JPH0591304A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which improves the sharpness of the picture which is generated by a color scanner or the like and has the write density in the main scanning direction lower than that in the subscanning direction. CONSTITUTION:An edge detecting circuit 240 for picture density data, a select circuit 250 which selectively outputs picture density data based on the detection result, plural modulating circuits 260 which modulate picture density data by plural reference waves, and a synthesizing circuit 270 which synthesizes modulated signals from plural modulating circuits are provided for the purpose of generating the modulated signal obtained by modulating picture density data from a picture density data storage circuit 210 by the reference wave signal, thereby improving the apparent resolving power and the sharpness of the picture.

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 by a modulation signal obtained by modulating an image signal with a reference wave signal to reproduce halftone, and more particularly to an image forming apparatus for modulating image density data. is there.

[0002]

2. Description of the Related Art In the field of image forming apparatus by electrophotography, a document image is read as an image signal by a scanner using a line sensor such as CCD, and the image signal is subjected to gradation correction, A / D conversion, and shading correction. The image density data subjected to is modulated by a reference wave signal to obtain a halftone reproduced digital image.

In the image signal for reading an original image with a scanner, the size of the aperture of the solid-state image pickup device incorporated in the line sensor of the scanner determines the size of the pixel in the main scanning direction. Further, due to the aperture, the edge portion of the image is read as halftone density. When a latent image is formed on the photoconductor using the image density data obtained from this image signal, the recording pixels corresponding to the edge portion of the latent image are averagely recorded in the recording pixels when the density is intermediate. As a result, the sharpness of the image is reduced and the image is recorded. This cannot be dealt with by adding MTF correction or the like to the image signal. When the edge portion is smoothly interpolated by the intermediate density with the interpolation data, the recording pixel corresponding to the edge portion is recorded as the average density in the pixel, so that the resolution of the recorded image is reduced. Therefore, intermediate density processing is required at the image edge portion.

[0004]

Conventionally, the resolution of an image has been determined by the size of the aperture of a solid-state image sensor incorporated in a line sensor for reading a document. An object of the present invention is to provide an image forming apparatus that improves apparent resolution with respect to such restrictions and improves sharpness of an image to be formed.

[0005]

According to the present invention for achieving the above object, image recording is performed by a modulation signal obtained by modulating image density data having a writing density in the main scanning direction lower than that in the sub-scanning direction with a reference wave. In the apparatus, having a plurality of reference waves, and selectively combining the image density data and a specific reference wave from the reference waves based on the result from the edge detection circuit of the image density data. An image is formed by the obtained modulated image signal.

Here, the reference wave may be a reference wave having a phase difference as one embodiment, and the reference wave may be a triangular wave and a sawtooth wave as another embodiment.

[0007]

EXAMPLE A configuration of the image forming apparatus 400 of this example will be described.

FIG. 7 is a perspective view showing a schematic structure of the image forming apparatus of this embodiment.

The color image forming apparatus 400 is obtained by uniformly charging the photoconductor, A / D converting the image density from the computer or the scanner, performing image processing, and then D / A converting the digital image density data again. Dot-shaped electrostatic latent image with spot light that is pulse-width-modulated or intensity-modulated based on a modulation signal obtained by comparing an analog image density signal with a reference wave signal and binarizing it, or by differential amplification Is formed, a dot-shaped toner image is formed by reversal development with toner, a color toner image is formed on the photoconductor 401 by repeating the charging, exposing and developing steps, and the color toner image is transferred. , Separate and fix to obtain a color image.

The image forming apparatus 400 includes a drum-shaped photoconductor (hereinafter, simply referred to as a photoconductor) 401 that rotates in the arrow direction, and a scorotron charger 402 that applies a uniform charge to the photoconductor 401. , Scanning optical system 430, developing devices 441 to 444 loaded with yellow, magenta, cyan and black toners, pre-transfer charger
461, scorotron transfer device 462, separator 463, fixing roller 4
64, a cleaning device 470, and a static eliminator 474.

FIG. 6 is a cross-sectional view showing a specific example of the structure of the high-γ photoconductor.

The structure of the high γ photoconductor of this embodiment will be described below. The photoconductor 401 includes a conductive support 401A, an intermediate layer 401B, and a photoconductive layer 401C as shown in FIG. Photosensitive layer 401C
Has a thickness of about 5 to 100 μm, preferably 10 to 50 μm.
Is. The photosensitive member 401 is a drum-shaped conductive support 401A made of aluminum having a diameter of 150 mm, and an intermediate layer having a thickness of 0.1 μm and made of an ethylene-vinyl acetate copolymer on the support 401A.
401B is formed, and the photosensitive layer 4 having a thickness of 35 μm is formed on the intermediate layer 401B.
It is configured with 01C.

