JPH02170694A - Color picture processing device - Google Patents

Abstract

PURPOSE:To improve the reduction of the density and the degradation of the picture quality by generating a black signal from brightness information out of color information separated to three colors in a color picture processing device of an electrophotographic digital color copying machine or the like capable of full color copying. CONSTITUTION:A color picture processing device 10 consists of a scanner part 10A, a picture processing part 10B, and a printer part 10C. The scanner part 10A converts an optical image related to picture information of an original obtained by optical scanning into an electric signal. A color conversion processing system included in the picture processing part 10B consists of a color picture processing (color conversion) means 20, a monochromatic picture processing (monochromatic conversion) means 25, a color code generating (achromatic color discriminating) means 30, and a selector 32. The color picture processing means 20 converts three colors R, G, and B into four colors Y, M, C, and BK in this example. The G signal is supplied as the lightness signal (brightness signal) to the monochromatic picture processing means 25. The selector 32 is so controlled that the color picture processing means 20 is used for a color picture and the monochromatic picture processing means 25 is used for a monochromatic picture.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a color image processing device suitable for application to an electrophotographic digital color copying machine capable of full-color copying, and in particular a color image processing device that processes a black signal based on brightness information. The present invention relates to a color image processing device created by

[Background of the Invention] Color image processing devices such as electrophotographic digital color copying machines capable of full-color copying separate the color image information of a document into three primary colors, for example, R, G, and B, to obtain three primary color signals. There is a system that converts this into, for example, Y, M, C, BK (black) signals in order to roughly match the color signals of the output system of the printer section.

In a color image processing apparatus having such a color signal processing system, a monochrome image (black and white original) is processed using the Y and M signals described above.
, C or Y, M, C, BK.

When using Y, M, and C, base removal (UCR (Un
This method reproduces a monochrome image by using a value obtained by multiplying the common amount of Y, M, and C by a constant value (a constant of 1 or less) as the amount of black. In addition, when using Y, M, C, BK, heat sensitive addition method (OCA (Under Co1or Addi
tion) method), and like the UCR method, a predetermined color is added to Y, M, and C to reproduce a monochrome image.

[Problem to be solved by the invention] When reproducing black using Y, M, and C in this way,
As is well known, the black density decreases, the black cannot be reproduced satisfactorily, and the copy image quality is not very good.

In the latter case, although the decrease in black density can be compensated for, since BK is now used in addition to Y, M, and C, there are other disadvantages such as color shift and a decrease in recorded image quality. be.

Therefore, this invention solves these problems, and in particular, creates a black signal from the brightness signal of the original, that is, the brightness signal, and reproduces a monochrome image, thereby improving the decrease in density and deterioration of image quality. The present invention provides a color image processing device with the following features.

[Means for Solving the Problems] In order to solve the above-mentioned problems, a color image processing device according to the present invention separates a color image into three colors, and separates the color image into three colors.
A color image processing device that reproduces a color image based on color, characterized in that a black signal is created from brightness information among color information separated into three colors. .

[Function] The input color image signals (density signals) of R, G, and B are supplied to the color image processing means 20 and the monochrome image processing means 25, and in the case of a color image, the color image processing means 20 is used. In the case of a monochrome image, the image is converted into a black and white density signal using the monochrome image processing means 25.

Among the input image signals separated into three colors, G (No. 8) representing the brightness of the original is supplied to the monochrome image processing means 25 and converted into a black and white density signal.

A monochrome image is reproduced by the output density signal of the monochrome image processing means 25.

In this way, if a monochrome image is created based on the density signal obtained from the dedicated processing means 25, the density will not be too low. Since the monochrome image processing means 25 outputs a density signal only for achromatic colors, black is reproduced as black. In other words, no color shift occurs.

[Embodiment 1] Hereinafter, an example of the color image processing apparatus according to the present invention will be described in detail with reference to FIG.

FIG. 2 shows a schematic configuration of a color image processing device 10 according to the present invention.
The image forming apparatus is composed of a scanner section 10A, an image processing section 10B, and a printer section 10C.

The scanner part 10A refers to a series of processing systems for converting an optical image related to image information of a document obtained by optical scanning into an electrical signal. In this example, three primary color image signals (analog signals) R, G, and B are shown as the electrical signals.

The printer unit 10C records the image signal as a visible image based on the image signal (pulse radiation modulation (PWM) processed output, multi-value processed output, etc.) finally output from the image signal unit. This refers to the processing system up to this point.

