JP2009188944A - Color processing apparatus and color processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem, wherein reproduction of an important color cannot be compatible with gray reproduction, when a gray target value is switched, according to observation conditions, when creating a color conversion table for color space conversion. <P>SOLUTION: Observation condition for image is acquired (S3), and a correction parameter corresponding to the observation condition is set (S4). A color gamut in an input color space is mapped to an output color space (S5), and in the color gamut after mapping, gray correction is then performed within a correction range, based on the correction parameter (S6). On the basis of a color value in the input color space and a color value in the output color space after gray correction, a color conversion table is then created. Thus, the gray correction range corresponding to the observation condition is set, optimal gray reproduction for each observation condition can be performed, and the effect of unwanted correction on other colors can be excluded. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color processing apparatus and a color processing method for correcting gray lines when creating a color conversion table for converting color values in a first color space into color values in a second color space.

  In recent years, there have been increased opportunities to output images input by image input devices such as digital cameras and scanners using image output devices such as printers. The image acquired by the image input device in this way is once stored as data in the RGB color space of the input device, but this RGB color space depends on the device. Therefore, it is converted into color space data such as the standard color space sRGB color space or AdobeRGB color space and stored.

  FIG. 21 shows an example of a color reproduction range of the sRGB color space, a general printer color reproduction range, and a human visible range. Hereinafter, the color reproduction range is referred to as a color gamut. In FIG. 21, a horseshoe region Rv indicated by a solid line represents a human visible range, and a triangular region Rs indicated by a dotted line represents an sRGB color gamut. A curved area Rp indicated by a broken line indicates a color gamut of a general printer. As shown in FIG. 21, since the sRGB color gamut Rs is different from the printer color gamut Rp, for example, when an sRGB image is output by a printer, the sRGB color gamut is corrected in order to correct the color gamut difference. It is necessary to perform processing for associating the signal value with the color signal value of the printer.

  Here, referring to FIG. 22, general color gamut mapping will be described using color conversion processing of an RGB image as an example. Here, the input color space is described as sRGB. First, in step S1M, a perceptual color space value corresponding to the pixel value RGB of the sRGB image is calculated. Examples of the perceived color space value include Lab in the CIELAB color space, Luv in the CIEUV color space, Jab in the CIECAM02 color space, and the like. In the following description, Jab is used as the perceptual color space value.

  Next, in step S2M, processing is performed such that the input color value falls within the output color gamut while referring to the color gamut data of the output device so that the input color value can be reproduced within the output color gamut range. The process of associating the input color value with the output color value in step S2M is generally called color gamut mapping. The color gamut data used in step S2M is given as a correspondence table describing a pair of colorimetric values corresponding to each color signal value of the output device, for example, as shown in FIG. In general, this correspondence table is obtained by dividing each R, G, B into several slices such as 9 slices and 17 slices, and describing the colorimetric values corresponding to the RGB values at the grid points of each slice as a pair. . Based on the color gamut data described in this way, in the color gamut mapping process, for example, it is determined whether or not the input color is in the output color gamut (color gamut inside / outside determination). If the input color is within the output color gamut, the color value of the input color is retained, and if the input color is outside the output color gamut, the input color is pasted to the surface of the output color gamut. Perform processing (convergence mapping).

  FIG. 24 shows an outline of processing (convergence mapping) for pasting an input color on the surface of the output color gamut. In FIG. 24, when the output color gamut surface (boundary) is Bp, the input color is Pin, and a certain convergence point in the output color gamut is Pf, the input color paste destination is a line segment passing through the points Pf and Pin. This is the intersection Pin ′ between l and Bp.

  In step S3M, the post-mapping color value J′a′b ′ mapped by the pasting method as described above is input, and the device RGB value R′G corresponding to the input color value is determined from the color gamut data of the output device. 'B' is calculated. This calculation is performed by a known interpolation calculation such as cubic interpolation or tetrahedral interpolation. In step S4M, R′G′B ′ is output by the printer, and in step S5M, the output color is measured by the colorimeter, so that a desired color value can be obtained.

  However, in the color conversion process shown in FIG. 22, in step S2M, processing with high calculation costs such as determination of the inside / outside of the color gamut and calculation of the intersection with the surface of the color gamut occurs. Doing so requires a great deal of processing time. In addition, if the color conversion is further performed in step S2M after performing the color conversion in step S1M in order to calculate the J′a′b ′ value from the input RGB value, the quantization error is accumulated. Therefore, in order to speed up processing and eliminate accumulated errors, a method of tabulating pairs of device RGB values R′G′B ′ corresponding to input RGB values and mapped color values as a color conversion table Is often used. When the relationship between RGB and R′G′B ′ is tabulated, in order to calculate R′G′B ′ corresponding to an arbitrary input RGB, R′G′B ′ is calculated by performing an interpolation operation. be able to.

