JP2000152015A - Picture processor and picture processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture processor and a picture processing method which obtain pictures of high quality independently of patterns of various original pictures by suppressing the occurrence of color irregularity or a moire pattern which is made conspicuous by patterns of original pictures. SOLUTION: An inputted picture signal is resolved to colors and is read, and the gradation is converted into color units. A screen pattern is selected for the purpose of changing the copy mode (S1930) in accordance with the picture signal subjected to gradation conversion, and the extent of phase shift in the unit of one line in the main scanning direction is changed into resolved color units (S1950). Image formation in the main scanning direction is controlled based on combination of extents of phase shift in changed color units.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser beam,
More particularly, the present invention relates to an image processing apparatus and an image processing method such as a color printer or a color copier for recording a plurality of colors, which relates to thermal transfer, ink jet, and other types of printers and copiers.

[0002]

2. Description of the Related Art Conventionally, various types of copying machines and printers of laser beam, thermal transfer, ink jet, and other types have been proposed. Most of these types of printers and copiers are of the digital type, in which the recording means is scanned in the main scanning direction and the recording medium is scanned in the sub-scanning direction.
A system in which an image is formed in a two-dimensional manner is generally used.

In particular, a color printer and a color copier generally form a color image by performing the above-described operation for a plurality of colors.

[0004]

Although such an image processing apparatus operates satisfactorily, it has the following problems in forming a color image.

When a color image is formed by overlapping a single-color image on a recording material, it is inevitable that the recording position of the image slightly shifts for each color. Unevenness and moiré patterns occur. In order to avoid these problems, a method of providing a screen angle for each color image has been used.

However, especially when the reference recording cycle is 600
In the digital recording system up to DPI, the screen angle and the screen ruling that can be formed are limited, and the number of screens differs for each color, so that an optimal arbitrary screen angle cannot be assigned to each color. 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 has a halftone structure such as a printed image, or has a unique texture by digital halftoning processing such as another digital printer, the original image information and the screen pattern unique to the image forming apparatus as described above. However, there is a problem that interference occurs between the color filters and uneven color and moiré patterns occur.

Further, increasing the reference recording frequency in order to increase the settable number of screen lines and the degree of freedom of the screen angle causes a problem that the apparatus becomes complicated, large, and the manufacturing cost increases. there were.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and suppresses the occurrence of color unevenness and moiré patterns which are remarkable due to the pattern of an original image. It is an object of the present invention to provide an image processing apparatus and an image processing method capable of obtaining a high-quality image. An image forming apparatus and an image processing method according to the present invention mainly include the following configurations.

That is, an image processing apparatus for an apparatus that forms an image by scanning a line on a recording medium is described below.
Input means for inputting a color image signal composed of a plurality of color component signals, generating means for generating a pattern signal of a predetermined period, and generating a signal by pulse width modulation of the color component signal according to the pattern signal Pulse width modulating means, setting means for setting a phase shift amount for shifting the phase of the pattern signal on a line basis, and shifting the phase shift of the pattern signal on a line basis in accordance with the output of the setting means. And phase shifting means that are compatible with each other.

The image processing apparatus has input means for inputting a color image signal represented by a plurality of color component signals, and dither processing means for dithering the color component signals. With different dither patterns,
A dither pattern for each of the color component signals is adaptively selected from the plurality of types of dither patterns.

An image processing method for an apparatus for forming an image by scanning a line on a recording medium includes an inputting step of inputting a color image signal composed of a plurality of color component signals, and a pattern signal having a predetermined period. And a pulse width modulation step of generating a pulse width modulation signal for the color component signal in accordance with the pattern signal, and setting a phase shift amount for shifting the phase of the pattern signal in line units. And a phase shifting step of shifting the phase of the pattern signal on a line-by-line basis according to the setting result of the setting step.

Further, the image processing method has an input step of inputting a color image signal represented by a plurality of color component signals, and a dither processing step of dithering the color component signals.
The dither processing step includes a plurality of types of dither patterns, and adaptively selects a dither pattern for each of the color component signals from the plurality of types of dither patterns.

The image processing apparatus has an input means for inputting a color image signal composed of a plurality of color component signals, and a halftone processing means for performing halftone processing on the color component signal. The processing means includes a plurality of types of halftone processing methods, and adaptively selects a halftone processing method to be applied to each color component. Further, the image processing method includes an input step of inputting a color image signal composed of a plurality of color component signals, and a halftone processing step of performing a halftone processing on the color component signal, wherein the halftone processing step includes: A plurality of types of halftone processing methods are provided, and a halftone processing method to be applied to each color component is appropriately selected.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments according to the present invention will be described below in detail with reference to the drawings.

[Embodiment 1] In a first embodiment, an electrophotographic copying machine and color printer shown in FIGS. 1 and 3 will be described as a typical image processing apparatus to which the present invention can be suitably applied. . The present invention is described with reference to FIGS.
The present invention can be applied not only to the electrophotographic copying machine and color printer shown in FIG.

<Image Signal Processing Unit> FIG. 1 is a block diagram of an image signal processing unit I of a color copying machine according to this embodiment.
FIG. 18 is a flowchart thereof.

The image signal read by the color separation by the reader unit R (S1810) is subjected to desired image processing (S1820), and then subjected to magenta, cyan, yellow, and black (hereinafter referred to as Y, M, C, and Bk) are converted into image signals MRV, CRV, YRV, and KRV (hereinafter, abbreviated as RV) of 256 tones for each of the four colors (S1830), and input to the image signal processing unit I. Similarly, the image signal RV input from the external interface F is also input to the image signal processing unit I. The input image signal RV is temporarily stored in the image memory 101 for each color.
(S1840).