In this example, an electrophotographic recording method using a photosensitive drum is adopted as the printer section 10C, and a semiconductor laser is used as a light source for forming the electrostatic latent image. Therefore, this printer section 10C is configured as an electrophotographic laser printer.

As an example of developing a color image using a semiconductor laser and an image forming member (photoreceptor drum), the example shown below uses developer (toner) for each color of Y, M, C, and BK as shown in FIG. ) are superimposed on the image forming body to reproduce a predetermined color. Therefore, according to this example, no transfer drum is used.

The image processing unit 10B is a processing unit that performs appropriate image signal processing on the input image signal, and specifically refers to scaling processing, filtering processing, shading processing, PWM processing, etc. In addition to these processes, it also generally refers to color ghost processing.

In addition to these, a color conversion processing system that converts into an image signal to be used by the printer section 10C, which will be described later, is included. As shown in FIG. 3, this color conversion processing system 10B is composed of a color image processing means 20, a monochrome image processing means 25, a color code generation means (achromatic color discrimination means) 30, and a selector 32.

Color code and black and white/color original discrimination means 4 described later
The selector 32 is controlled by the discrimination output of No. 7 or a scan code (described later) formed based on the discrimination output, and either a color image or a monochrome image is selected.

In the color image processing means 20, the 83 colors of R, G, Y, M
, C, and BK. Y, M
, C, and BK are used to match the colors (tones) of the output system of the printer section 10C. The G signal is supplied to the monochrome image processing means 25 as its brightness signal (brightness signal).

In this way, the color image processing means 20 is used for color images, and the monochrome image processing means 25 is used for monochrome images.
was used to improve black reproducibility, especially in monochrome images. This is because when reproducing black using Y, M, C, and BK, the density inevitably decreases, so monochrome images are created using MONO, which is exclusively for monochrome images.
This is what I tried to reproduce. In this way, a monochrome image can be reproduced with the desired density.

FIG. 5 particularly shows an example of the mechanical part of the digital color copying machine configured as described above.

The scanner part 10A will be explained first. By turning on the copy button provided on the color copier, the scanner part 1
0A (original reading section) is driven.

First, the original 82 on the original table 81 is optically scanned by an optical system.

This optical system uses a halogen lamp (or fluorescent lamp) 86
and a carriage 84 provided with a reflective mirror 87. ■Movable mirror unit 8 equipped with mirrors 89 and 89゛
It can be composed of 8.

The carriage 84 and the movable unit 88 are caused to travel on the slide rail 83 at predetermined speeds and directions, respectively, by a stepping motor (not shown). 9
2.93 is a roller, and 95 is a belt.

When using a halogen lamp as a light source, a system with an IR cut filter placed in front of the lens is used.

When optically scanning a color original, a commercially available warm white fluorescent lamp may be used as the light source 86 in order to prevent optical emphasis or attenuation of specific colors.

In this case, to prevent flickering, these fluorescent lights 86 are
It is lit and driven by a high frequency power source of approximately 40kHz. In addition, in order to maintain a constant temperature of the tube wall or to promote warm-up, the tube wall is kept warm by a heater using a POSISTOR.

Optical information (image information) obtained by irradiating the original 82 with a halogen lamp 86 is transmitted to a reflecting mirror 87 and a mirror 89.
, 89° to the optical information conversion unit 100.

A standard white plate 97 is provided on the left end side of the platen glass 81. This is to normalize the image signal (white signal) to a reference white signal (reference signal) by optically scanning the standard white plate 97.

The optical information conversion unit 100 includes a spectroscopic system 102 in addition to the lens 101. As shown in FIG. 6, the spectroscopic system 102 is composed of four prisms 103A to 103D and two dichroic coat films 105 and 106.

105 is a dichroic coating film that reflects red R; 10
6 is a dichroic coat H'A that reflects blue B. The color-separated images, which are each reflected light, are sent to the corresponding optical sensor,
In this example, the images are formed on CCDs 107-109. Each color separation image is converted into an electrical signal (image signal) by each CCD 107-109.

The printer section 10C (image writing section) has a deflector 935. As the deflector 935, 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 passes through this deflector 93.
5, the deflected laser beam passes through an optical path of a lens 116 and a mirror 117, and then impinges on the image forming body 80.

When the deflection scan is started, the beam scan is detected by a laser beam index sensor (not shown), and beam modulation using the first color signal (eg, Y signal) is started.

