JP3092713B2 - Color image forming equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly, to a color image forming apparatus used for an electrophotographic or thermal transfer type printer.

2. Description of the Related Art Conventionally, a full-color electrophotographic copying machine is configured as shown in FIG.

In the figure, 1 is a photosensitive drum, 2 is a primary charger, 3
Denotes a surface voltmeter for measuring the surface potential of the photosensitive drum 1. Around the photosensitive drum 1, a plurality of developing units 101M and 101 using a two-component developer in which a toner and a carrier are mixed.
A movable platform 12 on which C, 101Y, and 101Bk can be loaded and movable in the left and right direction
A developing device 100 having 0, a transfer drum 5, a pre-discharger 6, and a cleaning device 7 are arranged.

The optical system 10 includes a document illumination lamp 20, a first mirror 11, a second mirror 12, a third mirror 13, an imaging lens 14, a CCD 15 having B, G, and R filters, and a laser scanner unit 1.
6. Consists of fixed mirrors 17 and 18. The lamp 20 and the mirror 11 scan the original on the platen glass 28 at twice the speed of the mirrors 12 and 13. The reflected light of the document forms an image on the CCD 15 via the lens 14. The original image is color-separated by a CCD 15 having B, G, and R filters, converted into an electric signal, subjected to image processing such as A / D conversion, and thereafter, a laser driver in a laser scanner unit 16 is provided. Sent to The laser beam oscillated by the image signal passes through a polygon scanner in the unit 16 and mirrors 17 and 18 to form a latent image on the photosensitive drum 1.

A fixing device 20 and a paper feeding device 30 are disposed on the right side of the copying machine.
5, 35 are arranged.

The photosensitive drum 1 has four developing colors M (magenta), C
(Cyan), Y (yellow), and Bk (black), charging, exposure, development, transfer, and cleaning are performed by the primary charger 2, the optical system 10, the developing device 100, the transfer drum 5, and the cleaning device 7. It is applied.

Here, the transfer drum 5 is a transfer paper cassette of the paper feeding device 30.
The leading edge of the transfer paper P fed from 31 or 32 through the transport system 35 is gripped by the gripper 5a, and the transfer paper P is attracted to the transfer sheet 5b by the attraction charger 4 disposed inside the transfer drum 5. Then, the photosensitive drum 1 is rotated and transferred so as to transfer a developed image for each developing color. A transfer charger 5c is arranged in the transfer area.

Thereafter, the transfer paper P on which the toner images of the respective development colors are sequentially transferred is released from the gripper 5a, is separated from the transfer sheet 5c by the separation charger 8 and the separation claw 8 ', and is fixed by the conveyance system 25 to the fixing device 20. Sent to. After the toner image on the transfer paper P is fixed on the transfer paper P by the fixing device 20, the transfer paper P is discharged onto the tray 23.

[Problems to be Solved by the Invention] However, the above-described conventional example has the following problems.

Color unevenness such as interference fringes having a relatively long period occurs in one image due to uneven rotation of the polygon mirror.

Color unevenness occurs due to a deviation of a transfer position for each developing color due to a vibration of the transfer drum or a slight bending of the transfer sheet.

FIG. 3A shows an example thereof. That is, the screen angle between the image forming pattern 201 of the first color and the image forming pattern 202 of the second color slightly shifts.
Color overlapping positions and non-overlapping positions occur in a long cycle, and appear as color unevenness.

In order to solve such a problem, means for forming an image at a different screen angle for each developing color has been proposed. According to the proposal, as shown in FIG. The portions and the non-overlapping portions are uniformly dispersed, and a uniform image without color unevenness is obtained.

On the other hand, in recent digital copiers, a variety of area editing functions are incorporated, and by using these functions, various processing can be performed on a designated area. For example, as an editing function in a color copying machine, a "color mode" in which an image in an area can be reproduced in an arbitrary color, a "base color mode" in which a white background portion of an image in the area can be arbitrarily colored, and an A “paint mode” that can be painted in any color has been commercialized.

