JPH02249364A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To improve the color reproduction of a low saturation at a color gradation picture and to reduce color ghost of a black character by varying an area coloring an achromatic color and a chromatic color in response to the result of discrimination of a picture discrimination processing means discriminating the kind of a picture from a color read signal. CONSTITUTION:A color code outputted from a color code generating section 2 is supplied to a color code correction section 5, and a color code of an intermediate color is corrected into a color code whether or not the code is a black or chromatic color code based on the discrimination signal (signal discriminating a color gradation picture and an achromatic (black) character picture) generated by a picture discrimination section 4. That is, when the picture under processing is a color gradation picture, the color code of the intermediate color is corrected into a chromatic color code and when the picture during processing is a black character picture, the intermediate color code is corrected into the black color code. Thus, the color reproduction with low saturation in the color gradation picture is improved and color ghost of black character is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a color image processing device, and more specifically,
The present invention relates to a color image processing device with excellent color reproducibility.

(Background of the invention) Red R1 Green G for color images such as character drawings and photographic images.

It is divided into blue B and optically read, and this is yellow Y.

There is a color image processing device that converts (color reproduction or color correction) into recording colors such as magenta M, cyan C1 and black, and records on recording paper using an electrophotographic color output device based on this. .

FIG. 8 is an explanatory diagram showing the state of color discrimination (chromatic color/achromatic color discrimination) in the color image processing apparatus as described above. In the cube shown, the front side in the horizontal direction is R
The concentration is The vertical direction is the density of B, and the depth direction is the density of G. Therefore, the lower left front, where the R, G, and B densities are all zero, is white, and the upper right back, where all the densities are maximum, is black. Therefore, the area connecting white and black corresponds to an achromatic color (gray) area, and the other areas correspond to chromatic color areas.

By the way, there are the following conflicting problems regarding the setting of this achromatic color area.

■Color ghost (
In order to reduce the amount of unnecessary color (that occurs at the edges of black text), I want to make the achromatic color area as wide as possible.

■In the case of color gradation, in order to accurately reproduce colors with low saturation (for example, brown, dark blue, purple, etc.), it is desirable to make the achromatic color area as narrow as possible.

(Problem to be solved by the invention) Due to the above-mentioned conflicting demands, the reality is that a compromise is made by setting an achromatic color range within a range that would not cause dissatisfaction with both parties. .

However, in reality, the low saturation color reproduction of color gradation teeth was not satisfactory. That is, since the achromatic color area has a constant width as described above, the low chroma portion is reproduced as black.

On the other hand, even when reproducing black character images, color ghosts occur, making it impossible to obtain satisfactory results.

The present invention has been made in view of the above-mentioned problems, and its purpose is to improve low saturation color reproduction in color gradation teeth, and to reduce color ghosts in black characters. The objective is to realize a color image processing device.

(Means for Solving the Problems) The present invention solves the above problems in a color image processing device that performs image processing by dividing color read signals into achromatic colors and chromatic colors. The present invention is characterized in that an image discrimination processing means for discriminating the type is provided, and an area for color classification into achromatic colors and chromatic colors is changed according to the discrimination result of the image discrimination processing means.

(Function) In the color image processing device of the present invention, the color-coded areas of achromatic colors and chromatic colors are changed depending on the processing result of image discrimination.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an embodiment of the present invention.

In the figure, reference numeral 1 denotes a density conversion unit that converts 8-bit digital data for each of RlG and B provided from the outside into 6.6.5-bit data. 2 is the density conversion section 1
This is a color code generation unit that receives R, G, and B data from the computer, discriminates between white/black/chromatic colors/intermediate colors, and outputs a color code. 3 receives R, G, B data,
Y, M.

This is a color reproduction unit that performs color reproduction processing to generate data for C and C. Reference numeral 4 denotes an image discriminating section which receives G 8-bit data and discriminates whether it is a black character surface or a color gradation image based on the density gradient thereof. Reference numeral 5 denotes a color code correction section which receives data from the image discrimination section 4 and sorts intermediate color codes into chromatic or achromatic color codes. 6 is Y, M, C from color reproduction section 3 according to the corrected color code.
, K selectively passes the density data.

7 is a color ghost correction unit that performs color ghost correction;
8 is a filter processing section that performs various filter processing, and 9 is a gradation correction section that corrects gradation characteristics.

Hereinafter, the overall general operation of this embodiment will be explained, and then the present invention will be explained in detail.