As the conductive support 401A, a drum of aluminum, steel, copper or the like having a diameter of about 150 mm is used. In addition to this, paper, a belt-like one in which a metal layer is laminated or vapor-deposited on a plastic film, or an electric carrier is used. It may be a metal belt such as a nickel belt made by the Chu method. Further, the intermediate layer 401B withstands a high charge of ± 500 to ± 2000 V as a photoconductor, for example, in the case of positive charge, it blocks injection from the electroconductive support 1C to obtain excellent light attenuation characteristics due to an avalanche phenomenon. As described above, it is preferable that the intermediate layer 401B has hole mobility, so that, for example, Japanese Patent Application No.
It is preferable to add 10% by weight or less of the positively chargeable charge transport material described in the specification No. 5. As the intermediate layer 401B,
Usually, for example, the following resins used for the photosensitive layer for electrophotography can be used.

(1) Vinyl-based polymers such as polyvinyl alcohol (poval), polyvinyl methyl ether, polyvinyl ethyl ether, etc. (2) Polyvinyl amine, poly-N-vinyl imidazole, polyvinyl pyridine (quaternary salt), polyvinyl pyrrolidone, vinyl pyrrolidone Nitrogen-containing vinyl polymer such as vinyl acetate copolymer (3) Polyether polymer such as polyethylene oxide, polyethylene glycol, polypropylene glycol (4) Polyacrylic acid and its salts, polyacrylamide, acrylic acid such as poly-β-hydroxyethyl acrylate Polymer (5) Methacrylic acid-based polymers such as polymethacrylic acid and its salts, polymethacrylamide, and polyhydroxypropylmethacrylate (6) Methylcellulose, ethylcellulose, carbohydrate Ether fibrin-based polymers such as dimethylcellulose, hydroxyethylcellulose and hydroxypropylmethylcellulose (7) Polyethyleneimine-based polymers such as polyethyleneimine (8) Polyalanine, polyserine, poly-L-glutamic acid, poly (hydroxyethyl) -L-glutamine, Polyamino acids such as poly-δ-carboxymethyl-L-cysteine, polyproline, lysine-tyrosine copolymer, glutamic acid-lysine-alanine copolymer, silk fibroin, casein (9) Starch acetate, Hydroxyl ethyl starch,
Starch and its derivatives such as hydroxyethyl starch, amine starch and phosphate starch (10) Soluble polymers such as polyamide soluble nylon and methoxymethyl nylon (8 type nylon) soluble in a mixed solvent of water and alcohol Photosensitive layer 401C Is a phthalocyanine fine particle having a diameter of 0.1 to 1 μm made of a photoconductive pigment without using a charge transporting substance, an antioxidant and a binder resin, and a solvent of the binder resin. The phthalocyanine fine particles are mixed and dispersed to prepare a coating solution, and the coating solution is coated on the intermediate layer, dried, and optionally heat-treated to form the layer.

When the photoconductive material and the charge transport substance are used in combination, the photoconductive pigment and one of the photoconductive pigments are used.
/ 5 or less, preferably 1/1000 to 1/10 (weight ratio), is 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 the present embodiment, since the color toner image is superposed on the photoconductor, a photoconductor having infrared spectral sensitivity and an infrared semiconductor laser are used so that the beam from the scanning optical system does not block the color toner image. ..

The light attenuation characteristics of the high γ photoconductor of this embodiment will be described below.

FIG. 5 is a schematic diagram showing the characteristics of the high-γ photoconductor.

In the figure, V ₁ is the charging potential (V), V ₀ is the initial potential before exposure (V), and L ₁ is the irradiation light amount of the laser beam required to attenuate the initial potential V ₀ to 4/5 ( μJ / cm ² ),
L ₂ represents the irradiation light amount (μJ / cm ² ) of the laser beam required for the initial potential V ₀ to be attenuated to ⅕.