Further, in recent years, there is a case where color correction is required to reproduce gray (a color having the same R, G, B values) of an RGB image with a preferable color. Such color correction is realized by moving each gray color value to its reproduction target value. Further, in order to maintain a smooth gradation in gray and gray peripheral colors, a region including gray and a gray target value is provided as a correction range, and a function is set such that the amount of movement is zero at the boundary of the correction range. It is necessary to move the color within the correction range. Therefore, the following techniques are known as techniques for moving the peripheral colors with the movement of a specific color. First, when reproducing a specific color with a target value, an area including the specific color is defined as an adjustment range, and the color value within the adjustment range is linearly mapped together with the mapping of the specific color, so that the specific color and its surroundings There is a technique for maintaining gradation with colors (for example, see Patent Document 1). Similarly, there is a technique in which an area including a specific color and a target value is defined as an adjustment range, and a peripheral color is adjusted according to the distance from the specific color and the target value (see, for example, Patent Document 2).
Japanese Unexamined Patent Publication No. 06-21159 JP 2004-112694 A

  However, in recent years, images have been observed under various viewing conditions, and colors that are perceived as favorable may differ depending on the viewing conditions. Therefore, in order to realize preferable gray reproduction even under different observation conditions, it is necessary to switch the gray target value depending on the observation conditions. Such target value switching is realized by preliminarily determining a gray target value for each observation condition by subject experiment or the like, holding the gray target value, and switching the gray target value according to the observation condition. .

  However, when the gray target value is switched using the above-described conventional method, the correction range size is constant regardless of gray or the gray target value, and the following inconvenience occurs. That is, even if an optimum correction range size is determined so that the correction range does not include important colors (skin colors, etc., colors that should be retained individually) under certain reference observation conditions, The correction range may include even important colors. Therefore, when the correction range includes an important color as described above, it is impossible to reproduce both the important color with a predetermined color and gray with a target value.

  On the other hand, when the correction range size is changed according to gray or the gray target value, for example, when the correction range size is defined as a ratio (size ratio) to the gray movement amount, the gray movement amount is The size is adaptively increased or decreased accordingly. However, when an optimal size ratio is determined under a certain standard observation condition and gray correction is performed using the size ratio under a different observation condition, the following problem still occurs. That is, when the gray movement amount under a different observation condition is larger than the gray movement amount under the reference observation condition, a wider area is defined as the correction range. For this reason, since an unnecessarily large area is set as the correction range, it is impossible to achieve both the target color reproduction of the important color and the gray target color reproduction.

  SUMMARY An advantage of some aspects of the invention is that it provides a color processing apparatus and a color processing method having the following functions. In other words, the color conversion table for converting the color value in the first color space to the color value in the second color space can be obtained by performing the optimum gray reproduction for each observation condition and unnecessary correction effects on other colors. Create to eliminate.

  As a means for achieving the above object, the color processing apparatus of the present invention comprises the following arrangement.

  That is, a color processing device for creating a color conversion table for converting color values in the first color space into color values in the second color space, an observation condition acquisition unit for acquiring image observation conditions; Correction parameter setting means for setting a correction parameter according to the viewing condition, mapping means for mapping a color gamut in the first color space to the second color space, and the mapping means for the second color space Gray correction means for performing gray correction within the correction range based on the correction parameter in the color gamut mapped to the color gamut, and the color value in the first color space and the first after gray correction by the gray correction means. A color conversion table is created based on the color values in the second color space.

  For example, the gray correction unit corrects the gray peripheral color within the correction range according to the distance from the center of the correction range.

  For example, the gray correction unit sets the correction range and a gray reproduction target value based on the correction parameter.

  According to the present invention having the above configuration, when creating a color conversion table for converting color values in the first color space into color values in the second color space, the gray correction range is set according to the observation conditions. Set. Thereby, it is possible to eliminate the influence of the optimum gray reproduction for each observation condition and unnecessary correction to other colors.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

<First Embodiment>
Apparatus Configuration FIG. 1 is a block diagram showing a hardware configuration of a color processing apparatus 1 according to this embodiment. In the figure, 101 is a UI (user interface) unit that receives input from a user, 102 is a color gamut data acquisition unit that acquires color gamut data, and 103 is an observation condition acquisition unit that acquires observation conditions of an output image. Reference numeral 104 denotes a correction parameter setting unit that sets correction parameters according to viewing conditions, 105 denotes a color gamut mapping unit that executes color gamut mapping based on the color gamut data, and 106 corrects a gray line in the post-mapping color gamut. It is a gray correction unit that performs correction based on parameters. Reference numeral 107 denotes a color space value conversion unit that converts color values in the color gamut after gray correction into device color space values, 108 denotes an output unit that outputs the converted device color space values, and 109 denotes color gamut data of the input color gamut. And a color gamut data holding unit that holds the color gamut data of the output color gamut. Further, 110 is an observation condition holding unit that holds the observation conditions acquired by the observation condition acquisition unit 103, and 111 is a correction parameter holding unit that holds a correction parameter correspondence table that describes the correspondence of correction parameters according to the observation conditions. is there. Reference numeral 112 denotes a buffer memory for temporarily storing data being calculated.

Color Processing Overview Color processing in the color processing apparatus 1 of the present embodiment will be described below using the flowchart of FIG. 2 and the UI example of FIG.

  A setting screen 1000 illustrated in FIG. 3 is displayed on the UI unit 101 and receives input from the user regarding input color gamut data, output color gamut data, and observation conditions. In the setting screen 1000, reference numeral 1001 denotes an input color gamut acquisition unit that acquires a file path that holds input color gamut data, and 1002 denotes an output color gamut acquisition unit that acquires a file path that holds output color gamut data. . Reference numeral 1003 denotes an observation condition acquisition unit that acquires identification information of a light source and illuminance when a user observes an image. In the observation condition acquisition unit 1003, reference numeral 1004 denotes a light source number acquisition unit that acquires a light source number corresponding to a light source when observing an image, and 1005 denotes an illuminance number acquisition unit that acquires an illuminance number corresponding to illuminance. Reference numeral 1006 denotes an OK button for notifying that the user has finished inputting. When the OK button 1006 is pressed, the file path of input color gamut data, the file path of output color gamut data, the light source number, and the illuminance number input by the user are written in the buffer memory 112.

