JPH11112808A - Image processor, image processing method, computer readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a color deviation at the time of reproducing an original image by executing gradation correction to at least one of plural components, which is different from that for another component. SOLUTION: Plural dot strings arraying in a sub-scanning direction are divided into A, B, A, B,... in a main scanning direction. When a pixel is the odd-number row, one concerning the two pixels of A-string and B-string which are adjacent in the sub-scanning direction, A-string pixel is gradation-corrected through the use of a characteristic curved line for the A-string of a lookup table(LUT). Then, the pixel of the B-string is gradation-corrected through the use of the characteristic curved line for the B-string of the LUT. In the case of the pixel of an even-number row, the pixel of the A-string is gradation- corrected through the use of the characteristic curved line for the B-string of the LUT. Then, the pixel of the B-string is gradation-corrected through the use of the characteristic curved line for the A-string of the LUT. Thus, gradation correction is executed to at least one component within the plural ones, which is different from that of another component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an image processing apparatus, an image processing method, and a computer-readable storage medium for performing gradation correction according to an input image.

[0002]

2. Description of the Related Art Generally, in an image processing apparatus for reproducing an original image based on a digital image signal, when an image forming process is performed at a high resolution, since the reproduction of individual pixels is unstable, a bright image is reproduced. There is a problem in that the (highlight) portion has noticeable roughness (roughness of the screen). In particular, in an electrophotographic digital copying machine, which is a typical image processing apparatus, when the slope of the γ characteristic curve in the γ correction unit becomes large, discharge unevenness or the like is caused by contamination of the charging surface of a charger for charging the photosensitive drum. It is easily affected, and the reproducibility of the halftone image is significantly reduced. Therefore, two adjacent
There has been proposed a method of reducing the roughness of a highlight of a reproduced image by mutually correcting the gradation of pixels.

[0003]

However, in the above conventional example, when two adjacent pixels are modulated as one set, as shown in FIGS. 17 (a) and (b), the displacement in the sub-scanning direction for each color. As a result, an image in which color unevenness is conspicuous may be reproduced (note that, in the figure, a circle is represented as a black dot, and a triangle is represented as a magenta dot). This is due to uneven rotation of the photosensitive drum.

Accordingly, an object of the present invention is to provide an image processing apparatus, an image processing method, and a computer-readable storage medium for reducing a color shift when an original image is reproduced.

[0005]

To achieve the above object, an image processing apparatus according to the present invention has the following configuration.

That is, an image processing apparatus comprising a correction means for performing gradation correction on a color image signal comprising a plurality of input components, wherein the correction means is arranged adjacent to an image represented by the image signal in a main scanning direction. When performing gradation correction on odd-numbered column pixels and even-numbered column pixels in accordance with different correction characteristic information, at least one of the plurality of components is subjected to gradation correction different from other components. Features.

Further, different gradation correction is performed on odd-numbered row pixels and even-numbered row pixels adjacent to each other in the main scanning direction of an image represented by M, C, Y, and K plane-sequentially input image signals. And a plurality of correction means for performing
The gradation correction of the C and Y image signals and the gradation correction of the K image signal are performed by different correction units among the plurality of correction units.

An image processing apparatus having a correction means for performing gradation correction on an input image signal, the correction means comprising: an odd column pixel adjacent to an image represented by the image signal in a main scanning direction; When performing gradation correction on the even-numbered column pixels according to different correction characteristic information, the correction unit performs gradation correction on a color component signal other than a black component signal of the image signal. I do.

Further, in order to achieve the above object, an image processing method according to the present invention has the following configuration.

That is, an image processing method for performing gradation correction on a color image signal composed of a plurality of input components, wherein an odd-numbered column pixel and an even-numbered column pixel adjacent to each other in a main scanning direction of an image represented by the image signal When performing tone correction in accordance with different correction characteristic information for at least one of the plurality of components, at least one component is subjected to tone correction different from the other components.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic color digital copying machine as a typical image processing apparatus will be described in detail with reference to the drawings.