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

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

The photosensitivity at the position corresponding to the mid-exposure period when the light attenuation curve attenuates the initial potential (V ₀ ) to 1/2 is E
_When the photosensitivity at the position corresponding to the initial stage of exposure when the initial potential (V ₀ ) is attenuated to _9/10 is E _9/10 , then (E _1/2 ) / (E _9/10 ) ≧ 2, preferably a photoconductive semiconductor which gives a relationship of (E _1/2 ) / (E _9/10 ) ≧ 5. Here, the photosensitivity is defined by the absolute value of the potential decrease amount with respect to the minute exposure amount.

The light attenuation curve of the photoconductor 401 is such that the absolute value of the differential coefficient of the potential characteristic, which is the light sensitivity as shown in FIG. 5, is small when the amount of light is small, and attenuates sharply as the amount of light increases. Specifically, as shown in FIG. 5, the light attenuation curve shows a leveled light attenuation characteristic for a short period L ₁ in the early stage of exposure due to poor sensitivity characteristics, but from the middle of exposure L ₁ to L ₂ However, the sensitivity becomes extremely high, and the characteristic becomes extremely high γ, which drops almost linearly. Specifically, the photoconductor 1 is +500 to +2000.
It is considered that a high gamma characteristic is obtained by utilizing the avalanche phenomenon under high charging of V. 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 a phenomenon occurs.

Next, the image formation of the present invention will be described. The image forming apparatus of the present invention is applied to, for example, a copying machine. In this case, in the main scanning direction of the image reading by the CCD of the original, the size of the pixels in the main scanning direction is determined by the elements arranged in a line shape of the semiconductor laser, and in the sub-scanning direction, for example, the document feeding speed (linear velocity). The size of the pixel in the sub-scanning direction is determined by this. When the pixel size in the main scanning direction is 400 dpi, the document is generally moved at a linear velocity such that the pixel size in the sub-scanning direction is also 400 dpi. Now, when trying to increase the resolution, it suffices to increase the number of rotations of the polygon and replace the semiconductor laser with one that modulates at a higher speed, but this is not easy. If the resolution is doubled in the main and sub-scanning directions, the data transfer and image processing speeds are naturally 4
You need twice as much. Also, the CCD image sensor needs to have twice the number of pixels. Rather, by keeping the CCD semiconductor laser optical system as it is and reducing the moving speed of the original document by half, the pixel size becomes 400 dpi × 800 dpi, which is half the area of the previous pixel, and the resolution in the sub-scanning direction is improves. However, the main scanning direction has not been improved. In the image forming apparatus of the present invention, the moving speed of the document for reading an image is reduced to, for example, 1/2 and the peripheral speed (linear velocity) of the photosensitive drum is reduced to 1/2, so that the writing density in the main scanning direction is reduced. Image density data lower than the writing density in the sub-scanning direction is recorded by a modulation signal that is modulated with a reference wave. Obviously, by keeping the sub-scanning speed and the peripheral speed of the photoconductor as it is, the scanning speed of the semiconductor laser optical system is doubled, and the image processing speed is doubled, so that high-density recording can be performed without lowering the copy speed. It can also be In the first embodiment, the reference wave combined with the image density data is a plurality of reference waves having a phase difference, and the image density data and the reference wave are identified based on the result from the edge detection circuit of the image density data. The image formation is performed by the modulated image signal obtained by selectively combining with the reference wave of. In particular, a high-γ photoconductor is effective for forming a latent image by accurately responding to a reference wave.

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

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 A / D converts the image information from the color scanner 151 provided in the reading device in which the reading density in the scanning direction for reading the original is lower than the reading density in the sub-scanning direction. An image data processing circuit 150 including a circuit 152, a density conversion circuit 153, a masking VCR circuit 154 and the like is a circuit for inputting image density data from a scanner and performing image processing.

The modulation signal generation circuit 200 reads the image density data of one scanning line unit from the image density data storage circuit 210, and selects the image density data corresponding to the edge from the continuous image density data of one scanning line as the edge. Detected by the detection circuit 240, the modulated signals are modulated by the modulation circuits 260A to 260C by the reference wave having the phase difference corresponding to the direction of the edge, and the modulated signals are generated by the synthesizing circuit 270 as the reference clock DCK ₀ . By synthesizing in synchronization, the raster scanning circuit 300 can generate continuous modulation signals in units of one scanning line.
To send to.

The modulation signal generation circuit 200 includes an image density data storage circuit 210, a readout circuit 220, a latch circuit 230, an edge detection circuit 240, a selection circuit 250, modulation circuits 260A to 260C, a synthesis circuit 270, a reference clock generation circuit 280, Delay circuit group 290
Composed of.

