JP3131653B2 - Image forming device - Google Patents

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 performing dot recording of image data for one pixel with a modulation signal obtained by modulating a reference wave signal or the like to reproduce characters and halftone images with excellent clarity. It is about.

[0002]

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

An image signal of a document image read by a scanner is read as a halftone density at an edge portion of the image due to an aperture of a solid-state image pickup device incorporated in the scanner. When a latent image is formed on a photoreceptor using image density data obtained from this image signal, recording pixels corresponding to an edge portion of the latent image are averagely recorded in the recording pixels when the density is intermediate. Therefore, the image is recorded with reduced sharpness. This cannot be dealt with even by adding MTF correction or the like to the image signal.

[0004] On the other hand, the same problem arises even when an interpolated character or figure is created from CG or font data. That is, when the edge portion is smoothly interpolated with the intermediate density using the interpolation data, the recording pixel corresponding to the edge portion is recorded as an average density in the pixel, so that the resolution of the recorded image is reduced.
For this reason, intermediate density processing is required at the image edge.

[0005]

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

[0006]

An object of the present invention is to record a pixel by density data corresponding to the pixel in a scanning direction in the pixel and in a scanning direction in the pixel.
In an image forming apparatus that performs high-density pixel printing by performing the above process at a plurality of small pixel positions divided in the sub-scanning direction, the recording density of each small pixel is determined from the density distribution of adjacent pixels including the target pixel. The recording density distribution within the pixel is determined, and the recording of each small pixel in the main scanning direction within the pixel of interest is
When the calculation for calculating the center of gravity of the density data of each small pixel located in the scanning direction is performed, the density information is modulated by a reference wave having a phase corresponding to the position of the center of gravity , and recording in the main scanning direction is performed.
In each case, the recording of each small pixel in the sub-scanning direction is
This is achieved by an image forming apparatus characterized in that recording is performed by a scanning line that scans a portion in the main scanning direction .

In a preferred embodiment, there are a plurality of recording positions in the pixel, and the density information is modulated by a selected reference wave.

[0008]

Embodiment (Embodiment 1) The configuration of an image forming apparatus 400 according to an embodiment of the present invention will be described. FIG. 10 is a perspective view showing a schematic configuration of the image forming apparatus of the present embodiment.

The color image forming apparatus 400 compares an analog image density signal obtained by D / A conversion of digital image density data from a computer or a scanner after uniformly charging a photosensitive member with a reference wave signal. A dot-like electrostatic latent image is formed by spot light that has been binarized or pulse-width-modulated or intensity-modulated based on a modulation signal obtained by differential amplification, and this is reverse-developed with toner to form a dot. A color toner image is formed, and the charging, exposing and developing steps are repeated to form a color toner image on the photoreceptor 1, and the color toner image is transferred, 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 which rotates in the direction of an arrow, and a scorotron charger 402 which applies a uniform charge on the photosensitive member 401. , Scanning optical system 430, developing units 441 to 444 loaded with yellow, magenta, cyan and black toners, pre-transfer charger
461, scorotron transfer unit 462, separator 463, fixing roller 4
64, 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 FIG. 9 shows a specific configuration example thereof.

The photosensitive member 401 comprises a conductive support 401A, an intermediate layer 401B and a photosensitive layer 401C as shown in FIG. The thickness of the photosensitive layer 401C is about 5 to 100 μm, preferably 10 to 100 μm.
5050 μm. The photosensitive member 401 uses a drum-shaped conductive support 401A made of aluminum having a diameter of 150 mm.
0.1μm thick ethylene-vinyl acetate copolymer
Of the intermediate layer 401B having a thickness of 35 μm
m photosensitive layer 401C.

