JP2695533B2 - Color image forming apparatus and color correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus and a color correction method in the color image forming apparatus. More specifically, the present invention relates to a color image forming apparatus such as a digital color copying machine having a feature of a masking method for toner color correction and a color correcting method in the color image forming apparatus.

[0002]

2. Description of the Related Art In a conventionally known digital color copying machine, first, a color scanner guides reflected light from an original image to a sensor having RGB spectral characteristics shown in FIG. 6 to form RGB data (R: Red, G:
Green, B: blue).

The above-mentioned RGB data is YMC data which is in a complementary color relationship when it is output to the printer section of a copying machine, for example.
(Y: yellow, M: magenta, C: cyan). The amount (main density) of the Y, M, and C toners to be placed on the photoconductor is determined according to the amount of reflected energy indicated by the YMC data.

The main densities of Y, M, and C, which are complementary colors of R, G, and B, are obtained from the following equations (1) to (3). [Y] = 1- [B] (1) [M] = 1- [G] (2) [C] = 1- [R] (3) where [R]: Original image R reflectance [G]: Original image G reflectance [B]: Original image B reflectance [Y]: Y toner main density [M]: M toner main density [C] : C is the main density of the toner.

By the way, each toner has an actual spectral characteristic shown in FIG. However, the establishment of the above equations (1) to (3) is premised on that the toner of M has the ideal spectral characteristic (M1) shown in FIG. That is, in reality, the toner of M shows the spectral characteristic (M2) of FIG. 8, so that a black image is formed when output according to the equations (1) to (3). Therefore, toner color correction is necessary.

In a digital color image forming apparatus,
Toner color correction is performed using Y using masking processing, for example.
This is performed by a method using a color correction table for each MC color. This is a method in which each YMC data is substituted into a masking equation and YMC correction data that is uniquely determined when YMC data is determined is provided as a table.

[0007]

However, according to this method, since the YMC analog data is processed as 256 gradation data obtained by dividing the YMC analog data into 256, when YMC is used as full data of 256 gradations, a table is created. It requires a large memory capacity of 16 Mbytes per color.

That is, if a large capacity memory is used, the cost of the device is increased, the circuit configuration is complicated, and the processing speed is lowered. On the other hand, if the number of gradations is reduced and a memory with a small capacity is used, the reproducibility of the image will deteriorate.

Therefore, it is an object of the present invention to provide a color image forming apparatus and a color correcting method in the color image forming apparatus capable of performing color correction of toner using a memory having a small capacity.

[0010]

In order to achieve the above object, in the color correction method in the color image forming apparatus of the present invention, the input image data of the input image data is weighted according to the weight of each coefficient of the reflection densities of the three primary colors forming the masking equation. The feature is that the corrected color image data is calculated by allocating the number of gradations and solving the masking equation.

The corrected color image data may be stored as a color correction table at an address corresponding to the number of gradations of the semiconductor memory element.

Further, the color image forming apparatus of the present invention is corrected by allocating the gradation number of the input image data according to the weight of each coefficient of the reflection densities of the three primary colors forming the masking equation and solving the masking equation. A semiconductor memory device that stores color image data at an address corresponding to the number of gradations; a means for creating an address signal corresponding to the number of gradations from the input main color image data and sub color image data, Means for reading and outputting color image data from the semiconductor memory element in response to the address signal.

Further, the color correction method in the color image forming apparatus of the present invention solves the masking equation by allocating the gradation number of the input image data according to the weight of each coefficient of the reflection densities of the three primary colors forming the masking equation. In the color correction method in the color image forming apparatus for calculating the color image data corrected by, the lower bit of the sub color image data, which is the color image data corresponding to a coefficient other than the coefficient having the largest weight among the coefficients To reduce the number of gradations, and when the most significant bit of the deleted lower bits of the sub color image data is 1, the data value of the upper bit of the sub color image data is set to 1 It is characterized by increasing only.

