JP2000358165A - Image processing apparatus and method - Google Patents

Abstract

(57) [Problem] In a low-resolution digital recording method, a possible screen angle and a screen ruling are limited.
An optimum screen angle cannot be assigned to each color, and moire cannot be effectively prevented. SOLUTION: A CPU 118 analyzes color information of an input image signal obtained by a video counter 100 and sets a synchronization control section 110 based on the analysis result, thereby setting different halftone processing for each color component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method, and more particularly, to a color printer or a color copying machine for recording an image based on a plurality of color component signals.

[0002]

2. Description of the Related Art Laser beam, thermal transfer, ink jet and other systems have been proposed as copier and printer systems. Most of these types of printers and copiers are digital systems, and form a two-dimensional image by scanning a recording medium in a main scanning direction and a recording medium in a sub-scanning direction. In particular, a color printer or a color copier forms a color image by performing the above-described operation on a plurality of colors.

[0003]

However, the above technique has the following problems.

When a color image is formed by superimposing a single-color image on a recording material, it is inevitable that the recording position of the image slightly shifts for each color. And moiré patterns occur. In order to avoid these problems, there is a method of providing a different screen for each color image.

However, the standard recording cycle is 600d.
In the digital recording system up to about pi, the screen angle and the screen ruling that can be formed are limited, and the screen ruling differs for each color, so that an optimal arbitrary screen angle cannot be assigned to each color. For this reason, the screen ruling and the screen angle have to be set depending on how the colors stand out.

On the other hand, when the original image is a print image having a halftone dot structure or a print image subjected to digital halftoning processing and having a unique texture, the original image information and the above-described screen unique to the image forming apparatus are used. There is a problem that interference occurs with the pattern, and color unevenness and a moiré pattern occur.

Further, the degree of occurrence of the above-mentioned problem varies depending on the ratio of the color information of the original image. With a single screen pattern, the occurrence of color unevenness and moiré patterns is effectively suppressed in accordance with various original images. Can not do. In particular, it is difficult to effectively suppress a moiré pattern that becomes prominent depending on the color of the original image.

Further, if the reference recording frequency is further increased in order to increase the degree of freedom in setting the screen ruling and the screen angle, the apparatus becomes complicated, large, and the manufacturing cost increases.

An object of the present invention is to solve the above-mentioned problem, and to provide an image processing apparatus and a method thereof that can obtain a high-quality image by effectively suppressing the occurrence of moire with a simple configuration. The purpose is to:

[0010]

The present invention has the following configuration as one means for achieving the above object.

An image processing apparatus according to the present invention is an image processing apparatus for performing halftone processing on an input image signal, wherein the analysis means analyzes color information of the input image signal, and the analysis means analyzes the color information. Control means for setting different halftone processing for each color component based on the result.

An image processing method according to the present invention is an image processing method for performing halftone processing on an input image signal, wherein color information of the input image signal is analyzed, and each color component is analyzed based on the analysis result. Is set different halftone processing.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image processing apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0014]

First Embodiment In a first embodiment, an electrophotographic copying machine and color printer shown in FIGS. 1 and 2 will be described as a typical image forming apparatus to which the present invention is applied. The application of the present invention is not limited to an electrophotographic copying machine and a color printer as shown in FIGS. 1 and 2, but may be applied to various types of copying machines and printers such as an inkjet system, a thermal transfer system, and other systems, and further, a facsimile machine. The present invention is applicable to various image forming apparatuses.

[Image Signal Processing Unit] FIG. 1 is a block diagram showing a configuration example of the image signal processing unit I of the color copying machine of the present embodiment.

The video counter 100 of the image signal processing section I has magenta M, cyan C, yellow Y and black K colors, which are color separation image signals output by the reader section R.
Image signals MRV, CRV, YRV, and KRV (hereinafter collectively abbreviated as “RV”) of 256 gradations are input, and an image signal RV is also input from an external interface F. The input image signal RV is temporarily stored in the image memory 101 for each color. The function of the video counter 100 will be described later.

The image signal RV stored in the image memory 101
Are read out for each color in synchronization with the image forming timing, latched by a flip-flop (FF) 103, and then input to an LUT 105 prepared independently for each color. For example, in the LUT 105 composed of a RAM, a printer gradation characteristic such that a desired input / output characteristic is obtained by the CPU 118 is written in advance. Therefore, the image signal RV of each color input to the LUT 105 is subjected to tone correction independently for each color.