[First Embodiment] First, an outline of the present embodiment will be described. In a color digital copying machine as an image processing apparatus, M (magenta) is used to reduce color misregistration when an original image is reproduced. , C (cyan), Y (yellow), and K (black) image signals are subjected to gradation correction according to different characteristics.

<Digital Copier> First, the overall configuration and image forming operation of the digital copier will be described with reference to FIGS.

FIG. 1 is a sectional view showing a schematic configuration of a digital copying machine as a first embodiment of the present invention.

FIG. 2 is a block diagram of an image forming process in the digital copying machine according to the first embodiment of the present invention.

The digital copying machine shown in FIG. 1 includes a reader unit for reading an original image, and a printer unit for reproducing the original image on recording paper based on an image signal of the original image read by the reader unit. The operations of the reader unit and the printer unit described below are controlled by controllers 100 and 200, respectively. Note that the controller 200 is the CPU 2
14, and controls according to a program stored in the ROM 213 in advance. Also, the controller 100
Also includes a CPU (not shown), and it goes without saying that control is performed according to a program stored in the ROM in advance.

When a copy start key (not shown) is pressed in the reader unit, the controller 100 starts exposure scanning of the original 30 placed on the original platen glass 31 by the exposure lamp 32. The reflected light image from the original 30 obtained by the exposure scanning is collected on the full-color sensor 34.

The full-color sensor 34 has R (red),
Line sensors of three colors G (green) and B (blue) are arranged at a predetermined distance from each other in the sub-scanning direction, and a plurality of light receiving elements are arranged in a line in each line sensor. The full-color sensor 34 detects the incident original 3
The reflected light image from 0 is separated into a plurality of pixels by a plurality of photoelectric conversion elements, and a photoelectric conversion signal (color-separated image signal) is generated according to the density of each pixel.

In FIG. 2, the image signal output from the full-color sensor 34 is adjusted in gain and offset by an analog signal processing unit 201, and the A / D converter 20
In step 2, each color component is converted into an RGB digital signal of, for example, 8 bits (0 to 255 levels: 256 tones).

The RGB digital signal input to the shading correction unit 203 is optimized in gain corresponding to each light receiving element in order to eliminate the variation in sensitivity of the light receiving elements arranged in a line in the full color sensor 34. General shading correction is performed.

The line delay unit 204 corrects a spatial shift contained in the image signal output from the shading correction unit 203. This spatial shift is caused by the line sensors of the full-color sensor 34 being arranged at a predetermined distance from each other in the sub-scanning direction. Specifically, based on the B (blue) color component signal, the R (red) and G (green) color component signals are line-delayed in the sub-scanning direction to synchronize the phases of the three types of color component signals. .

The input masking unit 205 converts the color space of the image signal output from the line delay unit 204 into, for example, an NTSC-RGB standard color space by the matrix operation of the formula 1. That is, the color space of each color component signal output from the full-color sensor 34 is determined by the spectral characteristics of the filter of each color component.
The conversion into the B standard color space.

[0023]

(Equation 1)

The input interface 250 receives color image data from an external device (not shown) such as a computer as necessary.

The LOG conversion unit 206 is constituted by, for example, a look-up table (LUT) composed of a ROM or the like (not shown), and the RGB output from the input masking unit 205.
The luminance signal is converted into a CMY density signal.

The line delay memory 207 includes a LOG conversion unit 206 for a period (line delay period) during which a black character determination unit (not shown) generates a control signal UCR, FILTER, SEN, or the like based on the output of the input masking unit 205. The image signal output from is delayed.

It should be noted that the control signal UCR is based on masking UC
A control signal for controlling the R unit 208. The control signal FILTER is a control signal used by the output filter 210 to perform edge enhancement. Also, the control signal SE
N is a control signal used to increase the resolution when a black character determination unit (not shown) determines a black character.

The masking / UCR unit 208 extracts a black component signal K from the image signal output from the line delay memory 207. Further, in order to correct the color turbidity of the recording color material in the printer unit, a matrix operation is performed on the MCYK image signal, and M, C,
For example, an 8-bit plane-sequential color component image signal is output in the order of Y and K. The matrix coefficients used for the matrix calculation are set by a CPU (not shown) in the controller 100.