The original image is read by an image reading unit (not shown), and R, G
, B is converted into 8-bit digital data. The R, G, and B digital data are
The signal is supplied to the density conversion section 1. In the density conversion section 1, the 8-bit data is converted into 6 and 6 bits, respectively, in accordance with human visual characteristics.
．． Converted to 5-bit data. And R, G, B
The output data of the density conversion section 1 is applied to a color code processing section 2 and a color reproduction section 3. The color code processing unit 2 outputs a color code indicating whether each pixel belongs to white, black, achromatic color, or intermediate color, as described later, based on the level of each R, G, and H data.

FIG. 2 is an explanatory diagram showing the state of generation of a color hood in the color code generation section 2. In the cube in the figure, the front side in the horizontal direction is the density of R. The vertical direction is the density of B, and the depth direction is the density of G. Therefore, R,
The lower left front where the G and B densities are all zero is white (color code: 00), and the upper right back where all the densities are maximum is black. Here, we set a narrow achromatic color (color code: II) area (color code: II) connecting white and black (achromatic color is recorded with black toner, henceforth referred to as black), and a relatively wide intermediate color area (color code: ;01). Then, the area other than this is defined as a chromatic color area (color code: 10
). That is, only areas that are achromatic (black) are always set as black areas in both cases of black text and color gradation images. Then, in the case of a color gradation surface, an area of low saturation is set, and in the case of a black character image, an area where there is a possibility of color ghost is set as an intermediate color area.

Therefore, the color code generation unit 2 generates the above 2-bit color code (white; 00. black, 11., intermediate color; 01.
．． Outputs chromatic color; lO).

This color code is supplied to the color code correction section 5. Then, the color code correction unit 5 changes the intermediate color code (Ol) from black (11) to black (11) based on the discrimination signal (signal for discriminating between a color gradation surface and a black character image) generated by the image discrimination unit 4. Correct the color code to be colored (■0). That is, when the image being processed is a color gradation surface, the intermediate color code is modified to a chromatic color code to improve the reproducibility of low chroma colors. Furthermore, if the image being processed is a black character image, the intermediate color code is corrected to a black color code to suppress the occurrence of color ghosts.

FIG. 3 is an explanatory diagram for explaining the state of image discrimination. In the figure, X is the pixel of interest for which image discrimination is to be performed, ■ is the pixel one line before, W is the pixel one pixel before, and Y
is the pixel after one pixel, and Z is the pixel after one line. Here, the density gradient is determined using the density data (8 bits) of each pixel.

That is, the density gradient S of the pixel of interest X is determined by the following formula % Formula % In this way, the S parameter of the density gradient of the surrounding pixels is determined.

In addition to this S parameter, S' -IV-XI+1W-XI -...■S'
-IV-Zl+1W-Yl -... ■Although the parameter S' uses only two peripheral pixels, the discrimination ability is not sufficient, and S' has three pixels in the sub-scanning direction.
It has the disadvantage that it requires a large number of image memories because it requires pixels.

Therefore, we will use the S-parameter of equation 0, which has a small capacity and high discrimination ability.

FIG. 4 is a block diagram showing details of the figure image discriminating section 4. As shown in FIG. In the figure, 11 is a register that holds data of pixel Y;
12 is a register that holds the data of pixel X, 13 is a register that holds the data of pixel W, 14 is a subtractive absolute value circuit that performs subtraction between W and Y and generates the absolute value (IW-Yl), and 1516 is a register that holds the data of pixel X. Register holding data of pixel V, 1
7 is the absolute λ・1 value (IV-X,
18 is a subtraction absolute value circuit that generates 14 and 17. (IW-YI+1V-Xl
), 19 is a threshold generation circuit that generates a density gradient threshold value, and 2o is a comparison circuit that generates an image discrimination signal by comparing the addition output of the addition circuit 18 with the threshold value.

Next, this image discrimination will be explained from the aspect of color. C
In the chromaticity plane * * ab in IE's Lab uniform color space, each color code of black, intermediate color, and chromatic color is set in the color area as shown in FIG. 5A.

The area of this color code is defined by the following formula: Q, R, G,
It is determined by the reading level of B (8 bits; 0 to 255).

Here, Ifz = (R+2G+B) 15°Wo-
It is 255.

(1) When Q≦15 and G>180, color code 200 (2) (2) When Q≦7.5 and G≦180, color code =
11 (black) (3) When 7.5≦Q≦15 and G≦180, color code 201 (intermediate color) (4) Q>15 Color code = 10 (chromatic color) The parameter S is determined as follows, and this S is compared with the threshold value T. When 3S>T, it is determined that it is a black character, and the intermediate color area is set as the black area (Fig. 5B
). Further, when S≦T, it is determined that it is on the color gradation side, and the intermediate color area is set as a chromatic color area (FIG. 5C).

