JPH0440072A - Color correcting system for digital color picture processor - Google Patents

Abstract

PURPOSE:To satisfactorily reproduce a color by executing value conversion corresponding to an output destination after correcting a color, which is out of a color reproducing range, into the range when executing color correction, color control, color conversion or the other processing by a system value. CONSTITUTION:A value converting means 7 is provided to convert the system value to the value of each primary color to be handled at the output destination, a storing means 2 is provided to store information concerning the color reproducing area of the output destination according to the system value, and correcting means 3 and 6 are provided to correct a system value 5, which is out of a color reproducing area, into the color reproducing area by deciding the system value is out of the color reproducing area of the output destination or not. Then, when outputting the edited system value 1 to an output device 8, the correcting means 6 corrects the system value 1 based on the information concerning the color reproducing area of the output destination and afterwards, the system value is converted to the value of each primary color by the value converting means 7 and outputted. Thus, even when a picture is outputted from the output device 8 as it is, the color can satisfactorily be reproduced without sharply changing hue or chrominance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital color image processing device that performs editing processing on image data using values consisting of information regarding brightness, hue, and saturation as system values.

[Conventional technology]

Figure 5 is a diagram showing an example of the configuration of a system that handles image data.
FIG. 6 is a diagram for explaining a color system employed in a color digital image processing apparatus, and FIG. 7 is a diagram showing an outline of the configuration of the color digital image processing apparatus.

The system shown in FIG. 5 is configured so that image data of a color original read by a scanner 23 can be transferred to a workstation 21 and displayed on a CRT display 22 or printed out from a printer 25. This is an example, and the file 24 stores the image data. In such a system, the image data read by the scanner 23 is transferred to the output CRT.
Conversion and adjustment are required to match the performance and characteristics of the display 22 and printer 25.

In color digital image processing devices such as the above-mentioned systems, copiers, faxes, printers, etc., BGR, which is the primary color of additive color mixture such as CRT, and YMC (K), which is the primary color of subtractive color mixture such as printers, have traditionally been used mainly. It was the value of image data handled within the system (system value). B
GR is a reflected signal (luminance signal) and is used as a reading signal of a CCD sensor or an output display signal of a CRT display.
When expressed in 56 gradations, black is expressed when each value is 0, white is expressed when each value is 255, and gray is expressed when BGR is the same value. YMC is a density signal and is used as a print output signal of a printer, and when expressed in 8 bits and 256 gradations as shown in Figure 6(b), when each value is O, it is white; When is 255, it represents black, and when YMC is the same value, it represents gray. These are all color representations based on color mixture, but in certain colors, B, G, RSY
It is difficult to imagine how the color will change if the value or M%C is changed. Therefore, I want to make the color a little brighter,
It is difficult to know by what percentage each primary color should be increased or decreased in response to a request to make colors more vivid.

Therefore, recently, Ll)a6b1, HVC, YES, etc.
Increasingly, values that suit the visual characteristics of people are being adopted as system values. FIG. 7 shows an example of the configuration. In FIG. 7, an I
When a color original is read from the IT 31 and a BGR color separation signal is output, it is first converted into L"a"b* by the system Balinese conversion circuit 32 and then input to the editing circuit 33. Edit the image data with *. If the output side is a printer or the like, the image data from the editing circuit 33 is converted into YMC by a system value conversion circuit 34.

1-118$b6, as shown in Figure 6(C), Lo represents brightness, a*, b* represents hue and saturation, and HVC also represents L" a as shown in ED(d). Similar to "b", ■ represents brightness, H represents hue, and C represents saturation.

Therefore, if you adopt the HVC color system, if you want to make the color brighter, you only need to adjust ■, and if you want to make the color more vivid, you can adjust C to make it a little redder. In response to a request for output, H can be adjusted intuitively and quantitatively. Therefore, the degree of color recognition in editing is also improved. Also,
When compressing image data, BGR and YMC have equal weights, so it is necessary to process each with the same compression rate.
In C, the compression ratio of brightness and luminance, which are sensitive to the human eye, is reduced, and the compression ratio of hue and saturation is increased, thereby increasing the overall data compression ratio.

That is, compared to BGR and MMC which depend on the characteristics of CRT and color materials, absolute color values such as Lsa*b* and HVC have advantages even when considering system compatibility.

