JP2002142112A - Method and device for processing and forming image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method, etc., by which a halftone image can be reproduced well even when the tone reproducing characteristic of an electrophotography device changes due to the history, etc., of a photoreceptor, the device, etc., without deteriorating the graininess of the image nor lowering the resolution of the image due to the periodic structure of a screen. SOLUTION: In the image processing method, output image signals are generated by comparing inputted image signals with a threshold matrix prestoring thresholds used for deciding whether or not the picture elements in a screen cell composed of a plurality of picture elements of a dot screen are to be recorded, and the image signals are outputted to an image forming device having a nonlinear region in part of its image signal-output density characteristic. The image forming device is constituted to generate the output image signals by using a threshold matrix in which nonrecorded isolated picture elements which are not recorded by means of the image forming device are arranged, when picture elements are isolated between thresholds having largely inclined image signal-output density characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus used in an image forming apparatus such as a copying machine or a printer adopting a digital electrophotographic system, and an image forming method and apparatus using the same. The present invention relates to an image processing method and apparatus excellent in reproducibility of a halftone image, and an image forming method and apparatus using the same.

[0002]

2. Description of the Related Art Conventionally, when a halftone image is created in an image forming apparatus such as a copying machine or a printer adopting the digital electrophotographic system, processing of an image signal and image formation are performed as follows. Done. First, in an image processing apparatus, an input image signal such as a luminance signal, a brightness signal, and a density signal created by, for example, a scanner, a digital camera, or computer graphics is adapted to the tone reproduction characteristics of the image forming apparatus. Into an output image signal processed as described above.

Next, in accordance with the image signal output from the image processing apparatus, the lighting intensity and the lighting time of a light source such as a semiconductor laser or an LED of the exposure apparatus are modulated, and the exposure apparatus responds to the image signal. The exposure image is scanned and exposed on the photosensitive drum. Then, a charge density distribution (electrostatic latent image) corresponding to the scanning exposure pattern is formed on the surface of the photosensitive drum, and the electrostatic latent image is developed by, for example, toner particles previously mixed with carrier particles. That is,
A toner image is formed on the surface of the photoconductor drum by changing the amount of toner adhesion according to the electrostatic latent image formed on the photoconductor drum. The toner image formed on the surface of the photosensitive drum is transferred to a white support (paper or the like), so that a halftone image is formed on the support.
Then, the toner image formed on the white support is heat-fixed to the support by a fixing device having a heating roll or a heating belt to obtain a halftone image.

Accordingly, the pattern of the finally obtained toner image is determined mainly by the electrostatic latent image formed on the photosensitive drum.

Here, as a system for modulating a latent image pattern in accordance with the intensity of an image signal output from the image processing apparatus, that is, as a gradation reproduction system, the light source is turned on and off while the intensity of the light source is kept constant. By scanning a laser beam or the like emitted from a light source to form a binary exposure pattern and modulating the area ratio of an exposed portion, and a density modulation method for scanning a light source that modulates exposure intensity. Three modulation schemes, which are a combination of the two, are used.

[0006] Among these, the electrophotographic method has the following problems from the viewpoint of obtaining smooth halftone reproduction and obtaining an image with good graininess.
An area modulation method is often used. In this case, using a screen having a periodic structure typified by halftone dots and lines, it is possible to perform tone reproduction by modulating the size and line width of the halftone dots according to the intensity of the image signal. Are known.

Here, from the viewpoint of graininess and stability of gradation reproduction, it is preferable that a halftone screen be used.
Hardcopy '99 p. Introduced at 303.

As a binarization method in gradation reproduction using the halftone screen, a dither method is widely used. In this case, a screen structure is formed by periodically arranging screen cells each including a plurality of pixels. Lighting of each pixel in the screen cell is determined by comparing the image signal with a conversion table called a dither matrix or a threshold matrix that describes the correspondence between the image signal and the lighting of the pixel. . Then, a halftone dot is generated by lighting a plurality of adjacent pixels,
Tone reproduction is performed by changing the size of a halftone dot. Therefore, the number of gradation steps matches the number of pixels constituting one screen cell, and the number of screen lines is determined by the periodic structure of the matrix.

Further, in consideration of the development step and the transfer step in the image forming step, it is known that the dot concentration type of the systematic dither method is effective among the digital screen methods (published by the Electrophotographic Society of Japan). Magazine Vol.2
5, no. 1, 31 pages (1981)).

[0010]

However, the prior art described above has the following problems. That is, in the above-mentioned electrophotographic system,
In the case of using a dot concentration type threshold matrix disclosed in Japanese Patent Application Laid-Open No. 584/1984 or the like, Japan Hardcopy indicates that the nonlinearity of changes in output values such as luminance, brightness, density, and color of an output image with respect to an image signal is high. '99 p.
Introduced at 303. In particular, it describes that the nonlinearity is high in a region where the density of the image signal is low. More specifically, it is described that the amount of offset from the zero point of the output image at the reproduction start point at which toner adhesion starts is large, and that the output value rises sharply from the reproduction start point. As described above, when the output value sharply rises from the reproduction start point, there is a problem in that a tone jump in which the output density rapidly changes appears in a highlight portion of the halftone image.

In order to reduce the offset amount of the tone reproduction start point from the zero point of the output image and to make the rise of the output density from the reproduction start point gentle,
No.-17944, Journal of the Imaging Society of Japan 37 (4) p. 5
46, Japan Hardcopy '94 p. 17
7, etc., the image processing apparatus described above:
It is known that a conversion table, gradation correction, and the like are performed so that an output value of a preferable image with respect to an input image signal, that is, a good halftone reproduction is obtained.

However, the reproduction starting point when the image forming apparatus is actually used, and the rising of the output thereafter, are as follows:
It may fluctuate due to the use history of the photoreceptor, the developer, and the electrophotographic image forming apparatus, or a change in the use environment. Therefore, the reproduction start point in a preset conversion table or gradation correction curve, There is still a problem that the gradation correction is not preferable because of the rising of the output value, and good halftone reproduction cannot be obtained.

In addition, Japan Hardcopy '9
9 p. 303, Japan Hardcopy '95
p. As reported in 143 and the like, there is known a method of reducing the number of screen lines in order to improve the non-linearity of gradation characteristics. However, in this case, since the screen structure is conspicuous, new problems such as deterioration in graininess and deterioration in resolution arise.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to prevent deterioration in granularity and resolution due to a periodic structure of a screen. And an image processing method and apparatus capable of reproducing a halftone image satisfactorily even when the gradation reproduction characteristics change due to the history of the photoreceptor, the developer, the electrophotographic apparatus, and the use environment, and the image. An object of the present invention is to provide a forming method and an apparatus.

