JPH0732460B2 - Color image processor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus, and more specifically, it is possible to electrically process a color density signal and obtain a color copy or a color display by using a color output unit. The present invention relates to a color image processing device.

Conventional technology Office automation (O
As a pioneer of A), there is a copier as a widely used device. The majority of copiers on the market today are for black and white, and colors are rarely seen except in special cases. The main reason for this is that the cost of the color copying machine is high, but other than that, there is a lack of image quality stability.

For example, looking at the image quality when a copy of a text original is made in a black-and-white copying machine, and then the copy is made as a copy (grandchild copy), even if the grandchild copy is repeated 4 to 5 times, it is practically manageable. The copy quality that can withstand is maintained. On the other hand, if the same operation is performed on a color character document with a color copying machine, the image quality is severely deteriorated after a few times, and color noise becomes noticeable. That is, not only is the shape of the characters written on the original deformed and the color density becomes lighter (or darker), but also colors that do not exist on the original are generated (or disappeared). The difference between the two is that a black-and-white copier is made to be suitable for copying document originals in which halftone reproduction is not so important, while a color copier is a copy of a photograph in which halftone reproduction is very important. Because it is made to be suitable for.

It is relatively good to take a grandchild copy of a text original with a black-and-white copying machine because the gradation characteristic of the black-and-white copying machine, that is, γ (gamma) characteristic is established. FIG. 1 shows an example of γ characteristics of a black-and-white copying machine and a color copying machine. 1A shows the γ characteristics in the case of a black-and-white copying machine, and FIG. 1B shows the γ characteristics in the case of a color copying machine. The horizontal axis represents the reflection density of the original, and the vertical axis represents the reflection density of the copy after copying. Is. It can be seen that in a black-and-white copying machine, when the document reflection density is intermediate, the copy tends to be unified into either high density or low density.
It is possible to change the γ characteristic of the color copying machine and make the characteristic tilt like the black and white copying machine. In that case, however, the colors of the complicated original will gradually converge to any one of the total of six primary colors and their mixed colors as the grandchild copies are overlaid. In other words, subtle colors are not preserved no matter how dark their density level is.

As a conventional similar technique, for example, there is a pseudo-color method in which a specific color is associated with each gradation of the density level of a black-and-white original and is output. By associating gradation and color,
The two methods, generally called the rainbow conversion, and the warm-cold conversion method, which is favorably used for computer tomography (CT) images in the medical field, are particularly famous. However, in this case, the input image is monochrome, the output color is appropriately associated with the gradation, and a color that does not actually exist is output. None of these conventional similar techniques has a conventional example in which an input image is a color image.

The present invention has been made in view of the above circumstances, and color correction or color copying is performed by performing color correction according to the correlation between a color represented by an input image signal and a plurality of preset specific colors. The purpose is to improve the image quality during display.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram of a color copying machine according to an embodiment of the present invention. In the figure, a color grayscale image on an original 1 reaches a dichroic mirror 3 for three-color separation via a lens 2, where the spectrum of light of three colors of yellow (Y), magenta (M), and cyan (C) is obtained. And is imaged on the CCD solid-state image pickup elements 4-1, 2, and 3. Further, here, it is converted into three electric signals for the optical spectrums of Y, M and C, and after being amplified to a predetermined level by the video amplifiers 5-1 2 3 and then A / D
The digital signals Y, M and C are quantized by the converters 6-1, 2 and 3, respectively. A signal processing circuit 7 converts the signals Y, M, and C into signals Y ', M', and C ', respectively. This will be described in more detail with reference to FIG. 10-1, 2, 3 are D / A converters, 8
-1,2,3 are ink jet printer heads with Y, M, C inks, and 9 is a paper drum.

Yellow (Y), cyan (C), and magenta (M) have a complementary color relationship with blue (B), green (G), and red (R).
Full color printing is possible by changing the color mixture ratio of C or R, G, B (RGB is additive color mixing, YMC
Is suitable for subtractive color mixing). In the above-described embodiment, the ink jet printer head is assumed to be of a type capable of performing halftone recording by correcting the strength of the input voltage depending on the size relationship of the ink particles, but other types of dither method are used to perform halftone printing. It may be expressed, or a dot pattern method for expressing a halftone with a specific pattern may be used.

