JPH02168243A - Color picture processing device - Google Patents

Abstract

PURPOSE:To improve deterioration in picture quality owing to the dislocation of black levels by independently performing chromatic density adjustment and achromatic density adjustment. CONSTITUTION:Input color picture signals R, G and B are density-adjusted in density converting circuits 15 to 17 to perform color balance adjustment. However, this adjustment is performed independent of black level adjustment. To cope with this, a color picture processing means 20 and a monochromic picture processing means 25 are independently provided and each output is selected according to the contents of a picture, whereby suitable picture processing is attainable even if color and monochromic pictures are mixed. Consequently, even if the density of R, G and G is controlled to adjust color balance to a user's a desirable color, the black level never changes. Thus, deterioration in picture quality owing to the dislocation of black levels can be improved.

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 particularly a color image processing device that performs color balance adjustment separately. The present invention relates to a color image processing device capable of adjusting black level density.

[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 the original sound into three primary colors, for example, R, G, and B. (No. 3 is obtained, and in order to roughly match the color signal of the output system of the printer section, it is converted into Y, M, and C signals, for example.

When adjusting the color balance (color density adjustment) of a copied color image in a color image processing apparatus having such a color signal processing system, the following processing method can be considered.

The first method is to change the color balance by adjusting the signal levels of R, G, and B, and the second method is to adjust the signal levels of R, G, and B to change the color balance.

Adjust the color balance by adjusting the C signal level; S side?
It's a person.

In either case, the color can be adjusted to the user's preference.

[Problem to be solved by the invention] However, if the first or second method is adopted, the color balance and the black level will change accordingly, resulting in a loss of image quality.

That is, in any case, black must be reproduced using the three colors R, G, and B or the three colors Y, M, and C, so in order to adjust the color balance as described above, ,
R, G, B or Y, M.

This is because when the density level of C is adjusted, the black level also changes accordingly.

[Means for Solving the Problems J] In order to solve the above problems, the color image processing device according to the present invention is capable of reproducing color images, and includes the following steps: The special feature is that the density of each achromatic color can be adjusted independently.

[Function] R, G, B input color image (signal 31 is density conversion circuit 1
In steps 5 to 17, the density is adjusted and the color balance is adjusted. However, this color balance adjustment is performed independently of the black level adjustment.

The density-adjusted R, G, and B color image signals (density signals) are supplied to the color image processing means 20, and in this example, the Y
, M, C, BK (black) density No. 48.

In addition to the color image processing means 20, a monochrome image processing means 25 is provided.
No. G is supplied as a brightness signal.

The output of the monochrome image processing means 25 reproduces an achromatic image such as black characters.

The black level is adjusted in the monochrome image processing means 25. Therefore, adjusting the black level is separate from adjusting the color balance of chromatic colors, so how can you adjust the color balance without affecting the black level, and adjust the density of the already adjusted black level to achromatic colors? The image is reproduced.

If the color image processing means 20 and monochrome image processing means 25 are provided independently and the output of each is selected depending on the content of the image, even if color images and monochrome images are mixed, image processing corresponding to each can be performed. Since it is possible to take color drawings and monochrome drawings, my husband's? It can be processed without compromising image quality.

[Example] 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 that convert an optical f-image related to the image information of Go Hara obtained by optical scanning into an electrical signal. In this example, bimodal signals (analog signals) of three primary colors R, G, and B are shown as the electric signals.

[Printer section] OC refers to the final image (91) based on the image signal output from the signal section (pulse width modulation (PWM) processed output or multi-value processed output, etc.).
This refers to the processing system used to record this as a visible image.

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 charge i19. 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 a photoreceptor drum 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 this 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.

FIG. 5 shows an example of a digital color copying machine constructed as described above, particularly its several parts.

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 unit) 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 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 one-ra, 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, to maintain a constant temperature of the tube wall or promote warm-up,
It is kept warm by a POSISTOR heater.

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 an 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 103Δ to 103D and two dichroic coat films 105 and 106.

105 is a dichroic coating film N that reflects red R.
106 is a dichroic coat 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 focused on CODs 107-109. Each color separation image is generated by electricity (3
signal (image signal).

The blink 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 that has been modulated by the color signal is 9
The laser beam deflected and scanned by 35 and directed toward Cq passes through an optical path of a lens 116 and a mirror 117, and is focused on an image forming body 80.

When deflection scanning is started, a laser beam index sensor (not shown) detects the beam scanning and beam modulation using the first color 48 (eg, Y signal) is started.

Whether the first color signal is the same color, or roughly what color the second and third color signals are, is determined by the contents of a 3-bit digital signal called a scan code (No. 8) output from the main unit of the device. The scan code is 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.
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 the m image.

