JPS6398671A - Color copying method - Google Patents

Abstract

PURPOSE:To practically detect a black image by a simple process by counting black-and-white picture elements in a block of mXn picture element constitution and regarding a part which is considered to be a black-and-white block as an object of development using only black toner. CONSTITUTION:The image of a color original 0 is read by a color scanner while separated into red, green, and blue picture elements. Data on the every m.n picture elements are made into a block with an m.n matrix. Black-and- white picture elements in this block are counted to judge whether each picture element in one block is a black-and-white picture element or a color picture element, so that they are developed in a black-and-white or color binary picture element map memory. When it is known that all blocks are black-and-white or color blocks, an electrostatic latent image is worked accordingly. Namely, an analog color copying machine erases the electrostatic latent image in block units by a dot eraser 22 according to the storage contents of a block map memory. Consequently, the black image part of a color original is copied and reproduced in pure black by using black toner.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a color copying method.

(Prior art) An analog or digital color copying device that has a color scanner that separates and reads a color document into red, green, and blue, and a developing device for each color that uses yellow, magenta, cyan, and black toner. It has been known.

In this type of color copying method, black pixels can be reproduced by superimposing images of cyan, magenta, and yellow toner colors, but the black color reproduced with these three toner colors is not necessarily pure black; The copying apparatus described above, which does not look very beautiful, has a developing device that uses black toner, so it is desirable to visualize black images on color originals using only black toner.

For this reason, conventional attempts have been made to read a color original by color separation, detect a black image area, and develop this black image area using only black toner.

For example, in the method disclosed in JP-A-60-104967, a line image is defined as a thermal image, a line image and a gradation image are distinguished, and the line image is reproduced with black toner. I try to do that. However, in actual color manuscripts, line images are not necessarily black images, so
With this method, it is not possible to completely reproduce a black image as pure black.

Various algorithms have been proposed for detecting black image areas from data obtained by reading color originals, but none are perfect yet. 5 The ones that are close to perfect require a huge amount of calculations to process the data. Therefore, it lacks practicality.

(Purpose) The present invention was made in view of the above-mentioned circumstances, and
The objective is to provide a novel color copying method that allows black images to be practically detected through simple processing.

(composition) The present invention will be explained below.

The color copying method of the present invention prints a color original in red.

It has a color scanner that separates and reads the colors into green and blue, and a developing device for each color that uses yellow, magenta, cyan, and black toner. It may be implemented in an analog or digital color reproduction machine.

The above-mentioned developing devices are four developing devices: a yellow developing device using yellow toner, a magenta developing device using magenta toner, a cyan developing device using cyan toner, and a black developing device using black toner.

Now, in this specification, the following two methods are proposed.

The first type of method has the following characteristics.

Data obtained by reading a color original is divided into blocks of mXn pixels. And for each block,
Count the number of black and white pixels in the block. If the number of black and white pixels in the block is 50% or more of m×n,
The block is a black and white block, and the black and white block is subjected to development with black toner. That is, when the black developing device performs development, the electrostatic latent image on the photoreceptor is made up of only black and white blocks.

The electrostatic latent image itself is formed as an analog latent image or a dot latent image using an area modulation method within each black and white block.

The second type of method is a further improvement of the first type of method. That is, in this second type of method,
The number Y of image pixels in a block composed of m×n pixels and the number X of black and white pixels among these Y image pixels are counted.

Then, the relationship between Y and X above is examined using X/Y, and X/Y is
When it is 0.75 or more, that is, when the proportion of black and white strokes in the image pixels is 75% or more, the block is treated as a black and white block and is targeted for development with only black toner. Namely.

When the black developing device performs development, the electrostatic latent image on the photoreceptor is made up of only black and white blocks. The electrostatic latent image itself is formed as an analog latent image, a dot latent image using an area modulation method, or the like within each black and white block.

The above two methods of the present invention are based on J! It is based on the following discoveries made by the author.

In other words, the Ministry of Invention and Innovation has discovered that regardless of text or design, if areas with a large amount of black are developed with black toner and areas with a small amount of black are developed with yellow, magenta, and cyan color toners, black text and color can be developed. This allows you to copy originals containing mixed images as desired.

