JPH04181872A - Color picture processing unit - Google Patents

Abstract

PURPOSE:To realize optimum color reproduction in response to an input color picture by providing a color reproduction processing system implementing,color reproduction with equal color to an input color picture only in a color reproduction area of a picture output device to the processing unit in addition to the conventional color space compression mapping reproduction. CONSTITUTION:R, G, B picture signals inputted to the picture processing unit 102 are branched to two systems, input to a color coordinate discrimination circuit 110 and input to a density conversion circuit 112 and a density conversion table 111. The color coordinate discrimination circuit 110 discriminates whether the distribution of a color picture original on a color space is included in a color reproduction area of a picture output device 103 or exceeds the color reproduction area. The other system is further branched into two systems, the one system is subject to processing by the density conversion circuit 112 and a masking circuit 113, and when the color picture original is at the outside of the color reproduction area, an output signal by compressed color processing is selected and when the color picture original is within the color reproduction area, an output signal by equi-color reproduction processing is selected by a changeover circuit 114 and outputted to a picture output device 103.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a color image processing device that converts an input color image signal into an output color image signal and outputs the converted color signal to an output device that processes the converted color signal.

[Conventional technology]

In the conventional color image copying apparatus, as shown in FIG.
The G and B digital image signals are converted into color image signals by a subtractive color method using a logarithmic conversion circuit 402, a masking circuit 403, and an inking UCR circuit 404, and the image output device 4
05, it was configured to be printed and recorded using toner or ink. In general, the colors of printed materials, photographs, and images represented on a CRT, which are color image originals, are wider in the color space coordinate system than the color reproduction range created by mixing colors of toner or ink of an image output device. In order to achieve optimal color reproduction for all colors of the input color image signal, compression is usually performed on the color space.
Processing is also performed to give gradation to colors outside the color reproduction range. FIG. 5 is a diagram showing the conventional compression mapping in the above color space (on the a'-b'' axis). indicates the color reproduction range of the image output device, and indicates that the input color image original exceeds the color reproduction range of the image output device. Conventionally, as shown by the arrow, color reproduction outside the color reproduction range is On the other hand, in order to give the image gradation, the original color is gradually shifted as shown by the arrow.In other words, the color space is compressed and mapped. was being carried out.

[Problem to be solved by the invention]

However, in the above conventional example, the color space distribution of the color image original exists within the color reproduction area of the image output device, and although the same color as the original color can be reproduced, the reproduced color is compressed and mapped, and the original color is different from the original color. It had the disadvantage of being different. Furthermore, when the color image original is an output image from a copying device or an image output device (referred to as a grandchild copy or generation copy), the reproduced color is further compressed. When repeating grandchild copies in this way, the reproduced colors are compressed one after another, resulting in a disadvantage that they differ from the original image original. The arrow in FIG. 5 shows the locus of this reproduced color. Furthermore, if the color space distribution of a color image original exists within the color reproduction area of the image output device, and the original image is expressed in gradation within a small spatial area, such as a contour line display using gradation of a mountain or sea area on a map, etc. There was a drawback that the gradation was lost during reproduction.

[Means to solve the problem]

The present invention was made for the purpose of solving the above-mentioned problems, and includes the following configuration as one means for solving the above-mentioned problems. That is, in a color image processing device that converts an input color image signal by an additive color method into a corresponding color image signal by a subtractive color method and outputs the converted color image signal to an output device that processes the converted color signal, the input color image signal by a color additive method is at least A conversion means converts the signal into a color image signal using a corresponding subtractive color method using two types of methods and outputs the signal to an output device; a color reproduction area storage means stores a color reproduction area on the color space of the output device; a counting means for checking whether each pixel of the image signal is within the output device reproduction range stored in the color reproduction area storage means and counting the number of pixels outside the reproduction range; and a counting means for counting the number of pixels that are outside the reproduction range; and a selection means for selecting the optimum conversion means from the at least two conversion means according to the judgment result of the judgment means, and an output device that is equivalent to the input color image signal. enables color reproduction. The output device permanently displays the color image by mixing the toners or inks, and the color reproduction area storage means stores the color reproduction area in which the input color image signal is expanded by the color mixture of the toners or inks of the output device in the color space coordinate system. The selection means selects the selection means that applies optimum compression to the input color signal when the input color signal exceeds the converted color reproduction area of the color reproduction area storage means.

[Effect]

In the above configuration, the configuration of the color reproduction processing system for color image originals includes, in addition to conventional color space compression mapping reproduction, color reproduction that is the same color as the color image original only within the color reproduction area of the image output device. By providing a reproduction processing system,
When reading a document, a processing system can be selected according to the spread of colors in the color space coordinate system of the document, and optimal color reproduction can be achieved depending on the document.

