JP2005260801A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control color reproduction of color image output devices so as to match looks of colors without sense of incompatibility even in a gradation image with respect to an image represented by color image devices of different color reproduction ranges through comparatively simple calculation. <P>SOLUTION: In a color space conversion section 301, a target color (RGB value) to be a reference of gamut compression is converted into a sense equal color space (CIELab). In a target color calculation section 303, a target color corresponding to a hue (H) and a saturation degree (chromaticity) C of an input color is calculated, and input color data and target color data are sent to a gamut compression section 305. In the gamut compression section 305, the input color is compressed in a color reproduction range set by an output color reproduction range setting section 304. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus and an image processing method for controlling color reproduction of a color image input / output device with a limited color reproduction range when a color image is handled between a plurality of image input / output devices having different characteristics. The present invention relates to a technique suitable for image output devices such as facsimiles, color printers, color hard copies, etc., software for color printers operating on personal computers, workstations, and the like.

  Conventionally, when a system that handles image data, such as a printing system, is configured with image input / output devices with different characteristics such as displays, scanners, printers, etc., the difference in color reproduction range between each device is different between different devices. This is a problem when performing color conversion processing.

  In order to solve this problem, for example, when the color reproduction range of the monitor and the printer is different (see FIGS. 1 to 3), a human-perceived three-dimensional space (perception such as CIELAB) with lightness, saturation, and hue as axes. Based on the technology that compresses (maps) colors that cannot be reproduced by the output device on the uniform color space) (hereinafter referred to as gamut compression), and after adjusting the brightness range shown in FIGS. A number of methods have been proposed, including a method of compressing saturation to a color that can be reproduced in the direction of constant brightness, constant saturation, minimum color difference, and the like.

  For example, there is a method of matching the relative lightness normalized from the two points of the brightest part and the darkest part of the input color image and the output color image in a uniform color space for each page of the input color image (for example, Patent Documents). 1).

  Further, there is a method of matching the characteristic color in the input color image signal with a predetermined color while maintaining the lightness, saturation and hue linearity of the output color (see, for example, Patent Document 2).

  In addition, there is a method for finely controlling correction related to compression, such as compression so that the correction amount of the intermediate lightness portion is reduced without changing the saturation component in accordance with the lightness range of the color reproduction range (for example, (See Patent Document 3).

  Further, there is a method of reproducing a preferable skin color even in different storage media by converting a lightness achromatic color corresponding to the skin color into a certain chromaticity value (see, for example, Patent Document 4).

JP-A-10-210313 Japanese Patent Laid-Open No. 10-200774 JP 2002-33931 A Japanese Patent Laid-Open No. 2003-110859

  As described above, when a system that handles image data such as a printing system is configured with image input / output devices having different characteristics, such as displays, scanners, and printers, the difference in color reproduction range between the devices is absorbed. However, many image processing methods for color reproduction have been proposed.

  However, when processing is performed such that the relative brightness normalized from the two points of the brightest part and the darkest part of the input color image and the output color image is matched in a uniform color space represented by Patent Document 1, Depending on the hard copy observation environment such as the brightness of the illumination light and the whiteness of the recording medium, the color may become dark. For example, as shown in FIG. 4, when the skin color is reproduced by matching the relative brightness of the brightest part and the darkest part of the output color image without considering the brightness of the recording medium (paper white here), the absolute brightness of the skin color Changes depending on the brightness of paper white. Here, when paper white has sufficient brightness (whiteness), there is no problem because the paper white and the adaptation white point are almost the same, but there is not enough brightness (whiteness). Is not completely adapted to paper white, so if the relative brightness is maintained, important colors such as skin color are reproduced darkly, and the color appearance does not match the input image.

  A method for performing a process for matching a characteristic color in an input color image signal with a predetermined color while maintaining the lightness, saturation, and hue linearity of the output color as in Patent Document 2, and Patent Document 3 By using a method that finely controls the correction amount of the saturation component according to the lightness range of the color gamut, it is possible to cope with the above problems, but gradation and linearity with respect to lightness, hue, and saturation component. In addition, it is necessary to optimize the color mapping according to the comprehensive evaluation value obtained by further calculating the weight, and there is a problem that it takes time for the calculation.

  Further, as described in Patent Document 4, it is possible to reproduce a preferable skin color even on a recording medium having a different chromaticity by converting a light achromatic color corresponding to the skin color into a certain chromaticity value. Since the adjustment is made only for gray, color mapping (coincidence of color appearance) for the entire input color space corresponding to the recording method and the color reproduction range (gamut) of the recording medium is not supported.

The present invention has been made to solve the above-mentioned conventional problems,
The object of the present invention is to output a color image so that the color appearance can be matched with an image represented by a color image device having a different color reproduction range with a relatively simple calculation without any sense of incongruity with a gradation image. An object of the present invention is to provide an image processing apparatus and an image processing method for controlling the color reproduction of the apparatus.

  That is, an object of the present invention is to provide an image processing apparatus that controls the color reproduction of a color image output apparatus with respect to an input color image signal so that colors appear between color image devices having different color reproduction ranges. is there.

  An object of the present invention is to provide an image processing apparatus for controlling color reproduction of a color image output apparatus so that colors appear to match images represented by color image devices having different color reproduction ranges. .

  An object of the present invention is to provide an image processing apparatus for controlling color reproduction of a color image output apparatus so that colors appear with high accuracy without discomfort for images represented by color image devices having different color reproduction ranges. Is to provide.

  An object of the present invention is to provide an image processing apparatus for controlling the color reproduction of a color image output apparatus with respect to an input color image signal by matching the appearance of colors between color image devices having different recording media, viewing conditions, and color reproduction ranges. Is to provide.

  An object of the present invention is to provide an image processing apparatus that controls the color reproduction of a color image output apparatus so that the color appearance matches a photographic image represented by a color image device having a different color reproduction range. is there.

  An object of the present invention is to control the color reproduction of a color image output device so that the color appearance matches a graphic image represented by a color image device having a different color reproduction range by using a color reproduction range. It is to provide a processing apparatus.

  The object of the present invention is to control the color reproduction of the color image output device so that the color looks good especially on a document in which characters, graphics, images, etc. are mixed on color image devices with different color reproduction ranges. An object is to provide an image processing apparatus.

  An object of the present invention is to control the color reproduction of the color image output apparatus with respect to the input color image signal so that the color appearance between the color image devices having different color reproduction ranges matches.