In the case of the method of the present invention, there is a side effect that the dark parts of the picture are copied darker, but in the case of color copying of a color original to be copied, the above side effect does not become a problem. it is conceivable that.

Hereinafter, description will be given based on specific examples.

3 and 4 show a color copying machine to which the present invention is applied. The device shown in Figure 3 is of an analog type,
The apparatus shown in FIG. 4 is of a digital type. Since the configurations of these copying devices themselves are well known, the configurations will be briefly explained.

In the apparatus shown in FIG. 3, a color original O to be color-copied is flatly fixed on an original glass 10. As shown in FIG.

Reference numeral 12 indicates an exposure device. This exposure device 12 includes a movable lamp 121, movable mirrors 122, 123 . lens 1
24 and a half mirror 125, by turning on the movable lamp 121 and moving the movable mirrors 122 and 123 in the direction of the arrow, the color original 0
Perform illumination scanning.

At this time, image exposure of the photoreceptor 18 is performed by rotating the photoreceptor 18 in the direction of the arrow.

At this time, one color separation can be performed by switching the filters in the filter group [15].

In the conventionally known normal copying process, first, an electrostatic latent image corresponding to a red separated image of the original O is formed on the photoreceptor 18 charged by the charger 20, and this electrostatic latent image is transferred to the developing unit. 24 cyan color developer [visualized with cyan toner at 24C. The cyan visible image thus obtained is transferred onto the transfer paper S after being irradiated with light by the pre-transfer lamp 26.

The transfer paper S is discharged from a cassette (not shown), sent out to be held on the transfer drum 28 by a registration roller (not shown), held on the transfer drum 28, and has a cyan visible image transferred thereto by a transfer charger 30. Ru.

Thereafter, the photoreceptor 18 is charged and cleaned by a static eliminator 32 and a cleaner 34, and then the charger 2
0, it is uniformly charged again.

Similarly, formation of an electrostatic latent image corresponding to the green separated image, development by the magenta developing device 24M, transfer of the magenta visible image, formation of an electrostatic latent image corresponding to the blue separated image, and development by the yellow developing device ! Developed with 24Y.

Transfer of a yellow color visible image, image exposure with an original light image that is not color-separated (using an ND filter of a filter device), development by a black developing device 24B, and transfer of a black visible image are performed, and a color image is transferred onto the transfer paper S. A visible image is formed.

Then, the transfer paper S is transferred to the minute charger 36 and the separation claw 3.
It is separated from the transfer drum 28 by the action of the fixing device 4.
0, the color visible image is fixed and discharged from the apparatus.

Now, when illumination scanning of the original is performed, a part of the imaging light beam passes through the half mirror 125 and forms an image on the 1-1 magnification color sensor 16 via the mirror 14.

The operation of the same-size color sensor 16 is controlled by the controller 42, and the color original 0 is colored red and green.

The color is separated into blue and read, and the data for each pixel is sent to the controller 42. Therefore, in the apparatus shown in FIG. 3, the exposure device [12, the mirror 14, and the same-magnification color sensor 16] constitute a color scanner.

Further, in FIG. 3, the reference numeral 22 indicates a dot eraser.
The dot eraser 22 is a combination of an LED array and a convergent light transmitting array, and performs color correction, gradation correction, erasing, etc. for each electrostatic latent image under the control of the controller 42. At this time, the timing of blinking the LEDs in the LED array is controlled by the controller 42 using a rotary encoder 50 that detects the rotational position of the photoreceptor 18.

The apparatus shown in FIG. 4 is a digital color copying machine, and parts common to the apparatus shown in FIG. 3 are designated by the same reference numerals as in FIG. 3.

Reference numeral 12A indicates a color scanner, and the color scanner 12A includes a movable lamp 121. Movable mirror 122
．． 123, lens 125, color separator 127 using a dichroic ivy filter, and image sensor 16A.

16B and 16C, a color original 0 is illuminated and scanned by a lamp 121 and mirrors 122 and 123, the imaging light beam is separated into red, green, and blue by a color separator 127, and each color separated image is sent to an image sensor 16A. , 16B, 16
Read with C.

