JPH04260121A - Color image processor - Google Patents

Abstract

PURPOSE:To obtain the images having no sense of incompatibility each other with regard to outputted images, when color image data is outputted to different output devices. CONSTITUTION:A color signal converting circuit 101 converts each color component of R, G and B of inputted image data so that the outermost colors (that is, eight colors of white, black, red, green, blue, cyan, magenta and yellow) are subjected to mapping to the outermost color of a color reproducing range of a hard copy, so as to be held in the color reproducing range of the hard copy which becomes an output device.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus.

0002

2. Description of the Related Art Conventionally, common devices for outputting color images have been color CRT monitors and color hard copy devices. The former is R (red) and G on the CRT tube surface.
A color image is displayed through additive color mixture by intensity modulating the emission levels of the three-color phosphors (green) and blue (B). On the other hand, the latter are Y (yellow), M (magenta), C (cyan),
A color image is formed on paper by subtractive color mixing using a K (black) coloring material.

0003

[Problems to be Solved by the Invention] However, the two conventional image display devices described above have different color reproduction capabilities in principle, and as shown in FIG. 5, CRTs generally have better color reproduction than hard copies. Wide range.

Therefore, if two colors exist in an image, such as point A and point B shown in FIG. 5, when this image is displayed on a CRT, they may not be recognized as different colors. However, if you output using a hard copy device,
Since both points A and B are reproduced as the same color as point C,
The two colors become indistinguishable, and as a result, the information originally contained in the image is lost. Therefore, in order to solve this problem, when outputting a color image as a hard copy, a method may be considered in which the color signals in the image are converted so that they fall within the color reproduction range of the hard copy, and then output.

To give a specific example, point A in FIG.
By converting the points so that point B becomes point E, it is possible to differentiate the colors even on a hard copy. but,
In such a case, the conversion method is not uniquely determined, and depending on the conversion method, the output image may look unnatural as a whole. For example, even if the input color signal is converted to a color within the color reproduction range of the hard copy, what was originally reproduced as red on the CRT may become biased towards orange on the hard copy, or may be completely red. Inconveniences may occur, such as a color that should be pure black becoming bluish or dull.

Furthermore, there are cases where the entire color reproduction range of the hard copy cannot be used effectively.

The present invention has been made in view of the above-mentioned conventional example, and even when outputting a color image to a different output device,
It is an object of the present invention to provide a color image processing device that can perform appropriate color conversion.

[0008]

Means for Solving the Problems In order to achieve the above object, the color image processing apparatus of the present invention has the following configuration. That is, a color image processing apparatus that outputs color image data to a plurality of different output devices includes an input means for inputting the color image data, and a conversion means for converting a color signal in the color image data into a different color signal. death,
The conversion means sets a plurality of sets of color signals before conversion and color signals after conversion based on the output characteristics of an output device that outputs color signals after conversion, and uses the values of the color signals of the plurality of sets. A color image processing device is provided, characterized in that the conversion function of the conversion means is determined based on the color image processing device.

[0009]

[Operation] With the above configuration, the present invention operates to convert input color image data into color signals based on the output characteristics of the output device that outputs the color signals.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a block diagram showing the configuration of a color image processing apparatus which is a typical embodiment of the present invention. In FIG. 1, the color signal conversion circuit 101 converts the input color image signals (R, G, B) into the color reproduction range (R', G', B') of the printer unit, which will be described later.
Convert to 102 is a logarithmic conversion circuit that converts R', G', and B' into density signals; 103 is a black extraction circuit that extracts the minimum value of the output of the logarithmic conversion circuit 102; and 104 is a correction for unnecessary absorption characteristics of the printer's pigment. A masking circuit performs matrix calculations for the data, and simultaneously converts it into C, M, and Y plane sequential signals. 105 generates a black signal (K);
It is also a UCR (undercolor removal) circuit that removes unnecessary signals from C, M, and Y.

The C, M, Y, K field sequential signals obtained from the above circuit are converted into analog signals by a D/A conversion circuit 106, and compared with the output from a triangular wave generation circuit 107 by a comparator 108. , pulse width modulates the semiconductor laser 110 via the laser driver circuit 109. The laser beam is transmitted to the photosensitive drum 1 by a polygon mirror 111 that rotates at high speed.
12 is scanned, developed in a field-sequential manner by a developing mechanism (not shown), and transferred and fixed onto paper to obtain a hard copy output.

Next, details of the color signal conversion performed by the color signal conversion circuit 101 on input image data will be explained.