  An object of the present invention is to control the color reproduction of the color image output apparatus so that the color appearance matches an image represented by a color image device having a different color reproduction range.

  The object of the tenth aspect is to control the color reproduction of the color image output device so that the color appearance can be matched with high accuracy with respect to an image represented by a color image device having a different color reproduction range. .

  An object of the present invention is to control the color reproduction of a color image output apparatus with respect to an input color image signal by matching the color appearance between color image devices having different recording media, viewing conditions, and color reproduction ranges. .

  According to a first aspect of the present invention, there is provided an image processing apparatus for controlling color reproduction of a color image output apparatus with respect to an input color image signal, means for setting a color in an input color space as a target color, and the target color Means for calculating the lightness or saturation of the image, and color conversion means for storing the lightness or saturation of the target color so as to match the lightest part and the darkest part of the color reproduction range of the input color space with the color image output device It is what has.

  According to a second aspect of the present invention, there is provided an image processing apparatus for controlling color reproduction of a color image output apparatus with respect to an input color image signal, means for setting a color in the input color image as a target color, and the target color Means for calculating the lightness or saturation of the image, and color conversion means for storing the lightness or saturation of the target color and matching the lightest part and the darkest part of the color reproduction range of the input color image and the color image output device It is what has.

  According to a third aspect of the present invention, target color setting and color conversion in the image processing apparatuses according to the first and second aspects of the present invention are performed in accordance with the hue and saturation of the input color.

  According to a fourth aspect of the present invention, color conversion in the image processing apparatuses according to the first to third aspects of the invention is performed in a color perception space that depends on viewing conditions.

  According to a fifth aspect of the present invention, the target colors set in the image processing apparatuses according to the first to third aspects include at least information on memory colors such as human skin, sky, and plants.

  In a sixth aspect of the present invention, the target colors set in the image processing apparatuses of the first to third aspects include at least the highest chroma color for each hue that can be reproduced by the color image output apparatus.

  According to a seventh aspect of the present invention, the target color in the image processing apparatuses of the first to third aspects is set for each type of document object to be imaged.

  According to an eighth aspect of the present invention, there is provided an image processing method for controlling color reproduction of a color image output apparatus with respect to an input color image signal, and storing the lightness or saturation of an arbitrary target color to store the input color. Color reproduction is performed by matching the lightest part and the darkest part of the color reproduction range of the space and the color image output apparatus.

  According to a ninth aspect of the present invention, in an image processing method for controlling color reproduction of a color image output apparatus for an input color image signal, the brightness or saturation of a target color in the set input color image is calculated. The lightness or saturation of the target color is stored, and color reproduction is performed by matching the lightest part and the darkest part of the color reproduction range of the input color image and the color image output device.

  According to a tenth aspect of the present invention, target color setting and color conversion in the image processing methods of the eighth to ninth aspects of the invention are performed in accordance with the hue and saturation of the input color.

  According to an eleventh aspect of the present invention, color conversion in the image processing method according to claims 8 to 10 is performed in a color perception space that depends on viewing conditions.

  According to a first aspect of the present invention, there is provided an image processing apparatus for controlling color reproduction of a color image output apparatus with respect to an input color image signal, means for setting a color in an input color space as a target color, and the target color Means for calculating the lightness or saturation of the image, and color conversion means for storing the lightness or saturation of the target color so as to match the lightest part and the darkest part of the color reproduction range of the input color space with the color image output device Therefore, it is possible to provide an image processing apparatus that controls color reproduction of a color image output apparatus with respect to an input color image signal so that colors appear between color image devices having different color reproduction ranges. .

  According to a second aspect of the present invention, there is provided an image processing apparatus for controlling color reproduction of a color image output apparatus with respect to an input color image signal, means for setting a color in the input color image as a target color, and the target color Means for calculating the lightness or saturation of the image, and color conversion means for storing the lightness or saturation of the target color and matching the lightest part and the darkest part of the color reproduction range of the input color image and the color image output device Therefore, it is possible to provide an image processing apparatus that controls color reproduction of a color image output apparatus so that colors appear to match images represented by color image devices having different color reproduction ranges. it can.

  In the third invention according to the present invention, the target color setting and color conversion in the image processing apparatuses of the first and second inventions are performed in accordance with the hue and saturation of the input color. It is possible to provide an image processing apparatus that controls the color reproduction of a color image output apparatus so that colors appear with high accuracy with respect to images represented by different color image devices.

  According to a fourth aspect of the present invention, since color conversion in the image processing apparatus according to the first to third aspects of the invention is performed in a color perception space that depends on the observation conditions, the recording medium, the observation conditions, and the color reproduction range. It is possible to provide an image processing apparatus that controls color reproduction of a color image output apparatus with respect to an input color image signal by matching color appearances between different color image devices.

  In the fifth invention according to the present invention, since the target color set in the image processing apparatuses of the first to third inventions includes at least information on memory colors such as human skin, sky, and vegetation, color reproduction is performed. It is possible to provide an image processing apparatus that controls the color reproduction of a color image output apparatus so that the color appearance matches a photographic image represented by a color image device having a different range.

  In the sixth invention according to the present invention, the target color set in the image processing apparatuses according to the first to third inventions includes at least the highest saturation color for each hue that can be reproduced by the color image output apparatus. To provide an image processing device for controlling color reproduction of a color image output device so that a color appearance matches a graphic image represented by a color image device having a different color reproduction range by using the color reproduction range. it can.

  According to a seventh aspect of the present invention, since the target color in the image processing apparatus according to the first to third aspects of the invention is set for each type of document object to be imaged, color images having different color reproduction ranges. It is possible to provide an image processing apparatus that controls the color reproduction of a color image output apparatus so that the color looks good especially on a document in which characters, graphics, images, and the like are mixed on the device.

  According to an eighth aspect of the present invention, there is provided an image processing method for controlling color reproduction of a color image output apparatus with respect to an input color image signal, and storing the lightness or saturation of an arbitrary target color to store the input color. Since color reproduction is performed by matching the brightest and darkest parts of the color reproduction range of the color image output device with the space, input is performed so that the color appearance between color image devices with different color reproduction ranges matches. The color reproduction of the color image output apparatus for the color image signal can be controlled.

  According to a ninth aspect of the present invention, in an image processing method for controlling color reproduction of a color image output apparatus for an input color image signal, the brightness or saturation of a target color in the set input color image is calculated. Since the lightness or saturation of the target color is stored and the input color image and the color reproduction range of the color image output device have the lightest part and the darkest part, the color reproduction is performed. The color reproduction of the color image output device can be controlled so that the color appearance matches images represented by different color image devices.

