JP2007142911A - Image processing apparatus, image processing method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of decreasing the amount of data handled in image processing, while preventing degradation of image quality. <P>SOLUTION: The image processing first generates an image of first image data that is an object of processing reduced and generates second image data, and then the second image data are analyzed. Thereafter, on the basis of the result of the analysis of the second image data, a look-up table used for conversion of changing at least part of colors of the image data is generated. Then the first image data are converted, while the look-up table is being referred to. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for processing image data.

  Conventionally, automatic image processing has been performed in accordance with the contents of image data to be processed. For example, in the technique of Patent Document 1, the parameter SV based on the image data GD included in the image file GF and the image processing control information GC, which is the image quality adjustment processing condition at the time of shooting, also included in the image file GF. And are acquired. Then, based on the parameter FP calculated from them, each tone curve of RGB is determined, and automatic image quality adjustment is performed using the tone curve.

  In the technique of Patent Document 2, the color balance is automatically adjusted based on the subject focal length and lens focal length included in the Exif data area in the image data, and the size of the area occupied by the memory color in the image. Processing is performed.

JP 2002-344989 A JP 2004-172745 A

  However, in the above technique, consideration has not been given to reducing the amount of data handled in image processing while performing processing according to the target image.

  An object of the present invention is to provide a technique capable of reducing the amount of data handled in image processing while performing processing according to a target image.

  In order to achieve the above object, the present invention executes the following processing when performing image processing. That is, first, the image of the first image data to be processed is reduced to generate second image data. Then, the second image data is analyzed. Thereafter, based on the result of the analysis of the second image data, a lookup table for performing conversion for modifying the color of at least a part of the image data is generated. Then, the first image data is converted with reference to the lookup table.

  In such an aspect, a lookup table is generated based on the second image data reflecting the contents of the first image data, and image conversion is performed with reference to the lookup table. For this reason, the process according to the image made into the object of an image process can be performed. On the other hand, the second image data is image data having a data amount smaller than that of the first image data obtained by reducing the image of the first image data. For this reason, in the above aspects, the processing load is smaller than in the aspect in which the first image data is directly analyzed during image processing.

  When the first image data includes gradation values of n types (n is an integer of 2 or more) of the first color system, the lookup table has n types as input values and output values, respectively. An n-dimensional color correction lookup table having a combination of tone values of the above components is preferable. Then, when generating the lookup table, it is preferable to perform the following processing. That is, an n-dimensional lookup table having combinations of gradation values of n types of components as input values and output values, respectively, in the color space of the first color system determined based on the result of analysis An original lookup table having tone values determined according to some color ranges as input tone values is generated. After that, among the combinations of the input tone values of the original lookup table, the corresponding output tone values are modified for the first combination representing the color included in the color range to generate a color correction lookup table.

  According to such an aspect, when image processing is performed with reference to an n-dimensional lookup table having output gradation values for some combinations of gradation values, the colors are modified for some color ranges. There are the following advantages when performing image processing including processing to be performed. That is, it is possible to change the color range more accurately to a desired color as compared with an aspect of referring to an n-dimensional lookup table in which the input gradation value is fixed regardless of the color range in which the color is changed. it can. Note that the original look-up table includes an input tone value and an output floor, which are an input value of a part of the tone curve of each of n components of the first color system and an output value corresponding to the input value. A look-up table having a key value can be used.

  When generating the original look-up table, the first color system representing the first reference point, which is at least one point on the boundary of the color range in the color space of the first color system. It is preferable that a combination of gradation values is an input gradation value included in the original lookup table.

  According to such an aspect, it is possible to perform image processing with reference to an n-dimensional lookup table having output gradation values for the color at the boundary between the color range in which the color is changed and the other color space. . As a result, the combination of input tone values located near the boundary of the color space, compared to the case where a lookup table in which input tone values are determined without considering the color range for color modification is considered. The color can be modified to the desired color.

  Further, when modifying the output tone value of the original lookup table, it is preferable to perform the following processing. That is, first, a combination of output gradation values corresponding to the first combination of input gradation values is converted into a combination of gradation values based on the second color system having a lightness component. Then, the magnitudes of the gradation values of at least some components of the converted gradation value combination are modified. Thereafter, the combination of gradation values after the size change is reconverted into a combination of gradation values of the components of the first color system, and an output gradation value of the original lookup table is obtained.

  With such an aspect, it is easy to modify the brightness and tone of a color in a part of the color space in accordance with human senses and preferences.

  Note that when changing the size of the second color system tone value after conversion, the tone value of each component of the second color system is determined according to the above color range. It is preferable to change the magnitude by a predetermined amount in accordance with the magnitude of the gradation value for the gradation value within the first gradation value range. The first reference point is a point in the color space of the second color system, and the maximum value or the minimum value of the first gradation value range of each component of the second color system is determined. It is preferable that the point corresponds to the point having the gradation value of each component.

  Further, a combination of gradation values having the maximum value or the minimum value of the first gradation value range of each component of the second color system as the gradation value of each component (at the upper end of the gradation value range of each component) It is assumed that the combination of only the values and the combination of only the values at the lower end, or the combination of the upper end value and the lower end value) may be converted into a combination of gradation values of the first color system. In this case, it is also preferable that the input gradation value of the original lookup table is determined as follows. That is, the combination of gradation values of the first color system obtained by converting the combination of gradation values at the end of the first gradation value range is the color range in the color space of the first color system. This is a combination of gradation values representing points on the boundary. Then, at least a part of the gradation values among the third combination of gradation values is set as the input gradation value included in the original lookup table.

  According to this aspect, the n-dimensional lookup table has an output gradation value for the color having the maximum value or the minimum value of each component of the second color system in the color range in which the color is changed. Can be generated. As a result, desirable modifications can be made to such colors and colors that approximate them.

  Further, when modifying the gradation values of the second color system, it is preferable to perform the following processing on the gradation values of at least some components of the second color system. That is, the size is changed by a certain amount for a gradation value within a second gradation value range that is a predetermined gradation value range and included in the first gradation value range. . For gradation values that are within the first gradation value range and not included in the second gradation value range, the gradation value closer to the second gradation value range is closer to a certain amount. Modify the size to change the size.

  According to such an aspect, the n-dimensional lookup table can be generated by simply modifying the tone values of the tone values within the second tone value range. It is also possible to generate an n-dimensional lookup table that modifies color tone values so that the entire image does not become unnatural. The aspect in which the second gradation value range is “included in the first gradation value range” includes an aspect in which the second gradation value range coincides with the first gradation value range.

  When generating the original look-up table, it is a combination of gradation values of the first color system, and the maximum value or minimum value of the second gradation value range is used as the gradation value of each component. It is preferable that a combination of gradation values corresponding to a combination of gradation values of the second color system having the input gradation value included in the original lookup table.

  According to such an aspect, the color having the maximum value or the minimum value of each component of the second color system in the color range in which the color is changed by a certain amount is set so as to have an output gradation value. A dimension lookup table can be generated. As a result, desirable modifications can be made to such colors and colors that approximate them.

  Note that the color range may be a range surrounded by a polyhedron having a plurality of color points as vertices in the color space represented by the first color system. Then, when generating the original lookup table, at least a part of the gradation value combinations representing the plurality of color points as the first reference point is selected as the original lookup table. It is preferable to use the input gradation value of the uptable. With such an aspect, it is possible to easily specify a color range for color modification and generate a lookup table having combinations of input tone values corresponding to points on the boundary of the color range. .

  Further, the candidate color range having the largest area occupied by the color included in the candidate color range in the image of the second image data among the plurality of predetermined candidate color ranges may be determined as the color range. preferable.

  With such an aspect, it is possible to generate a lookup table that can effectively change the color of a color that is easy to be noticed by a person with a large portion in the image while reducing the load. . Note that the size of the area occupied by the color included in the candidate color range in the image of the second image data can also be calculated from the second image data itself represented by the first color system. For example, the image data can be converted into image data of the second color system and calculated from the converted image data.

  Note that the candidate color range can be a color range in which the color is to be modified based on the memory color. Note that the “memory color” refers to a color that is stored as the color of the subject by the human being in the image.

  When generating the original lookup table, it is preferable to perform the following processing. That is, first, n tone curves having discrete tone values of the same type of components of the first color system as input values and output values are generated based on the analysis results. Then, based on the n tone curves, an original lookup table having a smaller number of gradations of input values than the tone curve is generated for at least one component.