The gamma correction unit 209 controls the masking and U to adjust the image signal to the ideal gradation characteristics of the printer unit.
The density correction is performed on the image signal output from the CR unit 208. The output filter (spatial filter processing unit) 210 performs edge enhancement or smoothing processing on the image signal output from the γ correction unit 209 according to a control signal from a CPU (not shown) in the controller 100.

The LUT 211 includes an LUT (not shown) for matching the density of the original image with the density of the output image;
It has LUTs shown in FIG. 4 described later, and the data of these tables is stored in advance in, for example, the ROM 213 or the like.

A pulse width modulator (PWM) 212 outputs a pulse signal having a pulse width corresponding to the level of the input image signal, and the pulse signal drives a laser light source (not shown) 41 (the laser shown in FIG. 1). Input to driver 3).

In FIG. 1, a laser beam E emitted from a semiconductor laser in a laser driver 3 is rotated by a polygon mirror 3a.
Lens 3b such as an f / θ lens and a fixed mirror 3 for directing the laser beam E toward the photosensitive drum 1.
The spot image is formed on the photosensitive drum 1 by c. The laser beam E scans the photosensitive drum 1 in a direction substantially parallel to the rotation axis of the photosensitive drum 1 (main scanning direction), and repeatedly scans the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 (sub-scanning direction).
To form an electrostatic latent image.

In the printer section, the photosensitive drum 1 has amorphous silicon, selenium, OPC, etc. on its surface.
It is supported rotatably in the direction of the arrow in FIG. Around the photosensitive drum 1, a pre-exposure lamp 11, a corona charger 2,
Laser exposure optical system 3, surface potential sensor 12, four developing units 4y, 4c, 4m, 4bk of different colors, photosensitive drum 1
The upper light amount detecting means 13, the transfer device 5, and the cleaning device 6 are arranged.

In the printer section, the controller 200
Prior to image formation, the photosensitive drum 1 is rotated in the direction of the arrow in FIG. 1 and is uniformly discharged by the pre-exposure lamp 11, and then uniformly charged by the primary charger 2. Thereafter, the photosensitive drum 1 is exposed and scanned by the laser light E modulated according to the above-described image information signal, so that an electrostatic latent image having an area gradation characteristic is formed according to the image information signal. 1 is formed.

The developing units 4y, 4c, 4m, and 4bk develop the electrostatic latent image on the photosensitive drum 1 using yellow, magenta, cyan, and black color toners as recording materials, respectively. Specifically, the controller 200 converts the electrostatic latent image formed on the photosensitive drum 1 into a predetermined developing device 4
A negatively-charged visible image (toner image) using a resin as a substrate is formed on the photosensitive drum 1 by performing reversal development using a two-component developer composed of a toner and a carrier according to y, 4c, 4m, and 4bk. These toners are formed by using a styrene copolymer resin as a binder and dispersing recording materials of each color. Each developing device is provided with an eccentric cam 24y, 2
By the operation of 4c, 24m, and 24bk, a structure is provided in which the photosensitive drum 1 is selectively approached in accordance with each separated color. Here, the reversal development is a development method in which a toner charged to the same polarity as the latent image is attached to a region of the photoconductor exposed to light, and the toner is visualized.

In the present embodiment, the transfer device 5 includes a transfer drum 5a, a transfer brush charger 5b as transfer means, a suction roller 5g opposed to a suction brush charger 5c for electrostatically adsorbing recording paper, and an inner charger. 5d, outer charger 5e,
And a transfer peeling sensor 5h. In addition, in the peripheral opening area of the transfer drum 5a which is rotatably supported,
A recording paper holding sheet 5f made of a dielectric material such as polycarbonate is integrally stretched in a cylindrical shape.

The controller 200 controls the recording paper cassette 7
The transfer system and the transfer device 5 transfer the recording paper in the
And is supplied to a position facing the photosensitive drum 1 via the recording medium holding sheet 5f by electrostatic force. Then, the toner image formed on the photosensitive drum 1 is transferred to the transfer drum 5a.
Is transferred onto the recording paper on the recording paper holding sheet 5f according to the rotation of.

