JP2001094799A - Image processing method, apparatus and recording medium - Google Patents

Abstract

(57) [Problem] To provide a high-quality output image by favorably absorbing a difference in shape of a color gamut in an input / output device. A color signal in a first color gamut is converted to a second color signal.
An image processing method for performing mapping conversion to a color signal in a color reproduction gamut, wherein a first signal conversion step of mapping conversion of a color signal in a first color gamut to a color signal in a third color gamut; A calculating step of calculating a lightness correction condition for the third color gamut based on a boundary of a third color gamut and the boundary of the second color gamut;
And a second signal conversion step of adjusting the lightness of the third color gamut while maintaining the chromaticity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image processing method, apparatus, and recording medium for performing gamut mapping.

[0002]

2. Description of the Related Art In recent years, with the spread of personal computers / workstations, desktop publishing (DTP) and CAD have been widely and generally used. Under such circumstances, a color reproduction technology for actually reproducing colors expressed on a monitor by a computer using color materials has become important. For example, in DYP, in a computer system having a color monitor and a color printer, a color image is created / edited / processed on a monitor and output by a color printer. Here, the user strongly desires that the color image on the monitor and the printer output image match perceptually. However, in color reproduction technology, it is difficult to achieve such a perceptual match between a color image and a printer output image. This difficulty is due to the following reasons.

In a color monitor, a color image is expressed by emitting light of a specific wavelength using a phosphor. On the other hand, in a color printer, light of a specific wavelength is absorbed using ink or the like, and a color image is expressed by the remaining reflected light. As described above, due to the difference in the image display form, the color gamut is greatly different when the two are compared.
Further, even in the case of a color monitor, the color reproduction range is different between a liquid crystal monitor, an electron gun type cathode ray tube, and a plasma type monitor. Even in a color printer, the color gamut is different due to a difference in paper quality and the like, a difference in the amount of ink used, and the like. For this reason, in an image on a color monitor and an output image of a color printer, or in an output image of a color printer output on a plurality of types and types of paper, the colors of these images are completely matched in a colorimetric sense. It is impossible. Therefore, when a display color image on each output medium is perceived by a human, a great difference is felt between the images.

[0004] Here, the perceptual difference of a display color image is absorbed between display media having different color reproduction ranges,
As a technique for achieving a perceptual coincidence of display images, there is a gamut mapping technique for mapping a certain color gamut into another color gamut using a uniform color system. As an example of the gamut mapping technique, there is a technique of performing a linear mapping in a lightness-chroma dimension for each hue in a uniform color system. According to such a technique, the monitor color gamut as shown in the schematic diagram of FIG. 3 is mapped into the printer color gamut as shown in the schematic diagram of FIG.

[0005]

However, an image corrected and output according to the above-described conventional technique is generally not perceptually preferable. In order to solve such a problem, a non-linear gamut mapping that preserves the saturation of the low saturation portion and the brightness of the medium brightness portion is effective. However, since the monitor color gamut and the printer color gamut have significantly different shapes, there are many cases where the color appearance becomes unnatural even when the non-linear gamut mapping is used.

The difference between the monitor color gamut and the printer color gamut will be briefly described. For example, FIG. 4 is a schematic diagram of a printer color gamut in a green hue,
The printer color gamut is indicated by a solid line, and the monitor color gamut is indicated by a dotted line. As is clear from FIG. 4, the monitor color gamut and the printer color gamut are non-similar in the green hue, and have greatly different shapes. Next, FIG. 21 shows a schematic diagram of a red hue. In FIG. 21, the monitor color reproduction range is indicated by a solid line, and the printer color reproduction range is indicated by a dotted line. As is clear from FIG. 21, in the red hue, the monitor color reproduction range and the printer color reproduction range have relatively similar shapes.

In order to make the color appearance natural between the image on the monitor and the image output from the printer, gamut mapping for absorbing such a difference is required.

SUMMARY OF THE INVENTION It is an object of the present invention to satisfactorily absorb the difference in the shape of the color gamut in an input / output device so that a high quality output image can be obtained.