  According to such an aspect, an n-dimensional lookup table having a data amount smaller than that of an n-dimensional lookup table having output tone values for all combinations of tone curve input tone values is generated by a simple method. Can do.

  Further, when generating the original lookup table, it is also preferable to perform the following processing. That is, when generating the original look-up table, a plurality of input tone values of a tone curve predetermined as input tone value candidates that the original look-up table should have are input to the first group and the first group. When divided into a second group having a larger increase rate of the corresponding output gradation value than that of one group, an input gradation value included in the second group is an input gradation value included in the original lookup table. As at least part of.

  According to such an aspect, even when an operation is performed using a plurality of output gradation values of the generated n-dimensional lookup table and an output gradation value for the input gradation value is obtained, the input level Compared to an n-dimensional lookup table having uniform tone values, the output value error is reduced.

  The present invention can be realized in various forms, for example, an image processing method and an image processing device, an image data generation method and an image data generation device, a color conversion method and a color conversion device, a printing method and printing. Apparatus, print control method and print control apparatus, computer program for realizing the function of the method or apparatus, recording medium recording the computer program, data signal including the computer program and embodied in a carrier wave, etc. Can be realized.

Next, embodiments of the present invention will be described in the following order based on examples.
A. First embodiment:
A1. Overall configuration of the device:
A2. Processing in the LUT generation module:
B. Second embodiment:
C. Variation:

A. First embodiment:
A1. Overall configuration of the device:
FIG. 1 is a block diagram illustrating a software configuration of the printing system according to the first embodiment. In the computer 90, an application program 95 operates under a predetermined operating system. In addition, a video driver 91 and a printer driver 96 are incorporated in the operating system.

  The application program 95 converts the original image data ORG composed of the three color components of red (R), green (G), and blue (B) into CD- in accordance with a user instruction input from the mouse 130 or the keyboard 120. Read from R140. Then, in response to a user instruction, processing such as image retouching is performed on the original image data ORG. The application program 95 displays the processed image on the CRT display 21 via the video driver 91. When the application program 95 receives a print instruction from the user, it issues a print instruction to the printer driver 96 and outputs the processed image to the printer driver 96 as initial image data PID. The initial image data PID is image data in which the color of each pixel is expressed in the sRGB color system. More specifically, the initial image data PID is image data having gradation values (0 to 255) of red (R), green (G), and blue (B) color components for each pixel.

  The printer driver 96 receives the initial image data PID from the application program 95, and print image data FNL that can be processed by the printer 22 (here, multiple values for six colors of cyan, magenta, yellow, black, light cyan, and light magenta). Signal).

  In the example shown in FIG. 1, the printer driver 96 includes a reduced image generation module 101, a lookup table generation module 102, a color tone adjustment module 103, a resolution conversion module 97, a color conversion module 98, and a half A tone module 99 and a rearrangement module 100 are provided.

  The reduced image generation module 101 generates reduced image data PID2 based on the initial image data PID received from the application program 95. The reduced image data PID2 represents the same object as the initial image data PID, and is image data having a smaller number of pixels constituting the image than the initial image data PID.

  The lookup table generation module 102 (hereinafter referred to as “LUT generation module 102”) analyzes the reduced image data PID2, and generates a three-dimensional lookup table 104a based on the analysis result. The three-dimensional lookup table 104a has a combination of red, green, and blue gradation values Vri, Vgi, and Vbi as input values, and a combination of red, green, and blue gradation values Vro, Vgo, and Vbo as output values. Is a look-up table. The three-dimensional lookup table 104a has output values (Vro, Vgo, Vbo) representing colors different from the input values for at least some of the input values (Vri, Vgi, Vbi).

  The color tone adjustment module 103 converts the initial image data PID received from the application program 95 with reference to the three-dimensional LUT 104a to generate image data PIDr. The image data PIDr is image data having the gradation values of the red (R), green (G), and blue (B) color components for each pixel and the same number of pixels as the initial image data PID.

  In the image processing in the reduced image generation module 101, the lookup table generation module 102, and the color tone adjustment module 103, the user can input an instruction via the mouse 130 or the keyboard 120 at a predetermined timing. On the other hand, even when there is no instruction from the user, image processing in the reduced image generation module 101, the lookup table generation module 102, and the color tone adjustment module 103 is automatically performed.

  The resolution conversion module 97 converts the resolution of the image data PIDr to the resolution used when printing by the printer 22.

  The color conversion module 98 converts the image data MID1 into the image data MID2 while referring to the three-dimensional lookup table 104b of the color conversion table 104. The image data MID2 is a gradation value of each pixel with a density value of cyan (C), magenta (M), yellow (Y), black (K), light cyan (LC), and light magenta (LM) used by the printer 22. This is image data representing a color. The three-dimensional lookup table 104b has a combination of gradation values of red, green, and blue as input values, and a combination of gradation values of cyan, magenta, yellow, black, light cyan, and light magenta as output values. It is a lookup table having. The three-dimensional lookup table 104b is not generated based on the reduced image data PID2 or the initial image data PID, but is prepared in advance regardless of the initial image data PID.

  The halftone module 99 performs halftone processing on the image data MID2 in which the density of each color of each pixel is represented by the gradation value of each color, whereby image data in which the density of each color is represented by the presence or absence of dots in each pixel. Conversion to MID3 (also referred to as “print data” or “dot data”).

  The image data MID3 generated in this way is rearranged in the order of data to be transferred to the printer 22 by the rearrangement module 100, and is output as final print image data FNL.

  The printer 22 includes a mechanism for transporting the paper P by a paper feed motor, a mechanism for reciprocating the carriage 31 in a direction MS perpendicular to the transport direction SS of the paper P by a carriage motor, and ink ejection and dots mounted on the carriage 31. The print head 28 for forming, a P-ROM 42 for storing various setting data, and a CPU 41 for controlling these paper feed motor, carriage motor, print head 28, P-ROM 42 and operation panel 32 are configured. ing. The printer 22 receives the print image data FNL, and in cyan (C), magenta (M), yellow (Y), black (K), light cyan (LC), and light magenta (LM) according to the print image data FNL. Dots are formed on the print medium and printing is performed.

  Note that “light cyan” is an ink color having the same hue as cyan and a lightness higher than cyan. Light cyan and cyan can be replaced with each other when reproducing some colors. That is, light cyan and cyan can be recorded at different recording rates to express cyan color components with similar densities.

  Further, “light magenta” is an ink color having the same hue as magenta and having a higher lightness than magenta. Light magenta and magenta can be replaced with each other when reproducing some colors. That is, light magenta and magenta can be recorded at different recording rates to express magenta color components having similar densities.

  In the present specification, the “printing apparatus” refers only to the printer 22 in a narrow sense, but represents the entire printing system including the computer 90 and the printer 22 in a broad sense.

A2. Processing in the LUT generation module:
FIG. 2 is a flowchart showing processing in the LUT generation module 102. In step S100, the LUT generation module 102 first analyzes the reduced image data PID2 and calculates a parameter representing the characteristics of the reduced image data PID2.

  In step S100, for example, the LUT generation module 102 obtains the brightness Vy by the following equation for each pixel of the reduced image data PID2. Vr is the red gradation value of each pixel, Vg is the green gradation value of each pixel, and Vb is the blue gradation value of each pixel.

  Vy = 0.30Vr + 0.59Vg + 0.11Vb (1)

  Then, an average value Vya and standard deviation σy of the brightness Vy are obtained for the reduced image data PID2. The average value Vya and the standard deviation σy of the brightness Vy of the reduced image data PID2 obtained in this way are parameters representing the characteristics of the reduced image data PID2, and thus the characteristics of the initial image data PID.

  In step S100, the LUT generation module 102 determines a color range to be adjusted based on the memory color, and determines a target memory color parameter Pmc corresponding to the color range. The target memory color parameter Pmc is also a parameter that is determined based on the characteristics of the reduced image data PID2 and represents the characteristics of the reduced image data PID2.