The image signal RV input to the image memory 101 is read out for each color in synchronization with the image processing timing (S1850), latched by the flip-flop (FF) 103, and is independent for each color. The data is input to the LUT 105. The LUT 105 is composed of, for example, a RAM in which printer gradation characteristics such that desired input / output characteristics are obtained by the CPU 118 are written in advance. The image signal RV of each color input to the LUT 105 is subjected to gradation correction independently for each color. (S1860).

M and C gradation-corrected by LUT 105
Image signals MRV and CRV of the FIFO memory 106, 1
07, the Y and Bk image signals YRV and KRV are Li
These are input to the Fo memories 108 and 109, respectively. When the main scanning synchronization signal RLSYNC * of the reader unit is Low, the write address counter of the FiFo memory or LiFo memory is reset. When the main scanning video enable signal RLVE * of the reader unit R is LOW, the pixel of the video signal of the reader unit R is reset. In synchronization with the clock RCLK, the video signals of the respective colors are transmitted to the FIFO memories 106, 107 and L
The data is written to the iFo memories 108 and 109, respectively.

Next, when the main scanning synchronization signal PLSYNC * for each color of the printer unit P is Low, the read address counter of the Fifo memory and the Lifo memory of the corresponding color is reset, and the video enable for each color of the printer unit is independent. When the signal PVE * is Low, each color-independent video signal PV is synchronized with the color-independent pixel clock PCLK corresponding to each color-independent video signal of the printer unit, and the corresponding color-specific video signal PV is stored in the Fifo memory 106, 107 or Li of the corresponding color.
It is read from the Fo memories 108 and 109. A video signal of each color read out as a normal image for M and C and a mirror image for Y and K is supplied to a laser controller 11.
1 and M, M by the high-speed D / A converter independent for each color.
It is converted to C, Y, Bk analog image signals (S187
0), and further subjected to PWM by a pulse width modulation (PWM) device independent for each color and sent to a laser drive circuit independent for each color (S1880). In the laser drive circuit, M, C, Y, and
According to the Bk video signal, the four semiconductor lasers are driven to generate laser beams corresponding to the M, C, Y, and Bk images (S1890). According to the above-described processing, a laser beam is generated to perform image processing in the standard copy mode.

The laser light generated by the image signal processing unit I is applied to the polygon scanner 31 shown in FIG.
Scanning is performed on a photosensitive drum independent of each color of Y and Bk. Also,
The laser light of each color to be scanned is supplied to a laser detector 112 to 115 constituted by a light receiving element such as a photodiode.
And is input to the synchronization control unit 110 as a laser detection signal independent of each color of M, C, Y, and Bk. The synchronization control unit 110 converts the M, C, Y, and Bk independent main scanning synchronization signals PLSYNC * and the M, C, Y, and Bk independent pixel clocks PCLK based on the input BD signals of each color. The main scanning video enable signal PVE * independent of M, C, Y, and Bk of the printer unit is generated based on the generated BD signal.

<Printer Unit P> FIG. 3 is a cross-sectional view showing a main part of a color electrophotographic copier / printer (hereinafter, a color printer) to which the present invention is applied. In the figure, reference numeral 331 denotes a polygon scanner for scanning the photosensitive drum with the laser light generated in the image signal processing unit I. The printer unit includes four image forming units, that is, upstream sides in the transport direction of the recording medium (see FIG. 3), image forming units Pa, Pb, Pc and Pd are arranged in this order from the right,
Image formation of four different colors (magenta, cyan, yellow, and black) is performed through each process of exposure, development, and transfer.

The image forming units Pa, Pb, Pc and P
In d, an electrophotographic photosensitive drum (hereinafter simply referred to as “photosensitive drum”) 3 as a dedicated electrophotographic photosensitive member is used.
01a, 301b, 301c, and 301d are provided, and a toner image formed by a developer (toner) formed on these photosensitive drums is carried and conveyed by a conveyance belt 2 that moves adjacent to each image forming unit. Recording medium 3 transferred onto the recording medium 3 to be transferred and further onto which the toner image is transferred
Reference numeral 40 denotes a configuration in which the toner image is fixed and heated and pressed by the fixing unit 304, and then discharged outside the apparatus.

Here, the image forming section will be described in order from the latent image forming section. Exposure lamps 305a, 305b, 305c are provided around and above the rotatable photosensitive drums 301a, 301b, 301c and 301d. And 5d, chargers 306a, 306b, and 3 serving as charging means
06c and 306d, potential sensors 308a and 308
b, 308c and 8d are provided. First, the photosensitive drums 1a to 1d are charged by the chargers 306a to 306d.
Are uniformly charged.

Next, as described above, the image signal processing unit I (11
The laser light generated in 6) is transmitted to the polygon scanner 30
1 scans the photosensitive drums 301a, 301b, 301c and 1d, and forms an electrostatic latent image on each photosensitive drum according to an image signal.

Developing devices 309a and 309 serving as developing means
b, 309c and 309d have magenta,
A predetermined amount of developer (toner) of each color of cyan, yellow and black is filled by a supply device (not shown). The electrostatic latent images on the photosensitive drum are developed by developing units 9a to 9d.
Is developed by the developer, and the photosensitive drums 301a to 301a to
A visible image (toner image) corresponding to the electrostatic latent image by the exposure is formed on 301d.

The recording medium 3 to which the toner image is to be transferred
Is carried in a cassette 310, is carried on a belt-shaped transport belt 302 via a paper feed roller 311 and a registration roller 312, and is transported to each of the photosensitive drums 301a to 301d.

