JPH03230678A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To improve the color reproducibility of a low saturation part of a color gradation picture and the reproduction of a black letter picture by selecting the picture processing depending on codes of achromatic and chromatic colors. CONSTITUTION:The unit consists of input terminals 1R, 1G, 1B, a density conver sion section 2, a color reproduction section 3, a selector 4, a single color repro duction section 5, a color code generating section 6, a color code correction section 7, a picture discrimination section 8, a filter processing section 10, a gradation correction section 11 and a printer unit 12. Then the picture processing is selected depending on codes of achromatic and chromatic colors. That is, a low saturation part of a color gradation picture except a part having a large density gradient is separated into chromatic colors and the picture processing corresponding to the chromatic colors is implemented, and since a character edge of a black letter picture has a large density gradient, the part is separated into an achromatic color and the picture processing corresponding to the achro matic color is implemented. Thus, the color reproducibility of the low saturation of the color gradation picture and the reproducibility of the black letter picture are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image processing device that performs image processing by dividing color read signals into achromatic colors and chromatic colors.

[Background of the invention] Color images such as text and photographs are optically read by dividing them into red R1, green G, and blue B, and these are divided into yellow Y and magenta M1.
There is a color image processing apparatus that converts (color reproduction or color correction) into recording colors such as cyan C and IK, and records the images on recording paper using an electrophotographic color output device.

FIG. 6 shows how chromatic colors and achromatic colors are discriminated in the color image processing apparatus as described above.

In the cube shown in the figure, the horizontal direction is the R density, the vertical direction is the B density, and the depth direction is the G density. Therefore,
The point where the density of R, G, and B are all zero (lower left front) is white, and the point where they are all maximum (upper right back) is black. In this case, an area connecting a white point and a black point (indicated by a broken line cylinder) corresponds to an achromatic area, and the other area corresponds to a chromatic area.

By the way, when setting this achromatic color area, there are conflicting demands such as (1) and (2) below.

■Achromatic colors are used to reduce color ghosts (unnecessary colors that occur at the edges of black characters) that occur in black character images due to pixel misalignment between R, G, and B of the CCD sensor and lens aberrations. It is necessary to set the area as wide as possible.

■In order to accurately reproduce low-saturation colors (for example, brown, dark blue, purple, etc.) within the color gradation, it is necessary to set the achromatic color area as narrow as possible.

[Problems to be Solved by the Invention] Therefore, conventionally, the achromatic color area is set as a compromise between these conflicting demands.

Therefore, for example, color reproduction in low chroma portions of color gradations was not satisfactory. In other words, since the achromatic color area cannot be set so narrowly, the low chroma area of the color gradation is divided into achromatic colors, image processing corresponding to the achromatic color is performed, and this low chroma area is reproduced as an achromatic color. There were some inconveniences.

Furthermore, the reproduction of black character images, for example, was not satisfactory. In other words, since the achromatic color area cannot be set so wide, the edge portion of the character is divided into chromatic colors and image processing corresponding to the chromatic color is performed, resulting in the inconvenience that color ghosts occur in the edge portion of the character.

The object of the present invention is to improve the color reproduction of low chroma portions of color gradations and the reproduction of black character images.

[! ! [Means for Solving the Problem] The present invention includes a means for dividing a color read signal into intermediate colors and chromatic colors, and generating means for generating intermediate color and chromatic color codes respectively; An image discriminating means for discriminating the type, and according to the discrimination result of the image discriminating means, the first color is divided into achromatic colors and chromatic colors from intermediate colors that are color-coded by the means, and codes for achromatic colors and chromatic colors respectively. The second color component that generates means and
The first and second color components are provided with image processing switching means for switching image processing according to achromatic color and chromatic color codes generated by the means.

[Function] In the image discrimination means, for example, the density gradient of the image is detected,
When this density gradient is larger than a predetermined value, it is determined to be a black character image, and when it is smaller than a predetermined value, the color gradation is negative.
It is determined that The intermediate color is divided into an achromatic color when it is determined to be a black character image, and a chromatic color when it is determined to be a color gradation image.

Therefore, except for areas with large density gradients, the color gradation is -
The low chroma portion of the image is divided into chromatic colors, and image processing corresponding to the chromatic color is performed, so that the color reproduction of this low chroma portion is improved.

In addition, because the density gradient is large at the edge of a black character image, it is color-coded into an achromatic color, and image processing corresponding to the achromatic color is performed, so that no color ghost occurs at the edge of the character.
Since black is reliably reproduced, the reproduction of black characters is improved.

