JPH02280573A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To improve the gradation characteristic in a color gradation picture and to improve the resolution in a character picture by varying a region coloring an achromatic color and a chromatic color according to the mode set externally and executing the picture processing different from the chromatic color area and the achromatic color area. CONSTITUTION:A color code generating section 2 sets an area of an achromatic color tying white and black levels narrow and sets a comparatively wide intermediate color area. Then other areas are used for chromatic areas. Then in the case of color gradation picture, an area of low saturation is set as an intermediate color area and in the case of a black character picture, an area having possibility of color ghost is set as an intermediate color area. The color code is fed to a color code correction section 5. When the picture during processing is a color gradation picture, the color code of an intermediate color is corrected as the chromatic color code to improve the reproducibility of the color with low saturation. Moreover, when the picture during processing is a black character picture, the color code of intermediate color is corrected into a black level color code to suppress the production of color ghost.

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 that has excellent color reproducibility in both character images and color gradation teeth.

(Background of the Invention) Color images such as character drawings and photographic images are divided into red, R, green, blue, and B and optically read.

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. 5 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.

■Achromatic colors are used to reduce color ghosts (unnecessary colors that appear at the edges of black characters) that occur in black character images due to color shifts between R, G, and B of the CCD sensor and chromatic aberration of the lens. It is necessary to make the 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 necessary to make the achromatic color area as narrow as possible.

(Problem to be Solved by the Invention) Due to the conflicting demands mentioned above, a compromise has been made by setting a photo mode and a text mode, and setting an achromatic color range within a range that does not cause dissatisfaction with each mode. It was reality.

However, in reality, the color reproduction of low saturation within the color gradation in the photo mode 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, and satisfactory results have not been obtained.

The present invention has been made in view of the above-mentioned problems, and its purpose is to improve low-saturation color reproduction within color gradations and improve gradation characteristics, as well as improve the resolution of character images. The object of the present invention is to realize a color image processing device that can improve color image processing and reduce color ghosts.

(Means for Solving the Problems) The present invention solves the above-mentioned problems in a color image processing device that performs image processing by dividing a color read signal into achromatic colors and chromatic colors, according to a mode set from the outside. The present invention is characterized in that it is configured to change the area in which the achromatic color and chromatic color separation are performed, and to perform different image processing on the chromatic color area and the achromatic color area.

(Function) In the color image processing device of the present invention, the color-coded regions of achromatic colors and chromatic colors are changed according to the set mode, and different image processing is performed in each region.

(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 each of R2O 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 white/black/chromatic color/intermediate color, 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 processing mode setting section for setting (selecting) a character mode for processing character images and a photo mode for processing within color gradation. The mode setting in the image processing mode setting section 4 is performed from outside (operation section, etc.). Reference numeral 5 denotes a color code correction section that receives an image processing mode setting signal from the image processing mode setting section 4 and sorts the intermediate color code into a chromatic color or an achromatic color load. A selector 6 selectively passes the Y, M, C, and K density data from the color reproduction section 3 according to the corrected color hood. 7 is a color ghost correction section 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. Note that the filter processing section 8 and the gradation correction section 9 perform different processing in each mode depending on the image processing mode setting signal.

The operation of this embodiment will be explained below.

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 then supplied to the density conversion section 1. In the density conversion unit 1, the 8-bit data is converted into 6.0 pixels each according to human visual characteristics. 6.
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 B data.

FIG. 2 is an explanatory diagram showing how the color code is generated by the color code generating section 2. As shown in FIG. 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 area (color code; 11), which connects white and black (achromatic colors are recorded with black toner, henceforth referred to as black), and a relatively wide intermediate color area (color code). ;Ol). Then, the area other than this is set as a chromatic area (color code: 10)
. In other words, only areas that are achromatic (black) are always set as black areas in both black character images and color gradation images. Then, in the case of a color gradation side, an area of low saturation is set, and in the case of a black character image, an area where there is a possibility of a color ghost is set as an intermediate color area. CIE
When shown in the L*a*b* uniform color space, it becomes as shown in FIG. 3A.

