JPH05130387A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent recording picture by generating a recording position modulation signal resulting from modulating a density signal of a noted picture element with a reference wave and not implementing the recording position modulation to a low or high density part. CONSTITUTION:Picture density data from a picture density data storage circuit 210 are read by a read circuit 220 and a reference wave phase decision circuit 240 and select circuits 250A-250C are used to divide a noted picture element into a small picture elements and the density of each small picture element is subject to RE processing to share the density of the noted picture element thereby obtaining the density gravity center. A reference wave of a phase corresponding to the gravity center is selected and a picture discrimination circuit circuit 231 discriminates the density of the noted picture element, a character area and an intermediate tone area. Then a modulation circuit 260 uses the selected reference signal to generate a picture by using a recording position modulation signal obtained through the modulation of an original picture density signal of each color. Thus, sharpness is improved without causing a change in a color tone of a color picture formed by a scanner or font data or the like.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In the field of electrophotographic image forming 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 to refer to image density data. A digital image obtained by halftone reproduction by modulating with a wave signal is obtained.

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. Therefore, the sharpness of the image is reduced and the image is recorded. Conventionally, it has been known that the image signal is subjected to MTF correction by sharpening with a differential filter, a Laplacian filter or the like. However, this means that only the edges of the image are emphasized, and the uniformity of the halftone image is relatively reduced.

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

[0005]

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

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

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

[0008]

SUMMARY OF THE INVENTION The above object is to provide a color image forming apparatus for performing high-density pixel recording by using density data of small pixels in a pixel of interest determined corresponding to density data of pixels adjacent to the pixel of interest. In the above method, when the recording position of each color is modulated in the main scanning direction and the sub-scanning direction based on the density of the target pixel and the density distribution of the adjacent pixel, the target pixel determines the recording position of each color from the density distribution of the adjacent pixel. It is achieved by a color image forming apparatus. Further, means for discriminating the image of the pixel of interest, and if the image discrimination discriminates a halftone area, only the achromatic color component is subjected to recording position modulation from the density distribution of the adjacent pixels, and if discriminated as a character area. And an image forming device for performing recording position modulation on all color components.

[0009]

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

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

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

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

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

As the conductive support 401A, a drum of aluminum, steel, copper or the like having a diameter of about 150 mm is used. In addition to this, paper, a belt-shaped material obtained by laminating or vapor-depositing a metal layer on a plastic film, or an electric electrode. It may be a metal belt such as a nickel belt made by the Chu method. Further, the intermediate layer 401B withstands a high charge of ± 500 to ± 2000 V as a photosensitive member. For example, in the case of positive charge, injection from the electroconductive support 401A is blocked, and excellent light attenuation characteristics due to an avalanche phenomenon are obtained. As described above, it is desirable that the intermediate layer 401B has hole mobility.
No. 8975 describes positively chargeable charge transport materials.
It is preferable to attach less than or equal to wt%.

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

(1) Polyvinyl alcohol (poval),
Vinyl polymers such as polyvinyl methyl ether and polyvinyl ethyl ether, (2) polyvinyl amine, poly-
N-containing vinyl polymers such as N-vinylimidazole, polyvinylpyridine (quaternary salt), polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer, (3) polyether-based polymers such as polyethylene oxide, polyethylene glycol and polypropylene glycol, (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 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, lysine-tyrosine copolymer, glutamic acid-lysine-alanine copolymer, silk fibroin, casein and other polyamino acids, (9) Starch acetate, Hydroxyl ethyl starch, Hydroxy ethyl starch , Starch such as amine starch and phosphate starch and its derivatives, (10) Soluble nylon which is polyamide,
A polymer soluble in a mixed solvent of water and alcohol such as methoxymethyl nylon (8 type nylon).

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

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

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

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

FIG. 11 is a graph showing the characteristics of the high γ photoconductor. In the figure, V ₁ is a charging potential (V), V ₀ is an initial potential before exposure (V), 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. The photoconductor potential of the exposed portion is 10V.

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 E.
Assuming that 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 Preferably, 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. 11, the absolute value of the differential coefficient of the potential characteristic, which is the photosensitivity, is small when the amount of light is small, and increases sharply as the amount of light increases. Specifically, as shown in Fig. 11, the light attenuation curve shows a nearly flat light attenuation characteristic in the early stage of exposure because of poor sensitivity characteristic for a short period of time. The sensitivity becomes an ultra-high γ characteristic that drops almost linearly. Specifically, the photoconductor 401 is considered to obtain a high γ characteristic by utilizing the avalanche phenomenon under the high charge of +500 to + 2000V. That is, the carriers generated on the surface of the photoconductive pigment in the 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.

