JPH1013698A - Color image forming device and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To considerably simplify the scale of device, to apply the device to almost all cases such as black character drawing and color gradation image and to form satisfactory images by performing recording setting with which the resolution of black with high probability to be used for the character line drawing is relatively improved. SOLUTION: Y, M, C and Bk component signals are converted into pulse width modulation(PWM) signals and in the case of recording through an electrophotographic system, concerning the YMC components, the PWM signals are generated by using the triangular wave of long wavelength but concerning the Bk component, the PWM signal is generated by using the triangular wave of short wavelength. Based on these generated PWM signals, the visible images of respective color components are recorded on one recording medium while being superimposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color image forming apparatus and a control method thereof.

[0002]

2. Description of the Related Art In general, it is desired to form an image with clear and detailed details of a character / line drawing portion due to its nature.
In addition, it is desired that the gradation of the color gradation image is maintained.

For the above reasons, when copying a document in which a character line image and a color gradation image are mixed, the respective images are separated, and the recording resolution for the character line drawing portion is set higher than that of the gradation image to output. A technology to do this has already been proposed.

[0004]

However, if the recording resolution of the character / line image portion is increased, the highlight portion becomes rough, and the time required for formation is increased.
In addition, there is a problem that the cost of the apparatus increases.

Further, an error may occur in the determination of image area separation (separation between a character / line image portion and a color gradation image portion), resulting in a problem that an unintended image is formed.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and the apparatus scale is relatively high by setting a relatively high resolution of black, which is likely to be used for a character and a line drawing. Which aims to provide a color image forming apparatus which can be applied to almost all cases of black character line drawing and color gradation image and can form a good image, and a control method thereof. It is.

To solve this problem, for example, a color image forming apparatus of the present invention has the following configuration. That is, a color image forming apparatus that forms and outputs a color image on a predetermined recording medium, wherein a first resolution conversion unit that generates an image signal of a first resolution for a black component in image data to be recorded is provided. A second resolution converting means for generating an image signal of a second resolution for components other than the black component in the image data to be recorded;
Recording means for recording an image based on the image signal converted by the conversion means.

[0008]

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

FIG. 1 is a schematic view showing a configuration example of an image recording apparatus according to an embodiment of the present invention. As shown, the embodiment shows a case where the present invention is applied to a color copying machine. The color copying machine mainly includes an image reading unit (reader unit) 1100 and a printer unit 1109. Each component will be described below together with its operation.

The original 1101 is placed with its reading surface facing the platen glass 1103, and the original
2 fixed. Thereafter, the optical unit 1104 turns on the internal lamp 1105 and moves while moving at a speed V in the direction of the arrow shown in the figure from the right end position in the figure.

The reflected light from the original 1101 is transmitted to the optical unit 11
After being reflected by a mirror and a mirror unit 1105 (moving in a direction indicated by an arrow at a speed of V / 2) provided in the camera unit 04, an image formed by a sensor unit 1107 via a lens 1106 is detected. Sensors 1107R, G, and B for each color component are provided in the sensor unit 1107, where each luminance color component is converted into an electric signal. The RGB signals obtained by the sensor unit 1107 are taken into the image processing unit 1108 of the present apparatus, where the processing described later is performed to generate recording color components of Y, M, C, and BK, and based on the respective color components. The visible image is superimposed and formed by the printer unit 1109.

The printer unit 1109 includes an image processing unit 11
The signal of the recording color component from 08 is supplied as a video signal to the laser driver 1110 shown in synchronization with the carrier clock. The laser driver 1110 drives the semiconductor laser element 1111 according to the input video signal.
The laser light generated as a result is
One side is irradiated, and as a result, the laser beam is oscillated in the horizontal direction. Laser light, which is reflected light from the rotating polygon mirror 1112, passes through a lens 1113 having f · θ characteristics, is further reflected by a mirror 1114, and is irradiated on a photosensitive drum 1115. Since the laser light is oscillated by the rotating polygon mirror 1112 and passes through the f · θ lens 113, the photosensitive drum 1115 is scanned and exposed.