As the conductive support 401A, a drum made of aluminum, steel, copper, or the like having a diameter of about 150 mm is used. In addition, a belt-shaped metal sheet laminated or vapor-deposited on paper or a plastic film, or an electroconductive support sheet is used. It may be a metal belt such as a nickel belt made by a brazing method. The intermediate layer 401B withstands a high charge of ± 500 to ± 2000 V as a photoreceptor. For example, in the case of a positive charge, injection of electrons from the conductive support 1C is prevented, and excellent light attenuation characteristics due to an avalanche phenomenon are obtained. It is desirable that the intermediate layer 401B has a hole mobility, for example, as described in Japanese Patent Application No. 61-1889 previously proposed by the present applicant.
It is preferable to add 10% by weight or less of the positive charge type charge transporting substance described in the specification of Japanese Patent No. 75-75. As the intermediate layer 401B, for example, the following resin which is usually used for a photosensitive layer for electrophotography can be used.

(1) Vinyl polymers such as polyvinyl alcohol (Poval), polyvinyl methyl ether, polyvinyl ethyl ether, etc. (2) Polyvinylamine, poly-N-vinylimidazole,
Nitrogen-containing vinyl polymers such as polyvinyl pyridine (quaternary salt), polyvinyl pyrrolidone, vinyl pyrrolidone-vinyl acetate copolymer, etc. (3) Polyether polymers such as polyethylene oxide, polyethylene glycol, polypropylene glycol, etc. (4) Polyacrylic acid and salts thereof, Acrylic polymers such as polyacrylamide and poly-β-hydroxyethyl acrylate (5) Polymethacrylic acid and its salts, methacrylic polymers such as polymethacrylamide and polyhydroxypropyl methacrylate (6) Methyl cellulose, ethyl cellulose, Ether cellulose polymers such as carboxymethylcellulose, hydroxyethylcellulose and hydroxypropylmethylcellulose (7) polyethyleneimine polymers such as polyethyleneimine ( ) Polyalanine, polyserine, poly -L- glutamic acid, poly - (hydroxymethyl d ethyl) -L- glutamine, poly -δ- carboxymethyl -L- cysteine, polyproline, lysine - tyrosine copolymer, glutamic acid - lysine
-Polyamino acids such as alanine copolymer, silk fibroin, casein, and the like. (9) Starch acetate, hydroxyethyl ethyl starch, starch acetate, hydroxyethyl starch,
Starch such as amine starch and phosphate starch and derivatives thereof (10) Polymer soluble in water and alcohol mixed solvent such as polyamide such as soluble nylon and methoxymethyl nylon (8 type nylon) Is prepared by mixing and dispersing phthalocyanine fine particles of 0.1 to 1 μm in diameter made of a photoconductive pigment and an antioxidant without using a charge transport material together with a binder resin solvent to prepare a coating solution. The liquid is applied to the intermediate layer, dried, and if necessary, heat-treated to form.

When a photoconductive material and a charge transporting material are used in combination, the photoconductive pigment and one of the photoconductive pigments may be used.
The photosensitive layer is formed by dispersing a small amount of a charge transporting substance of / 5 or less, preferably 1/1000 to 1/10 (weight ratio) in a photoconductive material, an antioxidant and a binder resin. By using such a high γ photoreceptor, a sharp latent image can be formed irrespective of the spread of the beam diameter, and recording with high resolution can be performed effectively.

In this embodiment, the color toner image is transferred to the photosensitive member 401.
A photoconductor and an infrared semiconductor laser having a spectral sensitivity on the infrared side are used so that the beam from the scanning optical system is not blocked by the color toner image because the beam is superimposed on the top.

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

FIG. 8 is a graph showing characteristics of the high γ photoreceptor. In the figure, V ₁ is a charged potential (V), V ₀ is an initial potential (V) before exposure, and L ₁ is an irradiation light amount (μJ / cm) of a laser beam required for the initial potential V ₀ to attenuate to 4/5. ² ) and L ₂ represent the irradiation amount (μJ / cm ² ) of the laser beam required for the initial potential V ₀ to decrease to 1/5.

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), is L ₂ / L ₁ = 1.2. Also, the photoconductor potential at the exposed part is 1
0V.