The image signals MRV and CRV whose gradation has been corrected by the LUT 105 are stored in a first-in first-out (FIFO) memory 1.
At 06 and 107, the image signals YRV and KRV are input to last-in first-out (LIFO) memories 108 and 109, respectively.

The write address counters of the FIFO memory and the LIFO memory are reset when the main scanning synchronization signal RSYNC * of the reader unit R is at a low level. When the main scanning video enable signal RLVE * of the reader unit R is at a low level, the video signals of each color are synchronized with the pixel clock RCLK of the video signal of the reader unit R, and the FIFO memories 106 and 107, and the LIFO memory 108 and Written to 109. Note that “*” attached to the end of the signal name means low active.

Next, when the main scanning synchronization signal PSYNC * for each color of the printer section P shown in FIG. 2 is at a low level, the read address counter of the FIFO memory and the LIFO memory of the corresponding color is reset. Then, when the video enable signal PVE * for each color of the printer unit P is at L low level, in synchronization with the pixel clock PCLK for each color of the printer unit P,
The video signal PV of each color is stored in the corresponding FIFO memory 106 or 1
07, or read from the LIFO memory 108 or 109.

The M and C video signals are read as normal images, and the Y and K video signals are read as mirror images.
And converted into M, C, Y and K analog image signals by high-speed digital / analog (D / A) converters independent of each color. Each of these analog signals is subjected to pulse width modulation by a pulse width modulator (PWM) for each color, and then sent to a laser drive circuit for each color. The laser drive circuit drives the four semiconductor lasers according to the transmitted M, C, Y, and K video signals, and generates laser light corresponding to each of the M, C, Y, and K color images. Image signal processing unit
The laser light generated in I is scanned by the polygon scanner 301 of the printer unit P to form an electrostatic latent image on a photosensitive drum independent for each color.

A laser beam scanned by the polygon scanner 301 is detected by laser detectors 112 to 115 each formed of a light receiving element such as a photodiode, and is input to the synchronization controller 110 as a laser beam detection (BD) signal. Is done. The synchronization control unit 110 generates a main scanning synchronization signal PSYNC *, a pixel clock PCLK, and a main scanning video enable signal PVE * for each color of the printer unit P, based on the input BD signal of each color.

[Printer Unit] FIG. 2 is a schematic view showing a configuration example of the printer unit P.

A polygon scanner 301 scans the photosensitive drum with laser light. In the printer section P,
The four image forming units, that is, the image forming units 302, 303, 304, and 3 in order from the upstream side (the right side in the drawing) in the recording paper conveyance direction.
Numerals 05 are arranged to form images of four different colors (magenta, cyan, yellow and black) through respective processes of charging, exposure, development and transfer. Since the configurations of these image forming units are the same, the image forming units 30 will be described below.
Only 2 will be described.

In the image forming unit 302, an electrophotographic photosensitive drum (hereinafter simply referred to as "photosensitive drum") 318 as a dedicated electrophotographic photosensitive member is arranged. An electrostatic latent image is formed on the surface of the photosensitive drum 318 by a laser beam from the polygon scanner 301. Around the photosensitive drum 318, a primary charger 315 for charging the surface of the photosensitive drum 318 to a predetermined potential to prepare for forming a latent image, and a photosensitive drum 318
Developing device for developing a latent image on top to form a toner image
313, a transfer charger 319 that discharges from the back surface of the transfer belt 306 that conveys the recording paper to transfer the toner image on the photosensitive drum 318 to the recording paper on the transfer belt 306, and cleans the surface of the photosensitive drum 318 after the transfer. Cleaners for cleaning and neutralizing3
17 and an auxiliary charger 316, and a pre-exposure lamp 330 for erasing residual charges are arranged. The developing device 313 applies a developing bias to the sleeve 3 for developing.
14 are included.

Next, a procedure for forming an image on a recording paper or the like will be described.

Reference numeral 308 denotes a paper feed unit which supplies recording paper or the like stored in the cassette 309 or 310 to the transfer belt 306. The recording paper supplied from the paper supply unit 308 is charged by the attraction charger 311 and is attracted to the transfer belt 306. A transfer belt roller 312 rotates the transfer belt 306, and
A pair with the adsorption charger 311 charges the recording paper or the like by adsorption. A paper leading edge sensor 329 detects the leading edge of the recording paper or the like on the transfer belt 306. The detection signal of the paper leading edge sensor 329 is sent from the printer unit P to the image processing unit reader unit 101,
The image signal processing unit I uses it to generate a synchronization signal. In particular, the image writing signal is turned on based on the detection signal of the paper edge sensor 329, and the formation of the electrostatic latent image on the photosensitive drum 318 corresponding to the M color is started at a certain timing.