One of the developing units 1116C, M, Y, and Bk in the rotatable developing unit 1116 contacts the photosensitive drum 1115. The developing unit in contact with the image processing unit 110
8 is the same as the original color component of the video signal output to the laser driver 1110 at that time. As a result, the photosensitive drum 1
The electrostatic latent image formed at 115 is visualized by the developing device in contact at that time, and the toner image is transferred onto the recording paper wound around the transfer drum 1119. In addition,
In the case of the drawing, it is indicated that the magenta component is being developed.

The recording paper is transported into the apparatus from either the paper feed cassette 1117 or 1118, and is wound around the transfer drum 1119 by the action of static electricity.

In this way, by sequentially performing the above-described processing for the four-color components, the four-color component toner is transferred onto the recording paper wound around the transfer drum 1119. When the transfer process of the four color components is completed, the transfer drum 1
The recording paper wound around 119 is peeled off by a peeling claw (not shown), and then conveyed toward the fixing device 1120.
The toner is fixed and finally discharged out of the apparatus.

The toner used in the apparatus of this embodiment is formed by dispersing colorants of each color using a styrene polymer resin as a binder.

FIG. 2 is a block diagram mainly showing the image processing unit 1108.

In FIG. 1, a CPU 214 has a ROM 2
In accordance with a program stored in advance in, for example, the control unit 16 controls the entire embodiment including the following components. RAM 21
5 is used as a work area by the CPU 214,
The ROM 216 stores image processing parameters and the like in addition to the control program.

The operation unit 217 has a display 218 such as a keyboard, a touch panel, and an LCD. The operation unit 217 transmits instructions from an operator to the CPU 214, and displays operating conditions and states of the apparatus by the CPU 214.

Further, the address counter 212 generates a clock CL for each pixel generated by the clock generator 211.
K is counted, and a main scanning address signal representing a pixel address of one line is output. The decoder 213 decodes the main scanning address signal output from the address counter 212, and outputs a signal 219 for driving the CCD sensor 1105 on a line-by-line basis, such as a shift pulse or a reset pulse.
A signal VE indicating an effective area in a signal for one line output from the CD sensor 1105, a line synchronization signal HSYNC
Generate etc. Note that the address counter 212 is cleared by the signal HSYNC and starts counting the main scanning addresses of the next line.

An image signal output from the CCD sensor 1105 is input to an analog signal processing unit 201 to adjust gain and offset, and then, for example, an 8-bit RGB digital image for each color component in an A / D conversion unit 202. The signal is converted into a signal, and the shading correction unit 203 performs a known shading correction using a signal obtained by reading the reference white plate 1121 (see FIG. 1) for each color.

The line delay unit 204 corrects a spatial shift included in the image signal output from the shading correction unit 203. This spatial displacement is caused by the line sensors of the CCD sensor 105 being arranged at a predetermined distance from each other in the sub-scanning direction. Specifically, based on the B color component signal, the R and G color component signals are line-delayed in the sub-scanning direction, and the phases of the three color component signals are synchronized.

The correction unit 1108 performs luminance correction on the image signal output from the line delay unit 204, as will be described in detail later.

The input masking section 205 includes a correcting section 110
The color space of the image signal output from 8 is converted into the NTSC standard color space by the matrix operation of Expression (1).
In other words, the color space of each color component signal output from the CCD sensor 105 is determined by the spectral characteristics of the filter of each color component, and is converted into the NTSC standard color space.

[0025]

(Equation 1)

The LOG conversion unit 206 is constituted by a look-up table composed of, for example, a ROM, and converts the RGB luminance signal output from the input masking unit 205 into a CMY density signal.

The delay memory 207 delays the CMY density signal output from the LOG converter 206 in order to synchronize with the results of various processes (not shown).

A masking / UCR unit 208 extracts a black component signal K from the image signal output from the line delay memory 207, and further performs a matrix operation for correcting the color turbidity of the recording color material of the printer unit 1109 by a YMCK image. A signal is applied to each of the reading operations of the reader unit 1100 so that M,
For example, an 8-bit color component image signal is output in the order of C, Y, and K. The matrix coefficients used for the matrix calculation are set by the CPU 214.

The gamma correction unit 209 performs density correction on the image signal output from the masking / UCR unit 208 in order to match the image signal with the ideal gradation characteristics of the printer unit 1109. Output filter (spatial filter processing unit) 2
10 performs edge enhancement or smoothing processing on the image signal output from the gamma correction unit 209 according to a control signal from the CPU 214.