  In the tenth aspect of the present invention, since the target color setting and color conversion in the image processing methods of the eighth to ninth aspects of the invention are performed according to the hue and saturation of the input color, the color reproduction range. Therefore, it is possible to control the color reproduction of the color image output apparatus so that the color appearance can be matched with high accuracy with respect to images represented by different color image devices.

  In an eleventh aspect of the present invention, since color conversion in the image processing method according to claims 8 to 10 is performed in a color perception space depending on the observation conditions, the recording medium, the observation conditions, and the color reproduction range are The color reproduction of the color image output apparatus can be controlled with respect to the input color image signal by matching the color appearance between different color image devices.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Configuration of image processing system)
FIG. 5 shows a configuration example of an image processing system according to the present invention. In the example of FIG. 5, the image processing system includes a computer 101, an image display device (display) 100 connected to the computer, image output devices 1021 to 1023, an image input device 1024, and device specifics supplied from the computer. The color signal (RGB signal, CMY signal, CMYK signal, etc.) is converted into a color signal specific to the selected image input / output device.

  The computer 101 can be installed with various applications and software such as a printer driver. The display 100 is an output device for displaying image data. The image output devices 1021 to 1023 are output devices for printing out image data. The image input device 1024 is an input for capturing image data. The image output devices 1021 to 1023 are color printers, color copiers having a printer function, and display devices for color displays. The image input device 1024 is a color scanner, a digital camera, and the like. Further, the number of image input / output devices is not limited to 1021 to 1024, and any number of image input / output devices may be connected.

  FIG. 6 is a diagram for explaining processing functions of the computer 101 and the image processing apparatus 200 in the image processing system of FIG. Referring to FIG. 6, the computer 101 has a function of sending a drawing command to the image processing apparatus 200 through an application and software such as a printer driver.

  On the other hand, the image processing device 200 includes a color conversion processing device 201, a rendering processing device 202, a band buffer 203, a gradation processing device 204, a page memory (storage device) 205, etc., and a drawing command sent from the computer 101. Is converted into data that can be processed by the image output apparatus.

(Operation of image processing system)
An operation until the computer 101 generates a drawing command will be described. First, an operator edits image data while displaying it on a display using an application installed in the computer. When the editing operation is completed, the image output device 1021 to be output is selected and printing is instructed.

  Here, when printing is instructed, a setting screen can be displayed on the display 100 so that various printing conditions can be set.

  When the computer 101 receives a command for instructing printing from the application, the computer 101 transmits document data in the application to the printer driver. The printer driver converts the document data into a drawing command that can be received by the image processing apparatus 200, and transmits the drawing command to the image processing apparatus 200.

  Next, the operation of the image processing apparatus in this embodiment will be described. The image processing apparatus 200 transmits the color data of the drawing command to the color conversion processing apparatus 201 while transmitting and receiving the drawing command to and from the computer 101. The color conversion processing device 201 performs color conversion processing on the received RGB format color data, converts the color data into color data (for example, CMYK) suitable for the image output devices 1021 to 1023, and transmits the color data to the rendering processing device 202. To do. The rendering processing device 202 converts the command format data into raster format image data and stores it in the band buffer 203. Then, the gradation processing device 204 reads raster format image data from the band buffer 203, applies dither processing or the like, converts it into gradation data that can be processed by the image forming device, and generates them to the image output devices 1021 to 1023. Transmitted gradation data. As a result, the image output devices 1021 to 1023 can perform printout.

  In the examples of FIGS. 5 and 6, rendering processing, color conversion processing, gradation processing, and the like are performed by the image processing apparatus 200 independent of the computer 101 and the image output apparatuses 1021 to 1023. A part of the functions may be implemented in the computer 101, or may be implemented in the image output devices 1021 to 1023. Alternatively, it may be mounted in a printer control device provided independently of the image output devices 1021 to 1023.

  The image processing apparatus 200 of the present invention can also be realized by software. For example, the function of the image processing apparatus 200 can be realized by a printer driver that exists as a program in a computer.

(Configuration of Color Conversion Processing Apparatus 201 in Embodiment 1)
Next, a color conversion processing apparatus 201 that is a feature of the present invention will be described with reference to FIG. An RGB → Lab (LCH) color space conversion unit that receives a signal corresponding to an input color or a target color and converts it into a device-independent color signal (for example, L * a * b * or JCH). 301, a target color setting unit 302 that sets a target color that is a reference for gamut compression, and a device-independent conversion from a representative target color set by the target color setting unit 302 by an RGB → Lab (LCH) color space conversion unit 301 A target color calculation unit 303 that calculates a target color corresponding to the input LCH, an output color reproduction range setting unit 304 that sets color reproduction range (gamut) information of the selected color output device, and an output color reproduction range setting for the input color. The gamut compression unit 305 that performs (color) compression within the color reproduction range set by the unit 304, and receives a corrected device-independent color signal from the gamut compression unit 305 in FIG. The color signals for the image output apparatus 1021 to 1023 (for example, CMYK signal) is constituted by Lab (LCH) → CMYK color space conversion unit 306 for converting the.

(Operation of the color conversion processing apparatus 201 in Embodiment 1)
Next, the operation will be described. First, an RGB input signal which is color data of a drawing command received from the printer driver is sent to the RGB → Lab (LCH) color space conversion unit 301. The RGB → Lab (LCH) color space conversion unit 301 converts the CIELab, which is a perceptual uniform color space, using a preselected input device profile. The RGB signal, which is image information in a CRT display or the like, can be expressed by the following formula (sRGB (8 bits: 0 to 255)) that is standard RGB depending on the color temperature, chromaticity coordinates, and photoelectric conversion characteristics of the display. Using 1) to Equation (4), the device converts to a device-independent color signal represented by lightness (L), saturation (C), and hue (H), and transmits it to the target color setting unit 302.
r = (R / 255) ^2.2
g = (G / 255) ^2.2
b = (B / 255) ^2.2 (1)
X = 0.4124 × r + 0.3576 × g + 0.1805 × b
Y = 0.2126 * r + 0.7152 * g + 0.0722 * b
Z = 0.0193 * r + 0.1192 * g + 0.9505 * b (2)
L * = 116 (Y / Y0) ^1/3 -16, (Y / Y0> 0.008856)
a * = 500 [(X / X0) ¹ /3-(Y / Y0) ^1/3 ], (X0, Y0, Z0 are values of the reference reflecting surface)
b * = 200 [(Y / Y0) ¹ /3-(Z / Z0) ^1/3 ], (3)
Lightness: L
Saturation: C = (a ² + b ² ) ^0.5
Hue: H = atan 2 (b, a) × 180 / π
However, when a = b = 0, H = 0,
When H <0, H = 360 + H (4)

  Also, with respect to the target color information in the target color setting unit 302, when the target color is an RGB value, the RGB → Lab (LCH) color space conversion unit 301 uses the profile of the input device selected in advance, It is converted into CIELab, which is a perceptual uniform color space, and transmitted to the target color calculation unit 303.