[0015]

That is, according to the first aspect of the present invention, an image signal to be inputted and a threshold value for determining whether or not to record each pixel in a screen cell composed of a plurality of pixels of a halftone screen. Image processing for generating an output image signal by comparing the image signal with a threshold matrix stored in advance, and outputting the processed image signal to an image forming apparatus having a non-linear region in a part of the image signal-output density characteristic In the method, a threshold matrix in which non-recording isolated pixels in which a pixel is not recorded in the image forming apparatus when a pixel is isolated is arranged between thresholds having a large inclination of an image signal-output density characteristic of the image forming apparatus is used. And generating an output image signal.

According to a second aspect of the present invention, there is provided a threshold matrix in which an input image signal and a threshold for determining whether to record each pixel in a screen cell composed of a plurality of pixels of a halftone screen are stored in advance. An image processing apparatus that generates an output image signal and outputs the processed image signal to an image forming apparatus having a non-linear region in a part of the image signal-output density characteristic. A threshold matrix storage unit that stores in advance a threshold value for determining whether to record each pixel in a screen cell composed of a plurality of pixels of the screen, a threshold matrix read from the threshold matrix storage unit, and the input image signal. A screen generating unit including a comparing unit that generates an output image signal by comparing the threshold value matrix storing unit; A threshold matrix in which non-recording isolated pixels in which the pixel is not recorded in the image forming apparatus when the pixel is isolated are stored between threshold values having a large inclination of the image signal-output density characteristic of the pixel. Image processing device.

Further, according to the third aspect of the present invention, when an electrostatic latent image is formed on the surface of the image bearing member by exposing the surface of the image carrier according to an image signal by the exposure unit, the image is output to the exposure unit. In an image forming method configured to perform processing on an image signal, an input image signal and a threshold value for determining whether to record each pixel in a screen cell including a plurality of pixels of a halftone screen are set in advance. By comparing the stored image with the threshold matrix to generate an output image signal, when outputting the processed image signal to an image forming apparatus having a non-linear region in a part of the image signal-output density characteristic,
An output image is formed by using a threshold matrix in which non-recording isolated pixels in which the pixel is not recorded in the image forming apparatus when the pixel is isolated between the thresholds in which the inclination of the image signal-output density characteristic of the image forming apparatus is large. An image forming method characterized by generating a signal.

According to a fourth aspect of the present invention, there is provided an image carrier, an exposing means for exposing an image on a surface of the image carrier according to an image signal to form an electrostatic latent image, and the exposing means. And an image processing unit for processing an image signal to be output to the image forming apparatus, wherein the image processing unit records an input image signal and each pixel in a screen cell including a plurality of pixels of a halftone screen. By comparing the threshold for determining whether or not to a threshold matrix stored in advance,
Means for generating an output image signal and outputting the processed image signal to an image forming apparatus having a non-linear region in a part of the image signal-output density characteristic, the screen comprising a plurality of pixels of the halftone screen A threshold matrix storage unit in which a threshold for determining whether to record each pixel in the cell is stored in advance, and a threshold matrix read from the threshold matrix storage unit is compared with the input image signal to output an image signal. A screen generating unit having a comparing unit for generating the image forming apparatus, wherein the threshold matrix storage unit stores the image forming apparatus when a pixel is isolated between thresholds having a large inclination of an image signal-output density characteristic of the image forming apparatus. And a threshold matrix in which non-printing isolated pixels in which the pixel is not recorded are stored.

Further, according to a fifth aspect of the present invention, there is provided a laser driving unit for controlling lighting of the exposure unit in accordance with the image signal, wherein the exposure unit is a laser light source, and the laser light source is an image carrier. An optical system for forming a laser beam to be formed thereon, a scanning unit for scanning the laser beam to form a pulse width modulated exposure image on a photoconductor, and the laser driving unit includes 5. A laser driving means having a response lower than a frequency corresponding to a scanning time, and is controlled so as not to be reproduced by the image forming apparatus when an isolated pixel is used as a signal. An image forming apparatus as described in the above.

According to a sixth aspect of the present invention, there is provided an adjusting means for adjusting at least one of a charging potential of the image carrier, an exposure amount, and a developing bias, and the isolated pixel is adjusted by the adjustment. 5. The image forming apparatus according to claim 4, wherein the image forming apparatus is controlled so as not to be reproduced by the image forming apparatus.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 2 is a schematic configuration diagram showing a digital color electrophotographic copying machine as an image forming apparatus to which the image processing method and apparatus according to one embodiment of the present invention are applied.

In FIG. 2, reference numeral 1 denotes a digital color electrophotographic copying machine. This digital color electrophotographic copying machine 1 is roughly divided into a scanner section 100 and
An image processing unit 200 as an image processing apparatus;
(aster output scanner) optical unit 30
0 and an image forming unit 400.

At the upper end of the digital color electrophotographic copying machine 1, a scanner unit 100 for reading an image of a document (not shown) is provided. This scanner unit 100
Reads an image of a document (not shown) by a light source, and reads an image of a reflected light from the document via a reduction optical system including a full-rate mirror 2, half-rate mirrors 3, 4 and an imaging lens 5, and an image reading device such as a CCD. The element 6 is scanned and exposed, and a color image of the document is read by the image reading element 6 at a predetermined dot density (for example, 16 dots / mm).

The color image of the original read by the scanner unit 100 is converted into an image processing unit 200 as a three-color original density image signal of, for example, red (R), green (G), and blue (B) (8 bits each). The image processing unit 200 applies a picture, character separation process, gradation, color correction, spatial frequency (MTF) correction to the density image signal of the original, and furthermore, an image signal output from the image forming unit 400. Predetermined image processing such as correction processing according to the density characteristics is performed.

The image signals that have been subjected to the predetermined image processing by the image processing unit 200 as described above are yellow (Y),
The ROS optical unit 300 outputs image signals of each color of magenta (M), cyan (C), and black (BK) (each of 8 bits).
In the ROS optical unit 300, image exposure with the laser light LB is performed in accordance with the image signal of each color.

An image forming section 400 capable of forming a plurality of toner images of different colors is provided inside the digital color electrophotographic copying machine 1. This image forming section 400
Mainly includes a photosensitive drum 7 as an image carrier on which an electrostatic latent image is formed, a charging scorotron 8 as charging means for uniformly charging the surface of the photosensitive drum 7 to a predetermined potential, A ROS optical unit 300 as an exposure unit that performs image exposure on the surface of the photoconductor drum 7; and a plurality of toner images of different colors by developing an electrostatic latent image formed on the photoconductor drum 7 And a rotary developing device 9 as a developing means.