Reference numeral 13 indicates a part of the printer. The structure of a part of the printer is similar to the apparatus shown in FIG. Created.

The developing unit 25 includes a cyan developing device 25C, a magenta developing bag [25M], and a yellow developing device 25Y.

It has a black developing device 25B, and each of these color developing devices develops an electrostatic latent image to be developed.

The visible image is transferred and fixed onto the transfer paper in the same manner as in the apparatus shown in FIG.

The above is an overview of the color copying apparatus shown in FIG. 3.4.

Below, the features of the color copying method of the present invention will be explained in relation to these two types of color copying apparatuses.

First, the first type of method will be explained with reference to FIG.

In FIG. 1, the input image is an image of a color original O, which is read by separating the colors into red, green, and blue for each pixel by the color scanner described above. That is, the luminance signal is converted into a density signal and read, and the information of each pixel is converted into data as image density by red separation, image density by green separation, and image density by blue separation.

These data for each pixel are divided into m'n blocks as an m×n matrix. The theoretical limit for the numerical values of m and n is that m, n) 1 < leprosy, but it is convenient for both m and n to be 6 to 12 < leprosy, and in this example, m=n”
It is said to be 8. The data of one pixel for each color separation is 8
It's bit.

Therefore, the read data is divided into blocks of 8×8 matrices, and the number of black and white pixels within this block is counted. For this purpose, each pixel must
It must be determined whether it is a black and white pixel or a color pixel.For this determination, black and white images, that is, intangible color images, have approximately the same density when color-separated, regardless of the color of the color separation. Take advantage of the fact that it remains constant.

When one pixel is separated into red, green, and blue, the image density is called R, G, and B, respectively. Therefore, to determine whether it is a black and white pixel or a color pixel, the density differences between these image densities R, G, and B, IR-Gl, IG-Bl,
Find IB-R1, the largest one of them, ΔID
Set to max. When ΔIDmax≦0.1, it is assumed that there is no substantial difference between the image source degrees R2G and B, and the pixel is determined to be a black and white pixel. As data, black and white pixels are 1. Color pixels are set to 0. A color pixel is determined according to the condition of ΔIDmax≧0.11.

In this way, each pixel in one block is determined one by one as to whether it is a monochrome pixel or a color pixel, and is expanded into a monochrome or color binary pixel map memory.

The binary pixel map memory outputs one block at a time as an 8 x 8 matrix, and the number of black and white pixels in that block is 50% or more of the total number of pixels of the block, 64.
That is, when there are 32 or more blocks, the block is defined as a monochrome block, and in other cases, the block is defined as a color block. Then, the results are expanded block by block into a monochrome or color binary block map memory.

Note that this determination process is performed by a controller, which is, for example, a microcomputer. □Table 1 shows specific examples.

Table 1 The underlined number in the density difference column of Table 1 is ΔIDmax.

In this way, once it is known for each block whether it is a monochrome block or a color block, the electrostatic latent image is modified accordingly.

That is, in the analog type color copying machine shown in FIG. 3, depending on the contents of the block map memory,
The dot eraser 22 erases the electrostatic latent image block by block.

That is, from the electrostatic latent images developed by the cyan, magenta, and yellow developing devices, all the latent image portions corresponding to black and white blocks are erased, and conversely,
From the electrostatic latent image to be developed by the black developing device, all electrostatic latent image portions corresponding to other color blocks are erased, leaving behind the latent image portions of the black and white blocks.

In addition, in the digital color copy i[1 shown in Fig. 4, the electrostatic latent image to be developed by the cyan, magenta, and yellow color developing devices is written with a laser scanner so that black and white block portions are omitted. form. Conversely, when forming an electrostatic latent image to be developed by the black developing device, only the latent image of the black and white block portion is formed.

In this way, the Illll power stagnation in the black and white block section will be
Since the image is developed using only black toner, a black image on a color document can be expressed using pure black toner.

The above is the first type of method. This method still has the problem that if there is colored text on a white background, the block in this area is determined to be a black and white block, so the colored text is copied in black.