  The target colors (RGB and CIELAB values) set here are set as RGB values and CIELAB values directly on the printer driver by the operator via the computer 101, and are actually displayed on the display 100 in FIG. The pixel of the selected image is directly selected by the operator and set as the corresponding RGB value, the RGB value or CIELAB value corresponding to the representative memory color such as skin color is set in advance, or the selected image A target color setting unit 302 sets and stores, for example, one set with the highest saturation color (CIELAB value: Lh1p in FIG. 3) for each hue that can be reproduced by the output device (printer).

  The target color calculation unit 303 calculates a target color according to the hue H and saturation (saturation) C of the input color. For example, in the target color setting unit 302, as shown in FIG. 8, when a table of target colors (lightness L in the example of FIG. 8) in typical hue H and saturation (saturation) C is set, Values corresponding to the hue H and saturation (saturation) C of the input color calculated by the RGB → Lab (LCH) color space conversion unit 301 are selected from the target color table or calculated by linear interpolation, and input. A target color for the color is obtained, and input color data and target color data are sent to the gamut compression unit 305.

  In the example of FIG. 8, the highest saturation color for each hue that can be reproduced by the image output apparatus (printer) is set as the target color, and the target color of each hue approaches as it goes toward lower saturation (saturation). In the achromatic axis, they are completely matched.

  The control from the achromatic color axis to the saturated color is performed by a linear or non-linear expression with the saturation C as a variable, so that the dynamic (brightness) of the image output device (printer) is maintained while maintaining the continuity of the color space. Regardless of the size of the range, the brightness of important colors having different hues such as skin color, greenery of plants, and blue sky can be brought close to ideal values.

  In the gamut compression unit 305, for example, a process of compressing (mapping) into a color that can be reproduced by the selected image output apparatus 1021 in FIG.

Here, processing in the gamut compression unit 305 according to the present embodiment will be described. In the gamut compression unit 305, according to the target color corresponding to the hue H and saturation (saturation) C of the input color calculated by the target color calculation unit 303, first, the target color is related to the gamut as shown in FIG. In the case of storing the lightness of the image, lightness compression and saturation compression as shown in the following equations are performed.
When L ≧ Lhc1T,
L ′ = (Lwp−Lhc1T) × (L−Lhc1T) / (Lwm−Lhc1T) + Lhc1T
L ′ = (Lhc1T−Lbp) × (L−Lbm) / (Lhc1T−Lbm) + Lbp when L <Lhc1T
C ′ = C × α × (L ′ / L)
However,
Lwp: Maximum brightness of the printer Lbp: Minimum brightness of the printer Lwm: Maximum brightness of the display Lbm: Minimum brightness of the display Lhc1T: Target color (lightness) corresponding to the hue H1 and saturation (saturation) C1 of the input color
α: Compression coefficient (5)

  In this embodiment, the target color is set in the LCH space based on the CIELAB color space. However, the hue H and the saturation S in the HSL (Ostwald color system) based on the input color space (RGB) are used. The target color may be set according to the above.

In this HSL (Ostwald Color System) space, for example, RGB graphic images are obtained by compressing the brightness so as to preserve the saturation of the target color in consideration of the highest saturation color of the image output device (printer). Color reproduction using the primary color (YMC) of an advantageous printer and high-saturation color that cannot be reproduced by a monitor is possible, and photographic images that emphasize memory color reproduction by controlling nonlinearly according to the saturation S Both output and output are possible. In the example of FIG. 10, a color near the maximum saturation of the monitor is set as a target color, and the saturation is stored so that the target color is mapped to the maximum saturation color for each hue that can be reproduced by the image output device (printer). In this example, brightness compression and saturation compression as shown in the following equations are performed. Also in this case, the target color of each hue approaches as it goes toward lower saturation (saturation), and the achromatic color axis is completely matched, and the color continuity is preserved.
When L ≧ Lhc1T,
L ′ = (Lwp−Lh1p) × (L−Lhc1T) / (Lwm−Lhc1T) + Lh1p
L ′ = (Lh1p−Lbp) × (L−Lbm) / (Lhc1T−Lbm) + Lbp when L <Lhc1T
C ′ = C × α × (L ′ / L)
However,
Lwp: Maximum brightness of the printer Lbp: Minimum brightness of the printer Lwm: Maximum brightness of the display Lbm: Minimum brightness of the display Lhc1T: Target color (lightness) corresponding to the hue H1 and saturation (saturation) C1 of the input color
α: Compression coefficient

  The input color compressed in accordance with the dynamic range of the printer as described above is further output in the gamut compression unit 305, for example, as shown in FIG. 11, in which output color in which the maximum saturation information for each hue and brightness is stored or loaded. It is compared with the color reproduction range (gamut) information of the reproduction range setting unit 304, and if it is within the gamut (less than the corresponding hue and lightness maximum saturation), it is sent to the Lab (LCH) → CMYK color space conversion unit 306 as it is. In the case of out of gamut (corresponding hue and maximum saturation of lightness), for example, gamut outermost data in the same hue and in the direction of minimum color difference (hue of output color reproduction range setting unit 304, maximum saturation for each lightness) A mapping process is performed.

  The color signal (L′ C′H ′) compressed in the color reproduction range of the output device (for example, the image output device 1021 in FIG. 5) in the gamut compression unit 305 is output in the Lab (LCH) → CMYK color space conversion unit 306. The color is converted to the set printer control signal CMYK.