[0009]

In order to achieve the above object, an image processing method according to the first invention of the present application converts a color signal in a first color gamut into a color signal in a second color gamut. An image processing method for performing mapping conversion, comprising: a first signal conversion step of mapping conversion of a color signal in a first color gamut to a color signal in a third color gamut; and a boundary of the third color gamut. And the third color gamut based on
And a second signal conversion step of adjusting the lightness of the third color gamut based on the lightness correction conditions while maintaining the chromaticity. It is characterized by.

[0010]

FIG. 1 is a block diagram showing a system configuration of a color signal conversion device as an embodiment according to the present invention.

[0011] 101 is a CPU, 102 is a main memory,
103 is a SCSI interface, 104 is a network interface, 105 is an HDD, 106 is a graphic accelerator, 107 is a color monitor, 108 is a color signal converter, 109 is a color printer, 110 is a keyboard / mouse controller, 111 is a keyboard,
12 is a mouse, 113 is a local Lure network,
Reference numeral 114 denotes a PCI bus.

The image data stored in the HDD 105 is transmitted to the SCS II / F 10 by a command from the CPU 101.
3 via the PCI bus 114 and the main memory 1
02. Further, image data stored in a server connected to the LAN or image data on the Internet is transferred to the main memory 102 via the PCI bus 114 via the network I / F 104 in accordance with a command from the CPU 101. The image data stored in the main memory 102 is transferred to the graphic accelerator 106 via the PCI bus 114 according to a command from the CPU 101. The graphic accelerator 106 performs D / A conversion of the image data, transmits the image data to the color monitor 107 via the display cable, and the image data is displayed on the color monitor 107. Here, when the user instructs the printer 109 to output the image held in the main memory 102, the CPU 101 firstly sets the color gamut information of the appropriate color monitor and the color gamut information of the appropriate printer to H.
The data is transferred from the DD 105 to the main memory 102, and thereafter, the two pieces of color gamut information are transferred to the color signal converter 108. Further, the CPU 101 instructs the color signal converter 108 to perform initialization for conversion from RGB data to CMYK data. The initialization operation will be described later in detail. When the operation is completed, the RGB image data stored in the main memory 102 is stored in the C memory.
The image data is transferred to the color signal conversion device 108 via the PCI bus 114 according to a command from the PU 101. After performing color signal conversion on the RGB image data based on the result of the gamut mapping, the color signal conversion device 108 transmits the CMYK image data as the conversion result to the printer 109. As a result of the above series of operations, CMYK image data is output from the printer 109.

FIG. 2 shows a color signal converter 108 according to this embodiment.
FIG. 3 is a block diagram showing the configuration of FIG.

Reference numeral 201 denotes an LUT creation unit, which creates a lookup table (LUT) for conversion from RGB to CMYK by operating each device in the LUT creation unit 201 according to a designated procedure. A RAM 202 stores the LUT created by the LUT creation unit 201. An interpolator 203 stores CMYK data to be output with respect to the input RGB data in the RAM 20.
The calculation is performed by performing an interpolation operation using the LUT stored in Step 2. 215 and 216 are terminals;
, RGB image data held in the main memory is input by a raster scan method, and CMYK data corresponding to the input RGB data is output from a terminal 216 to the printer.

Next, each device in the LUT creation unit 201 will be described. Reference numerals 213 and 214 denote terminals. Information about the color gamut of the printer is input from 213, and information about the color gamut of the monitor is input from 214. A monitor color gamut storage device 204 stores the input monitor color gamut information, and a printer color gamut storage device 205 stores the input printer color gamut information. 2
Reference numeral 06 denotes a mapping parameter calculation device, which calculates a compression parameter necessary for a compression operation described later with reference to the printer color gamut information and the monitor color gamut information.

Reference numeral 207 denotes a lightness / chromaticity separation color gamut mapping device, which refers to the calculated compression parameters and the monitor color gamut information to map a monitor color gamut. Hereinafter, the mapping result of the monitor gamut by the brightness / chromaticity separation gamut mapping device 207 is referred to as a first intermediate mapped gamut. Reference numeral 208 denotes a color gamut storage device which stores information on a first intermediate mapped color gamut, which is a result of compression / mapping of the monitor color gamut.

