JPH02144566A - Color image processor - Google Patents

Abstract

PURPOSE:To accurately discriminate the color information of a color original without increasing the scale of a circuit by deciding it based on information for identifying a white color, an achromatic color and a chromatic color, which is given every picture element, whether the original is a black-and-white one or a color original and controlling image forming processing based on the decided result. CONSTITUTION:An encoded signal (color code data) corresponding to the chromatic color, the achromatic color and the white color is outputted every picture element from a color code generation means 30. The color code data is supplied to a means 47 for discriminating the black-and-white color and the chromatic color so as to decide whether the original is the black-and-white one or the color original. The decision output is incorporated in a CPU which controls a color original processor so as to decide the appropriate number of image forming processing times, etc. Therefore, whether the original is the black-and- white one or the color original is decided by applying the output from the color code generation means as it is. Thus, the constitution of a discrimination means for discriminating the black-and-white original from the color original is simplified.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a color image processing device suitable for application to an electrophotographic digital color copying machine capable of full-color copying, and particularly a color image processing device that mainly uses black characters. The present invention relates to a color image processing device that is controlled.

[Background of the Invention] Many electrophotographic digital color copying machines capable of full-color copying are configured so that a desired color copy can be obtained only after a plurality of image forming processes.

For example, yellow Y,
When reproducing a desired color original using three colors, magenta M and cyan C, or four colors including black (ink color) BK, in most cases, three colors are used.
By repeating the image forming process twice or four times and overlapping the developer, the desired color original can be copied for the first time.

[Problems to be Solved by the Invention] In a color image processing apparatus that copies color originals using such a superposition method, the number of image forming processes must be controlled depending on the color originals used.

Even if it is a color original, if it is Y, M, C,
A color image can be developed with a corresponding developer in a single imaging process. However, in the case of other chromatic color or monochrome originals, it is necessary to repeat the image forming process corresponding to the target color.

Therefore, in this type of color image processing apparatus, detecting color information of a color original is a very important issue. In order to accurately detect color originals, it is relatively easy to increase the scale of the circuit and configure the color information discrimination means, but this increases costs and hinders miniaturization of the circuit board. .

Therefore, the present invention takes these points into consideration and proposes a color image processing device that is capable of accurately determining color information of a color document without increasing the circuit scale.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a color image processing device that reproduces a color original by reversing a plurality of image forming processes. The document is characterized in that it determines whether it is a black and white document or a color document based on the provided information that identifies white, achromatic colors, and chromatic colors, and controls the image forming process based on the determination result. be.

[Operation] The color code generating means 30 generates a chromatic color for each pixel.
Coded signals (color code data) corresponding to achromatic colors and white are output.

This color code data is roughly supplied to monochrome and chromatic color discrimination means 47, and it is determined whether the document is a monochrome document or a color document. Specifically, for example, color code data is obtained by Bliss Ganning a color document, the frequency of the color code data is detected, and a determination is made between a color document and a monochrome document based on the mutual relationship between the frequencies (FIGS. 15 and 15). (See Figure 16).

The judgment output is taken into the CPU that controls the color document processing apparatus, and the appropriate number of image forming processes can be determined. In other words, based on the judgment output, the scanner part 10
The number of optical scans of A and the number of rotations of the image forming body 80 provided in the printer section 10C are set.

〔Example〕

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

In this example, as described above, color originals are printed in Y and M formats.

This is a case where the image processing system is applied to an image processing system that is expressed using four colors, C and BK, and uses a dedicated black BK to reproduce black characters in black and white originals among the original colors.

The reason why black characters are reproduced using a special black color in this way is that if black is expressed using Y, M, and C, the density of the black inevitably tends to be low.

In addition, when reproducing black text using a dedicated black BK, one document contains a color image (color original) such as a color photograph, and a monochrome image (black and white) such as black text. Even if there are images containing a mixture of
Another advantage is that color images can be faithfully reproduced as color images, and monochrome images can be faithfully reproduced as monochrome images.

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 electrical signals No. 18.

The printer section 10C is the image signal outputted from the image processing section OB (the output that has been subjected to pulse radiation modulation (PWM) processing or multi-value processing).

It is a processing system that records the output as a visible image based on the output corresponding to M, C, and BK.