The second type of method described below solves this problem. See Figure 2. Although the principle restriction for n and m is m, n>1, the case where n=m=8 is taken as an example here as well.

The input image is obtained by reading a color original with a color scanner and converting the luminance signal of each pixel into a density signal for each color separated image, each of which is 8 bits.

On the one hand, from the image densities R, G, and B based on the density signals, the maximum value ΔIDmax of the density difference for each pixel is calculated, as in the first type method, and the value of ΔIDmax is 0.0.
Is it a black and white pixel depending on whether it is less than 1 or more than 0.11?

Color pixels are determined for each pixel, and the results are as follows.

Developed in black and white or color binary pixel map memory.

On the other hand, the image densities R, G, and B are used to determine whether the pixel is a background pixel or an image pixel. For this judgment, generally the image density of the background pixel is R,
Both G and B are 0. Take advantage of the fact that it is smaller than IO.

Therefore, from the image density R, G, and B for each pixel, IDR=R
-0,10 IDC = G -0,10 IDB = B -0,10 are calculated, IDR<O, IDG<O, IDB<0
When all of these are true, the pixel is determined to be a background pixel, and
In other cases, the pixel is assumed to be an image pixel.

In this way, the 8.times.8 pixel matrix is used as one block, and the background pixels and image pixels in each block are discriminated, and the results are expanded into one pixel or background binary-pixel map memory.

In the next step, the number B of image pixels in each block and the number A of pixels that are one image pixel and black and white pixels in the block are determined. Therefore, the number of pixels A is the number of black and white pixels among the B image pixels.

These pixel numbers A and B are subjected to an arithmetic process called A/B. When the result of the calculation is 1≧0.75, the block is determined to be a monochrome block, and otherwise, it is determined to be a color block. This judgment is then made for each block,
The results are developed into a black and white or color binary block map memory.

Therefore, in the analog type color copying apparatus shown in FIG. 3, the electrostatic latent image portion to be developed by the cyan, magenta, and yellow color developing devices.

The dot eraser erases the latent image portions corresponding to the black and white blocks, and conversely, the dot eraser erases the latent image portions corresponding to the color blocks from the electrostatic latent image to be developed by the black developing device.

In addition, in the digital color copying apparatus shown in FIG. 4, the electrostatic latent images to be developed by the cyan, magenta, and yellow color developing devices are formed except for the black and white block portions, and are developed by the black developing device. The desired electrostatic latent image is formed except for the color block portion.

Specific examples are shown in Table 2.

Table 2 (Effects) According to the present invention, a novel color copying method can be provided. Since this method is configured as described above, the black image portion of a color original can be copied and reproduced as pure black using black toner.

[Brief explanation of the drawing]

FIG. 1 is a flowchart for explaining the first type of method of the present invention, FIG. 2 is a flowchart for explaining the second type of method, and FIGS. 3 and 4 are for explaining the method of the present invention. 1 is a diagram illustrating analog and digital color copying apparatuses to which the invention can be applied. 16...Color life-size sensor, 16A, 16B
, 16C... Image sensor-124, 25...
・Developing unit. Foil 4 Mouth Dust 2 Diagram

Claims (1)

[Claims] 1. An analog or digital system having a color scanner that separates and reads a color original into red, green, and blue, and a developing device for each color that uses yellow, magenta, cyan, and black toner. A color copying method executed in a color copying device, in which black and white pixels in a block consisting of m×n pixels are counted, and the number of black and white pixels in the block is 50% or more of m×n. , a color copying method characterized in that the block is a black-and-white block, and the portion designated as a black-and-white block is subjected to development with only black toner. 2. Executed on an analog or digital color copying machine that has a color scanner that separates and reads a color original into red, green, and blue, and a developing device for each color that uses yellow, magenta, cyan, and black toner. A color copying method in which image pixels in a block consisting of m×n pixels and black and white pixels in the image pixels are counted, and the proportion of black and white pixels among the image pixels in this block is calculated. A color copying method characterized in that when the percentage is 75% or more, the block is treated as a black and white block and is subjected to development with only black toner.