  The outline of color processing in the color processing apparatus 1 will be described below with reference to the flowchart shown in FIG.

  First, in step S1, it is determined whether or not the OK button 1006 on the setting screen 1000 has been pressed. If the user does not press the button, the user waits for an input, but if the user presses the OK button 1006, the process proceeds to step S2. When the OK button 1006 is pressed here, as described above, the file path of the input color gamut data, the file path of the output color gamut data, the light source number, and the illuminance number input by the user are displayed in the buffer memory 112. Is written on.

  In step S 2, the color gamut data acquisition unit 102 reads input color gamut data and output color gamut data from the color gamut data holding unit 109 in accordance with the file path information written in the buffer memory 112, and stores it in the buffer memory 112. Write. In step S3, the observation condition acquisition unit 103 acquires the observation conditions (in this case, the light source number and the illuminance number) written in the buffer memory 112. Specific processing contents in the observation condition acquisition unit 103 will be described later.

  Next, in step S4, the correction parameter setting unit 104 sets correction parameters used in a gray correction unit 106, which will be described later, according to the observation conditions acquired in step S3. The specific processing content in the correction parameter setting unit 104 will be described later.

  In step S5, the color gamut mapping unit 105 maps the input color gamut acquired in step S2 to the output color gamut. As this mapping method, any mapping method may be used as long as it is a method of mapping the input color gamut to the output color gamut, such as colorimetric mapping or perceptual mapping.

  In step S6, the gray correction unit 106 executes gray correction on the color gamut after mapping in step S5 based on the correction parameter set in step S4. The specific processing contents in the gray correction unit 106 will be described later.

  In step S7, the color space value conversion unit 107 converts the perceived color space value of the corrected color gamut in step S6 into a device color space value. This conversion from the perceptual color space value to the device color space value is performed by using a correspondence table between the device color space value RGB and the perceptual color space value Jab described in the output color gamut data, such as tetrahedral interpolation or cube interpolation. This is done by a known interpolation operation.

  In step S8, the output unit 108 pairs the device value RGB of the input color gamut acquired in step S2 with the converted device value R′G′B ′ in step S7 (color conversion table). Is output. This correspondence table describes device values in the input color space and device values after conversion. Therefore, by performing an interpolation operation using the correspondence table, a device value after gray correction can be obtained for an arbitrary device value in the input color space.

● Observation condition acquisition process (S3)
Here, the specific operation of the observation condition acquisition unit 103 in step S3 described above will be described with reference to the flowchart of FIG.

  First, in step S301, the light source number written in the buffer memory 112 is acquired by input from the UI unit 101. In step S302, the illuminance number written in the buffer memory 112 is acquired in the same manner. In step S <b> 303, the acquired light source number and illuminance number are written in the observation condition holding unit 110.

Correction parameter setting process (S4)
Next, the specific operation of the correction parameter setting unit 104 in step S4 described above will be described using the flowchart of FIG.

  First, in step S401, the light source number written in the observation condition holding unit 110 is acquired by the observation condition acquisition unit 103, and the illuminance number is acquired in the same manner in step S402.

  In step S <b> 403, the correction parameter corresponding to the acquired light source number and illuminance number is acquired from the correction parameter correspondence table held in the correction parameter holding unit 111.

  FIG. 6 shows an example of the correction parameter correspondence table. As shown in FIG. 6, the correction parameter correspondence table describes correction parameters corresponding to combinations of light source numbers and illuminance numbers. As correction parameters, a gray mapping source, a gray mapping destination determined in advance by a subject experiment, and a correction coefficient are described. By using the correction parameter correspondence table described in this way, correction parameters corresponding to the light source number and illuminance number selected by the user are acquired. For example, when the light source 1 and the illuminance 2 are selected, (J2, a2, b2), (J2 ′, a2 ′, b2 ′), k2 are acquired as the correction parameters, respectively.

  As described above, when the correction parameter is acquired in step S403, the acquired correction parameter is written in the buffer memory 112 in step S404.

  As described above, the correction parameter setting unit 104 acquires correction parameters suitable for the user's observation conditions by referring to the correction parameter correspondence table for each observation condition determined in advance by subject experiment or the like, and stores it in the buffer memory 112. Write. Using the correction parameters, the gray correction unit 106, which will be described later, executes gray correction, whereby the user's observation conditions can be reflected in the gray correction process.

● Gray correction processing (S6)
Next, a specific operation of the gray correction unit 106 in step S6 described above will be described using the flowchart of FIG.

  First, in step S601, an input color value of a color gamut after mapping in the color gamut mapping unit 105 is acquired. In step S602, the correction parameter for the input color value is calculated based on the correction parameter set by the correction parameter setting unit 104 and the white point and black point in the post-mapping color gamut.