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

Then, as shown in FIG. 3, developers (toners) for each of the colors Y, M, C, and BK 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 section 10B is a processing section for performing appropriate image processing on the input image signal, and refers to scaling processing, filtering processing, hatching processing, PWM processing, color ghost processing, and the like.

In addition to these, an image processing system (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. This color conversion system is a main part of the present invention, and as shown in FIG. ) 301 selector 32, discriminating means 47 for discriminating between black and white originals and color originals, and the like.

The selector 32 is controlled based on the color code and the discrimination output of the monochrome/color discrimination means 47, 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 can be converted into four colors as an example. Y, M
, C, and BK are used to match the colors (tones) of the output system of the printer section 10C. The G signal can be supplied to the monochrome image processing means 25 as a brightness signal of a color original.

The color code generating means 30 outputs color code data related to chromatic colors, white, and achromatic colors, and supplies this to the determining means 47 directly or indirectly.

The determining means 47 determines whether the document is a color document or a monochrome document based on the input color code data. The judgment output is supplied to a CPU (not shown) which controls the apparatus, and controls the image forming process. The details will be described later.

FIG. 4 shows an example of the mv1 part of the digital color copying machine configured as described above.

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

First, the original 82 on the original table 81 is optically scanned by the 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 with mirrors 89 and 89°
Consists 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). 92
．． 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 enhancement of specific colors and g-attenuation.

In this case, to prevent flickering, these fluorescent lights 86 are
It is lit and driven by a high frequency power source of approximately 40 kHz. 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. 5, the spectroscopic system 102 is composed of four prisms 103A to 103D and two dike coating films 105 and 106.

105 is a dichroic coating film that reflects red R; 10
6 is a dichroic coat film that reflects blue B. The color-separated images, which are the respective reflected lights, are imaged onto corresponding optical sensors, in this example CCDs 107-109. Each color separation image is converted into an electric signal (image signal) by each CCD107-109.

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.
The deflected laser beam is deflected and scanned by a lens 116 and a mirror 117, and an image is formed on an image forming body 80 through an optical path formed by a lens 116 and a mirror 117.

When deflection scanning is started, beam scanning is successfully detected by a laser beam index sensor (not shown), and beam modulation using a first color signal (for example, Y (No. 8)) is started.

What color is used as the first color signal, and furthermore, what colors are used as the second to fourth color signals, depends on the content of a 3-bit digital signal called a scan code output from the control section of the main body of the device. It's decided.

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 formed by a developer M12 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.

Image forming processes such as electrostatic latent image processing and development processing are executed in the order of cyan and black toner images, and a required multicolor toner image is formed on the image forming member 80 (see FIG. 3). 12
4 is a cyan developing device, and 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 a total of four development processes.

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 fed from the paper feeding device 141 via the feed roll 142 and the timing roll 143 is
The image forming member 80 is conveyed onto the surface of the image forming member 80 while being timed with the rotation of the image forming member 80 . Then, the multicolor toner image is transferred onto the recording paper P by the transfer pole 130 to which a high voltage is applied from the high voltage power supply.
131.

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 cleaning is completed, the blade 127 can release the pressure, but in order to remove unnecessary toner that is left behind when the blade 127 is released, an auxiliary cleaning roller 129 is provided. By doing this, unnecessary toner is sufficiently cleaned and removed.

FIG. 6 shows a specific example of the circuit system of the image processing apparatus 10 according to the present invention. Therefore, the figure shows details of the image processing section 10B.

Image signals R', G output from CCDs 107 to 109
, B are supplied to the A/D converters 2 to 4 via input terminals IR to IB, thereby being converted into digital signals of a predetermined number of bits, 8 bits 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
Transducers 2-40 are used as reference signals.

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. Each of the density conversion circuits 11 to 13 and 15 to 17 can have a look-up table (LU'r) configuration using a ROM.

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 color code generation means 30.

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 as shown in curves Lb to Ld in FIG. 9, for example. Then, a manual select signal for RlG and B is supplied from the terminal 8a, and the density selection signal (No. 8 (R/G/B)) is used to select the corresponding gamma characteristic from the density adjustment circuit 8.
is supplied to adjustment density conversion circuits 15-17.

