JPS62178282A - Method for correcting color in color electrophotographic method - Google Patents

Abstract

PURPOSE:To attain color correction improved at gradation reproducibility by irradiating an erasing pattern simultaneously or immediately before or after an exposure process to a photosensitive body and changing an erasing rate or the erasing pattern in accordance with a decomposed color. CONSTITUTION:A charger 12, an eraser 18 and developing devices 20, 22, 24, 26 are arranged on the periphery of the photosensitive body 10 and a color original '0' to be copied is set up on an original setting glass 16. A filter device F is formed on an exposure optical system 14 for projecting an original image to the photosensitive body 10. Plural erasing rates or erasing patterns corresponding to previously decomposed colors are stored in a memory 54 and one of them is read out by the selection of a selection key or a photoelectric transducing output from a CCD 51 receiving the reflected optical image from the original. Thus, the eraser 18 executes erasing by changing the erasing rate or the erasing pattern in accordance with the decomposed color. Consequently, color correction improved at gradation reproducibility can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a color correction method in color electrophotography.

(Prior Art) In electrophotographic images obtained by electrophotography, so-called gradation reproducibility is not very good.

well known.

A method of irradiating an erase pattern is also known in order to improve tone reproducibility in electrophotographic images. This method is a method in which a uniformly charged photoconductive photoreceptor is irradiated with dot-shaped light spots in a net pattern. The dot-like light spots may be irradiated in a mesh pattern before forming the electrostatic latent image, or may be performed simultaneously with the exposure step.

Since the electrostatic latent image is erased in the area illuminated by the light spots, the net-like pattern of the light spots to be irradiated onto the photoreceptor is called an erase pattern.

As is well known, the gradation reproducibility of an electrophotographic image is determined by the gradation reproduction characteristic, the so-called γ characteristic, which determines the correspondence between the image density of an original and the image density of an electrophotographic image. The closer the slope of the curve giving the γ characteristics is to 45 degrees, the better the gradation reproducibility is.

Conventionally, improvements in gradation reproducibility by irradiating erase patterns have been carried out with the aim of bringing the slope of the curve giving the γ characteristic closer to 15 degrees, and this has been successful.

By the way, in Carlson color electrophotography, in order to adjust color reproducibility and gradation reproducibility, it is necessary to adjust the charging potential, exposure amount,
Various strict process controls such as development bias are required, and these are susceptible to fluctuations in environmental conditions and other factors.

(Objective) Therefore, an object of the present invention is to provide a color correction method for color electrophotography in which a method for improving gradation reproducibility by irradiating an erase pattern is applied to color electrophotography.

(Structure) In order to achieve the above-mentioned object, the present invention uses a photosensitive material that is exposed to light at the same time as an exposure step of irradiating a uniformly charged photoconductive photoreceptor with a color-separated original light image, or before and after the exposure step. Perform an erase process that irradiates the body with an erase pattern,
A color electrophotographic method in which an electrostatic latent image corresponding to a color-separated image is developed with colored toner is characterized in that the erase rate or erase pattern is changed depending on the color-separated colors.

An embodiment of the present invention will be described in detail below.

The inventors have been researching the problem of gradation reproduction characteristics (γ characteristics) caused by irradiation of erase patterns.

During the course of this research, we discovered that the γ characteristics change depending on the erase rate or erase pattern.

The present invention is based on this discovery and is therefore characterized by varying the erase rate or erase pattern depending on the separated colors.

The process of irradiating a uniformly charged photoconductor with a light image of the original is called the exposure process, but the erase pattern can be irradiated before or after the exposure process, or at the same time as the exposure process, as long as the photoconductor is charged. But that's fine.

Hereinafter, specific embodiments will be described with reference to the drawings.

FIG. 1 shows only the main parts of an example of a color electronic copying apparatus to which the present invention is applied. To explain the main symbols in the figure, numeral 10 indicates a photoconductive photoreceptor. This photoreceptor has a photoconductive layer made of As2Se, is drum-shaped, and is driven to rotate in the direction of the arrow.