Reference numeral 209 denotes a lightness adjustment color gamut mapping device, which refers to the calculated compression parameters and the first intermediate mapped color gamut information, and determines only the brightness of each color in the first intermediate mapped color gamut. Perform the mapping. In the mapping, the chromaticity of each color is preserved. Hereinafter, the chromaticity adjustment gamut mapping device 209 will be described.
Is referred to as a second intermediate mapped color gamut. 210 is a color gamut storage device,
The information of the second intermediate mapped color gamut, which is the mapping result of the first intermediate mapped color gamut, is stored.

Reference numeral 211 denotes a color gamut correction device, which maps the second intermediate mapped color gamut to the printer color gamut with reference to the second intermediate mapped color gamut information and the printer color gamut information. Hereinafter, the mapping result is referred to as a mapped color gamut.

Reference numeral 212 denotes an LUT creation device, which outputs a predetermined relationship between a monitor color gamut and a mapped color gamut, and RGB data for outputting a predetermined color on a monitor, and a predetermined color on a printer. RG with reference to CMYK data
Create an LUT for conversion from B data to CMYK data.

In this embodiment, the L ^* a ^* b ^* color space is used as a uniform color system in the above series of mapping operations.

The operation of the LUT creation unit 201 having the above configuration will be described.

First, color gamut information of a color monitor and color gamut information of a printer are transmitted in accordance with a command from the CPU 101. The transmitted two pieces of color gamut information are stored as monitor color gamut information and printer color gamut information in the monitor gamut storage device 204 and the printer gamut storage device 205 in the LUT creation unit 201, respectively. When the transmission is completed, the CPU 101 instructs to perform initialization for color signal conversion.

When this instruction is received by the color signal converter 108, the inside of the LUT generator 201 operates as follows.

First, the mapping parameter calculation device 206 operates, and calculates various parameters required for the operation of the brightness / chromaticity separation color gamut mapping device 207 and the brightness adjustment color gamut mapping device 209. When the parameter calculation is completed, next, the brightness / chromaticity separation gamut mapping device 207 operates to compress / map the monitor color gamut to the first intermediate mapped color gamut in the uniform color system. In this operation, a method of nonlinearly compressing the brightness and the saturation is used.

The mapping operation by the lightness / chromaticity separation color gamut mapping device 207 in this embodiment will be described in detail later, but a brief description will be given with reference to FIGS. 3, 4 and 11. FIG. 3 is a schematic diagram of a monitor color reproduction range in a green hue. FIG. 4 is a schematic diagram of a printer color gamut in a green hue, in which the printer color gamut is indicated by a solid line, and the monitor color gamut is indicated by a dotted line. FIG.
Is a schematic diagram of a first intermediate mapped color gamut in a green hue, wherein the first intermediate mapped color gamut is indicated by a solid line, a monitor color gamut is indicated by a dashed line, and a printer color gamut is indicated by a dotted line.

The lightness / chromaticity separation color gamut mapping device 207 separates the lightness component and the chromaticity component from the colors in the monitor color reproduction gamut, and non-linearly maps the lightness component and the chromaticity component. With this operation, the monitor color gamut shown in FIG. 3 is mapped to the first intermediate mapped color gamut shown in FIG.

When the operation of the brightness / chromaticity separation gamut mapping device 207 is completed, the first intermediate mapped gamut information is stored in the gamut storage device 208, and the brightness adjustment gamut mapping device 209 subsequently operates. The second for the first intermediate mapped color gamut
Maps to the intermediate mapping color gamut. The operation will be described in detail later, but a brief description will be given with reference to the schematic diagrams in FIGS. FIG. 15 is a schematic diagram of the second intermediate mapped color gamut in the green hue, in which the second intermediate mapped color gamut is indicated by a solid line, and the first intermediate mapped color gamut is indicated by a dashed line.

The lightness adjustment color gamut mapping device 209 separates the lightness component and the chromaticity component from the colors in the first intermediate mapped color reproduction gamut, and performs non-linear mapping of only the lightness component while keeping the chromaticity component constant. The brightness input / output function for realizing the mapping differs depending on the chromaticity. By the mapping, the first intermediate mapped color gamut shown in FIG. 11 is mapped to the second intermediate mapped color gamut shown in FIG.