As shown in FIG. 2, the ROS optical section 300 modulates a semiconductor laser (not shown) in accordance with image signals of respective colors, and outputs laser light LB from the semiconductor laser.
Is emitted in accordance with the gradation data of the image signal. The laser beam LB emitted from the semiconductor laser is deflected and scanned by the polygon mirror 10, and is scanned and exposed on the photosensitive drum 7 via the fθ lens 11, the micro mirror 12, and the mirror 13. At that time, the laser beam LB is
Scanning means such as a polygon mirror 10 and micromirrors 12 and 13 scans in the main scanning direction, that is, the axial direction on the photosensitive drum 7, and the rotation of the photosensitive drum 7 causes the sub-scanning direction, that is, a circle on the photosensitive drum 7. It is scanned in the circumferential direction. Further, it is preferable that the optical system is adjusted so that the beam diameter on the photosensitive drum 7 becomes a desired size.

When a ROS device is used as the exposure means, it is preferable to provide a screen generator that converts the laser drive signal into a binary laser signal whose pulse width is modulated in the main scanning direction, as described later. Further, the laser drive signal is temporarily stored in the image buffer,
It is preferable to include a unit that sends a laser driving signal to the laser driving unit in synchronization with the page start signal and the main scanning start signal. Then, the semiconductor laser, which is the light source of the ROS device, is turned on according to ON / OFF of the drive signal.
It is preferable to provide a laser driving unit for turning on / off.

The photosensitive drum 7 on which the laser light LB is scanned and exposed by the ROS optical section 300 is driven to rotate at a predetermined speed in a direction indicated by an arrow by driving means (not shown). The surface of the photosensitive drum 7 is uniformly charged in advance to a predetermined potential by a charging scorotron 8 serving as a charging unit, and then is scanned and exposed to a laser beam LB corresponding to a color image signal, so that black (Bk) is obtained. , Yellow (Y), magenta (M), and cyan (C) are sequentially formed. The surface potential of the photosensitive drum 7 uniformly charged to a predetermined potential by the charging corotron 8 is measured by an electrometer 14.
The detection data obtained by the electrometer 14 is sent to an image density adjusting means, which will be described later, and is controlled so that the charged potential of the photosensitive drum 7 becomes a predetermined value. The electrostatic latent image formed on the photosensitive drum 7 includes four color developing units 9Bk, 9Y, 9M, and 9C of black (Bk), yellow (Y), magenta (M), and cyan (C). Are sequentially developed by a rotary type developing device 9,
The toner image has a predetermined color. Further, the developing units 9Bk, 9Y, 9M, and 9C of the rotary developing device 9 are supplied with toner of a corresponding color by a predetermined amount by a toner supply device (not shown).
When a pattern for density detection is formed on the photosensitive drum 7, the density of the pattern for density detection is
It is detected by the density sensor 15.

As the developing device 9 as the toner developing means, known means such as a two-component magnetic brush developing device and a one-component magnetic brush developing device can be used. A component magnetic brush developing device is preferred. From the same viewpoint, the volume average particle diameter of the toner provided in the developing device is preferably 3 μm or more and 7 μm or less.

The toner image formed on the photosensitive drum 7 is transferred onto a recording paper 17 as a support held on a transfer drum 16 arranged adjacent to the photosensitive drum 7 by a transfer corotron 18. Are sequentially transferred in a multiplex manner. As a transfer unit, a transfer corotron or a transfer roll facing the photosensitive drum 7 with a recording paper 17 as a support therebetween is used. Further, the photosensitive drum 7
Instead of directly transferring the toner image formed thereon onto the recording paper 17 as a support, an intermediate roll as an intermediate transfer body having a transfer corotron or a transfer roll as a transfer unit on the back surface, or the like. It is also preferable to use a device that once transfers onto the intermediate belt and then transfers onto the support using an intermediate roll, a transfer corotron or a transfer roll facing the intermediate belt with the support interposed therebetween. The recording paper 17
2, a plurality of paper feed trays 19, 20, 21, 2 arranged at the lower part in the color electrophotographic copying machine 1 are shown.
2 is fed by a feed roll (not shown), and is transported by a transport roller 23 and a registration roller 24.
The toner is conveyed to the surface of the transfer drum 16 at a predetermined timing. The recording paper 17 is held on the surface of the transfer drum 16 while being electrostatically attracted to the surface of the transfer drum 16 by the charging of the suction corotron 25 and the pressing force of the suction roll 26.

The recording paper 17 is transferred to the transfer drum 16.
After the toner images of a predetermined number of colors sequentially formed on the photosensitive drum 7 are transferred while being held on the surface of the transfer drum 16, the toner images are separated from the surface of the transfer drum 16 by the discharge of the separation corotron 27, and then fixed. The sheet is conveyed to a fixing device 28 as a means. The fixing device 28 fixes the toner image on the recording paper 17 by heat and pressure, and discharges the toner image onto a discharge tray (not shown) to complete the color image printing process.
As the fixing unit, a known fixing unit such as an oven fixing device, a radiant fixing device, and a pressure fixing device can be used in addition to the hot roll fixing device as described above.

In FIG. 2, reference numeral 29 denotes a cleaning device for removing toner, paper dust and the like remaining on the photosensitive drum 7;
Numeral 30 denotes a pair of neutralizing corotrons for neutralizing the transfer drum 16.

FIG. 3 is a block diagram showing a control circuit of the digital color electrophotographic copying machine constructed as described above.

In FIG. 3, reference numeral 100 denotes a scanner unit. In the scanner unit 100, image data read by the image reading element 6 is amplified to an appropriate level by an amplifier 31, and then A / D-converted. 8 in converter 32
It is converted to a bit digital signal. After being subjected to correction such as shading correction and color correction by the input color correction unit, the image data is sent to the image processing unit 200.

The image signal sent to the image processing unit 200 is
As shown in FIGS. 3 and 4, after the picture (image) image and the character (text) image are separated by the picture / character separation circuit 34, the gradation and color correction circuit 35 performs the gradation and color of the image signal. Is corrected, and the spatial frequency (MTF) correction circuit 36
, And is converted into black, yellow, magenta, and cyan image signals. Next, the image signal of each color is sent to a screen generator 37, subjected to a screen process using a halftone screen, temporarily stored in an image buffer 38, and then output to a laser driver 39.