The light sensitivity at the position corresponding to the middle stage of the exposure where the initial potential (V ₀ ) is attenuated to 1/2 in the light attenuation curve is E1 /
When E9 / 10 is the light sensitivity at the position corresponding to the initial exposure in which the initial potential (V ₀ ) is attenuated to 9/10, (E1 / 2) / (E9 / 10) ≧ 2 A photoconductive semiconductor which gives a relationship of (E1 / 2) / (E9 / 10) ≧ 5 is selected. Here, the light sensitivity is defined by the absolute value of the amount of potential decrease with respect to the minute exposure amount.

In the light decay curve of the photosensitive member 401, as shown in FIG. 8, 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. 6, in the initial stage of exposure, the light decay curve shows an almost flat light decay characteristic due to poor sensitivity characteristics for a short period of time. The sensitivity becomes an ultra-high γ characteristic that decreases almost linearly. It is considered that the photoreceptor 1 specifically obtains a high gamma characteristic by utilizing an avalanche phenomenon under high charging of +500 to + 2000V. In other words, the carriers generated on the surface of the photoconductive pigment in the early stage of the exposure are effectively trapped in the interface layer between the pigment and the coating resin, and the light attenuation is surely suppressed, and as a result, extremely rapid after the middle stage of the exposure. It is understood that an avalanche phenomenon occurs.

In the present invention, it is preferable to have a high γ characteristic, but it is possible to achieve a normal light quantity and a proportional decrease in potential.

Next, the image formation according to the present invention will be described. In this image formation, one pixel of interest of the image density data is formed of n × m (horizontal × vertical) small pixels, and the pixel of interest is formed. The distribution of the density data of adjacent pixels is replaced with the distribution of n × m small pixels in the one pixel, and the data of the target pixel multiplied by a constant P is distributed according to the distribution. A reference wave having a different phase is selected based on the image density data of the small pixel, and the density data of the target pixel is modulated by the reference wave to form an image. Image density data processing within the pixel of interest
This is referred to as a resolution improvement process (RE process). This RE
One that selects one of reference waves having different phases based on the processed image density data, and forms an image using a pulse width modulated image signal obtained by combining this reference wave with the original image data. It is. In particular, a high γ photoreceptor is effective for forming a latent image accurately in response to a reference wave.

FIG. 4 is a plan view showing the target pixel as m5, and adjacent pixels including the target pixel as m1 to m9 when the target pixel is divided into, for example, 3 × 3. FIG. Each small part when divided into × 3 small pixels is s1 to s9
It is an enlarged view which shows the case represented by. m1 to m9 and s1 to
s9 also represents the density of that portion.

More specifically, in the RE processing, the density of the small pixel si is determined by the following equation in a case where the target pixel is m5 and the pixel is divided into 3 × 3 small pixels.

Si = (9 × m5 × P × mi / A) + (1−P) × m5 where i = 1, 2,..., 9 and P is also referred to as the intensity of the RE processing. It is a power coefficient, and a numerical value in the range of 0.1 to 0.9 is desirable. It should be noted that some effects can be expected even if P = 1 to simplify the processing. A is the sum of m1 to m9.

In the above equation, (9 × m5 × P × mi / A)
Is a value obtained by multiplying the density of the pixel of interest by P, according to the ratio of the density of the adjacent pixel, and (1-P) × m
Item 5 is the distribution of the remaining density of the target pixel evenly to each small pixel, which means that the blur factor is taken into account.

In the case of a multicolor image, the above RE processing is performed independently for all the colors R, G, B or Y, M, C and black (BK).

FIG. 1 is a block diagram showing an embodiment of an image processing circuit used in the image forming apparatus of the present invention (pixels of 3.times.
FIG. 2 is a block diagram illustrating a reference wave phase determination circuit according to the present embodiment, and FIG. 3 is a block diagram illustrating a modulation circuit according to the present embodiment.