The color gamut corrector 208 maps the second intermediate mapped color gamut to the printer color gamut with reference to the intermediate mapped color gamut information and the printer color gamut information. Although the operation of the color gamut correction device 208 will be described later in detail, FIG.
A brief description will be given with reference to FIGS. FIG.
Reference numeral 9 is a schematic diagram of a mapped color gamut in a green hue, in which the mapped color gamut is indicated by a solid line, and the second intermediate mapped color gamut is indicated by a dashed line.

The color gamut correction device 208 separates the lightness component and the chromaticity component from the colors in the second intermediate mapped color reproduction gamut and non-linearly maps the chroma components of the chromaticity component while maintaining the lightness component constant. I do. By the mapping, the second intermediate mapped color gamut shown in FIG. 15 is mapped to the mapped color gamut shown in FIG.

Next, the LUT creation device 209 creates an LUT for conversion from RGB data to CMYK data with reference to the mapping color gamut, which is the final mapping result, and stores it in the RAM.
Write the LUT to 202. When the series of operations described above is completed, a notification to the effect that the initialization has been completed is transmitted to the CPU 101.

The operation of each unit of the color signal converter 108 will be described below in detail.

The operation of the brightness / chromaticity separation gamut mapping device 207 will be described. In the present embodiment, a non-linear mapping between a lightness component and a chromaticity component is realized as follows.

In the non-linear mapping of the lightness component, the mapping is realized by one input / output function independent of the chromaticity. The input / output function in the mapping is controlled so as to preserve the lightness at a medium brightness, so that the differential value of the input / output function becomes small near the highest brightness and near the lowest brightness, that is, the compression ratio is increased. Is controlled as follows.
Further, in order to prevent the occurrence of a false contour or the like, the input / output function is controlled so that at least the first derivative is continuous at all points (so as to be C1 continuous). FIG. 5 shows an example of a non-linear mapping of a brightness component realized by the present embodiment.
The control parameters of the non-linear mapping of the brightness component described above are calculated and set by the mapping parameter calculating device 206.

In the non-linear mapping of the chromaticity component, the chromaticity component is further separated into a hue component and a chroma component, and the non-linear mapping is performed on each of them.

The mapping of the saturation component will be described with reference to the flowchart of FIG. First, in step 601, a color M to be mapped is specified. In step 602, the contour saturation compression ratio Rb for the hue of the color M is obtained from the mapping parameter calculation device 206. Then step 6
At 03, the color Bm at the monitor color reproduction gamut boundary with the same brightness and the same hue as the color M is calculated. FIG. 7 is a schematic diagram showing the relationship between the color M and the color Bm. In FIG. 7, the solid line represents the monitor color gamut, and the dotted line schematically represents how the saturation of the outline of the monitor color gamut is mapped by the main chroma mapping. . Step 60
In 4, the saturation Cm of the color M and the saturation Cbm of the color Bm are calculated, and the ratio R is calculated as R = Cm / Cbm. Next, in step 605, a saturation input / output function g (·) for performing saturation mapping is acquired from the mapping parameter calculation device 206. In step 606, the saturation is mapped from the parameters calculated / acquired using the following equation. _{Cm_mapped} is the saturation after the mapping.

_{Cm_mapped} = Cbm × g (R) Here, the saturation input / output function g (·) has the following conditions. G (•) is [0,1] g (•) monotonically increases g (0) = 0 g (1) = Rb g (•) is at least C1 continuous g ′ (0) = 1 · g ′ (1) = γ, γ: γ> 0, γ is a constant for controlling compression. Determined for each hue and changes in inverse proportion to Rb. G ′ (x) ≠ 0, x: 0 ≦ x ≦ 1 FIG. 8 shows a schematic diagram of the saturation input / output function g (·). That is, the lower the saturation, the more the saturation is stored, and the higher the saturation, the higher the compression ratio. Furthermore, since the input / output function is at least C1 continuous, the change rate of the saturation changes smoothly, and the occurrence of a false contour or the like is suppressed.

Next, the mapping of hue components will be described with reference to the flowchart of FIG. First, in step 901, a color M to be mapped is specified. Step 9
02, the hue input / output function h (·) at the lightness of the color M
From the mapping parameter calculation device 206. In addition,
The approximate hue input / output function h (·) changes depending on the brightness. In step 903, hue mapping is performed using the following equation. In the following equation, Hue_m is the hue of the color M, and Hue_m
_{_mapped} is the hue after the mapping.