[Problem to be solved by the invention]

As mentioned above, the values normally handled by the output device are the primary colors of a mixture, and colors are reproduced depending on the mixing ratio, so the brightness, hue, and saturation differ slightly depending on the increase or decrease in each primary color. In other words, the color specification based on the primary colors of the mixed color is based on information different from the human visual perception characteristics based on brightness, hue, and saturation.

On the other hand, Lta*b* and HVC consist of information regarding brightness, hue, and saturation, and are values that match human visual perception characteristics. However, when viewed as data handled by the system, the former has the problem that colors can be reproduced using all the values assigned to each primary color, whereas the latter has values that cannot be reproduced.

In other words, in BGR and YMC, which are the primary colors of mixed colors, the 6th
As shown in Figures (a) and (b), if each primary color is represented by 8 bits in the orthogonal coordinate system, a cube expressed within a size of 8 pits and 256 exists as a color that can actually be reproduced. It becomes a space where you can However, I”
In a"b" and HVC, the saturation value is 0 for black and white with no hue or saturation at the edge of the image on the brightness axis, so there is an unreproducible space that does not actually exist, such as the outside where saturation is not 0. The problem is that this can occur. In other words, a space where two cones butt each other as shown by the solid line in FIG. 6(6) basically exists as a reproduction space. Therefore, even if each item is represented by 8 bits on the system, the space in which data can be represented is the 6th I! As shown by the dotted line in 1(d), it becomes a cylindrical space, but in terms of brightness and saturation, the saturation only reaches its maximum near the middle of the brightness axis where the two cones meet, and the brightness varies in size. Even if it shifts in the direction of , the range of saturation becomes narrower, and the range that cannot be reproduced becomes larger.

On the other hand, no matter what value is used within the system, when it is ultimately printed out or displayed on a CRT, it is necessary to convert the value to match the output device.

Moreover, the system variny adopted by these output devices is usually either BGR, which is the primary color of additive color mixture, or MMC (K), which is the primary color of subtractive color mixture, such as in printers. Therefore, if you adopt the system value that matches the human visual characteristics, which consists of information on brightness, hue, and saturation as described above, when outputting, you will need to use MMC (K) and BGR that match the output device. It becomes necessary to convert the value. At that time, as mentioned above, there may be cases where the color cannot be reproduced by a printer or CRT, or the color signal has a value that does not actually exist.

This mainly occurs when hue, brightness, saturation, etc. are adjusted or converted independently.

Note that the system Baliney conversion methods include those that use a DLUT (direct lookup table) that has a conversion table for all values, those that use a combination of LUT and matrix operations, and those that use matrix operations. be. Among these, in the case of DLUT, it is possible to avoid conversion to a color outside the above reproduction range at the time of LUT creation, but in other cases, when a value that cannot actually be reproduced is input, , it is not known what color will be output, and good color adjustment and color conversion cannot be performed.

The present invention is intended to solve the above-mentioned problems, and an object of the present invention is to provide a color correction method for a digital color image processing apparatus that corrects data outside the color reproduction range.

[Means to solve the problem]

To this end, the color correction method of the digital color image processing device of the present invention is shown in FIG. As shown, there is a value conversion means 7 for converting the system value into the value of each primary color handled at the output destination, a storage means 2 for storing information regarding the color gamut of the output destination based on the system value, and a value converting means 7 for converting the system value into the value of each primary color handled at the output destination, and a storage means 2 for storing information regarding the color gamut of the output destination based on the system value, and a value conversion means 7 for converting the system value into the value of each primary color handled at the output destination. The correction means 6 is provided with a correction means 3.6 for determining whether or not the system value 5 is outside the color reproduction gamut and correcting the system value 5 to be within the color reproduction gamut. The present invention is characterized in that after the system value 1 is corrected based on the information regarding the color gamut of the output destination, the value conversion means 7 converts it into the value of each primary color and outputs it.

Further, the storage means 2 stores the maximum value of the color gamut according to the saturation corresponding to the brightness and hue, and the correction means 3.6 stores the maximum value of the color gamut when the saturation is larger than the maximum value of the color gamut. It is characterized by being configured so that it can be modified.