The conveyor belt 302 is a dielectric greasy film such as polyethylene terephthalate, polyvinylidene fluoride resin film sheet or polyurethane resin film sheet, and its both ends are overlapped and joined to form an endless shape. Or a seamless (seamless) belt. (In the case of a belt having a seam, there may be a configuration in which means for detecting the position of the seam is provided and the toner image is not transferred on the seam.)
The transport belt 302 is stretched between an upstream roller 313a and a downstream roller 313b. When the transport belt 302 starts rotating, the recording medium 3 is transported from the registration rollers 312 onto the transport belt 302. .
At this time, the image writing signal is turned ON, and an image is formed on the most upstream photosensitive drum 1a at a certain timing.

The toner image on the photosensitive drum 311a is transferred onto the recording medium 340 by the transfer charger 315a applying the electrolysis under the uniform pressure condition by the transfer pressing member 314a under the photosensitive drum 301a. (Note that the transfer pressing portions 314b and 314c and the transfer charger 315b are also provided for the other image forming portions Pb, Pc and Pd.
315c and 315d are provided).

The recording medium 340 is held on the conveyor belt 302 by an electrostatic attraction force de, and thereafter is conveyed to the next image forming section Pb, and the photosensitive drum 301 is moved in the same manner as described above.
By b, the cyan toner image is transferred. Thereafter, yellow and black toner images are transferred by the photosensitive drums 301c and 301d, respectively, in the same manner as described above.

The recording medium 3 onto which the four color toner images have been transferred as described above is separated from the separation charger 316 and the separation charger 31.
7, the toner is removed from the transport belt 302 by the attenuation of the attraction force, and is transported to the fixing unit 304.

The recording medium 340 conveyed from the conveyance belt 302 to the fixing unit 304 heats the toner image here.
The pressurized recording medium 340 is then discharged out of the machine.

On the other hand, after the transfer of the toner, that is, each of the photosensitive drums 301a to 301d from which the toner image has disappeared, the developer remaining on the surface thereof is cleaned by the cleaning units 318a and 318.
18b, 318c and 318d to prepare for the next subsequent latent image formation. Conveyor belt 302
The toner remaining on the belt is removed by belt neutralizers 319 and 320.
And the electrostatic attraction force is removed, and is scraped off by a rotatable fur brush 321. still,
As another means for removing the toner, a blade or a nonwoven fabric and a combination thereof are also used.

As described above, in the image processing apparatus of the present invention, as described above, a color image is formed on an image processing sheet using a color toner by an image processing apparatus as shown in FIG.

Next, an image scanning method according to the first embodiment will be described. In the following description, the rotation direction of the photosensitive drum is referred to as a sub-scanning direction, and the generatrix direction of the photosensitive drum is referred to as a sub-scanning direction.

The laser beam modulated in accordance with the image data is scanned at high speed by a polygon scanner 331 rotating at high speed, reflected by mirrors 332 to 334, and is exposed to the photosensitive drum 301a. Is subjected to dot exposure corresponding to the image. Laser light 1
Horizontal scanning corresponds to one horizontal scan of an image.

On the other hand, since the photosensitive drum 301a is rotating at a constant speed in the direction of the arrow, the above-mentioned laser beam scanning is performed in the main scanning direction, and the photosensitive drum 301a is rotated in the sub-scanning direction at a constant speed, so that a planar image is successively exposed. Is done.

In the first embodiment, as shown in FIG. 3, polygon mirrors 331 are coaxially arranged in two stages. The upper polygon mirror 331a scans the second and third image forming units, that is, the M and C image forming units Pb and Pc from the upstream side in the transfer material transport direction with a laser beam, and outputs the lower polygon. The mirror 331b is provided at the first and fourth image forming units, that is, Y and B
A laser beam scans the k image forming units Pa and Pd.

That is, the laser beams of M and C are scanned by the upper polygon mirror 331a, and the laser beams of Y and Bk are scanned by the lower polygon mirror 331b, and the surface of each photosensitive drum is exposed to dots corresponding to the image of each color. I do.

In the first embodiment, eight polygon mirrors are used in the upper and lower stages, and the rotation frequency is 255.9.
Hz and the process speed, which is the rotation speed of the photosensitive drum of each color or the transfer speed of the transfer material, is 130 mm / s.
ec. With the above setting, the sub-scanning density of the image of each color is 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 of 2047.2 Hz with respect to each polygon mirror surface. Then, the laser detection signal BD for each color is input to the synchronization control unit 110.

As described above, the synchronization control unit 110 generates a main scanning synchronization signal PLSYNC * independent of M, C, Y, and Bk of the printer unit based on the input BD signal of each color and the pixel clock PCLK. Based on the above-described main scanning synchronization signal PLSYNC *, M, C, Y,
A main scan video enable signal PVE * independent of Bk is generated.

FIG. 4 is a timing chart of signals related to main scanning. Hereinafter, description will be made with reference to FIG.

In the first embodiment, the frequency of the pixel clock PCLK is set to 32.76 MHz.
In the configuration of the laser beam scanning optical system according to the first embodiment, by setting the frequency of PCLK to the above value corresponding to the scanning frequency of the main scanning as described above, the scanning density of the main scanning can be reduced. Is twice as high as the scanning density, that is, set to 800 DPI.

Next, the dot exposure corresponding to the image signal will be described.

As described above, in the first embodiment, the recording frequency and the scanning density of the sub-scan are set to 400 DPI. In the first embodiment, the reference recording frequency and scanning density (hereinafter, reference recording frequency,
A pixel dot exposure pattern of each color is formed based on the (reference scanning density).