FIG. 6 shows the cumulative distribution obtained from the histogram of the density gradient parameter S of intermediate colors.

In the figure, the color gradation side indicates the proportion of chromatic color codes, and the black letters indicate the proportion of black codes.

Where the two intersect, the discrimination rate will be the same. In this case, the discrimination rate becomes 82.4% at the threshold value T-51.

Therefore, the threshold value T is set to 51 to discriminate between the color gradation side and the black character image.

After the color code is corrected in this way, based on the corrected color code and scan code (code indicating the color recorded by the printer),
, C, selectively passes through the selector 6. That is, when the corrected color code is a chromatic color (10), Y, M, and C from the color reproduction section 3 pass through the selector 6. Further, when the corrected color code is black, K from the color reproduction section 3 passes through the selector 6.

Then, color ghost correction, filter processing, floor and M correction are performed, and the image is output. Then, it is supplied to an external printer unit or the like, and an image is formed on the recording paper.

As described above, in the present invention, the color code is divided into chromatic color/black/white/intermediate color, and the intermediate color is divided into black or chromatic color according to the result of image discrimination. For this reason,
In a black character image, the intermediate color area becomes a black area, and color ghosts do not occur. Furthermore, on the color gradation side, the intermediate color area becomes a chromatic color area, and chromatic colors with low saturation can also be reproduced satisfactorily.

Hereinafter, the configuration and operation of each part of a color copying machine to which the color image processing apparatus of the present invention is applied will be explained with reference to FIG. Note that this color copying machine uses a color dry development method. In this example, two-component non-contact development and reversal development are employed.

That is, the transfer drum used in conventional color image formation is not used, and the images are superimposed on the electrophotographic photosensitive drum that forms the image. In the example below, yellow and magenta are printed on the OPC photoreceptor (drum) for image formation in order to reduce the size of the apparatus.

A four-color image of cyan and black is developed with four rotations of the drum,
After development, transfer is performed once to transfer onto recording paper such as plain paper.

By turning on the copy button of the color copying machine, the original reading section A is driven. And the manuscript table 128
An original 101 is optically scanned by an optical system.

This optical system uses a light source such as a halogen lamp at 129°]30
and a carriage 132 provided with a reflective mirror 131.
It is composed of a movable mirror unit 134 provided with V mirrors 133 and 133'.

The carriage 132 and the movable unit 134 are caused to travel on slide rails 136 at predetermined speeds and directions, respectively, by a stepping motor 135.

Optical information (image information) obtained by irradiating the original 101 with the light sources 129 and 1.30 is transmitted to the optical information conversion unit 13 via the reflecting mirror 131 and the mirrors 133 and 133'.
Guided by 7.

A standard white plate 138 is provided on the back side of the left end of the platen glass 1.28. This is because the image signal is normalized to a white signal by optically scanning the standard white plate 138.

The optical information conversion unit 137 includes a lens 139, a prism 140, and two dichroic mirrors 1°02.103.
and a CCD 104 that captures a red color-separated image, a CCD 105 that captures a green color-separated image, and a CCD 106 that captures a blue color-separated image.

The optical signal obtained by the optical system is collected by the lens 139, and separated into blue optical information and yellow optical information by the dichroic mirror 102 provided in the prism 140 described above. Furthermore, dichroic mirror 103
The yellow optical information is color-separated into red optical information and green optical information.

In this way, the color optical image is decomposed by the prism 140 into three-color optical information of red, R, green, and blue.

Each color separation image is formed on the light receiving surface of each CCD, thereby obtaining an image signal converted into an electrical signal.

After the image signal is processed by the signal processing system, each color signal is output to the writing section B.

The signal processing system includes various signal processing circuits such as the density converter 1 to gradation corrector 9 shown in FIG. 1, as well as an A/D converter and the like.

The writing section B has a deflector 141. As this deflector 141, in addition to a galvanometer mirror, a rotating polygon mirror, etc.
A deflector consisting of an optical deflector using crystal or the like may be used. The laser beam modulated by the color signal is deflected and scanned by this deflector 141.

When deflection scanning is started, beam scanning is detected by a laser beam index sensor (not shown), and beam modulation using a first color signal (for example, a yellow signal) is started. The modulated beam is applied to an image forming member (photosensitive drum) 1 which is charged with a negative charge by a charger 154.
42 is scanned.