  FIG. 8 shows a specific example of the correction parameter calculation method. As shown in FIG. 8, first, consider a line segment connecting a white point in the post-mapping color gamut and a gray mapping source set as a correction parameter. Then, a plane including the input color value and parallel to the ab plane, that is, a plane having the same lightness as the input color value is considered, and an intersection between the plane and the line segment is determined as a gray mapping source of the input color value and the equal lightness. And Further, a gray mapping destination having the same lightness as the input color value can be determined by a similar procedure. That is, for the line segment connecting the white point in the post-mapping color gamut and the gray mapping destination set as the correction parameter, the intersection of the input color value and the plane parallel to the ab plane is set as the input color value. And the gray map destination of equal brightness.

  Further, the correction coefficient corresponding to the input color value can be calculated by linear interpolation based on, for example, the white point brightness, the gray mapping original brightness, and the input color value brightness. Here, when the white point lightness is Jw, the gray mapping original lightness is J1, and the input color value lightness Ji is 0, the correction coefficient at the white point is 0, and the correction coefficient at the gray mapping source is k1, the input color value The correction coefficient ki can be calculated by the following equation (1).

  According to the above equation (1), it is possible to calculate the input color value correction coefficient ki when the input color value lightness Ji is not less than the gray mapping original lightness J1 and not more than the white point lightness Jw. By the same procedure, it is possible to calculate the correction coefficient for the input color value when the input color value lightness is equal to or higher than the black spot lightness and lower than the gray mapping original lightness.

  Returning to FIG. 6, in step S603, based on the correction coefficient in the input color value calculated in step S602, it is determined whether or not the input color value is within the correction range.

  Here, FIG. 9 shows a specific example of the inside / outside determination of the input color value. In this embodiment, when correcting a gray line, an area including a gray mapping source and a gray mapping destination is defined as a correction range in order to maintain the gradation between the gray line and its surrounding colors. With the movement of the gray line, the color value within the correction range is also moved according to the distance from the center point of the gray mapping source and the gray mapping destination. The size of the correction range is determined by the correction coefficient set by the correction parameter setting unit 104. For example, if the shape of the correction range is a circle centered at the midpoint Pc between the input color value and the gray mapping source P o of equal brightness and the input color value and the gray mapping destination P t of equal brightness, the size of the correction range is large. The height can be controlled by the radius of the circle. Therefore, in the present embodiment, the size of the correction range is controlled by multiplying the distance between the center point Pc and the gray mapping source Po by a correction coefficient. Therefore, if the correction coefficient is less than 1.0, Po and Pt exist outside the correction range, so the correction coefficient of this embodiment must be 1.0 or more. In order to satisfactorily maintain the gradation of the color value within the correction range, a larger value such as 2.0 may be set as the correction coefficient.

  Such internal / external determination of the input color value with respect to the correction range determined by the correction coefficient is performed as follows. For example, as shown in FIG. 9, first, an input color value, a gray mapping source Po of equal lightness, and an input color value Pi are connected by a half line, and an intersection Pb between the half line and a correction range boundary is obtained. Then, as a result of comparing the distance between the gray mapping source Po and the input color value Pi and the distance between the gray mapping source Po and the intersection point Pb, if the latter is greater than the former, that is, the following equation (2) holds: It is determined that the input color value is within the correction range.

  On the other hand, when the latter is smaller, that is, when the following expression (3) is satisfied, it is determined that the input color value is outside the correction range.

  If the input color value Pi is within the correction range, the process proceeds to step S604 to correct the input color value Pi. If the input color value Pi is outside the correction range, the correction is not performed, and step S605 is performed. Proceed to

  In step S604, the input color value is corrected based on the correction parameter calculated in step S602. In the present embodiment, as described above, with the movement of the gray line, the color value (that is, the gray peripheral color) within the correction range is also moved according to the distance from the center point of the gray mapping source and the gray mapping destination. As a specific example of this movement, the coordinate origin O, the input color value Pi, the gray map source Po of the input color value, the gray map destination Pt, the intersection point Pb between the half line passing Pi and Po and the correction range boundary in FIG. It shows using. That is, the color value (input color value mapping destination) Pi ′ after movement of the input color value is calculated by the following equations (4), (5), (6).

  As a result, the mapping destination Pi ′ of the input color value Pi has a movement amount of 0 at the correction range boundary Pb and increases as it approaches the gray mapping source Po, in other words, as it approaches the center Pc of the correction range. I understand that. That is, the mapping destination Pi ′ of the input color value Pi is determined according to the distance from the center Pc of the correction range.

  In step S605, it is determined whether or not processing has been completed for all input color values after mapping. If the process has not been completed for all input color values, the process returns to step S601. If the process has been completed for all input color values, the gray correction process in step S6 ends.

  As described above, the gray correction unit 106 can obtain a desired gray reproduction by moving the gray line to the reproduction target. Furthermore, the area including the gray line and its reproduction target is set as a correction range, and the gray peripheral color is moved according to the distance from the center of the correction range so that the movement amount becomes 0 at the boundary of the correction range. I am letting. Thereby, a smooth gradation can be maintained even in the correction range.

  As described above, according to the present embodiment, when creating a color conversion table for converting the color value of the input color gamut into the color value of the output color gamut, the gray target color and the gray correction range ( Set the correction coefficient. Thereby, it is possible to eliminate the influence of the optimum gray reproduction for each observation condition and unnecessary correction to other colors.

Second Embodiment
Hereinafter, a second embodiment according to the present invention will be described.

  In the first embodiment described above, an example in which a correction range (that is, a correction coefficient) for each observation environment is stored in advance is shown. However, in the second embodiment, the correction range for each observation environment is based on a user instruction. It is characterized by calculating.