In the screen generator 37, as shown in FIG. 1, an image signal and a threshold matrix describing the relationship between the image signal and the lighting of each pixel are compared with a comparison circuit 53.
, And is converted into a binary image signal for controlling lighting of a pixel corresponding to the image signal. In this example, the threshold matrix stores a threshold table corresponding to a plurality of dots, and includes information on the arrangement of dots (that is, the screen angle and the number of lines). The binary image signal thus obtained is sent to the image buffer 38. The image buffer 38 temporarily stores the binary image signal, and synchronizes with the page start signal indicating the position of the output device and the main scanning start signal, and the laser driver 42 of the ROS optical unit 200.
Send to Then, based on the binary image signal sent to the laser driver 42 of the ROS optical unit 200, when the image signal is “0”, the semiconductor laser of the ROS is turned off, and when the image signal is “1”, the ROS semiconductor laser is turned off. Semiconductor laser is turned on.

As shown in FIG. 3, the image processing section 200 is provided with a patch signal generating means 43 for generating an image signal when a reference patch is formed on the photosensitive drum 7. Reference patch data with an image area ratio of 50% is generated. The binary image signal and the reference patch data are supplied to the selector 4 controlled by the controller 44.
5, only one of the data is stored in the image buffer 38 and sent to the laser driver 42 in synchronization with the position signal from the output device.

On the other hand, the electrometer 14
And a controller 44 for controlling the density of the toner image formed on the photosensitive drum 7 to be constant based on the detection signal of the density sensor 15, and the grid voltage VG of the charged scorotron 8 according to the control signal of the controller 44. There is provided a charger controller 46 for changing, and also a developing bias controller 47 for changing a developing bias voltage VB applied to each developing device of the rotary developing device 9 according to a control signal of the controller 44. Further, a toner supply device 48 is connected to each developing device of the rotary developing device 9 so that toner is supplied in accordance with a control signal of the controller 44. Further, the controller 44 also sends a control signal to the laser light amount control unit 49 of the optical unit 200, and the light emission amount of the semiconductor laser is adjusted via the laser driver 39.

According to the present invention, there is provided an image forming apparatus capable of reproducing halftones of a digital electrophotographic system without deterioration in granularity or resolution due to the visibility of a screen structure, and a photosensitive member and a developer. An image processing method and apparatus, and an image forming method and apparatus for solving the problem of deterioration in tone reproducibility due to a change in tone reproduction characteristics due to a history of an electrophotographic apparatus or a change in use environment.

The present invention is intended to stably obtain a preferable halftone image in a monochromatic image. Needless to say, a plurality of color screens are overlapped to form a color halftone image. Of course, it is suitable as an image forming apparatus and method.

In the image processing method according to an embodiment of the present invention, an input image signal and a threshold value for determining whether or not to record each pixel in a screen cell composed of a plurality of pixels of a halftone screen are stored in advance. The output image signal is generated by comparing the threshold
In an image processing method for outputting a processed image signal to an image forming apparatus having a non-linear region in a part of the output density characteristic, a pixel is output between a threshold value having a large inclination of an image signal-output density characteristic of the image forming apparatus. The image forming apparatus is configured to generate an output image signal using a threshold matrix in which non-recording isolated pixels in which the pixel is not recorded in the image forming apparatus when isolated.

The image processing apparatus according to one embodiment of the present invention sets an input image signal and a threshold value for determining whether or not to record each pixel in a screen cell including a plurality of pixels of a halftone screen. An image processing apparatus for generating an output image signal by comparing with a threshold matrix stored in advance and outputting the processed image signal to an image forming apparatus having a non-linear region in a part of the image signal-output density characteristic A threshold matrix storage unit that stores in advance a threshold value for determining whether to record each pixel in a screen cell composed of a plurality of pixels of the halftone screen, a threshold matrix read from the threshold matrix storage unit, Screen generating means for comparing the input image signal with an input image signal to generate an output image signal; The step stores a threshold matrix in which non-recording isolated pixels in which the pixel is not recorded in the image forming apparatus when a pixel is isolated between thresholds having a large inclination of the image signal-output density characteristic of the image forming apparatus. It is configured as follows.

FIG. 4 is a block diagram showing an image forming apparatus to which the image processing apparatus according to one embodiment of the present invention is applied in accordance with the flow of image signals.

In FIG. 4, reference numeral 100 denotes an image input device. As the image input device 100, in the digital color electrophotographic copying machine described above, the scanner unit 1 is used.
00 is used. However, the present invention is not limited to this, and it goes without saying that a digital camera or computer graphics may be used as the image input device 100. Then, the multi-valued input image signal input from the image input device 100 is, as described above,
The image processing unit 200 (including an independent image processing device) performs a picture, character separation, color and gradation correction processing, and the like by a known method, and creates a multi-valued image signal.

The multi-valued input image signal subjected to the picture, character separation, color and gradation correction processing, and the like is input to the screen generator 37. As shown in FIG. 1, the screen generator 37 corresponds to a threshold matrix, which is a table describing thresholds for determining whether or not to light each pixel in a screen cell composed of a plurality of pixels of a halftone screen, for a plurality of dots. A threshold matrix storage circuit 52 which stores the threshold value matrix and a comparison circuit 53 which compares the threshold matrix read from the threshold matrix storage circuit 51 with the input image signal to generate an output image signal. The same table is always repeated by increasing the number of dots included by enlarging the storage table, and a table of this size is prepared.

The image signal output from the screen generator 37 is input to an image buffer 38. The image buffer 38 stores a lighting control signal for each screen cell of an image signal output from the screen generator 37, and an image signal for sending to the ROS optical unit 200 as an exposure signal synchronized with a page start signal and a scan start signal. It has sending means.

The image signal output from the image processing unit 200 is input to the laser driver 39 of the image forming unit 400, and the laser driver 39
The semiconductor laser of the OS optical unit 300 is driven according to an image signal formed of a halftone screen, and the halftone image is exposed on the photosensitive drum 7 of the image forming unit 400, and the halftone image is formed on the recording paper 17. It is formed.

As shown in FIG. 5, the digital color electrophotographic copying machine 1 as an image forming apparatus for forming a halftone image receives a ROS signal in accordance with a binary image signal output from a laser driver 39. The semiconductor laser in the optical section is turned on or off, and a halftone dot is exposed on the surface of the photosensitive drum 7 to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 7 is A visible toner image is formed by developing with the developing device 9 and then transferred and fixed on a recording paper 17 as a support, thereby forming a color image and the like.

In the digital color electrophotographic copying machine 1, the minimum reproducible pixel size, that is, the image exposure is performed on the photosensitive drum 7 to form an electrostatic latent image, and the electrostatic latent image is developed. The minimum pixel size which is actually a toner image to which toner adheres according to the electrostatic latent image and is transferred and fixed on the recording paper 17 is the contrast between the potential of the photosensitive drum 7 and the DC component of the developing bias, the image buffer. 38
And the responsiveness of the laser driver 39, the emission intensity of the laser light source, the characteristics of the ROS optical system, and the developing conditions.