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

In the present invention, this RE processing is performed when the density data of the pixel of interest is equal to or higher than the first threshold value, that is, equal to or higher than a specific density. That is, in many areas corresponding to the highlight portion, the RE processing is not performed on the background portion of the document, and the m × n small pixels have uniform density. In the case of a CRT, this data can be displayed.

However, in the case of laser recording, which will be described later, it is difficult to perform uniform display. Therefore, the reference wave having the center of density at the center is selected. As a result, it is possible to prevent the generation of a noisy image while maintaining the uniformity in the highlight portion.

On the other hand, in the case of a high density portion, if the density gradient is large, if a reference wave in which the density recording position is not in the center is selected, dots are formed across adjacent pixels.

In order to prevent the density variation and the collapse of the recording dots between pixels due to this, a specific second value is set even in the high density area.
If it is equal to or more than the threshold value of, the reference wave having the center of concentration at the center is selected.

In the case of a CRT, since uniform display is possible, m × n small pixels are processed as uniform density. That is, RE processing is not performed.

That is, in the color image forming apparatus for performing high-density pixel recording, the specific density data of the target pixel is determined by the density distribution data in the target pixel determined corresponding to the density data of the pixel adjacent to the target pixel. The color image forming apparatus is characterized in that recording position modulation is performed from the determined density distribution when the threshold value is equal to or greater than 1.

Further, it is preferable that the color image forming apparatus is characterized in that the recording position modulation is performed from the determined density distribution when the specific density data of the pixel is equal to or less than the second threshold value.

FIG. 5A is a plan view showing the above target pixel as m5 and adjacent pixels including the target pixel m5 as m1 to m9 when the target pixel m5 is divided into 3 × 3.
(B) is an enlarged view showing a case where each small portion when the target pixel m5 is divided into 3 × 3 small pixels is represented by S1 to S9. m1 to m9 and S1 to S9 also represent the densities of those portions.

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

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

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

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

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

FIG. 7A is a diagram showing an example of dividing the target pixel m5 into 2 × 2, and FIG. 7B is an example of adjacent pixels related to the small pixels S1 to S4 in the target pixel. It is a figure.

Calculation of the concentrations of S1, S2, S3 and S4 is given by
Is done according to.

[0042]

[Equation 1]

In FIG. 8A, the target pixel m5 is 2 × 2.
FIG. 8B is a diagram showing another example in the case of being divided into, and FIG. 8B is a diagram showing another example of the adjacent pixels related to the small pixels s1 to s4 in the target pixel. Concentration calculation of S1, S2, S3, S4 is Equation 2
Is done according to.

[0044]

[Equation 2]

FIG. 1 is a block diagram showing an embodiment of an image processing circuit used in a color image forming apparatus of the present invention (an example in which a target pixel is divided into 3 × 3), and FIG. 2 is shown in this embodiment. 3 is a block diagram showing the reference wave phase determination circuit of FIG. 3, and FIG. 3 is a block diagram showing the modulation circuit of the present embodiment.

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

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

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

The image density data storage circuit 210 is a normal page memory (hereinafter simply referred to as page memory 210), a RAM (random access memory) for storing in page units, and at least one page (for one screen). It has a capacity for storing corresponding multi-valued image density data. Further, if 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 readout circuit 220 reads out continuous image density data in units of one scanning line in synchronization with the reference clock DCK ₀ by using the index signal as a trigger from the image density data storage circuit (page memory) 210, and the reference wave phase. It is sent to the decision circuit 240, the image discrimination circuit 231, and the MTF correction circuit 232.

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

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

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

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

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

As shown in FIG. 2, the reference wave phase determination circuit 240 comprises a 1-line delay circuit 242, a 1-clock delay circuit 243, and an arithmetic processing circuit 241, and by the 1-line delay circuit 242,
In the image density data for the first one scanning line for the three scanning lines of the image density data sent for each one scanning line, a delay of two line scanning time is added to the image density data for one intermediate scanning line. Does not delay the image density data for the last one scanning line. Further, each image density data is delayed by 2 reference clocks or 1 reference clock by the 1-clock delay circuit 243, and all image density data of pixels including the target pixel and adjacent to the target pixel are calculated at the same time. Processing circuit
Send to 241.

In the arithmetic processing circuit 241, the RE processing is performed to obtain the density data of the small pixels. The density data of the small pixels obtained include the small scan line including S1, S2, S3 ... In FIG. 5, the small scan line including S4, S5, S6 ... and S7, S8, S9. It is divided into small scanning lines that include the three small scanning lines of the small pixels and corresponds to one scanning line of the original pixel.