The color of the first color signal, or roughly the colors of the second and third color signals, is determined by the content of a 3-bit digital signal called a scan code output from the main body of the apparatus. The scan code can be determined based on the discrimination output of monochrome/color document discrimination means 47, which will be described later.

A laser beam scans an image forming member (photosensitive drum) 80 that has been given a negative charge by a charger 121 .

An electrostatic latent image corresponding to the Y signal is formed on the image forming body 80 by the main scanning by the laser beam and the sub scanning by the rotation of the image forming body 80 .

This electrostatic latent image is transferred to a developing device 12 containing yellow toner.
The development can be completed by 2. A predetermined bias voltage is applied to the developing device 122 from a high voltage power supply. A yellow toner image is formed by development.

Toner is supplied to the developing device 122 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 is rotated with the cleaning blade 127 released from the pressure, and then, as in the case of the first color signal, a second color signal (for example, the M signal) is used to superimpose the yellow toner image and make it static. A latent image is formed. Then, a magenta toner image is developed using the magenta toner contained in the developing device 123.

Such electrostatic latent image processing and development processing are completed in the order of cyan and black, and the required multicolor toner image is formed on the image forming body 80 (see FIG. 4). 124 is a cyan developing device; 125 is a black developing device.

In the case of a monochrome image, a monochrome image is formed on the image forming body by one development process. When a color image and a monochrome image coexist, the color image is reproduced by performing development processing a maximum of four times.

In this case, the black colors in the color image are Y, M, and C.

In the case of a monochrome image, black is reproduced using only BK.

As described above, the development process is a so-called non-contact two-component development process in which each toner is caused to fly toward the image forming body 80 while AC and DC bias voltages from a high-voltage power source are applied. An example of jumping development is shown.

On the other hand, the recording paper P that has been completely fed from the paper feeder 141 via the feed roll 142 and the timing roll 143 is
The image forming member 8o is conveyed onto the surface of the image forming member 80 while being timed with the rotation of the image forming member 8o. Then, the multicolor toner image is transferred onto the recording paper P by the transfer pole 130 to which the high voltage has been applied from the high voltage power source, and the multicolor toner image is transferred onto the recording paper P.
31.

The separated recording paper P is conveyed to the fixing device 132, where it undergoes a fixing process and a color image is obtained.

The image forming body 80 after the transfer is cleaned by the cleaning device 126 and prepared for the next image forming process.

In the cleaning device 126, a predetermined DC voltage is applied to a metal roll 128 provided on the blade 127 in order to facilitate recovery of the toner cleaned by the blade 127. This metal roll 128 is the image forming body 8
0 in a non-contact manner.

After the cleaning is completed, the blade 127 is released from the pressure bond. In order to remove unnecessary toner left behind when the blade 127 is released, an auxiliary cleaning roller 129 is further provided, and this roller 129 is rotated in the opposite direction to the image forming body 80 and the pressure bond is removed. By doing this, unnecessary toner is sufficiently cleaned and removed.

FIG. 1 shows a specific example of the circuit system of the color image processing apparatus 10 according to the present invention. Therefore, the figure shows details of the image processing unit] and OB.

Image signals R, G output from CCDs 107 to 109
, B are supplied to A/D converters 2 to 4 via input terminals IR to IB, and are converted into digital signals having a predetermined number of bits, 8 pits in this example. Shading correction is performed simultaneously with A/D conversion. 5 to 7 indicate shading correction circuits.

The shading correction circuits 5 to 7 have the same configuration. To illustrate the shading correction circuit 5, as shown in FIG. 7, in this example, it is composed of a memory 5A for 15 horizontal lines and an average value circuit 5B that takes the average value of 16 horizontal lines. The white signal (normalized signal) is
It is used as a reference signal for transducers 2-4.

The shading-corrected digital image signal is supplied to a density conversion system.

In this example, in addition to the standard density conversion circuits 11 to 13, density conversion circuits 15 to 17 for adjustment are provided, respectively. All density conversion ports "1811-13.15-17 are ROM
A lookup table (LUT) configuration can be adopted.

In density conversion, the relationship between the brightness level and density of the image signal is
As shown in the curve La in the figure, this is a non-linear characteristic, so it is provided to correct this. The outputs of the standard density conversion circuits 11 to 13 are supplied to a color code generation means 30 which functions as a non-engraved color discrimination means.