First, as an example, let us consider the reproduction of red. Assuming that the image signal is represented by 8 bits for each color of R, G, and B, the red color with the highest saturation that can be displayed on a CRT is a color signal of R=255, G=0, and B=0. This color is located at the RC point on the CIExy chromaticity diagram shown in FIG. However, since the red color with the highest saturation that can be reproduced on a hard copy is at the RH point, in the conventional method, all colors between the RH point and the RC point are output as the color at the RH point. . Conversely, R=160
, G=20, B=10, the color displayed on the CRT is RH
If it is equal to a point, this color signal can be output as a hard copy and reproduced as the same RH point.

Therefore, the input color signal R=255, G
=0, B=0 by the color signal conversion circuit, once R'=
160, G'=20, and B'=10, it is possible to fit the color between the RH point and the RC point into the color reproduction range of the hard copy. As a way to achieve this, consider the following matrix operation. ┌R'┐ ┌a11 a12 a13 a14 a1
5 a16 a17 a18 ┐ ┌R
┐│G′│=│a21 a22
a23 a24 a25 a26 a27 a28 │
×│G │└B′┘
└a31 a32 a33 a34 a35 a36
a37 a38 ┘ │B
│

│R×G/255 │

│R×B/2
55 │

│G×B/255
│
│
R×G×B │

│ /(255
×255)│

└255 ┘


...(1) aij is a predetermined coefficient and can be determined as follows. For the red color mentioned above, R = 255, G = 0, B = 0, and R' =
160, G' = 20, and B = 10. However, in the same way, other primary colors, such as white, black, green, blue, cyan, magenta, and yellow, A similar relationship can be assumed for the seven colors as well. This conversion function is, for example, as follows.

White: R = 255, G = 255
, B = 255 ┐ →R
'=255, G'=255, B'=255 │
Black: R = 0, G =
0, B = 0 │
→R'= 10, G'= 10, B'=
10 │ Green: R =
0, G = 255, B = 0 │
→R'=20, G'=100,
B'= 20 │ Blue :R
= 0, G = 0, B = 255
│ …(2) →R'
= 15, G'= 10, B'=100 │
Cyan: R = 0, G = 255
, B = 255 │ →R
'= 10, G'=100, B'=200 │
Magenta: R = 255, G = 0,
B = 255 │ →R'
= 200, G' = 10, B' = 100 | Yellow: R = 255, G = 255, B
= 0 │ →R'=
255, G' = 250, B' = 10 ┘ By substituting the above relationships into equation (1), 24 simultaneous linear equations are created and there are 24 unknowns aij, so aij can be uniquely determined. be able to.

FIG. 2 shows how the color reproduction range of a CRT is mapped to the color reproduction range of a hard copy using equation (1).

Therefore, according to this embodiment, the primary color points (RC
, GC, BC, CC, MC, YC, and white WC (not shown), black KC) are the primary color points of the hard copy (
RH, GH, BH, CH, MH, YH, and WH, KH) as shown by the arrows. Also, the central points A, B, and C are also A', B', and C'.
Since it is mapped to points, each can be reproduced as a different color. [Second Embodiment] In the first embodiment, all colors that can be reproduced on a CRT are mapped within the color reproduction range of a hard copy. Doesn't necessarily mean it's included.

In this embodiment, it is considered that the coefficients of equation (1) are changed for each image depending on the distribution of color signals of the input image.

FIG. 3 is a block diagram showing the configuration of the color image processing apparatus of this embodiment. In FIG. 3, the same parts as in the configuration of the color image processing apparatus in the first embodiment are given the same apparatus reference numerals, and the explanation thereof will be omitted.

In this embodiment, the input image data signal is temporarily stored in the frame memory 401. Next, C.P.
U402 refers to the contents of the frame memory 401 and detects the most saturated color signal value included in the image data.

For example, the most saturated red color (hereinafter referred to as
(referred to as the outermost color), the SR value is determined for each pixel according to the following equation, and the R, G, and B values of the pixel with the maximum SR are set as the red outermost color.

SR = R-G-B... (3) Similarly, find the outermost color for the other seven colors (the outermost color of green is SG = -R+G-B, the outermost color of cyan is the maximum). is S
C=-R+G+B is the maximum, and so on).

[0024] The R, G, and B values obtained in this way are (2
) and find aij, the optimum coefficients for the image currently being processed can be obtained. The obtained aij is sent from the CPU 402 to the color signal conversion circuit 4.
03, and thereafter the same processing as in the first embodiment is performed.