Here, the main scanning by the laser beam and the image forming body 142 are performed.
Due to the sub-scanning caused by the rotation of the image forming member 142, an electrostatic latent image corresponding to the first color signal is formed on the image forming body 142.

This electrostatic latent image is transferred to a developing device 14 containing yellow toner.
3 to form a yellow toner image.

Note that a predetermined developing bias voltage from a high voltage source is applied to this developing device.

Toner is supplied to the developing device 143 when necessary by controlling a toner replenishing means (not shown) based on a command signal from a system control CPU (not shown). . The yellow toner image described above is rotated with the cleaning blade 147a released from pressure, and an electrostatic latent image is formed based on a second color signal (for example, a magenta signal) in the same manner as in the case of the first color signal. .The developing device 1 contains magenta toner.
44, this is developed to form a magenta toner image.

Needless to say, a predetermined developing bias voltage is applied to the developing unit 144 from a high voltage power supply.

Similarly, an electrostatic latent image is formed based on the third color signal (cyan signal), and a developing device 145 containing cyan toner is provided.
A cyan toner image is formed. Further, an electrostatic latent image is formed based on the fourth color signal (black signal), and is developed in the same manner as the previous time using the developing device 146 filled with black toner.

Therefore, multicolor toner images are formed on the image forming body 142 in an overlapping manner.

Although the formation of a four-color multicolor toner image has been described here, it goes without saying that a two-color or single-color toner image can be formed.

As described above, the development process is a so-called two-component development process in which each toner is caused to fly toward the image forming body 142 while AC and DC bias voltages from a high-voltage power source are applied. An example of non-contact development was shown.

Furthermore, toner replenishment to the developing units 144', 145, and 146 is performed based on a command signal from the CPU, as described above, with a predetermined amount of toner.

On the other hand, the recording paper P fed from the paper feeding device 148 via the feed roll 149 and the timing roll 150 is conveyed onto the surface of the image forming body 142 in a state in which the timing is synchronized with the rotation of the image forming body 142. Ru. Then, the multicolor toner image is transferred onto the recording paper P by the transfer pole 151 to which a high voltage is applied from the high voltage power source, and the separation pole 152
separated by

The separated recording paper P is conveyed to the fixing device 153, where it undergoes a fixing process and a color image is obtained.

The image forming body 142 after the transfer is transferred to a cleaning device 147
is cleaned and prepared for the next imaging process.

In the cleaning device 147, a predetermined DC voltage is applied to the metal roll 147b in order to facilitate recovery of the toner cleaned by the cleaning blade 147a. This metal roll 147b is placed on the surface of the image forming body 142 in a non-contact state. cleaning blade 1
47a is released from pressure bonding after cleaning is completed, but in order to release unnecessary toner that is left behind at the time of release, an auxiliary roller 147C is further provided, and this auxiliary roller 147c is rotated in the opposite direction to the image forming body 142 and is pressed against the image forming member 142. As a result, unnecessary toner is sufficiently cleaned and removed.

Incidentally, in the above embodiment, an example in which the color image processing apparatus of the present invention is applied to a color copying machine has been described, but it goes without saying that the color image processing apparatus of the present invention can be used in various types of equipment other than this.

(Effects of the Invention) As described in detail above, in the present invention, when classifying chromatic colors and achromatic colors, an intermediate color area is set, and this intermediate color area is divided into chromatic colors or achromatic colors depending on the type of image. I did it like that. Therefore, it is possible to realize a color image processing device that can improve low chroma color reproduction at color gradations and reduce color ghosts of black characters.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram explaining how color code is generated, FIG. 3 is an explanatory diagram explaining how image discrimination is performed, and FIG. Figure 5 is a configuration diagram showing an example of the configuration of the image discrimination section, Figure 5 is an explanatory diagram showing the state of color classification, Figure 6 is a characteristic diagram showing the relationship between density gradient and image discrimination, and Figure 7 is the entire color copying machine. FIG. 8 is an explanatory diagram showing how a conventional color code is generated. 1... Density conversion section 2... Color code generation section 3... Color reproduction section 4... Image discrimination section 5.
...Color code correction section 6...Selector 7...Color ghost correction section

Claims (1)

[Scope of Claims] A color image processing device that performs image processing by classifying a color read signal into achromatic colors and chromatic colors, further comprising an image discrimination processing means for discriminating the type of image from the color read signal; 1. A color image processing device, characterized in that the color image processing device is configured to change an area for color classification into achromatic colors and chromatic colors according to a determination result of a processing means.