[Effect]

In the color correction method of the digital color image processing apparatus of the present invention, information regarding the color gamut of the output destination based on the system value is stored in the storage means 2, and when outputting the edited system value 1 to the output device 8. After the correction means 6 corrects the system value 1 based on the information regarding the color gamut of the output destination, the value conversion means 7 converts it into the value of each primary color and outputs it, so that the image can be directly output from the output device 8. Even when output, good color reproduction is possible without significant changes in hue or saturation. Moreover, by determining and correcting the color reproduction gamut based on saturation, it outputs at the maximum saturation that can be reproduced without changing the brightness and hue processed by System Balini 1, reducing deterioration of reproduced colors. I can do it.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing one embodiment of a color correction method for a digital image processing apparatus according to the present invention.

In Figure 1, system value 1, which is suitable for human visual perception characteristics, has information regarding brightness, hue, and saturation, as described above, and includes, for example, color correction, color adjustment, color conversion, and other editing. This is the image data that has been processed, that is, the color is to be reproduced by the output device 8 from now on. Therefore, according to the example of FIG. 7, the system value 1 is the output of the editing circuit 33, and the system value 1 is inputted, converted into a system value of the output device 8, and outputted from the determination means 3 to the value conversion means 7. The configuration up to this point is the system value conversion circuit 34 shown in FIG. The color reproduction gamut information storage means 2 stores information regarding the color reproduction range defined by brightness, saturation, and hue, and the discrimination means 3
inputs the system value 1 and refers to the information regarding the color gamut stored in the color gamut information storage means 2 to determine the system value handled by the output device 8, for example, MMC (
K), when converting to BGR, it is determined whether the color is within the reproduction range or not. Data within the reproduction range 4 is data for which the system value 1 is determined to be a color value within the reproduction range by the determining means 3, and data outside the reproduction range 5
is data for which the determining means 3 determines that the system value 1 is a color value outside the reproduction range. The correction means 6 corrects the out-of-reproduction-range data 5 to a value within the reproduction range, and performs correction processing by referring to information regarding the color reproduction range stored in the color gamut information storage means 2, for example. The value conversion means 7 performs parinny conversion on the data within the reproduction range 4 or the data after correction by the correction means 6, and converts it into a system value handled by the output device 8, such as YMC (K
), the image is converted into BGR and outputted, and the output device 8 is, for example, a color image output terminal of a copying machine, a color printer, a color display, or the like.

Figure 2 is a diagram showing an example of the configuration of a circuit that converts system values from HVC to BGR, Figure 3 is a diagram showing an example of the configuration of a color reproduction area storage table, and Figure 4 explains correction processing using a comparator. This is a diagram for

In FIG. 2, the color reproduction area storage table 11 is
As shown in the figure, saturation C defined by hue H and brightness V
The maximum value C□ is stored as color reproduction area information. For example, if ■ is set every 1.0 in a range of 10, and C is set every 10 degrees in a 360° range, this color reproduction area information is 10 x 36 = 360 CIl
The color gamut is expressed by l M M. The comparator 12 determines whether the input system value is a color within the reproduction range and also makes corrections thereto.

In the example shown in FIG. 2, when HVC is entered manually as a system value, first, C, , 8 are read out from the color reproduction area storage table 11 corresponding to the input HV. On the other hand, the comparator 12 reads out the input C from the color reproduction area storage table 11 as C□. , and outputs C' with the following modifications.

If C > C, , then C' = C11111N
In the case of C≦C*aH, the system value conversion means 13 converts the input HV and C′ corrected by the comparator 12 into DLUT method, LU
Combination method of T and M) IJ operations, M) IJ
The conversion from HVC to BGR is performed using a multicast calculation method or the like.

For example, as shown in FIG. 4, there are H, V, C, and H2VI C2 as input system values, and corresponding Cm values are stored in the color reproduction area storage table 11.
A case where a, l, and Cmaw2 are stored will be explained. If the input system values are H, V, C, then by the above correction process, since C1 is larger than C2, 8□, C1 is replaced with 81, and the corrected C'
However, the input system value is HsV+C2
In this case, since C3 is conversely smaller than C1.degree.2, the input C2 is directly output as the corrected C' to the system value converting means 13, and is converted into a system value handled by the output device.