Thereafter, the recording paper or the like is conveyed by the transfer belt 306, and toner images are formed on the surface of the recording paper by the image forming units 302 to 305 in the order of MCYK. The recording paper or the like that has passed through the image forming unit 305 is separated from the transfer belt 306 after the charge is removed by the charge remover 324 to facilitate separation from the transfer belt 306. Reference numeral 325 denotes a peeling charger, which prevents image disturbance due to peeling discharge when recording paper or the like is separated from the transfer belt 306. The separated recording paper and the like are charged by pre-fixing chargers 326 and 327 in order to compensate for toner attraction and prevent image disturbance, and then the toner image is heat-fixed by fixing unit 307 and is discharged out of the apparatus. Is discharged.

On the other hand, a transfer belt from which recording paper and the like are separated
306 is neutralized by the transfer belt static eliminators 322 and 323 and is electrostatically initialized.
Then, the dirt is removed, and preparations for adsorbing the recording paper or the like are made again.

The transfer belt 306 is a dielectric resin film such as a polyethylene terephthalate, a polyvinylidene fluoride resin film sheet, or a polyurethane resin film sheet, and its both ends are overlapped and joined to form an endless shape. Or
A seamless (seamless) belt is used. In the case of a belt having a seam, a sensor for detecting the seam may be provided so that the transfer of the toner image is not performed at the seam.

[Laser Scanning Method] Next, the laser scanning method will be described. The rotation direction of the photosensitive drum is the sub-scanning direction, and the generatrix direction perpendicular to the rotation direction of the photosensitive drum is the sub-scanning direction.

A description will be given of an M-color image forming section as an example.
The laser light modulated according to the video signal MRV is scanned by the polygon scanner 301 rotating at high speed, and forms electrostatic dots corresponding to an image on the surface of the photosensitive drum 318 via three mirrors. One horizontal scan of the laser beam
Corresponds to one line. Since the photosensitive drum 318 is rotating at a constant speed in the clockwise direction in FIG. 2, the image is sequentially formed by scanning the laser beam in the main scanning direction and the constant speed rotation of the photosensitive drum 318 in the sub-scanning direction. Is formed.

In the present embodiment, as shown in FIG. 2, the polygon mirrors 301 are coaxially arranged in two stages. The upper polygon mirror is the M and C image forming unit
The lower polygon mirrors correspond to the laser beams that scan 302 and 303, and the Y and K image forming units 304 and 305
Corresponds to the laser beam that scans. That is, M and C
The laser beam scanning the image forming units 302 and 303 of
The laser beam that scans the Y and K image forming units by the upper polygon mirror is scanned by the lower polygon mirror to form an electrostatic latent image on the surface of each photosensitive drum.

The polygon mirror 301 has eight mirrors on the upper and lower stages, and has a rotation frequency of 255.9 Hz. Also,
The process speed, which is the rotation speed of each photosensitive drum and the conveyance speed of the recording paper, is 130 mm / sec. With these settings, the sub-scanning density of each color image becomes 400 dpi.

Next, the main scanning of the laser will be described.

The above-described laser detectors 112 to 115 detect a laser beam at a cycle corresponding to 2047.2 Hz corresponding to each surface of the polygon mirror 301. Then, these laser detection signals BD are input to the synchronization control unit 110. As described above, the synchronization control unit 110 controls the input BD
Based on the signal and the pixel clock PCLK, M,
Independent main scanning synchronization signals PSYNC * are generated for C, Y, and K, and M, C, Y, and K are determined based on the main scanning synchronization signals PSYNC *.
, An independent main scan video enable signal PVE * is generated.

FIG. 3 is a timing chart of signals related to main scanning. In the configuration of the laser beam scanning optical system described above, by setting the frequency of the pixel clock PCLK to 32.76 MHz corresponding to the scanning frequency of the main scanning described above, the scanning density of the main scanning becomes smaller than the scanning density of the sub-scanning. 800dpi which is twice as large as

[Dot exposure pattern] As described above,
In the present embodiment, the recording frequency and the scanning density of the sub-scan are set to 400 dpi. In the present embodiment, the dot exposure pattern of each color is controlled based on the above-described reference recording frequency and scanning density (hereinafter, referred to as “reference recording frequency” and “reference scanning density”).