Apparatus Configuration FIG. 10 is a block diagram showing a hardware configuration of the color processing apparatus 2 according to the second embodiment. In the figure, 201 is a UI (user interface) unit that receives input from a user, 202 is a color gamut data acquisition unit that acquires color gamut data, and 203 is an observation condition acquisition unit that acquires observation conditions for an output image. Reference numeral 204 denotes a correction parameter setting unit that sets correction parameters according to the viewing conditions, 205 denotes a display unit that displays the set correction coefficient, color gamut, and correction range, and 206 denotes a correction coefficient update unit that updates the correction coefficient. is there. Reference numeral 207 denotes a color gamut mapping unit that executes color gamut mapping based on the color gamut data, and 208 denotes a gray correction unit that corrects the gray line of the color gamut after mapping based on the correction parameter. Reference numeral 209 denotes a color space value conversion unit that converts a color value in the color gamut after gray correction into a device color space value, 210 denotes an output unit that outputs the converted device color space value, and 211 denotes color gamut data of the input color gamut. And a color gamut data holding unit that holds the color gamut data of the output color gamut. Reference numeral 212 denotes an observation condition holding unit that holds the observation conditions acquired by the observation condition acquisition unit 103, and 213 denotes a correction parameter holding unit that holds a correction parameter correspondence table describing correction parameter correspondences according to the observation conditions. is there. Reference numeral 214 denotes a buffer memory for temporarily holding each piece of data being calculated.

Color Processing Overview Color processing in the color processing apparatus 2 of the second embodiment will be described below using the flowchart of FIG. 11 and the UI example of FIG.

  A setting screen 2000 shown in FIG. 12 is displayed on the UI unit 201 and receives input from the user regarding input color gamut data, output color gamut data, and observation conditions, and displays a correction range. In the setting screen 2000, reference numeral 2001 denotes an input color gamut acquisition unit that acquires a file path that holds input color gamut data, and 2002 denotes an output color gamut acquisition unit that acquires a file path that holds output color gamut data. . Reference numeral 2003 denotes a color gamut setting button for notifying that the user has completed setting the color gamut data. When this button is pressed, the file path of the input color gamut data input by the user and the file of the output color gamut data are displayed. The path is written to the buffer memory 214. Reference numeral 2004 denotes an observation condition acquisition unit that acquires observation conditions during image observation, and 2005 denotes an illuminance acquisition unit that acquires illuminance during image observation. The illuminance acquisition unit 2005 can accept only numerical values within a certain range. As the lower limit and the upper limit of the numerical range, for example, the illuminance lower limit value and the illuminance upper limit value described in the correction parameter correspondence table shown in FIG. Reference numeral 2006 denotes an observation condition setting button for notifying that the setting of the observation condition by the user is completed. When the observation condition setting button 2006 is pressed, the illuminance input by the user is written in the buffer memory 112. Reference numeral 2007 denotes a correction coefficient acquisition unit that displays the correction coefficient and acquires its update. Reference numeral 2008 denotes a correction coefficient setting button for notifying that the input of the correction coefficient by the user has been completed. Reference numeral 2009 denotes a correction range display unit that displays a color gamut cross section, a gray mapping source, a gray mapping destination, and a correction range. Reference numeral 2010 denotes an OK button for notifying that the user has finished inputting.

  The outline of color processing in the color processing apparatus 2 will be described below with reference to the flowchart shown in FIG.

  First, in step S21, the UI unit 201 determines whether or not the color gamut setting button 2003 on the setting screen 2000 has been pressed. If the user does not press the button, the user input is awaited. If the user presses the color gamut setting button 2003, the file path of the input color gamut data and the file path of the output color gamut data are written to the buffer memory 214. The process proceeds to step S22.

  In step S 22, the color gamut data acquisition unit 202 reads input color gamut data and output color gamut data from the color gamut data holding unit 211 in accordance with the file path information written in the buffer memory 112, and stores it in the buffer memory 112. Write. In step S <b> 23, the UI unit 201 determines whether the observation condition setting button 2006 on the setting screen 2000 is pressed. If the user does not press the button, the user input is awaited. If the user presses the observation condition setting button 2006, the illuminance input to the illuminance acquisition unit 2005 is written to the buffer memory 214, and the process proceeds to step S24. In step S <b> 24, the observation condition acquisition unit 203 acquires the illuminance written in the buffer memory 214. Specific processing contents in the observation condition acquisition unit 203 will be described later.

  Next, in step S25, the correction parameter setting unit 204 sets correction parameters used in a gray correction unit 208 described later according to the illuminance acquired in step S24. The specific processing content in the correction parameter setting unit 204 will be described later.

  In step S <b> 26, the display unit 205 displays the setting items set by the user and the correction range based on the settings on the setting screen 2000. Note that specific processing contents in the display unit 205 will be described later.

  In step S27, the UI unit 201 determines whether the correction coefficient setting button 2008 on the setting screen 2000 has been pressed. If pressed, the correction coefficient updated by the correction coefficient acquisition unit 2007 of the setting screen 2000 is newly written to the buffer memory 214, and the process proceeds to step S28. On the other hand, if the correction coefficient setting button 2008 has not been pressed by the user, the process proceeds to step S29.