In the density conversion circuits 15 to 17 for adjustment, a desired gamma characteristic is selected, thereby obtaining a desired color balance. Each of the adjustment density conversion circuits 15 to 17 stores density data corresponding to a plurality of gamma characteristics, such as those shown by curves Lb to Ld in FIG. 8, for example. Then, a manual selection signal for RlG and B is supplied from the terminal 8a, and thereby a density selection signal (R/G/B) for selecting the corresponding gamma characteristic is sent from the density adjustment circuit 8 to the adjustment density conversion circuit 15 to 17.

Manual selection signals for R, G, B and BK, which can be supplied from terminal 8b as will be described later, can be set on the operation panel (not shown) provided on the color copying machine.

In this example, 6-bit data is used for the R and G density signals, and 5-bit data is used for the B density signal.

The density conversion outputs DR, DG, and DB, to which predetermined gamma characteristics have been imparted for color balance adjustment, are used as signals for image processing, and are first supplied to the color image processing means 20.

The color image processing means 20 is provided with conversion ROMs 21 to 24 dedicated to Y, M, C, and BK.
, M, C, and BK density signals can be referenced.

Here, Y, M, and C are obtained from the R, G, and B density signals.

In order to convert to a BK density signal, it may be possible to use a well-known conversion formula (such as a linear masking method), but this conversion formula has a large error, resulting in a large discrepancy between the reproduced color and the original color.

In this example, in order to improve this point, the results of simulation using a computer are stored in each color image processing means 20 as density data, especially so that the deviation from the original color is minimized as much as possible.

An example of what kind of data is stored is shown below.

In order to reproduce the same color tone as the original, in this example, discrimination such as color difference ff1 (here, ΔE"ab is used) is used to
Density data is generated such that the color difference is minimized. An example of the generation procedure is shown below.

Step 4: First, a color chart is created in order to examine the output characteristics of the printer section 10C. In this example, Y, M, and C are printed in the printer section 10C.
, BK each has the ability to output four density levels.

In the digital copying machine of this example, toners are superimposed on each other, so the colors that can be expressed with color toners are 256' colors.

These colors are outputted to the printer section 10C to obtain a color chart. The obtained color chart is placed on the document table of the scanner part 10A, and converted into brightness signals of 8 bits each for R, G, and B by scanning. This R,G.

The B brightness signal is converted into CIE XYZ coordinates and saved as data.

→In order to convert the R, G, and B signals of the camera (I) into CIE-XYZ coordinates, it is necessary to investigate the characteristics of the scanner part 10A. Therefore, we selected about 20 colored papers from the Munsell color chart, measured them with a colorimeter, and determined the CI E of the colored papers.
- Obtain the value in the XYZ coordinate system.

Next, by placing the colored paper on the document table of the scanner part 10A and scanning it, R, G, and B brightness signals of the colored paper by the scanner part 10A are obtained.

Since there is a linear relationship between the two types of colored paper values obtained in (I) and (II) in this way, the following equation holds true.

Here, the parameters a to i are obtained from the two types of values by approximation using the least squares method. That is, by determining the parameter a=i, the R, G, and B signals from the scanner part 10A can be converted into the XYZ color system, and the characteristics of the scanner part 10A can be investigated.

As mentioned above, the printer is capable of displaying 256 colors in one dot, or requires the ability to display even more colors for color reproduction.

In order to solve this problem, a four-level dither method is used in this example. This uses three threshold matrices with a dot size of 4 x 4, and the input is an integer value from 0 to 48,
It is possible to output a 4-level signal with a size of 4×4.

It takes a lot of effort to output this huge amount of reproduced colors to a printer and measure all of them. Therefore, the generation of dot patterns and coloring are all done by computer simulation. A specific example will be explained below.

In this example, processing is performed to use as much BK (black) signal, that is, the amount of black toner as possible.

In color printing, when Y, M, and C inks overlap in the same place, it means black. Processes that replace the black component with black ink and reduce the amount of other chromatic inks used are generally inking (UCA) and undercolor removal (UCA).
It is called R).

In this example, if the color signals Y, M, and C are all higher than the O level, C,
A method is used in which the levels of the M and Y signals are lowered equally and the black level is increased by that amount. Expressed as a formula, it is as follows.

BK+PxIlin (C, M, Y)=BK'C-BK
XS=C'M-BKXS=M'Y-BKXS=Y' Here, 'win()' is a function that takes the minimum value among the numbers in parentheses, and P indicates the degree of BK toner replacement. It is a parameter.

S is a changeover switch between UCA and UCR, and when in UCR, S=
1. During UCA, S=O. In this example, P=1, S
= 1, and as a result: 100% UCR was performed.