The color conversion here can be realized by using memory map interpolation (color conversion) or the like. As shown in FIG. 12, when the CIELAB color space is used as an input color space, the memory map interpolation divides the CIELAB color space into unit solids (here, cubes) of the same type, and sets input coordinates (Lab values). In order to obtain the output value P, a cube including the coordinates of the input is selected, the output values on the preset vertices of eight points of the selected cube and the positions in the cube of the input (from each vertex) Linear interpolation is performed on the basis of the distance. In this embodiment, the output value P corresponds to the C, M, Y, and K values, respectively, and the coordinates (L * a * b *) on the input space used for the interpolation calculation are the first After setting K corresponding to the maximum black (minimum black), the actual input / output (Lab-CMYK) relationship was measured, and this data was used to calculate L * a * b * C, M, Y, and K values for the values are preset.
Here, a method of converting gamut compression such as lightness compression and saturation compression into device signals after calculating according to the combination of output devices, hue H, and saturation C has been described in advance. However, there is a method of directly calculating the device CMYK signal from the input RGB signal by three-dimensional memory map interpolation as shown in FIG.

(Configuration of Color Conversion Processing Device 201 in Embodiment 2)
Next, a color conversion processing apparatus 201 that is a feature of the present invention will be described with reference to FIG. An RGB → Lab (LCH) color space conversion unit that receives a signal corresponding to an input color or a target color and converts it into a device-independent color signal (for example, L * a * b * or JCH). 301, a target color setting unit 302 for setting a target color as a reference for gamut compression, an input color reproduction range setting unit 307 for setting color reproduction range (gamut) information of an input image, an input image before gamut compression An image storage unit (storage buffer) 308 for temporarily storing data, and a device-independent input LCH converted by the RGB → Lab (LCH) color space conversion unit 301 from the representative target color set by the target color setting unit 302 A target color calculation unit 303 that calculates a target color corresponding to the output color reproduction range setting unit 304 that sets color reproduction range (gamut) information of the selected color output device, and an input color A gamut compression unit 305 that performs (color) compression on the color reproduction range set by the output color reproduction range setting unit 304, receives a corrected device-independent color signal from the gamut compression unit 305, and receives the image output device 1021 in FIG. -1023 color signals (for example, CMYK signals), Lab (LCH) → CMYK color space conversion unit 306 is configured.

(Operation of the color conversion processing apparatus 201 in the second embodiment)
Next, the operation will be described. First, an RGB input signal which is color data of a drawing command received from the printer driver is sent to the RGB → Lab (LCH) color space conversion unit 301. The RGB → Lab (LCH) color space conversion unit 301 converts the CIELab, which is a perceptual uniform color space, using a preselected input device profile. The RGB signal, which is image information in a CRT display or the like, according to the color temperature, chromaticity coordinates, and photoelectric conversion characteristics of the display, for example, when sRGB that is standard RGB is assumed, the above-described (1) to (4) ) Is converted into a device-independent color signal represented by lightness (L), saturation (C), and hue (H) and transmitted to the target color calculation unit 303.

  Also, with respect to the target color information in the target color setting unit 302, when the target color is an RGB value, the RGB → Lab (LCH) color space conversion unit 301 uses the profile of the input device selected in advance, It is converted into CIELab, which is a perceptual uniform color space, and transmitted to the input color reproduction range setting unit 307.

  The input color reproduction range setting unit 307 detects at least the maximum brightness and the minimum brightness in the input image, and transmits the detected values to the gamut compression unit 305 as input color reproduction range information.

  The image storage unit (storage buffer) 308 temporarily stores the input image data before gamut compression until the input color reproduction range setting unit 307 detects the color reproduction range of the input image. After the color reproduction range (maximum brightness and minimum brightness) is determined, the input image data is transmitted to the target color calculation unit 303.

  The target colors (RGB and CIELAB values) set here are set as RGB values by allowing the operator to select pixels of the input image actually displayed on the display 100 in FIG. 5 via the computer 101. Are set and stored in the target color setting unit 302.

  The target color calculation unit 303 calculates a target color according to the hue H and saturation (saturation) C of the input color. For example, in the target color setting unit 302, as shown in FIG. 8, when a table of target colors (lightness L in the example of FIG. 8) in typical hue H and saturation (saturation) C is set, A value corresponding to the hue H and saturation (saturation) C of the input color calculated in the RGB → Lab (LCH) color space conversion unit 301 is selected from a table of target colors (lightness L in the example of FIG. 8). Alternatively, it is calculated by linear interpolation, the target color for the input color is obtained, and the input color data and the target color data are sent to the gamut compression unit 305.

  In this embodiment, the target color is set in the LCH space based on the CIELAB color space. However, the hue H and the saturation S in the HSL (Ostwald color system) based on the input color space (RGB) are used. The target color may be set according to the above.

  In the gamut compression unit 305, for example, a process of compressing (mapping) into a color that can be reproduced by the selected image output apparatus 1021 in FIG.

Here, processing in the gamut compression unit 305 according to the present embodiment will be described. In the gamut compression unit 305, first, when the target color corresponding to the hue H and the saturation (saturation) C of the input color calculated by the target color calculation unit 303 has a gamut relationship as shown in FIG. Then, lightness compression and saturation compression are performed as in the following equation.
L ′ = (Lwp−Lh1CT) × (L−Lhc1T) / (LwI−Lhc1T) + Lhc1T when L ≧ Lhc1T
L ′ = (Lhc1T−Lbp) × (L−LbI) / (Lhc1T−LbI) + Lbp when L <Lhc1T
C ′ = C × α × (L ′ / L)
However,
Lwp: Maximum brightness of the printer Lbp: Minimum brightness of the printer LwI: Maximum brightness of the input image LbI: Minimum brightness of the input image Lhc1T: Target color (lightness) corresponding to the hue H1 and saturation (saturation) C1 of the input color
α: Compression coefficient (6)

  The input color compressed in accordance with the dynamic range of the printer as described above is further output in the gamut compression unit 305, for example, as shown in FIG. 11, in which output color in which the maximum saturation information for each hue and brightness is stored or loaded. It is compared with the color reproduction range (gamut) information of the reproduction range setting unit 304, and if it is within the gamut (less than the corresponding hue and lightness maximum saturation), it is sent to the Lab (LCH) → CMYK color space conversion unit 306 as it is. In the case of out of gamut (corresponding hue and maximum saturation of lightness), for example, gamut outermost data in the same hue and in the direction of minimum color difference (hue of output color reproduction range setting unit 304, maximum saturation for each lightness) A mapping process is performed.

  By performing such processing, the brightness range of the input image is adjusted to the dynamic value of the image output device (printer) while bringing the brightness of important colors having different hues such as skin color, greenery of plants, and blue sky close to ideal values. It is possible to match the (lightness) range, and it is possible to reproduce the color of an attractive photographic image.