In the present invention, in the main scanning direction (photosensitive drum 7
An isolated pixel having a different width (in the axial direction) is prepared, and output characteristics when the isolated pixel is output by the digital color electrophotographic copying machine are obtained in advance as shown in FIG. Is configured to set the width of one pixel under the condition that is not formed. Further, the digital color electrophotographic copying machine is configured to include a means for setting the width of one pixel under the condition that a toner image is not formed as described above. As a means used for this setting, for example, as shown in FIG.
6, means for controlling the frequency response of the image buffer 38 and the laser driver 39, a laser light amount control unit 49 for modulating the light emission intensity of the laser light source, a development bias control unit 47 for changing the development conditions (development bias voltage and the like), and the like. Used. However, the present invention is not limited to these means as long as the desired purpose, that is, the purpose of not forming a toner image with respect to an image signal of an isolated pixel is satisfied.

Here, an isolated pixel indicates a pixel in which a pixel before and after this pixel in the main scanning direction is not illuminated.

Further, as shown in FIG. 11, the image processing apparatus 200 according to this embodiment has a threshold matrix storage circuit 52 for storing a threshold matrix for producing a conventional dot concentration type halftone screen. As shown in FIG. 6, the image forming apparatus may be provided with a grasping means for grasping in advance the relationship between the input image signal and the output value of the outputted image density when the threshold matrix is used. At the time of manufacture, the relationship between the input image signal and the output value of the output image density when a conventional threshold matrix is used is grasped, and in the actual image forming apparatus, the characteristics as shown in FIG. The threshold matrix storage circuit 52 is configured to store only a new threshold matrix that corrects. More specifically, in an apparatus such as an original machine having the same configuration as an actual image forming apparatus, an input is performed by using a threshold matrix for creating a conventional dot concentration type halftone screen as shown in FIG. The relationship between the image signal and the output value of the output image density is grasped in advance as shown in FIG.
The data of the table of the new threshold matrix that corrects the characteristics as shown in
The data of the table may be transplanted (stored).

In this embodiment, when the pixel is isolated between the threshold values in which the slope of the image signal-output density characteristic of the image forming apparatus is large, the threshold value matrix storage circuit 52 controls the image forming apparatus. It is configured to store a threshold matrix in which non-recording isolated pixels in which no pixels are recorded are arranged.

The output value to be measured may be image density, reflectance, brightness, color difference from the colorimetry of the support, and the like. It is not limited.

In the present invention, instead of the threshold matrix for forming the conventional dot concentration type halftone screen, the slope of the curve between the image signal and the output value is changed as shown in FIG. , A new threshold matrix in which the isolated pixels are inserted between the thresholds of the high region. Thereby, the linearity of the curve between the image signal and the output value can be improved as shown in FIG.

FIG. 7 shows the relationship between image signals and output values by the image forming apparatus to which the present invention is applied. As is apparent from FIG. 6, as the threshold matrix storage circuit 52, in FIG. 6, when a pixel is isolated between threshold values having a large gradient of the image signal-output density characteristic of the image forming apparatus, the image forming apparatus When a threshold matrix in which non-recording isolated pixels in which no pixels are recorded are stored is used, an area where the slope of the curve between the image signal and the output value is large is corrected to reduce the slope of the curve. To make it substantially linear, and the reproducibility of halftone can be improved.

In order to achieve the purpose of not forming a toner image for an image signal of an isolated pixel, it is preferable to use the frequency response of the image buffer 38 and / or the laser driver 39.

Preferably, in order to achieve the object that a toner image is not formed with respect to an image signal of an isolated pixel, control of the charging potential of the photosensitive member and / or the emission intensity of the laser light source and / or the developing bias is performed. Good to follow.

Here, the output value in the case of a black and white image using black toner is CIE which has a good correlation with the characteristics of human eyes.
ΔE using L ^* a ^* b ^* , that is, the color difference of the colorimetric values of CIEL ^* a ^* b ^* between the support and the output image is preferable. Here, Delta] E ^{is, ΔE = (ΔL * 2 +} Δa * 2 + Δb * 2) 1/2 ΔL * = the support L ^* - the L ^* Δa ^* = support output image a ^* - the output image a ^* [Delta] b ^* = support b ^* - a b ^* of the output image.

It is preferable to use a screen generator 37 such that the periodic structure of the screen cells, that is, the screen ruling is 170 / inch or more. When the number of lines is less than 170 / inch, the linearity of the relationship between the image signal and the output value is increased, but the structure of the screen is easily visually recognized so that the granularity is impaired. The sharpness of the line drawing deteriorates,
A more favorable halftone image cannot be obtained.

As shown in FIG. 6, when the dot concentration type halftone screen is used, generally, the slope of the curve becomes high in a region where the image signal is low. Therefore, the image processing device 20
When the correction is performed at 0, the correction accuracy in this region deteriorates,
There is a problem that the tone reproducibility is deteriorated due to a change in the gradation reproducibility due to the history of the photoreceptor, the developer, the electrophotographic apparatus, and a change in the use environment.

In the present invention, the threshold matrix for forming the dot-concentrated halftone screen is replaced with a threshold matrix for forming the dot concentration type halftone screen. A new threshold matrix with pixels inserted is provided. This enhances the linearity of the curve between the image signal and the output value. The relationship between the image signal and the output value according to the present invention is as shown in FIG.

Since the linearity of the curve between the image signal and the output value is improved, when correction is performed by the image processing apparatus 200, the correction accuracy in this area is improved, and the history of the photosensitive member, the developer, the electrophotographic apparatus, and the use Halftone reproducibility due to a change in tone reproduction characteristics due to environmental changes or the like can be suppressed to a small value.

In the above configuration, in the image forming apparatus to which the image processing apparatus according to this embodiment is applied, there is no deterioration in granularity or resolution due to the periodic structure of the screen as described below. Even when the gradation reproduction characteristics change due to the history of the photoconductor, the developer, the electrophotographic apparatus, and the use environment, the halftone image can be reproduced well.

That is, in the image processing apparatus 200 according to this embodiment, as shown in FIG. 4, the multi-value input from the scanner unit 100 or the digital camera or the like is performed so that the finally obtained image can be seen preferably. Are subjected to color and gradation correction processing and spatial frequency correction processing by a known method, and a multi-valued image signal is created.

As shown in FIG. 1, the multi-valued image signal subjected to the color and gradation correction processing is used as a threshold matrix, and a lighting control signal for each screen cell is obtained by comparing the image signal with the threshold matrix. Sent to the screen generator 37 having a halftone generating function to form
3 is compared with the threshold matrix.