  FIG. 3 is a diagram showing a part of the contents of the memory color table 105. The LUT generation module 102 has a memory color table 105. The LUT generation module 102 determines the target memory color parameter Pmc based on the memory color table 105. The memory color table 105 stores hue (H), saturation (S), and brightness (B) ranges for M (M is an integer of 2 or more) color ranges Cm1 to CmM. For example, in FIG. 3, the color range Cm1 is a color in the range of H = 190 to 270 °, S = 30 to 90%, and B = 0 to 100%. The color range Cm1 is a blue sky color. Similarly, the memory color table 105 stores a plurality of color ranges Cm2 to CmM for the green color of wood, the color of human skin, and the like.

  FIG. 4 is a flowchart showing a procedure for determining a target memory color parameter representing the content of adjustment relating to the memory color. In step S110, the LUT generation module 102 first converts the reduced image data PID2 represented in the sRGB color system to the HSB image data PID3 represented in the HSB color system. In step S120, the size of the area occupied by each color (see FIG. 3) included in the memory color range Cm1 to CmM in the image of the HSB image data PID3 is calculated. The size of the area is represented by the number of pixels.

  Thereafter, in step S130, the color range of the memory color that occupies the largest area in the image of the HSB image data PID3 is determined as the target memory color that is to be adjusted for the memory color. The HSB image data PID3 is data generated by converting the reduced image data PID2, and the reduced image data PID2 is an image generated by reducing the initial image data PID. Therefore, the color range determined as the target memory color occupies the widest area in the image of the initial image data PID and the image of the reduced image data PID2.

  In step S140 of FIG. 4, the number of the target memory color is stored as the target memory color parameter Pmc. For example, when the color range Cm1 is selected as the target memory color, Pmc = 1. When the color range Cmi (i = 1 to M) is selected as the target memory color, Pmc = i. In step S100 of FIG. 2, the LUT generation module 102 performs, for example, the above processing to determine parameters Vya, σy, and Pmc representing the characteristics of the reduced image data.

  In step S200 of FIG. 2, the LUT generation module 102 generates a three-dimensional lookup table 104a based on a plurality of parameters Vya, σy, Pmc obtained as a result of the analysis of the reduced image data PID2 in step S100.

  In the first embodiment, instead of analyzing the initial image data PID itself, the reduced image data PID2 is analyzed, and the three-dimensional lookup table 104a is generated based on the analysis result. For this reason, the processing load is small as compared with an aspect in which the initial image data PID itself is analyzed to generate a three-dimensional lookup table. The reduced image data PID2 is an image obtained by reducing the initial image data PID. Therefore, the three-dimensional lookup table 104a is generated reflecting the characteristics of the initial image data PID.

  FIG. 5 is a flowchart showing a procedure for generating the three-dimensional lookup table 104a in step S200 of FIG. In step S210, first, setting parameters for determining the shape of the tone curve are calculated based on the average value Vya and the standard deviation σy of the brightness Vy obtained in step S100.

  The LUT generation module 102 calculates a brightness adjustment parameter dl as a tone curve setting parameter by the following equation (2). The brightness adjustment parameter dl is a parameter for adjusting the brightness of the image to the target brightness by the finally generated three-dimensional lookup table 104a. In the formula (2), “a” is a positive constant. Vyc is a target value of average brightness, and is, for example, a central value of brightness gradation values. In the first embodiment, the lightness gradation value is 0 to 255 according to the equation (1), so Vyc is 128.

  dl = a × (Vyc−Vya) (2)

  In step S210, the LUT generation module 102 calculates a contrast adjustment parameter dc as a setting parameter using the following equation (3) or (4). The contrast adjustment parameter dc is a parameter for adjusting the contrast of the image by the finally generated three-dimensional lookup table 104a. Note that b and σy0 in equation (3) are positive constants. σy0 is a target value of the standard deviation of the lightness gradation value.

dc = b × (σy0−σy) (when σy <σy0) (3)
dc = 0 (when σy ≧ σy0) (4)

  In step S220, the LUT generation module 102 generates a tone curve based on the brightness adjustment parameter dl and the contrast adjustment parameter dc. The tone curve generated in step S220 has discrete input values and output values. In the first embodiment, the same tone curve is used for the gradation values of red, green, and blue.

  6A and 6B are diagrams showing an example of a tone curve generation method in step S220 in FIG. The horizontal axis of each graph represents red, green, and blue input gradation values Vi, and the vertical axis represents their output gradation values Vo. In step S220 of FIG. 5, the LUT generation module 102 first outputs a provisional output gradation having a reference input gradation value Vir1 = 64 which is a gradation value that is ¼ from the bottom of the range that the input gradation value can take. The value Vor1 ′ is determined by the following equation (5).

  Vor1 '= Vir1 + dl (5)

  That is, when the average brightness value Vya is less than Vyc (128), the reference input tone value Vir1 is increased by | dl |. On the other hand, when the average brightness value Vya is larger than Vyc, the reference input tone value Vir1 is decreased by | dl |. Then, the provisional tone curve C1p is generated as a spline curve that passes through the point O (0, 0), the point p1 '(Vir1, Vor1'), and the point pmax (Vimax, Vomax). Vimax is the maximum value of the input gradation value, and Vomax is the maximum value of the output gradation value. FIG. 6A shows an example in which the average brightness value Vya is smaller than Vyc = 128.

  Thereafter, the LUT generation module 102 further determines a reference output tone value Vor1 corresponding to the reference input tone value Vir1 = 64, which is a quarter tone value from the bottom, using the following equation (6).

  Vor1 = Vor1'-dc (6)

  From Expressions (3), (4), and (6), when the lightness standard deviation σy is less than σy0, the output gradation value of the reference input gradation value Vir1 is decreased by dc. On the other hand, when the standard deviation of the brightness is σy0 or more, the output tone value of the reference input tone value Vir1 remains the provisional output tone value Vo1 '. FIG. 6B shows an example in which the standard deviation σy of lightness is less than σy0.

  Further, the LUT generation module 102 sets the output gradation value Vo2 of the reference input gradation value Vir2 = 192, which is a gradation value of ¼ from the upper range of the input gradation value, by the following equation (7). decide. Note that Vo2 'is an output tone value of the reference input tone value Vir2 in the provisional tone curve C1p (see FIG. 6A) generated based on the brightness adjustment parameter dl.

  Vor2 = Vor2 '+ dc (7)

  From Expressions (3), (4), and (7), when the standard deviation σy of lightness is less than σy0, the output gradation value of the reference input gradation value Vir2 is increased by dc. On the other hand, when the standard deviation of brightness is σy0 or more, the output tone value of the reference input tone value Vir2 remains the provisional output tone value Vo2 '. FIG. 6B shows an example in which the lightness standard deviation σy is less than σy0.

  On the other hand, the LUT generation module 102 outputs the output gradation value Vo3 of the reference input gradation value Vir3 = 128 which is a gradation value ½ from the bottom, and outputs the reference input gradation value Vir3 in the provisional tone curve C1p. The same value as the gradation value Vo3 ′.

  Then, the LUT generation module 102 converts the tone curve C1 into a point O (0, 0), a point p1 (Vir1, Vor1), a point p3 (Vir3, Vor3), a point p2 (Vir2, Vor2), and a point pmax (Vimax, Vimax, (Vomax) as a spline curve. As a result, with respect to the input tone value on the same side as the reference input tone value Vir1, as the input tone value closer to the reference input tone value Vir1, the value closer to the reference output tone value Vor1 is used as the output value. A tone curve is determined to have. As for the input tone value on the same side as the reference input tone value Vir2, the closer the input tone value to the reference input tone value Vir2, the closer the reference output tone value Vor2 is to the output value. Thus, the tone curve is determined. As for the input tone value on the same side as the reference input tone value Vir3, the input tone value closer to the reference input tone value Vir3 is the reference output tone value corresponding to the reference input tone value Vir3. The tone curve is determined so as to have a value close to Vor3 as an output value. In step S220 of FIG. 5, the tone curve is generated as described above.

  In step S230 of FIG. 5, the tone curve generated in step S220 is analyzed to determine the input tone value of the three-dimensional lookup table 104a.

  FIG. 7 is a flowchart showing a procedure for determining the input gradation value of the three-dimensional lookup table 104a in step S230 of FIG. In step S310, first, the first candidate gradation value is determined by analyzing the tone curve generated in step S220 of FIG.