Further, the color image forming apparatus of the present invention is corrected by allocating the gradation number of the input image data according to the weight of each coefficient of the reflection densities of the three primary colors forming the masking equation and solving the masking equation. Means for calculating color image data, and means for erasing lower bits of sub color image data which is color image data corresponding to coefficients other than the coefficient having the highest weight among the coefficients for reducing the number of gradations And a circuit for increasing the data value of the upper bit of the sub color image data by 1 when the most significant bit of the deleted lower bits of the sub color image data is 1. I am trying.

[0015]

According to such a configuration, the color image data corrected by solving the masking equation by allocating the gradation number of the input image data according to the weight of each coefficient of the reflection densities of the three primary colors forming the masking equation is obtained. Since the calculation is performed, the color image data per color can be reduced without significantly affecting the image reproducibility.

By storing the corrected color image data as a color correction table at an address corresponding to the number of gradations of the semiconductor memory element, it is possible to prevent the circuit configuration from becoming complicated due to the arithmetic processing.

Further, in order to reduce the number of gradations, lower bits of the sub color image data are deleted, and when the most significant bit of the lower bits is 1, the upper bit of the sub color image data is high. When the bit data value is increased by 1, the deviation of the calculation processing result when the sub color image data has the same gradation number as the main color image data is reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the digital color electronic copying machine shown in FIG. In FIG. 1, an image of a document 3 placed so as to be pressed by a document retainer 2 on a contact glass 1 is scanned by a scanning optical system 4, and its image information uses a light as a medium to form a condensing lens 5.
Is guided to a light receiving element 6 such as a CCD, where it is converted into an electric signal, and then subjected to signal processing in an image processing section 7, and thereafter, a laser scanner unit (LSU) 8 causes a latent image on the photosensitive drum 9. Depicted as a statue. Prior to this, the surface of the photosensitive drum 9 is a main charger (charging part) 1
It is charged by 0.

FIG. 2 mainly shows the main parts of the image processing section 7 and the laser scanner unit 8 and shows their relationship. In the image processing unit 7, the color image data YD, MD, CD input by the data correction circuit 41 are corrected, and the color image data is corrected by the pulse generation circuit 11 based on the color image data value corrected by the data. A pulse having a width corresponding to the value of is output, and this pulse activates the semiconductor laser 13 of the laser scanner unit 8 via the drive circuit 12 to emit a laser beam 16. The laser beam 16 scans the surface of the photosensitive drum 9 by the polygon mirror 15 rotated by the motor 14, and writes a latent image on the surface of the photosensitive drum 9.

When forming a full-color image, the laser beam 16 is first used based on the yellow color image data YD.
To form a latent image on the photosensitive drum 9 and
Development is performed by the developing device 17Y. The Y developing device 17Y has yellow toner and develops the latent image on the photosensitive drum 9 with this yellow toner. Then, the image developed on the photosensitive drum 9 with the yellow toner is transferred onto the paper wound around the surface of the transfer drum 19. This paper is supplied from the paper feed cassette 20 or 21 through the paper feed path.

This sheet remains mounted on the surface of the transfer drum even after the yellow image is transferred, and is used for transferring the image of the next color. The photoconductor drum 9 is the cleaning unit 2
After the residual toner is wiped off by 2 and discharged by a discharging unit (not shown), the main charger 10 charges it again. Then, this time, the magenta color image data M
Laser beam 16 for writing latent image based on D
The latent image corresponding to the magenta image formed on the photoconductor drum is formed by the M developing device 17M. At this time, the M developing device 17M is brought to a position facing the photoconductor drum 9 instead of the Y developing device 17Y.

In this embodiment, the developing device is a Y developing device 17Y for developing yellow and an M developing device 1 for developing magenta.
A C developing device 17C for developing 7M and cyan, and a BK developing device 17BK for developing black are sequentially mounted in the vertical direction on a moving body 18 which moves in the vertical direction as shown in the figure, and a latent image formed by the laser beam 16 is formed. It is selectively brought to the developing position (position facing the photoconductor drum 9) corresponding to the written color image data.