The image processing circuit 1000 of this embodiment is a circuit constituting a driving circuit of a scanning optical system, and includes an image data processing circuit 100, a modulation signal generation circuit 200, and a raster scanning circuit 300.

The image data processing circuit 100 is a circuit for interpolating and outputting an edge portion of font data, and includes an input circuit 110 composed of a computer and a font data generation circuit 12.
0, font data storage circuit 130, interpolation data generation circuit 14
0, a 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 generation circuit 120. The font data generation circuit 120 selects an address signal from the four types of input signals and sends it to the font data storage circuit 130. The font data recording circuit 130 sends font data corresponding to one character corresponding to the address signal to the font data generating 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 jaggies and jumps in the image density data generated at the edge portion of the font data using the intermediate density, and sends the result to the image density data storage circuit 210 composed of a frame memory. For the generated color, the corresponding color is converted into density data of each of Y, M, C, and 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 and the density ratio is different.

The modulation signal generation circuit 200 includes an image density data storage circuit 210, a readout circuit 220, a latch circuit 230, an image discrimination circuit 231, an MTF correction circuit 232, a reference wave phase determination circuit 240, select circuits 250A to 250C, and a modulation circuit. 260A to 260C, a reference clock generation circuit 280, a triangular wave generation circuit 290A, a delay circuit group 290B, and the like.

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

The read circuit 220 reads the image density data of consecutive one scan line units continuously in synchronization with the reference clock DCK ₀ with an index signal as a trigger from the image density data storage circuit (page memory) 210, reference wave phase The information is sent to the decision circuit 240, the image determination circuit 231 and the MTF correction circuit 232.

The latch circuit 230 is a circuit that latches the image density data during the time when the process of the reference wave phase determination circuit 240 described later is being executed.

The reference clock generation circuit 280 is a pulse generation circuit that generates a pulse signal having the same repetition cycle as the pixel clock and outputs the pulse signal to the readout circuit 220, the triangular wave generation circuit 290A, the delay circuit group 290B, and the modulation circuits 260A to 260C. I do. For convenience the clock referred to as a reference clock DCK _0.

290A is a triangular wave generating circuit which is a reference clock DCK.
Performing waveform shaping of the triangular wave phi ₀ reference is the reference wave with the same period and pixel clock based on _0. In addition, the delay circuit group 290B
In this example, a plurality of clocks DCK _{1 to} DCK _{1 to} D having a phase difference of 1 / n cycle (1/6 cycle in this example) with respect to the reference clock DCK ₀
CK4 is generated and based on this, triangular waves φ _{1 to} φ ₄ which are reference waves having different phases (here, triangular wave φ ₁ delayed by 1/6 cycle,
Triangular wave φ ₂ delayed by 2/6 cycle, triangular wave φ ₃ advanced by 1/6 cycle, 2 /
A triangular wave φ ₄ ) advanced by 6 cycles is output.

The select circuits 250A to 250C have input portions for the triangular waves φ _{1 to} φ ₄ out of phase with the reference triangular wave φ ₀ .
One of the above-mentioned triangular waves is selected by a selection signal from a reference wave phase determination circuit 240, which will be described later, and is synthesized by the synthesis circuits 270A to 270C.
Output to The combining circuits 270A to 270C sequentially combine the triangular waves input from the selection circuits 250A to 250C and send the combined signals to the input terminals T of the modulation circuits 260A to 260C.

The modulation circuit 260A~260C has the same circuit configuration as shown in FIG. 3, the triangular wave shifted D / A conversion circuit 261, a comparator 262, the reference triangular wave phi ₀ or 1/6 cycle out of phase And the input part T of the synthetic wave of
D / A conversion by the image density data in synchronism with the reference clock DCK ₀ D / A conversion circuit 261 is sent from the latch circuit 230, comparator the triangular wave sent from the select circuit 250A~250C reference wave To obtain a pulse width modulation signal.