_{Hue_m_mapped} = h (Hue_m) An example of the hue input / output function h (·) is represented in a schematic diagram as follows.
As shown in FIG. In FIG. 10, the hue angle is represented by a
^{* In the} b ^* chromaticity coordinate system, the hue angle is 0ra in the positive direction of the b ^* axis.
It is expressed by radian notation where d is a counterclockwise rotation and is positive.

The lightness / chromaticity separation gamut mapping device 2 described above
By the mapping operation 07, the monitor color gamut shown in the schematic diagram of FIG. 3 is mapped to the first intermediate mapped color gamut shown in the schematic diagram of FIG. In FIG. 11, the color gamut indicated by the solid line is the first intermediate mapped color gamut, the color gamut indicated by the dashed line is the monitor color gamut, and the color gamut indicated by the dotted line is the printer color gamut. Area.

In the following, the brightness adjustment color gamut mapping device 20
Operation 9 will be described with reference to the flowchart in FIG.

First, in step 1201, a color M to be mapped is specified. Note that the color M here is a color in the first intermediate mapped color reproduction range, and does not represent a color in the monitor color reproduction range. In step 1202, the upper boundary Bu of the first intermediate mapped color gamut at the same chromaticity as the color M is calculated. FIG. 1 shows the relationship between the color M and the upper boundary Bu.
3 is shown. In step 1203, the lower boundary B1 of the first intermediate mapped color gamut at the same chromaticity as the color M is calculated. FIG. 13 shows the relationship between the color M and the upper boundary B1. In step 1204, the upper lightness correction value Ad_u at the same chromaticity as the color M is obtained from the mapping parameter calculation device 206. The upper lightness correction value Ad_u is a lightness correction value for the upper boundary Bu, and is given as a real number with the lightness increasing direction being positive. FIG. 13 schematically shows the relationship between the upper brightness correction value Ad_u and the upper boundary Bu. Here the color Bu
_{_mapped} is a result of mapping Bu by the brightness adjustment color gamut mapping device. In FIG. 13, the color gamut indicated by the solid line is the boundary of the first intermediate mapped color gamut, the color gamut indicated by the one-dot broken line is the boundary of the second intermediate mapped color gamut, and is indicated by the dotted line. The color gamut to be used is the printer color gamut.

In step 1205, the lower lightness correction value Ad_l at the same chromaticity as the color M is obtained from the mapping parameter calculator 206. The lower lightness correction value Ad_l is a lightness correction value for the lower boundary Bl, and is given as a real number with the lightness increasing direction being positive. FIG. 13 is a schematic diagram showing the relationship between the lower brightness correction value Ad_l and the lower boundary Bl. Here, the color _{Bl_mapped} is a result of mapping Bl by the lightness adjustment color gamut mapping device. Then step 120
In step 6, an input / output function p (•) for performing mapping of brightness adjustment is derived from the four parameters obtained above. Here, the derivation of the input / output function p (·) is determined so as to satisfy the following condition. Note that L _Bl is the brightness of Bl, L _Blm is the brightness of _{Bl_mapped} , L _Bu is the brightness of Bu,
L _Bum is the lightness of _{Bu_mapped} . · P (·) is a platform [L _Bl, L _Bu] · P (·) monotonically increasing · P (L _Bl) in the base _{= L Blm · P (L Bu} ) = L Bum · P (·) is at least C1 continuous p '(L _B1 ) = α, α: α> 0, α is a constant for controlling compression. It is determined according to Ad_l for each chromaticity. Ad_
When l is positive, α ≦ 1, and when Ad_l is negative, α ≧ 1. P '(L _Bu ) = β, β: β> 0, β is a constant for controlling compression. It is determined according to Ad_u for each chromaticity. Ad_
If u is positive, β ≧ 1, and if Ad_u is negative, β ≦ 1. The input / output function p (·) is calculated so as to satisfy the above condition, and furthermore, is calculated so that the brightness change amount is as small as possible so that the brightness is preserved as much as possible in the middle part of the platform. In the present embodiment, the input / output function p (·)
, A C2 continuous cubic spline function is used. An advantage of using a C2 continuous cubic spline function is that the input / output function p (·) does not depend on the number of contacts due to the conditions at the end points.
Is uniquely determined. Further, since the input / output function is smoothly defined, an effect is expected in suppressing a false contour. Here, examples of the input / output function p (•) in the present embodiment are shown in FIGS.
(B). In FIG. 14 (a), while the brightness is almost maintained in the middle part of the platform, it is largely compressed near the high brightness and near the low brightness. By the way, L _Bl
= 40, L _Blm = 45, Ad_l = 5, L _Bu = 68, L
_Bum = 64 and Ad_u = -4. FIG.
In (b), the brightness adjustment amounts Ad_l and Ad_
Since the absolute value of u is large, the function of preserving the brightness in the middle part of the table works, but it is not completely preserved. It is greatly expanded near lightness, and largely compressed near lightness. By the way, L _Bl = 60, L _Blm = 4
6, Ad_l = -14, L _Bu = 84, L _Bum = 75, A
d_u = -9. It should be noted that a color having the same chromaticity as the color M naturally uses the same input / output function p (•).