Therefore, the color code generating section 2 outputs the above-mentioned 2-bit color code (white: 00.black, U, intermediate color: old, chromatic color, 1G).

This color code is supplied to the color code correction section 5. Then, the color code correction unit 5 uses the image processing mode setting signal (signal for setting the color gradation image mode/character image mode) generated by the image processing mode setting unit 4 as a reference, and the color code of the intermediate color ( 01) to the color code of black (11) or chromatic color (lO). In other words, if the image being processed is on the color gradation side, the intermediate color code should be modified to the chromatic color code.
), to improve the reproduction of low-saturation colors.

Also, if the image being processed is a black character image, the intermediate color code should be changed to black (Figure 3B).
Suppress the occurrence of color ghosts.

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.

And color ghost correction and filter processing.

Tone correction is performed. In this filter processing, MTF correction, smoothing processing, etc. are performed.

MTF correction is a process for correcting resolution that has decreased due to various causes. Therefore, it is desirable to change the amount of MTF correction between text mode and photo mode.

For example, in text mode, the amount of correction is made stronger, and in photo mode, the amount of correction is made weaker. To do this, Nx
A convolution filter using image data of N (N-3°5.7) pixels may be employed and the filter coefficients may be changed depending on the mode. That is, the convolution filter is set to a bypass filter for character images, and is set to a low-pass filter for color gradation.

Furthermore, when processing the gradation side, smoothing processing is performed to reduce beat interference (moiré) caused by halftone dots.

In the gradation correction section 9, when processing the gradation side, the gradation (γ)
to obtain smooth gradation characteristics. Also,
When processing character images, set γ to a high value to obtain sharp images.

Then, the image signal for which image processing has been completed is supplied to an external printer unit or the like, and an image is formed on recording paper.

As described above, in this embodiment, the color code is
The image is divided into black, white, and intermediate colors, and the intermediate color is divided into black or chromatic color depending on the processing mode, and the content of image processing is changed depending on the mode. Therefore, in a black character image, the intermediate color area becomes a black area, color ghosts do not occur, and the resolution is improved and a sharp image is obtained. Also, on the color gradation side, the intermediate color area becomes a chromatic color area,
In addition to being able to reproduce low-saturation chromatic colors well,
Images with excellent gradation reproducibility can be obtained.

Next, 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° and 130°.
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 a slide rail 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 130 is transmitted to the reflecting mirror 131 and the mirror 1.
33, 133', the optical information conversion unit 137
guided by.

There is a standard white plate 1 on the back side of the left end of the platen glass 128.
38 are provided. 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, two dichroic mirrors 102 and 103, a CCD 104 for capturing a red color-separated image, a CCD 105 for capturing a green color-separated image, and a blue color-separated image. and a CCD 106 on which images are taken.

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 multiple rotations and sub-scanning, 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 non-contact 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 development is 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 the pressure bonding after cleaning is completed, and in order to remove unnecessary toner that is left behind when the pressure is released, an auxiliary roller 147C is further provided, and this auxiliary roller 147c
By rotating and pressing in the opposite direction to the image forming member 142, 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. Additionally, the image processing content can be changed depending on the type of image. As a result, we have created a color image processing device that can improve low-saturation color reproduction and gradation characteristics in color gradation images, improve resolution in character images, and reduce color ghosts. can do.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the configuration of an embodiment of the present invention, Fig. 2 is an explanatory diagram illustrating how color codes are generated, Fig. 3 is an explanatory diagram showing how colors are divided, and Fig. 4 is a color copying diagram. FIG. 5 is an explanatory diagram showing the conventional color code generation process. 1... Density conversion unit 2... Color code generation unit 3... Color reproduction unit 4... Image processing mode setting unit 5... Color code correction unit 6... Selector 7... Color ghost Correction section

Claims (1)

[Claims] In a color image processing device that performs image processing by dividing a color read signal into achromatic colors and chromatic colors, the area where color separation is performed between achromatic colors and chromatic colors is changed according to an externally set mode, and the chromatic color area 1. A color image processing device characterized in that the device is configured to perform different image processing on an achromatic color region and an achromatic color region.