FIG. 8 is a flowchart showing a procedure for determining the first candidate gradation value in step S310 of FIG. FIG. 9 is a diagram illustrating a method for determining the input gradation value of the three-dimensional lookup table 104a on the tone curve C1. In step S311 (S232) of FIG. 8, first, for a plurality of input tone values having a constant interval di with respect to the tone curve, output tone values corresponding to each other and output of the next smallest input tone value are performed. The difference from the gradation value is obtained. For example, the input tone values Vi _k having a spacing of 16 gradations each other until 0~255 (k = 1~17), the output tone value Vo _k, each corresponding to 16 gradations larger next input gradation obtaining a value Vi _{k + 1} of the output tone value Vo _{k + 1,} the difference dv _k. Each difference dv _k is associated with an input gradation value Vi _k . In FIG 9, it shows a tone curve C1 in broken lines, indicated by the black dot points on the tone curve corresponding to the input tone values Vi _k.

In step S312 (S234) of FIG. 8, an input gradation value Vi _k having a difference dv _k greater than a threshold value Th is selected. In step S313, it is determined whether or not the number of input gradation values Vi _{k for which} the difference dv _k is greater than the threshold value Th is greater than L2 (L2 is a positive integer). If the determination result is Yes, the process proceeds to step S314. In step S314 (S236), ranking the input tone values Vi _k selected in step S312 (S234) in descending order of the difference dv _k. Then, in step S315 (S238), determines the L2 amino input tone values from those difference dv _k is larger as the first candidate tone values.

L2 is a number that is smaller by 10 than the number Nmax that is predetermined as the maximum number of input gradation values of the three-dimensional lookup table 104a. Nmax is an integer of 11 or more. In the first embodiment, for example, Nmax is 17 and L2 is 7. In the example of FIG. 9, in step S315 (S238) of FIG. 8, seven input gradation values Vi _{6 to} Vi ₁₂ are selected based on the magnitude of the difference dv _k .

In step S315 (S238) in FIG. 8, the minimum input gradation value Vimin and the maximum input gradation value Vimax are also selected as the first candidate gradation values. Thereafter, the process ends. In the example of FIG. 9, since Vi ₁ and Vi ₁₇ are Vimin and Vimax, respectively, Vi ₁ and Vi ₁₇ are selected as the first candidate gradation values in addition to Vi ₆ to Vi ₁₂ . FIG. 9 shows an example in which the first candidate gradation value is determined along steps S314 and S315. 9 are denoted by circle points on the corresponding tone curves to those selected as the first candidate tone values of the input tone values Vi _k.

On the other hand, when it is determined in step S313 that the input gradation value selected in step S312 (S234) is L2 or less, the process proceeds to step S316. In step S316, all the input gradation values selected in step S312 (S234), the minimum input gradation value Vimin, and the maximum input gradation value Vimax are selected as the first candidate gradation values. That is, in the procedure of FIG. 8, a maximum of L2 input gradation values are selected based on the difference dv _k .

  In step S310 in FIG. 7, a maximum of L2 first candidate gradation values are determined as described above. In the first embodiment, the same tone curve is used for red, green, and blue tone value conversion. Therefore, in the processing so far, the first candidate gradation value is the same for each color component of red, green, and blue.

  In step S320 of FIG. 7, the second candidate gradation value corresponding to the color range Cmi of the target memory color parameter Pmc determined in step S100 of FIG. 2 is read. The second candidate gradation values are gradation values of eight points pc1 (Vcr1, Vcg1, Vcb1) to pc8 (Vcr8, Vcg8, Vcb8) that define each color range Cmi in the red, green, and blue sRGB color spaces. It is. Each color range Cmi is a color range inside the polyhedron having these eight points pc1 to pc8 as vertices in the sRGB color space. Second candidate gradation values Vcr1 to Vcr8, Vcg1 to Vcg8, and Vcb1 to Vcb8 corresponding to each color range Cmi are stored in the memory color table 105 in advance. Note that the second candidate gradation value does not always match for each of the red, green, and blue color components. The second candidate gradation value corresponding to this memory color will be described later.

  In step S330, for each of the red, green, and blue color components, it is determined whether or not there is an approximation of the second candidate gradation value among the first candidate gradation values. Here, “approximate” means that the first candidate gradation value exists within the range of plus or minus dn (dn is a positive integer) of the second candidate gradation value. In the first embodiment, for example, dn has 4 gradations. If the determination result of step S330 is Yes, the process proceeds to step S340. On the other hand, when the determination result of step S330 is No, the process proceeds to step S350 without passing through step S340.

  In step S340, the first candidate gradation value of each color component approximates to the second candidate gradation value of each color component, that is, the difference from any second candidate gradation value is four gradations. Exclude items within. The second candidate gradation value is not the same for each color component of red, green, and blue. For this reason, as a result of the processing in step S340, the first candidate gradation value usually does not match for each color component of red, green, and blue.

  In step S350, the first and second candidate gradation values are determined as input gradation values of the three-dimensional lookup table 104c for each color component. Note that the input tone value of the three-dimensional lookup table 104a is the same as the input tone value of the three-dimensional lookup table 104c.

FIG. 10 is a diagram showing a grid of the three-dimensional lookup table defined by the first candidate gradation value determined in step S310 in FIG. A “grid” is a point specified in the color space by a combination of input gradation values. FIG. 10 shows a grid positioned on the plane of the blue input gradation value Vbi = 0. The horizontal axis represents the red gradation value Vri, and the vertical axis represents the green gradation value Vgi. Each grid on the plane of Vbi = 0 is indicated by a black dot surrounded by a circle as in FIG. A straight line corresponding to the _first candidate gradation values Vi _{1 to} Vi ₁₇ on the red and green axes is indicated by a one-dot chain line. The first candidate gradation value determined in step S310 in FIG. 7 is the same for each color component. For this reason, in FIG. 10, the grid arrangement is symmetric with respect to the straight line Lrg of Vri = Vgi.

  FIG. 11 is a diagram showing a grid of the three-dimensional lookup table 104c defined by the input gradation value determined in step S350 in FIG. FIG. 11 shows a grid located on the plane of the blue input gradation value Vbi = 0 in the three-dimensional lookup table 104c. The horizontal axis represents the red gradation value Vri, and the vertical axis represents the green gradation value Vgi. In FIG. 11, each grid is indicated by a black dot.

In FIG. 11, black points pp1 to pp8 surrounded by triangles are grids defined by the second candidate gradation values determined in step S320 of FIG. Points pp1 to pp8 (Vcr1, Vcg1) to (Vcr8, Vcg8) in FIG. Vcr8, Vcg8, Vcb8) are projected onto a red-green plane. Also in FIG. 11, a straight line corresponding to the _first candidate gradation values Vi _{1 to} Vi ₁₇ on the red and green axes is indicated by a one-dot chain line. The straight lines corresponding to the second candidate gradation values Vcr1 to Vcr8 on the axis of the red gradation value Vri and the second candidate gradation values Vcg1 to Vcg8 on the axis of the green are indicated by broken lines.

In the example of FIG. 11, the difference between the second candidate gradation value Vcr4 and the first candidate gradation value Vi ₆ corresponding to the point pp4 is within dn, that is, within 4. As a result, in step S340 of FIG. 7, the gradation value Vi ₆ is excluded from the first candidate gradation value. Vi ₆ does not become the input gradation value of red in the three-dimensional lookup table 104c. In FIG. 11, the sign of the gradation value Vi ₆ on the axis of the red gradation value Vri and the corresponding one-dot chain line are shown with a cross.

Similarly, in the red tone value, the first candidate tone value Vi ₈ is excluded from the first candidate tone value because it approximates the second red candidate tone value Vcr1 corresponding to the point pp1. Is done. Also, in the red tone value, the first candidate tone value Vi ₁₁ is also excluded from the first candidate tone value because it approximates the red second candidate tone value Vcr7 corresponding to the point pp7. The Therefore, these gradation values are not the input gradation values of red in the three-dimensional lookup table 104c. In FIG. 11, the symbols of the gradation values Vi ₈ and Vi ₁₁ on the axis of the gradation value Vri of red, and the alternate long and short dash lines are also shown with a cross.

In the example of FIG. 11, the input tone values that are the red input tone values of the three-dimensional lookup table 104c are Vi ₁ , Vcr8, Vcr4, Vi ₇ , Vcr5 in ascending order on the axis of the red tone value Vri. a fourteen _{Vcr1, Vi 9, Vi 10,} Vcr3, Vcr7, Vi 12, Vcr2, Vcr6, Vi 17. The red input tone value of the three-dimensional lookup table 104c on the axis of the red tone value Vri is indicated by a circle.