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 (one screen). It has a capacity for storing corresponding multi-valued image density data. Further, in the case of a device used in a color printer or a copying machine, it is equipped with a page memory for storing image density signals corresponding to color components of a plurality of colors, for example, yellow, magenta, cyan and black. Become.

The read circuit 220 reads the image density data of one scanning line unit which is continuous in synchronization with the reference clock DCK ₀ by using the index signal as a trigger, and sends it to the latch circuit 230 and the edge detection circuit 240.

The edge detection circuit 240 sequentially subtracts the image density data of one scanning line which is continuously input, and sends this difference value to the select circuit 250. When this difference value is the specific value α and is α or more, “1” is output, and when it is −α or less, “−1” is output. In this way, positive and negative signs are added according to the direction of the edge. When the sign is positive, it means that the edge is on the left side in the scanning line direction, and when the sign is negative, it means that the edge is on the right side in the scanning line direction. If the image data other than the edge, that is, the differential value is between −α and + α, the difference value is “0”.

The latch circuit 230 is the edge detection circuit 2 described above.
This is a circuit that latches the image density data only while the processing of 40 is being executed.

The select circuit 250 outputs the image density data from the output terminals D _{0 to} D ₂ which differ depending on the difference value. Specifically, if the difference value is “0”, the image density data is sent from the output terminal D _0, and the image density data sent from D ₁ and D ₂ is of the image density on a white background. Difference value "-1"
If so, output the image density data from the output terminal D ₂ ,
_As the image density data sent from ₀ and D ₁ , the image density data corresponding to the image density of the white background is sent. If the difference value is “+1”, the image density data is sent from the output terminal D ₁ ,
The image density data sent from D ₀ and D ₂ is the image density data corresponding to the image density of the white background. Although this example shows the simplest example, it is preferable to perform the above determination based on the two-dimensional information. In this case, it is preferable to determine the difference value by referring to the ROM table.

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 for convenience sake, this clock is used as the reference clock DCK _0.
That.

290A is a triangular wave generation circuit, which is a reference clock DCK ₀
Based on the above, the waveform of the triangular wave of the pixel clock is shaped. The delay circuit group 290 is a circuit that generates a plurality of pixel clocks DCK ₁ and DCK ₂ that have a phase difference of 1 / n cycle to the reference clock DCK ₀ , and here, 1 / n with respect to the reference clock DCK ₀ .
Pixel clock DCK _{1 with} a phase difference delayed by 3 cycles and pixel clock DCK ₂ with a phase advanced by 1/3 cycle with respect to reference clock DCK ₀ are generated, and 1/90% with respect to the triangular wave of the reference clock generated It outputs a triangular wave whose phase is shifted by 3 cycles.

The modulation circuits 260A to 260C have the same circuit configuration as shown in FIG. 2, and the D / A conversion circuit 261, the comparator 262, and the triangular wave or the triangular wave input section whose phase is shifted by 1/3 cycle. Has a select circuit 250
The image density data sent from the D / A converter circuit 261 performs D / A conversion in synchronization with the reference clock DCK _0, and the triangular wave is compared as a reference wave to obtain a pulse width modulation signal. As a result, the edge processing is applied to the portion corresponding to the edge in the continuous image density data as the scanning line.

The synthesis circuit 270 is the above-mentioned modulation circuit 260A-260.
This is a circuit that combines the modulated signals from C.

The raster scanning circuit 300 includes an LD drive circuit, an index detection circuit and a polygon driver. Neither is shown.

The LD drive circuit oscillates the semiconductor laser 431 with the modulation signal from the synthesizing circuit 270, and a signal corresponding to the light quantity of the beam from the semiconductor laser 431 is fed back and driven so that the light quantity becomes constant. ..

The index detection circuit detects the surface position of the polygon mirror 436 which rotates at a predetermined speed by the index signal from the index sensor 439, and according to the cycle in the main scanning direction, the modulated digital image density described later by the raster scanning method. Optical scanning is performed by signals.
The scanning frequency is 2204.72 Hz, the effective print width is 297 mm or more, and 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 36 at 16535.4 rpm.

The above-mentioned image processing circuit 1000 has been described as a laser printer, but the invention is not limited to this, and instead of the image data processing circuit 100, a color scanner 151, A /
D conversion circuit 152, density conversion circuit 153, masking UCR circuit 1
If the image data processing circuit 150 configured by 54 and the like is a circuit for inputting image density data from a scanner and performing image processing, it can be applied to other image forming apparatuses such as copying machines.