That is, the operation principle of the color copying machine of the embodiment is
Color-separated into Y, M, C, and CCD solid-state image sensor 4-1, 2, 3
After that, the signal processing circuit 7 performs a unique digital process on the way, and then the Y, M, and C ink nozzles are driven, and the color copying by subtractive color mixing is performed again on the paper on the paper drum 9. Is what you are trying to get.

FIG. 3 is a more detailed block diagram of the signal processing circuit 7 shown in FIG. The three-color input image signals Y, M, and C are supplied to the input signal lines 71-1, 2, and 3, respectively. Reference numerals 72-1 to 72-7 are digital color band pass filters, and decompose the input color signal into seven colors. Of course, the number of colors is not limited to seven, and any number of colors may be used. Here, the seven colors are orange (O
R), red (R), green (G), blue (B), peach (RK), purple (P
L) and yellow (Y) are used. In addition, black is considered to be one of the special colors and can be processed by a similar processing circuit.
That is, also for black (BK), by providing a digital color bandpass filter, it is possible to generate a color code 99 as shown in Table 1 of the related art. Also, white is represented by the white background of the original because it is not printed. Reference numeral 73 denotes a maximum value detection circuit, which selects and outputs the maximum output from the above seven color band pass filter outputs. Therefore, the maximum value M is output to the signal line 77, and the color code P for the maximum value is output to the signal line 79. Reference numeral 74 is a comparator that determines the magnitude of the maximum value M and a predetermined slice level value S, sets the Q signal of the output line 78 to high level (H) when M> S, and low level (L) otherwise.
To 75 is a color generator, and its output line 76-1,
The color signals of Y ', M'and C'are generated in 2, 3'. When the signal line 78 is L, it indicates that the color is not specified and white is generated. When the signal line 78 is H, various color signals are generated according to the color code signal P sent from the signal line 79. Table 1 shows the relationship between the color signals P'and the color signals Y ', M', and C '.

In the table, y, m and c are coefficients that determine the ratio of the yellow output Y ', the magenta output M'and the cyan output C'for forming 7 colors plus white and black. In the embodiment, the maximum output value is 63, and the output values of Y ', M'and C'in this case are shown in the table. Also, since the absolute sensitivity of the ink jet is adjusted so that it becomes black when y = m = c = 1, the output value Y'is obtained by giving the relative outputs of y, m and c as shown in Table 1. , M ', C'are determined, and various colors can be generated. For example, when printing orange, Y '
Is 19, M'is 12, and C'is 0. In accordance with this, the ink jet printer heads 8-1, 2, and 3 in FIG. 2 are driven, and yellow, magenta, and cyan inks are respectively printed on the paper surface. The mixture is mixed at a ratio of 19: 12: 0, and an orange color is formed on the paper surface.

It is also easy to change the color tone and output. For example, in Table-1, when the blue color code 06 is obtained, the correlated red color signal 31,31,0 is output, and when the red color code 01 is obtained, the correlation is performed. It suffices to output the blue color signals 0, 31, 31. By doing so, it is possible to obtain the output of the color tone in which red and blue are interchanged.

In FIG. 3, if one example of the constituent elements is specifically shown, the comparator 74 is a TTL IC S manufactured by Texas Instruments Incorporated.
Two N7485s and the maximum value detection circuit 73 can be configured by combining a plurality of similar ICs. The color generator 75 can be easily constructed by using three bipolar memory MB7051 manufactured by Fujitsu. Values Y ', M', and C ', which are obtained by multiplying the coefficients y, m, and c shown in Table-1 by the maximum output value 63, are rounded to the decimal point and read out with the color code P. The method can configure a color generator. The digital color band pass filters 72-1 to 72-7 will be described in detail below with reference to FIG.

FIG. 4 is a block diagram of an embodiment of the digital color bandpass filter according to the present invention. The figure shows 72-
Although only the digital color band pass filter No. 3 is shown, the other films have the same circuit configuration as in FIG. This circuit performs the following operations between the input signals Y, M, C and the output signal G. That is, the general formula Here, Ys, Ms, and Cs are standard signal values of yellow, magenta, and cyan, and are obtained by multiplying the values y, m, and c shown in Table 1 for each color by the maximum output value 63 of the color signal. For example, the CF on the left side of the green expression (1) is replaced with G, and since both yellow (Y) and cyan (C) are 0.5 and magenta (M) is 0, Ys, Ms and Cs are 31,0, respectively. 31. Formula (1) is for obtaining the correlation between the input color signals Y, M, C and the standard color signals Ys, Ms, Cs, and CF = 1 when the correlation is maximum (that is, when the same color is determined). , And as the correlation decreases, it approaches CF = 0.