FIGS. 5 to 8 show the main scanning timing of each color in the laser controller 111. FIG.

In the first embodiment, the above-described main scanning recording frequency of 32.76 MHz is used as a reference frequency, and a quarter of the screen clock M with a frequency of 8.19 MHz is used.
SCLK, CSCLK, YSCLK and KSCLK are generated, and the analog video signal input corresponding to the cycles of MSCLK, CSCLK, YSCLK and KSCLK is PWM-modulated. The M, C, Y, and Bk semiconductor lasers are driven according to the PWM-modulated video signal, and the photosensitive drums 301a to 301d are exposed according to the image signals.

At the same time, screen clocks MSCLK,
The phases of CSCLK, YSCLK and KSCLK are shifted for each main scanning line. In the standard copy mode in this embodiment, MSCLK is
As shown in FIG.
LK is shifted by three periods. Similarly, CSCLK is shifted by one cycle of the pixel clock CPCLK every main scanning line, and YSCLK is shifted by two cycles of the pixel clock YPCLK every main scanning line. KS
No phase shift is performed on CLK.

As described above, the image dot formation pattern of the output image in each color when pixel dot exposure is performed is shown in FIG.
Shown in Regarding M, main scanning 800 DPI, sub-scanning 4
As described above, by controlling the pixel dot exposure timing based on the reference recording frequency of 00 DPI, as shown in FIG.
An image of 08.4 DPI and 226.6 lines at 18.4 degrees is formed. Hereinafter, for C, main scanning 200 DPI, sub-scanning 4
00DPI, an image of 226.6 lines at 71.6 degrees is formed, and for Y, main scan 200 DPPI, sub-scan 400
DPI, an image of 282.8 lines at 45 degrees is formed, and for Bk, main scanning 200 DPI, sub-scanning 400 DPI,
An image with a 90-degree line is formed.

As described above, the setting of the screen angle of each color in the standard copy mode effectively suppresses the moiré pattern caused by the interference of the screen pattern of each color, and also sets M, M used in a general print image.
Moiré patterns due to interference between the screen angles of the C, Y, and Bk plates and the screen patterns of the M, C, Y, and Bk colors of the printer unit in the present embodiment are set to be effectively suppressed.

From the viewpoint of interference between the screen patterns of the respective colors, the screen angles of the respective colors M, C, Y, and Bk are 18.4 degrees, 71.6 degrees, 45 degrees, and 90 degrees, respectively, as described above.
In general, the angle difference between the colors is 15 degrees or more, in which moiré is generally inconspicuous in practical use.

Further, from the viewpoint of the interference of the screen pattern when the print image is the original image, the most common screen angle of each plate of the print image is M = 75.
Degrees, C is 15 degrees, Y is 90 degrees, and Bk 45 degrees. When the same color of the print image and the printer unit P is compared with each other, the difference in the angle between the screen patterns is M. 56.6 degrees, C is 56.6 degrees, Y
Is 45 degrees and Bk is 45 degrees, which is an angle of 30 degrees or more at which moire is most inconspicuous.

However, original images to be copied have various screen angles in addition to those having the above-mentioned general screen angles. In addition to the printed image, for example, an image output by a color inkjet printer or a color laser beam printer, a screen angle, a screen ruling, or a general screen different from the conventional printed image subjected to the digital half-toning process. It often occurs that an original image having a screen pattern different from the dot pattern is copied.

In such a case, with the combination of the screen angles of the respective colors in the above-described standard copy mode, the moire pattern due to interference with the original image is conspicuous, and the quality of the output image may be deteriorated to an unacceptable level. .

<Image Processing by Changing Screen Pattern> In this embodiment, in order to solve the above-mentioned problem, a function that can easily change the screen pattern and angle of each color without complicating the device configuration is adopted. This will be described below. FIG. 19 is a flowchart showing a process for changing the screen pattern.

The screen pattern of each color of the printer unit P can be changed from the operation panel 121 of the reader unit R in FIG. Specifically, a screen rotation mode switch is provided on the operation panel, and by operating the switch, three types of screen patterns can be selected separately from the standard copy mode. When the change of the copy mode is designated by the above switch (S1920),
One of the screen patterns is selected (S193)
0). The CP controlling the leader R by selection
Communication is performed between the U 120 and the CPU 118 of the printer unit P (S1940), and the CPU 118 determines the screen clocks MSCLK, CSCLK, YSCLK, and KSCL based on the information of the selected screen pattern.
The phase shift amount for each main scanning line of K is changed for each color (S1950).

In this embodiment, a total of four types of screen clocks SCL are obtained by shifting the phase of the screen clock SCLK for each color by three periods from the pixel clock PCL0.
K, one of the above four screen clocks is selected for each main scanning line, and the screen clocks MSCLK, CSCLK, YSCLK, and SCLK of each color are selected. The selection of the phase shift amount of the screen clock is controlled by a phase shift amount selection signal SFT from the CPU 118.

Based on the information on the selected screen pattern, the CPU 118 controls the phase shift amount selection signal F in accordance with a preset combination of the phase shift amounts.
By switching and controlling the SFT for each main scanning line (S1960), a desired screen pattern is formed (S1970).

Hereinafter, three screen patterns different from the standard copy mode will be described.

FIG. 10 shows a screen pattern of each second color different from the standard mode. In the second pattern, only M and C are changed, and specifically, the screen angles of M and C are interchanged. That is, M is 63.4.
And C are set to -63.4 degrees. This screen pattern works effectively when the screen angles of the M and C planes of the original image are changed from the general angles.