Finally, in step 1207, using the input / output function p (•) obtained in step 1206, the lightness Lm before the mapping of the color M is compared with the lightness Lm after the mapping.
_{_mapped} is _calculated as _{Lm_mapped} = p (Lm), and the brightness adjustment mapping is performed.

By the mapping operation of the brightness adjustment color gamut mapping device 209 described above, the first intermediate color gamut shown in the schematic diagram of FIG. 11 is mapped to the second intermediate color gamut shown in the schematic diagram of FIG. You. In FIG. 15, the color gamut indicated by the solid line is the second intermediate mapped color gamut, the color gamut indicated by the one-dot broken line is the first intermediate mapped color gamut, and the color gamut indicated by the dotted line is This is the printer color gamut.

Hereinafter, the operation of the color gamut correction device 211 will be described. In the present embodiment, the color gamut correction device 211 has a color gamut reduction mapping correction function in addition to the color gamut expansion mapping correction function. Hereinafter, this will be described in detail with reference to the flowchart of FIG.

First, the color gamut correction device 211 executes step 160
In step 1, the color M to be mapped is determined. The color M here
Is a color in the second intermediate mapped color reproduction range. Next, in step 1602, the printer color gamut boundary Bp for the same lightness / same hue as the color M is calculated, and in step 1603
Calculates the second intermediate mapped color gamut boundary Bi at the same brightness / same hue as the color M. Step 160
At 4, the upper limit color gamut boundary Bsup at the same brightness / same hue as the color M is calculated. The upper current color gamut is a color gamut for specifying the upper limit of use of the printer color gamut, and is calculated and stored by the color gamut correction device 211 in advance. These colors M, Bp, Bi, Bs
FIG. 17 is a schematic diagram showing the relationship of up. However, in FIG. 17, the color gamut indicated by the solid line is the boundary of the second intermediate mapped color gamut, the color gamut indicated by the dashed line is the boundary of the upper limit color gamut, and the color reproduction indicated by the dotted line is The gamut is the printer color gamut. Subsequently, in step 1605, the color B calculated in the above steps
An input / output function q (·) for performing mapping of color gamut correction is derived from p, color Bi, and color Bsup. Where the input / output function q (•)
Is expressed so as to satisfy the following condition, when the saturation of the color Bp is expressed as _Cp , the saturation of the color Bi is expressed as _Ci , the saturation of the color Bsup is _expressed as _Csup , and _Cmax = max [ _Cp , _Csup ]. Q (·) is [0, _Ci ] q (0) = 0 q ( _Ci ) = _Cmax · q ′ (0) = 1 q ′ ( _Ci ) = γ, γ: γ> 0, Q ′ (x) ≠ 0, x: 0 ≦ x ≦ _Ciγ is a value for controlling the enlargement / compression ratio of the saturation correction near the maximum saturation, and is automatically determined. Where _Ci > _Cp
In this case, γ <1, and the mapping by the input / output function q (·) is a compression operation. _{If Ci} ≦ _Cp , γ ≧ 1, and the mapping by the input / output function q (·) is a decompression operation. In the present embodiment, a C2 continuous cubic spline function is used as the input / output function q (·). An advantage of using a C2 continuous cubic spline function is that the input / output function q (·) can be uniquely determined from the conditions at the end points regardless of the number of contact points. Further, since the input / output function is smoothly defined, an effect is expected in suppressing a false contour.