Now, the image on the photosensitive drum 9 developed with magenta toner is transferred onto the paper on the surface of the transfer drum 19 (the paper on which the yellow image has been previously transferred and formed). By repeating the same operation, the cyan and black images are further transferred onto the paper to form a full-color image. After that, the paper on which the full-color image is formed is separated from the transfer drum 19, sent to the fixing unit 24 by the conveying unit 23, fixed by the fixing unit 24, and then discharged from the electronic copying machine.

The data correction circuit shown in FIG.
7, 58, 59. The correction circuit 57 is a Y correction circuit whose main color image data is yellow.
Reference numeral 59 denotes an M correction circuit and a C correction circuit which have magenta and cyan as main color image data, respectively. Correction circuit 57,
Since the insides of 58 and 59 have the same configuration, only the Y correction circuit 57 among them will be described in detail here with reference to FIG.

In FIG. 4, 101 to 104 and 107
Reference numerals 110 to 110, 115 to 117, and 119 are all latch circuits formed by ICs and are used for synchronizing data. The yellow color image data YD input from the input terminal 100 is latch circuits 101, 102.
Through the first ROM 105 and the second ROM 106. Meanwhile, through the input terminals 120 and 121, M of FIG.
The 8-bit magenta and cyan color image data MD and CD supplied from the correction circuit 58 and the C correction circuit 59 are passed through the increment determination circuits 128 and 129 to the selector 11 respectively.
1 and the selector 111 converts one into 5 bits and the other into 4 bits so that the first and second ROMs 105, 10
6 is input.

In the increment determination circuit 128, the value represented by the upper 5 bits of the magenta color image data MD of 8 bits is corrected by the value of the lower most significant bit (that is, the 6th bit). There is. Specifically, if the 6th bit is 1, carry is carried out, and if it is 0, carry is not carried out. In the same way,
In the increment determination circuit 129, the lower most significant bit (the fifth bit in this case) of the value represented by the upper 5 bits of the cyan color image data CD of 8 bits is used.
If the digit of 1 is 1, carry is carried out, and if it is 0, carry is not carried out. MD that has been treated in this way
Upper 5 bits of CD and upper 4 bits of CD are supplied from the selector 111 to the first and second ROMs 105 and 106, respectively. The image data output from the selector 111 after being subjected to such a carry-over process may be given to the first and second ROMs 105 and 106 as 8-bit data. The increment determination circuits 128, 129
May be deleted so that carry is not performed and the color image data MD and CD are used.

In the first and second ROMs 105 and 106, data that has been color-corrected in advance is stored as table data, and the input color image data is used as an address.
Corrected data values are extracted from the table data.

In this way, the first and second ROM 10
The corrected yellow color image data output from the output terminals 5 and 106 is clocked by the clock C in the latch circuits 107 and 108.
After being synchronized with a clock having a frequency of ½ of K, they are added on the line 122 and given to the line buffer 118 through the latch circuit 115 operating with the clock CK. The line buffer 118 is a first-in-first-out type buffer, although not particularly limited thereto. The output of the line buffer 118 is led to the output terminal 123 via the latch circuit 119, and
Is supplied to the pulse generation circuit 11.

On the other hand, the 8-bit yellow color image data respectively derived from the latch circuits 103 and 104 at the output terminals 124 and 125 are the M correction circuit 5 of FIG.
8 and C correction circuit 59. The input terminal 12
The 8-bit magenta color image data MD and the cyan color image data CD supplied to 0 and 121 are output from the M correction circuit 58 and the C correction circuit 59 and transmitted as described above. However, they are M correction circuit 58,
It is output to the output terminals corresponding to the output terminals 124 and 125 of the Y correction circuit 57 in the C correction circuit 59.