Then, it is converted into a pulse width modulated binary laser drive signal which is scanned along the main scanning direction of the ROS optical unit 300. This signal is temporarily stored in the image buffer 38 and sent to the laser driver 39 in synchronization with the page start signal and the main scanning start signal. Then, the ROS optical unit 2
A semiconductor laser as a light source of 00 is turned on / off.

The ROS optical unit 200 includes a laser light source, an optical system for forming an image of the laser beam on the photoconductor, and a scanning unit for scanning the laser beam on the photoconductor drum 7. As shown in the figure, scanning is performed in the main scanning direction, that is, in the axial direction on the photosensitive drum 7 by a scanning unit such as a polygon mirror 10. Scan in the direction. Also, depending on the optical system,
The beam diameter on the photosensitive drum 7 is adjusted to a desired size.

As described above, an electrostatic latent image having a halftone dot structure is formed on the photosensitive drum 7.

This electrostatic latent image is developed by each developing unit of the developing device 9, transferred to the support 17 by the transfer means, and fixed by the fixing means to obtain a halftone image.

The minimum reproducible pixel size of the output device is determined by the charged potential of the photosensitive drum 7, the responsiveness of the image buffer 38 and the laser driver 39, the emission intensity of the laser light source, the characteristics of the optical system, and the developing conditions. Mainly determined.

In the present invention, an isolated pixel whose width in the main scanning direction is changed is prepared, and an output characteristic as shown in FIG. The width of the pixel is set under the condition that no is formed. This setting can be dealt with by adjusting the charging potential of the photosensitive drum 7, the responsiveness of the image buffer 38 and the laser driver 39, the emission intensity of the laser light source, the characteristics of the optical system, the development conditions, and the like. That is, the method is not limited to this method as long as the purpose of not forming a toner image with respect to an image signal of an isolated pixel is satisfied.

As a method for achieving the purpose of not forming a toner image with respect to an image signal of an isolated pixel, it is preferable to adjust the frequency response of the image buffer 38 and / or the laser driver 39. In this embodiment, the exposure signal is turned off when the pixel is substantially an isolated pixel, and the exposure signal is turned on only when two or more pixels of the main scanning signal blink.

More preferably, as a method of achieving the object that a toner image is not formed with respect to an image signal of an isolated pixel, control of the charging potential of the photosensitive drum 7 and / or the emission intensity of the laser light source and / or the developing bias is performed. Good to follow.

Further, the relationship between the image signal when the dot concentration type halftone screen is used and the output value of the output image is grasped in advance as shown in FIG. A threshold matrix is used in which an isolated pixel is formed between thresholds having a high slope of the curve.

As shown in FIG. 6, in a method using a dot concentration type halftone screen, the slope of a curve in a low image signal area is generally high. Therefore, when the correction is performed by the image processing apparatus, the correction accuracy of this area is deteriorated, and the tone reproducibility is deteriorated due to a change in the gradation reproduction characteristics due to the history of the photoconductor, the developer, the electrophotographic apparatus, and a change in the use environment. This brings the problem.

In the present invention, the threshold matrix for forming the dot-concentration type halftone screen is replaced with a threshold matrix for forming the isolated matrix between the threshold of the region where the curve of the image signal and the output value is high. A new threshold matrix with pixels inserted is used. This enhances the linearity of the curve between the image signal and the output value. FIG. 7 shows the relationship between the image signal and the output value according to the present invention.

Here, the periodic structure of the screen cells, that is, the screen ruling is preferably 170 / inch or more. When the number of lines is less than 170 / inch, the linearity of the relationship between the image signal and the output value is increased, but the structure of the screen is easily visually recognized so that the granularity is impaired. The sharpness of the line drawing becomes poor, and a more preferable halftone image cannot be obtained.

[0081]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the present invention will be described below with reference to the drawings. However, the following description is an example of the present invention, and does not limit the scope of the present invention.

Embodiment 1 FIG. 4 also shows an image processing apparatus according to Embodiment 1 of the present invention.

The image processing apparatus 200 is used for RGB, CM
A table for converting an input image signal such as YK into CIEL ^* a ^* b ^* is provided inside the gradation and color correction circuit 35. For monochrome image, the gradation correction to the black image signal from the L ^*, such as L ^* in the L ^* and the output image of the input image are equal. Also, color - in the case of an image has the L ^* a ^* b ^* and the output image L ^* a ^* b ^* as equals L ^* a ^* conversion table b from ^* to CYMK the input image. The output image signal is 1200 DPI 8 bits.

The specifications of the screen generator 37 of this embodiment are as follows. In the case of the present threshold matrix, the threshold matrix includes one screen cell.

FIGS. 8 and 9 show the screen cells, their periodic structures, and the lighting order of the threshold matrix. As can be seen from FIGS. 8 and 9, the screen matrix of this embodiment has 20 pixels in the main scanning direction and 5 pixels in the sub-scanning direction (2 pixels).
0 × 5). The screen angle is 0 degree and the number of gradations is 100 gradations. It is needless to say that the angle of the screen does not have to be 0 degree, and for example, the screen angle may be different for each color of the screen.

In FIGS. 8 and 9, the gradation of an image signal is, for example, 50%, that is, an image signal having 256 gradations of 8 bits and a value of the image signal corresponding to 50%.
In the case of “8”, only the pixels whose thresholds described in the matrices shown in FIGS. 8 and 9 are 50 or less are turned ON.

Further, considering the resolution of the screen generator 37 and the process speed of the developing device 9 described later, the main scanning direction is 4800 × the sub-scanning direction is 1200D.
Because of PI, the screen ruling is 4800/2
0, 1200/5, and 240 lines / inch.

Also, as shown in FIG. 1, the comparison circuit 52 compares the 1200 DPI 8-bit input image signal input to the screen generator 37 of the image processing apparatus with the threshold matrix shown in FIGS. ,
0 degree angle, 240 screen lines, 10 gradation levels
A binary image signal having a screen structure of 0 + 1 gradation is created.

In determining the threshold matrices of FIGS. 8 and 9, the gradation characteristics when using the dot concentration type screen shown in FIG. 10 were measured. The lighting order of the threshold matrices is shown in FIGS. 11 and 12. Shown in As a matter of course, the structure of the threshold value matrix is the same as that of FIGS. 8 and 9, and only the lighting order is different.

The laser driver 39 is 1200 DPI
The frequency response in the main scanning direction of a pixel having a considerable size in the sub-scanning direction is adjusted to correspond to 2400 DPI. As a result, the laser driver 39 uses the resolution of the screen generator 27 of 1200 × 4800 DPI.
No response is made to an isolated pixel having a considerable size, and no exposure signal corresponding to the isolated pixel is formed.