FIG. 11 shows a screen pattern of each of the third colors. In the third pattern, only Y and Bk are changed, and specifically, the screen angles of Y and Bk are changed. That is, Y is set to 90 degrees and Bk is set to 45 degrees. This screen pattern is effective when the original image is an image having no screen pattern, or is an image in which a black plate occupies a main part, in which Bk is set to the most stable 45 degrees, and the screen line By setting the number to be the highest, it is possible to output a higher quality image.

In the present embodiment, the third screen pattern is adopted as a standard printer mode when image data is input via the external interface F and an image is formed by the printer unit P. this is,
In the case of the printer mode, it is based on the fact that the original image information mainly has no screen pattern.

FIG. 12 shows a screen pattern of each of the fourth colors. The fourth pattern is to change the screen pattern of all colors, specifically, the screen angles of M and C are exchanged, and the screen angles of Y and Bk are exchanged. That is, M is 63.4 degrees and C is -63.4 degrees.
Degrees, Y is set to 90 degrees, and Bk is set to 45 degrees. This screen pattern is effective, for example, when the original image is an image formed in the standard copy mode of the present embodiment, and reduces the occurrence of a moiré pattern that is likely to occur when image processing is performed using the same screen pattern as the original image. It has the effect of suppressing.

As described above, in the present embodiment, the screen pattern of each color is appropriately set, and a plurality of these settings are provided, and the screen pattern of each color can be appropriately selected according to the original image. When the original image has a halftone dot structure such as a printed image or has a unique texture by digital halftoning processing such as another digital printer, the original image information And a moiré pattern generated by interference between the screen patterns of the respective colors of the printer unit P as described above can be effectively suppressed.

[Second Embodiment] In a second embodiment, another example of an electrophotographic copying machine and color printer will be described as a typical image processing apparatus to which the present invention can be suitably applied.

<Image Signal Processing Unit> FIG. 2 is a block diagram of the image signal processing unit I of the color copying machine of the present embodiment.

The image signal read by the color separation in the reader unit R is subjected to desired image processing, and then subjected to magenta, cyan, yellow, and black (hereinafter referred to as Y, M,
C, Bk) Image signals MRV, CR of 256 tones for each of four colors
V, YRV, KRV (hereinafter abbreviated as RV),
It is input to the image signal processing unit I. Similarly, the image signal RV input from the external interface F is also input to the image signal processing unit I. The input image signal RV is input to LUTs 205a to 205d independent of each color. LUT20
Reference numerals 5a to 5d are, for example, RAMs in which printer gradation characteristics such that desired input / output characteristics are obtained by the CPU 218 are written in advance. The image signals RV of respective colors output to the LUTs 205a to 205d are independent of each color. The gradation is corrected.
The tone-corrected image signal RV is applied to the dither processing unit 2 for each color.
02a-d, multi-valued dither processing is performed, and then input to the image memory 201.

The M and C image signals MRV and CRV output from the image memory 201 are stored in the FIFO memory 20.
6,207, Y and Bk image signals YRV, KRV
Are input to the LiFO memories 208 and 209, respectively. The main scanning synchronization signal RLSYNC * of the reader unit is Lo.
When w, the write address counter of the FiFo memory or LiFo memory is reset, and when the main scanning video enable signal RLVE * of the reader unit R is LOW,
The video signal of each color is synchronized with the pixel clock RCLK of the video signal of the reader unit R by the FIFO memory 206, 2
07 and LiFo memories 208 and 209, respectively.

Next, when the main scanning synchronizing signal PLSYNC * of each color of the printer unit P is Low, the read address counter of the Fifo memory and Lifo memory of the corresponding color is reset, and the video enable of each color of the printer unit is independent. When the signal PVE * is Low, each color-independent video signal PV is synchronized with the color-independent pixel clock PCLK corresponding to each color-independent video signal of the printer unit, and the color-independent video signal PV is stored in the corresponding FIFO memory 206, 207 or Li of the corresponding color.
It is read from the Fo memories 208 and 209. The video signal of each color read out as a normal image for M and C and a mirror image for Y and K is converted into an analog image signal of M, C, Y and Bk by a high-speed D / A converter independent of each color. Converted and color-independent pulse width modulation (PWM)
Each of them is PWMed and sent to a laser drive circuit independent of each color. In the laser drive circuit, four semiconductor lasers are driven in accordance with the M, C, Y, and Bk video signals sent from the respective color independent PWM devices, and laser light corresponding to each of the M, C, Y, and Bk images is generated. Generate.

The laser light generated by the image signal processing section I is applied to the polygon scanner 331 shown in FIG.
Scanning is performed on a photosensitive drum independent of each color of C, Y, and Bk. In addition, the laser light of each color to be scanned is supplied to a laser detecting unit 212 to 2 configured by a light receiving element such as a photodiode.
15 and is input to the synchronization control unit 210 as an independent laser detection signal for each color of M, C, Y, and Bk.
The synchronization control unit 210 converts the M, C, Y, and Bk independent main scanning synchronization signals PLSYNC * and the M, C, Y, and Bk independent pixel clocks PCLK based on the input BD signals of the respective colors. The main scanning video enable signal PVE * independent of M, C, Y, and Bk of the printer unit is generated based on the generated BD signal.

<Printer Unit P> The configuration of the printer unit P of the color electrophotographic copying machine and printer (hereinafter referred to as a color printer) of the present embodiment is the same as that of the color printer of the first embodiment shown in FIG. Further, since the image processing process in the printer unit P is the same as that in the first embodiment, detailed description will be omitted.

In this embodiment, eight polygon mirrors are used in the upper and lower stages, and the rotation frequency is 295.2 Hz.
And the process speed, which is the rotation speed of the photosensitive drum of each color or the transfer speed of the transfer material, is set to 100 mm / sec.
Is set to With the above setting, the sub-scanning density of the image of each color is 600 DPI.