The "color mode" includes a "full color mode" for reproducing the original color exactly as it is, a "mono color mode" for treating the original image as a shaded image and reproducing the desired mono color, and a "free color mode". Mode.
The “full color mode” includes a “four color full color mode” using four colors of magenta, cyan, yellow, and black, and a “three color full color mode” using no black. The “mono color mode” includes “magenta mode”, “cyan mode”, “yellow mode” and “black mode” using only one development color, and “red mode”, “green mode” and “green mode” using two development colors. There is a "blue mode". "In the free color mode, the ratio of magenta, cyan, yellow, and black can be set arbitrarily to reproduce the desired single color. In the" base color mode ", each of the background portion and the image portion in the area, and the" paint mode " In each of the modes, each mode of “4 full colors”, “3 full colors”, “magenta”, “cyan”, “yellow”, “black”, “red”, “green”, “blue”, and “free color” can be set.

According to the above proposal, when "4 colors full color", the first color is processed at 45 °, the second and third colors are processed at 0 °, the fourth color is processed at 26.6 °,
In the "two-color mode" of "red", "green", and "blue", an example is given in which the first color is processed at 45 ° and the second color is processed at 0 °.

However, if the number of colors used for each area is different, controlling the screen angle for each color is not necessarily effective for all areas. For example, as shown in FIG. 4, when forming a color image having three areas reproduced in "red", "green", and "blue", respectively, applying the above-described example of the screen angle, Magenta 45 ° and yellow 0 °, cyan 45 ° and yellow 0 ° for the green area, magenta 45 ° and cyan 0 ° for the blue area, and inconsistency in the screen angle of cyan, some measures are required.

In addition, when a plurality of types of screen angles are applied to one development color as necessary, a difference in density reproducibility due to the screen angle appears, and in a full color mode, a difference in tint appears.

An object of the present invention is to solve the above technical problem and provide a color image forming apparatus that has a plurality of regions and performs optimal screen angle control even when the number of colors used for each region is different. is there.

It is another object of the present invention to provide a color image forming apparatus capable of reproducing optimal density and color tone according to screen angle control.

[Means and Actions for Solving the Problems] In order to achieve the above object, the present invention provides a color image forming apparatus for sequentially forming images of a plurality of colors for each color, in which a plurality of images to be formed are specified in advance. Control means for controlling a screen angle in image formation for each of the colors used in each of the plurality of areas when different colors are used among the plurality of colors for each of the areas when forming an image. It is characterized by having.

According to another aspect of the present invention, there is provided a color image forming apparatus for sequentially performing image formation of a plurality of colors for each color, wherein an image to be formed includes a plurality of regions designated in advance. When a color used among the plurality of colors is different for each of the regions, a control unit that controls a screen angle in image formation according to a combination of the colors used in each of the plurality of regions is provided. I do.

Further, in order to achieve the above object, the present invention provides a color image forming apparatus for sequentially performing image formation of a plurality of colors for each color, wherein a plurality of screen angles can be selected for each of the plurality of colors used for the image formation, Control means for selectively determining a screen angle in the image formation for each of the plurality of colors; and performing density conversion processing on the color image signal to be image-formed to guarantee density according to the determined screen angle. And a density conversion unit.

In order to achieve the above object, the present invention provides a color image forming apparatus for sequentially performing image formation of a plurality of colors for each color, wherein the image formation is selectively performed in accordance with the type of color used for the image formation. Control means for determining a screen angle;
Color correction processing means for performing a color correction process on the color image signal to be formed in accordance with the determined screen angle so as to guarantee color tone.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

In the following description, magenta is M, cyan is C,
Yellow is represented by Y, black by Bk, red by R, green by G, blue by B, 4 full color by 4C, and 3 full color by 3C.

<First Embodiment> FIG. 1 is a block diagram of an image forming pattern generating apparatus according to a first embodiment. In the figure, reference numeral 300 denotes a CPU that controls the entire apparatus, 301 denotes a ROM storing programs and the like of the CPU 300, 302 denotes a RAM that stores editing information and the like, and 303 denotes an I / O port.