Here, the input / output function q in the present embodiment
Examples of (•) are shown in FIGS. 18A and 18B. FIG. 18A shows a case where _Ci ≦ _Cp , and is a decompression operation. FIG. 18B shows a case where _Ci > _Cp ,
Is a compression operation.

Finally, in step 1606, using the input / output function q (•) obtained in step 1605,
Convert the saturation of the color M. If the saturation of the color C is expressed as _Corg and the converted saturation is expressed as _Cmod , _Cmod = q ( _Corg ).

By the mapping operation of the solid color gamut correction device 211 described above, the second intermediate color gamut shown in the schematic diagram of FIG. 15 is mapped to the mapped color gamut shown in the schematic diagram of FIG. FIG.
9, the color gamut indicated by a solid line is a mapped color gamut, the color gamut indicated by a dashed line is a second intermediate mapped color gamut, and the color gamut indicated by a dotted line is a printer color gamut. It is.

According to the present embodiment, it is possible to perform gamut mapping for breathing a difference in shape between the monitor color gamut and the printer color gamut. Further, in each mapping, a sharp change rate in the change rate of the color change is prevented in advance, thereby maintaining the gradation in the output image, preventing the occurrence of a false contour, and enabling preferable image reproduction.

In the upper limit of the performance of the output device, a high contrast can be reproduced vividly.

In the above embodiment, an example in which the monitor color gamut is mapped to the printer color gamut has been described. However, the present invention can be applied to gamut mapping in a combination of other devices.

(Other Embodiments) The functions of the above-described embodiments (for example, a computer connected to an apparatus or a system connected to the various devices so as to operate various devices so as to realize the functions of the above-described embodiments) , FIGS. 6, 11,
Software program code for realizing the functions realized by the flowcharts of 12 and 14),
The present invention also includes a computer (CPU or MPU) of the system or apparatus implemented by operating the various devices according to a stored program.

In this case, the program code of the software implements the functions of the above-described embodiment, and the program code itself and means for supplying the program code to a computer, for example, the program code The storage medium storing the information constitutes the present invention.

As a storage medium for storing such a program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-RO
M, magnetic tape, non-volatile memory card, ROM and the like can be used.

When the computer executes the supplied program code, not only the functions of the above-described embodiment are realized, but also the OS (operating system) running on the computer, or another program. Needless to say, the program code is included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with application software or the like.

Further, the supplied program code is stored in a memory provided in a function expansion board of the computer or a function expansion unit connected to the computer, and then stored in the function expansion board or the function storage unit based on the instruction of the program code. It is needless to say that the present invention includes a case where a provided CPU or the like performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0059]

According to the present invention, the difference in the shape of the color reproduction range in the input / output device can be favorably absorbed, and a high-quality output image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a system configuration of a color signal conversion device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a color signal conversion device according to a first embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a monitor color gamut in a green hue.

FIG. 4 is a schematic diagram illustrating a printer color gamut in a green hue.

FIG. 5 is a diagram illustrating an example of an input / output function for realizing a non-linear mapping of a brightness component.

FIG. 6 is a flowchart illustrating a chroma component mapping operation of the brightness / chromaticity separation gamut mapping device 207 according to the first embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating a spatial relationship between a color M and a color Bm.

FIG. 8 is a diagram illustrating an example of a saturation input / output function g (·) for realizing a nonlinear mapping of a saturation component.

FIG. 9 is a flowchart showing a hue component mapping operation of the brightness / chromaticity separation gamut mapping device 207 according to the first embodiment of the present invention.

FIG. 10 is a diagram illustrating an example of a hue input / output function that realizes mapping of hue components.

FIG. 11 is a schematic diagram illustrating a first intermediate mapped color gamut in a green hue.

FIG. 12 is a flowchart illustrating an operation of the brightness adjustment color gamut mapping device 209 according to the first embodiment of the present invention.

FIG. 13 is a schematic diagram showing a spatial relationship of each color obtained in steps 1201 to 1205.