【Example】

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a copying apparatus which is an embodiment of the present invention. As shown in FIG. 1, this copying apparatus includes an image input device 101 that is a color image input section, an image processing device 102 that converts an image input signal read by the image input device 101 into an image output signal, and an image processing device 102 that converts an image input signal read by the image input device 101 into an image output signal. Image aperture 10 receives the image output signal converted by device 102 and provides a corresponding permanent visible display with multiple colored toners or inks.
Consists of 3 components. The image signals processed by the image processing device 102 are not limited to color image originals and printed matter read by the image input device 101, but also include CG (computer graphics) images and images captured by an electronic still camera. can be handled. The image processing device 102 also includes a color coordinate discrimination circuit 110, a density conversion table 111, a density conversion circuit 112, a masking circuit 113, and a switching circuit 114. Next, with reference to FIG. 2, the image input device 10 of this embodiment will be explained in the case where the color image is a printed document and the case where the color image is a CG image.
1 will be outlined. First, a case where the color image original is a printed matter will be explained. Original 2 placed on original platen glass 201 shown in FIG.
02 is illuminated by a halogen lamp 203 for document illumination,
An image is formed on a CCD line sensor 205 by a rod lens array 204 (for example, SELFOC ■). C.C.
The D line sensor 205 has red (R), green (G), and blue (
The color separation filter B) is applied dot-sequentially, and R, G, and B color separation signals of the original image are sequentially output. 206 is a sample and hold circuit, which samples and holds the output from the CCD line sensor 205 for each pixel;
The A/D conversion circuit 207 converts it into a digital signal. Image data converted to digital signals are not shown.
It is input to the shading circuit 208 together with the white data stored in advance, corrects the ratio camouflage due to variations in sensitivity between CCD pixels, and normalizes it to a predetermined number of bits. The input masking circuit 209 operates on the R, G, and B output signals from the shading circuit 208 using a predetermined matrix, and outputs image signals R', G', and B' standardized to the NTSC standard. The optimum solution for the matrix coefficient alJ is determined by, for example, the least squares method. Next, if the color original image is a CG color image,
RlG and B video signals output from the computer 210 are input to the input masking circuit 209 via the interface 211. If the video signal conforms to the NTSC standard, the input masking circuit matrix coefficients are passed through, i.e., output to the subsequent image processing device 102. Image processing device 1 that converts digital R, G, and B input signals into toner or ink output signals of multiple colors
The details of 02 will be explained. The R, G, and B image signals input to the image processing device 102 are processed by a color coordinate determination circuit 110 and a density conversion circuit 112 (described later).
and input to the density conversion table 111. The color coordinate determination circuit 110 determines whether the distribution of the color image original in the color space is within or exceeds the color reproduction area of the imager 103, using the method described below. The R, G, and B image signals input to the color coordinate determination circuit 110 are converted into tristimulus values x, y, and z of the XYZ color system. R
When the GB signal conforms to the NTSC system, the conversion formula is expressed by the following formula. ...(1) The image signal converted to X, ¥, Z3 stimulus values is then L”
It is converted into L'''a'b'' of the a''b'' color system. (Xo, Yo, Zo = onst) Figure 3 shows the situation in the L'a''b'' color system. The solid line hexahedron in the figure is the image output device 103 mentioned above.
When the image signal exists inside this hexahedron, the image output device can reproduce the color. The image signal converted into the L″a″b″ coordinates by equation (2) is determined for each pixel as to whether it is in the color reproduction area or not by the following method. It is equipped with a memory that stores color information of the inscribed square (solid represented by the dashed line in Figure 5) and data (achromatic color data) in the vicinity of the straight line connecting and W in the diagram.By equation (2), L'' a
The image signal with the "b°a"b° coordinates is referred to for each pixel in the memory data, and the number of pixels that deviate from the square is counted. Depending on whether the number is above or below a certain threshold, it is determined whether the color of the document is within the color reproduction area of the image output device, and a 1-bit determination signal is output. For example, when a color image original is an output image of this copying device (hereinafter referred to as "generation copy" or "generation copy")
(referred to as "grandchild copy"), all image data exists within the color reproduction area, and the color coordinate determination circuit 110 always determines that it is within the color reproduction area. The other one of the R, G, and B image signals input to the image processing device 102 is further branched into two systems, and one system is processed by the ^-'' degree conversion circuit 112 and the masking circuit 113. , the same processing as that of the logarithmic conversion circuit 402 and the masking circuit 403 described in the prior art shown in FIG. 4 is performed. That is, the color space of the color image original is set to be thicker than the color reproduction area of the image output device 103, the color space is compressed and reproduced,
Processing to output an image with gradation is also performed for color coordinates other than the color reproduction area. On the other hand, the image signal is also input to the density conversion table 105 at the same time as the color processing described above. Density conversion table 105
is a conversion table that takes R, G, and B image signals as input and outputs Y, M, and C signals as output values. Image output signals (Y, , Ml
, C, ,) and (Y2, Ml. C,, Ka) are compressed when the color image original exceeds the color reproduction area based on the determination result of the color coordinate determination circuit 110. Output signal (Y, , M,
, C, , ), and when the color image original is within the color reproduction area, the output signal (Y, , M
1, C2, and 2) are selected by the switching circuit 114,
The image is output to the image output device 103. The image output device 103 outputs this image output signal (Y, M,
C, K) are printed and recorded according to each output method such as PWM, dither, error diffusion method, etc.