The look-up table (LUT) 25 is
This is for matching the density of the original image with the density of the output image, and is configured by, for example, a RAM or the like, and the conversion table is set by the CPU 214. The pattern generator 29 generates an appropriate pattern during test printing. Pulse width modulator (PW
M) 26 outputs a pulse signal having a pulse width corresponding to the level of the input image signal, and the pulse signal is a laser driver 1110 for driving a laser light source 1107.
Is entered.

The gradation processing by the pulse width conversion processing in the embodiment will be described below.

FIG. 4 is a circuit diagram of the pulse width modulator (PWM) 26 in the embodiment.

The image signal (8-bit signal of any of Y, M, C, and Bk) from the look-up table 25 is supplied to the D / A converter in synchronization with the illustrated image clock.
Here, the image signal is converted into an analog signal having a voltage corresponding to the value indicated by the image signal. This analog signal is supplied to one input terminal of each of the comparators 404 and 405.

The other input terminal of the comparator 404 is supplied with a triangular wave from the triangular wave generator 402 (synchronized with the image clock) shown in FIG.
The other input terminal is supplied with a triangular wave from the triangular wave generator 403.

The point to be noted here is that the triangular wave generator 40
No. 3 is to generate a triangular wave having the same frequency as the image clock, while generating a triangular wave having a frequency (half the wavelength twice) of the image clock in the triangular wave generator 402.

As a result, the comparators 404 and 405
Generates a signal having a pulse width according to each triangular wave, as shown in FIG.

The pulse width modulated signals obtained by the comparators 404 and 405 have a width corresponding to the value indicated by the input digital image data. One of the signals is selected by the switch 406, and the 40
After being amplified to an appropriate level in step 7, the signal is supplied to the laser driver.

In this embodiment, the switch 40
Switching of 6 is controlled by the CPU 214.

That is, original reading (image reading at 400 dpi) is performed four times, and Y, M,
When the image formation of each color component of C and Bk is performed in this order, the first three times of Y, M, and C are compared by the comparator 4.
An image is formed by employing the pulse width modulation signal from the step S04. Then, at the time of recording the last Bk component, an image is formed using the pulse width signal from the comparator 405.

As a result, the black component, in other words, the character or line drawing portion of most originals is 400 dp.
i, the edge portion thereof can be recorded smoothly, and the Y, M, and C components are recorded by one recording pixel for a digital image of substantially two pixels. Is formed, an image to be formed does not touch, and an image with excellent gradation is formed.

In particular, according to the above configuration, although the resulting resolution is twice that of the black component than that of the other Y, M, and C components, a special circuit configuration (for example, the rotation of a rotating polygon mirror) is used. Since the speed, the rotation speed of the photosensitive drum, the video signal output clock to the semiconductor laser driver, and the like can be recorded without any change, the configuration of the apparatus can be greatly simplified.

However, in the above configuration, although the sub-scanning direction of the original is 400 dpi regardless of the color component, a good color image can be output by performing the above processing.
However, a circuit configuration for recording the Y, M, and C components at 200 dpi also in the sub-scanning direction may be added.

According to the present embodiment as described above,
From the current situation that black is often used as a character line drawing, by making only the recording resolution of the black component relatively higher than the recording resolution of the color component, the character line drawing becomes clearer,
It is possible to form a good image with no looseness in the color portion.

<Second Embodiment> In the above-described embodiment, the resolution of black is increased relative to that of Y, M, and C.
With this alone, there is a possibility that ruggedness occurs in the black highlight. Therefore, in the second embodiment, UC
An example in which the roughness of a black highlight portion is reduced by changing R (inking or undercolor removal) will be described.

The UCR is, for example, a value obtained when the RGB signal input from the reader is log-converted to MCY, where M = 10.
0, C = 150, Y = 200, min
(Y, M, C) = 100 multiplied by a certain ratio r, black B
k and removing the black component from each color component. In the case of the above numerical value, for example, if r = 0.5, M = 100−100 * 0.5 = 50 C = 150−100 * 0.5 = 100 Y = 200−100 * 0.5 = 150 Bk = 100 * 0.5 = 50.

In a normal UCR, as shown in FIG. 5, the inking amount r is constant regardless of the density. Where MC
When both Y have a value of 50, the highlight 25 level is output in black, and the roughness is conspicuous.

