, -1) in the sub-scanning direction.
,0), and (0,0) in the left diagonal direction,
If (0, 0) in the right diagonal direction, then (-1,
0) Output. In this case, move the recording position by -1 in the main scanning direction.
/3 Move.

The select circuit 243 corresponds to a first select circuit, and outputs image density data from different output terminals D0 to D2 in accordance with a select signal. Specifically, if it is "0", image density data is sent from the output terminal D0, and the image density data sent from D1 and D2 is of the image density of a white background. If it is ``-1'', image density data is sent from output terminal D2, and D0, D
The image density data sent from 1 is the image density data corresponding to the image density of a white background. If it is "+1", image density data is sent from the output terminal D1, and image density data sent from D0 and D2 corresponds to the image density of a white background.

The modulation circuits 260A to 260C have the same circuit configuration as shown in FIG. 2, and the D/A conversion circuit 261,
Consisting of a comparator 262 and a triangular wave generation circuit 263, the image density data sent from the select circuit 243 is synchronized with the reference clock DCK0 to the D/A conversion circuit 263.
This circuit performs D/A conversion using the triangular wave generating circuit 263 to form a waveform of a pixel clock having the same period as the reference clock DCK0, and compares these signals to obtain a pulse width modulation signal. The modulation circuits 260A to 260C all perform D/A conversion of image density data using a reference clock DCK0, and only the phase of the clock input to the triangular wave generation circuit 263 differs. Here, triangular wave generation circuit 2
The triangular wave reference clocks 63A to 263C are used to shift the phase of the reference clock by 1/3 cycle, and by selecting these modulation circuits 260A to 260C, it is possible to adjust the phase of continuous image density data as a scanning line by 1/3 period. Edge processing will be performed in the main scanning direction on the portion that is to be processed. Details will be described later.

The synthesis circuit 270 is the modulation circuit 260 described above.
This is a circuit that synthesizes modulated signals from A to 260C.

[0047] Select circuit 245 and delay circuit 291,
292 corresponds to an LD drive circuit that drives the semiconductor laser array 31. The LD drive circuit oscillates the semiconductor laser selected based on the selection signal with the modulation signal from the synthesis circuit 270, thereby focusing the beam formed from the scanning optical system 30 in the sub-scanning direction.

The select circuit 245 corresponds to the second select circuit, and the omnidirectional edge detection circuit 241
Semiconductor lasers 31a to 31c are activated by a select signal from
This circuit turns on only one of the following. As a result, edge processing is executed in the sub-scanning direction. Details will be described later.

The delay circuits 291 and 292 prevent delays in the scanning start point caused by the tilt of the substrate of the semiconductor laser array 31 and the scanning optical system.

Although the above image processing circuit has been described as being applied to a laser printer, it is not limited to this, and if it is a circuit that inputs image density data from a scanner and performs image processing, it can be applied to a copying machine. It can be applied to other image forming apparatuses such as. FIG. 5(b) shows a laser spot on the photoreceptor 1 caused by the semiconductor laser array 31.

Semiconductor laser array 3 shown in FIG. 5(b)
The laser spot according to No. 1 is a semiconductor laser array having three light emitting elements at equal intervals, which are positioned at an angle with respect to the main scanning direction, and laser spots 31a, 31b, and 31c are focused on the photoreceptor 1. The distance h between the imaging centers of the laser spots is determined by the inclination angle of the semiconductor laser array 31. Laser spots 31a, 31b, and 31c indicated by solid lines in the figure are the delay circuits 29
1,292 is not functioning and a beam is imaged on the photoreceptor 1. When the delay circuits 291 and 292 function, the laser spot 31a is delayed to the laser spot 31a' shown by the dashed line, and the laser spot 31b is delayed to the laser spot 31b' shown by the chain line, and the laser spots 31a', 31b', The phases of the imaging centers of 31c are the same.

In the embodiment shown in FIG. 5(b), the number of scans per pixel in the main scanning direction is three, and one pixel is scanned in one scan by a semiconductor laser array consisting of three light emitting elements. It was designed to do this. If the number m of light emitting elements of the semiconductor laser array and the number m of scans per pixel in the main scanning direction are made to correspond (make equal), one scan will scan one pixel, and the distance between pixels will be Scanning unevenness that occurs will be reduced.