FIGS. 4 to 7 are timing charts showing the main scanning timing of each color in the laser control unit 111. FIG.

In the present embodiment, the above-described main scanning recording frequency of 32.76 MHz is set as a reference recording frequency, and a quarter of the screen clock MSCLK, CSCLK, YSC having a frequency of 8.19 MHz is used.
LK and KSCLK are generated and these screen clocks S
The analog video signal input corresponding to the cycle of CLK is pulse width modulated. The M, C, Y and K semiconductor laser elements are driven by the pulse width modulated video signal, and an electrostatic latent image corresponding to the image signal is formed on the photosensitive drums 302 to 305.

At the same time, the screen clocks YSCLK, CSCL
The phases of K, YSCLK and KSCLK are shifted for each main scanning line. In the standard copy mode in this embodiment,
The MSCLK is shifted by 3Tm by three periods of the pixel clock MPCLK for each main scanning line as shown in FIG. Similarly, for CSCLK, the pixel clock
One cycle of CPCLK is shifted by Tc (see FIG. 5), and YSCLK is equivalent to two cycles of pixel clock YPCLK for each main scanning line.
It is shifted by 2 Ty (see FIG. 6). No phase shift is performed for KSCLK (see FIG. 7).

FIG. 8 shows a dot exposure pattern for each color when the electrostatic dots are exposed as described above. Hereinafter, the dot exposure pattern shown in FIG. 8 is referred to as a standard pattern. In the standard pattern, M is controlled by controlling the exposure timing of electrostatic dots based on the reference recording frequency of 800 dpi in the main scan and 400 dpi in the sub-scan, as shown in FIG.
As shown in (2), a dot exposure pattern of 200 dpi in the main scan, 400 dpi in the sub scan, 223.6 lines (screen line), and -63.4 degrees (screen angle) is formed. In addition, main scanning 200
dpi, sub-scanning 400 dpi, 223.6 lines, 63.4 degree dot exposure pattern, main scanning 200 dpi, sub-scanning 400 dpi, 282.8
Line, 45 degree dot exposure pattern, main scan 2 for K
A dot exposure pattern of 00 dpi, sub-scanning 400 dpi, 200 lines, 90 degrees is formed.

As described above, it is necessary to set the screen angle of each color so as to effectively suppress the moire pattern due to the interference of the dot exposure patterns of each color. Generally, in order to effectively suppress moiré, it is necessary to set the angle between colors to 30 degrees or more, if possible, at least to 30 degrees.

In the dot exposure pattern shown in FIG. 8, the screen angles of the respective colors are -63.4 degrees, 63.4 degrees, and 4 degrees, respectively.
5 degrees, set to 90 degrees. In other words, the difference between the screen angles of M, C and K is set to 26.6 degrees or more. Also, C and Y
The angle of the screen angle is as small as 18.4 degrees, but Y is the least noticeable visually, so moire is relatively invisible.

However, depending on the color of the original image,
Moire may not be acceptable even with the 8 dot exposure pattern. For example, when the original image is a human image and is mainly composed of flesh color components, the color components are mainly Y and M. In such a case, in the dot exposure pattern of FIG.
And the screen angle between Y and Y is insufficient, and the moiré pattern generated in the flesh-colored portion may have an unacceptable level. Such a phenomenon also depends on the characteristics of the original image, and becomes remarkable in a noticeable portion of the image such as human skin or a relatively bright color region.

[Control of Dot Exposure Pattern] The present embodiment effectively solves the above problem by controlling the dot exposure pattern according to the color information of the original image.

The video counter 100 of the image signal processing unit I
The input image signal RV is integrated for each pixel, and the integrated amount of the image signal is calculated for each color.

The signal amount of each color integrated by the video counter 100 is calculated by the image signal processor I and the printer controller 117.
Is sent to the CPU 118 which controls the printer unit P via the. C
The PU 118 controls the dot exposure pattern by comparing (S1) the signal amounts of Y, M, and C according to the process shown in FIG. For example, normally, the standard pattern shown in FIG. 8 is adopted (S2), but Y
The dot exposure pattern is changed when the signal amount Iy is larger than the signal amount (Im or Ic) of M or C by a predetermined ratio (for example, 5%) or more.