The reference wave phase determination circuit 240 comprises a one-line delay circuit 242, a one-clock delay circuit 243, and an arithmetic processing circuit 241 as shown in FIG.
A delay of two scanning times is applied to the first one scanning line of image density data of three scanning lines of the image density data sent one scanning line at a time, and to an intermediate one scanning line of image data. Delay one line scanning time
(No delay is applied to the image data for the last scan line). Further, each image data has a one-clock delay circuit 243.
Thus, the image density data of all the pixels including the target pixel and adjacent to the target pixel are simultaneously sent to the arithmetic processing circuit 241.

The arithmetic processing circuit 241 performs the above-mentioned RE processing to obtain density data of small pixels. The obtained small pixel density data includes a small scan line including s1, s2, s3,..., A small scan line including s4, s5, s6, and s7, s in FIG.
Are divided into small scanning lines including 8, s9,..., And three small scanning lines of these small pixels correspond to one scanning line of the original pixel.

The arithmetic processing circuit 241 further calculates the barycenter of the density data in the original one pixel of each small scanning line, and outputs different selection signals from the output terminal OA as follows depending on the barycentric position. . That is, s of pixel m5
When the center of gravity of 1, s2, s3 (the first small scanning line) is near the center of s2, a signal for selecting the reference triangular wave φ ₀ having no phase shift is output. When the center of gravity is near the boundary between s2 and s1, A signal to select the triangular wave φ ₁ whose phase is delayed by 1/6 cycle
When it is near the center of 1, a triangular wave φ with a phase delayed by 2/6 cycle
A signal for selecting a _2, a signal for selecting a triangular wave phi ₃ advanced phase 1/6 cycle when the center of gravity is in the vicinity of the boundary s2 and s3, proceed 2/6 cycle when the center of gravity is in s3 near the center A signal for selecting the triangular wave φ ₄ is output from the output terminal OA to the selection circuit 250.
Output to A. Similarly, from the output terminal OB, s4, s of the pixel m5
The triangular wave selection signal of the second small scanning line determined by the density centroid of 5, s6 is supplied to the select circuit 250B, and the triangular wave of the third small scanning line determined by the density centroids of s7, s8, s9 of the pixel m5 from the output terminal OC. The selection signal is output to the selection circuit 250C. FIG. 6 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, a halftone or a halftone dot, and activates the reference wave phase determining circuit 240 when it is judged that the image is a character or a halftone dot. The MTF correction circuit 232 is disabled and the image data is left unprocessed via the latch circuit 230 without processing.
Send to 60A-260C. When it is determined that the tone is halftone, the selection of the triangular wave by the reference wave phase determination circuit 240 is not performed, and the modulation using only the reference triangular wave φ ₀ is performed.
After the image data read out by the MTF correction circuit 232 is corrected by the MTF correction circuit 232,
To 260C.

The modulation circuits 260A to 260C modulate the image data signal, which is the image density information input via the latch circuit 230, with the specific reference waves having different phases to generate pulse width modulated signals. The modulation signal is sent to the raster scanning circuit 300 as three units of three consecutive small scanning lines (one line of the original image density data).

The raster scanning circuit 300 includes a laser driver (not shown), an index detection circuit, and a polygon driver (not shown).

The laser driver oscillates a semiconductor laser array 431 having a plurality of (three in this embodiment) laser light-emitting units with modulation signals from the modulation circuits 260A to 260C. Is fed back, and driving is performed so that the light amount becomes constant.

The index detection circuit detects the surface position of the polygon mirror 436 rotating at a predetermined speed based on the index signal from the index sensor 439, and modulates the modulated digital image density to be described later in a raster scanning system according to the cycle in the main scanning direction. Optical scanning is performed using signals. The scanning frequency is 2204.72Hz, the effective printing width is 297mm or more,
The effective exposure width is 306 mm or more.

The polygon driver rotates the DC motor at a predetermined speed and rotates the polygon mirror 436 at 16535.4 rpm.