In FIG. 4, reference numeral 112 is a flip-flop circuit, which inputs a clock CK from an input terminal 126 and supplies a clock having a frequency of 1/2 of the clock CK to the latch circuits 102 to 104 and 107 to 109. Since the latch circuits 115 to 117 operate on the clock CK, the input terminals 1 are not directly connected via the flip-flop 112.
A clock is given from 26.

In this embodiment, two ROMs (first ROM 105 and second ROM 106) storing the correction data are used. This is the clock CK input to the input terminal 126.
Since it is generally a high-speed clock, one ROM cannot handle one clock, so two clocks are used so that the read and read speeds can be reduced by half. If the ROM can operate at high speed, the first and second ROMs
Either one of the ROMs 105 and 106 may be used, or only one of them may be prepared. Reference numeral 113 denotes a delay circuit that regulates the output when only one ROM is used. For example, when only the first ROM 105 is used, the delay circuit 113 delays the output of the first ROM 105 given from the first ROM 105 through the latch circuit 109. Latch circuit 11
It is provided to give to 6.

Further, a delay circuit 114 for delaying the output of the latch circuit 101 and giving it to the latch circuit 117 is prepared in order to cope with a case where neither of the ROMs 105 and 106 is used, that is, a case where no correction is applied. ROM10
The selection of whether to use two 5, 106, only one, or neither, is determined by the mode selection signal provided through the input terminal 127. This mode selection signal is given from an external CPU.

Next, a description will be given of the characteristic construction of the embodiment in which the color correction of toner is performed by the masking method in this electronic copying machine. Of course, it is also possible to perform the calculation required for masking by the method described below. However, if such a calculation is performed for each color correction, the circuit becomes complicated. Therefore, in this embodiment, if the YMC input data is determined, a correction table that uniquely determines the corrected YMC output data at that time is set in advance. The color correction can be performed without any calculation processing by creating and ROMizing. Therefore, first, the creation of the color correction table will be described.

Generally, in a single color toner, the toner amount
When (ratio of toner occupying the paper surface) changes, the ratio of the R, G, and B reflection densities of the monochromatic toner is constant regardless of the toner amount (proportional law).

For example, if the amount of magenta (M) toner is 70%,
At 80%, the following equation (4) is established. [Dr70] / [Dr80] = [Dg70] / [Dg80] = [Db70] / [Db80] ... (4)

[Dr70]: R reflection density at 70% M toner amount [Dr80]: R reflection density at 80% M toner amount [Dg70]: 70% M toner amount G reflection density [Dg80]: G reflection density when the M toner amount is 80% [Db70]: B reflection density when the M toner amount is 70% [Db80]: B when the M toner amount is 80% It is the reflection density.

On the other hand, when overprinting with a single color toner is performed, the density of the duplicate becomes equal to the sum of the reflection densities of R, G, and B (addition rule).

By the establishment of the above-mentioned proportionality law and additive law, the following color mixing equations (5) to (7) of reflection densities are established under the condition that the density of the copy is reproduced to be the same as the density of the original. Dr = [C] + m [M] + yr [Y] (5) Dg = cg [C] + [M] + yg [Y] (6) Db = cb [C] + mb [M] + [Y ] …… (7)

Here, Dr: R reflection density of the original document Dg: G reflection density of the original document Db: B reflection density of the original document mr: M reflection ratio of R to G reflection density mb: M reflection ratio of G Reflection Density Ratio of B to Reflection Density About yr: Y Reflection Density Ratio of R to B Reflection Density yg: Y About G Reflection Density Ratio of B to B Reflection Density cg: C About G Reflection Density Ratio of R to R cb: is the ratio of the reflection density of B to the reflection density of R for C. Incidentally, Dr, Dg and Db are data read by a color scanner including the scanning optical system 4, the condenser lens 5, the light receiving element 6 and the like.