When the dot exposure pattern is changed, the signal amount Ic of C and the signal amount Im of M are compared (S3).
C signal amount Ic is a predetermined ratio (for example, 3%) than M signal amount Im
If more, the second dot exposure pattern is adopted (S4), otherwise, the third dot exposure pattern is adopted (S4
Five).

The CPU 118 sends a phase shift amount selection signal FSET to the synchronization control unit 110 based on the selected dot exposure pattern so that the phase shift amounts of the screen clocks MSCLK, CSCLK, YSCLK and KSCLK for each main scanning line are set. Send. Note that the processing program shown in FIG. 9 is stored in a ROM or the like built in the CPU 118.

In the present embodiment, a total of four types of screen clocks SCLK, in which the phase of the screen clock SCLK is shifted from the pixel clock PCLK by 1, 2, and 3 periods, can be set for each color. Therefore, one of the four screen clocks is selected for each line of the main scanning, and the screen clocks MSCLK, CSCLK, YSCLK, and KSCLK of each color are selected. The selection of the phase shift amount of the screen clock is
It is controlled by a phase shift amount selection signal FSFT output from 18. CPU 118 based on the selected dot exposure pattern
However, a desired dot exposure pattern can be obtained by controlling the signal FSFT for each main scanning line according to a preset combination of phase shift amounts.

FIG. 10 is a view showing a second dot exposure pattern in which the Y and M dot exposure patterns of the standard pattern shown in FIG. 8 are interchanged. FIG. 11 shows a third dot exposure pattern in which the dot exposure patterns of Y and C of the standard pattern are interchanged. As described above, when the second dot exposure pattern is selected, in the case where Y and C are the main color components, by setting the screen angles of Y and C to -63.4 degrees and 63.4 degrees, Moire between Y and C can be sufficiently suppressed. When the third dot exposure pattern is selected, Y and M are the main color components, and the screen angles of Y and M are set to 63.4 degrees and -63.4 degrees, so that Y and M are set. Can be sufficiently suppressed.

Further, the integration of the image signal is not performed over the entire area of the original image, but is performed at the center of the original image, for example, at an area ratio of 25%.
And the above-described dot exposure pattern control can be performed. This makes it possible to select an optimal dot exposure pattern for the main part of the original image.

As described above, according to the present embodiment, the dot exposure pattern of each color is appropriately set, and
Having multiple combinations of dot exposure patterns for each color, and making it possible to select the combination as appropriate according to the color information of the original image, effectively suppressing the occurrence of moiré that becomes prominent depending on the color of the original image Can be. Therefore, it is possible to form a high-quality image irrespective of an original image having various color characteristics.

[0055]

Second Embodiment In a second embodiment, an example in which the present invention is applied to an electrophotographic copying machine and a color printer different from the image forming apparatus of the first embodiment will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[Image Signal Processing Unit] FIG. 12 is a block diagram showing a configuration example of the image signal processing unit I of the color copying machine according to the second embodiment.

The video counter 100 of the image signal processing unit I has a color separation image signal R output by the reader unit R.
In addition to the input of V, the image signal RV is also input from the external interface F. The input image signal RV is independent of each color.
Input to LUT 205a to 205d. Each of the LUTs 205a to 205d is constituted by a RAM in which, for example, a printer 118 is written in advance by the CPU 118 so as to obtain desired input / output characteristics.
The image signal RV of each color input to the UTs 205a to 205d is subjected to tone correction independently for each color. The tone-corrected image signal RV is input to the corner color independent dither processing units 202a to 202d, subjected to multi-value dither processing, and stored in the image memory 201.

Since the configuration after the image memory 201 and the configuration of the printer unit P are the same as those of the first embodiment shown in FIGS. 1 and 2, detailed description thereof will be omitted.

However, the polygon mirror 301 of the present embodiment
Has eight mirrors on the top and bottom, and the rotation frequency is 29
5.2 Hz. The process speed, which is the rotation speed of each photosensitive drum and the transport speed of the recording paper, is 100 mm / sec. With these settings, the sub-scanning density of each color image is 600d
becomes pi.

Next, the main scanning of the laser will be described.