[Example] Below, the 11th!11t1111! An embodiment of the present invention will be described with reference to the drawings.

In the same figure, red R9 from the image reading unit (not shown)
8-bit digital data for each of green G and blue B is supplied to the density conversion section 2 from input terminals IR, IG, and IB. In this density conversion section 2, R, G.

The 8-bit data of B is converted to 6-bit data in accordance with human visual characteristics.

The R, G, and B data from the density conversion section 2 are supplied to the color reproduction section 3. In this color reproduction section 3, R9G, B
From the data, yellow Y, magenta M, cyan C9, and black data for chromatic image processing are generated. Y and M output from this color reproduction section 3.

The C and K data are supplied to the selector 4.

Further, the G data from the density conversion section 2 is transferred to the monochromatic color reproduction section 5.
is supplied to In the monochromatic color reproduction section 5, black data '' for achromatic image processing is generated from the G data. In addition,
This black data may be generated from R or B data, or may be generated from two colors or all of the colors R to B. The data is supplied to selector 4.

Further, the R, G, and B data from the density conversion section 2 are supplied to the color code generation section 6. This color code generation unit 6 calculates the level (density) of R, G, and B data.
The colors are divided into intermediate colors and chromatic colors. The color code generation unit 6 outputs a color code indicating whether the color belongs to an intermediate color or a chromatic color.

Here, the setting of the intermediate color area and the chromatic color area is performed as shown below.

That is, as shown in Figure 2A, create a cylinder with radius r using L and 8 Kyoto color systems (the L wooden direction is not shown in the same figure), and set the inside of it as an intermediate color area. , set the outside as a chromatic region. In this case, the inside of the cylinder is an area that can be either achromatic or chromatic depending on the image information, and for example, r=15.

In the color code generation unit 6, R, G, and H data are converted into L*8 data and b car color system, and it is determined whether the color coordinate position is inside or outside the cylinder with radius r. Ru. When it is inside the cylinder, a color code indicating that it belongs to an intermediate color, for example "01", is output, and when it is outside the cylinder, a color code indicating that it belongs to a chromatic color, for example "IO" is output.

Note that this color code generation section 6 is configured with a table made of, for example, a ROM.

Returning to FIG. 1, the color code output from the color code generation section 6 is supplied to the color code modification section 7.

Further, the G data supplied to the input terminal IG is supplied to the image discrimination section 8. The image discrimination section 8 discriminates from the density gradient of G whether it is a bad character image or a color gradation. In this case, the determination may be made using all the data of R2O and B, but this increases the cost. Therefore, in this example, only the G data that best matches the visibility is used for discrimination.

FIG. 3 shows pixels used for image discrimination. In the figure, X is the pixel of interest for image discrimination, ■ is the pixel one line before, W is the pixel one screen before, and Y is the pixel one line before.
The pixel after the pixel, 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 equation.

5=21V-Xl+IW-Yl ---■ In this way, the S parameter of the density gradient is determined from the surrounding pixels.

In addition to this S parameter, S'=IV-XI+IW-Xl ---■S"=lV
-Zl+1W-Yl ◆-・■ Parameters can also be considered. However, since S' uses only two peripheral pixels, its discrimination ability is insufficient, and S'' requires three pixels in the sub-scanning direction, resulting in a large memory capacity.

Therefore, in this example, the S-parameter of equation 0 is used, which requires a small memory capacity and has a high discrimination ability.

41st! I is a diagram showing a specific configuration of the image discrimination section 8.

In the figure, 21 is a register that holds the data of pixel Y, 22 is a register that holds the data of pixel This is a subtraction absolute value converting circuit that generates IW-Yl, and the absolute value IW-Yl from this subtracting absolute value converting circuit 24 is supplied to an adder 28.

Further, 25 is a line memory i, 26 is a register that holds the data of the pixel V, and 27 is a subtraction absolute value circuit that performs subtraction between V and X to generate an absolute value I V - X l.
Absolute value from this subtracted absolute value north #27 I V-X I
is amplified twice by the amplifier 1129 and then supplied to the adder 2.

In addition 1128, the absolute values IW-Yl and 21V-Xl are added, and the added signal +w-y++21V-X
+ is supplied to comparison W30 as an S parameter. Further, the comparison 1130 is supplied with the density gradient threshold T from the dark value generation W31.