A color image signal 319 (for example, four types of digital signals of M, C, Y, and Bk) is converted into an analog image signal 320 by a D / A converter 310 for each color component, and is input to a comparator 311. . The comparator 311, analog image signal 3
20 is compared with the triangular wave 321 generated by the triangular wave generation circuit 309 to generate a pulse width modulated PWM signal 322. The PWM signal 322 is sent to a laser drive circuit (not shown) to control the laser lighting timing and form a latent image on the photosensitive drum.

Reference numeral 306 denotes a 2-bit down counter that uses the horizontal synchronization signal HSYNC as a clock, and repeats counting in units of four lines in the sub-scanning direction. As for the output 315 of the counter 306, both the bits 0 and 1 are input to the A-side input (bits 0 and 1) of the selector 305. Bit 0 of the counter output 315
Is input to bit 1 of the B side input of the selector 305,
Bit 0 of the side input is fixed to “0”. The select signal 312 of the selector 305 is transmitted to the CP via the I / O port 303.
Provided from U300, and when signal 312 is "0",
The output signal 316 of the selector 305 changes every sub-scanning line as "11, 10, 01, 00". When the signal 312 is "1", the output signal 316 repeatedly changes as "10, 00, 10, 00". I do. The output signal 316 is input as the select signal 314 of the selector 308 via the AND gate 304. And And Gate 3
The gate signal 313 to 04 is given from the CPU 300 via the I / O port 303.

The shift register 307 is a delay line that generates a signal 324 in which a clock 317 having a frequency four times the PWM pulse is used as a clock and the clock 318 for generating a triangular wave is sent by 0 °, 90 °, 180 °, and 270 °, respectively. The above selector 308 is a CPU 300
Selects one of the four types of delay pattern signals 324 generated by the shift register 307 in accordance with the select signal 312 and the gate signal 313 controlled by the control circuit 312, and outputs the selected signal to the triangular wave generation circuit 309 as a signal 323. Then, the triangular wave generation circuit 309 generates a triangular wave 321 according to the delay pattern 324 (signal 323) selected by the selector 308.

In the above configuration, when the control signals 312 and 313 are "0,0" or "1,0" respectively, the clock for generating the triangular wave is always a 0 DEG delay, and the screen angle is 0 as shown in FIG. 5 (a). It becomes ゜. Also, control signals 312, 31
When 3 is "0,1", the clock for triangular wave generation changes to 0 DEG, 90 DEG, 180 DEG, and 270 DEG as the sub-scan advances one line at a time, and the screen angle is shown in FIG. 5 (b). As 26.6
It becomes ゜. When the control signals 312 and 313 are "1,1", the clock for triangular wave generation changes to 0 DEG, 180 DEG, 0 DEG, and 180 DEG as the sub-scan advances one line at a time, and the screen angle changes as shown in FIG. It becomes 45 ° as shown in c).

Next, an algorithm for determining the screen angle by examining the colors used in the area will be described below with reference to the flowchart shown in FIG.

First, it is checked whether or not there is an area using all four colors of M, C, Y, and Bk (step S601). If YES (Yes), the pattern A (M: 45 °, C: 0 °, Y) is used. : 0 ゜, Bk: 26.6 ゜) (step S602). In the embodiment, the number of usable colors is four.
In contrast to color, as described above, it has only three types of screen angles, so in an area using four colors,
Either two colors will be imaged at the same screen angle.

Therefore, independent screen angles are given to M of the first color and Bk of the fourth color, where the transfer position is relatively likely to shift due to the vibration at the time of suction and separation of the transfer paper, so that Y is the least visually noticeable. Gives the same screen angle.

In step S601, when NO (there is no area to use all four colors), for the same reason as described above, three colors including M and Bk, which are likely to be shifted, ie, (M, C, Bk) or (M , Y,
Check whether there is an area of Bk) (step S603), and answer YES.
At this time, the pattern A is selected (step S604). However, in step S603, when NO, three colors including M (M,
Check whether there is an area of (C, Y) (step S605), and answer YES.
In step S6, it is checked whether or not there are two colors including Bk, that is, an area of (M, Bk) or (C, Bk) or (Y, Bk).
06). Here, when YES, the pattern A is selected (step S607), and when NO, the pattern B (M: 45 °, C: 0 °, Y: 26.6)
{Bk: 0}) is selected (step S608).