[Other Examples]

<Embodiment 2> In the first embodiment described above, an example will be described in which the color space distribution of a color image document is determined by the color coordinate determination circuit 110, and in this case, the data to be stored in the memory is For the purpose of reduction, it was set as the largest square within the color reproduction area of the image output device. However, the present invention is not limited to the above example, and more accurate determination can be made by using signal values within the color reproduction area as the data. <Embodiment 3> In the above-mentioned first embodiment, an example was explained in which the color space of the color coordinate determination circuit 110 is expressed using the L″a″b° uniform color coordinates, but the color space of the color coordinate determination circuit 110 is A similar effect can be obtained by representing using the color reproduction area of the image output device defined by the Luv color system, the XYz color system, or the RGB signal system. It is effective to perform the above-mentioned determination, for example, at the time of blisscanning. That is, in a color copying machine, place the original on the original table,
When the copy start key is pressed, preliminary scanning is normally performed to detect the document size, etc. before performing the actual printing operation. By executing the above-mentioned algorithm at this time, it is possible to execute the optimum processing procedure in the main scan. The above-described embodiments can be applied to any type of copying machine capable of forming color images, such as laser beam printers, thermal transfer printers, dot printers, and inkjet printers. As explained above, according to the above embodiment, the color space distribution of a color image original is detected, it is determined whether the color image exists within the color reproduction area, and the output of a different color processing system is selected depending on the original. By doing so, it is possible to reproduce colors with maintained gradation for color image originals that extend outside the color reproduction range of the image output device, and to reproduce colors that are faithful to the original for color image originals that are within the color reproduction range. , which has the effect of obtaining an optimal output image. Further, even in repeated grandchild copies, there is an effect that an image with no deviation in reproduced colors can be obtained.

【Effect of the invention】

As described above, according to the present invention, as a configuration of a color reproduction processing system for a color image original, in addition to the conventional color space compression mapping reproduction, only the color within the color reproduction area of the image output device is the same color as the input color image. By providing a color reproduction processing system that reproduces colors according to the input color image signal, the processing system can be selected according to the color spread in the color space coordinate system of the input color image signal, and the optimal color reproduction according to the input color image can be achieved. can be realized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a diagram showing the detailed configuration of the image input device of this embodiment, and Fig. 3 is an image output in L″a*b* uniform color space. FIG. 4 is a block diagram showing the configuration of a conventional color reproduction processing section; FIG. 5 is a diagram showing compression mapping of color space by conventional color reproduction processing. In the figure, 101... Image input device, 102... Image processing device, 103... Image output device, 110... Color coordinate discrimination circuit, 111... Density conversion table, 112...
...Density conversion circuit, 113...Masking circuit, 11
4...Switching circuit, 201...Original table glass, 202
... Original, 203... Halogen lamp for illuminating the original,
204...Rod lens array, 205...CCD
Line sensor, 206... Sample hold circuit, 2
07... A/D conversion circuit, 208... Shading circuit, 209... Input masking circuit, 210...
- Computer, 401... Image reading device, 402
... Logarithmic conversion circuit, 403 ... Masking circuit, 4
04... Inking UCR circuit, 405... Image output device. Patent applicant Canon Co., Ltd. Agent Patent attorney Yasunori Otsuka (and 1 other person) Figure 3 Figure 4

Claims (2)

[Claims] (1) Conversion means for converting input color image signals into output color image signals using at least two methods, color reproduction area storage means for storing a color reproduction area on the color space of an output device, and an input color image a counting means for checking whether each pixel of a signal is within the reproduction range of the output device stored in the color reproduction area storage means and counting the number of pixels outside the reproduction range; and according to the counting result of the counting means. and selecting means for selecting an optimal conversion means from the at least two conversion means, the color image processing device being characterized in that the output device can reproduce colors equivalent to an input color image signal. (2) The output device permanently displays a color image by mixing colors of toners or inks, and the color reproduction area storage means stores a color reproduction area formed by mixing colors of toners or inks of the output device in a color space coordinate system. 2. The selection means selects the selection means that applies optimal compression to the input color signal when the input color signal exceeds the converted color reproduction area of the color reproduction area storage means. color image processing device.