Toner replenishment of the developing unit 122 is performed by controlling a toner replenishing means (not shown) a1 based on a command signal from a system control CPU (not shown), so that toner is replenished when necessary. Become.

The yellow toner image is rotated with the cleaning plate 127 released, and then, as in the case of the first color signal, a second color signal (for example, an open signal) is used to overlay 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 performed in the order of cyan and black, and a required multicolor toner image is formed on the image forming member 80 (see FIG. 4). 124 is a cyan developing device, and 125 is a black developing device.

In the case of a monochrome image, a monochrome object 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 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
It is generally fed onto the surface of the image forming body 80 in a state in which the timing is synchronized with the rotation of the image forming body 80 . Then, the transfer i! to which a high voltage is applied from the high voltage power supply! A multicolor toner image is transferred onto the recording paper P by 130 and separated by a separation pole 131.

The separated recording paper P is conveyed to the fixing device 132 and undergoes a fixing process to obtain a color image.

The image forming body 80 after the transfer is cleaned by a cleaning device 26 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 provided, and this roller 129 is rotated in the opposite direction to the image forming body 80. By pressing, unnecessary toner is sufficiently cleaned and removed.

FIG. 1 shows a specific example of a color image processing apparatus 10 according to the present invention, particularly the circuit system. Therefore, the figure shows details of the image processing section 10B.

Image signals R, G output from CCDs 107 to 109,
B is supplied to the A/D converters 2 to 4 via input terminals IR to IB, and is converted into a predetermined number of bits, in this example 8 bits of digital (shading). 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. White No. 48 (normalized signal) is A/
D converter 2-40 standard (can be used as No. 5).

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

In this example, 4? In addition to the f'a degree conversion circuits 11 to 13, density conversion circuits 15 to 17 for adjustment are provided, respectively. All density conversion times '#111 to 13.15 to 17 are lookup tables (LtJ T ) by ROM.
configuration can be adopted.

In density conversion, the relationship between the intensity level of the image signal and the density 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 generating means 30 which functions as an achromatic color determining means.

In 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, for example, as shown by curves Lb-Ld in FIG. Then, a manual select signal for RlG and B is supplied from the terminal 8a, and 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. 15-17.

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 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 8 are 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 is possible to use a well-known conversion formula (such as the linear masking method), but this conversion formula has a large error, so the difference between the reproduced color and the original color is large.

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 α degree 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, density data that minimizes the color difference is generated based on the discrimination amount such as color difference (here, △E "ab" is used). An example of the generation procedure is as follows. Shown below.

- 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, the toners are superimposed on each other, so the colors expressed using color toners are 256' colors.

These colors are output to the printer section 10C to obtain a color chart. The obtained color chart is placed on a 10A scanner (Rh5), and is scanned into R, G, B? ! It is converted into a brightness signal of the r8 pit. This R,G.

Convert the B brightness signal to CIE's XYZ signal and save it as data (.

→Ma (I) (7) In order to convert the R, G, and B signals into CI E -XYZ coordinates, the characteristics of the scanner part 10A must be investigated. Therefore, about 20 colors of colored paper are selected from the Munsell color chart, and a total of 11 colors are obtained using a colorimeter, and the values of the colored paper in the CIE-XYZ coordinate system are obtained.

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 (1) and (11) 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, a = i
By finding the parameters of
The R, G, and B signals can be converted into the XYZ color system, and the characteristics of the scanner part 10A can be investigated.

As mentioned above, the printer can display 256 colors with one dot, but color reproduction requires the ability to display even more colors.

In order to solve this problem, a four-value deza method is used in this example. This uses three threshold matrices with dot sizes of 4x4, and inputs integer values from O 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 for all 11 colors was performed 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. Processing that changes the black component to black ink in an 8':8 ratio and reduces the amount of other chromatic inks used is generally inking (UCA) and undercolor removal (
It is called UCR).

In this example, if the color signals Y, M, and C are all greater 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+Pxfflin (C, M, Y)=BK'C-B
KXS=C'M-BKXS=M'Y-BKXS=Y' Here, 'm1n()' is a function that takes the minimum value among the numbers in (), and P is the degree of BK toner replacement. This is a parameter that indicates

S is the changeover switch between UCA and UCR, and S= for UCR.
1. When in UCA, s=o. In this example, P=1, S
= LL: was set so that 100% UCR was performed as a result.

In this example, BK=O in the above equation so that BK' can be obtained from h of the YMC black component. Therefore, the types of colors reproduced by blinking 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, reproduce the color dot pattern 2 to the third power of 49.
Let it happen. First, one Y, M, C signal (0 to 48) is determined. For example, Y=30. When M=20 and c=10, Y'=20. M' = 10, C' = O1BK
'=lO.