  The color signal (L′ C′H ′) compressed in the color reproduction range of the output device (for example, the image output device 1021 in FIG. 5) in the gamut compression unit 305 is output in the Lab (LCH) → CMYK color space conversion unit 306. The color is converted to the set printer control signal CMYK.

  The color conversion here can be realized by using memory map interpolation (color conversion) or the like. As shown in FIG. 12, when the CIELAB color space is used as an input color space, the memory map interpolation divides the CIELAB color space into unit solids (here, cubes) of the same type, and sets input coordinates (Lab values). In order to obtain the output value P, a cube including the coordinates of the input is selected, the output values on the preset vertices of eight points of the selected cube and the positions in the cube of the input (from each vertex) Linear interpolation is performed on the basis of the distance. In this embodiment, the output value P corresponds to the C, M, Y, and K values, respectively, and the coordinates (L * a * b *) on the input space used for the interpolation calculation are the first After setting K corresponding to the maximum black (minimum black), the actual input / output (LAB-CMYK) relationship was measured, and this data was used to calculate L * a * b * C, M, Y, and K values for the values are preset.

(Configuration of Color Conversion Processing Device 201 in Embodiment 3)
Next, a color conversion processing apparatus 201 that is a feature of the present invention will be described with reference to FIG. As illustrated in FIG. 16, the color conversion processing apparatus 201 according to the third embodiment receives a signal corresponding to an input color or a target color, and a perceptual color signal (for example, JCH) that represents the appearance of a color under a set observation condition. RGB → JCH (QMH) color space conversion unit 401 for converting to QMH), target color setting unit 402 for setting a target color as a reference for gamut compression, and representative target colors set by the target color setting unit 402, RGB → A target color calculation unit 403 that calculates a target color corresponding to the input JCH converted by the JCH (QMH) color space conversion unit 401, and sets the color reproduction range (gamut) information of the color output device under the selected viewing condition. An output color reproduction range setting unit 404, a gamut compression unit 405 that performs (color) compression on the color reproduction range set by the output color reproduction range setting unit 404, and a gamut compression unit 4 5 includes a JCH (QMH) → CMYK color space conversion unit 406 that receives a corrected device-independent color signal from 5 and converts it into color signals (for example, CMYK signals) for the image output apparatuses 1021 to 1023 in FIG. ing.

(Operation of Color Conversion Processing Device 201 in Embodiment 3)
Next, the operation will be described. First, an RGB input signal, which is color data of a drawing command received from the printer driver, is sent to the RGB → JCH (QMH) color space conversion unit 401. The RGB → JCH (QMH) color space conversion unit 401 uses a preselected input device profile and observation conditions, and a perceptual color signal (for example, defined by CIECAM) that represents the appearance of color under the set observation conditions. JCH and QMH) (see FIG. 17). The RGB signal that is image information in a CRT display or the like is based on the color temperature, chromaticity coordinates, and photoelectric conversion characteristics of the display. ), RGB → XYZ conversion is performed, and then, for example, the operations shown in (7) to (35) defined in CIECAM97s are performed to perform XYZ → JCH (QMH) conversion.

試験色の三刺激値：Ｘ、Ｙ、Ｚ
参照白色の三刺激値：Ｘｗ、Ｙｗ、Ｚｗ
Rc=(D*(1.0/Rw)+1-D)*R
Gc=(D*(1.0/Gw)+1-D)*G
if(B<0)
Bc=(D*(1.0/pow(Bw,p))+1-D)*fabs(pow(B,p))*(-1.0)
Else
Bc=(D*(1.0/pow(Bw,p))+1-D)*pow(B,p) （１０）
Rcw=(D*(1.0/Rw)+1-D)*Rw;
Gcw=(D*(1.0/Gw)+1-D)*Gw;
Bcw=(D*(1.0/pow(Bw,p))+1-D)*pow(fabs(Bw),p); （１１）
ただし、
p=pow((Bw/1.0),0.083 4) （１２）
D=F−F/(1+2*pow(La,1/4)+La*La/300) （１３）
順応視野の輝度：Ｌa
順応の程度を表わす係数：F

Tristimulus values of test colors: X, Y, Z
Reference white tristimulus values: Xw, Yw, Zw
Rc = (D * (1.0 / Rw) + 1-D) * R
Gc = (D * (1.0 / Gw) + 1-D) * G
if (B <0)
Bc = (D * (1.0 / pow (Bw, p)) + 1-D) * fabs (pow (B, p)) * (-1.0)
Else
Bc = (D * (1.0 / pow (Bw, p)) + 1-D) * pow (B, p) (10)
Rcw = (D * (1.0 / Rw) + 1-D) * Rw;
Gcw = (D * (1.0 / Gw) + 1-D) * Gw;
Bcw = (D * (1.0 / pow (Bw, p)) + 1−D) * pow (fabs (Bw), p); (11)
However,
p = pow ((Bw / 1.0), 0.083 4) (12)
D = F−F / (1 + 2 * pow (La, 1/4) + La * La / 300) (13)
Brightness of adaptation field of view: La
Coefficient indicating the degree of adaptation: F

Rda=(40*pow((Fl*Rd/100),0.73))/(pow((Fl*Rd/100),0.73)+2)+1
Gda=(40*pow((Fl*Gd/100),0.73))/(pow((Fl*Gd/100),0.73)+2)+1
Bda=(40*pow((Fl*Bd/100),0.73))/(pow((Fl*Bd/100),0.73)+2)+1
（１６）
Rdaw=(40*pow((Fl*Rdw/100),0.73))/(pow((Fl*Rdw/100),0.73)+2)+1
Gdaw=(40*pow((Fl*Gdw/100),0.73))/(pow((Fl*Gdw/100),0.73)+2)+1
Bdaw=(40*pow((Fl*Bdw/100),0.73))/(pow((Fl*Bdw/100),0.73)+2)+1
（１７）
ここで、