In comparison @30, the S parameter is compared with the threshold T, and S
When it is AT, a signal of high level "l", for example, indicating a bad character stroke is output, and when S≦T, a signal of low level "0pa", indicating that it is a color gradation plane, is output. is output.

Returning to FIG. 1, the image discrimination signal output from the image discrimination section 8 is supplied to the color coat correction section 7. Of the color coats supplied from the color coat generation unit 6, this color coat correction unit 7 outputs the color code “10” indicating that it belongs to a chromatic color as is, and outputs the color code “O1” indicating that it belongs to an intermediate color. " is corrected by the image discrimination signal and output.

In other words, when the image discrimination signal is a high level "l" signal indicating a bad character image, the color code "01" indicating an intermediate color is changed to the color code "11" indicating belonging to an achromatic color. Fixed. At this time, the area setting is equivalently expressed as shown in FIG. 2B.

On the other hand, when the image discrimination signal is a low level "0" signal indicating that it is a color gradation surface, the color code "01" indicating an intermediate color is modified to the color code "lO" indicating belonging to a chromatic color. be done.

At this time, the area settings are equivalently expressed as shown in FIG. 2C.

The color code output from the color code correction section 7 is supplied to the selector 4. This selector 4 contains a scan code (a code indicating the color being recorded by the printer)
is supplied. The selector 4 selects and outputs color data corresponding to the color being recorded by the printer based on the scan code.

In this case, in a pixel portion whose color code is "10" indicating that it belongs to a chromatic color, Y is outputted from the color reproduction unit 3 as yellow black data.
M, C, and K data are output. On the other hand, the color code "11" indicates that the color code belongs to achromatic color.
In the pixel portion, zero is output as yellow Lucian data, and data '' is output as black data from the monochromatic color reproduction section 5.

The data output from the selector 4 is supplied to a printer unit 12 via a filter processing section 10 that performs various filter processing and a gradation correction section 11, and an image is formed on recording paper.

In this example, the area to be reconverted into an achromatic color and a chromatic color by post-processing is color-coded into intermediate colors, and the color code generation unit 6 outputs the color code "Ol" indicating that the area belongs to the intermediate color. .

Then, this color code "01" is modified by the color code modification unit 7 to a color code "11" indicating that the image belongs to an achromatic color when the density gradient is larger than the darkness value, and to a chromatic color when it is smaller than the threshold value. The color code is changed to "lO" to indicate that it belongs. Then, the color code output from the color code correction unit 7 is “lO
'', the selector 4 selects the Y, M, C, and K data output from the color reproduction section 3, and performs image processing corresponding to chromatic colors. On the other hand, when the color code is rl IJ, '' is selected for the data output from the monochromatic color reproduction section 5, and image processing corresponding to an achromatic color is performed.

Therefore, according to this example, in low chroma parts of the color gradation plane, excluding parts with large density gradients, the color code "10" indicating that it belongs to chromatic colors is output, and image processing corresponding to chromatic colors is performed. It will be done. Therefore, the low chroma portion is less often reproduced as an achromatic color, and the color reproducibility of the low chroma portion can be improved.

Further, since the density gradient is large in the character edge portion of the bad character image, a color code "11" indicating that the character belongs to an achromatic color is output, and image processing corresponding to the achromatic color is performed. Therefore, color ghosts do not occur in the character edge portions, and black is reliably reproduced, thereby improving the reproducibility of bad character images.

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 a color dry development method is used for development in this color copying machine. In this example, two-component non-contact development and reversal development are used.In other words, the transfer drum used in conventional color image formation is not used, but the overlapping is performed on the electrophotographic photoreceptor drum that forms the image. . In addition, in the following example, in order to reduce the size of the device, four-color images of yellow magenta, cyan, and black are developed on an OPC photoreceptor (drum) for image formation in four rotations of the drum, and then transferred after development. This is done once and the image is transferred onto recording paper such as plain paper.

By turning on the copy button of the color copying machine, the document reading section A is driven. The original 101 on the original table 128 is then optically scanned by the optical system.

This optical system includes a light source 129 such as a halogen lamp, a carriage 132 provided with a reflecting mirror 131, and a movable mirror unit 134 provided with V mirrors 133 and 133'.

The carriage 132 and the movable mirror unit 134 are caused to travel on a slide rail 136 at predetermined speeds and directions, respectively, by a stepping motor (not shown).

Optical information (image information) obtained by irradiating the original 101 with the light source 129 is transmitted to the reflecting mirror 131. V mirror 133.
133', it is led to an optical information conversion unit 137.