The reason for selecting step S607 is that there are regions of two or more colors including M and Bk, which are apt to shift. Step S6
The reason for selecting 08 is that there is no area of two or more colors including Bk, and that Y becomes the final color and may easily shift due to vibration during separation of the transfer paper.

On the other hand, in step S605, if NO,
It is checked whether there is a color, that is, an area of (M, C) or (M, Y) or (M, Bk) (step S609). If YES, two or more colors including Bk, that is, (C, Y) , Bk) or (C, Bk) or (Y, Bk) (step S61).
0). Here, when YES, the pattern A is selected (step S611), but when NO, it is checked whether or not there are two colors including Y, that is, an area of (C, Y) (step S612).
At the time of ES, pattern B is selected (step S613). However, when NO, the pattern C (M: 45M, C: 0 ゜, Y: 0 ゜, Bk:
0 ゜) is selected (step S614). Step S611,
For the same reason as in step S607 described above, and also in step S6
13 is selected for the same reason as in step S608 described above. The reason in step S614 is that each of C, Y, and Bk is used alone in a one-color area, or each of C, Y, and Bk is used in a two-color area together with M alone.

As described above, the examination of the area of two or more colors including M is completed, and in the above-mentioned step S609, if NO, it is checked whether or not there is an area of three colors (C, Y, Bk) not including M (step S609). Step S615). As a result, when YES, the pattern D (M: 0 ゜, C: 4
5 ゜, Y: 0 ゜, Bk: 26.6 ゜) is selected (step S616).
The reason for this is to give C a screen angle of 45 °, since C may be the first color and color misalignment may easily occur.

On the other hand, at the time of NO, it is checked whether or not there are two colors including C, that is, (C, Y) or (C, Bk) areas (step S617).
If YES, the pattern D is selected (step S619). However, when NO, the pattern E (M: 0 ゜, C: 45 ゜, Y: 0 ゜, B
k: 0 ゜) is selected (step S620). The reason for the selection in step S619 is that C is the first color, Bk is the last color, and both are used for the two-color area. The reason for the selection in step S620 is that Y and Bk are C
This is because only two colors are formed.

In step S617, if NO, the presence or absence of the (Y, Bk) area is checked as the last possibility of the area of two or more colors (step S621), and if YES, the pattern F (M: 0 ゜, C: 0) is checked.゜, Y: 4
5 ゜, Bk: 0 ゜) is selected (step S622). But NO
At this time, the pattern G (M: 0 ゜, C: 0 ゜, Y: 0 ゜, Bk: 0 ゜) is selected (step S623). The reason for the selection in step S622 is that the only area of two or more colors is (Y, Bk) and Y
This is because there is a possibility of the first color. Also, step
The reason for selection in S623 is that all areas are formed in one color.

By determining the screen angle of each color according to the above algorithm, optimal control is possible even when each of the plurality of regions has a different color combination.

<Second Embodiment> In the above-described first embodiment, a color combination to be given the highest priority is selected from a plurality of regions in a predetermined procedure, and an image is formed over the entire region at a screen angle optimal for the combination. The hardware configuration was simple for forming. However, for example, the pattern A, that is, 45
It is expected that the density formed between the image formed with ゜ and the pattern D, that is, the image formed with 0 °, is different. Similarly, the pattern A, that is, C:
0 ゜, Y: 0 ゜ and the pattern B, that is, C: 0
It is expected that the image formed with {, Y: 26.6} will have a different color.

In order to solve such a problem, in the second embodiment, a means for changing a screen angle for each area is used.
More optimal control is performed.

FIG. 7 is a block diagram showing the configuration of the circuit in the second embodiment.

In the figure, reference numerals 300 to 324 denote the same components as those shown in FIG.