Manual selection signals for R, G, B and BK supplied from terminal 8b as described later are 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 B11) 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.

Specifically, the color image processing means 20 processes R and G.

In order to match the density signals of 83 colors with the signals of the output system of the printer section 10C, color separation processing is performed to convert the density signals of 4 colors (Y, M, C, BK) (6-t data), for example.

Therefore, the color image processing means 20 has Y and M images.

Conversion ROMs 21 to 24 dedicated to C and BK are provided, and each density signal of Y, M, C, and BK is referred to by the input density signal.

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

In order to convert BK density to No. 8, it is possible to use a well-known conversion formula (such as the 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 of the color image processing means 20 as density data, especially in order to minimize the deviation from the original color. .

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, density data that minimizes the color difference is generated based on the discrimination amount such as color difference (here, ΔE "ab" is used). An example of the generation procedure is shown below. show.

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

In the digital copying machine of this example, the toners are superimposed on each other, so the colors that can be expressed using color toners are 4'=256 colors.

These colors are outputted to the printer section 10C to obtain a color chart. The obtained color chart is placed on the scanner part 10A (11 units), and converted into a lightness number 48 with -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 Ma(I) into ecIE-XYZ coordinates, the characteristics of the scanner part 10A must be investigated. Therefore, we selected about 20 colored papers from the Munsell color chart, measured them with a colorimeter, and determined the CI of the colored papers.
E - 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, the brightness of R, G, and B (No. 8) obtained by the scanner part 10A of the colored paper is 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 parameter a=i is obtained from the two types of values by approximation using the least squares method. That is, by determining the parameters a to i, the R, G, and B signals from the scanner part 10A can be converted to the XYZ color system, and the characteristics of the scanner part 1OA can be investigated.

As mentioned above, the printer can display 256 colors in one dot, but the ability to display even more colors is required 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 make the output into a 4-value No. 48 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+PXmin (C,M,Y)=BK'C-BKX
S=C'M-BKXS=M'Y-BKxS=Y' Here, 'm1n()' is a function that takes the minimum value among the numbers in (), and P indicates the degree of BK toner replacement. It is a parameter.

5LtUCA and UCR selector switch, S when UCR
= 1, and S = 0 during UCA. In this example, P is 1,
S=1 was set, resulting in 100% UCR.

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 the 4903rd power.

However, the number of reproduced colors is sufficient, and it can be safely assumed that the 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=20, C=10, Y'=20, M'=10, C'=0, B K'=0
is converted to

The values of Y', M', C', and BK' are multi-valued (0
~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 in the upper left corner of the matrix, Y' is greater than 1=17 and smaller than 33, so it becomes 2. Similarly, M' is ]1, C' is 01B
K' becomes 1. These Y', M', C'
, BK'' are superimposed as shown in FIG. 11 to obtain a multivalued dot pattern.

Here, the values of C', M', Y', and BK' at the same position correspond to the colors 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 (I) 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-XYZO values in 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 XE-XYZ coordinates are shifted to X, Y, and Z, then the following will be obtained: This is accompanied by the condition that the size of the dots is 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-(AX i-3i)/As 1 Y=(bear Yi-Si)/to5i Z=(^Zi-Si)/#+Si 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, set the parameters of CM and Y to 0 to 48.
are set independently, 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 (IIO allows the printer part 10C to also use a four-value dither with a matrix size of 4 x 4. All reproduced colors in this case are obtained by CIE XYZO values.

Hill-”--Ma...
) and obtain the relationship 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, '= 3.16 (Y/Yo) -16a''=50
0 [(X/Xo)-(Y/Yo)]b'=200 [
(Y/Yo)-(Z/Zo) First, this L* a*
The color closest to the color represented by b* is selected from among the 49 cubed colors produced by CIII) printers. 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. Because there is.

Therefore, the color closest to the color from the scanner part 10A is the one whose distance # (color difference, ΔE"ab in CI E-L"a"b" color space) is the shortest, and that is selected from among the colors reproduced by the printer section 10C, and the obtained relationship (scanner section 10A) is performed.
R, G, Ba degrees from the side 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 the state of this color tone reproduction.

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 contains image information. A G signal containing contour information is supplied as a brightness signal of image information, and is converted into density data having 64 gradations in this example.