  In step S28, the correction coefficient updating unit 206 acquires the correction coefficient newly written in step S27 and updates the correction coefficient, and then returns to step S26. Specific processing contents in the correction coefficient update unit 206 will be described later.

  In step S29, the UI unit 201 determines whether or not the OK button 2010 on the setting screen 2000 has been pressed. If the user does not press the button, the user input is awaited. If the user presses the OK button 2010, the process proceeds to step S30.

  In step S30, the color gamut mapping unit 207 maps the input color gamut acquired in step S22 to the output color gamut, similarly to the color gamut mapping unit 105 in the first embodiment described above.

  In step S31, the gray correction unit 208 performs gray correction on the color gamut after mapping in step S30 based on the correction parameter written in the buffer memory 214. The specific processing contents in the gray correction unit 208 will be described later.

  In step S32, the color space value conversion unit 209 converts the perceived color space value of the corrected color gamut in step S31 into a device color space value, in the same manner as the color space value conversion unit 107 in the first embodiment described above. To do.

  In step S33, as in the output unit 108 in the first embodiment described above, the output unit 210 and the device value RGB of the input color gamut acquired in step S22 and the device value R′G ′ after conversion in step S32 A correspondence table paired with B ′ is output.

● Observation condition acquisition process (S24)
Here, the specific operation of the observation condition acquisition unit 203 in step S24 described above will be described with reference to the flowchart of FIG.

  First, in step S <b> 701, the illuminance written in the buffer memory 214 is acquired by input from the UI unit 201. In step S <b> 702, the acquired illuminance is written in the observation condition holding unit 212.

Correction parameter setting process (S25)
Next, the specific operation of the correction parameter setting unit 204 in step S25 described above will be described using the flowchart of FIG.

  First, in step S <b> 801, the illuminance written in the observation condition holding unit 212 is acquired by the observation condition acquisition unit 203. In step S <b> 802, the correction parameter corresponding to the acquired illuminance is calculated based on the correction parameter correspondence table held in the correction parameter holding unit 111.

  FIG. 15 shows an example of a correction parameter correspondence table in the second embodiment. As shown in FIG. 15, the correction parameter correspondence table describes correction parameters corresponding to the illuminance lower limit value and the illuminance upper limit value, respectively. For each illuminance, a gray mapping source having different brightness, a gray mapping destination and a correction coefficient for the gray mapping source are described. By using such a correction parameter correspondence table, the gray line reproduction target of the input color gamut can be controlled in more detail like the mapping destination of the gray line indicated by a broken line in FIG.

  In step S802, when calculating the correction parameter for the illuminance acquired in step S801, the internal ratio between the illuminance lower limit value I1 and the illuminance upper limit value I2 according to the illuminance is used according to the correction parameter correspondence table. For example, the brightness Ji of the gray mapping source at the illuminance can be obtained by the following equation (7), where I is the illuminance.

  Similarly, other correction parameters can be obtained based on the internal division ratio between the illuminance lower limit value and the illuminance upper limit value obtained by the acquired illuminance.

  The illuminance described in the correction parameter correspondence table need not be limited to the illuminance lower limit value and the illuminance upper limit value. For example, a correction parameter for representative illuminance between the lower limit value and the upper limit value is determined in advance by subject experiment or the like. And may be described. In this way, by adding a representative illuminance and a correction parameter corresponding thereto between the lower limit value and the upper limit value, it is possible to calculate a correction parameter that is more suitable for the user's viewing conditions.

  When the correction parameter is calculated in step S802 as described above, the calculated correction parameter is written in the buffer memory 214 in step S803.

  As described above, the correction parameter setting unit 204 refers to the correction parameter correspondence table for each illuminance determined in advance by subject experiment or the like, thereby acquiring the correction parameter suitable for the user's observation condition by interpolation, and the buffer memory 112. Write to. Using the correction parameters, the gray correction unit 208 (to be described later) executes gray correction, so that the user's observation conditions can be reflected in the gray correction process.

  Although an example in which a linear function is used when calculating a correction parameter for illuminance input by the user is shown here, a nonlinear function such as a Bezier function or a spline function may be used.

Correction coefficient and correction range display process (S26)
Next, the specific operation of the display unit 205 in step S26 described above will be described using the flowchart of FIG.

  First, in step S901, the output color gamut acquired by the color gamut data acquisition unit 202 is acquired, and in step S902, the correction parameter written in the buffer memory 214 is acquired. In step S903, the correction coefficient of the correction parameter acquired in step S902 is displayed on the correction coefficient acquisition unit 2007 of the setting screen 2000.

  Next, the correction range is displayed. First, in step S904, the equal hue section of the output color gamut acquired in step S901 is displayed on the correction range display unit 2009 of the setting screen 2000. This display example is shown as a rectangle by a solid line in the correction range display unit 2009 in FIG. In step S905, the correction range display unit 2009 displays the points obtained by projecting the gray mapping source and the gray mapping destination of the correction parameter acquired in step S902 onto the Ja plane. This display example is indicated by a black dot in the correction range display section 2009 of FIG. In step S906, the intersection of the correction range boundary and the Ja plane is calculated based on the correction parameter acquired in step S902 and displayed on the correction range display unit 2009. This display example is indicated by a dotted line in the correction range display section 2009 of FIG.

  In addition, although the example which displays sectional drawing in Ja plane in step S904, S905, and S906 was shown here, the display method is not limited to this. A cross-sectional view with an equal hue plane in an arbitrary hue may be displayed, or may be displayed three-dimensionally on three-dimensional coordinates.