On the other hand, in the green gradation value on the vertical axis, the first candidate gradation value Vi ₇ approximates the second candidate gradation value Vcg6 of green corresponding to the point pp6. Excluded from. In the green gradation value on the vertical axis, the first candidate gradation value Vi ₁₂ approximates the second candidate gradation value Vcg4 of green corresponding to the point pp4. Excluded from. Therefore, these gradation values are not the input gradation values of green in the three-dimensional lookup table 104c. In FIG. 11, the symbols of the gradation values Vi ₇ and Vi ₁₂ on the axis of the green gradation value Vgi, and the corresponding alternate long and short dash lines are also shown.

11, the input tone value of the green of the three-dimensional lookup table 104c _{is, Vi 1, Vcg5, Vi 6} , Vcg1 in ascending _{order, Vcg6, Vi 8, Vcg2,} Vi 9, Vcg8, Vi 10, Vi 11, Vcg7 , it is a 15 Vcg4, Vcg3, Vi _17. The green input gradation value of the three-dimensional lookup table 104c on the axis of the green gradation value Vgi is circled.

  As described above, the second candidate gradation value is determined independently for red, green, and blue. For this reason, the number of input gradation values of the three-dimensional lookup table 104c determined in the process of FIG. 8 is not equal for red, green, and blue. As a result, also in FIG. 11, the number of input gradation values differs between red and green. The grid arrangement indicated by the black dots is not symmetric with respect to the straight line Lrg of Vri = Vgi. In step S230 of FIG. 5, the input gradation value of the three-dimensional lookup table 104c is determined as described above according to the flowchart of FIG.

  In step S240 of FIG. 5, the three-dimensional lookup table 104c is generated from the input gradation values determined in step S230 and the output gradation values corresponding to them. The three-dimensional lookup table 104c has gradation values of red, green, and blue as input values, and gradation values of red, green, and blue as output values.

The output gradation value of each color component in each grid of the three-dimensional lookup table 104c is determined based on the tone curve of that color component. For example, for any grid where the blue input tone value is Vbi = Vi ₁ , that is, 0, the blue output tone value corresponds to Vi ₁ in the blue tone curve defined in step S220 of FIG. Vo ₁ , that is, 0. In any grid in which the blue input tone value is Vi ₆ , the blue output tone value is Vo ₆ corresponding to Vi ₆ in the blue tone curve. Further, for the grid having the input tone value that was the second candidate tone value for blue, the output tone value of blue is the output tone value corresponding to the input tone value in the blue tone curve. It is. The same applies to the output gradation values of red and green.

  The three-dimensional lookup tables 104a and 104c generated in the first embodiment do not have input gradation values for all gradation values (0 to 255), but for some input gradation values. Only have output tone values. Specifically, the input gradation value included in the three-dimensional lookup table 104a is Nmax = 17 at the maximum for each color component. If some of the first candidate gradation values are excluded in step S340 of FIG. 7, the input gradation values are less than 17 for at least some of the color components (see FIG. 11). For this reason, the three-dimensional lookup table 104a104c generated in the first embodiment has a three-dimensional lookup having output gradation values for all possible values (0 to 255) of the input gradation values of the respective color components. Less data than tables.

  In step S250 in FIG. 5, the memory color is adjusted with respect to the three-dimensional lookup table 104c to generate the three-dimensional lookup table 104a. Specifically, the three-dimensional lookup table 104a is generated by modifying the output tone value of the grid included in the memory color range in the three-dimensional lookup table 104c generated in S240.

  FIG. 12 is a flowchart showing a procedure for modifying the output tone value of the grid included in the memory color range in the three-dimensional lookup table 104c. In step S252, first, a grid included in the color range of the memory color to be adjusted is specified from the grids of the three-dimensional lookup table 104c. This color range is the color range of the memory color corresponding to the target memory color parameter Pmc determined in step S100 of FIG. Specifically, the color range of the memory color is eight points pc1 (Vcr1, Vcg1, Vcb1) to pc8 (Vcr8, Vcg8, Vcb8) corresponding to the color range Cmi of the target memory color parameter Pmc in the sRGB color space. This is a range defined by a polyhedron having a vertex.

  FIG. 13 is a diagram illustrating a range of memory colors in the three-dimensional lookup table 104c. Points pc1 to pc8 are determined as follows.

As shown in the memory color table 105 of FIG. 3, the color range of the memory color is determined by the ranges for H, S, and B. Assuming that the memory color range is H = Hmin to Hmax, S = Smin to Smax, and B = Bmin to Bmax, the following eight colors (= 2 ⁿ ) are obtained by combining numerical values at both ends of these ranges. c1 to c8 are determined.

c1: (H, S, B) = (Hmin, Smin, Bmin)
c2: (H, S, B) = (Hmin, Smin, Bmax)
c3: (H, S, B) = (Hmin, Smax, Bmin)
c4: (H, S, B) = (Hmin, Smax, Bmax)
c5: (H, S, B) = (Hmax, Smin, Bmin)
c6: (H, S, B) = (Hmax, Smin, Bmax)
c7: (H, S, B) = (Hmax, Smax, Bmin)
c8: (H, S, B) = (Hmax, Smax, Bmax)

  Points pc1 (Vcr1, Vcg1, Vcb1) to pc8 (Vcr8, Vcg8, Vcb8) shown in FIG. 13 are points representing these colors c1 to c8 in the sRGB color system, respectively. In other words, the points pc1 to pc8 are the points c1 to c8 in the color space of the HSB color system, and the maximum value or the minimum value of the range to be modified with respect to H, S, B is set as the gradation of each component. It is a point corresponding to the points c1 to c8 as values. The colors c1 to c8 represented in the HSB color system and the points (colors represented in the sRGB color system) pc1 to pc8 in the sRGB color space have the same relationship such as c1 and pc1. Does not have. That is, for example, colors having different numbers such as c2 and pc7 may correspond. The RGB tone values (Vcr1, Vcg1, Vcb1) to (Vcr8, Vcg8, Vcb8) of the points pc1 to pc8 are stored in the memory color table 105 in advance in association with the memory colors Cm1 to CmM as described above. (Not shown in FIG. 3).

  In step S252 of FIG. 12, a grid included in a range surrounded by a polyhedron having points pc1 to pc8 corresponding to the memory color of the target memory color parameter Pmc determined in step S100 is specified. Then, the following steps S254 to S258 are performed on the grid included in the range surrounded by the points pc1 to pc8.

  In step S254, the output tone values (Vro, Vgo, Vbo) possessed by the grid are converted into HSB color system tone values. In step S256, the gradation values of H, S, and B expressed in the HSB color system are modified.

  FIG. 14 is a diagram showing an example of the contents of the gradation value modification in step S256. FIG. 14A shows the modification contents of the grid color included in Cm1, which is the blue sky color range. The memory color range is assumed to be H = H1 to H4, S = S1 to S4, and B = B1 to B4 (see FIG. 3). In the drawing, H2 and H3 are tone values of hues included in the range of H1 to H4. S2 and S3 are saturation gradation values included in the range of S1 to S4. B2 and B3 are brightness gradation values included in the range of B1 to B4.

  FIG. 14B is a diagram showing a color range in the HSB space defined by H = H1 to H4, S = S1 to S4, and B = B1 to B4. The color range shown in FIG. 14B is a three-dimensional area having a fan-shaped cross section with points c1 to c8 as vertices in the HSB color space. The coordinates of these points c1 to c8 in the HSB space are as described above. When these are indicated by H1, H4, S1, S4, B1, and B4, they are as follows.

c1: (H, S, B) = (H1, S1, B1)
c2: (H, S, B) = (H1, S1, B4)
c3: (H, S, B) = (H1, S4, B1)
c4: (H, S, B) = (H1, S4, B4)
c5: (H, S, B) = (H4, S1, B1)
c6: (H, S, B) = (H4, S1, B4)
c7: (H, S, B) = (H4, S4, B1)
c8: (H, S, B) = (H4, S4, B4)

  As described above, these points c1 to c8, which are the vertices of the region whose gradation value is to be changed in the HSB color space, correspond to the points pc1 to pc8 (see FIG. 13) in the sRGB space. That is, when the combination of gradation values of points c1 to c8 is converted from the HSB color system to the sRGB color system, the combination of gradation values of points pc1 to pc8 is obtained. However, in the points c1 to c8 represented in the HSB color system and the points pc1 to pc8 in the sRGB color space, those having the same number such as c1 and pc1 do not have a correspondence relationship.

