JPH04284579A - Method and device for processing color picture - Google Patents

Abstract

PURPOSE:To present color picture processing device and method which can reproduce colors faithfully for an original even at an equipment having respectively various color reproducing ranges. CONSTITUTION:Corresponding to the brightness, saturation and hue of inputted color image information, a coding part 4 codes the information, the coded color image information is compared with coded information stored in a color reproducing range block code storage part 5 which stores the color reproducing range as coded information, and it is discriminated whether the color of the color image information is within the color reproducing range or not. When it is judged that the information is within the reproducing range, the color image information is outputted as it is and when it is out of the reproducing range, the color image information is outputted after being converted to the outer edge part of the color reproducing range by a color discrimination part 15 and a conversion mode setting part 6.

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 method and apparatus for transmitting color image information between different types of devices such as scanners, printers, and displays to reproduce color images. Note that this reproduction of color image information includes recording in color on recording paper or the like and displaying a color image on a color display screen.

0002

2. Description of the Related Art Conventionally, when color image information is communicated and recorded/reproduced between different types of devices, the receiving device converts the color signals of the color image information sent thereto and reproduces the information. In this case, the receiving device converts the color information by dividing the received color image into uniform color reproduction ranges to match the color reproduction range of its own device. In such color reproduction range conversion, a uniform conversion method is applied to all colors to be converted.

0003

[Problems to be Solved by the Invention] Therefore, in the conventional example described above, in order to perform color conversion processing uniformly on all the colors to be converted, the brightness, hue, saturation, etc. of the reproduced color image are different from each other for each device. It may differ depending on the Specifically, in the case of yellow, if the brightness and hue match, even if the saturation differs slightly, the change in color will not be noticeable, but in the case of red, for example, the change in hue, brightness, or saturation will not be noticeable. Sensitive. Therefore, even if the saturation of the red reproduced color changes slightly,
There is a possibility that the difference in color may be sensitively recognized. As described above, in the past, it was not possible to perform color conversion by changing the conversion direction for a specific color, and therefore, depending on the reproduced color, preferred color reproduction could not be obtained.

The present invention has been made in view of the above-mentioned conventional examples, and an object of the present invention is to provide a color image processing method and apparatus that can reproduce colors faithful to the original even in devices having different color reproduction ranges. shall be.

[0005]

[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, it is a color image processing device that converts the color space range of color image information transmitted between different models, and includes a storage means for storing the color reproduction range as code information, and a storage means for storing the color reproduction range as code information, and converting the input color image information into brightness and saturation. and a coding device that codes according to the hue, and compares the color image information coded by the coding device with the code information stored in the storage device, so that the color of the color image information is within the reproduction range. a determining means for determining whether the color image information is within the reproduction range; an output means for outputting the color image information as it is when the determination means determines that the color is within the reproduction range; and converting means for converting the color to the outer edge of the color reproduction range.

In order to achieve the above object, the color image processing method of the present invention has the following configuration. That is, it is a color image processing method for converting the color space range of color image information transmitted between different models, which includes a step of encoding input color image information according to brightness, saturation, and hue, and the code. It is determined whether the converted color image information is within the color reproduction range, and if it is determined that it is within the reproduction range, the color image information is output as is, and if it is not within the reproduction range, the color image information is output. and converting the color to the outer edge of the color reproduction range and outputting the converted color.

[0007]

[Operation] In the above configuration, input color image information is coded according to brightness, saturation, and hue, and the coded color image information and color reproduction range are stored in the storage means that stores the code information. It is determined whether the color of the color image information is within the reproduction range. If it is determined that the color image information is within the reproduction range, the color image information is output as is, but if it is outside the reproduction range, the color of the color image information is converted to the outer edge of the color reproduction range and output.

Further, according to the color image processing method of the present invention, input color image information is coded according to brightness, saturation, and hue, and it is determined whether the coded color image information is within the color reproduction range. If it is determined that the color is within the reproduction range, the color image information is output as is, and if it is not within the reproduction range, the color of the color image information is converted to the outer edge of the color reproduction range and output. do.