Therefore, in the threshold value matrixes shown in FIGS. 8 and 9, an isolated pixel is formed for an input corresponding to a threshold value of 7, 9, 15, and 19, and the laser driver 39 does not respond. Output value change before and after can be reduced.

That is, when the input image signal corresponds to “1/100” in the threshold matrices of FIGS. 8 and 9, “1” is an isolated pixel, and no exposure signal is formed. Is not recorded. Note that the denominator is 10
0 indicates the total number of pixels of one screen cell.
Next, when the input image signal corresponds to “2/100”, as shown in FIG. 8 and FIG.
Since the pixels are continuous with "1", an exposure signal is formed and the pixels are recorded as shown in FIG. Hereinafter, similarly, until the input image signal is “6/100”, FIG.
As shown in (1), since the pixels are continuous, an exposure signal is formed and the pixels are recorded.

Next, when the input image signal corresponds to “7/100”, as shown in FIG. 15, the pixel of “7” is a pixel isolated along the main scanning direction. No exposure signal is formed and the pixel is not recorded.
When the input image signal is “8/100”,
As shown in FIG. 16, the pixel corresponding to “8/100” is not an isolated pixel but a continuous pixel of “5”, so that an exposure signal is formed and the pixel is recorded. At this time, the pixel of “8” has the value of the input image signal of “8/10
Although it is the case of “0”, the order of the pixels to be exposed is substantially the order of the pixel “6”, and thus becomes “7” as shown in FIGS. 11 and 12.

Next, when the input image signal is “9/100”, as shown in FIG. 17, the pixel of “9” is a pixel isolated along the main scanning direction.
No exposure signal is formed and the pixel is not recorded. Similarly, FIG. 18 shows the state of formation of exposure signals for pixels whose input image signal is up to “20/100”.

As a result, as shown schematically in FIG. 19, the image density L ^* of the output image recorded in the actual operation does not rise sharply even in the highlight portion as in the related art, and has a gentle gradient. Changes substantially linearly.

A laser ROS having a laser light source, an optical diameter, and a polygon mirror was used as an exposure device. The resolution in the sub-scanning direction corresponds to 1200 DPI. 1 / e
^{2 The} beam diameter is 30 μm in the main scanning direction and 40 μm in the sub-scanning direction.
m.

Photoreceptor, charging device, developing device, transfer device,
The fixing device is Acolor 63 manufactured by Fuji Xerox Co., Ltd.
0 was used. The detailed apparatus conditions are described in "Fuji Xerox Acolor 635/630 High Quality Digital Full Color Copier" described in Fuji Xerox Technical Report, 7, p22 (1992).

As shown in FIG. 7, the image obtained by the above-described apparatus configuration was excellent in halftone reproducibility, and good in graininess and resolution.

[0099] In the image forming apparatus using the image processing apparatus of the present invention, for example, even if a change in environment such as temperature and humidity, density of the output image with respect to the density of the input image L ^* L ^* is As shown in FIG. 24, the density of the output image hardly changes, but in the case of the image forming apparatus to which the conventional image processing apparatus is applied, when the environmental change such as temperature and humidity changes, the density of the output image with respect to the density L ^* of the input image is changed. L
^* , As shown in FIG. 25, changes significantly especially on the low concentration side. Example 2

FIG. 20 shows the screen cells, their periodic structures, and the lighting order of the threshold matrix. As can be seen from FIG. 20, the screen matrix of this embodiment is:
It is formed of 10 pixels in the main scanning direction and 5 pixels (10 × 5) in the sub-scanning direction. The screen angle is 0 degree and the number of gradations is 50 + 1 gradations.

Further, when the resolution of the screen generator is 1200 in the main scanning direction × 600 DPI in the sub-scanning direction in consideration of the process speed of the developing device described later, the number of screen lines is 120 lines / inch.

Also, the 600D sent from the image processing apparatus
A comparison is made between the 8-bit image signal of PI and the threshold matrix of FIG.
A binary image signal having a screen structure with 51 gradations of lines and gradations is generated.

In determining the threshold matrix shown in FIG. 20, the gradation characteristics when using the dot concentration type screen shown in FIG. 21 were measured. The lighting order of this threshold matrix is shown in FIG. As a matter of course, the structure of the threshold value matrix is the same as that of FIG. 20, and only the lighting order is different.

The laser driver 39 adjusted the frequency response in the main scanning direction of a pixel having a sub-scanning direction size equivalent to 600 DPI so as to correspond to 600 DPI. As a result, the laser driving unit does not respond to an isolated pixel having a size equivalent to a resolution of 1200 × 600 DPI of the screen generator, and no exposure signal corresponding to the isolated pixel is formed.

Accordingly, in the threshold matrix of FIG. 20, an isolated pixel is formed for an input corresponding to a threshold value of 4, 6, 10, or 12, and the laser driver 39 does not respond. Output value change can be reduced.

The exposure apparatus used was a laser ROS having a laser light source, an optical diameter, and a polygon mirror. The resolution in the sub-scanning direction is equivalent to 600 DPI. 1 / e ²
The beam diameter is 50 μm in the main scanning direction and 60 μm in the sub-scanning direction.
It is.

The other devices have the same configuration as that of the first embodiment.

As shown in FIG. 23, the image obtained by the above-described apparatus configuration was excellent in halftone reproducibility, granularity and resolution.

Comparative Example 1 The threshold matrix shown in FIG. 26 was used to form a conventional dot concentration type screen. Other devices have the same configuration as that of the first embodiment.

The image obtained by this apparatus configuration had a tone jump in a highlight portion, and was not preferable.

Comparative Example 2 The same apparatus as that of Example 2 was used except that the frequency response of the laser driving apparatus was equivalent to 1200 DPI.

In the image obtained by this apparatus configuration, although a tone jump is suppressed in a highlight portion, an unstable toner image is formed in a portion corresponding to an isolated pixel, and the stability of halftone reproduction is poor. In addition, the granularity was poor, which was not preferable.

[0113]

As described above, according to the present invention, there is no deterioration in granularity or resolution due to the periodic structure of the screen, and the history of the photosensitive member, the developer, the electrophotographic apparatus, It is possible to obtain an image free from the problem that the halftone reproducibility is deteriorated due to a change in the tone reproduction characteristic due to a change in the use environment.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a screen generator of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a circuit configuration of the image forming apparatus according to one embodiment of the present invention.

FIG. 4 is a block diagram showing an image processing apparatus according to one embodiment of the present invention.

FIG. 5 is a graph showing the width of an isolated pixel of the image processing apparatus according to one embodiment of the present invention.

FIG. 6 is a graph showing the relationship between an image signal and the density of an output image.