A standard white plate 138 is provided on the back side of the left end of the document table 128. This is because the image signal is normalized to a white signal by optically scanning the standard white plate 138.

Optical information conversion unit) 137 is a lens 139, a prism! 40. Two dichroic mirrors 102, 103 and an R-CCD 104 on which a red color separation image is captured;
It is composed of a G-CCD 105 that captures a green color-separated image, and a B-CCD 106 that captures a blue color-separated image.

The optical signal obtained by the optical system is focused by a 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, the yellow optical information is color-separated into red optical information and green optical information by the dichroic mirror 103. 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 separated image is formed on the light receiving surface of each CCD 104 to 106 to obtain an image signal converted into an electrical signal.The 0 image signal is processed by a signal processing system and then recorded for each color. The image signal for this purpose is output to the writing section B.

The signal processing system includes various signal processing circuits from the density converter 2 to the gradation corrector 11 shown in FIG. 1, as well as an A/D converter and the like.

The writing section B has a deflector 141. This deflection 1
As 141, in addition to a galvanometer mirror or a rotating polygon mirror, a deflector made 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 deflection W141.

When the deflection scan is started, the beam scan is detected by a laser beam index sensor (not shown) and the first
Beam modulation using a color signal (for example, a yellow signal) is started. The modulated beam is applied to an image forming member (photoreceptor drum) 14 which is charged in a negative manner by a charger 154.
2 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 power supply is applied to this developing device 143.

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 mentioned above is removed by the cleaning blade 147.
A is rotated with the crimping bond released, and a second color signal (for example, a magenta signal) is generated in the same manner as the first color signal.
An electrostatic latent image is formed based on this. Then, by using a developing device 144 containing magenta toner, 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 a black toner image is formed by the developing device 146 containing black toner.

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

Note that 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 involves applying AC and DC bias voltages from a high-voltage power supply.
An example of so-called non-contact two-component jumping development is shown in which each toner is caused to fly toward the image forming body 142 for development.

Further, toner replenishment to the developing devices 144, 145, and 14f3 is performed based on a command signal from the CPU, similar to the developer@143, with a predetermined amount of toner.

On the other hand, the recording paper P fed from the paper feeding device 14B via the feed roll 149 and the timing roll 150 is conveyed onto the surface of the image forming body 142 in a state synchronized with the rotation of the image forming body 142. be done. and,
A 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 supply, and the separation pole 1
52.

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 the cleaning device 14
7 to prepare for the next image forming body 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 after the release, 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.

In the above-mentioned embodiments, 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 present invention can be used in various other types of equipment.

[Effects of the Invention] As explained above, according to the present invention, areas that can be either achromatic or chromatic are color-coded into intermediate colors, and these intermediate colors are roughly divided into achromatic and chromatic colors depending on the density gradient of the image. The system classifies images by color and performs corresponding image processing. Therefore, except for areas with large density gradients, the low chroma portion of the color gradation image is divided into chromatic colors, and image processing corresponding to the chromatic colors is performed, so that the color reproducibility of this low chroma portion can be improved. In addition, because the density gradient is large at the edge of a black character image, it is color-coded into achromatic colors, and image processing corresponding to the achromatic color is performed, so that color ghosts do not occur at the edge of the character and it is reliably reproduced as black. Therefore, the reproducibility of black character images can be improved.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining area setting, and FIG. 31! I is a diagram showing pixels used for image discrimination, FIG. 4 is a diagram showing an example of the configuration of an image discrimination section, FIG. 5 is a configuration diagram showing the overall configuration of a color copying machine, and FIG. 6 is a conventional color code. FIG. 3 is a diagram for explaining generation. IR, IG, IB-・Input terminal 2...Density conversion section 3...Color reproduction section 4...Selector 5...Single color reproduction section 6...Color code generation section 7...Color Coat correction section 8...image discrimination section 10...filter processing section 11...tone correction section 12/Φ-printer unit

Claims (1)

[Claims] (1) a first color-coding means for color-coding the color reading signal into intermediate colors and chromatic colors, and generating intermediate-color and chromatic-color codes respectively; and image discrimination means for determining the type of image from the color reading signal; a second color-coding means for color-coding the intermediate colors color-coded by the first color-coding means into achromatic colors and chromatic colors according to the discrimination result of the image discriminating means, and generating codes for each of the achromatic colors and chromatic colors; 1. A color image processing device comprising: image processing switching means for switching image processing according to achromatic color and chromatic color codes generated by first and second color classification means.