  As described above, the display unit 205 displays the correction coefficient, and further displays a cross-sectional view of the color gamut cross section, the gray mapping destination, the gray mapping source, and the correction range. As a result, the user can visually grasp the range of influence by the gray correction on the output color gamut. Further, when the influence range is not the desired range, the user corrects the correction coefficient displayed on the correction coefficient acquisition unit 2007 in step S903 and presses the correction coefficient setting button 2008, thereby performing a subsequent step. In S28, the correction coefficient can be updated. Therefore, even when the correction range corresponding to the user's observation condition calculated based on the correction parameter correspondence table is not the desired range, the user can further adjust the displayed correction coefficient to Gray correction by the correction range can be executed.

Correction coefficient update process (S28)
Next, the specific operation of the correction coefficient updating unit 206 in step S28 described above will be described using the flowchart of FIG.

  First, in step S1001, the updated correction coefficient displayed on the correction coefficient acquisition unit 2007 of the setting screen 2000 is acquired. Next, in step S1002, the correction coefficient in the buffer memory 214 is updated with the acquired correction coefficient.

● Gray correction processing (S31)
Hereinafter, a specific operation of the gray correction unit 208 in step S31 described above will be described. The gray correction processing in the second embodiment is substantially the same as the processing in step S6 shown in FIG. 2 in the first embodiment described above. However, in the second embodiment, the calculation process of the correction parameter value shown in step S602 in FIG. 7 showing the details of the gray correction process (S6) in the first embodiment is different.

  This is because the number of gray mapping destinations and the number of gray mapping sources is different between the second embodiment and the first embodiment described above. In the first embodiment, when calculating a correction parameter for an input color value, the input color value brightness exists between white brightness-gray mapping original brightness, or between gray mapping original brightness-black brightness. The brightness to be referred to and the correction parameter are switched depending on whether they exist. On the other hand, in the second embodiment, as shown in FIG. 18, since the number of gray mapping destinations and gray mapping sources is different, the brightness to be referred to and the correction parameter are switched, and the input color value brightness is in any of the following ranges. Depending on whether it falls under. That is, whether the input color value lightness falls within the range of white lightness—lightness of gray mapping source 1; grayness of gray mapping source 1—lightness of gray mapping source 2; and lightness of gray mapping source 2—black lightness. Can be determined.

  By calculating the correction parameters for gray correction with such a configuration, even when there are a plurality of gray mapping sources and gray mapping destinations, the correction parameters for the input color values can be appropriately interpolated.

  As described above, according to the second embodiment, when the color conversion table is created, the correction parameter corresponding to the observation condition input by the user is calculated, and the gray line is corrected using the correction parameter. Gray reproduction suitable for the viewing conditions can be performed. Further, by displaying the influence range by the gray correction before performing the gray correction, when the influence range is not the desired range, the desired gray reproduction can be obtained by adjusting the influence range.

<Modification>
In the above-described first and second embodiments, the example in which the light source and the illuminance are used as the observation condition has been described. However, the observation condition in the present invention is not limited to this example. Any observation condition may be used as long as it is an external factor that affects the color perceived by humans, such as the background brightness and background chromaticity of the image, and the viewing viewing distance of the image. When background luminance is added to the observation conditions, for example, instead of the setting screen 1000 shown in FIG. 3, a background luminance number acquisition unit 3006 may be provided as in a setting screen 3000 shown in FIG. Further, as the correction parameter correspondence table at this time, a column describing the background luminance as shown in FIG. 20 may be added, and correction parameters corresponding to each light source, illuminance, and background luminance may be described.

  In each of the above embodiments, the value for controlling the radius of the circle is used as the correction coefficient. However, the present invention is not limited to this example. For example, the correction range is defined by an ellipse, and the major axis or short axis of the ellipse is defined. A value for controlling the axis may be used. Alternatively, the correction range may be defined by a free curve, and a value for controlling the radius of a circle circumscribing the free curve may be used as the correction coefficient.

  In each of the above embodiments, an example is shown in which a circle is used as the shape of the correction range boundary. However, this is a hexagonal or octagonal shape as long as it is a closed region that includes a gray mapping source and a gray mapping destination. It may be a polygon or any shape such as an ellipse or a free closed curve.

  Further, the observation condition selection method when the user selects the observation condition need not be limited to the radio button shown in the observation condition acquisition unit 1003 in FIG. 3, and one of a plurality of candidates such as a pull-down list can be selected. Any selection method may be used as long as the method can be selected.

  Moreover, although the example which makes a user input a light source, illumination intensity, background brightness | luminance, etc. was shown as observation conditions, this connects a measuring device to the color processing apparatus 1, for example, and acquires an environmental parameter directly from this measuring device. Needless to say, it's okay.

  In the color space value conversion units 107 and 209 in the above embodiments, the input image is described as an RGB image expressed in the sRGB color space. However, this is expressed in the color signal space in the image input / output device. A device RGB image may be used. In that case, instead of the standardized conversion formula, a conversion value may be calculated by prism interpolation, tetrahedral interpolation, or the like using a color space conversion table of device RGB values and Lab values.

  In each of the above-described embodiments, the example in which the CIECAM02 color space is used as the mapping color space and the color space for executing the gray correction has been described, but the present invention is not limited to this color space. For example, a CIELAB, CIEUV, or XYZ space may be used, or a color space considering color appearance such as CIECAM97 or CIECAM97s may be used.