FIG. 14A is a diagram illustrating an example of an input / output function p (·) for realizing a non-linear mapping of a lightness component. b is a diagram showing an example of an input / output function p (•) for realizing a non-linear mapping of a lightness component.

FIG. 15 is a schematic diagram illustrating a second intermediate mapped color gamut in a green hue.

FIG. 16 is a flowchart illustrating an operation of the color gamut correction device 211 according to the first embodiment of the present invention.

FIG. 17 is a schematic diagram showing a spatial relationship of each color obtained in steps 1601 to 1604.

FIG. 18A is a diagram illustrating an example of an input / output function q (·) for realizing a nonlinear mapping of a saturation component. b is a diagram illustrating an example of an input / output function q (•) for realizing a non-linear mapping of a saturation component.

FIG. 19 is a schematic diagram illustrating a mapped color gamut in a green hue.

FIG. 20 is a schematic diagram illustrating an example of gamut mapping.

FIG. 21 is a schematic diagram illustrating a monitor color gamut and a printer color gamut in a red hue.

Continued on the front page F term (reference) 2C262 AA24 AB11 BA01 BA16 CA10 EA13 FA14 5B021 AA01 LG07 5B057 CA01 CA08 CB01 CB08 CE17 CE18 CH01 CH11 DB06 DB09 5C077 LL19 MP08 PP31 PP32 PP33 PP35 PP36 PP37 PP38 PQ12 PQ22 P037 LB02 MA01 MA11 NA01 NA03 PA03 PA05

Claims (9)

[Claims] 1. A color signal in a first color reproduction range is
An image processing method for performing mapping conversion to a color signal in a color gamut, wherein a first signal conversion step of mapping conversion of a color signal in a first color gamut to a color signal in a third color gamut; Calculating a lightness correction condition for the third color gamut based on a boundary between a third color gamut and the boundary between the second color gamut; and holding chromaticity based on the lightness correction condition. While the third
And a second signal conversion step of adjusting the lightness of the color reproduction range. 2. The image processing method according to claim 1, wherein in the first signal conversion step, brightness and chromaticity are independently mapped. 3. The image processing apparatus according to claim 1, wherein the lightness correction condition adjusts the lightness in a non-linear manner so that the lightness correction amount in an intermediate lightness part of the third color gamut becomes small. Method. 4. The image processing method according to claim 1, wherein the brightness correction condition is a continuous input / output function. 5. The first signal conversion step separates a color signal into lightness and chromaticity, increases the compression ratio in the vicinity of high and low lightness for the lightness, and closes the high chroma in the chromaticity. 2. The image processing method according to claim 1, wherein the compression ratio is increased. 6. The output from the second signal conversion step based on the boundary of the fourth color gamut and the boundary of the third color gamut obtained in the second signal conversion step. 2. The image processing method according to claim 1, further comprising a third signal conversion step of performing an enlarged mapping on the color signal. 7. An output from the second signal conversion step based on a boundary of a fourth color reproduction area and a boundary of the third color reproduction area obtained in the second signal conversion step. 2. The image processing method according to claim 1, further comprising a third signal conversion step of performing an expansion mapping or a reduction mapping on the color signal. 8. A color signal in a first color gamut is converted into a second color signal.
An image processing device that performs mapping conversion to a color signal in a color reproduction range of: a first signal conversion unit that performs mapping conversion of a color signal in a first color reproduction range to a color signal in a third color reproduction range. Calculating means for calculating a lightness correction condition for the third color gamut based on a boundary between a third color gamut and the boundary between the second color gamut; and holding chromaticity based on the lightness correction condition. While the third
And a second signal converter for adjusting the brightness of the color reproduction range. 9. A recording medium on which a program is recorded so as to be readable by a computer, comprising: an image processing method for mapping a color signal in a first color gamut into a color signal in a second color gamut. A first signal conversion step of mapping a color signal in a first color gamut to a color signal in a third color gamut; and a boundary of the third color gamut and the second color reproduction. Calculating a lightness correction condition for the third color gamut based on the boundary of the gamut; and calculating the third lightness while maintaining the chromaticity based on the lightness correction condition.
A second signal conversion step of adjusting the lightness of the color gamut of the recording medium.