The laser detectors 112 to 115 detect a laser beam on each surface of the polygon mirror 301 at a cycle corresponding to 2362.2 Hz. Then, these laser detection signals BD are input to the synchronization control unit 110. As described above, in the synchronization control unit 110, based on the BD signal of each color that is input and the pixel clock PCLK, the M, C,
An independent main scanning synchronization signal PSYNC * is generated for Y and K, and an independent main scanning video enable signal PVE * is generated for M, C, Y and K based on the main scanning synchronization signal PSYNC *.

In the configuration of the laser beam scanning optical system described above, the frequency of the pixel clock PCLK is set to 28.34 MHz corresponding to the scanning frequency of the main scanning described above, so that the scanning density of the main scanning is reduced. Same scanning density as 600d
becomes pi.

[Dot Exposure Pattern] Next, the dot exposure corresponding to the image signal will be described.

As described above, in this embodiment,
The sub-scanning recording frequency and scanning density are set to 600 dpi. In the present embodiment, the dot exposure pattern of each color is controlled based on the reference recording frequency and the reference scanning density.

FIG. 13 shows a dot exposure pattern for each color when electrostatic dots are exposed in the standard mode.
That is, it is a diagram showing a standard pattern. In the standard pattern, 189.7 lines (screen lines) and 18.4 for M
A dither pattern image having a degree (screen angle) is formed. A dither pattern of 189.7 lines and 71.6 degrees is formed for C, a dither pattern of 212.1 lines and 45 degrees is formed for Y, and a dither pattern of 200 lines and 90 degrees is formed for K.

In the dot exposure pattern shown in FIG. 13, the screen angles of each color are 18.4 degrees, 71.6 degrees, and 45 degrees, respectively.
Degrees and 90 degrees, and the angle difference between each color is 15 degrees or more where moire is relatively inconspicuous. In particular, M and C have an angle of 36.5 degrees, and moire is effectively suppressed.

However, as described in the first embodiment, in the standard pattern, moire may not be allowed depending on the color of the original image, that is, the quality of the output image may be deteriorated to an unacceptable level. Therefore, in the present embodiment, in order to effectively suppress moire, the screen pattern can be easily changed according to the color information of the original image without complicating the device configuration.

[Control of Dot Exposure Pattern] As shown in FIG. 12, in this embodiment, four systems of dither processing units 202a to 202
2d, so that the dither processing units 202a to 202d can be arbitrarily applied to each color. That is, four-input one-output selectors (SEL) 203a to 203d and selectors 204a to 204d are provided at the front and rear stages of the dither processing units 202a to 202d, and the color-independent dither processing selection signals MDSET, CDSET, YDSET
The dither processing unit applied to each color is selected by and KDSET. As a result, a desired dither pattern can be formed for each color, and control of the dot exposure pattern is realized.

That is, the CPU 118 of the present embodiment calculates the signal amount of each color integrated by the video counter 100,
The dot exposure pattern is controlled by controlling the dither pattern of each color. That is, the CPU 118 controls the dot exposure pattern by comparing (S1) the signal amounts of Y, M, and C according to the processing shown in FIG. For example, the standard pattern shown in FIG. 13 is usually employed (S2). However, when the signal amount Iy of Y is larger than the signal amount of M or C (Im or Ic) by a predetermined ratio (for example, 5%) or more, Change the exposure pattern.

When changing the dot exposure pattern, a comparison is made between the signal amount Ic of C and the signal amount Im of M (S3).
C signal amount Ic is a predetermined ratio (for example, 3%) than M signal amount Im
If more, the second dot exposure pattern is adopted (S4), otherwise, the third dot exposure pattern is adopted (S4
Five).

The CPU 118 controls the dither processing selection signals MDSET, CDSET, YDSET and KDSET based on the selected dot exposure pattern. Therefore, a dither processing unit applied to each color is set in accordance with the dither processing selection signal, whereby a desired dither pattern is formed for each color.

FIG. 14 is a view showing a second dot exposure pattern in which the dot exposure patterns of Y and M of the standard pattern shown in FIG. 13 are interchanged. FIG. 15 is a diagram showing a third dot exposure pattern, in which the dot exposure patterns of the standard patterns Y and C are interchanged. As described above, when the second dot exposure pattern is selected, in the case where Y and C are the main color components, by setting the screen angles of Y and C to -71.4 degrees and 71.4 degrees, Moire between Y and C can be sufficiently suppressed. When the third dot exposure pattern is selected, Y and M are the main color components, and by setting the screen angles of Y and M to 71.4 degrees and -71.4 degrees, Y and M are set. Can be sufficiently suppressed.