As the semiconductor laser array 431, one in which three light emitting units are arranged in an array at equal intervals is used. Normally, it is difficult to make the interval between the light-emitting parts 20 μm or less,
An axis passing through the center of each light emitting unit is set parallel to the rotation axis of the polygon mirror 436 and inclined at a certain angle with respect to the main scanning direction. In this manner, the laser spot of the laser beam on the photoconductor 401 by the semiconductor laser array 431 can be vertically and closely scanned. But,
For this reason, the position of each laser spot in the scanning direction is shifted with respect to the scanning direction. In order to correct this shift, a delay circuit is inserted between the modulation circuits 260B and 260C and the laser driver connected thereto, and the shift is corrected by delaying each by an appropriate amount and taking timing.
Laser spots emitted from the semiconductor laser array 431 can be recorded in a line perpendicular to the scanning direction.

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

FIGS. 7A to 7D are time charts showing signals of respective parts of the modulation signal generating circuit according to the first embodiment.

[0053] In Figure shows part of the image density data read out based on (a) the reference clock DCK ₀ with an index signal as a trigger from the page memory 210. The image density data is converted into an analog value by the D / A conversion circuit 261. The higher the level, the lower the density, and the lower the level, the higher the density.

FIG. 7B shows a triangular wave which is a reference wave sequentially output from the select circuit 250.

(C) shows a reference wave (solid line) obtained by synthesizing the triangular wave and an image density signal (dot-dash line) converted into the analog value. 13 shows a modulation operation in the modulation circuit 260.

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

According to the modulation signal generation result, in the edge portion where the density changes steeply, halftone remains in the conventional modulation using the triangular wave without displacing the phase. It can be seen that the emphasis is performed and the characters and line drawings are reproduced clearly.

Next, the image forming process of the image forming apparatus 400 will be described.

First, the photosensitive member 401 is uniformly charged by the scorotron charger 402. An electrostatic latent image corresponding to yellow is stored on a drum-shaped photoconductor 401 in an image density data storage circuit 210.
It is formed by irradiating laser light light-modulated by yellow data (8-bit digital density data) from the inside. The electrostatic latent image corresponding to the yellow color is a first developing device
The first toner image (yellow toner image) is formed on the photoreceptor 401 by being developed by the dot 441 and having extremely high sharpness. The first toner image is charged on the photoconductor 401 again by the scorotron charger 402 without being transferred to the recording paper. Next, laser light is optically modulated by magenta data (8-bit digital density data), and the modulated laser light 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). In the same manner as described above, the toner is sequentially developed by the third developing device 443 to form a third toner image (cyan toner image), and a three-color toner image sequentially stacked on the photoconductor 401 is formed. Finally, a fourth toner image (black toner image) is formed, and a four-color toner image sequentially stacked on the photoconductor 1 is formed.

According to the image forming apparatus 400 of this embodiment, the photosensitive member has an excellent high gamma characteristic, and the excellent high gamma characteristic is obtained by charging and exposing the toner image over the toner image many times. Even when toner images are repeatedly formed by superposition, a latent image is stably formed. That is, even if a laser beam is irradiated from above the toner image based on the digital signal, a high-sharpness, high-dot electrostatic latent image without fringes is formed, and as a result, a high-sharpness toner image is obtained. Can be.

After these four-color toner images are charged (or may be omitted) by charging the photosensitive member 401 by the charger 461, they are transferred onto the recording paper supplied from the paper feeding device by the operation of the transfer device 462.

The recording paper carrying the transferred toner image is separated from the photosensitive member 401 by the separation electrode 463, conveyed by a guide and a conveyance belt, carried into the fixing device 464, heated and fixed, and discharged to the paper discharge tray.