The arithmetic processing circuit 241 further calculates the average density of each small scanning line and the barycentric position of the original density data in one pixel of each small scanning line to calculate the average density data of the laser drivers 301A to 301C. Based on the gravity center position data, different selection signals are output from the output terminals OA to OC to the select circuits 250A to 250C. That is, when the center of gravity of S1, S2, S3 (first small scanning line) of the pixel m5 is near the center of S2, a signal for selecting the reference triangular wave φ ₀ with no phase displacement is given by the center of gravity S.
When it is near the boundary between 2 and S1, the signal that selects the triangular wave φ ₁ whose phase is advanced by 1/6 cycle is selected, and when the center of gravity is near the center of S1, the triangular wave φ ₂ whose phase is advanced by 2/6 cycle is selected. Signal for selecting a triangular wave φ ₃ whose phase is delayed by ⅙ cycle when the center of gravity is near the boundary between S2 and S3,
When the center of gravity is near the center of S3, a signal for selecting a triangular wave φ ₄ delayed by 2/6 period is output from the output terminal OA to the select circuit 25.
Output to 0A. Similarly, from the output terminal OB, S of the pixel m5
4, the triangular wave selection signal of the second small scanning line determined by the density center of gravity of S5, S6 to the select circuit 250B, and the third small scanning line determined by the density center of gravity of S7, S8, S9 of the pixel m5 from the output terminal OC. The triangular wave selection signal is output to the selection circuit 250C. FIG. 9 is a diagram showing an example of the relationship between the triangular waves having different phases and the pixel of interest.

Further, the arithmetic processing circuit 241 causes each laser driver 301 according to the average density in the pixel m5 of each small scanning line.
The light emission output of A to 301C is controlled. For example, S1, S2
The semiconductor laser 301A is controlled to emit laser light in proportion to the average density of S3. FIG. 15 is a graph showing an example of the relationship between the drive current of the semiconductor laser and the laser emission output.

On the other hand, the image discriminating circuit 231 discriminates whether the image data of the pixel of interest is the first or second threshold value, and it is discriminated that it is the area outside the first and second threshold values. If the reference wave phase determination circuit 240
Does not output the triangular wave selected by, but sends a selection signal that outputs only the reference triangular wave φ ₀ to the select circuits 250A to 250C,
The MTF correction circuit 232 is not activated. This allows the readout circuit
Image density data other than that read from 220 is MTF correction circuit
The modulation circuits 260A to 260C are not corrected by the 232 but are corrected by the γ correction circuit 233 and are then corrected by the latch circuit 230.
Sent to.

As a result, a highly uniform noise-free image can be formed in the highlight and high density areas.

The image discrimination circuit 231 further discriminates whether the image is a character area or a halftone area under the above conditions. This determination is 5 × including the pixel of interest.
This is performed by changing the density at 5 pixels. When the density change is large, the pixel of interest is discriminated as a character region, and when it is small, it is discriminated as a halftone region. When it is determined that the area is a character area of a character or a line drawing, a selection signal that causes the modulation circuits 260A to 260C to output the triangular wave selected by the reference wave phase determination circuit 240 for all color components is output to the selection circuits 250A to 250C. , The MTF correction circuit 232 and the γ correction circuit 233 are inoperative, and the image density data is sent to the modulation circuits 260A to 260C via the latch circuit 230 without processing. As a result, clear characters and edge portions with no change in color tone are reproduced. Further, when it is determined that it is a halftone area, the same selection signal as that of the character area is output only for the achromatic color component, that is, black data, and the triangular wave selected by the reference wave phase determination circuit 240 is not output for the other components. , Send a selection signal that outputs only the reference triangular wave φ ₀ to the selection circuits 250A to 250C, and
The F correction circuit 232 and the γ correction circuit 233 are activated. As a result, the image density data other than black read by the read circuit 220 is corrected by the MTF correction circuit 232 and the γ correction circuit 233, and then is transmitted via the latch circuit 230 to the modulation circuits 260A to 260C.
Sent to.

As a result, it is possible to form an image free from moire and color skipping in the halftone area, and to give an effect of giving the image sharpness and tightness by the black image.

It is converted into density data of a specific color used for determining the phase of the reference wave, for example, R + 2G + B (where R is red density data, G is green density data, and B is blue density data). I am using one. For convenience (R +
The density data of 2G + B) will be represented by N.

By commonly using the phase of the reference wave for each recording color, it is possible to guarantee the gradation of the image and prevent the tint from changing. In addition, to determine the phase, G
It is preferable to use achromatic data having a component or a G component.