Around the photoreceptor 10, there are a charger 12, an eraser 18, a developing device 20, 22, 24, 26, and a static elimination lamp 2.
7° holder 28. A static eliminator 32 and a cleaner 34 are provided. Reference numeral 16 indicates an original placing glass, and a color original ◯ to be copied is placed flatly on this original placing glass 16.

The exposure optical system indicated by reference numeral 14 includes a lamp 140, a plane mirror 141, a roof mirror 142, a lens 144, and a plane mirror 1.
43 and a filter device F.

Further, in FIG. 1, the reference numeral 30 indicates a transfer device, the reference numeral 35 a separator, the reference numeral 37 a separating claw, and the reference numeral S a transfer sheet (through which the sheet is passed) as a recording sheet. Further, reference numeral 50 indicates a rotary encoder.

The eraser 18 is a combination of an LED array and a focusing light transmitting body array, and is configured to form an erect, same-size image of the lit LED on the photoreceptor 10 by using the focusing light transmitting body array. There is. The eraser 18 is disposed between the charger 12 and the exposure section for the original light image, so that after the photoreceptor 10 is charged and before the image is exposed,
The erase pattern may be irradiated onto the photoreceptor 10,
The exposure section and the erase pattern irradiation section may be located at the same position so that image exposure and erase pattern irradiation are performed simultaneously.

The LED array of the eraser 18 is turned on by the LED driver 58. The LED controller 56 receives a signal from the rotary encoder 50, detects the rotation of the photoreceptor 10, and synchronizes the lighting of the LED array by the LED driver 58 according to the rotation speed.

Irradiation of the erase pattern by the eraser 18 is
Since this is a characteristic feature of the present invention, it will be explained in detail later, but first, the color process will be briefly explained here. In the color electrophotographic process, a document is separated into three primary colors: red, green, and blue, and an electrostatic latent image is formed corresponding to each color separation image. Developed with toner colored in related colors: cyan, magenta, and yellow.

In the following description, exposing a photoreceptor to color-separated original images will be referred to as color-separated exposure, and the electrostatic latent images formed by color-separated exposure will be distinguished by the colors of the color-separated images. For example, an electrostatic latent image formed by color separation exposure with red color is called a red latent image.

Now, the color original 0 is placed on the original placing glass 16. Then, it is determined whether or not to irradiate the erase pattern depending on the document, and if further irradiation is to be performed,
Select and set the erase rate or erase pattern. This point will also be discussed later. In the following explanation, it is assumed that an erase pattern is irradiated.

Next, when a print button (not shown) is pressed, the photoreceptor 10 rotates in the direction of the arrow, and at the same time the static elimination lamp 2
7, the static eliminator 32 and the cleaner 34 operate, and the photoreceptor 1
Then, the charger 12 discharges and charges the photoreceptor 10 uniformly.

On the other hand, the lamp 140 emits light and moves to the left together with the plane mirror 141, illuminating and scanning the original O. At this time, the roof mirror 142 moves to the left at a moving speed that is 1/2 of the moving speed of the lamp 141, so that the photoreceptor 10 is irradiated with the original optical image. At this time, the blue filter F1 of the filter device F is placed in the exposure optical path.
Therefore, a blue latent image is formed on the photoreceptor 10. This blue latent image is irradiated by an eraser 18 at a set erase rate or erase pattern, and developed by a developing device 20 with a yellow 1-toner.

Transfer paper S according to the sea fence of the process.

It is held so as to wrap around the circumferential surface of the holder 28 (which rotates clockwise following the photoreceptor 10). Then, the yellow latent image is first transferred onto the transfer paper S by the transfer device 30.