Rda = (40 * pow ((Fl * Rd / 100), 0.73)) / (pow ((Fl * Rd / 100), 0.73) +2) +1
Gda = (40 * pow ((Fl * Gd / 100), 0.73)) / (pow ((Fl * Gd / 100), 0.73) +2) +1
Bda = (40 * pow ((Fl * Bd / 100), 0.73)) / (pow ((Fl * Bd / 100), 0.73) +2) +1
(16)
Rdaw = (40 * pow ((Fl * Rdw / 100), 0.73)) / (pow ((Fl * Rdw / 100), 0.73) +2) +1
Gdaw = (40 * pow ((Fl * Gdw / 100), 0.73)) / (pow ((Fl * Gdw / 100), 0.73) +2) +1
Bdaw = (40 * pow ((Fl * Bdw / 100), 0.73)) / (pow ((Fl * Bdw / 100), 0.73) +2) +1
(17)
here,

k=1/(5*La+1) （１９）
Fl=0.2*pow(k,4)*(5*La)+0.1*(1-pow(k,4))*(1-pow(k,4))*pow(5*La,1/3)
（２０）
n=Yb/Yw （２１）
Nbb=0.725*pow(1/n,0.2) （２２）
Ncb=Nbb; （２３）
z=1+Fll＊pow(n,0 .5) （２４）
Ｙｂ：背景の輝度率
Ｆｌ：順応輝度に応じた係数
Ｆｌｌ：明度コントラスト係数
ｎ：背景が刺激の見えに影響を及ぼす程度を表わす係数
a=Rda-12.0*Gda/11.0+Bda/11.0
b=(1/9)*(Rda+Gda-2*Bda)
h=(180/M_PI)*atan2(b,a)
if(h<0) h=360-fabs(h) （２５）
e=e1+(e2-e1)*(h-h1)/(h2-h1) （２６）
H=h1+100*(h-h1)/e1/((h-h1)/e1+(h2-h)/e2) （２７）
ただし、
if(h<=20.14){
e1=0.8565
e2=0.8
h1=0.0
h2=20.14
}
elseif(h<=90.0){
e1=0.8
e2=0.7
h1=20.14
h2=90.0
}
elseif(h<=164.25){
e1=0.7
e2=1.0
h1=90.0
h2=164.25
}
elseif(h<=237.53){
e1=1.0
e2=1.2
h1=164.25
h2=237.53
}
else {
e1=1.2
e2=0.8565
h1=237.53
h2=360.0
} （２８）
A=(2*Rda+Gda+(1/20)*Bda-2.05)*Nbb （２９）
Aw=(2*Rdaw+Gdaw+(1/20)*Bdaw-2.05)*Nbb （３０）
J=100*pow(A/Aw,c*z) （３１）
Q=(1.24/c)*pow((J/100),0.67)*pow((Aw+3),0.9) （３２）
s=(50*pow((a*a+b*b),0.5)*100*e*(10/13)*Nc*Ncb)/(Rda+Gda+(21/20)*Bda)
（３３）
C=2.44*pow(s,0.69)*pow((J/100),0.67*n)*(1.64-pow(0.29,n))
（３４）
M=C*pow(Fl,0.15) （３５）
ここで、
周囲の影響の大きさに関する係数：ｃ
クロマチックインダクション係数：Ｎｃ
無彩色応答：Ａ
白色に対する無彩色応答：Ａｗ
Ｊ：明度
ブライトネス：Ｑ
彩度：ｓ
クロマ：Ｃ
カラフルネス：Ｍ

k = 1 / (5 * La + 1) (19)
Fl = 0.2 * pow (k, 4) * (5 * La) + 0.1 * (1-pow (k, 4)) * (1-pow (k, 4)) * pow (5 * La, 1/3 )
(20)
n = Yb / Yw (21)
Nbb = 0.725 * pow (1 / n, 0.2) (22)
Ncb = Nbb; (23)
z = 1 + Fll * pow (n, 0.5) (24)
Yb: background luminance rate Fl: coefficient according to adaptation luminance Fll: lightness contrast coefficient n: coefficient representing the degree to which the background affects the appearance of the stimulus
a = Rda-12.0 * Gda / 11.0 + Bda / 11.0
b = (1/9) * (Rda + Gda-2 * Bda)
h = (180 / M_PI) * atan2 (b, a)
if (h <0) h = 360-fabs (h) (25)
e = e1 + (e2-e1) * (h-h1) / (h2-h1) (26)
H = h1 + 100 * (h-h1) / e1 / ((h-h1) / e1 + (h2-h) / e2) (27)
However,
if (h <= 20.14) {
e1 = 0.8565
e2 = 0.8
h1 = 0.0
h2 = 20.14
}
elseif (h <= 90.0) {
e1 = 0.8
e2 = 0.7
h1 = 20.14
h2 = 90.0
}
elseif (h <= 164.25) {
e1 = 0.7
e2 = 1.0
h1 = 90.0
h2 = 164.25
}
elseif (h <= 237.53) {
e1 = 1.0
e2 = 1.2
h1 = 164.25
h2 = 237.53
}
else {
e1 = 1.2
e2 = 0.8565
h1 = 237.53
h2 = 360.0
} (28)
A = (2 * Rda + Gda + (1/20) * Bda-2.05) * Nbb (29)
Aw = (2 * Rdaw + Gdaw + (1/20) * Bdaw-2.05) * Nbb (30)
J = 100 * pow (A / Aw, c * z) (31)
Q = (1.24 / c) * pow ((J / 100), 0.67) * pow ((Aw + 3), 0.9) (32)
s = (50 * pow ((a * a + b * b), 0.5) * 100 * e * (10/13) * Nc * Ncb) / (Rda + Gda + (21/20) * Bda)
(33)
C = 2.44 * pow (s, 0.69) * pow ((J / 100), 0.67 * n) * (1.64-pow (0.29, n))
(34)
M = C * pow (Fl, 0.15) (35)
here,
Factor related to the magnitude of ambient influence: c
Chromatic induction coefficient: Nc
Achromatic response: A
Achromatic response to white: Aw
J: Brightness brightness: Q
Saturation: s
Chroma: C
Colorfulness: M

  When the RGB signal characteristics of the input device are other than sRGB signals, color conversion to JCH (QMH) is performed after changing to XYZ corresponding to each color characteristic defined by the ICC profile or the like.

  Here, the perceptual amount defined in CIECAM97s is used, but a reference white point or the like is calculated using a partial adaptation model in consideration of the actual monitor and the color appearance of the hard copy, and the corresponding tristimulus values are calculated. XYZ, perceptual amount, etc. may be obtained or gamut compression may be performed.

  The operations of the target color calculation unit 403, the output color reproduction range setting unit 404, and the gamut compression unit 405 perform the same processing except that the color space (LCH → JCH, QMH) for processing is changed in the first embodiment. Therefore, it is omitted here.