Further, a laser h≦(
D/m) h≦(D/m), more preferably h<
(D/m), the scanning interval between adjacent pixels becomes (D/m) or more, and D/(m+2)<h<
(D/m) Overlapping of beams between pixels is reduced, scanning unevenness is eliminated, and a high-resolution image is obtained. According to experimental results, it is generally preferable to set D/m+2<h<D/m. Here, m is an integer greater than 2. In the example shown in FIG. 5(b) (corresponding to m=3), (D
/5)<h<(D/3) Compared to the case where the semiconductor laser array 31 was tilted and set at equal intervals, a better image with less scanning unevenness was obtained.

FIG. 4 is a schematic diagram when a latent image is formed using a modulation signal from the image processing apparatus of this embodiment.

The image forming apparatus 1000 of this embodiment expresses gradations by changing the area of dots. Further, the image forming apparatus 1000 is capable of forming a dot-like latent image on the photoreceptor 1 by shaking in all directions by shaking in the main scanning direction and the sub-scanning direction. An image processing circuit executes this scanning. Therefore, in the image forming apparatus 1000, as described above, an image signal created by a computer or read by a scanner is such that when an edge portion with a high image density falls on a reading pixel, the signal at the corresponding pixel is an intermediate density image in a uniform image. It will be the same as If the same reference wave is used without adopting a select circuit with edge detection in all directions, recording at the edge will be formed in isolation at the center of the pixel, as shown by the dotted line, as shown in Figure 4. become. Therefore, according to the image processing circuit, points at the edge portion are recorded closer to the edge in all directions including the main/sub-scanning directions. By forming an electrostatic latent image in this manner, the resolution of the edge portion is improved.

Next, the operation of the image processing circuit will be explained.

FIGS. 3A to 3I are time charts showing signals of each part of the image processing circuit of this embodiment.

In the figure, (a) shows the page memory 210
The reference clock DC is triggered by the index signal from
A portion of image density data for one scanning line read out based on K0 is shown. The image density data for one scanning line is simultaneously sent from the readout circuit 220 to the omnidirectional edge detection circuit 241 and the latch circuit 230. In the image density data, the higher the level, the lighter the density, and the lower the level, the higher the density. (b) shows the state of the main scanning direction edge detection circuit 241. As shown in the figure, level changes between pixels of continuous image density data, that is, differential values are output. Thereby, the slope of image density in one scanning line is detected. This differential value is the absolute value α
In the above cases, it is determined that there is a slope. Furthermore, the direction of the edge portion of the image density is detected. In other words, if the output value is a "positive value", it indicates that the edge is located on the left in the main scanning direction, and if the output value is a "negative value", it is located on the right in the main scanning direction. It shows that it is an edge. Edge detection in other directions is similarly performed in this way, and the moving position of the recording position in the main scanning and sub-scanning directions is determined from the ROM table. Output value "0"
'' indicates that image density data of the same level is continuous. This output signal is sent to the select circuit 243 based on the reference clock DCK0 as described above.

On the other hand, the latch circuit 230 latches the signal for a time corresponding to the processing speed of the omnidirectional edge detection circuit 241 and sends it to the select circuit 243 . Select circuit 243
transmits density data from different output terminals based on the select signal from the edge detection circuit 241. Below, (c) to (d) show combinations of selected reference waves and image data. As an example, the case where edges exist only in the main scanning direction as shown in FIG. 3(b) is shown. If an edge is detected in an oblique direction, the reference wave and laser to be combined are selected from the ROM table as described above.

(c) shows the modulation operation in the modulation circuit 260A, in which image density data is input to the modulation circuit 260A only when the output value from the omnidirectional edge detection circuit 241 is a positive value, Omnidirectional edge detection circuit 24
If the output value from 1 is any other value, white image density data is input. The triangular wave at this time is a triangular wave that has the same repetition period and is generated from the clock DCK2 whose phase is advanced by 1/3 period with respect to the reference clock DCK0. As a result, the output signal from the modulation circuit 260A obtains a modulation signal that is advanced by 1/3 period compared to the case where the pulse width is modulated with a triangular wave based on the reference clock DCK0, as shown in (f).

(d) shows the modulation operation in the modulation circuit 260B, and the image density data during the period when the select signal from the omnidirectional edge detection circuit 241 is "0" is changed to the image density of a white background at other output values. The data has been entered (
Output a modulated signal as shown in g).