FIG. 4 is a schematic diagram when a latent image is formed by a modulation signal from the image processing apparatus of the first embodiment.
The size of the pixel is 400 dpi, and the size of one pixel in the sub-scanning direction is 800 dpi, which is a long shape in the main scanning direction.

The image forming apparatus 400 of this embodiment expresses gradation by changing the area of dots. In the image signal generated by the computer or read by the scanner as described above, the signal at the corresponding pixel becomes the same as the intermediate density in the uniform image when the edge portion of the dark image density touches the read pixel. When the same reference wave is used without adopting the select circuit having the edge detection, the recording at the edge portion is formed separately in the central portion of the pixel as shown by the dotted line as shown in FIG. .. Therefore, according to the modulation signal generation circuit 200, the point of the edge portion is recorded closer to the edge in the main scanning direction. By forming the electrostatic latent image in this way, the resolution of the edge portion can be improved.

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

FIGS. 3 (a) to 3 (i) are time charts showing signals at respective parts of the modulation signal generating circuit of the first embodiment.

In the figure, (a) shows a part of the image density data for one scanning line read from the page memory 210 based on the reference clock DCK ₀ using the index signal as a trigger. The image density data for one scanning line is sent from the read circuit 220 to the edge detection circuit 240 and the latch circuit 230 at the same time. The image density data shows a lighter density on the higher level side, and a darker density on the lower level side.

(B) shows an output from the edge detection circuit 240, which outputs a level change between pixels of continuous image density data, that is, a differential value. Thereby, the inclination of the image density in one scanning line is detected. When this differential value is greater than or equal to the absolute value α, it is determined that there is inclination. Further, 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 side in the main scanning direction, and if the output value is a "negative value", it is located on the right side in the main scanning direction. It indicates that it is an edge. If the output value is "0", it indicates that the image density data of the same level are continuous. This output signal is sent to the select circuit 250 based on the reference clock DCK ₀ .

On the other hand, the latch circuit 230 is the edge detection circuit 240.
Select circuit by latching for a time corresponding to the processing speed of
Send to 250. The select circuit 250 is an edge detection circuit 240
The density data is sent out from different output terminals based on the output from.

(C) shows the modulation operation in the modulation circuit 260A, in which the image density data is input to the modulation circuit 260A only when the output value from the edge detection circuit 240 is a positive value. If the output value from the circuit 240 is any other value, the image density data of a white background is input. The triangular wave at this time is a triangular wave which has the same repeating cycle and is made from the clock DCK ₂ whose phase is advanced by 1/3 cycle with respect to the reference clock DCK ₀ . As a result, the output signal from the modulation circuit 260A obtains a modulation signal advanced by 1/3 cycle as compared with the case where the pulse width is modulated by the triangular wave with the reference clock DCK ₀ as shown in (f).

(D) shows the modulation operation in the modulation circuit 260B, in which the image density data during the period when the output value from the edge detection circuit 240 is 0 is input as the image density data of the white background at other output values. And outputs a modulated signal as shown in (g).

(E) shows the modulation operation in the modulation circuit 260C, in which the image density data of one pixel before is processed and input during the period in which the output value from the edge detection circuit 240 shows a negative value. is doing. That is, the edge detection circuit 240
If the output value from -1 is -1, the image density data is input as the other output values, and the image density data of the white background is input as the other output values. The triangular wave is a triangular wave delayed by 1/3 cycle with respect to the reference clock DCK ₀ . As a result, the output signal from the modulation circuit 260C is
As shown in (h), a modulated signal delayed by 1/3 cycle is obtained as compared with the case of pulse width modulation with a triangular wave by the reference clock DCK ₀ .

(I) shows a modulation signal output from the combining circuit 270. As described above, the modulation signal generation circuit 200 in this embodiment is formed closer to the edge in the main scanning direction. By forming the electrostatic latent image in this way, the resolution of the edge portion can be improved.

The image forming process of the image forming apparatus 400 will be described below.