Further, according to a preferred embodiment, when the color image information is not within the reproduction range, the color is discriminated according to the color characteristics of the color image information, and the brightness, saturation, and hue are determined according to the discrimination result. The method for converting each piece of information is determined.

0010

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

First, the method of storing the color reproduction range in this embodiment will be explained with reference to FIGS. 2 and 3. As shown in Figure 2, the standard uniform color space is divided into several stages of hue.
Each color space direction is finely divided into certain areas so that there are several levels of brightness and several levels of chroma, and the parts corresponding to the color reproduction range are stored as a collection of minute blocks.

[0012] Here, the standard uniform color space is CIE
It is expressed in the L* a* b* color space, and each block is assigned a 6-digit code number according to the format.

FIG. 3 shows an example of this. Here, the hue is divided into 20 levels, and the saturation and brightness are each divided into 10 levels.

FIG. 3 shows the color reproduction range of a certain device.
It shows a plane at a predetermined brightness level (for example, brightness 6),
Each of the codes in Figure 3 represents hue, brightness, and saturation in the standard uniform color space. Starting from the beginning of the code, each code has two digits in the order of color, brightness (06), and saturation. It has information on each. Hue is numbered counterclockwise from the + side of the a* axis, and brightness and saturation are numbered in order from lowest to highest. That is, the code "100609" represents green with a color of "10", a brightness level of "06", and a saturation level of "09".

[0015] When this method is applied to each device, such as a display or a printer, where each device has a different color reproduction range, color space data corresponding to each device is stored. In this case, although the number of blocks representing the color reproduction range differs for each device, colors represented by the same code number represent exactly the same color even if the devices are different models.

[0016] If the interval at which this color reproduction range is divided is narrowed, the image reproduction will be more accurate, and if this interval is widened, the accuracy will be lowered. Of course, the interval between divisions, the number of digits of the code number, and the reference color space in this case are not limited to those of this embodiment.

FIG. 1 is a block diagram showing the configuration of a color image processing apparatus according to this embodiment that performs such color space conversion.

R. of the input original information. G. B. The signal is
The color converter 1 converts the signal into an L*a*b* signal. Then, from these L* a* b* signals, the angle calculation unit 2 calculates the angle θ in the counterclockwise direction based on the + side of the a* axis, and the distance calculation unit 3 calculates the distance P from the L* axis. calculated (see Figure 4). Here, θ is tan −1(b*/a*) (a≠0) or si
n-1 {b*/SQRT(a* 2 +b* 2 )}
, cos-1{a*/SQRT(a* 2 +b*
2)} can be used for calculation. Also,
P is obtained from SQRT (a* 2 + b* 2). In addition, here, SQRT(a* 2 + b* 2 )≠
0, and SQRT(A) indicates the square root of A.

θ, P and L* thus obtained
is in L* a* b* space, where θ is hue and L
Since P has information on brightness and saturation, each is converted into two-digit information in the encoding unit 4, resulting in the six-digit block code N1 shown in FIG. 3 described above.

Reference numeral 5 denotes a color reproduction range block code storage unit, which is a memory in which all block codes of color reproduction range blocks of the device are stored in advance. From this color reproduction range block code storage unit 5, an outermost edge block code N having the same hue and same brightness as the input block code N1 is stored.
5 is read out, and the comparator 7 reads the block code N
1, it is determined whether the input RGB color signal is within the color reproduction range of the device. Here, the output signal S of the comparator 7 is used as a selection signal of the selector 12. If the block code N1 is within the color reproduction range, the block code N1 is selected, and if it is outside the range, the block code N3 (described later) is selected. ) and selector 1
2, it is output as block code N4.

As a result, if the input color signal is within the color reproduction range of the device, the block code N1 is selected by the selector 12 and output as the hand block code N4. Then, the inverse coding unit 13 converts the block code into an L* a* b* signal, and the inverse color converting unit 14 converts the R. G. B. converted into a signal. Here, the decoding performed by the decoding section 13 is performed using a*=P cos θ, b*=P sin θ.

[0022] The conversion performed in the color conversion section 1 and the inverse color conversion section 14 is RGB ←→ (primary conversion) XY
Z ←→ (nonlinear transformation) L* a* b* and
This can be achieved via CIE's XYZ. Also,
It is also possible to use ROM (table memory) for calculation of the nonlinear part.