The above-mentioned reflection density color mixing equations (5) to (7) are
By solving for [C], [M], and [Y], the following equations (8) to (10) are obtained. [C] = a11Dr + a12Dg + a13Db (8) [M] = a21Dr + a22Dg + a23Db (9) [Y] = a31Dr + a32Dg + a33Db (10)

Here, the coefficients a11 to a33 are experimentally set as shown in the following equations (11) to (13) (masking equation). [C] = 1.03 Dr-0.09 Dg-0.05 Db (11) [M] =-0.43 Dr + 1.04 Dg-0.06 Db (12) [Y] =-0.15 Dr-0.24 Dg + 1.06 Db (13) ) The reflection densities (Dr, Dg, Db) in equations (11) to (13) are calculated by the following equation (1)
It is expressed as in 4) to (16). Dr = -log ₁₀ [R] ...... (14) Dg = -log ₁₀ [G] ...... (15) Db = -log ₁₀ [B] ...... (16) Here, equations (14) to (15) Medium, [R] = 1- {C} / KC ...... (17) [G] = 1- {M} / KM …… (18) [B] = 1- {Y} / KY …… (19) In equations (17) to (19), main density before color correction of toner of {C}: C {M}: before color correction of toner of M {Y}: before color correction of toner of Y Main density, KC, KM, KY are the number of gradations of YMC data

Regarding the predetermined number of gradations (KC, KM, KY), since YMC is conventionally input with 256 gradations, KC = KM = KY = 255. However, in this embodiment, when the correction table of C is created, KC = 2
When 55, KM = 31, KY = 15 are set and a correction table for M is created, KC = 31, KM = 255, KY = 1
When setting 5 and creating the Y correction table, KC =
15, KM = 31 and KY = 255 are set. as a result,
The amount of data per color correction is 256 × 32 × 16 = 131 Kbytes.

Therefore, the masking equations (11) to (13) are
This is an expression having {C}, {M} and {Y} as variables. Further, the lower bits of the toner data (sub toner data) other than the main toner data (main color image data) to be substituted into the masking equation are deleted and processed. That is, the number of bits is assigned by weighting the coefficient of the masking equation. According to this,
A color correction table is created by reducing the actual number of gradations and performing correction calculation. For example, in the case of cyan, the number of bits is determined according to the weights of the coefficients 1.03, 0.09 and 0.05 in the equation (11). That is, 8 bits are assigned to the coefficient 1.03, 5 bits are assigned to 0.09, and 4 bits are assigned to 0.05. Here, the main toner data is 8 bits and the sub toner data (sub color image data) is 5 bits or 4 bits, which has a total of 17 bits.

Even when KC = KM = KY = 255, 0, 1, 2, 3, ... For coefficient 1.03, 0, 8, 16, 24, ... For coefficient 0.09, 0 for coefficient 0.05.
It is possible to allocate 8 bits for the coefficient 1.03, 5 bits for 0.09, and 4 bits for 0.05 by increasing the color image data such as 16, 32, 48 ,.

In FIG. 3, input terminals 51, 52, 53
Is input with {Y}, {M}, and {C} that are color image data of yellow, magenta, and cyan, respectively. These input color image data have an 8-bit structure, although not particularly limited thereto.

[C], [M], obtained as described above,
If you create a color correction table in ROM with [Y], the RGB values read from the color scanner and calculated
Corrected based on reflectance and corresponding address [C],
[M] and [Y] can be output.

By the way, when the sub-toner data has 16 gradations and 32 gradations as described above, the calculated values are slightly different from those calculated with the full data of 256 gradations for each color. In particular, in the case of a data value such as gray scale where YMC data significantly changes for all three colors, the deviation becomes large.