First, the photoconductor 401 is uniformly charged by the scorotron charger 402. An electrostatic latent image corresponding to yellow is formed on the drum-shaped photoconductor 401 that rotates at a low linear velocity corresponding to the original reading speed, and the image density data storage circuit 210
It is formed by irradiating a laser beam optically modulated with yellow data (8-bit digital density data) from the inside. The electrostatic latent image corresponding to the yellow is the first developing device.
The image is developed by 441, and a first dot-shaped toner image (yellow toner image) having extremely high sharpness is formed on the photoconductor 401. The first toner image is not transferred to the recording paper P, but is charged again on the photoconductor 401 by the scorotron charger 402. Then, the laser light is optically modulated by magenta data (8-bit digital density data), and the modulated laser light is irradiated on the photoconductor 401 to form an electrostatic latent image. This electrostatic latent image is transferred to the second developing device 442.
And is developed to form a second toner image (magenta toner image). Similarly to the above, the third developing device 443
Are sequentially developed to form a third toner image (cyan toner image), and a three-color toner image sequentially formed on the photoconductor 401 is formed. Finally, a fourth toner image (black toner image) is formed, and a four-color toner image sequentially formed on the photoconductor 1 is formed.

According to the image forming apparatus 400 of this embodiment, the photosensitive member has a high resolving power and has an excellent high gamma characteristic, and this excellent high gamma characteristic is charged and exposed from above the toner image. A latent image is stably formed even when toner images are repeatedly formed by repeating the development process many times. That is, even if a beam is emitted from above the toner image based on the digital signal, a dot-shaped electrostatic latent image with high fringes and high sharpness is formed, and as a result,
It is possible to obtain a toner image with high sharpness.

These four-color toner images are transferred onto the recording paper P supplied from the paper feeding device by the operation of the transfer device 462 after the photoconductor 401 is charged by the charging device 461 (may be omitted). It

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

Further, in the present embodiment, three reference waves whose phases are shifted to 0, ± 1/3 are used, but reference waves using other phases can also be used. For example, change the phase to (0, ± 1 /
4) Alternatively, values such as (0, ± 1/6) can be used. Further, it is preferable to use three or more reference waves and to use them at any time according to the image density and the edge detection output. For example, a reference wave when the phase is (0, ± 1/6, ± 2/6) may be used. FIG. 8 is a diagram showing the recording center in each phase in the pixel.

In the figure, the arrows for ± 1/6 and ± 2/6 correspond to the respective phases and indicate the position where recording is started. When the reference wave shown in FIG. 3 is used, the recording area spreads symmetrically from this position. In this case, when considering the recording pixel density, when recorded symmetrically at a position shifted by ± 2/6 pixels from the pixel center in the phase of ± 2/6, when occupying an area of 1/3 in the pixel,
It will enter adjacent pixels. In the phase of ± 1/6, when it is recorded from a position shifted ± 1/6 from the center of the pixel and occupies an area of 2/3 in the pixel, it also enters the adjacent pixel. From this, it is desirable that there is a condition for the reference wave to be combined with the image density data even if the recorded pixel is determined to be an edge by the edge detection circuit. In this case, if the image density data occupies 1/3 or less of the area occupied by pixels, ± 2/6 phase,
A preferable image without density jump can be obtained by selecting a reference wave having a phase of ± 1/6 from 1/3 to 2/3 and a phase of 0/3 even if an edge is detected. In the case of the reference wave of (0, ± 1/3) shown in this embodiment, it is more preferable to select the reference wave of phase 0 when the density occupies 1/3 or more in the pixel. In this way, by selecting the reference waves having different phases according to the image density data, it is possible to obtain an image having a high sharpness in harmony with the adjacent image density.

Next, a second embodiment of the present invention will be described. In the second embodiment, the reference wave combined with the image density data is a plurality of reference waves including a triangular wave and a sawtooth wave,
An image is formed by a modulated image signal obtained by selectively combining the image density data and a specific reference wave from the reference waves based on the result from the edge detection circuit of the image density data.

FIG. 9 is a block diagram showing an embodiment of the image processing circuit employed in the image forming apparatus of the second embodiment of the present invention. The block diagram showing the modulation circuit of the present embodiment of FIG. Is the same as that shown in FIG. The components (circuits) numbered in FIG. 9 that are the same as the components (circuit) numbered in FIG. 1 have the same functions, and therefore description thereof will be omitted.