Therefore, according to this embodiment, even if the input image data does not necessarily include all the colors within the reproduction range of the CRT, the most saturated color signal value of each color included in the image can be detected. Since color signal conversion is performed by C
Colors outside the color reproduction range of RT can also be distinguished and expressed as different colors. [Third Embodiment] In the two embodiments described above, if the correspondence of primary colors between output devices that reproduce image data is known, optimal color signal conversion can be performed based on this. Based on this, in this embodiment, for each input image data, information on the primary color of that image data (color signal with the highest saturation in the image) is provided.
is stored as an image data header, and color signal conversion is performed based on this header information. Note that in this embodiment, the processing after the color signal conversion is performed is the same as in the first embodiment, so the device reference numbers shown in FIG. 4 are also given the same numbers as in FIG. 1, and a description thereof will be omitted.

FIG. 4 is a block diagram showing the configuration of the color image processing apparatus of this embodiment. In FIG. 4, as for input image data, header data is input to a CPU 501, and data for each RGB color component is input to a color signal conversion circuit 502. Here, the range of color signals of the input image is given in advance as header information in the header section. The input header information is the value of each RGB component of each of the eight primary colors described above, totaling 24 bytes of data.

Once the color signal conversion circuit 502 converts R',
Once the values of G' and B' are determined, the subsequent processing starts with the first
Follow the example.

Therefore, according to this embodiment, the range of color signals of the input image is given in advance to the header section as header information, and the information necessary for color signal conversion processing can be handled separately and independently.

In the above three embodiments, the cases where eight primary colors are mapped together have been described, but the present invention is not limited to this. For example, it is also possible to map only the six primary colors of red, green, blue, cyan, magenta, and yellow. At this time, equation (1) may be changed to the following equation. ┌R'┐ ┌a11 a12 a13 a14 a1
5 a16 ┐ ┌R
┐│G′│=│a21 a22 a23 a24
a25 a26 │×│G
│└B'┘ └a31 a32 a33 a3
4 a35 a36 ┘ │B
│…(4)

│R×G/255 │

│R×B/255 │

└G×B/255
┘Also, the color space used is not limited to RGB, but other color spaces such as L* a* b
It is clear that the present invention can be used in the same way for any of the well-known color spaces such as the * color system, the L* υ * ν* color system, and the XYZ color system.

[0030]

As explained above, according to the present invention, color signals are converted between color image output devices having different output characteristics based on the output characteristics, so that the same color image data can be transferred to different output devices. Regarding the output, there is an effect that a color image output that does not look out of place with each other can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a color image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a CIExy chromaticity diagram illustrating color signal mapping conversion performed by a color signal conversion circuit.

FIG. 3 is a block diagram showing the configuration of a color image processing device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a color image processing apparatus according to a third embodiment of the present invention.

FIG. 5 is a CIExy chromaticity diagram illustrating the difference in color reproduction range between CRT and hard copy.

[Explanation of symbols]

101 Color signal conversion circuit 102 Logarithmic conversion circuit 103 Black extraction circuit 104 Masking circuit 105 UCR circuit 106 D/A conversion circuit 107 Triangular wave generation circuit 108 Comparator 109 Laser driver 110 Semiconductor laser 111 Polygon mirror 112 Photosensitive drum 401 Frame memory 402 CPU

Claims (6)

[Claims] 1. A color image processing device that outputs color image data to a plurality of different output devices, comprising: input means for inputting the color image data; and conversion for converting color signals in the color image data into different color signals. The converting means sets a plurality of sets of a color signal before conversion and a color signal after conversion based on the output characteristics of an output device that outputs a color signal after conversion, and converts the colors of the plurality of sets. A color image processing device characterized in that a conversion function of a conversion means is determined using a signal value. 2. The color image processing apparatus according to claim 1, wherein at least one of the plurality of different output devices is a color hard copy device. 3. The color image processing apparatus according to claim 1, wherein the conversion function is a matrix conversion operation. 4. The plurality of sets of pre-conversion color signals and post-conversion color signals include six primary colors of the color reproduction system, namely red, green,
2. The color image processing device according to claim 1, wherein the color image processing device includes color signal values corresponding to blue, cyan, magenta, and yellow. 5. The plurality of sets of color signals before conversion and color signals after conversion are determined from the distribution of color signals included in the color image data input by the input means. A color image processing device according to claim 1. 6. The color image data inputted by the input means includes header information that stores the plurality of sets of color signals before conversion. color image processing device.