When the transfer of the toner image of the original image onto the recording paper is completed, the controller 200 separates the recording paper from the transfer drum 5a by operating the separation claw 8a, the separation push-up roller 8b, and the separation charger 5h. After the toner image is fixed on the recording paper by the roller fixing device 9, the toner image is discharged onto the tray 10.

After transferring the toner image, the controller 200 cleans the residual toner on the surface of the photosensitive drum 1 with the cleaning device 6 including the cleaning blade 6a and the squeeze sheet, and prepares for the next image forming process. Further, in order to prevent scattering of powder on the recording paper holding sheet 5f of the transfer drum 5a, adhesion of oil on the recording paper, etc., the fur brush 14 and the fur brush 14 are interposed via the recording paper holding sheet 5f. Cleaning is performed using the backup brush 15 facing the cleaning brush. Such cleaning is performed before or after image formation, and is performed as needed when a jam (paper jam) occurs.

<Tone Correction Processing> In the present embodiment, two methods described below are used to perform a gradation correction processing on a set of two pixels adjacent in the sub-scanning direction.

(Method 1) FIG. 3 is a view for explaining the concept of gradation correction processing 1 as the first embodiment of the present invention. FIG. 4 is a diagram illustrating characteristics of a look-up table used for a gradation correction process according to the first embodiment of the present invention.

In the printer section of the image processing apparatus used, the latent image and the development are unstable in the range of 0 to 40 levels out of the 255 output levels of the input image signal. Assume that when reproduced, the roughness of the image is conspicuous. In such a case, when the original image is reproduced by the printer unit, it is desirable to avoid using signal levels of 0 to 40 levels as much as possible. Therefore, tone correction is performed on each pixel represented by the input image signal based on the concept described below.

That is, as shown in FIG. 3, a plurality of dot rows arranged in the sub-scanning direction are divided into A, B, A,
B,. . . And divide. Next, the pixels in the odd-numbered column (hereinafter, column A) and the pixels in the even-numbered column (hereinafter, column B) are used as shown in FIG.
Tone correction is performed using different characteristic curves of the UT.
When such gradation correction is performed, for example, when the level of the input image signal is 30 for two adjacent pixels adjacent in the sub-scanning direction, the image signal output from the LUT 211 is The pixel outputs 55-level image signals, and the B-column pixels output 5-level image signals.
As a result, two adjacent pixels (pixels in column A and pixels in column B) adjacent to each other in the sub-scanning direction are subjected to gradation correction as a set. Hereinafter, the gradation correction by this method is referred to as “method 1” for convenience of explanation.

FIG. 13 is a flowchart showing gradation correction processing 1 according to the first embodiment of the present invention. Software for implementing this processing is stored in the ROM 213 in advance, and the CPU 214 performs the processing according to the software. In the figure, in step S1, it is determined whether the pixel (multi-valued color image data) input to the LUT 211 this time is a pixel in column A (step S1).
Tone correction is performed using the characteristic curve for column A of T (step S2). On the other hand, in the case of NO, since the pixel belongs to column B, LU
Tone correction is performed using the characteristic curve for the B column of T (step S3).

In the actual correction process for each pixel, the distribution of the LUT to the characteristic curve for column A or the characteristic curve for column B may be performed using the pixel clock VCLK.

FIG. 5 is a diagram showing an example of a reproduced image of a dot after gradation correction according to the first embodiment of the present invention. This figure shows that when performing gradation correction using the LUT shown in FIG.
This is a reproduced image of a dot when the input image signal increases in the sub-scanning direction from low density to high density. FIG. 6 is a diagram illustrating an example of a reproduced image of dots in a low-density region after gradation correction according to the first embodiment of the present invention, and is a diagram in which the low-density region in FIG. 5 is extracted.

As can be seen from FIGS. 5 and 6, the density is 200.times.400 dpi in the low density range and 400.times.400 dpi in the higher density range. Therefore, when the above-described gradation correction is performed, the dots in row A become a stable image and the dots in row B are unstable, but the density fluctuation is also reduced since the density is lower than row A. That is, a stable reproduced image can be obtained as a whole.