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 Y, M, and C values we just decided are the points in the upper left corner of the matrix, Y' is greater than 1 to 17! Since it is smaller than <, 33, it becomes 2. Similarly, M' is 1, C' is O, BK
' becomes 1. These Y', M', C'BK'
The four multi-value matrices are superimposed as shown in FIG. 11 to obtain a multi-value dot pattern.

Here, the values of C', M'Y'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
, 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 yellow level is O8 and the black level 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 in the IE-XYZ coordinates are X, Y, and Z, then X= (1/16) #IX i Y= (1/16) Ha Yi Z= (1/16) Ha Zi. This involves the condition that the size of the dots is constant when actually outputting. If the size of the dot is large,
If it differs depending on (1), the following formula may be used.

That is, X= (#IX i-3i) /bear S iY= (#
+Yi-3i)/5i Z= (KumaZi-Si)/KidneySi 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 to 0 to 48, and a total of 493 reproduced colors are calculated.

Now, by (IN), the color of the document read by the scanner part 10A can be converted into CIE-XYZ values, and by (Ill), the color of the document read by the scanner part 10A can be converted to CIE-XYZ values, and by (Ill), the color of the document read by the scanner part 10A can be converted to
All the reproduced colors can be obtained by CIE XYZ values when using a four-value dither with a matrix size of 4×4.

CI+) and (Il) to maintain the same color tone as the Rama manuscript as much as possible.
A case will be described in which the data of 1) 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 it becomes a 5-pit 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 to XYZ by C11).
, 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 LIC are also effective.

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

L' = 116 (Y/Yo) -16a'' = 5
00 [(X/Xo) −(Y/Yo
)ko b”=200 [(Y/Yo)-(Z/Zo)1 Next, the color closest to this L Ra* b* is calculated by the printer at (Ill) as 49 cubed. A color is selected from among the colors. At this time, the discriminant quantity representing the similarity of colors is important, but it is sufficient to use the Euclidean distance on a uniform color space.

The reason why No. 13 to be compared was expressed 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 that has the shortest distance (color difference, ΔE"ab in CI E-L"a'b" color space), and Calculation processing is performed to select colors from among the colors reproduced by the printer section 10C, and the obtained relationship (scanner section 10A) is performed.
R, C from the side; Y, M, C representing the reproduced colors of the Ba multiplied signal printer.

(relationship with BK signal) and 1 is sufficient.

By the above method, if the color of the original is not within the color gamut, 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 the color is the most easily distinguishable.

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 can be processed in several tens of minutes using a large-scale computer, and the latter can be solved because the memory value (δ) is low.

Density No. 48 created in this way is stored in each of the color image processing means 20, and in addition to this color image processing means 20, a monochrome image processing means 25tJ is provided, which receives the G signal. It is supplied as a brightness signal of image information, and in this example is converted into *degree data excluding 64 gradations.

The monochrome image processing means 25 is supplied with a density adjustment signal for the black level from the density adjustment circuit 8 described above to control the black level, and also to control the black level from the automatic density adjustment circuit (EE circuit) 27. 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 can be prepared.

Then, the gamma characteristic is specified by the density adjustment signal for 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). ′! In the IJ theory, only the rising point may be shifted while leaving the 7 characteristics as is, as shown by the broken 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 in addition, in order to perform background level adjustment (automatic density adjustment) only in the case of an achromatic image, color code data (a little A color code of "Oo" or "11" indicating an achromatic color is also provided.

The use or non-use of the EE circuit 27 is determined by the E supplied to the terminal 28.
Although it is controlled by the presence or absence of the E selection signal (JJ selection by manual), it can also be configured to prohibit automatic adjustment of the background level when the black level density adjustment signal is manually selected.

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 (δ MONO) output by the monochrome image processing means 25 are respectively supplied to the selector 32, and when it is a color image, the density signal output from the color image processing means 20 is selected, and the achromatic color density signal is selected. Sometimes, 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, B'+1 degree signals from the standard 4a degree conversion circuits 11 to 13, and a color code ( 2 pits) is output. Therefore, this color code generating means 3
It is more convenient to configure 0 with ROM.

FIG. 14 shows the relationship between the color code and the density signal selected one time 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.

For convenience of explanation, the example shown in FIG. 14 is a description of four colors of Y, M, C, and BK and a color code related to a monochrome image.

The selected 6-bit density signal and color code 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 a color ghost is provided to remove these color ghosts. There is.

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 7-pixel color code data, and color ghost detection in the sub-scanning direction is performed using 7 lines x 1 pixel color code data.