Subsequently, the photoreceptor 10 is neutralized and cleaned, and then recharged by the charger 12, and the green filter F
A green latent image is formed by color separation exposure using 2. After this green latent image is irradiated with a predetermined erase rate or erase pattern by the eraser 18, the developing device 2
2, the image is developed with magenta j-toner. When the magenta visible image thus obtained is transferred onto the transfer paper S, the photoreceptor 10 is neutralized, cleaned, and recharged.
This time, color separation exposure using red filter F3 is performed. The red latent image created by this color separation exposure is the eraser 1
After being irradiated with a predetermined erase rate or erase pattern by 8, it is visualized with cyan toner by a developing device 24. When the cyan visible image thus obtained is transferred onto the transfer paper S, the transfer paper S is separated from the holder 28 by the splitter 35 and the separation claw 37, and the fixing device [(not shown) After each visible image is fixed in the imager (not shown), it is ejected from the apparatus.

Note that when copying a document in black and monochrome, the monochrome copy mode is selected using a selection button not shown. In the monochrome copying process, N is used as a filter.
A D filter F4 is used, and the light image of the original is irradiated onto the photoreceptor without color separation. The electrostatic latent image obtained by exposure is irradiated with an erase pattern by an eraser 18 (this irradiation can optionally be omitted) and visualized with black toner by a developer 26. The black visible image is transferred and fixed onto the transfer paper S.

In the color copying process, after the cyan visible image is transferred, the monochrome copying process described above may be further performed to further fix the black visible image on the color visible image.

Now, the LED array in the eraser 18 is an array of minute LEDs arranged in one row, and the arrangement density is 10 dots/mm.

The inventors assumed that a light spot irradiated by one LED is one pixel, which is 166 pixels of 4 x 4, and one unit in the erase pattern. - Erase rate models of 1 to L4 shown in Figure 5 (white circles are LED light emitting parts) and Figures 6 to 8
Irradiation using erase pattern models 21 to P3 shown in the figure (white circles are LED light emitting parts) and irradiation without erasing were performed for each color of color separation exposure. When we investigated how the reproduction characteristics changed, we obtained the results shown in FIGS. 9 to 14. In each figure, each γ characteristic curve corresponds to the characteristic when using the erase pattern model indicated by the symbol in parentheses.

Here, image density was measured using a Macbeth densitometer to measure the density of a color image (original, color copy image) and gray scale density, and convert the color image density into gray scale density.

That is, Fig. 9 shows the erase rate models L1 to L4 when exposing with the original light image (visualized with cyan toner) color-separated with the red filter F3 and the γ characteristics in the case without erasing, and the γ characteristics with the green filter F2. Figure 10 shows the γ characteristics for each erase rate model 1 to L4 and in the case of no erase when exposing a color-separated original light image (visualized with magenta toner). FIG. 11 shows each erase rate model Ll-L4 when exposed to a light image (visualized with yellow toner) and the γ characteristics in the case without erasing. Also, the original light image color-separated by red filter F3 (visualized with cyan toner)
Each erase pattern model 21 to P3 when exposed with
FIG. 12 shows the gamma characteristics in the case of 1 and 2 without erasing.
Figure 13 shows the γ characteristics of each erase pattern model P1 to P3 when exposed with a toner (visualized with a yellow toner) and the γ characteristics in the case of no erasing. FIG. 14 shows the γ characteristics of each of the erase pattern models P1 to P3 during exposure and in the case of no erase.

In this way, the optimum erase rate or erase pattern for various originals can be experimentally known in advance.

Now, in the case of the apparatus shown in FIG. 1, the plane mirror 141 is a half mirror, and the transmitted light is reflected by the plane mirror 145 and is incident on the CCD 51.

The CCD 51 receives the optical image of the original, photoelectrically converts it, and outputs it to the arithmetic circuit 52 . The arithmetic circuit 52 performs arithmetic processing on information regarding the image characteristics of the optical image of the original to form a pattern, and finds an erase rate or erase pattern for optimal color adjustment.

On the other hand, the memory 54 is stored in advance with erase rates according to a plurality of erase rate models L1 to L4 shown in FIGS. 2 to 5 or erase rates according to a plurality of erase pattern models P1 to P3 shown in FIGS. 6 to 8.・The pattern is memorized. These gradation effects are as already described with respect to FIGS. 10 to 14.