  By performing the above-described lightness compression in a color space that corresponds to the viewing environment in this way, it becomes possible to map the dynamic range in consideration of color adaptation and color appearance under different viewing conditions, especially for highlight side reproducibility. Excellent color conversion.

  The JCH (QMH)-> CMYK (CMYK-> QMH) color space conversion unit 406 is constructed based on a prediction formula for the relationship between CMYK and XYZ.

  Actually, there are a method in which a plurality of representative CMYK patches output in advance are measured, and the result is subjected to memory map interpolation, or a multilayer neural network or a polynomial is approximated by learning the relationship between CMY (K) and XYZ. .

  CMYK → XYZ → JCH (QMH) is predicted using the relationship between CMYK and XYZ and the arithmetic expressions (7) to (35) defined in CIECAM97s.

  Further, for CMYK → JCH (QMH), a four-dimensional lookup table is generated for a typical combination of CMYK and linear interpolation is performed. For the generation of this four-dimensional lookup table, K, which is a black amount, is determined in advance in the XYZ space by a method based on the conventional maximum black, etc., and XYZ (K) → QMH (K) first. Then, the combination of QMH (K) to CMY is calculated by the optimization operation such as the least square method or the Powell method from the above-mentioned relationship of CMYK → QMH.

  Of course, CMYK data for a typical QMH in a typical observation environment may be created and stored in advance.

(Description of Storage Medium Recording Program Code in Example 4)
Another object of the present invention is to supply a storage medium storing software program codes for implementing the functions of the above-described embodiments to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the storage medium Needless to say, this can also be achieved by reading and executing the program code stored in the.

  FIG. 18 shows a configuration of an information processing system as a specific configuration example of the image processing system. In this image processing system, a computer 101 such as a workstation, a printer 102, and a display 100 are connected. The workstation (computer 101) implements the color conversion processing function described above, and includes a display 100, a keyboard 112, a program reading device 111, an arithmetic processing device 110, and the like. In the arithmetic processing unit, a ROM 123 and a RAM 122 are connected to a CPU 121 capable of executing various commands via a bus. Also, a DISK 124 such as a hard disk, which is a large-capacity storage device, and a NIC 125 that communicates with devices on the network are connected to the bus.

  The program reading device 111 is a storage medium storing various program codes, that is, a floppy disk, a hard disk, an optical disk (CD-ROM, CD-R, CD-R / W, DVD-ROM, DVD-RAM, etc.), optical An apparatus for reading a program code stored in a magnetic disk, a memory card, or the like, such as a floppy disk drive, an optical disk drive, or a magneto-optical disk drive.

  The program code stored in the recording medium is read by the program reading device and stored in the DISK 124 or the like, and the program code stored in the DISK 124 or the like is executed by the CPU 121, thereby realizing the above-described image processing method or the like. Will be able to. Also, by executing the program code read by the computer, an OS (operating system) or device / driver running on the computer performs part or all of the actual processing based on the instruction of the program code. The case where the above-described function is achieved by the processing is also included.

  Further, after the program code read from the recording medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. This includes a case where the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

It is a figure explaining a prior art. It is a figure explaining a prior art. It is a figure explaining a prior art. It is a figure explaining a prior art. 1 shows a configuration example of an image processing system of the present invention. The concrete structure of an image processing system is shown. 1 shows a configuration of a color conversion processing apparatus according to a first embodiment of the present invention. It is a figure explaining target color information. It is a figure explaining the gamut compression part (lightness preservation | save) of Example 1. FIG. FIG. 3 is a diagram illustrating a gamut compression unit (saturation preservation) according to the first embodiment. It is a figure explaining the gamut information of an output color reproduction range setting part. It is a figure explaining a color space conversion part. It is a figure explaining another color space conversion part. 2 shows a configuration of a color conversion processing apparatus according to a second embodiment of the present invention. It is a figure explaining the gamut compression part of Example 2. FIG. 3 shows a configuration of a color conversion processing apparatus according to a third embodiment of the present invention. It is a figure explaining a color appearance model. The structural example in the case of implement | achieving this invention by software is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Display 101 Computer 200 Image processing apparatus 1021-1023 Image output apparatus 1024 Image input apparatus 201 Color conversion processing apparatus 301,306 Color space conversion part 302 Target color setting part 303 Target color calculation part 304 Output color reproduction range setting part 305 Gamut compression Part

Claims (11)

  In an image processing apparatus that controls color reproduction of a color image output apparatus for an input color image signal, means for setting a color in the input color space as a target color, and means for calculating the brightness or saturation of the target color Image processing, comprising: color conversion means for storing lightness or saturation of the target color and matching the input color space with the lightest and darkest parts of the color reproduction range of the color image output device apparatus.   In an image processing apparatus that controls color reproduction of a color image output apparatus for an input color image signal, means for setting a color in the input color image as a target color, and means for calculating the lightness or saturation of the target color Image processing comprising: color conversion means for storing the lightness or saturation of the target color to match the lightest part and the darkest part of the color reproduction range of the input color image and a color image output device apparatus.   3. The image processing apparatus according to claim 1, wherein the setting of the target color and the color conversion are performed according to a hue and a saturation degree of the input color.   The image processing apparatus according to claim 1, wherein the color conversion is performed in a color perception space that depends on an observation condition.   4. The image processing apparatus according to claim 1, wherein the set target color includes at least information on memory colors such as human skin, sky, and vegetation. .   The image processing apparatus according to claim 1, wherein the set target color includes at least a maximum saturation color for each hue that can be reproduced by the color image output apparatus. Image processing device.   4. The image processing apparatus according to claim 1, wherein the target color is set for each type of document object to be imaged.   In an image processing method for controlling color reproduction of a color image output device for an input color image signal, the color reproduction of the input color space and the color image output device by storing the lightness or saturation of an arbitrary target color An image processing method, wherein color reproduction is performed by matching a lightest part and a darkest part of a range.   In an image processing method for controlling color reproduction of a color image output device for an input color image signal, the brightness or saturation of a target color in the set input color image is calculated, and the brightness or saturation of the target color is calculated. An image processing method comprising: storing and reproducing a color by matching a lightest part and a darkest part of a color reproduction range of the input color image and a color image output device.   10. The image processing method according to claim 8, wherein the target color setting and color conversion are performed according to a hue and a saturation degree of an input color.   11. The image processing method according to claim 8, wherein the color conversion is performed in a color perception space that depends on an observation condition.

Images