The data used in the image discrimination circuit 231 is also common to each color for the same reason.

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

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

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

In FIG. 10, (a) shows the page memory 210.
Reference clock DCK _{0 using the} index signal as a trigger
3 shows a part of the image density data read out based on the data converted into an analog value by the D / A conversion circuit 261. The higher level shows a lighter density, and the lower level shows a darker density.

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

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

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

From the above-mentioned modulation signal generation result,
In the case of the pixel in the high density portion, the recording position modulation is not performed, while in the character area, the position of the small dot in the nth row in the pixel of interest is in the line direction of the original character or line drawing from the density data of the original adjacent pixel. As a result of the recording position modulation that moves to a position along the line, characters and line drawings are reproduced clearly. Also,
In the above-mentioned recording position modulation, only the black component is performed in the halftone region to prevent the change of the color tone, and the other color components are modulated by the triangular wave having no phase displacement.

Further, by sequentially shifting the reference wave phase in the sub-scanning direction, dots corresponding to halftone dots with a screen angle can be formed. For example, the screen angle is 45 ° for the yellow component and 2 for the magenta component.
6.6 °, -26.6 ° for the cyan component, and 0 ° for the black component can improve the uniformity of color reproduction and prevent the occurrence of moire fringes.

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

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

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

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

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

As the semiconductor laser array 431, as shown in FIG. 13, one in which three light emitting portions 431A to 431C are arranged in an array at equal intervals is used. Normally, it is difficult to set the distance d between the light emitting portions to 20 μm or less. Therefore, as shown in FIG. 13, the axis passing through the centers of the light emitting portions 431A to 431C is parallel to the rotation axis of the rotary polygon mirror 434, and the main scanning Install at an angle to the direction. In this way, the semiconductor laser array 431
Laser spot S of laser beam on photoconductor 401 by
As shown in FIG. 14, a, Sb, and Sc can be closely scanned vertically. However, for this reason, the positions of the respective laser spots Sa, Sb, Sc in the scanning direction deviate from the main scanning direction. In order to correct this shift, a δ delay circuit 311 is provided between the modulation circuit 260B and the laser driver 301B, and a modulation circuit 260C and the laser driver 301 are provided.
A 2δ delay circuit 312 is inserted between C and C to correct the deviation by delaying each by an appropriate amount and timing, and the laser spots Sa, Sb, Sc emitted from the semiconductor laser array 431 in the main scanning direction. S aligned vertically
It can be recorded as a, Sb ', Sc'.

When the RE process is performed by dividing the target pixel into 2 × 2 small pixels, a semiconductor laser array having two light emitting portions is used.

In the previous embodiment of the present invention, the average density in the main scanning direction is the laser emission output as the density information in each sub-scanning direction, and the image data from the reading circuit 220 is used. 18 and 19, the average density of each small scanning line obtained by the reference wave phase determination circuit 240 is used as density information and input to the modulation circuits 260A to 260C by each reference wave and each laser driver 301A.
A configuration for modulating ~ 301C can also be used.

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

First, the photoconductor 401 is uniformly charged by the scorotron charger 402. The electrostatic latent image corresponding to yellow is formed on the drum-shaped photoconductor 401 by the image density data storage circuit 210.
The laser beam modulated by the yellow data (8-bit digital density data) from the inside is formed by irradiation through the cylindrical lens 433, the rotary polygon mirror 434, the fθ lens 435, the cylindrical lens 436, and the reflection mirror 437. The electrostatic latent image corresponding to the yellow is developed by the first developing device 441, and the dot-shaped first toner image (yellow toner image) having extremely high sharpness is formed on the photoconductor 401.
Is formed. The first toner image passes under the cleaning device 470 which is retracted without being transferred to the recording paper, and is charged again on the photoconductor 401 by the scorotron charger 402.

Next, the laser beam modulated by the magenta data (8-bit digital density data) is irradiated onto the photoconductor 401 to form an electrostatic latent image. This electrostatic latent image is developed by the second developing device 442 and
Toner image (magenta toner image) is formed. In the same manner as described above, the third developing device 443 sequentially develops to form a third toner image (cyan toner image).
A three-color toner image is sequentially formed on the first layer. Finally, the fourth toner image (black toner image) is formed, and the photoconductor 40
A four-color toner image that is sequentially stacked on 1 is formed.

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

These four-color toner images are transferred 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 by a separator.
The sheet is separated from the photoconductor 401 by 463, is conveyed by a guide and a conveyance belt, is carried into a fixing roller 464, is heated and fixed, and is discharged to a sheet discharge tray.