However, when tone correction is performed on all the dots using the above method, the dots in the A and B columns are changed according to the magnitude of the input image signal as shown in FIG. Will be reproduced. That is, in the low density range (upper part in FIG. 5) of the input image signal, the sub-scanning direction is 400 dp.
i, but the main scanning direction is 200 dpi. Therefore, when the image to be reproduced is a character or the like and is an image signal in a low density region (for example, a thin character), a gap in the main scanning direction is formed as shown in FIG. Will be dropped. FIG. 8 shows a method for preventing such a problem.

(Method 2) FIG. 8 is a view for explaining the concept of the tone correction processing 2 according to the first embodiment of the present invention. In this case, first, as in the above-described case, a plurality of dot rows arranged in the sub-scanning direction are divided into A and A in the main scanning direction.
B, A, B,. . . And divide.

Next, regarding two pixels in column A and column B adjacent in the sub-scanning direction, (1) In the case of a pixel in an odd-numbered row, the pixel in column A is
The gradation correction is performed using the characteristic curve for column A in FIG.
Then, gradation correction is performed on the pixels in column B using the characteristic curve for column B in the LUT (FIG. 4). (2) In the case of pixels in even-numbered rows, the pixels in column A are
Tone correction is performed using the characteristic curve for column B in FIG.
Then, the gradation correction is performed on the pixels in column B using the characteristic curve for column A in the LUT (FIG. 4). Hereinafter, the gradation correction by this method is referred to as “method 2” for convenience of description.

FIG. 14 is a flowchart showing the tone correction processing 2 according to the first embodiment of the present invention. Software for implementing this processing is stored in the ROM 213 in advance, and the CPU 214 performs the processing according to the software. In the figure, in step S11, the LUT 211
It is determined whether the pixel (multi-valued color image data) input this time is an odd-numbered row of pixels. If the pixel is in an odd-numbered row, it is determined whether the pixel is in the column A (step S12).
Tone correction is performed using the characteristic curve for the column A of the UT (step S14), whereas, in the case of NO, gradation correction is performed using the characteristic curve for the column B of the LUT because the pixel is in the column B (step S15). . If NO in step S11,
The pixel inputted this time is a pixel in an even-numbered row, and step S
It is determined in step 13 whether the pixel belongs to column A, and if YES, the process proceeds to step S15 to perform gradation correction. On the other hand, in the case of NO, the process proceeds to step S14 to perform gradation correction.

In the actual correction process for each pixel, distribution to the characteristic curve for column A or the characteristic curve for column B of the LUT according to whether the row is an odd row or an even row is as follows.
The pixel clock VCLK may be used.

By performing such gradation correction, a resolution equivalent to 283 dpi is obtained at an oblique angle of 45 degrees, the maximum distance between dots is about ／ of 200 × 400 dpi, and light-colored characters (low density areas) The gap between characters (characters reproduced by image signals) is dramatically improved, and thin characters can be reproduced with high quality.

<Correction of Color Misalignment> Next, a method of correcting color misregistration in the sub-scanning direction will be described. When an image is reproduced by the printer unit of the image processing apparatus described with reference to FIGS. 1 and 2, due to uneven rotation of the photosensitive drum, etc., as shown in FIG. The center position of the dot is shifted in the sub-scanning direction by, for example, about 70 μm at the maximum.

The applicant of the present application has evaluated how much color difference occurs depending on the color when the center position of the dot is shifted as described above. The result is shown in FIG.

FIG. 9 is a diagram showing an example of the relationship between the shift amount of the dot center position and the color difference. FIG. 9 shows a case where two colors of a certain color in MCYK and another color are mixed. And MC
In the case of a mixed color of two colors of a certain color in Y and black (K), how much the difference between the center positions of the two-color dots compared to the case where the center positions overlap each other is This indicates whether there is a color difference (Lab).