(e) shows the modulation operation in the modulation circuit 260C, in which processing is performed on the image density data of one pixel before the period in which the select signal from the omnidirectional edge detection circuit 241 shows a negative value. and enter it. That is, the output value from the omnidirectional edge detection circuit 241 is "-1"
In the case of , image density data is inputted, and in other output values, image density data of a white background is inputted. The triangular wave is the reference clock DC
It is a triangular wave delayed by 1/3 period with respect to K0. As a result, the output signal from the modulation circuit 260C obtains a modulation signal delayed by 1/3 cycle compared to the case where pulse width modulation is performed using a triangular wave based on the reference clock DCK0, as shown in (h).

(i) shows a modulated signal output from the combining circuit 270. As described above, the image processing circuit in this embodiment uses the omnidirectional edge detection circuit 241 to detect the edges and the direction of the edges from the image density data, so that the image processing circuit detects the edges and the direction of the edges from the image density data in units of one scanning line shifted by the main scanning direction component of the deviation. The modulated signal is output to the data terminal of the select circuit 245.

Next, the select signal from the omnidirectional edge detection circuit 241 is delayed by a delay circuit 244 by the processing time in the modulation circuit and the synthesis circuit, and is sent to the select circuit 245. The select circuit 245 sends density data to only a specific laser to cause it to emit light based on the select signal from the omnidirectional edge detection circuit 241. Select circuit 245
The modulated signals from the output terminals D0 and D1 of the delay circuit 29
1 and 292, the semiconductor lasers 31a and 31b are caused to oscillate with a delay so as to correct the deviation of the starting point in the main scanning direction. In addition, since the semiconductor lasers 31a to 31c, which are the light emitting points of the semiconductor laser array 31, are set to be imaged by the scanning optical system 30 with a shift of 1/3 pixel width in the sub-scanning direction, the presence of edges This means that the sub-scanning direction component is shifted in the direction of

As described above, the image forming apparatus 100 of this embodiment
0 can improve the resolution of the edge portion by correcting and forming the edge portion of the electrostatic latent image.

The image forming process of image forming apparatus 1000 will be explained below.

First, the photoreceptor 1 is uniformly charged by the scorotron charger 2. An electrostatic latent image corresponding to yellow is formed on the photoreceptor 11 by irradiation with a laser beam modulated by yellow data (8-bit digital density data) from the frame memory 210. The electrostatic latent image corresponding to yellow is developed by the first developing device 41, and a first dot-shaped toner image (yellow toner image) with extremely high sharpness is formed on the photoreceptor 11. This first toner image is not transferred onto the recording paper P, but is charged again onto the photoreceptor 1 by the scorotron charger 2. Next, the laser light is optically modulated using magenta data (8-bit digital density data), and the modulated laser light is irradiated onto the photoreceptor 1 to form an electrostatic latent image. This electrostatic latent image is developed by the second developing device 42 to form a second toner image (magenta toner image). In the same manner as described above, the toner images are sequentially developed by the third developing device 43 to form a third toner image (cyan toner image), and a three-color toner image that is sequentially stacked on the photoreceptor 1 is formed. Finally, a fourth toner image (black toner image) is formed, and four-color toner images are sequentially stacked on the photoreceptor 1.

According to the image forming apparatus 1000 of this embodiment, the photoreceptor has excellent high gamma properties, and this excellent high gamma property is maintained over a large number of times through the steps of charging, exposing and developing the toner image. A latent image is stably formed even when toner images are repeatedly formed one on top of the other. That is,
Even if a beam is irradiated from above the toner image based on the digital signal, a dot-shaped electrostatic latent image with no fringes and high sharpness is formed, and as a result, a toner image with high sharpness can be obtained.

After the photoreceptor 1 is charged by a charger (this may be omitted), these four-color toner images are transferred onto recording paper P fed from a paper feeder by the action of a transfer device.

The recording paper P carrying the transferred toner image is separated from the photoreceptor 1 by a separation electrode, conveyed by a guide and a conveyor belt, carried into a fixing device, heated and fixed, and discharged onto a paper discharge tray.

In this embodiment, the phase is set to 0, ±1/
Although three reference waves shifted by 3 are used, reference waves with other phases can also be used. For example, if the phase is (0,
A value such as ±1/4) or (0, ±1/6) can be used. Further, it is preferable to use three or more reference waves and use them as needed depending on the image density and edge detection output. For example, a reference wave with a phase of (0, ±1/6, ±2/6) may be used. In this way, by selecting reference waves having different phases according to the image density data, it is possible to obtain an image with high sharpness that is in harmony with the density of adjacent images.