In this example, BK=O in the above equation so that BK' can be obtained only from the black component of MMC. Therefore, the types of colors reproduced by the printer are narrowed down to 49 to the third power.

However, the number of reproduced colors is sufficient and it can be safely assumed that color reproduction will not be affected.

Next, a reproduced color dot pattern of 49 to the third power is generated. First, one Y, M, C signal (0 to 48) is determined. For example, if Y=30, M=20SC=10, then Y'=20, M'=10. C'
= ○, BK'=10.

The values of Y', M', C', and BK' are determined through the threshold matrix shown in FIG.
~3) is converted into a matrix.

The threshold matrix consists of three, for example, the first matrix is 1 to 16, the second is 17 to 32, and the third is 3.
Numbers 3 to 48 are arranged randomly. here,
Assuming that the values of Y, M, and C just decided are the points at the upper left corner of the matrix, Y' is larger than 1 to 17 and smaller than 33, so it is 2. Similarly, M' is 1, C' is O, BK
' becomes 1. These Y', M', C', B
The four multi-value matrices of K' are superimposed as shown in FIG. 11 to obtain a multi-value dot pattern.

Here, C', M', Y', BK' at the same position
The value corresponds to the color of the color chart created in (I).

For example, C', M'Y' at the top left of the matrix
The value of BK' is C' = 1. M'=2. If Y' = O, BK' = 2, the cyan level of the colors in the color chart (1) is 1. The magenta level is 2. The corresponding color corresponds to a color in which the level of yellow is O1 and the level of black is 2.

Since the colors of the color chart have already been converted into CIE-XYZ values at step (I), a dither matrix in which these values are newly arranged is created.

FIG. 12 is an explanatory diagram for explaining such a matrix. The color reproduced by the printer unit 10C can be expressed as the average color of an area having a size of 4×4 dots as shown in FIG. Therefore, C of the color reproduced by the printer section 10C
If the values at the IE-XYZ coordinates are X, Y, and Z, then X= (1/16) II! lX1 Y= (1/16)&Yi Z= (1/16)haZi. This requires that the size of the dots be constant during actual output. If the size of the dots is
When it differs depending on (I), the following formula may be used.

That is, X=(8X1-5i)/to5i Y = (Bear Yi-8i) / Bear 5i Z = (8 Zi-Si)/to St However, Si is the area indicated by the dot.

In this way, the average color of the small area, that is, the printer unit 10
Colors reproduced by C can be calculated at the simulation level. Similarly, CMY parameters are independently set from 0 to 48, and a total of 493 reproduced colors are calculated.

(II) allows the colors of the document read by the scanner part 10A to be converted into CIE-XYZ values, and (IIN allows the printer part 10C to also use a four-level dither with a matrix size of 4 x 4. All reproduced colors in this case are obtained by CIE XYZ values.

■ --Ma... ゜Make sure to keep the same color tone as the original as much as possible between (II) and (II).
+ ) data are linked and the relationship is obtained as color tone reproduction processing information (reference density data).

In this example, the brightness signal of the document read by the scanner part 10A is converted into density, and R=G=6 bits, B
= Start when the signal becomes a 5-bit digital signal.

The signal at this time is for all cases (R, G=O ~ 63.B=O
~31). Then, each time, the following processing is performed.

The density-converted RGB signal is converted into XYZ by (11)
, and then converted to coordinates in a uniform color space. In this example, conversion to CI E-L"a"b" uniform color space is performed, but in addition, CI E-L"u"v
” and LHC are also effective.

The conversion formula for CI E-L"a"b" uniform color space is as follows.

L”= 116 (Y/Yo) -16a rate=500
[(X/Xo)-(Y/Yo)]b"-200[(Y/
Yo)-(Z/Zo)1 Next, the color closest to the color represented by L*a*b* is selected from among the 49 cubed colors produced by the printer in (II[). At this time, the discriminant quantity that represents the similarity of colors is important, but it is sufficient to use the Euclidean distance on the uniform color space.

The advantage of representing the signals to be compared on a uniform color space is that the uniform color space is designed so that the distance between two points in the uniform color space matches the human sense of color difference as much as possible. It is from.

Therefore, the color closest to the color from the scanner part 10A is the distance 11i (color difference * CI E-L "a"
b "8E" ab) in the color space is the shortest, and a calculation process is performed to select it from among the colors reproduced by the printer section 10C, and the obtained relationship (on the scanner section 10A side R, G, Ba degree multiplication signals Y, M, C representing the reproduced colors of the printer.