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

The laser detectors 212 to 215 detect a laser beam at a period of 2362.2 Hz on each polygon mirror surface. Then, the laser detection signal BD for each color is input to the synchronization control unit 210.

As described above, the synchronization control section 210 generates a main scanning synchronization signal PLSYNC * independent of M, C, Y, and Bk of the printer section based on the input BD signal of each color and the pixel clock PCLK. Based on the above-described main scanning synchronization signal PLSYNC *, M, C, Y,
A main scan video enable signal PVE * independent of Bk is generated.

In this embodiment, the pixel clock PC
The frequency of LK is set to 28.34 MHz. In the configuration of the laser beam scanning optical system in the present embodiment, corresponding to the scanning frequency of the main scanning as described above,
By setting the frequency of PCLK to the above value, the scanning density of the main scanning is the same as the scanning density of the sub scanning, that is, 60%.
0 DPI is set.

Next, the dot exposure corresponding to the image signal will be described.

As described above, in the present embodiment,
The recording frequency and the scanning density of the sub-scan are set to 600 DPI. In the present embodiment, a pixel dot exposure pattern of each color is formed based on the above-described reference recording frequency and scanning density (hereinafter, reference recording frequency, reference scanning density). The image signal output from the dither processing unit for each reference pixel of the above-described main scanning and sub-scanning 600 DPI is PWM synchronized with PCLK to generate laser light independent for each color, and is exposed to the photosensitive drum.

FIG. 13 shows an image dot formation pattern of an output image in each color when pixel dot exposure is performed as described above. For M, a dither pattern image of 189.7 lines and 18.4 degrees is formed. Hereinafter, an image of 189.7 lines and 71.6 degrees is formed for C, an image of 212.1 lines and 45 degrees is formed for Y, and an image of 200 lines and 90 degrees is formed for Bk.

As described above, the setting of the screen angle of each color in the standard copy mode effectively suppresses the moire pattern due to the interference of the screen pattern of each color, and sets M, M used in a general print image.
Moiré patterns due to interference between the screen angles of the C, Y, and Bk plates and the screen patterns of the M, C, Y, and Bk colors of the printer unit in the present embodiment are set to be effectively suppressed.

Also in the present embodiment, as in the first embodiment, from the viewpoint of interference between the screen patterns of the respective colors, the screen angles of the respective colors M, C, Y, and Bk are 18.4 degrees and 71 degrees, respectively, as described above. The angles are set to 6, 45, and 90 degrees, and the angle difference between the colors is generally 15 degrees or more where moiré is practically inconspicuous.

Further, from the viewpoint of the interference of the screen pattern when the print image is the original image, the most common screen angle of each plate of the print image is M = 75.
Degrees, C is 15 degrees, Y is 90 degrees, and Bk 45 degrees. When the same color of the print image and the printer unit P is compared with each other, the difference in the angle between the screen patterns is M. 56.6 degrees, C is 56.6 degrees, Y
Is 45 degrees and Bk is 45 degrees, which is an angle of 30 degrees or more at which moire is most inconspicuous.

However, in this embodiment, as in the case of the first embodiment, the combination of the screen angles of the respective colors in the standard copy mode described above shows a noticeable moiré pattern due to interference with the original image and the output image. May be degraded to an unacceptable level.

<Image Processing by Changing the Teaser Processing Unit> Therefore, in the present embodiment, in order to solve the above-mentioned problems, the screen pattern and angle of each color are easily changed without complicating the device configuration. Has a function that can be. FIG. 20 is a flowchart for explaining the process. This will be described in detail below.

As shown in FIG. 2, the image processing apparatus according to the present embodiment has four dither processing units 202a to 202d, and each of the dither processing units 202a to 202d can be arbitrarily applied to each color. I have. That is, four-input / one-output selectors 203a to 203d and selectors 204a to 204d are provided before and after the dither processing units 202a to 202d, and the dither processing selection signals MDSFT, CDSFT, YDSFT, and KDSFT of each color from the CPU 218 are provided.
Selects a dither processing unit applied to each color. As a result, a desired dither pattern is formed for each color.

In addition to the standard copy mode, three types of dither patterns can be selected from the operation panel 221 of the reader unit R. When the switch is operated and the change of the copy mode is designated (S2020-Yes), one of the dither patterns is selected (S2030). Leader R
(Not shown) controlling the printer unit and the printer unit R
Is communicated with the CPU 118 (S2040). C
The PU 118 selects a dither processing unit to be applied to each color based on the information of the selected dither pattern, thereby forming a desired dither pattern for each color (S2050).

Hereinafter, three types of dither patterns different from the standard copy mode will be described.

FIG. 14 shows a dither pattern of each second color different from the standard mode. In the second pattern, only M and C are changed, and specifically, the screen angles of M and C are interchanged. That is, M is 71.6 degrees,
C is set at 18.4 degrees. This dither pattern works effectively when the screen angles of the M and C planes of the original image are changed from the general angles.

FIG. 15 shows a dither pattern of each of the third colors. The third pattern changes only Y and Bk,
Specifically, the screen angles of Y and Bk are interchanged. That is, Y is set to 90 degrees and Bk is set to 45 degrees. This dither pattern is effective when the original image is an image having no screen pattern, or is an image in which a black plate occupies a main part, and Bk is set to the most stable 45 degrees, and By setting the number to be the highest, it is possible to output a higher quality image. The image processing unit is controlled according to the changed pattern (S2060), and image processing is performed (S2070).