Then, the monochrome image processing means 25 is supplied with the density adjustment signal for the black level from the density adjustment circuit 8 mentioned above, and the black level is controlled. A background adjustment signal is supplied.

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 (FIG. 9 - indicated by the dashed line).

The reason why the density adjustment signal for black level is made independent from the density adjustment signal for color balance adjustment is to prevent the black level from changing due to color balance adjustment.

The reason why the background level can be adjusted even in monochrome image processing is to reproduce a clear image by removing the gray background part of the document.

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. For this reason, the output of the monochrome image processing means 25 is supplied to the EE circuit 27 as density information, and also the ground level tone V! is supplied only in the case of an achromatic image. , to perform (automatic density adjustment),
Color code data (a color code of "00" or "11" indicating an achromatic color, which will be described later) is supplied.

When the EE circuit 27 is used or not, E is supplied to the terminal 28.
Although it is controlled by the presence or absence of the E-select signal (selected manually), it can also be configured to prohibit automatic adjustment of the background level when the black level density adjustment signal is manually selected.

The density signal outputted from the color image processing means 20 (for convenience, the same symbols as the color signals Y, M, C, and BK are used) and the monochrome density signal MONO outputted from the monochrome image processing means 25 are as follows. are respectively supplied to the selector 32,
When the image is a color image, the density signal output from the color image processing means 20 is selected, and when the image is achromatic, 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 R, G, and B density signals from the standard density conversion circuits 11 to 13 are supplied to the color code generating means 30, 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 four colors, C and BK, are available for selection, for convenience of explanation, the example shown in FIG. 14 is Y, M, and C.

Only the color codes related to BK4 colors and monochrome images are described.

The selected 6-bit density signal and color code are supplied to a color ghost correction circuit 40.

Although it varies depending on the color image processing means and 00 configuration, 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). Color ghost detection in the main scanning direction is performed using color code data of 7 pixels, and color ghost detection in the sub-scanning direction is performed using color code data of 7 lines x 1 pixel.

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

43 is a delay circuit for density (No. 3), 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 of pixels.

The color code with the color ghost corrected is used as a discrimination means 47 between a color original and a monochrome original, that is, a color image and a monochrome image.
and its discrimination output is sent to the CP installed in the main body of the device.
The image forming process is selected depending on whether the image is a color image or a monochrome image.

In other words, in accordance with this discrimination output, the number of optical scans of the scanner part 1OA, the number of rotations of the image forming body 80 provided in the printer part 1oc, etc. can be specified depending on the color of the color image.

The discriminating means 47 can form its discriminating output in the following manner.

First, before main scanning, the document 82 is pre-scanned (briscanned) to create histograms of R, G, and I11 degree signals. Next, as shown in Fig. 15, image information is displayed in color in pixel units based on the relationship between the total frequency of color code data representing chromatic colors and the total frequency of color code data (00°11) representing achromatic colors. chromatic color) or
Determine whether the image is monochrome (achromatic, white). The image forming process is determined based on the determined output.

For example, if the original is all red, Y, M.

Since red is reproduced by three image forming processes of C, in this case, the number of optical scans and the number of rotations (scans) of the image forming body 80 are set to three.

The relationship between chromatic colors, achromatic colors and their discrimination results is shown in the 16th section.
As shown in the figure.

The density signal output from the color ghost correction circuit 4o is further subjected to filtering processing according to the image content in a filtering processing circuit 5o.

For example, in the case of a character image, its resolution (for example, MTF
), and filtering processing that smoothes photographic images is performed.

This filtering process can be realized using, for example, a 3×3 Compolis cow three 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 white 4:3 signal level y and the signal 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 the scaling circuit 52.

The magnification processing is performed in the main scanning direction by data interpolation (including thinning) at a density of 4g, and in the sub-scanning direction by controlling the moving speed of the scanner portion 10A described above.

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

The shading process includes both a case where the outside of the image information is shaded as shown in FIG. 18A, and a case where the inside of the hollowed out image information is shaded as shown in FIG. 8, for example.

In the shading process shown in FIG. 5A, shading data may be output within the designated t: area, and the OR output of this and the density signal may be used as the shading signal.

The shading process shown in FIG. 3B may be performed on the density signal that has been subjected to the hollowing process.