In this embodiment, as a result of an experiment in which the value of the coefficient P of the RE process was variously changed, the value of P was 0.1 to 0.9.
Good images were obtained in the range of. However, when P is small, the sharpness of the character is insufficient, and when P is large, the edge portion of the character or the line drawing is overemphasized. Therefore, the preferable value range of P is 0.3 to 0.7. Was found to be in the range. As a result, when the manuscript is a character or a line drawing, the edge part appears clearly, and even small characters can be reproduced in detail. Moreover, the low-density portion and the high-density portion were not adversely affected. This is because the method stops recording position modulation for these pixels and effectively sets P = 0.

In this method, P can be used with a constant value, but it is preferable to use P by changing it according to the image (character area or halftone area). When the value in the case of the character area is P ₁ and the value in the case of the halftone area is P ₂ , it is preferable that P ₁ > P ₂ . That is, when the image is a character area, the value of P is large and preferably 0.9 to 0.4, and when the image is a halftone area, the value of P is small and is 0.6 to 0.1.

P = 0 corresponds to no recording position modulation.

In the present invention, the rate of RE processing can be arbitrarily changed even if a specific P value is used.

FIG. 16 is a graph showing an example of converting the relationship between the print position and the center of gravity in the main scanning direction, and FIG. 17 is a graph showing an example of converting the average density in the sub-scanning direction.

In the arithmetic processing circuit 241, the result obtained by arithmetic processing from the image density data is converted into a recording position by using a ROM 245 which is built-in or externally attached, for example, according to a preset conversion formula as shown in FIG. Can be changed. Similarly, the average density in the sub-scanning direction can be converted as shown in FIG.

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

[0097]

As described above, for a pixel of interest included in a specific density, the pixel of interest is divided into small pixels corresponding to the density data of the pixel of interest, and the density of each small pixel is The phase of the reference wave signal is selected from the image data subjected to the RE processing that distributes the density of the target pixel according to the distribution of the density data of adjacent pixels including the pixel, and the density signal of the target pixel is modulated by this reference wave. An excellent recorded image was obtained by generating the recording position modulation signal and not performing the recording position modulation on the low density portion and the high density portion. Further, image discrimination is performed by the image discrimination circuit, and recording position modulation is performed for all color components in the character area, and only achromatic color component (black) is recorded in the halftone area. As a result, it is possible to provide an excellent color image forming apparatus capable of improving the sharpness without changing the color tone of a color image formed from a scanner, CG, font data or the like.

In the above method, the recording beam of pixels is 3
Although the case of a book is shown, it is also possible to scan one pixel with one or two recording beams or to perform recording position modulation only in the main scanning direction. The effect can be further improved by using a high γ photoconductor.

[Brief description of drawings]

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

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

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

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

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

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

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

FIG. 8 is a diagram showing another example of a case where a pixel of interest in RE processing is divided into 2 × 2.

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

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

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

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

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

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

FIG. 15 is a graph showing an example of the relationship between the drive current of the semiconductor laser and the laser emission output.

FIG. 16 is a graph showing an example of converting the relationship between the center of gravity of the small scanning line in the main scanning direction and the recording position.

FIG. 17 is a graph showing an example of converting the average density of a small scan line in the sub-scanning direction.

FIG. 18 is a block diagram showing an image processing circuit according to another embodiment of the present invention.

19 is a block diagram showing the reference wave phase determination circuit of FIG. 18. FIG.

[Explanation of symbols]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical location H04N 1/40 B 9068-5C (72) Inventor Tetsuya Niitsuma 2970 Ishikawacho, Hachioji, Tokyo Konica Stocks In the company

Claims (4)

[Claims] 1. High density pixel recording is performed based on density data of small pixels in the target pixel determined corresponding to density data of a pixel adjacent to the target pixel, and the density data of the target pixel is determined. In an image forming apparatus that performs recording position modulation based on density distribution, modulation in the main scanning direction is performed by selecting a reference wave signal, and modulation in the sub scanning direction is performed according to the determined average density in the main scanning direction in the pixel of interest. An image forming apparatus characterized by being opened. 2. A means for determining an image of the pixel of interest, and a means for performing recording position modulation of only an achromatic component from the density distribution of the adjacent pixel when the image determination determines a halftone area. The image forming apparatus according to claim 1, wherein: 3. The apparatus according to claim 1, further comprising: a unit for discriminating an image of the pixel of interest, and a unit for modulating the recording position for all color components when discriminated as a character region by the image discrimination. The image forming apparatus according to item 1. 4. When the density data of the pixel is equal to or more than a first threshold value or less than a second threshold value, recording position modulation is performed from the determined density distribution. Image forming apparatus.