In the present embodiment, the third dither pattern is adopted as a standard printer mode when image data is input via the external interface F and image processing is performed by the printer unit P. This is based on the fact that the original image information mainly has no screen pattern in the printer mode.

FIG. 16 shows a dither pattern of each of the fourth colors. The fourth pattern is to change the dither pattern of all colors, specifically, the screen angles of M and C are exchanged and the screen angles of Y and Bk are exchanged. That is, M is 71.6 degrees, C is 18.4 degrees, and Y is 90
And Bk are set to 45 degrees. This dither pattern is effective, for example, when the original image is an image formed in the standard copy mode of the present embodiment, and reduces the occurrence of a moiré pattern that is likely to occur when image processing is performed using the same dither pattern as the original image. It has the effect of suppressing.

As described above, also in the present embodiment, the dither pattern of each color is appropriately set, and a plurality of these settings are provided so that the dither pattern can be appropriately selected according to the original image. While effectively suppressing the generation of moiré patterns due to interference between the original image and the original image when the original image has a halftone structure such as a printed image or has a unique texture by digital halftoning processing such as other digital printers It is also possible to effectively suppress a moiré pattern generated by interference between the information and the dither pattern of each color of the printer unit P as described above.

[Embodiment 3] The present invention is not limited to the above-described embodiment, and can be applied to an electrophotographic full-color copying machine of a one-drum surface sequential system as shown in FIG.
As in the first embodiment, also in the present embodiment, the screen pattern of each color is appropriately set, and a plurality of these settings are provided, and the screen pattern of each color can be appropriately selected according to the original image, so that the color pattern can be appropriately selected. Effectively suppresses the generation of moiré patterns due to the interference of the original image, and when the original image has a halftone structure by a printed image or the like, or has a unique texture by digital halftoning processing such as another digital printer. It is also possible to effectively suppress a moiré pattern generated by interference between the information and the screen pattern of each color of the printer unit P as described above.

[Embodiment 4] Further, the present invention is not limited to the above-described embodiment, but includes an ink jet system, a thermal transfer system,
The present invention is applicable without being limited to an image processing method such as an electrophotographic method using a linear exposure element such as an LED.

[0096]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

Examples of a storage medium for supplying the program code include a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, and CD.
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that the CPU included in the function expansion board 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 above-described flowcharts. Each module shown will be stored in a storage medium. That is, at least the “image forming module 2101”, “color separation / reading module 2102”, “screen pattern selection module 2103”, and “phase shift changing module 210”
4 "," Control module 2105 "," Tiza processing unit selection module 2106 "," Tiza pattern change module 2 "
107 "may be stored in the storage medium.

[0103]

According to the present invention, by controlling the image formation in the main scanning direction by changing the copy mode according to the input image, it is possible to suppress the occurrence of color unevenness and moiré patterns and to obtain various original image patterns. Regardless, high quality images can be obtained.

[0104]

[Brief description of the drawings]

FIG. 1 is an image signal processing unit I of a color copying machine according to a first embodiment.
It is a block diagram of.

FIG. 2 is an image signal processing unit I of a color copying machine according to a second embodiment.
It is a block diagram of.

FIG. 3 is an external view illustrating a configuration example of a printer unit of the color copying machine according to the first exemplary embodiment.

FIG. 4 is a diagram showing a timing chart of signals related to main scanning according to the first embodiment.

FIG. 5 is a diagram illustrating M in the laser control unit 111 according to the first embodiment.
FIG. 9 is a diagram showing (magenta) main scanning timing.

FIG. 6 shows C in the laser control unit 111 of the first embodiment.
FIG. 9 is a diagram showing (cyan) main scanning timing.

FIG. 7 shows Y in the laser controller 111 according to the first embodiment.
FIG. 9 is a diagram showing (yellow) main scanning timing.

FIG. 8 is a diagram illustrating a B in a laser controller 111 according to the first embodiment.
FIG. 6 is a diagram showing k (black) main scanning timing.

FIG. 9 is a diagram illustrating an image dot formation pattern of an output image in each color according to the first embodiment.

FIG. 10 is a view showing a screen pattern different from the standard copy mode of the first embodiment.

FIG. 11 is a diagram showing a screen pattern different from the standard copy mode of the first embodiment.

FIG. 12 is a diagram illustrating a screen pattern different from the standard copy mode according to the first embodiment.

FIG. 13 is a diagram illustrating the screen ruling, the screen angle, and the number of gradations for each color according to the second embodiment.

FIG. 14 is a diagram illustrating an image dot formation pattern of an output image in each color according to the second embodiment.

FIG. 15 is a diagram showing a screen pattern different from the standard copy mode of the second embodiment.

FIG. 16 is a diagram illustrating a screen pattern different from the standard copy mode according to the second embodiment.

FIG. 17 is a diagram showing a screen pattern different from the standard copy mode of the second embodiment.

FIG. 18 is a flowchart illustrating image formation in a standard copy mode.

FIG. 19 is a flowchart illustrating a change in a copy mode.

FIG. 20 is a flowchart illustrating a change in a copy mode.

FIG. 21 is a diagram showing a memory map of a recording medium.