Therefore, if the amount of black ink is set to almost zero in highlights as shown in FIG. 6 and suddenly increases in the middle, highlights are not output in black. It is possible to suppress the roughness of the light.

To realize this, a look-up table having a conversion curve as shown in FIG. 6 is prepared, and min (Y,
M, C). Thus, the inking amount r is output, and the above calculation is performed to correct M, C, Y, and Bk.

As described above, according to the second embodiment, roughness in highlight can be further eliminated.

Third Embodiment In the first and second embodiments, an example has been described in which four color components are developed using one photosensitive drum, but recording is performed using independent photosensitive drums. You may do it.

FIG. 7 is a sectional structural view of a color copying machine according to the third embodiment.

In the drawing, reference numerals 701 to 704 denote photosensitive drums, which are developing units 705 for Y, M, C, and Bk color components.
To 708 are in contact with the respective photosensitive drums. 70
Reference numerals 9, 710, and 720 (720 is exclusively for black) are rotary polygon mirrors. In the present embodiment, one rotary polygon mirror is irradiated with laser light corresponding to two color components from different directions to rotate. There are three polygon mirrors. 711 is a fixing device, and 712 is a paper feed cassette.

As in the first embodiment, the Bk component image formation may be recorded at a higher resolution than the YMC component image formation by appropriately switching triangular waves having different frequencies, as in the first embodiment. In the embodiment, the Bk component is positively recorded with an increased resolution. That is, assuming that the resolution of document scanning (not shown) is 400 dpi, YM
C is 400 dpi, and Bd component is 600 dpi.
Record with i.

Since the resolution becomes 1.5 times,
It is necessary to multiply the read image data by 1.5 times both vertically and horizontally. In other words, it is necessary to input two pixels and output three pixels in both the horizontal and vertical directions. This is not different from the image scaling process at all, and the scaling process itself employs known means, and a description thereof will be omitted. For example, 2
When one pixel is input, 1
Pixels (data of two average values and density gradient predicted values) are added and output as a total of three pixels. The feature of the third embodiment is that the scaling process is performed only on the Bk component of the generated YMCBk.

Inevitably, during the recording operation of the Bk component, which is the last process, the photosensitive drum 704 must be rotated at the same speed as the other drums. This is because there is a possibility that the recording paper is in contact with a plurality of photosensitive drums, and if the speeds are different, the recording paper is subjected to bending or pulling force. Therefore, when recording the Bk component,
It is necessary to change the rotation speed of the rotary polygon mirror 710 and the pixel clock based on the image signal of the Bk component to an appropriate state.

As described above, according to the third embodiment,
For color natural images, the highlights are output at 400 dpi with little roughness, and the character part is output at 600 dpi with a high resolution that can express details, so that high quality images that are compatible with natural images and characters can be obtained. Become.

<Fourth Embodiment> In the third embodiment, black (Bk) is also output in multiple values. In the fourth embodiment, the result of binarizing the resolution of black to 600 dpi is output. I do. The device configuration is the same as in FIG. In the present embodiment, the copy image is divided into black characters and a color natural image portion, the natural image portion is expressed by 256 gradations of 400 dpi of three colors (MCY), and the black character portion is formed by binary of 600 dpi. .

By performing the above, a natural image is output at 400 dpi with little highlighting, and the character portion is output at 600 dpi with a high resolution capable of expressing details. Is obtained.

<Fifth Embodiment> In the first to fourth embodiments, examples have been described in which the present invention is applied to a copying machine. However, the present invention is not limited to this.

As a fifth embodiment, an example applied to a color laser beam printer will be described.

The structure of the printing portion (print engine portion) of the color laser beam printer may be any of FIG. 1 and FIG. 7, but will be described with reference to FIG. However, the reader unit 1100 is required if it also functions as a copier, but if it is applied to a printer connected to a host computer purely, the reader unit 1100 is required.
100 is unnecessary.

FIG. 8 is a block diagram of a color laser beam printer according to the fifth embodiment.