  When the hue H of the output color of the grid (referred to as the color specified by the output gradation value of the grid) is in the range of H = H2 to H3, H is modified to (H + dH). . In the example of FIG. 14A, dH = −5. In the range of H = H1 to H2, the modification amount is set so that the modification amount decreases as the value of H is closer to H1, that is, approaches 0. Then, the modification amount is set so that the modification amount approaches dH as the value of H is closer to H2. In the range of H = H3 to H4, the modification amount is set so that the modification amount decreases as the value of H is closer to H4, and approaches dH as the value of H is closer to H3.

  By performing the modification by such a method, when the color of the image is adjusted with reference to the generated three-dimensional lookup table 104a, the color of the image, in particular, the hue is not unnatural. The output value of the dimension lookup table 104a can be determined.

  Further, as shown in the middle part of FIG. 14A, when the saturation S of the output color of the grid is in the range of S = S2 to S3, S is modified to (S + dS). In the example of FIG. 14A, dH = + 15. In the range of S = S1 to S2, the modification amount is set to be smaller as the value of S is closer to S1 and closer to dS as the value of S is closer to S2. In the range of S = S3 to S4, the modification amount is set so that the modification amount is smaller as the S value is closer to S4 and closer to dS as the S value is closer to S3.

  By performing modification in this way, when adjusting the color of the image with reference to the generated three-dimensional lookup table 104a, the color of the image, in particular, the saturation is not unnatural. The output value of the three-dimensional lookup table 104a can be determined.

  The same applies to the brightness B. However, since the modification amount dB is 0 in the color range Cm1, B is not modified in the range of B = B1 to B4 in the example of FIG. However, when the brightness is changed, the color of the image is adjusted by referring to the generated three-dimensional lookup table 104a by changing in the same manner as the hue and saturation described above. In this case, the output value of the three-dimensional lookup table 104a can be determined so that the color of the image, particularly the brightness, does not become unnatural.

  FIG. 15 is a diagram showing the memory color table 105. The values of H1 to H4, dH, S1 to S4, dS, B1 to B4, and dB used for the above-mentioned adjustment of the memory color, and the RGB gradation values (Vcr1, Vcg1, Vcb1) of the above points pc1 to pc8 ) To (Vcr8, Vcg8, Vcb8) are stored in the memory color table 105 in advance. That is, the memory color table 105 stores information as shown in FIG. The LUT generation module 102 calculates the size of each memory color area based on such a memory color table 105 (see step S120 in FIG. 4), and specifies a grid included in the memory color range (FIG. 12). Step S252), the output color of the grid is altered (see step S256).

  In step S258 of FIG. 12, the grid output color modified in step S256 is reconverted to the gradation value of the sRGB color system to obtain the grid output color. In step S260, it is determined whether or not the processing in steps S254 to S258 has been performed for all the grids included in the color range of the memory color to be adjusted. If there are grids that have not been subjected to the processes in steps S254 to S258, the process returns to step S254 to change the output color for those grids. If the processes in steps S254 to S258 have been performed for all the grids included in the color range of the memory color to be adjusted surrounded by the points pc1 to pc8, the process ends.

  In step S250 of FIG. 5, the output color of the grid included in the color range of the memory color among the grids of the three-dimensional lookup table 104c is adjusted by the procedure as described above, and the three-dimensional lookup table 104a is generated ( (See step S200 in FIGS. 1 and 2).

  The three-dimensional lookup table 104a generated in the first embodiment does not have input tone values for all tone values (0 to 255), but outputs only for some input tone values. It has a gradation value (see FIG. 11). Therefore, when the color tone adjustment module 103 (see FIG. 1) converts the initial image data PID while referring to the three-dimensional lookup table 104a to generate the image data PIDr, the three-dimensional lookup table 104a is present. When converting an input gradation value that has not been performed, an interpolation operation is performed. That is, out of the grids that the three-dimensional lookup table 104a has, four grids that are closest to the color to be converted are selected and subjected to tetrahedral interpolation, and each color component that these grids have. The output gradation position of the input gradation value to be converted is calculated from the output gradation value.

  In the first embodiment, when the three-dimensional lookup table 104c that is the basis of the three-dimensional lookup table 104a is generated, the output gradation value of the region where the increase in the output gradation value is large in the tone curve is determined. It has more input tone values (grids) than a region where the increment is small (see FIG. 9). Therefore, when referring to the look-up table 104a, even if the output gradation value is obtained by performing an interpolation operation in a region where the change rate of the output gradation value is large, the output gradation value is obtained for the input gradation values at uniform intervals. Compared to a three-dimensional lookup table having

  When the color tone is adjusted after the three-dimensional lookup table 104c is generated (see 103 in FIG. 1), interpolation is performed at the boundary between the color range in which the output tone value is adjusted and the color range in which the adjustment is not performed. When the image processing is performed, there is a possibility that the image processing according to the desired modification amount is not performed in the vicinity of the boundary. That is, in the example of FIG. 14A, the modification amount of H in the vicinity of H1 and H4 on the upper number line, and the modification amount of S in the vicinity of S1 and S4 on the number line in the middle are shown in FIG. ) May be different from the amount indicated by the straight line.

  However, in the first embodiment, the points pc1 to pc8 that define the boundary between the region in which the output color is modified after the generation of the three-dimensional lookup table 104c and the region where the output color is not changed are always the grids of the three-dimensional lookup tables 104c and 104a. (See pp1 to pp8 in FIG. 11 and FIG. 13). For this reason, after the three-dimensional lookup table 104c is generated, a preferable modification amount is likely to be modified in the vicinity of the boundary between the color range in which the output gradation value is adjusted and the color range in which the adjustment is not performed.

B. Second embodiment:
In the first example, the RGB tone curves were the same (see FIGS. 6 and 9). However, in the second embodiment, the tone curves of the respective color components for adjusting the color tone are different from each other. The portions other than the tone curve generation method of the second embodiment are the same as those of the first embodiment.

  In the second embodiment, the LUT generation module 102 analyzes the reduced image data PID2 (see step S100 in FIG. 2), average values Vra, Vga, Vba of the respective gradation values of red, green, and blue, and the standard deviation σr. , Σg, σb are calculated.

  Then, the LUT generation module 102 calculates the average of red, green, and blue according to the following formulas (8), (9), and (10) in calculating the tone curve setting parameters (see step S210 in FIG. 5). The tone value adjustment parameters dlr, dlg, and dlb are calculated. Note that Vrc, Vgc, and Vbc are target values of the average gradation values of red, green, and blue, respectively, and are, for example, the center value of each gradation value (128 in the second embodiment).

dlr = a × (Vrc−Vra) (8)
dlg = a × (Vgc−Vga) (9)
dlb = a × (Vbc−Vba) (10)

  In step S210, the LUT generation module 102 calculates contrast adjustment parameters dcr, dcg, dcb as setting parameters using the following equations (11) to (16). The contrast adjustment parameters dcr, dcg, dcb are parameters for adjusting the contrast of the image in the finally generated three-dimensional lookup table 104a. Note that b and σr0, σg0, and σb0 in the equations (11) to (16) are positive constants. σr0, σg0, and σb0 are target values of standard deviations of the gradation values of red, green, and blue.

dcr = br × (σr0−σr) (when σr <σr0) (11)
dcr = 0 (when σr ≧ σr0) (12)
dcg = bg × (σg0−σg) (when σg <σg0) (13)
dcg = 0 (when σg ≧ σg0) (14)
dcb = bb × (σg0−σg) (when σb <σb0) (15)
dcb = 0 (when σb ≧ σb0) (16)

  FIG. 16 is a flowchart illustrating a procedure of a tone curve generation method according to the second embodiment. This flowchart shows the content of step S220 of FIG. 5 in the second embodiment. In the following description, red will be described as an example of processing for each color component of red, green, and blue.