In FIG. 4, 101, 104, 105, 106, 113, 114 and 115 are multipliers, 102, 103, 116, 117, 118 and 121 are reciprocals, 107, 108,
And 109 are subtractors, 119 and 120 are adders, and 110, 111 and 11
2 is an absolute value calculator. The part surrounded by a broken line 122 in the figure is a normalization circuit. Before comparing Y, M, C and Ys, Ms, Cs, the amplitudes of the inputs Y, M, C are normalized here. Here, first, processing is performed to make the amplitude of Y equal to Ys. That is Ys
The reciprocal 1 / Ys of is obtained by the reciprocal calculator 102, and the multiplier 101 multiplies the input Y to obtain Y / Ys. The reciprocal of this value Ys / Y
Y _N is obtained by multiplying the original input Y with the multiplier 104 obtained in step 3. Therefore, the normalized output Y _N is made equal to Y s. At this time, Ys / Y is a normalization coefficient, and the multipliers 105 and 106 multiply the inputs M and C, respectively, to obtain the normalization outputs M _N and C _N , respectively. Result of the above operation Y _N ,
The relative ratio between M _N and C _N is the same as the original input Y, M, and C, but its amplitude is normalized to the size when Y is Ys. Next, in the subtractors 107, 108, and 109, the standard color signals Ys, Ms, and Cs are subtracted, and the absolute value circuits 110, 11
The absolute value output is obtained by 1,112. As for yellow, | Y _N −Ys | / Ys is obtained by the multiplier 113 and the reciprocal calculator 116. Similarly, 114, 117 and 115, 118 execute division for magenta and cyan. The results obtained above are summed by adders 119 and 120. The addition of +1 in the denominator on the right side of the equation (1) is executed in the adder 120 with the carrier input at H. Finally, the reciprocal unit 121 takes the reciprocal number and executes the calculation of the equation (1).

FIG. 4 shows a concrete example of the constituent elements. As the multiplier, an 8 × 8 bit parallel multiplier MPY008HJ5C manufactured by TRW, USA or a bipolar PROMMB7141H manufactured by Fujitsu can be used as the multiplier. If the input color signals Y, M and C are 6 bits, input Y is applied to the address inputs A _{0 to} A ₅ of MB7141H and 1 / Ys is applied to the remaining address inputs A _{6 to} A ₁₁ to output data 0 from _{1-0 6,}
It is possible to directly read the Y / Ys value calculated and stored in advance. The merit that uses PROM as a multiplier is not only the merit of price, but when the multiplication result needs to be rounded, the rounded value is stored in advance so that the rounding operation can be performed without an external gate circuit. There is a point that can be executed. Further, if the merit of using the PROM is increased, the functions of the reciprocal arithmetic units 102 and 103 and the multiplier 101 can be executed by one PROM. In other words, if the input variables Y and Ys are input to the address, the final value Ys / Y of all subsequent calculation results will be
It should be stored in the PROM. Similarly subtractor 10
An arithmetic circuit including the absolute value circuit 110, the subtractor 113, and the reciprocal calculator 116 can be realized by one PROM (MB7141H). In this case, the address input is Y, Ys and the data output is | Y
_N- Ys | / Ys calculation result.

Generally, any logic circuit whose input signal bit configuration is less than the number of PROM address lines and whose output signal bit configuration is less than the number of PROM data lines can be replaced by the PROM. However, it is not used for ordinary logic circuits due to the generation of grid noise due to the time irregularity of PROM output and cost problems. Adders 119 and 120 are Texas Instruments SN7
It can be configured using the 4LS283. Also, the reciprocal calculator 12 at the final stage
1 can be configured using MB7123H from Fujitsu. That is, the address 0 of the memory address corresponds to the case of the denominator 0 on the right side of the expression (1), and the maximum value 63 of the embodiment is written as the result of the reciprocal calculation. The value of the data is incremented by 1 each time the sequential address increases by 1.
Just write down the content that decreases. By doing so, it is possible to easily avoid the incomputability of the division in which the denominator becomes 0. When the absolute value circuit 110 is configured independently, it can be configured using MB7123H. In that case, for example, Bit6 is used as the code bit. By the way, as described above, since Y _N eventually becomes equal to Y s, the multiplier 104 can be omitted.