Next, a case will be described in which a block code N3 is created which is selected when the block code N1 encoded by the encoding section 4 is outside the color reproduction range of this device.

First, the block code N1 is detected by the color discriminator 15.
The color of the input color signal is determined. Then, the output K that is the determination result is input to the conversion mode setting section 6, the conversion direction corresponding to the color is read out, and the mode M is outputted from the conversion mode setting section 6. These block codes N1 and mode M determine the block code group N to be read from the color reproduction range block code storage section 5, and the block code group N that is read out from the color reproduction range block code storage section 5 is determined by the selector 8. One block code N2 among N is output.

Then, the subtracter 9 calculates the block code N
The difference d between the code numbers of block code N2 and block code N2 is taken. Here, since the block code indicates the spatial position as described above, the smaller the absolute value of the difference d is, the closer the blocks indicated by the block codes N1 and N2 are, and the more the blocks are of different colors. It can be said that there is little color difference. Here, the data output from the subtracter 9 includes the difference d between the block code N1 and the block code N2, and information on the block code N2 at that time.

Since the block code N2 is the first code in the block code group N read out from the color gamut block code storage section 5, it passes through the comparator 10 and is written to the optimal block code storage section 11. be included. Here, the optimal block code storage unit 11 stores the block code from the color reproduction range block code storage unit 5 that has the smallest difference d among the calculated ones after setting the conversion mode, and the difference d. This is the memory being stored. Then, the selector 8 outputs the second block code N2 in the block code group N, and the subtracter 9 similarly calculates the difference d from the block code N1, and the result is input to the comparator 10.

At this time, the comparator 10 reads the number N of the block code having the minimum difference d from the block code N1 at the present time and the difference d(D) at that time from the optimal block code storage unit 11, and The magnitude relationship between the difference d between the third block code N2 and the block code N1 and D read from the optimum block code storage section 11 is examined. If D>d, the contents of the optimal block code storage section 11 are rewritten to a new block code with the smaller difference d, and if D≦d, the contents remain unchanged.

In this way, the selector 8 sequentially selects the block code group N read out from the color reproduction range block code storage section 5 one after another, such as the third block code N2, the fourth block code, and so on. By outputting the code data to the subtraction unit 9, the above-described operation is repeatedly executed.

In this way, among the block code group N that finally matches the conversion mode setting, the block code of the block closest to the block with the block code N1 determined from the input color image signal is determined. N3
will be stored in the optimal block code storage section 11.

The block code N3 obtained in this way is selected by the selector 12 when the block code N1 is outside the color reproduction range of this device as described above.
The signals are converted into RGB color signals via the inverse coding section 13 and the inverse color conversion section 14.

As described above, even if the input color signal is a color that is outside the color reproduction range of the device, the conversion mode is determined according to the color at that time and the color is converted to the optimal color. In this way, we explained the process of converting one input color signal along the data flow, but if there are multiple input color signals, the above process is repeated for each color. The conversion is performed by

Next, referring to FIG. 5, a case will be described in which the color reproduction range is converted by a combination of the color discrimination section 15 and the conversion mode setting section 6.

Here, colors are classified based on the hue information in the upper two digits and the saturation information in the lower two digits of the block code N1 inputted to the color discrimination section 15. That is, as shown in FIG. 5, a table is created in which each color is grouped into groups such as A, B, C, and so on. The number of groups to be divided here must be equal to or less than the number of conversion modes in the conversion mode setting section 6. Here, when classifying into groups, the characteristics of the human eye may be taken into account. Group A: Colors in which a slight shift in hue is not a concern, but are sensitive to changes in brightness and hue. Group B: Colors that are sensitive to changes in hue, lightness, and saturation. Group C: Colors that do not care about slight shifts in saturation, but are sensitive to changes in brightness and hue.

As described above, the colors in the color space are divided into groups taking into account the characteristics of the human eye. The results of these groupings become the output K of the color discrimination section 15 and are input to the conversion mode setting section 6.