(relationship with the BK signal).

By the above method, even if the color of the document is not within the color gamut of the toner, it is possible to select the closest color and output it as a density signal.

FIG. 13 is an explanatory diagram showing how this color tone is reproduced.

In this figure, the signal on the scanner part 10A side exists outside the reproduction color gamut of the printer part 10C, but ΔE"
The color with the smallest ab is selected as the reproduced color. ΔE'
The smallest ab means that the color is the most difficult to distinguish.

Problems in this case include that a considerable amount of computer processing time is required and that a large capacity memory is required to store color tone reproduction processing information.

The former problem can be solved in several tens of minutes using a large-scale computer, and the latter problem can also be solved because the price of memory is decreasing.

The density signals created in this way are stored in each of the color image processing means 20, and in addition to the color image processing means 20, a monochrome image processing means 25 is also provided, which receives the G signal. The image information is supplied as a brightness signal,
In this example, it is converted into a density signal with 64 gradations. This density signal is used as a signal for monochrome image reproduction.

Now, the monochrome image processing means 25 is supplied with a density adjustment signal for black level from the density adjustment circuit 8 mentioned above to control the black level, and also receives a background signal from the automatic density adjustment circuit (EE circuit) 27. A regulation signal is provided.

Therefore, as the density data stored in the monochrome image processing means 25, a plurality of density data (for 64 gradations) corresponding to a plurality of gamma characteristics having different background levels are prepared.

Then, the gamma characteristic is specified by the density adjustment signal for the black level, and the background level is selected by the background adjustment signal. Adjustment of the background level is nothing but a process of shifting the gamma characteristic in the direction of the brightness signal axis, which is the input axis (Figure 9-
(Dotted chain line shown).

By adjusting the background level in monochrome image processing, it is possible to remove the gray background part of the document, thereby making it possible to reproduce a clear image.

This is because when the background is yellowish, as in old newspapers, for example, if this background is removed and copied, a clearer image can be copied.

Because of this, the EE circuit 27 can not only be supplied with the output of the monochrome image processing means 25 as density information, but also receive color code data as color information in order to perform background level adjustment (automatic density adjustment!) only in the case of an achromatic image. (A color code of "Oo" or "11" indicating an achromatic color, which will be described later) is supplied.

The use or non-use of the EE circuit 27 is determined by the E supplied to the terminal 28.
Although it is controlled depending on the presence or absence of the E-select signal (selected manually), when the black level density adjustment No. 43 is manually selected, the automatic adjustment of the background level may be prohibited.

Here, the background removal process is performed only on the monochrome image processing means 25 because it is necessary to reproduce colors while leaving the background (chromatic colors) of the chromatic original as is.

The reason why the density adjustment signal for black level is made independent from density adjustment No. 43 for color balance adjustment is to prevent the black level from changing due to color balance adjustment.

Density signals output from the color image processing means 20 (for convenience of explanation, the same symbols as the color signals Y, M, C.

Use BK. ) and the monochrome density signal M080 output by the monochrome image processing means 25 are respectively supplied to the selector 32, and when the image is a color image, the density signal M080 is output from the color image processing means 20. The density signal output from the monochrome image processing means 25 is selected.

In order to accomplish such processing, a color code generating means 30 is provided. The color code generating means 30 is supplied with R, G, and Be multiplied signals from the standard density conversion circuits 11 to 13, and a color code (2 bits) corresponding to the image information of chromatic colors and achromatic colors is generated depending on the combination of the densities. Output. Therefore, this color code generating means 30 is R
It is more convenient to configure it with OM.

FIG. 14 shows the relationship between the color code and the density signal selected by the color code. In this example, even in the case of the same color image, there are three colors: Y, M, and C, and Y, M.

Although it is possible to select four colors, C and BK, for convenience of explanation, the example shown in FIG. 14 only describes the four colors Y, M, C, and BK and color codes related to monochrome images.

The selected 6-pit density signals and color codes are supplied to a color ghost correction circuit 40.

Although it varies depending on the configuration of the color image processing means 20, chromatic colors such as red and yellow appear around black characters, and black appears around chromatic colors, so this is provided to remove these color ghosts. .

Since color ghost correction only needs to be performed for the color code, color ghost detection means 41 and 42 detect color ghosts in the main scanning direction (horizontal scanning direction) and the sub-scanning direction (drum rotation direction). What about color ghost detection in the main scanning direction? What about color ghost detection in the sub-scanning direction, which is performed using pixel color code data? This is done using color code data of line x 1 pixel.