The image processing circuit 2000 of the present embodiment generates three reference waves having no phase difference with the same pixel clock by the pulse signal from the reference clock generating circuit 280. One is the reference wave of the triangular waveform output from the triangular wave generation circuit 2100, and the other two are the rising sawtooth wave generation circuit 22.
The reference wave of the rising sawtooth waveform and the reference wave of the falling sawtooth waveform output from 00. In addition, the edge detection circuit 240
From the output of the above, the gradient of the image density in the scanning line is detected by the differential value. Regarding the detection here, as described in the first embodiment, if the output value is a "positive value", it is the edge located on the left side in the main scanning direction, and if the output value is a "negative value". For example, it indicates that the edge is located on the right side in the direction of the chief investigator. If the output value is "0", it means that the image density data of the same level are continuous. The select circuit 250 sends the density data from different output terminals D ₀ , D ₁ , D ₂ based on the output from the edge detection circuit 240.

FIG. 10 shows the modulation circuit 2260. The modulation circuit 2260A includes a select circuit 250 to an edge detection circuit 240.
Image density data in the period when the output value is 0 or "0" and the image density data of the white background are input in other output values, and the triangular wave of the pixel clock is input to the comparator 262 from the triangular wave generation circuit 2100 as the reference wave. .. FIG. 11D is a time chart showing signals at various parts of the modulation signal generation circuit shown in FIG.
Shows the modulation operation of the modulation circuit 2260A.
(G) shows the output modulation signal.

The image density data is input to the modulation circuit 2260B only when the output value from the select circuit 250 to the edge detection circuit 240 is a positive value.
If the output from 0 is any other value, the image density data of the white background is input. The rising sawtooth wave of the pixel clock is input as the reference wave from the rising sawtooth wave generation circuit 2200 to the comparator 262 of the modulation circuit 2260B. FIG. 11 (c) is a time chart showing signals at various parts of the modulation signal generation circuit shown in FIG. 11, and FIG. 11 (c) shows the modulation operation of the modulation circuit 2260B.
Indicates the output modulation signal.

The image density data is input to the modulation circuit 2260C only when the output value from the edge detection circuit 240 from the selection circuit 250 is a negative value.
If the output from 240 is any other value, the image density data of a white background is input. Further, the falling sawtooth wave of the pixel clock is input as a reference wave from the falling sawtooth wave generation circuit 2300 to the comparator 262 of the modulation circuit 2260C. 11 is a time chart showing signals at various parts of the modulation signal generation circuit shown in FIG.
(E) shows the modulation operation of the modulation circuit 2260C.
1 (h) shows the output modulation signal.

The modulation signals output from the modulation circuits 2260A, 2260B, 2260C are combined by the combining circuit 270 and output.
FIG. 11 (i) shows the modulated signal that is output as a result of this synthesis. Note that FIG. 11 (i) shows one scanning line, but when a latent image is formed by a modulation signal from the image processing apparatus of the second embodiment, it is different from that of the first embodiment. Similarly, a latent image is formed as shown in the schematic view of FIG. When the present inventors conducted an experiment on image information of each principal, it was confirmed that the second embodiment could achieve a slightly higher image quality than the first embodiment. It was found that there is no restriction on the image density data in the edge detection and the like as compared with the first embodiment, which is advantageous.

The present invention can be further improved on the selection of the reference wave. When the information obtained by the edge detection circuit 240 is used, a good image can be obtained for character reproduction, but it is recognized that the edge portion tends to be emphasized for halftone reproduction.
Therefore, it is more preferable to select the reference wave by combining information of image discrimination and edge detection. The image discriminating circuit 241 indicated by the broken line portion shown in FIGS. 1 and 9 is shown.

The image discrimination circuit 241 displays the image as characters / halftones /
Whether it is a halftone dot or not, and when it is determined to be a character or a halftone dot, a combination with a reference wave is selected based on the edge detection determination of the present invention described above. On the other hand, if it is determined to be halftone, the combination with the reference wave written from the center of the pixel is selected. That is, in the embodiment shown in FIG. 1, the modulation circuit
It is assumed that only 260A is used, and in the embodiment shown in FIG. 2, image modulation is performed only by the modulation circuit 2260A. It is preferable that a plurality of line memories are prepared and the above image determination and edge detection are performed based on two-dimensional information. In this way, a more preferable image reproduction was obtained.

As a circuit for combining the image data and the reference wave, other than the present invention, after selecting from a plurality of reference waves based on information of image discrimination and edge detection, the selected reference wave and the image of the reference wave are selected. It is also possible to adopt a configuration in which data is combined and modulated.