  FIGS. 17A and 17B are diagrams showing an example of a method for generating a red tone curve in step S222 of FIG. The horizontal axis of each graph represents the red input gradation value Vri, and the vertical axis represents the red output gradation value Vro. In step S222, the LUT generation module 102 generates a red tone curve based on the average gradation value adjustment parameter dlr and the contrast adjustment parameter dcr. The tone curve generation method based on the setting parameter is substantially the same as the method of generating the tone curve based on the brightness in the first embodiment. That is, first, a provisional output gradation value Vrr1 ′ having a reference input gradation value Vrr1 = 64, which is a gradation value that is ¼ from the lower possible range of the input gradation value of red, is expressed by the following equation (17). )

  Vror1 '= Vrrl + dlr (17)

  Then, the temporary tone curve C1pr is generated as a spline curve passing through the point O (0, 0), the point pr1 ′ (Vri1, Vror1 ′), and the point prmax (Vrimax, Vromax) (see FIG. 17A). . Vrimax and Vromax are the maximum values of the gradation value of red and are 255.

  Thereafter, the LUT generation module 102 further determines an output tone value Vrrl of the reference input tone value Vrir1 = 64, which is a tone value ¼ from the bottom of red, using the following equation (18).

  Vror1 = Vror1'-dcr (18)

  Also, the LUT generation module 102 sets the output tone value Vror2 of the reference input tone value Vrr2 = 192, which is a tone value that is ¼ from the range that the red input tone value can take, by the following equation (19 ) Note that Vror2 'is the output tone value of the reference input tone value Vrr2 in the temporary tone curve C1pr generated based on the average tone value adjustment parameter dlr.

  Vror2 = Vror2 '+ dcr (19)

  On the other hand, the LUT generation module 102 uses the output gradation value Vrr3 of the reference input gradation value Vrr3 = 128, which is a gradation value ½ from the bottom, as the reference input gradation value Vrr3 in the tentative tone curve. The value is equal to the output gradation value Vror3 ′.

  Then, the LUT generation module 102 converts the red tone curve C1r into a point O (0, 0), a point pr1 (Vrr1, Vror1), a point p3r (Vrr3, Vror3), a point p2r (Vrr2, Vror2), and a point prmax ( (Vrimax, Vromax) as a spline curve.

  The generation of the red tone curve has been described above, but the same applies to the green and blue tone curves. The tone curve of each color component is generated based on the average value and standard deviation of the tone values of each color component. For this reason, the shape of each tone curve is different.

  When the red, green, and blue tone curves are generated in step S222, the LUT generation module 102 adjusts the shapes of the red, green, and blue tone curves in step S224.

  FIG. 18 is a diagram showing an example of a tone curve modification method in step S224 of FIG. The LUT generation module 102 outputs the output tone values Vcbro and Vcbgo of the red, green and blue tone curves corresponding to the predetermined input tone value Vcbi based on the red, green and blue tone curves generated in step S222. , Vcbbo is calculated. Then, an average value VcboA of the output gradation values Vcbro, Vcbgo, Vcbbo is calculated. In the second embodiment, the input gradation value Vcbi is set to the central value 128 of the range that the input gradation value of each color component can take.

  When the output tone values Vcbro, Vcbgo, Vcbbo of the red, green, and blue tone curves corresponding to the input tone value Vcbi are not in the range of plus or minus Vw centering on the average value VcboA, the output is not in that range. Change the tone value.

  When the output gradation value Vcbo corresponding to the input gradation value Vcbi of a certain tone curve is larger than (VcboA + Vw), the LUT generation module 102 changes the output gradation value Vcbo to (VcboA + Vw). The output gradation values corresponding to the other input gradation values are each multiplied by c1 (c1> 0). c1 is closer to (VcboA + Vw) / Vcbo as the input gradation value is closer to Vcbi, and is closer to 1 as the input gradation value is closer to 0 or Vimax.

  In the example of FIG. 18, such a modification is performed on the green tone curve Cgo. In FIG. 18, the green tone curve Cgo before modification is indicated by the green tone curve Cgr after modification. In FIG. 18, a point on the tone curve Cgo before modification corresponding to the input gradation value Vcbi is indicated by pgo, and its output gradation value is indicated by Vcbgo. A point on the tone curve Cgr after modification corresponding to the input gradation value Vcbi is indicated by pgr.

  When the output gradation value Vcbo corresponding to the input gradation value Vcbi of a certain tone curve is smaller than (VcboA−Vw), the LUT generation module 102 changes the output gradation value Vcbo to (VcboA−Vw). To do. The output gradation values corresponding to the other input gradation values are each multiplied by c2 (c2> 0). c2 is closer to (VcboA−Vw) / Vcbo as the input gradation value is closer to Vcbi, and is closer to 1 as the input gradation value is closer to 0 or Vimax.

  In the example of FIG. 18, such a modification is performed for the blue tone curve Cbo. In FIG. 18, a blue tone curve Cbo before modification is shown, and a blue tone curve Cbr after modification is shown. In FIG. 18, a point on the blue tone curve Cbo before modification corresponding to the input gradation value Vcbi is indicated by pbo, and the output gradation value is indicated by Vcbbo. A point on the tone curve Cbr after modification corresponding to the input gradation value Vcbi is indicated by pbr.

  As described above, in step S224 of FIG. 16, the tone curve is modified so that the variation of the output tone value in the vicinity of the center of the input tone value in each tone curve falls within a predetermined range. By performing such processing, when color adjustment according to the tone curve is performed, that is, when color conversion is performed according to the finally generated three-dimensional lookup table 104a, before and after conversion. It is possible to prevent a situation in which the hue changes greatly.

  Hereinafter, based on the generated red, green, and blue tone curves, the three-dimensional lookup table 104a is generated in the same procedure as in the first embodiment. Even in such an aspect, the adjustment of the color tone for the color range of the memory color can be executed with a preferable modification amount.

C. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

C1. Modification 1:
In the above embodiment, when there are more than the predetermined number L of input gradation values corresponding to the difference dv _k greater than the threshold value Th, the input gradation values of the predetermined number L are selected from the ones having the larger difference. Thus, at least a part of the input gradation values included in the lookup table is used (see step S238 in FIG. 8). However, the determination of the input gradation value is not limited to such a method, and may be determined by another method.

  For example, all the input gradation values associated with the difference larger than the threshold value Th may be selected as the input gradation values of the lookup table. Alternatively, a predetermined number of input tone values may be selected as the input tone values of the lookup table from the beginning, in the descending order of the associated difference, without determining whether the threshold value is large or small.

  That is, the selection of the input tone value of the lookup table is performed by selecting the input tone value that is a candidate at a certain stage as the first increase rate of the output tone value corresponding to each input tone value. When the group is divided into a group having a smaller increase rate than the first group, at least a part of the input tone values of the first group having the larger increase rate is at least one of the input tone values of the lookup table. What is necessary is just to be selected as a part. With such an aspect, the input tone value of the lookup table is set for a portion where the change in the output tone value is larger than the change in the input tone value. As a result, when the look-up table is used for color tone adjustment (see the color tone adjustment module 103 in FIG. 1), the image quality is unlikely to deteriorate even if interpolation processing is performed.

C2. Modification 2:
In the above embodiment, when determining the input gradation value of the lookup table, the next smallest input is associated with a plurality of input gradation values having a certain interval among the input gradation values of the tone curve. The difference of the output gradation value from the gradation value was obtained. Then, the input gradation value of the lookup table is determined based on the magnitude of the difference. However, the input tone value of the lookup table may be determined by other methods.

  For example, the difference between the output gradation value and the next largest input gradation value is obtained by associating with each candidate input gradation value having a predetermined interval, and based on the magnitude of the difference, the look It is also possible to determine the input tone value of the uptable. Further, an increment of the output tone value with respect to an increment of the input tone value smaller than the interval between the candidate input tone values is obtained, and the input level of the lookup table is determined based on the magnitude of the increment of the output tone value. A key value may be determined. That is, the input tone value of the lookup table can be determined based on the increasing rate of the output tone value of the tone curve. Here, the “increase rate” of the output gradation value is an increase amount of the output gradation value with respect to a constant increase amount of the input gradation value.