On the other hand, C. It is also possible to create interpolated characters and figures from G and font data. That is, as shown in the image data processing circuit 100 in FIG. 1, edge portions are smoothly interpolated with intermediate density using interpolation data. That is, it is expanded into multivalued data and temporarily stored in the image density data storage circuit 210. The recorded pixels corresponding to the edge area are recorded in memory as the average density within the pixel, so
If recorded as is, the resolution will decrease. Therefore, as described above, a sharp image can be obtained by performing intermediate density processing for changing the recording position in a pixel for the edge portion of the image.

[0073]

As explained above, in an image forming apparatus that oscillates a plurality of lasers using a modulation signal obtained by modulating image density data with a reference wave signal to form an image on an image forming body, the image density of adjacent images can be adjusted. Image forming according to the present invention, comprising: a distribution detection circuit; and a combination modulation means for modulating image density by selectively combining a laser and a reference wave having a phase different from image density data based on the detection result. More specifically, in an image forming apparatus that oscillates a semiconductor laser array using a modulation signal obtained by modulating image density data with a reference wave signal to form an image on an image forming body, adjacent pixels are used as density distribution detection means for adjacent pixels. and combination modulation means for modulating image density by selectively combining a reference wave having a phase different from image density data and a semiconductor laser based on the detection result using main scanning and sub-scanning direction edge detection circuits. As a result, it was possible to provide an image forming apparatus that improves the sharpness of images created from scanners, CG, font data, and the like.

The present invention also provides that the combination modulation means includes a first selector circuit that selectively outputs the image density data;
By including a plurality of modulation circuits that modulate image density data using the reference waves having different phases, and a second selection circuit that selectively turns on only one of the semiconductor laser arrays, it is possible to It was possible to provide an image forming apparatus that improves the sharpness of images created from data and the like.

Furthermore, in an image forming apparatus that forms an image on an image forming body by oscillating a plurality of lasers modulated by image density data, the number of light emitting elements of the laser is equal to the number of scans per pixel in the main scanning direction. The image forming apparatus of the present invention, which is characterized in that it corresponds to the above, makes it possible to obtain high-resolution images without scanning unevenness.

[Brief explanation of the drawing]

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

FIG. 2 is a block diagram showing a modulation circuit of this embodiment.

FIGS. 3(a) to 3(i) are time charts showing signals of each part of the image processing circuit of this embodiment.

FIG. 4 is a schematic diagram when a latent image is formed using a modulation signal from the image processing device of this embodiment.

FIG. 5(a) is a perspective view showing a schematic configuration of the image forming apparatus of this embodiment, and FIG. 5(b) is a diagram showing a laser spot on a photoreceptor by a laser array.

FIG. 6 is a graph showing the characteristics of a high γ photoreceptor.

FIG. 7 is a cross-sectional view showing a specific configuration example of a high γ photoreceptor.

[Explanation of symbols]

1 Photoreceptor as an image forming body 31 Semiconductor laser array 241 Omnidirectional edge detection circuit 243, 245 Select circuit 260A~260C Modulation circuit 1000 Image forming device DCK0 Reference clock

Claims (7)

[Claims] 1. An image forming apparatus that forms an image on an image forming body by oscillating a plurality of lasers using a modulation signal obtained by modulating image density data with a reference wave signal, comprising: an image density distribution detection circuit for adjacent images; An image forming apparatus comprising: a combination modulation means for modulating image density by selectively combining a reference wave and a laser having a phase different from that of image density data based on a detection result. 2. The combination modulation means includes a first selector circuit that selectively outputs the image density data, a plurality of modulation circuits that modulate the image density data using the reference waves having different phases, and a plurality of lasers. 2. The image forming apparatus according to claim 1, further comprising a second select circuit that selectively turns on only one of them. 3. The image forming apparatus according to claim 1, wherein the plurality of lasers are semiconductor laser arrays. 4. The image forming apparatus according to claim 1, wherein the detection circuit is an edge detection circuit in main scanning and sub-scanning directions. 5. In an image forming apparatus that forms an image on an image forming body by oscillating a plurality of lasers modulated according to image density data, the number of light emitting elements of the laser is equal to the number of scans per pixel in the main scanning direction. An image forming apparatus characterized by being compatible with the above. 6. The image forming apparatus according to claim 5, wherein the scanning interval by the light emitting elements formed on the image forming body is set to be narrower than a value obtained by dividing one pixel width by the number of scans. . 7. The image forming apparatus according to claim 5, wherein the plurality of lasers are semiconductor laser arrays.