As can be seen from the drawing, compared to the case of mixing a certain color and another color, in the case of a mixed color of a certain color and black, if a shift occurs between the two color dots, the color difference Becomes larger. From this, in the case of a mixed color of a certain color and black, it is sufficient to reproduce the dots of these two colors so that color unevenness does not occur even if a positional shift occurs, that is, so that the color difference becomes small. You can see that.

Therefore, in the present embodiment, when the dots of each color of M, C, and Y are reproduced, the gradation is corrected by "method 2" (FIG. 8), and the dots of K (black) are reproduced. Is subjected to gradation correction by "method 1" (FIG. 6).

FIG. 15 is a flowchart showing a color shift correction process according to the first embodiment of the present invention. Software for implementing this processing is stored in the ROM 213 in advance, and the CPU 214 performs the processing according to the software. In the figure, in step S21, it is determined whether or not the data inputted this time is black (K) pixel data for multi-valued color image data inputted to the LUT 211 in MCYK plane-sequentially. If the pixel is a black pixel, the “gradation correction process 1” described with reference to FIG. 13 is performed (step S22). On the other hand, if the pixel is not a black pixel in step S21, it means that the pixel is one of the MCY color pixels, so that the “gradation correction process 2” described with reference to FIG.
3). In step S24, it is determined whether or not there is data to be input next to LUT 211. If YES, the process returns to step S21.

FIG. 10 shows the result of evaluating the deviation of the center position of the dot and the color difference when such processing is performed.

FIG. 10 is a diagram showing the relationship between the shift amount of the center position of the dot and the color difference when performing the gradation correction processing as the first embodiment of the present invention. By performing such gradation correction, the K (black) dots are connected in the sub-scanning direction (hereinafter, line-shaped), and even if the center of the dot is shifted relative to the color dot. Color unevenness can be made inconspicuous. The gradation correction according to the present embodiment is particularly effective for reproducing an image such as a natural image.

By performing the above-described gradation correction, it is possible to reduce the color shift between a certain color dot and a black (K) dot and obtain a good color image.

[Second Embodiment] In the above-described first embodiment, the black dots are arranged in a line to prevent color unevenness, but in the present embodiment, the M, C, and Y colors are eliminated. The color dots are aligned and the black dots are staggered to prevent color shift.

That is, when reproducing K (black) dots, tone correction is performed by "method 1" (FIG. 6).
To reproduce dots of each color of C and Y, "Method 2"
(FIG. 8). Therefore, in the case of the present embodiment, in step S22 of FIG.
Is performed, and in step S23, “gradation correction processing 1” is performed.

FIG. 11 shows the result of evaluating the deviation of the dot center position and the color difference in this case.

FIG. 11 is a diagram showing the relationship between the shift amount of the center position of the dot and the color difference when performing the tone correction processing as the second embodiment of the present invention. As can be seen from the figure, there is an effect that the color shift due to the shift of the center position between the color dot and the black dot can be reduced, and in particular, the quality of the image reproduction of a thin black character can be improved.

[Third Embodiment] In the first embodiment,
The black dots are arranged in parallel lines to prevent color unevenness. However, in the present embodiment, the LUT is used for the black dots.
Only the LUT for making the density of the original image in 211 and the density of the output image coincide is performed, and the LUT in FIG.
Is bypassed.

That is, when dots of each color of M, C, and Y are reproduced, gradation correction is performed by "method 2" (FIG. 8). When reproducing black dots, 40
Output as it is at 0 dpi. Therefore, in the case of the present embodiment, step S23 in FIG. 15 does not exist.

FIG. 12 shows the results of evaluating the deviation of the dot center position and the color difference in this case.

FIG. 12 is a diagram showing the relationship between the shift amount of the center position of the dot and the color difference when performing the gradation correction processing according to the third embodiment of the present invention.

According to the verification by the applicant of the present invention, when gradation correction is performed for all colors of MCYK as shown in FIG. 8, the center value of the dot is shifted by one pixel at the maximum (approximately 63.5 microns). However, in this embodiment, by outputting black dots at 400 dpi, there is a possibility that the MCY color dots are shifted by one pixel at the maximum, but in the case of a mixed color of the color dots and the black dots, It was found that the displacement was a maximum of about 31.8 microns, and the color difference could be reduced by half.
Accordingly, it is possible to reduce the color shift between the color dots and the black (K) dots, and to improve the quality of the image reproduction of the black characters,
A good color image can be obtained.