First, the area signal generator 400 generates an area signal 402 according to the editing information stored in the RAM 302. Details of the internal operation of the area signal generation section 400 will be described later.

Next, the LUT (lookup table) 401 outputs the area signal
402, count output signal 315 of counter 306, and I / O 303
Then, each of the color signals 404 given from the CPU 303 via the CPU 303 is inputted as an address, and the select signal 314 to the selector 308 is made a data output.

The color signal 404 consists of two bits and represents the color under image formation. It is “00” for M, “01” for C, “10” for Y, and “11” for Bk.

A signal 403 provided from the CPU 300 via the I / O 303 is a 4-bit area signal in the sub-scanning direction. In the second embodiment, four regions can be edited as described later, and each bit of the signal 403 is one.
Corresponds to one area. Here, “1” means that the area is inside the area, and “0” means that the area is outside the area.

Next, the detailed configuration of the above-described area signal generation section 400 will be described below with reference to the block diagram shown in FIG.

In the figure, a counter 801 is an up counter,
The horizontal synchronization signal HSYNC is used as a reset signal for each line,
The clock 405 indicating a pixel is counted. Count value 808
Are sent to the comparators 802 and 803. In the comparator 802, the CPU 300 compares the count value 808 with the main scanning start point value in the area previously set on the latch 805, and outputs a compare signal 809 when the values match, thereby setting the SR flip-flop 804. Similarly, in the comparator 803, the CPU 300
By comparing the main scanning end point value of the area set in 06 with the count value 808, and outputting a comparison signal 810 when they match, the SR flip-flop 804 is reset.

The next AND gate 811 is a two-dimensional area signal 814 for gating the output signal 807 of the flip-flop 804 indicating the main scanning area section with the sub-scanning area signal 813 output from the CPU 300 via the I / O 303 and finally using the same. Generate

The circuit shown in FIG. 8 generates one area signal 814. In this embodiment, there are four sets of the circuit shown in FIG. 8 in the area signal generator 400 shown in FIG. Further, since the sub-scanning area signal 813 has a margin in time, for example, C
The PU 300 takes in the HSYNC signal as an interrupt signal, counts it by software, turns on when the sub-scanning start point of the area is reached, and turns off when it reaches the sub-scan end point of the area.

With the above configuration, the optimal combination of screen angles can be determined independently for each area and set in the LUT 401.

FIG. 9 shows an example of a combination of screen angles with respect to a combination of colors in a certain area.

As shown in the figure, in the case of four colors, the first color M is set to 45.
゜, the final color Bk is 26.6 ゜, and the remaining second and third colors
Let C and Y be 0 °. In the case of three colors, the first color is set to 45 °, the final color is set to 26.6 °, and the remaining second color is set to 0 ° except for one color that is not used. Unused colors can be ignored. For two colors, the first color to be used is 45 °, and the final color is 0 °. And
For one color, it is 0 °.

Next, an example of region editing as shown in FIG. 10 will be described below.

As shown in the figure, the area 0 is four full colors and the area 1 is
Is processed in one color of magenta, the area 2 is processed in green, and the area 3 is processed in black in the image information part and in the background part in yellow.

When a combination of screen angles for such area editing is selected from the screen type shown in FIG.
, The screen type 12 for the area 1, the screen type 9 for the area 2, and the screen type 11 for the area 3.

The contents of the LUT 401 in the above-described region editing will be described below with reference to FIGS. 11 (a), (b) and FIG.

As shown in FIG. 11 (a), the coded sub-scan line 315 is stored in the address bits 0 and 1 of the LUT 401, the area signal 402 of four areas is stored in each of the bits 2 to 5, and the bit 6 is displayed. , 7 correspond to the coded color type 404.

When the screen angle is 45 °, the phase of the triangular wave generating clock is 0 °, 180 °, 0 as the sub-scan advances one line at a time.
{180}, the select signal 314 output to the selector 308 becomes 0, 2, 0, 2 as shown in FIG. 11 (b). Accordingly, data 0, 2, 0, 2 corresponding to the lower two bits of the address of the LUT 401 are set. Similarly, if the screen angle is 2
At 6.6 °, data 0,1,2,3 is set, and at 0 °, data 0,0,0,0 is set.