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, it has been confirmed through various experiments that if one pixel is used as a unit, density unevenness occurs due to PWM modulation, and sufficient gradation cannot be obtained. 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 supplied to No. 1 (No. 1 is once supplied to the D/A converter 62 and converted into an analog signal, and its analog sensitivity is
No. 8 is guided to the modulation section 63.

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

The screen signals Sa to Sc all have the same waveform,
Only the phase is different. With the first screen No. 13 Sa as a reference, the second screen signal Sb is out of phase by 900 degrees, and the third screen signal (= No. SC) is out of phase by 180 degrees.

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 screens No. 13 Sa and Sb, and modulation processing that emphasizes gradation is performed on the first screen signal Sa and the 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, a comparison output Ca shown in the figure E is obtained for the first screen No. 48 Sa and the density No. 4=. Similarly, the second
The second comparison output cb shown in FIG. 14 is obtained by combining the screen signal sb and the density signal.

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

By logically multiplying these comparison outputs Cc and Cd, a modulation signal Sn shown in the figure 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 Ce,
By ANDing Cd, the first screen signal Sa
This means that the levels of analog image No. 48 are compared in units of approximately one period of .

In other words, the level comparison is performed in units of twice the period of the data clock DCK. By performing PWM modulation on the analog image signal at a two-dot period in this manner, it is possible to reproduce gradations close to those of the input image.

One of these modulation signals Sm+Sn is selected by the selector 67, and the selected signal is t-co-modulated (No. 3 Sm or S
n 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 (photograph/text) 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 explained above, according to the present invention, it is possible to determine whether a black and white document or a color document is a black and white document based on the information that identifies white, achromatic color and chromatic color given to each pixel. It is designed to control the body formation process.

According to this, the color conversion processing system 10 constituting the image processing section
It is possible to determine whether the document is a monochrome document or a color document by directly using the output of the color code generating means provided in B. Therefore, the present invention has the feature that the configuration of the discriminating means for discriminating whether the document is a monochrome document or a color document can be simplified.

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

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the entire device to provide a general explanation of the color image processing device according to the present invention, FIG. 2 is a system diagram of the color image processing device, FIG. 3 is an explanatory diagram of color overlapping processing, and FIG. 4 is a block diagram of the entire device. FIG. 5 is a configuration diagram showing an example of the mechanism of a digital color double VM. FIG. 5 is a configuration diagram of a spectroscopic system. FIG. 6 is a system diagram showing an example of a circuit system of a color image processing device. FIG. 7 is a diagram of a shear ink correction circuit. System diagram, Fig. 8 is a characteristic diagram showing the relationship between brightness level and density level, Fig. 9 is a characteristic diagram showing gamma characteristics, Fig. 10 is an explanatory diagram of the threshold value matrix, and Figs. 11 and 12 are respectively An explanatory diagram of the matrix, Fig. 13 is an explanatory diagram showing the state of color reproduction, Fig. 14 is an explanatory diagram showing the relationship between color code and density output, Fig. 15 is an explanatory diagram of the histogram of the code corresponding to density, Fig. 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,
FIG. 9 is a system diagram of the PWM modulation circuit, and FIGS. 20 and 21 are waveform diagrams for explaining its operation. 8...Concentration adjustment circuit 10A, 10B, ridge 10C, 3, 1-Ll, 3, 15-17, 20, 21-24, 25, 27, fist 30, 32, 40, 47 ◆ 50, 52, 54, ・Color image processing device, scanner part, image processing unit, printer unit, standard density conversion circuit, tone N density conversion circuit, color image processing means, conversion ROM, monochrome image processing means, automatic density adjustment circuit, color code generation means, Selector, color ghost correction circuit, means for distinguishing between black and white originals and color originals, filtering processing circuit, variable magnification circuit, shading circuit, overlapping transfer method l: Part of the scanner spectroscopic system Figure 5: Shading correction Circuit diagram 7 Background level Figure 12

Claims (1)

[Claims] (1) In a color image processing device that reproduces a color original by repeating multiple image forming processes, a black and white original is reproduced based on information that identifies white, achromatic color, and chromatic color given to each pixel. A color image processing apparatus characterized in that it determines whether a document is a color original and controls the image forming process based on the determination result.