From the above description, the circuit of FIG. 4 of the embodiment can be constructed by a total of 11 ICs including 7 PROMs and 4 adders. Therefore, a color band pass filter for seven colors can be easily realized at a practical price.

The configuration of the embodiment of the present invention shown in FIGS. 3 and 4 is
Although it is intended to faithfully execute the operation according to the equation (1), even if the circuit is downsized by using the PROM skillfully as described above, it is attempted to realize color detection of more than 7 colors. Will grow bigger. Therefore, the third
If the output Q is binarized by the comparator 74 in the figure, if the calculation in the middle is reduced to about 4 bits,
It is also possible to represent all circuits except the color generator 75 in the circuit configuration shown in FIGS. 3 and 4 by one PROM element. In that case, the data to be written to the PROM becomes extremely complicated, but it can be easily programmed in a BASIC-like language using a personal computer. To outline the method, first, the execution program of the formula (1) is assembled as a subroutine, and in addition, a maximum value detection subroutine, a size determination subroutine by the slice level S, and a reference table shown in Table 1 are created. Enter more
Create a main program to obtain output P, Q from Y, M, C,
Secure a RAM area to hold the calculation result and input here Y,
The results calculated for M and C may be sequentially output and used.

Further, in the above-described embodiment, the color determination is performed by the formula (1), but other similar formulas for the purpose of color determination can be used. In the embodiment shown in FIG. 3, the color determination is performed for each pixel. It is obvious that color discrimination may be performed by averaging several pixels.

Further, the case where the maximum value detection circuit 73 is used has been described in the above embodiment. As is clear from Table-1, among the seven colors,
It can be seen that there is a considerable difference when the correlations of the coefficients y, m, and c that determine the ratio of the color signal inputs Y, M, and C are examined. Therefore, if a simple comparator circuit is connected immediately after a plurality of color band pass filters 72-1 to 72-7 so that the slice level can be appropriately set, it can be said that two or more outputs are unlikely to occur simultaneously. . Therefore, the maximum value detection circuit 73 can be omitted, and a color image processing device having a simplified configuration in which the color generator 75 is accessed by decoding the outputs of a plurality of comparators can be realized.

To summarize the operation of the color copying machine according to the above-described embodiment of the present invention, the color grayscale image of the original 1 in FIG. 2 is processed by the A / D converters 6-1, 6-2 and 6-3. Are separated into three digital color gradation signals of Y, M and C respectively. If the originals have the same color, the ratio of the sizes of Y, M, and C should be constant even if the densities are different.
Therefore, the signal processing circuit 7 (1) determines which combination the input Y, M, C signals indicate (2) the color density level (similarity) of the determined color and the predetermined slice level S Comparison (3) If the level is higher than the slice level S, it is considered that a salient color signal has been received, and a color signal of a correlated color is generated, and otherwise, for example, a white color signal is generated.

Therefore, in order to make it easy to understand, if the maximum value of the color density level of a certain color is expressed as 100% and the minimum value is expressed as 0%, and the slice level S in (2) above is set at 50%, the color density will be temporarily reduced. Even if the original has a light density of about 60%, it is possible to obtain a copy with high definition converted to 100% density again. On the contrary, even if the original has stains with a color density of about 30%, those stains are converted into white signals. That is, the copy printing is not performed in the embodiment. Therefore, it is possible to obtain a smooth and easy-to-read color copy even from a color original having a slightly mixed color. Further, even for a document manuscript written with mixed characters of red, blue, green, purple, etc., a grandchild copy can be obtained without degrading the character quality. Of course, if the present invention is configured in multiple colors, even subtle colors can be saved by the processing according to equation (1) and the threshold determination, so that a full-color image original can be copied without degrading the image quality.

As a special application of the present invention, various color editing functions such as erasing only characters written in red or converting blue into yellow can be easily executed.