For example, as shown by the dotted line (Cut) in FIG. 5, in a model in which YMC changes in 200 to 224 gradations by Y correction, output data has 10 gradations at 207 and 223 gradation points. It goes down more than that. Although 256 data of YMC are read in each 8-bit structure, only the upper 5 and 4 bits of the sub toner data are input at the time of being input to the color correction table as described above, and apparently 32 and 16 gradations are obtained. Changing. For this reason, the value input to the masking equation jumps greatly at the data change points of 32 and 16 gradations, which causes a deviation from the calculated value of the full data (solid line: Full).

That is, when obtaining the table of C, the expression (1
When the values of {M} and {Y} increase in 8) and (19),
The values of [G] and [B] approach 0, and in equations (15) and (16)
As [G] and [B] approach 0, that is, as the changes in [M] and [Y] increase, the values of Dg and Db both increase dramatically. Therefore, in the equation (11) represented by [C] = 1.03 Dr-0.09 Dg-0.05 Db, the minus coefficient applied before Dg and Db is heard, and the shift occurs as shown by the dotted line (Cut) in FIG. It will end up.

Therefore, when the most significant bit of the deleted lower bits of the sub toner data is set, it is desirable to count up the upper data by 1. This count-up data is corrected by the correction equations (11) to (1
By creating the color correction table by substituting into 3), the deviation is reduced as shown by the alternate long and short dash line (Up) in FIG. This is because, as shown by {C} with # in Table 3 below, what was changed at the same time before rounding is not changed at the same time by rounding. is there. In addition, in order to round off, when the most significant bit of the deleted lower bits of the sub-toner data is set, the circuit for increasing the upper data by 1 is increased by 1 bit (Fig. 4 increment determination circuits 128, 129) may be used.

The respective data in Table 1 correspond to those in FIG. 5, and are calculated by using the full data for all the data of the input values {C}, {M}, and {Y} from the color scanner. C]
Output value (Full), sub-data {M} and {Y} are trimmed of lower bits, and main data {C} is output value (Cut) of [C] when calculated using full data, and {M}, {Y}
The output value (Up) of [C] when calculated using the data counted up is shown.

Table 2 shows C corresponding to the output value (Cut).
8 bit {C}, 5 bit {M}, 4 determined according to the weight of the coefficient of Expression (11) when the correction table of
The correspondence between bit {Y} and the number of gradations (KC = 255, KM = 31, KY = 15) is shown.

Tables 3 and 4 are the same as Table 2 except that the output values are
Formula when creating a C correction table corresponding to (Up)
8-bit {C} determined according to the weight of the coefficient of (11),
5-bit {M}, 4-bit {Y} and number of gradations (KC = 255, K
(M = 31, KY = 15). In addition, in the same table, the value of {C} with * indicates the value when {M} changes, and the value of {C} with ☆ changes {Y}. It indicates that it is the hour value.

Table 5 shows the correspondence between the values of {C} marked with * and * and the values of {M} and {Y} in Table 3. When the most significant bit of the deleted lower bits of the sub toner data is set, the upper data is incremented by 1.
(Rounding off) and counting up the data with the correction formula (1
Since the color correction table is created by substituting in 1) to (13), {M} and {Y} do not change at the same time, and the occurrence of the deviation is suppressed. In other words, by the above rounding
By dispersing the changes in {M} and {Y}, the above deviation can be suppressed small. As can be seen from FIG. 5, the change indicated by the alternate long and short dash line (Up) due to the rounding is in line with the change indicated by the solid line (Full). However, for example, {C} = 204 to 2 which almost corresponds to FIG.
The change at 216 in No. 20 is due to the difference of the change rate being {M} (1/31) and {Y} (1/15).

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

[0059]

[Table 5]

[0060]

As described above, according to the present invention, the correction is performed by solving the masking equation by allocating the gradation number of the input image data according to the weight of each coefficient of the reflection densities of the three primary colors forming the masking equation. Since the color image data is calculated, the color image data per color is reduced, and as a result, the color correction of the toner can be performed with a memory having a small capacity with almost no change in the reproducibility of the image. As a result, the cost of the device can be reduced and the circuit configuration can be simplified without incurring a slowdown of the masking process.