The image processing circuit 3000 shown in FIG. 12 is obtained by modifying a part of the configuration of the embodiment shown in FIG.
A, 3260B, and 3260C compare the reference waves having different phases with the image density data input from the latch circuit 230, and output the modulated image density data to the select circuit 3250. The select circuit 3250 discriminates which one of character / halftone / halftone dot is input from the image discriminating circuit 241, and when it is halftone, for example, the input from the modulating circuit 3260A is output as it is. When it is determined that it is a character or a halftone dot, the select circuit 3250 selectively synthesizes the outputs from the modulation circuits 3260A, 3260B, 3260C according to the information of the edge detection circuit 240, and outputs the modulated continuous image density data. It was done.

Further, the image processing circuit 4000 shown in FIG.
The modulation circuit is obtained by partially modifying the configuration of the embodiment shown in
4260A, 4260B, and 4260C compare reference waveforms having different waveforms and image density data input from the latch circuit 230, and the modulated image density data is selected by the select circuit 42.
Output to 50. In the selection circuit 4250, the image discrimination circuit 241
It is determined whether the input is from a character / halftone / halftone dot, and when it is a halftone, for example, the input from the modulation circuit 4260A is output as it is. When it is determined that it is a character or a halftone dot, the select circuit 4250 causes the edge detection circuit 24
Outputs from the modulation circuits 4260A, 4260B, and 4260C are selectively combined according to the information of 0, and modulated continuous image density data is output.

In this embodiment, the laser pulse width modulation is used, but the difference between the reference wave and the image density data may be directly output as intensity modulation without being binarized. Also in this case, a sharp latent image can be formed by using a high-γ photoconductor.

Although the image forming apparatus of the present invention has a particularly excellent effect in a copying machine, it can be applied to a printer as a matter of course.

[0076]

According to the present invention, there is provided an image recording apparatus for recording by using a modulation signal obtained by modulating image density data whose writing density in the main scanning direction is lower than that in the sub scanning direction by a reference wave signal.
An image with a modulated image signal having a plurality of reference waves and obtained by combining the image density data and a specific reference wave from the reference waves based on information from the edge detection circuit of the image density data. By forming the image, it is possible to provide an image forming apparatus that improves the apparent resolution and improves the sharpness while solving the problems of the processing speed and the recording speed for an image created by a scanner or the like.
Further, the effect could be further improved by selecting the modulation method and the photoconductor characteristics.

[Brief description of drawings]

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

2 is a block diagram illustrating a modulation circuit of the first embodiment
It

3 is a time chart showing each part signal of the modulation signal generating circuit of the first embodiment.

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

5 is a graph showing characteristics of a high γ photoreceptor.

Der sectional view showing a specific configuration example of FIG. 6 high γ photoreceptor
It

7 is a perspective view showing a schematic configuration of an image forming apparatus of the present embodiment.

8 is a diagram showing a recording center in each phase in the pixel in the first embodiment.

FIG. 9 is a block diagram of an image processing circuit of the second embodiment der
It

[10] a block diagram illustrating a modulation circuit of the second embodiment
There is .

11 is a time chart showing each part signal of the modulation signal generating circuit of the second embodiment.

FIG. 12 is a block diagram of a third image processing circuit provided with an image discrimination circuit.

FIG. 13 is a block diagram of a fourth image processing circuit provided with an image discrimination circuit.

[Explanation of symbols]

 100 Image data processing circuit 200 Modulation signal generation circuit 210 Image density data storage circuit 220 Read circuit 230 Latch circuit 240 Edge detection circuit 250 Select circuit 260A-260C Modulation circuit 270 Synthesis circuit 280 Reference clock generation circuit 290 Delay circuit group 300 Raster scanning circuit 400 Image forming device 1000, 2000 Image processing circuit 2260A to 2260C Modulation circuit 2100 Triangle wave generator 2200 Rising sawtooth wave generator 2300 Falling sawtooth wave generator

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Claims (4)

[Claims] 1. An image recording apparatus for recording by a modulation signal obtained by modulating image density data having a writing density in the main scanning direction lower than that in the sub-scanning direction with a reference wave, wherein the image recording apparatus has a plurality of reference waves. Based on the result from the edge detection circuit of the density data, it is possible to form an image by a modulated image signal obtained by selectively combining the image density data and a specific reference wave from the reference waves. A characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the plurality of reference waves are triangular waves having different phases, or a triangular wave and a sawtooth wave. 3. The image forming apparatus according to claim 1, wherein the image signal is modulated by laser light. 4. The image forming apparatus according to claim 1, wherein the photosensitive member used in the image forming apparatus is a high γ photosensitive member.