In the figure, reference numeral 81 denotes a CPU that controls the entire apparatus, and reference numeral 82 denotes a ROM that stores operation processing procedures of the CPU 81 and various font data. Reference numeral 83 denotes a RAM used as a work area of the CPU 81, and a reception buffer for storing data received from the host computer is secured. An operation panel 84 is provided with switches for giving various instructions and an LCD for displaying messages. Reference numeral 85 denotes an interface for exchanging data with the host computer.
Reference numeral 6Bk denotes an image memory for storing bitmap data of each recording color component. Reference numeral 87 denotes an engine interface for performing pulse width modulation on data output from the image memory and outputting it as a video signal to the printer engine.

The printer engine 87 in the present embodiment
Has a recording resolution of 300 dpi and 600 dpi,
These resolution changes are performed by changing the rotation speed of the rotary polygon mirror 1112 and the synchronization clock for transferring the video signal of the engine interface 87 as a video signal.

In the above configuration, an example will be described in which the print data from the host computer is, for example, a page description language. Also, various conversion processes such as UCR process are performed by C
It is assumed that the PU 81 performs the operation by software.

In this embodiment, the YMC component is recorded at 300 dpi, and the Bk component is recorded at 600 dpi for both the main scanning and sub-scanning. Therefore, Bk
The image memory 86Bk for the component has a capacity four times the capacity of the other color components.

For the sake of simplicity, it is assumed that the host computer behaves as if a printer having a resolution of 300 dpi is connected.

Therefore, in processing for various commands in the received print data, normal pattern development is performed for the YMC component, and pattern development is performed for the Bk component by changing information specified by the command. That is, for the Bk component, for example, if the character size indicated by the print data is 12 points, it is twice as large as 2 points.
This is corrected to four points, and a pattern having a dot size twice as large in height and width is generated. If the drawing command of the straight line is represented by the coordinates of the starting point and its length and direction, the coordinates of the starting point and its length are doubled and drawn (the direction does not change). Of course, if the straight line is represented by the start point coordinates and the end point coordinates, both of them will be corrected. That is, by changing the resolution, all the affected parameters are corrected.

When bit map data (not limited to one bit per pixel) is received from the host computer, the Bk component in the bit map is subjected to interpolation processing and developed in the image memory 86Bk.

The CP of the fifth embodiment having the above configuration
The operation processing procedure of U81 will be described with reference to the flowchart of FIG. The print data receiving process is a process of reading out data latched in the interface 85 and storing the data in a receiving buffer in the RAM 83 by an interrupt signal generated when data is supplied to the interface 85. And the description is omitted. Here, the main processing of the printing processing will be described.

First, data is read from the reception buffer in step S1, and the data is analyzed in step S2.
In this analysis process, at least the designated color of the designated character or line drawing is analyzed, and it is determined which combination of the designated colors can be realized by YMCBk.

When the process proceeds to step S3, it is determined whether or not it is necessary to perform drawing for the Y component. Here, if it is determined that drawing for the Y component is necessary, the process proceeds to step S7, where the bit map is developed in the image memory 86Y.

In the following, in the judgment processing of steps S4 to S6, it is judged whether or not it is necessary to draw the components of M, C and Bk. If it is judged that the drawing is necessary, steps S8 to S11 are executed. Bitmap development in the image memory to be performed

Here, the point of interest is when it is determined that drawing of the Bk component is necessary. In this case, for the print command under analysis or its data, information correction accompanying the resolution conversion is performed in step S10, and bitmap development is performed in step S11 according to the corrected information.

As described above, when print data is sequentially read, bitmap development is performed. In step S12, however, it is determined that bitmap development for one page has been performed, that is, a page break command has been read. In this case, the process proceeds to step S13, where Y, M, C, Bk
The images are recorded in the order of.

As described above, for YMC, 3
Since 00 dpi and Bk components are 600 dpi, the image stored in the image memory 86Bk can be changed to another color by changing the rotating polygon mirror or the image clock during image formation by issuing laser light of the Bk component. It will be recorded with the same size as the components.

Originally, if color components such as Y, M, C, etc. are in harmony with each other, such as gradation expression, humans will not feel uncomfortable, and it is sufficient to have an appropriate resolution. However, the sharpness of black Bk, which is diversified in character line drawings, is required. According to the above configuration, all of these problems can be solved. In addition, by allocating a large amount of memory only for necessary components, instead of allocating a large amount of memory for all color components, it is possible to reduce the cost of the entire apparatus, and to human vision, It becomes possible to give substantially the same feeling as increasing the resolution of the color components.