Next, the conversion mode setting section 6 sets a mode to correspond to the conditions grouped by the color discriminating section 15. That is, Mode 1: Changes the hue without changing the brightness and saturation. However, if the hue is shifted by three blocks or more, the saturation may be shifted by one block. Mode 2: No restrictions. (Mechanically searches for the closest block) Mode 3: Changes only the saturation without changing the brightness or hue.

With the above method and configuration, the direction of conversion can be changed for each color.

In the above-mentioned embodiment, three types of color groups and conversion modes were set. There is no reason why this grouping and conversion mode setting must be set to three types, and any number of types may be used. Furthermore, if there is sufficient memory capacity, all colors may be grouped in one-to-one correspondence and a conversion mode may be provided.

Furthermore, in the above-mentioned embodiment, the classification was performed based on the appearance of color when viewed by a human, but the classification may be performed colorimetrically as shown below. Group A: Colors with a saturation code of 9 to 10 Group B: Colors with a saturation code of 5 to 8 Group C: Colors with a saturation code of 1 to 4 Also, all colors are grouped into the same group without grouping. By doing so, the same conversion may be performed for colors outside the color reproduction range of the device.

The present invention may be applied to a system made up of a plurality of devices, or to a device made up of one device. It goes without saying that the present invention can also be applied to cases where the present invention is achieved by supplying a program to a system or device. As described above, according to this embodiment, even if the device has a color reproduction range unique to the device, such as a display or a printer, original color information can be faithfully reproduced.

Furthermore, for colors that are outside the color reproduction range unique to the device, the characteristics of the human eye or the colorimetric scale are taken into consideration for each color, and the group and conversion mode of the set color discrimination unit are used to , it is possible to convert the color to the outer edge of the device's unique color reproduction range to obtain the optimal color.

Furthermore, the direction of conversion can be changed by changing the grouping and conversion mode settings in the color discrimination section.

[0042]

As explained above, according to the present invention, color images faithful to the original can be reproduced even in devices having different color reproduction ranges.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of a color image processing apparatus according to an embodiment.

FIG. 2 is a diagram showing an example of color space division in this embodiment.

FIG. 3 is a diagram for explaining a block code of a lightness 6 portion of the color space divided as shown in FIG. 2;

FIG. 4 is a diagram for explaining encoding in this embodiment.

FIG. 5 is a diagram for explaining grouping in the color discrimination section in the embodiment.

[Explanation of symbols]

1 Color conversion section 2 Angle calculation section 3 Distance calculation section 4 Coding section 5 Color reproduction range code storage unit 6 Conversion mode setting section 7 Comparator 8,12 Selector 9 Subtractor 10 Comparator 11 Optimal block code storage unit 13　Reverse encoding section 14 Reverse color conversion section 15 Color discrimination section

Claims (4)

[Claims] 1. A color image processing device that converts the color space range of color image information transmitted between different models, comprising:
storage means for storing the color reproduction range as code information; encoding means for encoding input color image information according to brightness, saturation, and hue; and color image information encoded by the encoding means and the determining means for determining whether the color of the color image information is within the reproduction range by comparing the code information stored in the storage means; A color image processing device comprising an output means for outputting image information as it is, and a conversion means for converting the color of the color image information to an outer edge of the color reproduction range when the color is outside the reproduction range. 2. The converting means further comprises color determining means;
conversion mode setting means, the color discrimination means classifies color information according to the characteristics of human eyes, and the conversion mode setting means determines the conversion direction of the color information according to the discrimination result determined by the color discrimination means. 2. The color image processing apparatus according to claim 1, wherein the color image processing apparatus is configured to: 3. A color image processing method for converting the color space range of color image information transmitted between different models, the method comprising:
A process of encoding input color image information according to brightness, saturation, and hue, and determining whether the encoded color image information is within the color reproduction range, and determining that it is within the reproduction range. and outputting the color image information as it is, and when the color is not within the reproduction range, converting the color of the color image information to the outer edge of the color reproduction range and outputting it. Processing method. 4. When the color image information is not within the reproduction range, the color is determined according to the color characteristics of the color image information, and a method of converting each information of the brightness, saturation, and hue is determined according to the determination result. Claim 3 characterized in that:
Color image processing method described in .