Incidentally, in this embodiment, as a result of an experiment in which the value of the coefficient P of the RE processing was variously changed, the value of P was 0.1 to 0.9.
In the range, good images were obtained, and particularly in the range of 0.4 to 0.5, excellent results were obtained. That is, conventionally, when a document is a character or a line drawing, an edge portion is unclear, and the edge portion appears sharply, and even a small character can be reproduced in detail. In addition, there was no adverse effect when the image had a halftone such as a photograph. (Embodiment 2) FIG. 11 is a block diagram showing another embodiment of the image processing circuit used in the image forming apparatus of another embodiment of the present invention. FIG. 10 shows a case of a color copying machine having the configuration shown in FIG. As shown in the figure, the configuration is the same as that of the first embodiment except for the image data processing circuit 150. The image data processing circuit 100 includes a color scanner 151, an A / D conversion circuit 15 and the like.
2. Instead of the image data processing circuit 150 including the density conversion circuit 153 and the masking UCR circuit 154, the selector 155 transfers image data for each color. After that, the recording density distribution and the phase selection of the reference wave are performed on the image density data in the same manner as in the first embodiment, and the image data is modulated by the reference wave. The present invention can be applied to an image forming apparatus such as a copying apparatus. With this circuit, an image with high sharpness could be obtained as in Example 1.

[0064]

As described above, the target pixel is divided into small pixels, and the density of each small pixel is determined by the RE processing in which the density of the target pixel is distributed according to the distribution of the density data of the adjacent pixels including the target pixel. The phase of the reference wave signal is selected from the image data subjected to the above, the target pixel density signal is modulated by the reference wave to generate a modulation signal, and an image forming apparatus that performs image recording with the modulation signal uses a scanner or C It is possible to provide an excellent image forming apparatus in which the sharpness of an image formed from .G. Or font data is improved and moiré fringes do not appear even in a copy of an original consisting of halftone dots.

Further, by scanning one pixel with a plurality of recording beams and using a high γ photoreceptor, the effect was further improved.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating an example of a reference wave phase determination circuit of the circuit of FIG. 1;

FIG. 3 is a block diagram illustrating an example of a modulation circuit of the circuit of FIG. 1;

FIG. 4 is a diagram for explaining RE processing used for determining a reference wave phase;

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

FIG. 6 is a diagram for explaining RE processing used for determining a reference wave phase.

FIG. 7 is a time chart showing signals of respective parts of the modulation signal generation circuit of the embodiment of FIG. 1;

FIG. 8 is a graph showing characteristics of the high γ photoconductor used in the present example.

FIG. 9 is a cross-sectional view showing a specific configuration example of a high γ photoconductor used in the present embodiment.

FIG. 10 is a perspective view illustrating a schematic configuration of an image forming apparatus of the present invention.

FIG. 11 is a block diagram showing an image processing circuit according to another embodiment of the present invention.

[Description of Signs] 100 Image data processing circuit 200 Modulation signal generation circuit 210 Image density data storage circuit (page memory) 220 Readout circuit 230 Latch circuit 231 Image discrimination circuit 232 MTF correction circuit 240 Reference wave phase determination circuit 241 Operation processing circuit 250A ~ 250C Select circuit 260A ~ 260C Modulation circuit 280 Reference clock generation circuit 290A Triangular wave generation circuit 290B Delay circuit group 300 Raster scanning circuit 400 Image forming device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 B41J 2/52 H04N 1/23 103

Claims (1)

(57) [Claims] An image forming apparatus that performs high-density pixel recording by performing pixel recording using density data corresponding to a pixel at a plurality of small pixel positions divided in a scanning direction and a sub-scanning direction in the pixel. Is determined from the density distribution of adjacent pixels including the pixel of interest, the recording density distribution within the pixel of interest is determined, and the recording of each small pixel in the main scanning direction within the pixel of interest is determined by the main scanning method.
The calculation for obtaining the center of gravity of the density data of each small pixel located in the direction is performed, the density information is modulated by a reference wave having a phase corresponding to the position of the center of gravity , and recording in the main scanning direction is performed.
The recording of each small pixel in the sub-scanning direction is mainly performed on the divided small pixel part.
An image forming apparatus that performs recording using a scanning line that scans in a scanning direction .