Therefore, the optimum erase rate or erase pattern calculated by the arithmetic circuit 52 is selected from the information stored in the memory 54, and an instruction to follow it is sent to the LED controller 5.
G, the LED driver 58 lights up the LED array, and the required erase is performed by the eraser 18.
Executed by

Note that it is also possible to manually select which erase rate or erase pattern from the information stored in the memory 54. That is, the operation panel 60 connected to the memory 54 has selection keys 60A displaying cyan, magenta, and yellow corresponding to the colors of the copied image, and letters UP and DOWN indicating the shading tendency of these colors. "1" means the level in the displayed selection key 60B and each of the above-mentioned shading trends.

Selection keys 60C on which the number "2" is displayed are arranged, and color adjustment can be performed by selecting these keys.

For example, erase rate models L1 to L1 shown in FIGS. 2 to 5
To explain the case where L4 is stored in the memory 54, when copying in the normal state without operating the operation panel 60, cyan (Fig. 9), magenta (Fig. io), yellow (11th In FIG. 3, erasing is performed at an erase rate according to the erase rate model L2 (FIG. 3).

Therefore, when copying a certain original, if the redness of the copied image is slightly lacking, select "Magenta" with the selection key 60A on the operation panel 6°, and then select "Magenta" with the selection key 60B.
Select “Up” and press. Select the level depending on the reddish level you want to correct.
If you press ", cyan (Figure 9) and yellow (Figure 11) will be modeled with the same erase rate! , 2, the erase rate for magenta (FIG. 10) is O, that is, there is no erasure. Also, if level "1" of the selection key 60C is pressed, magenta (Fig. 10) is erase rate model L1.
The erase rate follows.゛On the other hand, if the copied image has too much red and you want to reduce the red, press the "Magenta" button on the selection key 60A, then press the "Down" key on the selection key 60B, and then press the "Down" button on the selection key 60B. 1", cyan (FIG. 9) and yellow (FIG. 11) remain unchanged at the erase rate according to the erase rate model L2, and magenta (10th) changes to the erase rate according to the erase rate model L3.

In this way, it is possible to arbitrarily adjust the cyan, magenta, and yellow colors depending on the characteristics of the document to be reproduced and the color that is particularly desired to be reproduced, thereby obtaining a desired color reproduction.

For example, for each color of cyan, magenta, and yellow, there is no erase, Ll, L2. L3. (If you combine the five erase rate patterns of .

Color adjustment is also possible in which the erase rate for each color of cyan, magenta, and yellow is automatically selected from among these to achieve the optimal gray balance that matches the original.

The color adjustment by changing the erase rate has been described above, but the color adjustment can also be performed in accordance with the above description when changing the erase pattern. Further, it is also possible to perform color adjustment by changing the erase rate and erase pattern together.

(Effects) According to the present invention, color adjustment can be easily carried out without performing various strict process controls such as charging potential, exposure amount, and developing bias, which is advantageous.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the main parts of a color electrophotographic apparatus suitable for implementing the present invention, FIGS. 2 to 5 are diagrams illustrating various erase rates, and FIGS. 6 to 8 are diagrams showing various erase patterns. 9 to 14 are gradation reproduction characteristic diagrams for each erase state and color. Ll, L2. L3. L4...Erase rate model, PL, P2゜P3. P41...Erase pattern model. Kyu / X 0C Mai 1 + l Suga 1 Te/4

Claims (1)

[Claims] An erase method in which an erase pattern is irradiated onto a photoconductor at the same time as an exposure process in which a uniformly charged photoconductive photoconductor is irradiated with a color-separated original light image, or before and after the exposure process. A color electrophotographic method in which an electrostatic latent image corresponding to a color-separated image is developed with colored toner, and is characterized by changing the erase rate or erase pattern depending on the color-separated colors. Color correction method in color electrophotography.