<Modification of Each Embodiment> FIG. 16 is a diagram illustrating a gradation correction process as a modification of each embodiment of the present invention. As shown in the drawing, when a latent image of a reproduced image is formed on the photosensitive drum 1, dots extending in the sub-scanning direction are formed by making the spot diameter of the laser beam into an elliptical shape long in the sub-scanning direction. Thereby, the color shift in the sub-scanning direction can be further reduced.

In each of the above-described embodiments, the present invention is applied to an electrophotographic color digital copying machine. However, the present invention is not limited to this. It is needless to say that the present invention can be applied to the case of reproducing.

[0074]

[Other Embodiments] Even if the present invention is applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), as in this embodiment, one device is used. (For example, a copying machine, a facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium storing program codes 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 implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, magnetic tape, non-volatile memory card, ROM, etc. 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. ) And the like perform part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in 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 a CPU or the like provided in the function expansion board or the function expansion unit performs a part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0080]

As described above, according to the present invention,
It is possible to provide an image processing apparatus, an image processing method, and a computer-readable storage medium that reduce a color shift when an original image is reproduced.

[0081]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of a digital copying machine as a first embodiment of the present invention.

FIG. 2 is a block diagram of an image forming process in the digital copying machine according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the concept of gradation correction processing 1 according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating characteristics of a look-up table used in a gradation correction process according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of a reproduced image of a dot after gradation correction according to the first embodiment of the present invention.

6 is a diagram illustrating an example of a reproduced image of dots in a low-density region after gradation correction according to the first embodiment of the present invention, and is a diagram in which the low-density region in FIG. 5 is extracted.

FIG. 7 is a diagram illustrating an example of a reproduced image obtained by a gradation correction process 1 according to the first embodiment of the present invention.

FIG. 8 is a view for explaining the concept of gradation correction processing 2 as the first embodiment of the present invention.

FIG. 9 is a diagram illustrating an example of a relationship between a shift amount of a center position of a dot and a color difference.

FIG. 10 is a diagram illustrating a relationship between a shift amount of a dot center position and a color difference when a gradation correction process is performed as the first embodiment of the present invention.

FIG. 11 is a diagram illustrating a relationship between a shift amount of a center position of a dot and a color difference when a gradation correction process is performed as a second embodiment of the present invention.

FIG. 12 is a diagram illustrating a relationship between a shift amount of a center position of a dot and a color difference when a gradation correction process is performed as a third embodiment of the present invention.

FIG. 13 is a flowchart illustrating a tone correction process 1 according to the first embodiment of the present invention.

FIG. 14 is a flowchart illustrating a tone correction process 2 according to the first embodiment of the present invention.

FIG. 15 is a flowchart illustrating a color misregistration correction process according to the first embodiment of the present invention.

FIG. 16 is a diagram illustrating a gradation correction process as a modified example of each embodiment of the present invention.

FIG. 17 is a diagram illustrating a general color shift that occurs when an original image is reproduced.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (17)