FIG. 12 shows the final LU corresponding to the editing example shown in FIG.
FIG. 9 is a diagram showing data contents set in T401. The crosses in the data column in the figure indicate that the corresponding area and color are not printed and can be ignored. Also,
Since the area signal is not coded, address bit 2
Any one of 〜 to 5 is always “1”.

As described above, by using the means for switching and controlling the screen angle in accordance with the region and the color, it is possible to perform the optimal screen angle control even when performing editing by a combination of a complicated region and a color.

Third Embodiment Next, a third embodiment according to the present invention will be described below with reference to FIGS.

FIG. 13 is a block diagram showing a circuit configuration in the third embodiment. In FIG. 13, reference numerals 300 to 325 and 400 to 405 denote components similar to those in FIG. 7 used in the second embodiment, and FIGS. Reference numeral 505 denotes a new component in the third embodiment.

First, the color-separated R, G, and B three light amount signals 502 are converted into density signals 503 of developed colors M, C, Y, and Bk in a color correction unit 500, which will be described later. After the difference is corrected, it is sent to D / A converter 310.

The LUT 504 in this embodiment is the LUT 4 described in FIG.
As in the case of 01, a delay pattern select signal 314 of the clock for generating a triangular wave in each main scanning line is output, and a code signal 505 corresponding to the screen angle is output. That is, the code signal 505 has a screen angle of 0.
In the case of ゜, the data is 0, 26.6 ゜, and in the case of data 1,45 ゜, it is data 2.

In this embodiment, the color correction unit 500 and the density correction unit 501 are controlled by a code signal 505 indicating the screen angle, thereby guaranteeing the optimal color and density for the screen angle.

Next, the configuration of the color correction section 500 will be described below with reference to the block diagram shown in FIG.

Reference numerals 510, 511, and 512 denote minus LOG converters for converting R, G, and B signals into C, M, and Y signals, respectively. Reference numeral 513 denotes a black generation unit that generates a Bk signal from the C, M, and Y signals using, for example, min (C, M, Y).

522, 523, 524, 525 are multipliers, respectively, and Y,
The signals of M, C, and Bk are multiplied by the coefficients set in the latch groups 518, 519, 520, and 521. 526 is an adder and a multiplier 52
The outputs of 2,523,524,525 are added to generate a density signal 503 corresponding to the developed color.

Using these multipliers and adders, a so-called masking operation for correcting characteristics of toner and the like is performed.

The above-described latch group 518 includes 12 latches corresponding to combinations of four development colors and three screen angles.
A coefficient for multiplying each latch by the Y signal is preset by the CPU 300. Similarly, the latch group 519 has the coefficient of M, the latch group 520 has the coefficient of C, and the latch group 521 has the coefficient of M.
Bk coefficients are set respectively.

The selector 514 selects one of the twelve outputs of the latch group 518 in accordance with the screen angle code signal 505 from the LUT 504 and the developed color code signal 404 specified by the CPU 300. Similarly, selectors 515, 516, 517 are
19,520,521 respectively.

Next, the configuration of the density correction unit 501 will be described below with reference to the block diagram shown in FIG.

540, 541, 542 are output signals 503 of the color correction unit 500,
This is an LUT for performing density conversion processing for absorbing the influence of the screen angle. 540 is screen angle 0 ス ク リ ー ン, 541 is 26.
6 ゜ and 542 correspond to 45 ゜. Each of the 540, 541, 542 has four types of LUTs corresponding to each developing color. The selectors 543, 544, 545 select the LUT output corresponding to each developing color, and the selector 546 selects the screen angle code signal 505.
Select the LUT output corresponding to.

As described above, according to the third embodiment, by selecting a masking coefficient and a density conversion pattern according to the screen angle, an image forming apparatus with stable tint and density with respect to the screen angle conversion can be provided. Can be provided.