As described above in FIG. 6(d), the space of the HVC is formed by abutting two cones, but in reality it is distorted. For example, when comparing yellow and blue, the former has higher brightness, and the latter has lower brightness. For example, when looking at a cross section cut at constant L*, on the high brightness side,
The yellow one has a more protruding shape, and the blue one has a more protruding shape on the lower brightness side. Therefore, when looking at the cross section of the yellow and blue hues that include the L" axis, on the high brightness side, blue becomes closer to white and has a smaller saturation value, but yellow has a larger saturation value. On the other hand, on the low brightness side, blue has a higher saturation value.

Note that the present invention is not limited to the above embodiments, and various modifications are possible. For example, in the above embodiment, the HVC method was adopted, but Lma*b
*The system value can be similarly adopted as a system value that is a value that matches the visual characteristics of a person and includes information about the system, YES, and other brightness, hue, and saturation. In addition, for correction within the reproduction range, fix the two elements of HV and change C to Cm a
Although the processing is performed to limit the distance to X, the shortest distance to a point within the reproduction range may be found in the coordinate space and the correction may be made to that point. Furthermore, as is clear from the system shown in Figure 5, if HVC is the system value for the entire system and the configuration is to output to a CRT display or printer as appropriate, the M
Since it is necessary to perform value conversion into MC (K) and BGR, it goes without saying that the configuration is provided with color reproduction area information and value conversion parameters corresponding to each.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, color correction, color adjustment, color conversion, and other processing are performed using system values that match the human visual characteristics expressed by brightness, saturation, and hue. If configured as above, even if a color outside the color reproduction range is output as a result of the processing, it will be corrected to within the range and then value conversion will be performed to match the output destination, ensuring good color reproduction. It can be carried out. In addition, image data read by a scanner, etc., or image data created by Combi 5-Taggraph, etc. is converted into common system values that match human visual characteristics, processed or stored, and then adjusted to the output destination. Since value conversion is performed, good average color reproduction is possible even in systems that share input means and output means with different characteristics.

Furthermore, by correcting the color gamut with the maximum saturation value corresponding to the brightness and hue, it is possible to output with the maximum saturation that can be reproduced without changing the brightness and hue processed with system value 1. , it is possible to achieve good color reproduction without significant changes in hue or saturation and with reduced deterioration of reproduced colors.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the color correction method of the digital image processing device according to the present invention, and FIG.
FIG. 3 is a diagram showing an example of the configuration of a circuit for converting from VC to BGR; FIG. 3 is a diagram showing an example of the configuration of a color reproduction area storage table;
Fig. 4 is a diagram for explaining correction processing using a comparator, Fig. 5 is a diagram showing a configuration example of a system that handles image data, and Fig. 6 is a diagram for explaining a color system adopted in a color digital image processing device. FIG. 7 is a diagram showing an outline of the configuration of a color digital image processing apparatus. 1... System value, 2... Color gamut information storage means, 3... Discrimination means, 4... Data within the reproduction range,
5--data outside the reproduction range, 6--correction means, 7--
- Value conversion means, 8... output device. Applicant Fuji Xerox Co., Ltd. Agent Patent Attorney Ryukichi Abe (7 others) Figure 1 Figure 2 Figure 5 Figure 7 Figure 3] Figure 3 Figure 4 Figure 6

Claims (2)

[Claims] (1) In a digital color surface image processing device that performs editing processing on image data using values consisting of information regarding brightness, hue, and saturation as system values, value conversion converts system values into values of each primary color handled at the output destination. storage means for storing information regarding the color gamut of the output destination based on system values; and correction means for determining whether the system value is outside the color gamut of the output destination and correcting the system value outside the color gamut to within the color gamut. , and is configured such that the correction means corrects the system value based on information regarding the color gamut of the output destination, and then the value conversion means converts it into values of each primary color and outputs the values. Color correction method for color image processing equipment. (2) The storage means stores the maximum value of the color gamut according to the saturation corresponding to the lightness and hue, and the correction means corrects the saturation to the maximum value when the saturation is larger than the maximum value of the color gamut. 2. A color correction method for a digital color image processing apparatus according to claim 1, wherein the color correction method is configured as follows.