In the above embodiments, the number of gradations in each color component including the black component has been described as being the same. However, the number of gradations of black may be smaller than that of other colors. As a result, for example, it is possible to greatly reduce the memory capacity in the case where the process of temporarily storing the document image in the image memory is performed.

In the above embodiment, an example using a laser beam printer has been described. However, the present invention may be applied to any recording method within the scope of the present invention.

Further, means for realizing the functions of the above-described embodiment and known means may be appropriately switched.

[0081]

As described above, according to the present invention, the recording scale is set to relatively increase the resolution of black, which has a high probability of being used for character and line drawing, thereby greatly simplifying the apparatus scale. It can be applied to almost all cases of a black character line drawing and a color gradation image, and a good image can be formed.

[0082]

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a color copying machine according to a first embodiment.

FIG. 2 is a diagram showing a block configuration diagram of an image processing unit 1108 in FIG.

FIG. 3 is a diagram showing a waveform of pulse width modulation in the first embodiment.

FIG. 4 is a circuit diagram of pulse width modulation in the first embodiment.

FIG. 5 is a diagram showing a normal inking amount.

FIG. 6 is a diagram illustrating a change in an inking amount according to the second embodiment.

FIG. 7 is a sectional structural view of an apparatus according to a third embodiment.

FIG. 8 is a block diagram of an apparatus according to a fifth embodiment.

FIG. 9 is a flowchart illustrating a processing procedure according to a fifth embodiment.

Claims (12)

[Claims] 1. A color image forming apparatus for forming and outputting a color image on a predetermined recording medium, wherein a black component of image data to be recorded generates a first resolution image signal at a first resolution. Conversion means; second resolution conversion means for generating a second resolution image signal for components other than black components in the image data to be recorded; image signals converted by the first and second conversion means Recording means for recording an image based on the image data. 2. The image processing apparatus according to claim 1, wherein the recording unit is an electrophotographic image recording unit, and the first resolution conversion unit is configured to generate a pulse width modulation signal corresponding to a value of black component image data. 2. The color image forming apparatus according to claim 1, wherein the frequency of the pattern signal used as the signal is higher than the frequency of the pattern signal used in the second resolution conversion means. And a UCR process for performing a UCR process based on the image data of the read document and generating the black component image data when generating the black component image data. 2. The color image forming apparatus according to claim 1, further comprising control means for controlling according to the previous minimum value of the YMC component. 4. When the minimum value of the YMC component is small, the control means reduces the ratio data for black image generation,
4. The color image forming apparatus according to claim 3, wherein the ratio data is increased when the minimum value of the MC component is large. 5. The color image forming apparatus according to claim 4, wherein the ratio data changes sharply at a predetermined value. 6. The color image forming apparatus according to claim 1, wherein the number of gradations of the black component is smaller than that of the other color components. 7. A control method in a color image forming apparatus for forming and outputting a color image on a predetermined recording medium, wherein a black component in image data to be recorded generates a first resolution image signal. A first resolution conversion step, a second resolution conversion step of generating a second resolution image signal for components other than black components in the image data to be recorded, and a first and second conversion steps. And a recording step of recording an image based on the image signal. 8. The recording process according to claim 1, wherein the recording is an electrophotographic image recording process, and the first resolution conversion process is performed when a pulse width modulation signal corresponding to a value of black component image data is generated. The method according to claim 7, wherein the frequency of the pattern signal used as the signal is higher than the frequency of the pattern signal used in the second resolution conversion step. 9. A document reading step for reading an image from a predetermined image reading device, and a UCR process based on the image data of the read document to generate a black image when generating black component image data. And controlling the ratio data according to the minimum value of the YMC component before the UCR process. 8. The control method of the color image forming apparatus according to claim 7, further comprising: 10. The control step, when the minimum value of the YMC component is small, reduces the ratio data for black image generation,
10. The control method according to claim 9, wherein the ratio data is increased when the minimum value of the YMC component is large. 11. The control method for a color image forming apparatus according to claim 10, wherein the ratio data changes abruptly at a predetermined value. 12. The method according to claim 7, wherein the number of gradations of the black component is smaller than that of the other color components.
13. The method for controlling a color image forming apparatus according to item 13.