<Other embodiments>
The present invention can take the form of, for example, a system, apparatus, method, program, or storage medium (recording medium). Specifically, the present invention may be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a photographing device, a web application, etc.), or may be applied to a device composed of one device. good.

  The present invention also provides a software program that implements the functions of the above-described embodiments directly or remotely to a system or apparatus, and the system or apparatus computer reads out and executes the supplied program code. Achieved. The program in this case is a computer-readable program corresponding to the flowchart shown in the drawing in the embodiment.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  Recording media for supplying the program include the following media. For example, floppy disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As a program supply method, the following method is also possible. That is, the browser of the client computer is connected to a homepage on the Internet, and the computer program itself (or a compressed file including an automatic installation function) of the present invention is downloaded to a recording medium such as a hard disk. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to make it. That is, the user can execute the encrypted program by using the key information and install it on the computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, and then executed, so that the program of the above-described embodiment can be obtained. Function is realized. That is, based on the instructions of the program, the CPU provided in the function expansion board or function expansion unit can perform part or all of the actual processing.

1 is a block diagram illustrating a configuration of a color processing apparatus according to an embodiment of the present invention. It is a flowchart which shows the outline | summary of the color processing in this embodiment. It is a figure which shows UI example in this embodiment. It is a flowchart which shows the observation condition acquisition process in this embodiment. It is a flowchart which shows the correction parameter setting process in this embodiment. It is a figure which shows the example of the correction parameter corresponding table | surface in this embodiment. It is a flowchart which shows the gray correction process in this embodiment. It is a figure which shows the specific example of the calculation method of the correction parameter in this embodiment. It is a figure which shows the specific example of the inside / outside determination of the input color value in this embodiment. It is a block diagram which shows the structure of the color processing apparatus which is 2nd Embodiment concerning this invention. It is a figure which shows the outline | summary of the color processing in 2nd Embodiment. It is a figure which shows UI example in 2nd Embodiment. It is a flowchart which shows the observation condition setting process in 2nd Embodiment. It is a flowchart which shows the correction parameter setting process in 2nd Embodiment. It is a figure which shows the example of the correction parameter corresponding table | surface in 2nd Embodiment. It is a flowchart which shows the correction coefficient and correction range display process in 2nd Embodiment. It is a flowchart which shows the correction coefficient update process in 2nd Embodiment. It is a figure which shows the specific example of the calculation method of the correction parameter in 2nd Embodiment. It is a figure which shows UI example in the modification of this invention. It is a figure which shows the example of the correction parameter corresponding table | surface in a modification. It is a figure which shows the relationship of a general color gamut. It is a flowchart which shows the color conversion process of a general RGB image. It is a figure which shows the example of general color gamut data. It is a figure which shows the example of general convergence point mapping.

Claims (14)

A color processing device that creates a color conversion table for converting color values in a first color space into color values in a second color space,
An observation condition acquisition means for acquiring an image observation condition;
Correction parameter setting means for setting correction parameters according to the observation conditions;
Mapping means for mapping a color gamut in the first color space to the second color space;
Gray correction means for performing gray correction within a correction range based on the correction parameter in the color gamut mapped to the second color space by the mapping means;
A color processing apparatus that creates a color conversion table based on a color value in the first color space and a color value in a second color space after gray correction by the gray correction unit.   The color processing apparatus according to claim 1, wherein the gray correction unit corrects a gray peripheral color within the correction range according to a distance from a center of the correction range.   The color processing apparatus according to claim 1, wherein the gray correction unit sets the correction range and a gray reproduction target value based on the correction parameter.   The color processing apparatus according to claim 1, wherein the observation condition includes information for identifying illuminance.   The color processing apparatus according to claim 1, wherein the correction parameter is determined in advance for each observation condition. The correction parameter is determined in advance for each representative observation condition,
The color processing apparatus according to claim 5, wherein the correction parameter setting unit calculates a correction parameter corresponding to the viewing condition based on the correction parameter of the representative viewing condition.   7. The color processing apparatus according to claim 1, wherein the correction parameter includes a predetermined gray color value, a reproduction target value thereof, and a correction coefficient for determining the correction range. .   The color processing apparatus according to claim 7, wherein the correction range includes the gray color value and a reproduction target value thereof.   The color processing apparatus according to claim 1, further comprising an update unit that updates the correction range based on a user instruction. A color processing method for creating a color conversion table for converting color values in a first color space into color values in a second color space,
An observation condition acquisition step of acquiring an image observation condition;
A correction parameter setting step for setting a correction parameter according to the observation condition;
A mapping step of mapping a color gamut in the first color space to the second color space;
A gray correction step of performing gray correction within a correction range based on the correction parameter in the color gamut mapped to the second color space in the mapping step;
A color processing method, wherein a color conversion table is created based on a color value in the first color space and a color value in the second color space after the gray correction in the gray correction step.   The color processing method according to claim 10, wherein in the gray correction step, gray peripheral colors in the correction range are corrected according to a distance from a center of the correction range.   12. The color processing method according to claim 10, wherein, in the gray correction step, the correction range and a gray reproduction target value are set based on the correction parameter.   The program for functioning a computer as a color processing apparatus of any one of Claims 1 thru | or 9.   A computer-readable recording medium on which the program according to claim 13 is recorded.

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