Further, the integration of the image signal is not performed over the entire area of the original image, but is performed at the center of the original image, for example, at an area ratio of 25%.
And the above-described dot exposure pattern control can be performed. This makes it possible to select an optimal dot exposure pattern for the main part of the original image.

As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained.

[0075]

[Modification] In the first and second embodiments described above,
Although a color copying machine having four photosensitive drums has been described as an example, the present invention can also be applied to a one-drum surface sequential type color copying machine having one photosensitive drum. First
As in the embodiment, by appropriately setting the dot exposure pattern of each color, and having a plurality of combinations of dot exposure patterns of each color, the combination can be appropriately selected according to the color information of the original image. Thus, it is possible to effectively suppress the occurrence of a moiré pattern.

Further, the present invention is not limited to the above-described embodiment, and is applicable to an image forming apparatus such as an ink jet system, a thermal transfer system, and an electrophotographic system using a linear light emitting device such as an LED array instead of a laser beam. It is.

[0077]

[Other Embodiments] The present invention can be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), and can be applied to a single device (for example, a copying machine). Machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (a computer) of the system or the apparatus. It is needless to say that the present invention can also be achieved by a CPU or an MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. Also,
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the operating system (OS) running on the computer based on the instructions of the program code.
It is needless to say that a case in which the functions of the above-described embodiments are implemented by performing part or all of the actual processing.

Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the program code is read based on the instruction of the program code. Needless to say, the CPU included in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowchart shown in FIG.

[0081]

As described above, according to the present invention,
It is possible to provide an image processing apparatus and a method for obtaining a high-quality image by effectively suppressing moire with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an image signal processing unit of a color copying machine according to a first embodiment;

FIG. 2 is a diagram showing an overview of a printer unit of a color copying machine;

FIG. 3 is a timing chart of signals related to main scanning,

FIG. 4 is a timing chart showing main scanning timing of each color in a laser control unit;

FIG. 5 is a timing chart showing main scanning timing of each color in a laser control unit;

FIG. 6 is a timing chart showing main scanning timing of each color in a laser control unit;

FIG. 7 is a timing chart showing main scanning timing of each color in the laser control unit;

FIG. 8 is a diagram showing a standard dot exposure pattern in the first embodiment,

FIG. 9 is a flowchart showing control of a dot exposure pattern;

FIG. 10 is a view showing a second dot exposure pattern in the first embodiment;

FIG. 11 is a diagram showing a third dot exposure pattern in the first embodiment;

FIG. 12 is a block diagram illustrating a configuration example of an image signal processing unit of a color copying machine according to a second embodiment;

FIG. 13 is a diagram showing a standard dot exposure pattern according to the second embodiment;

FIG. 14 is a view showing a second dot exposure pattern in the second embodiment;

FIG. 15 is a diagram showing a third dot exposure pattern in the second embodiment.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B057 CE13 CE16 CH01 CH11 DB02 DB06 DB09 DC22 DC25 5C077 LL03 MP08 NN04 NN08 NP01 PP33 PQ12 PQ17 PQ22 TT02 TT06 5C079 HB03 LC04 LC14 MA01 MA11 NA02 NA27 PA02 PA03

Claims (8)

[Claims] 1. An image processing apparatus for performing halftone processing on an input image signal, comprising: analysis means for analyzing color information of the input image signal; An image processing apparatus having control means for setting different halftone processing. 2. The image processing apparatus according to claim 1, wherein the analysis result indicates an information amount for each color component of the input image signal. 3. The image processing apparatus according to claim 2, wherein the control unit sets the halftone processing based on a correlation of an information amount for each color component of the input image signal. 4. The image processing apparatus according to claim 1, wherein the control unit sets a different screen angle for each color component according to the analysis result. 5. The image processing apparatus according to claim 1, wherein the control unit sets a different screen line for each color component according to the analysis result. 6. The image processing apparatus according to claim 1, wherein the control unit sets different dither processing for each color component according to the analysis result. 7. An image processing method for performing halftone processing on an input image signal, wherein color information of the input image signal is analyzed, and different halftone processing is set for each color component based on the analysis result. An image processing method comprising: 8. A recording medium on which is recorded a program code for image processing for performing halftone processing on an input image signal, wherein the program code includes at least a step of analyzing color information of the input image signal. An image processing method comprising: a code; and a code for setting a different halftone process for each color component based on the analysis result.