For color codes where color ghosts occur, change to a color ghost detection coat (for example, roIJ)! i! ! Then, the color ghost correction section 45 at the next stage corrects the data into regular color code data. In other words, a color code in which a color ghost occurs can be corrected to a color code of "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 for 7 line pixels (slightly depleted).

The color code corrected for color ghosting is supplied to black-and-white (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 may form its discriminating output in the following manner.

For example, while scanning the original 82 and creating histograms for R, G, and 80 degree No. 48, as shown in FIG. It is determined whether the image information is a color image (chromatic color) or a monochrome image (achromatic color). 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 further subjected to filtering processing according to the image content in a filtering processing circuit 50.

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

This filtering process can be realized 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.

M i "F is calculated from the signal level y of the white signal and the signal level X of the black signal by the following equation.

MTF=(y-x/y+x)X100 (%) The density No. 18 that has been subjected to the fill ringing process 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) of density signals, and in the sub-scanning direction by controlling the moving speed of the scanner part 10A described above. .

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 the 18th ROM, and the case of shading the inside of the hollowed-out image information as shown in FIG. 8, for example.

In the shading process shown in FIG. 3A, it is sufficient to output shading data within a designated area and use the OR output of this and the density signal as a signal after shading.

The tethering process shown in FIG. 2B 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, 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 signal that has been completely supplied to the D/A converter 62 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 S a = S c 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. First screen signal Sa
With reference to , the second screen signal Sb is out of phase by 90 degrees, and the third screen signal SC is out of phase by 180 degrees.

These three screens (M numbers 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 the first screen signal Modulation processing that emphasizes gradation is performed on Sa and the third screen signal Sc.

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

As a result, a comparison output Ca shown in the figure E is obtained from the first screen signal Sa and the density signal. Similarly, the second comparison output cb of H in the same figure is obtained from the second screen signal sb and the density signal.

When these are logically multiplied, the modulation output Sm as shown in (■) in the same figure is obtained.
or can be obtained. This is 17 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 that shown in FIG. 8, a modulation signal Sm PWM-modulated in units of dots (pixels) can be obtained. In the figure, Δ indicates 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 modulated signal Sn shown in FIG. 1 is obtained.

Here, since the third screen (g Sc) mentioned above is a signal obtained by inverting the phase of the first screen (g Sa) and is obtained at the same timing, the comparison output C
By ANDing c and Cd, the levels of the analog image signals are compared in approximately one cycle of the first screen signal Sa.

In other words, the level comparison is performed in units of twice the period of the data clock DCK. By performing PWM modulation on analog image No. 48 at a two-dot period in this manner, 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.

For manual trimming, the mode can be fixed to one of the modes (photograph/text) set externally, and for automatic trimming, the mode is selected according to the image information of the original.

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, the density adjustment of chromatic colors and the density adjustment of achromatic colors can be performed independently.

According to this, even if the color balance is adjusted to the user's favorite color by adjusting the density of R, G, and B, the black level does not change at all. Therefore, it has the feature of improving image quality deterioration caused by black level deviation.

Therefore, the color image processing apparatus according to the present invention is extremely suitable for application to digital color copying machines, digital color links, 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, and FIG. 3 is a block diagram of the entire color image processing device. 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 shading correction diagram. A system diagram of the circuit, 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 matrix, Figs. 11 and 12 are explanatory diagrams of the matrices, respectively, Fig. 13 is an explanatory diagram showing the state of color reproduction, Fig. 14; Relationship between color code and density output FIG. 15 is an explanatory diagram of the histogram of the code corresponding to F gl, FIG. 16 is a diagram showing the relationship between image content and its discrimination result, FIG. 17 is an explanatory diagram of filtering processing, and FIG. 18 19 is a diagram showing the shaded aspect, FIG. 19 is a system diagram of the PWM modulation circuit, and FIGS. 20 and 21 are
death! are waveform diagrams for explaining the respective operations. 8...Density adjustment circuit 10...Color image processing device 10A...Skinner part 10B・IOC・11-13・15-17・20・21-24・25・27・30・32・ 40 ・ 50 ・ 52 ・ 54 ・ 60 ・ ・Image processing section ・Printer section ・Standard density conversion circuit ・Adjusted 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, filtering processing circuit, variable magnification circuit, shading circuit, PWM modulation circuit Patent applicant Konica Co., Ltd. Agent Patent attorney Kunio Yamaguchi 82: Original and stop: Color image processing device and 30 Figure 3 Overlay transfer method Figure 4 1C2: Part of the scanner's spectroscopic system Figure 6 5: Naging correction circuit Figure 7

Claims (1)

[Claims] (1) A color image processing device capable of reproducing color images, characterized in that density adjustment of chromatic colors and density adjustment of achromatic colors can be performed independently.