[Claims] 1. An image processing apparatus comprising: a correction unit that performs gradation correction on a color image signal including a plurality of input components, wherein the correction unit is adjacent to an image represented by the image signal in a main scanning direction. When performing gradation correction on odd-numbered column pixels and even-numbered column pixels in accordance with different correction characteristic information, at least one of the plurality of components is subjected to gradation correction different from other components. Characteristic image processing device. 2. When the correction means corrects the density values of the odd-numbered column pixels and the even-numbered column pixels in accordance with two different types of correction characteristic information, the correction unit converts the black component signal of the plurality of components into the two types of black component signals. 2. The image processing apparatus according to claim 1, wherein the correction is performed according to any one of the correction characteristic information, and the component signal other than the black component is corrected according to the other correction characteristic information. 3. The correction means stores correction characteristic information used for correction in one of the two types of correction characteristic information according to whether a pixel to be corrected is an odd-row pixel or an even-row pixel. 3. The image processing apparatus according to claim 2, further comprising changing means for changing the image data alternately. 4. The method according to claim 2, wherein the gradation correction of the black component signal is performed.
4. An image processing apparatus, wherein the correction means according to claim 3 performs the gradation correction of a color component signal other than the black component using the correction means according to claim 3. 5. A method according to claim 2, wherein gradation correction of a color component signal other than said black component is performed by said correction means, and gradation correction of said black component signal is performed by said correction means. Characteristic image processing device. 6. An image processing apparatus comprising a correction means for performing gradation correction on an input image signal, the correction means comprising: an odd column pixel adjacent to an image represented by the image signal in a main scanning direction; When performing gradation correction on the even-numbered column pixels according to different correction characteristic information, the correction unit performs gradation correction on a color component signal other than a black component signal of the image signal. Image processing device. 7. An image display apparatus according to claim 1, wherein each of odd-numbered row pixels and even-numbered row pixels adjacent to each other in the main scanning direction of the image represented by the M, C, Y, and K plane-sequentially input image signals has different tone corrections. And a plurality of correction means for applying M, C, Y
An image processing apparatus, wherein the gradation correction of the image signal and the gradation correction of the K image signal are performed by different correction units among the plurality of correction units. 8. An image display apparatus according to claim 1, wherein the odd-numbered row pixels and the even-numbered row pixels adjacent to each other in the main scanning direction of the image represented by the M, C, Y, and K plane-sequentially input image signals have different tone corrections. An image processing apparatus comprising: a correction unit that performs gradation correction of the M, C, and Y image signals. 9. The image according to claim 1, wherein the correction unit increases the density value of one pixel and decreases the density value of the other pixel. Processing equipment. 10. The method according to claim 1, wherein the plurality of correction units store a sum of density values of the adjacent odd-numbered column pixels and even-numbered column pixels and distribute the sum to the pixels. The image processing device according to claim 8. 11. The image processing apparatus according to claim 1, wherein the image processing apparatus is an electrophotographic color printer and includes an irradiating unit that irradiates a laser beam onto the photoconductor so as to form a latent image of a reproduced image on the photoconductor. The image processing apparatus according to any one of claims 1 to 10, wherein a spot diameter of the laser beam irradiated by the irradiation unit has an elliptical shape long in a sub-scanning direction. 12. An image processing method for performing tone correction on a color image signal composed of a plurality of input components, comprising: an odd column pixel and an even column pixel adjacent to each other in a main scanning direction of an image represented by the image signal. An image processing method, wherein when performing tone correction in accordance with different correction characteristic information for at least one of the plurality of components, at least one component is subjected to tone correction different from the other components. 13. When correcting the density values of the odd-numbered column pixels and the even-numbered column pixels in accordance with two different types of correction characteristic information, a black component signal of the plurality of components is corrected by using the two types of correction characteristic information. 13. The image processing method according to claim 12, wherein the correction is performed according to any one of the correction characteristic information, and the component signal other than the black component is corrected according to the other correction characteristic information. 14. A method according to claim 1, wherein the correction characteristic used for the correction is alternately changed to one of the two types of correction characteristics according to whether the pixel to be corrected is an odd-row pixel or an even-row pixel. 14. The image processing method according to claim 13, wherein: 15. The correction according to claim 13 when performing the tone correction of the black component signal, and the correction according to claim 14 when performing the tone correction of a color component signal other than the black component. Performing an image processing. 16. The correction according to claim 13 when performing tone correction of a color component signal other than the black component, and performing the correction according to claim 14 when performing tone correction of the black component signal. Performing an image processing. 17. A computer-readable storage medium storing an image processing program for performing tone correction on an input color image signal composed of a plurality of components, the program comprising a main program of an image represented by the image signal. When gradation correction is performed on odd-numbered row pixels and even-numbered row pixels adjacent to each other in the scanning direction according to different correction characteristic information, at least one of the plurality of components has a different gradation correction from the other components. A storage medium having a function of performing the following.