As described above, according to the embodiment of the present invention, the color band pass filter means having the normalizing means can discriminate the input color information very well even if the density of the color original document varies. Therefore, a markedly clear color copy or color display can be obtained even from an original image having a low density.

Further, according to the present invention, since the reliability of the color code generated after the discrimination of the input color information is extremely high, on the contrary, it becomes possible to easily control the output density of the color copy or the color display. Moreover, there is an effect that the deterioration of the image quality due to this does not occur.

Effects As described above, according to the present invention, input means (in the embodiment, A /
Corresponding to the D converters 6-1 to 6-3) and the image signal input from the input means to obtain a normalization coefficient based on a color component of one of the plurality of color components, and the normalization coefficient is calculated. A normalizing means (normalizing circuit 122 in the embodiment) for normalizing the image signals of the plurality of color components according to the normalizing coefficient, and the input means based on the image signal normalized by the normalizing means. Extraction means (in the embodiment, digital color bandpass filters 72-1 to 72-7) for extracting, for each pixel, the correlation between the color represented by the input image signal and a plurality of preset specific colors, and Selection means (maximum value detection circuit 73 in the embodiment) for selecting, for each pixel, a specific color having the maximum correlation extracted by the extraction means from among a plurality of specific colors
And a comparing means (a comparator 74 in the embodiment) for comparing the correlation value for the selected specific color with a predetermined threshold value, and a means for outputting a color code corresponding to the selected specific color ( In the embodiment, the maximum value detection circuit 73), when the correlation value is determined by the comparison means to be larger than the threshold value, the specific color represented by the color code is generated, and the comparison means is used. When it is determined that the correlation value is less than or equal to the threshold value, a color correction unit (color generator 75 in the embodiment) for performing color correction for each pixel by generating white color, and the color correction unit performs color correction. By having the output means (in the embodiment, the D / A converters 10-1 to 10-3) for outputting the applied image signal, the correlation value between the color of the input pixel and the specific color and the predetermined threshold value are provided. Depending on the relationship with the value A specific color or white can be selectively output, and a clear color image output can be obtained. In particular, according to the present invention, since the correlation with the specific color is extracted based on the normalized image signal, accurate color correction can be performed.

[Brief description of drawings]

FIG. 1A is a document reflection density vs. copy reflection density characteristic of a black-and-white copying machine, FIG. 1B is a document reflection density vs. copy reflection density characteristic of a conventional color copying machine, and FIG. 2 is related to the present invention. FIG. 3 is a block diagram of the color copying machine of one embodiment, FIG. 3 is a more detailed block diagram of the signal processing circuit of FIG. 2, and FIG. 4 is a more detailed block diagram of the color band pass filter of FIG. Here, 1 ... manuscript, 2 ... lens, 3 ... dichroic mirror, 4-1, 4-2, 4-3, ... CCD solid-state image sensor,
5-1,5-2,5-3 ... Video amplifier, 6-1, 6-2, 6-3
... A / D converter, 7 ... Signal processing circuit, 8-1,8-2,
8-3 ... Inkjet printer head, 9 ... Paper drum, 10-1, 10-2, 10-3 ... D / A converter.

Claims (1)

[Claims] 1. An input unit for inputting an image signal composed of a plurality of color components for each pixel, and an image signal input from the input unit based on a color component of one color among the plurality of color components. Find the normalization factor,
A normalization unit that normalizes the image signals of the plurality of color components according to the normalization coefficient, and an image signal that is input from the input unit based on the image signal that is normalized by the normalization unit. Color and
Extraction means for extracting the correlation with a plurality of preset specific colors for each pixel, and selection means for selecting, for each pixel, the specific color with the maximum correlation extracted by the extracting means among the plurality of specific colors. A comparison unit that compares a correlation value and a predetermined threshold value for the selected specific color, a unit that outputs a color code corresponding to the selected specific color, and the correlation value by the comparison unit. Generating a specific color represented by the color code when it is determined to be greater than the threshold value, and generating white color when the correlation value is determined to be less than or equal to the threshold value by the comparison means. 2. A color image processing apparatus comprising: a color correction unit that performs color correction for each pixel by means of; and an output unit that outputs an image signal that has been color corrected by the color correction unit.