FIG. 7 is a graph showing a relationship between an image signal and a density of an output image when the image processing apparatus according to the embodiment of the present invention is applied;

FIG. 8 is a diagram illustrating a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 9 is a diagram illustrating a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIGS. 10A and 10B are graphs respectively showing a relationship between an image signal and a density of an output image before and after application of the image processing apparatus according to an embodiment of the present invention.

FIG. 11 is a diagram illustrating an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 12 is a diagram illustrating an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 13 is an explanatory diagram showing an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 14 is an explanatory diagram illustrating an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 15 is an explanatory diagram illustrating an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 16 is an explanatory diagram showing an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 17 is an explanatory diagram illustrating an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 18 is an explanatory diagram showing an image exposure order of a threshold matrix used in the image processing apparatus according to the first embodiment of the present invention.

FIG. 19 is a graph showing a relationship between an image signal to which the image processing apparatus according to the first embodiment of the present invention is applied and the density of an output image.

FIG. 20 is a diagram illustrating a threshold matrix used in the image processing apparatus according to the second embodiment of the present invention.

FIG. 21 is a graph illustrating a relationship between an image signal and a density of an output image before applying the image processing apparatus according to the second embodiment of the present invention.

FIG. 22 is a diagram illustrating an image exposure sequence of a threshold matrix used in the image processing apparatus according to the second embodiment of the present invention.

FIG. 23 is a graph showing a relationship between an image signal after application of the image processing apparatus according to the second embodiment of the present invention and the density of an output image.

FIG. 24 is a graph showing the relationship between the density of an input image and the density of an output image after applying the image processing apparatus according to the embodiment of the present invention.

FIG. 25 is a graph showing the relationship between the density of an input image and the density of an output image to which a conventional image processing apparatus is applied.

FIG. 26 is a diagram showing an image exposure order of a threshold matrix used in a conventional image processing apparatus.

[Explanation of symbols]

200: image processing unit, 37: screen generator,
38: image buffer, 52: threshold matrix storage circuit, 53: comparison circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA04 AA24 AA26 AB07 AB13 BB01 BB06 BB14 BB22 BB23 BC10 DA09 EA12 2C362 AA54 AA63 CA01 CA03 CB37 CB80 5B057 AA11 BA02 CA01 CA08 CA12 CB01 CB4 CCB CB4 CCB CB14 CCB DD06 DD08 DD16 EE12 FF05 FF15 5C077 LL04 LL06 LL19 MP08 NN09 NN19 PP32 PP33 PP36 PQ08 PQ22 SS02 TT03 TT06

Claims (6)

[Claims] An output image is obtained by comparing an input image signal with a threshold matrix preliminarily storing a threshold value for determining whether or not to record each pixel in a screen cell composed of a plurality of pixels of a halftone screen. An image processing method for generating a signal and outputting a processed image signal to an image forming apparatus having a non-linear area in a part of the image signal-output density characteristic, wherein the image signal-output density characteristic of the image forming apparatus is An image processing method for generating an output image signal using a threshold matrix in which a non-recording isolated pixel in which the pixel is not recorded in the image forming apparatus when the pixel is isolated between thresholds having a large inclination is used. . 2. An output image by comparing an input image signal with a threshold matrix in which thresholds for determining whether or not to record each pixel in a screen cell composed of a plurality of pixels of a halftone screen are stored in advance. In an image processing apparatus for generating a signal and outputting a processed image signal to an image forming apparatus having a non-linear area in a part of the image signal-output density characteristic, a screen cell including a plurality of pixels of the halftone screen A threshold matrix storage unit in which a threshold for determining whether or not to record each pixel is stored in advance, and a threshold matrix read from the threshold matrix storage unit is compared with the input image signal to generate an output image signal. A screen generation unit having a comparison unit, wherein the threshold matrix storage unit stores an image signal-output density characteristic of the image forming apparatus; The image processing apparatus characterized by between large gradient threshold, stores a threshold matrix of arranging the non-recording isolated pixels included in the pixel is not recorded by the image forming device when the pixels are isolated. 3. When an electrostatic latent image is formed by exposing an image on a surface of an image carrier according to an image signal by an exposure unit, processing is performed on the image signal output to the exposure unit. Comparing the input image signal with a threshold matrix preliminarily storing a threshold value for determining whether or not to record each pixel in a screen cell composed of a plurality of pixels of the halftone screen. By
When generating an output image signal and outputting the processed image signal to an image forming apparatus having a non-linear region in part of the image signal-output density characteristic, the image signal-output density characteristic of the image forming apparatus An image forming method comprising: using a threshold matrix in which non-recording isolated pixels in which a pixel is not recorded in the image forming apparatus when the pixel is isolated between thresholds having a large inclination are used to generate an output image signal. . 4. An image carrier, an exposure unit that performs image exposure on a surface of the image carrier in accordance with an image signal to form an electrostatic latent image, and an image that processes an image signal output to the exposure unit. In the image forming apparatus provided with a processing unit, the image processing unit previously stores an input image signal and a threshold value for determining whether to record each pixel in a screen cell including a plurality of pixels of a halftone screen. Means for generating an output image signal by comparing the threshold value matrix with the threshold value matrix, and outputting the processed image signal to an image forming apparatus having a non-linear region in a part of the image signal-output density characteristic, Threshold matrix storage means for storing in advance a threshold value for determining whether or not to record each pixel in a screen cell comprising a plurality of pixels of the halftone screen; Screen generating means for comparing the input threshold value matrix with the input image signal to generate an output image signal, wherein the threshold value matrix storage means includes an image signal-output density characteristic of the image forming apparatus. An image forming apparatus which stores a threshold matrix in which non-recording isolated pixels in which the pixel is not recorded in the image forming apparatus when the pixel is isolated between thresholds having a large inclination of. 5. A laser driving unit for controlling lighting of an exposure unit according to the image signal, and the exposure unit is a laser light source, and the laser light source is a laser beam for forming an image on an image carrier. An optical system, comprising scanning means for scanning the laser beam to form a pulse width modulated exposure image on the photoreceptor, wherein the laser driving means is lower than the frequency corresponding to the main scanning time of the pixel 5. The image forming apparatus according to claim 4, wherein the image forming apparatus is a responsive laser driving unit, and is controlled so that the signal is not reproduced by the image forming apparatus when an isolated pixel is used as a signal. 6. An image forming apparatus, comprising: an adjusting unit for adjusting at least one of a charging potential, an exposure amount, and a developing bias of the image carrier, so that the isolated pixel is not reproduced by the image forming apparatus. The image forming apparatus according to claim 4, wherein the image forming apparatus is controlled to: