JP3099344B2 - Image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital color image processing apparatus that performs editing processing on image data using a value including information on brightness, hue, and saturation as a system value.

[Conventional technology]

FIG. 5 is a diagram showing a configuration example of a system for handling image data, FIG. 6 is a diagram for explaining a color system adopted in the color digital image processing device, and FIG. 7 is a configuration of the color digital image processing device It is a figure showing an outline.

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

In such systems and color digital image processing apparatuses such as copiers, fax machines and printers, BGR, which is an additive primary color such as a CRT, and YMC (K), which is a subtractive primary color such as a printer, are mainly used. It was the value (system value) of the image data handled in the system. BGR is
It is a reflection signal (luminance signal), which is used as a reading signal of a CCD sensor or an output display signal of a CRT display. As shown in FIG. Black when 0, each value is 255
Is white when BGR is equal, and gray when BGR is equal. YMC
Is a density signal, which is used as a print output signal of the printer. When represented by 8 bits and 256 gradations as shown in FIG. 6 (b), when each value is 0, it is white, and each value is A value of 255 indicates black, while a value of YMC is equal to gray.
Since these are color specifications based on mixed colors, it is difficult to imagine how the color changes when B, G, R, Y, M, and C are changed in a certain color. Therefore, it is difficult to know at what rate each primary color should be increased or decreased in response to a request to slightly increase the color or increase the color.

Therefore, recently, the number of cases where values suitable for human visual perception characteristics, such as L ^* a ^* b ^* , HVC, and YES, are adopted as system values is increasing. FIG. 7 shows an example of the configuration. In FIG. 7, a color original is read from an IIT 31 having a CCD sensor and the like, and when a BGR color separation signal is output, the color separation signal is first converted to L ^* a ^{* by} a system value conversion circuit 32 ^.
b ^* and then input to the editing circuit 33.
The editing process is performed on the image data using L ^* a ^* b ^* . When the output side is a printer or the like, the image data of the editing circuit 33 is converted to YMC by the system value conversion circuit 34 by the system value conversion circuit 34.

L ^* a ^* b ^* represents lightness by L ^* as shown in FIG. 6 (c), hue and saturation by a ^* and b ^* , and HVC is also represented by L as shown in FIG. 6 (d). ^{As with *} a ^* b ^* , V is the lightness,
H represents hue and C represents saturation. Therefore, HVC
When the color system is adopted, it is necessary to adjust only V for a request to make the color brighter, and to adjust C to make the color more vivid, and to make the color slightly reddish. Since H can be adjusted for the request,
Quantitative treatment can be performed intuitively. Therefore, the degree of color recognition in editing is also improved. In the case of compressing image data, BGR and YMC have the same weight, so it is necessary to apply the same compression ratio to each of them, but in L ^* a ^* b ^* and HVC, In addition, the compression ratio of brightness and luminance, which are sensitive to human eyes, can be reduced, the hue and the recompression ratio can be increased, and the overall data compression ratio can be increased.

In other words, while BGR and YMC depend on the properties of CRT and color materials, absolute color values such as L ^* a ^* b ^* and HVC have an advantage even in consideration of system compatibility. .

[Problems to be solved by the invention]

As described above, the values handled by the normal output device are primary colors of mixed colors, and colors are reproduced according to the mixing ratio. Therefore, lightness, hue, and saturation slightly differ depending on the increase or decrease of each primary color. That is, the color specification based on the mixed primary colors is a color specification based on information different from the human visual perception characteristics based on brightness, hue, and saturation. On the other hand, L ^* a ^* b ^* and HVC are lightness, hue,
The value is composed of information on saturation, and is a value suitable for human visual perception characteristics. However, when viewed as data handled by the system,
The former has the problem that colors can be reproduced with all of the values assigned to each primary color, while the latter has the problem that some values cannot be reproduced.

That is, in the case of BGR or YMC which is a mixed primary color, if each primary color is represented by 8 bits in a rectangular coordinate system as shown in FIGS. Is a space where the legislative body represented by exists as a color that can be actually reproduced. However, L ^* a ^* b
^{In *} and HVC, the saturation value is 0 at black and white without hue or saturation at both ends of the lightness axis, so there is a non-reproducible space that does not actually exist like the outside where the saturation is not 0 Problem. In other words, a space where two cones meet as shown by the solid line in FIG. 6 (d) basically exists as a reproduction space. Therefore, in the system, for example, even if each is represented by 8 bits, the representable space of the data is a cylindrical space as shown by the dotted line in FIG. 6 (d). Saturation is only maximized near the middle of the lightness axis where the cones are abutted, and the range of saturation becomes narrower even if the lightness shifts in either direction, and the range where reproduction is impossible It gets bigger.

On the other hand, no matter what value is used in the system, when finally printing out or displaying on a CRT, value conversion according to the output device is necessary. Moreover, the system value usually employed in these output devices is either BGR, which is an additive primary color, or YMC (K), which is a subtractive primary color such as a printer. For this reason, if a system value suitable for human visual perception characteristics consisting of information on brightness, hue, and saturation as described above is adopted, the YMC (K) and BGR that match the output device when outputting are used. Value conversion is required. At this time, as described above, a color signal that cannot be reproduced by a printer, a CRT, or the like or a color signal having a value that does not actually exist may occur. This mainly adjusts hue, lightness, saturation, etc. independently,
This can happen when converting.

The system value conversion method includes a method using a DLUT (direct lookup table) having a conversion table for all values, a method using a combination of an LUT and a matrix operation, a method using a matrix operation, and the like. Of these, in the case of the DLUT, it can be avoided at the time of creating the LUT that the color is converted to a color outside the above reproduction range, but in other cases, when a value that cannot be reproduced is actually input, It is not known what color is output, and good color adjustment and color conversion are not performed.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problem, and to provide a color correction method for a digital color image processing apparatus that corrects data outside a color reproduction range.

[Means for solving the problem]

Therefore, the color correction method of the digital color image processing apparatus according to the present invention is based on a digital color image processing apparatus that performs editing processing on image data using a value including information on lightness, hue, and saturation as a system value.
As shown in the figure, a value conversion means 7 for converting a system value into values of respective primary colors handled at an output destination, a storage means 2 for storing information relating to a color gamut of an output destination according to the system value, and a system value indicating a color of an output destination Correction means 3 and 6 for judging whether or not the value is outside the reproduction range and correcting the system value 5 outside the color reproduction range to within the color reproduction range, and when outputting the edited system value 1 to the output device 8, the correction means 6, the system value 1 is corrected based on the information on the color gamut of the output destination,
And outputs the converted values of the primary colors.

Further, the storage means 2 stores the maximum value of the color gamut according to the saturation corresponding to the lightness and the hue, and the correction means 3 and 6 stores the maximum value when the saturation is larger than the maximum value of the color gamut. It is characterized in that it is configured to be corrected.

[Action]

According to the color correction method of the digital color image processing apparatus of the present invention, information on the color gamut of the output destination by the system value is stored in the storage unit 2, and when the edited system value 1 is output to the output device 8. After the correction unit 6 corrects the system value 1 based on the information on the color gamut of the output destination, the value conversion unit 7 converts the value into the value of each primary color and outputs it. Even when output, good hue and saturation are not largely changed, and good color reproduction is possible. In addition, by judging and correcting the color gamut based on the saturation, the output can be output at the maximum reproducible saturation without changing the brightness and hue processed in System Value 1, so that the degradation of the reproduced colors can be reduced. it can.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

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

In FIG. 1, a system value 1 corresponding to human luminous characteristics has information on lightness, hue, and saturation as described above, and includes, for example, color correction, color adjustment, color conversion, and other editing. This is the image data after the processing, that is, the color data 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. From the discriminating means 3 for inputting the system value 1 and converting it to the system value of the output device 8 and outputting it, the value conversion means 7 Is a system value conversion circuit 34 shown in FIG. The color gamut information storage means 2 stores information on a color gamut defined by lightness, saturation, and hue.
Is a system value handled by the output device 8 with reference to the information about the color reproduction range stored in the color gamut information storage means 2 with the system value 1 as an input.
(K), at the time of conversion to BGR, it is determined whether or not the color is within the reproduction range. The data 4 within the reproduction range is data for which the determination unit 3 has determined that the system value 1 is a color value within the reproduction range, and data 5 outside the reproduction range.
Are data for which the determination unit 3 has determined that the system value 1 is a color value outside the reproduction range. The correction unit 6 corrects the out-of-reproduction-range data 5 to a value within the reproduction range. For example, the correction unit 6 performs correction processing with reference to information on the color reproduction range stored in the color-reproduction-region information storage unit 2. The value conversion means 7 converts the value of the data 4 within the reproduction range or the data corrected by the correction means 6 into a value, and the system value handled by the output device 8, for example, YMC
(K), which is converted to BGR and output, 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.

FIG. 2 is a diagram showing a configuration example of a circuit for converting a system value from HVC to BGR, FIG. 3 is a diagram showing a configuration example of a color reproduction area storage table, and FIG. FIG.

In FIG. 2, the color reproduction area storage table 11
As shown in the figure, saturation C defined by hue H and lightness V
_Is stored as color reproduction area information. For example, if C _max is set every 1.0 in a range of 10 and H every 10 ° in a range of 360 °, the color reproduction range information is obtained by 10 × 36 = 360 C _maxes. Will be expressed. The comparator 12 determines whether or not the input system value is a color within the reproduction range and corrects it.

In the example shown in FIG. 2, when an HVC is input as a system value, first, _Cmax is read from the color reproduction area storage table 11 corresponding to the input HV. On the other hand, the comparator 12 stores the input C in the color reproduction area storage table 11.
And outputs the modified C ′ as compared with C _max read out from

When C> C _max , C ′ = C _{max When} C ≦ C _max , C ′ = C The system value conversion means 13 converts the input HV and C ′ corrected by the comparator 12 The conversion from HVC to BGR is performed using the DLUT method, the combination method of LUT and matrix operation, the matrix operation method, and the like.

For example, as shown in FIG. 4, there are H ₁ V ₁ C ₁ and H ₂ V ₁ C ₂ as system values input, and C _max1 and C _max2 are respectively stored in the color reproduction area storage table 11 corresponding to each of them. The following is a description of the case. If the input system value is H ₁ V ₁ C ₁ ,
C ₁ is larger because C after Fixed replaced with the C _max1 'than C _max1, but entered the system Value is H ₂ V ₁
In the case of C ₂ is, C ₂ intact as C 'after the correction of C ₂ input is smaller in the opposite than C _max2, and output to the system value converting unit 13 converts the system value handled by the output device.

As described above with reference to FIG. 6D, the space of the HVC is obtained by abutting two cones, but is actually distorted. For example, comparing yellow and blue, the former is at higher brightness and the latter is at lower brightness. For example, looking at a section cut at L ^* constant, on the high lightness side,
The yellow color protrudes, and the blue color protrudes on the lower brightness side. Therefore, when viewed in a cross section of yellow and blue hues including the axis L ^* , on the high lightness side, blue is closer to white and has a smaller saturation value, but yellow has a larger saturation value. On the other hand, on the low lightness side, the value of saturation is higher in blue.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, the description has been given of the case where the HVC method is adopted, but L ^* a ^* b
^{* The same} can be applied to the case where a value corresponding to the human visual perception characteristic, which is made up of the method, YES, and other information on brightness, hue, and saturation, is used as the system value. In addition, in the correction within the reproduction range, the processing of limiting the two elements of HV and limiting C to C _max was performed. However, the shortest distance to a point within the reproduction range in the coordinate space was obtained, and the You may make it correct to a point. In addition, as is clear from the system shown in FIG.
In the case of a configuration that outputs to a display or a printer as appropriate, it is necessary to convert the value to YMC (K) or BGR according to each output device. Therefore, the corresponding color reproduction area information and value conversion parameters Needless to say, the configuration is provided.

〔The invention's effect〕

As is clear from the above description, according to the present invention, color correction, color adjustment, color conversion, and other processing are performed with a system value suitable for human luminous characteristics expressed by brightness, saturation, and hue. In such a configuration, even if a color outside the color reproduction range may be output as a result of the processing, the value is corrected within the range and then the value conversion is performed according to the output destination.
Good color reproduction can be performed. In addition, image data read by a scanner or image data created by computer graphics or the like is temporarily converted into a common system value suitable for human visual characteristics and processed or stored,
After that, since the value conversion is performed according to the output destination, even in a system in which input means and output means having different characteristics are shared, an average good color reproduction can be realized.

Furthermore, by correcting the color reproduction range with the maximum value of saturation corresponding to lightness and hue, it is possible to output with the maximum reproducible saturation without changing the lightness and hue processed by System Value 1. In addition, it is possible to achieve good color reproduction in which the hue and saturation are not largely changed and the deterioration of reproduced colors is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a color correction method of a digital image processing apparatus according to the present invention, and FIG.
FIG. 3 is a diagram illustrating a configuration example of a circuit that converts C to BGR,
FIG. 4 is a diagram showing a configuration example of a color reproduction area storage table, FIG. 4 is a diagram for explaining correction processing by a comparator, FIG. 5 is a diagram showing a configuration example of a system that handles image data, and FIG. FIG. 7 is a view for explaining a color system adopted in the color digital image processing apparatus, and FIG. 7 is a view showing a schematic configuration of the color digital image processing apparatus. 1 ... System value, 2 ... Color reproduction area information storage means, 3 ... Determination means, 4 ... Data within reproduction range, 5 ...
Data outside the reproduction range, 6... Correction means, 7... Value conversion means, 8.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (1)

(57) [Claims] 1. An image processing apparatus for performing editing processing on image data using a value comprising information on lightness, hue, and saturation as a system value, wherein the value conversion means converts the system value into a value of each primary color handled at an output destination. And storage means for storing a maximum value of saturation corresponding to lightness and hue as a color reproduction area of an output destination based on system value; and determining whether the system value is outside the color reproduction area of the output destination stored in the storage means. The system value outside the color gamut has correction means for correcting the saturation to the maximum value of the color gamut, and the correction means corrects the saturation of the system value based on the color gamut of the output destination. And an image processing apparatus configured to convert the values into values of respective primary colors by a value converting means and output the converted values.