The color code in which a color ghost has occurred is converted to a color ghost detection code (for example, roll), and then corrected to regular color code data in a color ghost correction section 45 at the next stage. In other words, the color code in which the color ghost occurs is corrected to the color code "10".

Reference numeral 43 denotes a delay circuit for the density signal, which is provided to match the time axis with the color code delayed for color ghost detection.

In this example, the memory is composed of 7 lines x 7 pixels.

The color code in which the color ghost has been corrected is supplied to monochrome (monochrome) and color discrimination means 47, and the discrimination output is supplied to a CPU provided in the main body of the color copying machine, and the color code is supplied to a monochrome (monochrome) and color discrimination means 47, and the discrimination output is supplied to a CPU provided in the main body of the color copying machine to distinguish between a color image and a monochrome image. Copy sequence (
(number of optical scans, etc.) is selected. The discriminating means 47 can form its discriminating output in the following manner.

For example, by scanning the original f1182 and creating histograms of R, G, and B density signals, as shown in FIG. Determine whether the information is a color image (chromatic) or a monochrome image (achromatic). A color code is determined based on the discrimination output.

The relationship between chromatic colors/achromatic colors and the discrimination results at that time is shown in the 16th section.
As shown in the figure.

The density signal output from the color ghost correction circuit 40 is subjected to filtering processing according to the image content in a rough filtering processing circuit 50.

For example, in the case of a character image, its resolution (for example, MTF
), and for photographic images, filtering processing is applied to flatten them.

This filtering process is implemented using, for example, a 3×3 convolution filter. An example is shown in FIG.

The figure particularly shows the case where it is configured as a cross filter,
A in the same figure is a filter for resolution correction, and B in the same figure is a filter for smoothing. Which filter to use is specified externally. This designation signal can also be generated automatically.

The numerical values shown in FIG. 17 are filter coefficients, but this is an example.

The MTF is calculated from the signal level y of the white signal and the No. 48 level X of the black signal using the following formula.

MTF= (y-x/y+x) X100 (%
) The filtered density signal is subjected to scaling processing such as enlargement and reduction in a scaling circuit 52.

The magnification processing is performed in the main scanning direction by data interpolation (including thinning) of density signals, and in the sub-scanning direction by controlling the moving speed of the scanner part 10A mentioned above. It is done.

The scaled density signal is then subjected to a shading process in a shading circuit 54.

The shading process includes both the case of shading the outside of the image information as shown in FIG. 18A, and the case of shading the inside of the hollow image information as shown in FIG. 18B. .

The shading process in A of the same figure outputs the shading data within the specified area, and OR outputs this and the density signal to the 1st value after shading.
It can be used as No. 3.

The shading process shown in FIG. 3B can be performed by performing the process shown in FIG.

In addition to halftone dots, waveforms, stripe waveforms, etc. can also be used for the mesh.

The shaded density signal is roughly supplied to a PWM modulation circuit 60, where the density signal is subjected to PWM modulation.

It is assumed that PWM modulation includes three-value or four-value multi-value processing. PWM modulation is a process performed to provide gradation for photographic images and resolution for character images.

In this case, the resolution is PWM in units of 1 pixel.
There is no problem with modulation, but in the case of gradation reproduction, when one pixel is used as a unit, it has been confirmed through various experiments that sufficient gradation cannot be obtained because density unevenness occurs due to PWM modulation. Ta. Therefore, in this example, two pixels are set as a unit only during photographic image processing.

FIG. 19 shows an example of the PWM modulation circuit 60, and the terminal 6
The concentration signal supplied to the D/A converter 1 is once supplied to the D/A converter 62 and converted into an analog signal, and the analog concentration signal is guided to the modulation section 63.

On the other hand, a screen signal generating means 65 is provided, in which three screen signals 5a=Sc shown in FIGS. 20 and 21 are generated.

The screen signals S a ”=S c all have the same waveform and differ only in phase.The first screen signal S
Based on a, the second screen signal Sb is 90'
The third screen signal SC is 1800 degrees out of phase.

These three screen signals S a = S c are supplied to the modulation section 63 . Then, modulation processing that emphasizes resolution is performed on the first and second screen signals Sa and Sb, and modulation processing that emphasizes gradation is performed on the first screen signal Sa and third screen signal Sc.

Starting with the former, analog density signals (image D/A output, Fig. 20,
G) are compared in level.