[0061] Incidentally, by storing as the color correction table address corresponding to the corrected color image data to the gradation number of the semiconductor memory device, it is possible to simplify the circuit configuration.

Further, in order to reduce the number of gradations, the lower bits of the sub color image data are deleted, and when the most significant bit of the lower bits is 1, the upper bit of the sub color image data is If the bit data value is increased by 1, the sub color image data can be made to have the same number of gradations as the main color image data to reduce the deviation of the color correction result from the case of using a large capacity memory. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a digital color electronic copying machine embodying the present invention.

FIG. 2 is a block diagram showing a main configuration of an embodiment of the present invention.

FIG. 3 is a block diagram showing a data correction circuit that constitutes an embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a correction circuit used in an embodiment of the present invention.

FIG. 5 is a graph showing the effect of color correction in the example of the present invention and the conventional example.

FIG. 6 is a graph showing CCD spectral characteristics of a color scanner applicable to the present invention.

FIG. 7 is a graph showing spectral characteristics of toner applicable to the present invention.

FIG. 8 is a graph showing spectral characteristics of magenta toner applicable to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Contact glass 2 ... Original pressing 3 ... Original 4 ... Scanning optical system 5 ... Condensing lens 6 ... Light receiving element 7 ... Image processing circuit 8 ... Laser scanner unit 9 ... Photosensitive drum 10 ... Main charger 11 ... Pulse generating circuit 12 ... drive circuit 13 ... semiconductor laser 14 ... motor 15 ... polygon mirror 16 ... laser beam 17Y ... Y developing device 17M ... M developing device 17C ... C developing device 17BK ... BK developing device 18 ... moving body 19 ... transfer drum 20, 21 ... Paper feed cassette 22 ... Cleaning section 23 ... Conveying section 24 ... Fixing section 57 ... Y correction circuit 58 ... M correction circuit 59 ... C correction circuit 100 ... Input terminal 105 ... First ROM 106 ... Second ROM 111 ... Selector 112 ... Flip-flop circuit 113, 114 ... Delay circuit 118 ... Buffer CK ... clock 101～104,107～110,115～117,11
9 ... Latch circuit 120, 121 ... Input terminal 122 ... Line 123-125 ... Output terminal 126, 127 ... Input terminal

Continuation of the front page (56) Reference JP 63-155867 (JP, A) JP 63-116277 (JP, A) JP 63-254865 (JP, A) JP 4-49775 (JP , A)

Claims (3)

(57) [Claims] 1. Color image data corrected by solving the masking equation by allocating the number of gradations of input image data according to the weight of each coefficient of reflection densities of the three primary colors forming the masking equation A semiconductor memory element stored at a corresponding address; a means for generating an address signal corresponding to the number of gradations from the input main color image data and sub color image data; A color image forming apparatus comprising: means for reading and outputting color image data. 2. A color image formation for calculating corrected color image data by allocating the number of gradations of input image data according to the weight of each coefficient of reflection densities of three primary colors forming the masking equation and solving the masking equation. In the color correction method in the device, the number of gradations is reduced by deleting the lower bits of the sub color image data that is color image data corresponding to a coefficient other than the coefficient with the highest weight among the coefficients, and In a color image forming apparatus, the data value of the upper bit of the sub color image data is increased by 1 when the most significant bit of the deleted lower bits of the sub color image data is 1. Color correction method. 3. A means for calculating corrected color image data by allocating a gradation number of input image data according to a weight of each coefficient of reflection densities of three primary colors forming a masking equation and solving the masking equation. A means for erasing the lower bits of the sub color image data which is color image data corresponding to a coefficient other than the coefficient having the highest weight among the respective coefficients for reducing the number of gradations; And a circuit for increasing the data value of the upper bit of the sub color image data by 1 when the most significant bit of the scraped lower bits is 1.