[Explanation of symbols]

 101 Image Memory 110 Synchronization Control Unit 111 Laser Control Unit 118 CPU 120 CPU 121 Operation Panel 211 Laser Control Unit 301a Photosensitive Drum 309a Developing Unit 331 Polygon Mirror

Continued on front page F-term (reference) 2C262 AA02 AA03 AA05 AA16 AA24 AA26 AB01 AC19 BB06 BB25 BB27 BB45 EA02 2H030 AD11 AD17 5C077 LL03 MP08 NN04 NN09 NN17 NN19 PP33 PP38 PP39 PQ04 PQ05 TT04 P03 TT04 PQ05 TT03 LC14 MA02 MA04 NA02 PA02 PA03

Claims (23)

[Claims] 1. An image processing apparatus for an apparatus for forming an image by line-scanning a recording medium, comprising: input means for inputting a color image signal composed of a plurality of color component signals; Generating means for generating a pattern signal; pulse width modulating means for generating a signal by pulse width modulating the color component signal in accordance with the pattern signal; and shifting for shifting the phase of the pattern signal in line units. An image processing apparatus comprising: setting means for setting a phase amount; and phase shifting means for shifting the phase of the pattern signal in line units in accordance with an output of the setting means. 2. The image processing apparatus according to claim 1, wherein the phase shift amount differs for each of the color component signals. 3. An image according to claim 1, further comprising image forming means for forming a color image on a recording medium based on a pulse width modulation signal generated by said pulse width modulation means. Processing equipment. 4. The image forming means has a plurality of photoconductors, has an exposure means for exposing each of the photoconductors, and forms an electrostatic latent image on each of the photoconductors, and then develops the image. 4. The image processing apparatus according to claim 3, wherein a visible image of a plurality of colors is formed, and a color image is formed by transferring the image onto the recording medium directly or via an intermediate transfer member. 5. The image forming means has an exposure means for performing a plurality of exposures on a single photosensitive member, forms a plurality of electrostatic latent images, develops the latent images, and sequentially transfers the latent images directly to the recording medium. ,
4. The image processing apparatus according to claim 3, wherein a plurality of color images are formed by sequentially transferring the image to an intermediate transfer member and then transferring the image onto the recording medium. 6. The image forming means has an exposing means for performing a plurality of exposures on one photosensitive member, develops after forming a plurality of electrostatic latent images, and forms a plurality of color images on the photosensitive member. The image processing apparatus according to claim 3, wherein the image processing apparatus forms an image. 7. The system according to claim 1, wherein the color component signal is a signal represented by a plurality of bits for each pixel, and the pattern signal has a plurality of pixels of the color component signal as one cycle.
7. The image processing device according to any one of claims 1 to 6. 8. The image processing apparatus according to claim 1, wherein said plurality of color components are magenta, cyan, yellow, and black. 9. Dither processing means for inputting a color image signal represented by a plurality of color component signals, and dither processing means for dithering the color component signal, wherein the dither processing means includes a plurality of types of dither patterns. And an adaptively selecting a dither pattern for each of the color component signals from the plurality of types of dither patterns. 10. An image processing apparatus according to claim 9, wherein said plurality of types of dither patterns form different screen angles. 11. An image processing apparatus according to claim 10, wherein said dither processing means forms a different screen angle for each of said color component signals. 12. An image forming apparatus according to claim 9, further comprising image forming means for forming a color image on a recording medium based on the color component signal dithered by said dither processing means. Image processing device. 13. The image forming means has a plurality of photoconductors, and has an exposure means for exposing each of the photoconductors, and forms an electrostatic latent image on each of the photoconductors and then performs development. 14. The image processing apparatus according to claim 12, wherein a color image is formed by forming a plurality of visible images in a plurality of colors, and transferring the images onto the recording medium directly or by using an intermediate transfer medium as a medium. 14. The image forming means has an exposing means for performing a plurality of exposures on one photosensitive member, forms a plurality of electrostatic latent images, develops the latent images, and transfers the latent images directly to the recording medium. 13. The image processing apparatus according to claim 12, wherein a plurality of color images are formed by sequentially transferring the image to an intermediate transfer member and then transferring the image to the recording medium. 15. The image forming means has an exposing means for performing a plurality of exposures on one photosensitive member, forms a plurality of electrostatic latent images, develops the latent images, and forms a plurality of color images on the photosensitive member. The image processing apparatus according to claim 12, wherein an image is formed. 16. An image processing apparatus according to claim 9, wherein said plurality of color components are magenta, cyan, yellow, and black. 17. The image processing apparatus according to claim 9, further comprising a selection unit that selects a desired dither pattern from the plurality of types of dither patterns. 18. An image processing method for an apparatus for forming an image by scanning a line on a recording medium, comprising: an input step of inputting a color image signal composed of a plurality of color component signals; A step of generating a pattern signal; a step of generating a pulse width modulation signal for the color component signal in accordance with the pattern signal; and a phase shift amount for shifting the phase of the pattern signal in line units. And a phase shifting step of shifting the phase of the pattern signal on a line-by-line basis according to the setting result of the setting step. 19. A dither processing step for inputting a color image signal represented by a plurality of color component signals; and a dither processing step for dithering the color component signals, wherein the dither processing step includes a plurality of types of dither patterns. And an adaptively selecting a dither pattern for each of the color component signals from the plurality of types of dither patterns. 20. Input means for inputting a color image signal composed of a plurality of color component signals, and halftone processing means for performing halftone processing on the color component signals, wherein the halftone processing means has a plurality of types. An image processing apparatus comprising the following halftone processing method, and adaptively selecting a halftone processing method to be applied to each color component. 21. A system according to claim 2, further comprising a selection unit for manually selecting a halftone processing method applied to each color component from the plurality of types of halftone processing.
0. The image processing apparatus according to item 0. 22. An image processing apparatus according to claim 20, wherein said plurality of types of halftone processing methods form different screen angles. 23. An input step of inputting a color image signal composed of a plurality of color component signals; and a halftone processing step of performing halftone processing on the color component signals. An image processing method comprising the steps of: (a) selecting a halftone processing method to be applied to each color component;