As a result, the comparison output Ca shown in FIG. Output cb is obtained.

When these are logically multiplied, the modulation output Sm as shown in Figure I is obtained.
is obtained. This is 1/1 of the first screen signal Sa.
This is equivalent to comparing the levels of analog density signals using a screen signal with a cycle of 2.

This 1/2 screen signal is the data clock DCK
Since the period is the same as (B in the same figure), a modulation signal Sm PWM-modulated in units of dots (pixels) can be obtained. A in the figure shows a digital density signal (image data).

Modulation processing when emphasis is placed on gradation is as follows.

A third comparison output Cc is generated from the first screen signal Sa used as a gradation screen signal and the analog density signal.
(Fig. 21E) is obtained. Similarly, a fourth comparison output Cd (H in the figure) is obtained from the third screen signal Sc and the density signal.

By logically multiplying these comparison outputs Cc and 'Cd, the modulation signal Sn shown in FIG. 1 is obtained.

Here, since the third screen signal Sc mentioned above is a signal obtained by inverting the phase of the first screen signal Sa and is obtained at the same timing, the comparison output Cc,
The first screen signal S by ANDing cd
This means that the levels of the analog image signals are compared in units of approximately one cycle of a.

In other words, the level comparison is performed in units of twice the period of the data clock DCK. If the analog image signal is PWM-modulated at a two-dot period in this way, it is possible to reproduce a gradation close to that of the input image.

One of these modulation signals Sm and Sn is selected by a selector 67, and the selected modulation signal Sm or Sn is supplied to the printer section 10C.

The selector 67 is manually or automatically controlled from the outside.

When the mode is manual, it is fixed to one of the modes (photo image/character image) set externally, and when it is automatic, it is selected according to the image information of the document.

Therefore, when automatic is selected, the above-mentioned color code can be used as the selection signal.

[Effects of the Invention] As described above, according to the present invention, when reproducing a color image by separating the colors into three colors, a black signal is created from the brightness information of the original.

According to this, even if it is a color original, a monochrome image can be reproduced based only on the brightness information, so there is no risk that the black density will decrease or color shift will occur and the image quality of the monochrome image will deteriorate.

Therefore, the color image processing apparatus according to the present invention is extremely suitable for application to digital color copying machines, digital color printers, etc. as described above.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a circuit system of a color image processing device according to the present invention, FIG. 2 is a block diagram of the entire color image processing device to provide a general explanation of the entire color image processing device, and FIG. 3 is a block diagram of the entire color image processing device. System diagram, Fig. 4 is an explanatory diagram of color overlapping processing, Fig. 5 is a system diagram showing an example of the circuit system of a color image processing device, Fig. 6 is a configuration diagram of the spectroscopic system, and Fig. 7 is a diagram of the shading correction circuit. System diagram, Figure 8 is a characteristic diagram showing the relationship between brightness level and density level, Figure 9 is a characteristic diagram showing gamma characteristics, and Figure 1 is a characteristic diagram showing the relationship between brightness level and density level.
Figure 0 is an explanatory diagram of the threshold matrix, Figures 11 and 12
The figures are each an explanatory diagram of the matrix, Fig. 13 is an explanatory diagram showing the state of color reproduction, Fig. 14 is a diagram showing the relationship between color code and density output, and Fig. 15 is an explanation of the histogram of the code corresponding to density. 16 is a diagram showing the relationship between image content and its discrimination result, FIG. 17 is an explanatory diagram of filtering processing, FIG. 18 is a diagram showing the shading mode, and FIG.
The system diagram of the WM modulation circuit, FIGS. 20 and 21, are waveform diagrams for explaining its operation, respectively. 30 ・ 32 ・ 40° ・ 50 ・ 52 ・ 54 ・ 60 ・ ・Color code generation means・Selector・Color ghost correction circuit・Filtering processing circuit・Scaling circuit・Shading circuit・PWM modulation circuit 0A 0B 0G 11~13 15 〜１７ ２１〜２４ ・Density adjustment circuit・Color image processing device・Part of scanner・Image processing section・Printer section・Standard density conversion circuit・Adjusted density conversion circuit・Color image processing means・Conversion ROM ・Monochrome image processing means・Auto Density adjustment circuit

Claims (1)

[Claims] (1) In a color image processing device that separates a color image into three colors and reproduces the color image based on these three colors, among the color information separated into the three colors, black and white are A color image processing device characterized in that a signal is generated.