According to the first aspect of the present invention, in the case where different colors are used among a plurality of colors for each area when forming an image, the image formation is performed for each color used for each of the plurality of areas. Since the screen angle is controlled, according to the second aspect, when different colors are used among a plurality of colors for each area when forming an image, the image formation in the image formation is performed according to a combination of colors used in each of the plurality of areas. Since the screen angle is controlled, it is possible to appropriately control the screen angle even when different colors are used among a plurality of colors for each area when forming an image.

According to a third aspect of the present invention, in a color image forming apparatus that sequentially forms images of a plurality of colors for each color, a plurality of screen angles can be selected for each of the plurality of colors used for the image formation. Control means for selectively determining a screen angle in the image formation, and density conversion means for performing density conversion processing on the color image signal to be image-formed to guarantee density according to the determined screen angle. Therefore, an optimum screen angle can be selected for each of a plurality of colors used for image formation, and even if an optimum screen angle is selected for each of the plurality of colors by the density conversion means, image formation with stable density can be realized.

Further, according to claim 4, control means for selectively determining a screen angle in image formation according to the type of color used for image formation, and in accordance with the determined screen angle,
Color correction processing means for performing a color correction process on the color image signal on which the image is formed so as to guarantee color tone enables appropriate density conversion and color correction according to the determined screen angle.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration in the first embodiment, FIG. 2 is a sectional view of a conventional color copier, FIG. 3 (a) is a diagram for explaining color unevenness, and FIG. FIG. 4B is a diagram showing an image without color unevenness, FIG. 4 is a diagram for explaining region editing, FIGS. 5A to 5D are diagrams for explaining screen angles, and FIG. FIG. 7 is a flowchart showing a procedure for determining a screen angle in the first embodiment, FIG. 7 is a block diagram showing a circuit configuration in the second embodiment, FIG. 8 is a block diagram showing a configuration of the area signal generator 400, and FIG. 9 is a diagram showing a screen type corresponding to a combination of colors, FIG. 10 is a diagram showing an example of area editing in the second embodiment, FIG. 11 (a) is a diagram for explaining input / output signals of the LUT 401, FIG. FIG. 11 (b) is a diagram showing the screen angle and the data to be set, and FIG. FIG. 13 is a block diagram showing a circuit configuration in the third embodiment, FIG. 14 is a block diagram showing a configuration of a color correction unit 500, and FIG. FIG. 3 is a block diagram showing a configuration. In the drawing, 300 CPU, 305 selector, 306 counter, 307 shift register, 308 selector, 309
... triangular wave generator, 310 ... D / A converter, 311 ... comparator, 400 ... area signal generator, 401 ... LUT, 500
.., A color correction unit, 501, a density correction unit, and 504, a LUT.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/525 H04N 1/46 H04N 1/40 G03G 15/01

Claims (4)

(57) [Claims] 1. A color image forming apparatus for sequentially forming an image of a plurality of colors for each color, wherein an image to be formed is composed of a plurality of areas designated in advance. A color image forming apparatus comprising: a control unit that controls a screen angle in image formation for each of the colors used in each of the plurality of regions when different colors are used. 2. A color image forming apparatus for sequentially forming an image of a plurality of colors for each color, wherein an image to be formed is composed of a plurality of regions designated in advance. A color image forming apparatus comprising: a control unit that controls a screen angle in image formation according to a combination of the used colors in each of the plurality of regions when different colors are used. 3. A color image forming apparatus for sequentially performing image formation of a plurality of colors for each color, wherein a plurality of screen angles can be selected for each of the plurality of colors used for the image formation, and the screen angle is selectively selected for each of the plurality of colors. Control means for determining a screen angle in image formation; and density conversion means for performing density conversion processing on the color image signal to be image-formed in order to guarantee density according to the determined screen angle. Color image forming apparatus. 4. A color image forming apparatus for sequentially performing image formation of a plurality of colors for each color, a control means for selectively determining a screen angle in the image formation in accordance with a type of a color used in the image formation. A color image forming apparatus comprising: a color correction processing unit configured to perform a color correction process on the color image signal to be formed so as to guarantee color tone in accordance with the determined screen angle.