C3. Modification 3:
In the above embodiment, when the tone curve of each color component is determined based on the analysis result of the reduced image data, a process for adjusting the brightness and a process for adjusting the contrast are performed. (See FIGS. 6 and 17). However, when determining the tone curve of each color component, other processes can be performed. For example, for a predetermined input tone value range including the minimum input tone value Vimin, a tone curve can be formed so that the minimum output tone value Vomin is output. Then, a tone curve can be formed so as to output the maximum output gradation value Vomax for a predetermined input gradation value range including the maximum input gradation value Vimax.

  Further, in the above-described embodiment, the operation amount for determining the shape of the tone curve is determined using the target average value and the target dispersion regarding the brightness and tone value of the color component. (See formulas (2), (4), (8) to (11), (13) and (15)). However, the operation amount when determining the shape of the tone curve can be determined based on other amounts. For example, the operation amount can be determined based on the maximum value or the minimum value of the brightness or the gradation value of the color component. That is, the tone curve can be generated based on the result of direct or indirect analysis of image data to be subjected to image processing.

C4. Modification 4:
In the above embodiment, the initial image data PID and the reduced image data PID2 are image data in which the color of each pixel is expressed in the sRGB color system. However, the image data to be processed is image data in which colors are expressed in other color systems such as the xyz color system, the L ^* a ^* b ^* color system, the L ^* u ^* v ^* color system. There may be.

C5. Modification 5:
In the above embodiment, the adjustment of the color relating to the memory color is performed by once converting the combination of the output gradation values of the sRGB color system into the combination of the output gradation values of the HSB color system and then outputting the output gradation of the HSB color system. The values were changed and inversely converted into combinations of output gradation values of the sRGB color system. However, when some colors are modified, such as adjusting the color related to the memory color, it is converted to another color system such as L ^* a ^* b ^* color system or L ^* u ^* v ^* color system. You can also However, the converted color system is preferably a color system including a gradation value related to lightness as one gradation value. With such an aspect, it is possible to adjust the color so that the brightness, brightness, and saturation are changed according to the human sense.

C6. Modification 6:
When determining the input tone value of the lookup table based on the tone curve of each color component, the threshold value Th and the number Nmax of input tone values can be made different for each color component. For example, for a color component with a small change in the increase rate of the output gradation value in the tone curve, the number N of input gradation values is set smaller than a color component with a large change in the increase rate of the output gradation value in the tone curve. You can also

C7. Modification 7:
In the above embodiment, when generating a tone curve for each color component, the output tone value for the 1/4 tone value from the bottom of the range that the input tone value can take is modified to adjust the brightness of the image. The function to perform was added to the tone curve (see FIG. 6A). However, when the brightness adjustment function is added to the tone curve, output corresponding to other input tone values, such as changing the output tone value for the tone value of 1/3 or 1/2 from the bottom, is performed. You may carry out by changing a gradation value. That is, when the brightness adjustment function is added to the tone curve, it can be performed by modifying the output tone value corresponding to the predetermined input tone value.

  Further, in the above embodiment, when generating the tone curve of each color component, the output gradation values for the gradation values from the bottom 1/4 and the top 1/4 from the range that the input gradation value can take are obtained. It was modified to give a contrast adjustment function to the tone curve (see FIG. 6B). However, when the function for adjusting the contrast of the image is added to the tone curve, the output is applied to the gradation value of 1/3 or 1/2 from the bottom and the gradation value of 1/3 or 1/2 from the top. You may carry out by changing the output gradation value corresponding to other input gradation values, such as changing a gradation value.

  That is, when the contrast adjustment function is added to the tone curve, the output gradation value corresponding to the predetermined first input gradation value is decreased, and a predetermined second value larger than the first input gradation value is set. This can be done by increasing the output tone value corresponding to the input tone value. At this time, for the third input tone value that is larger than the first input tone value and smaller than the third input tone value, when the first and second input tone values are modified, It is preferable not to modify the output tone value.

  Furthermore, when determining the shape of the tone curve, the tone is set so that the input tone value of each color component representing a predetermined range of colors such as skin color approaches the tone value of each color component representing the target color. The shape of the tone curve can be determined in consideration of other factors such as determining the shape of the curve. That is, the tone curve is automatically generated based on the initial image data PID or the reduced image data PID2.

C8. Modification 8:
In the first embodiment, first the first candidate gradation value based on the shape of the tone curve is determined, and then the second candidate gradation value based on the target memory color is determined (step S310 in FIG. 7). And S320). However, either of the first and second candidate gradation values can be determined first, or can be determined in parallel.

C9. Modification 9:
In the first embodiment, the second candidate gradation value is a gradation value of a color that defines a color range in which the output gradation value is modified based on the memory color (see FIGS. 11 and 13). However, the second candidate gradation value can also be a gradation value determined based on other factors. That is, the second candidate gradation value is generated based on a parameter that determines the color range to be modified in an aspect in which the output gradation value is modified for a part of the color range after the three-dimensional lookup table is generated. The determined gradation value can be used.

  For example, when the color range for which the output tone value is to be modified is a spherical color range determined by the tone value of each color component representing the color of the center point and the radius, the second color range is used. The candidate gradation value can be a gradation value determined based on the gradation value of each color component representing the color of the center point and the size of the radius. However, it is preferable that the tone value of the color located on the boundary of the color range to be modified in the color space defined by the input tone value of the lookup table is the second candidate tone value.

C10. Modification 10:
In the first example, the first candidate gradation value within the range of plus or minus dn of the second candidate gradation value is excluded from the first candidate gradation value (step S340 in FIG. 7). reference). And dn was 4. However, other criteria can be used when excluding the first candidate tone value having a value close to the second candidate tone value. For example, the value dn that serves as a reference for determining whether or not the second candidate gradation value is in the vicinity of the second candidate gradation value can be determined by the ratio of the first candidate gradation value to the interval di. dn is preferably a value less than 30% of the interval di of the first candidate gradation values, and more preferably a value less than 20% of di. Further, dn is more preferably a value less than 15% of the interval di of the first candidate gradation values.

C11. Modification 11:
In the above embodiment, the tone curve is generated by a spline curve that passes through a reference point. However, when the tone curve is generated, it can be generated by other curves such as an (m + 1) degree curve passing through m points (m is an integer of 3 or more) serving as a reference.

C12. Modification 12:
In the above embodiment, the maximum number L2 of the first candidate tone values based on the difference dv _k was seven. The maximum number Nmax of input gradation values in the three-dimensional lookup table 104a is 17. However, the maximum number L2 of the first candidate gradation values and the maximum number Nmax of the input gradation values of the three-dimensional lookup table 104a can be other numbers. However, it is preferable that L2 = Nmax−2−2 ⁿ . Here, n is the number of color components that the initial image data PID has. Therefore, 2 ⁿ is the number of points that define each color range Cmi (see FIG. 13). For example, when the initial image data PID to be processed is sRGB color system image data, since n = 3, L2 = Nmax−10.

C13. Modification 13:
In the above embodiment, the reduced image data is analyzed, the shape of the tone curve is determined based on the analysis result, and the lookup table is generated based on the tone curve (see FIG. 5). However, when the lookup table is generated based on the analysis result of the reduced image data, the lookup table can be generated without changing the shape of the tone curve based on the analysis result.

  For example, as described in the first embodiment, a specific modification may be performed for a specific range of colors, such as a tree green or sky blue (see FIGS. 3 and 13). In such a case, the reduced image data generated from the image data to be processed is analyzed to determine which range of colors is to be processed and which range of colors is not to be processed (step of FIG. 1). Based on the determination, an n-dimensional lookup table may be generated. At this time, the tone curve that is the basis of the n-dimensional lookup table can be generated without being based on the analysis result of the reduced image data.

  That is, as one aspect of the present invention, when a lookup table used for image conversion is generated, the analysis result of the reduced image data of the image data to be converted is directly or indirectly reflected, and the lookup table The mode which produces | generates can be employ | adopted.

C14. Modification 14:
In the above embodiment, the three-dimensional lookup table 104a is generated based on the reduced image data PID2 generated by reducing the initial image data PID. However, in another aspect, a part of the initial image data PID may be sampled and analyzed, and a lookup table used when adjusting the image based on the analysis result may be generated. In other words, the look-up table for adjusting the color of the image data can be generated directly or indirectly based on the image data to be processed.

C15. Modification 15:
In the above embodiment, tetrahedral interpolation is performed when referring to the lookup table 104a. However, when referring to the look-up table 104a, other interpolation is used, such as cubic interpolation that performs interpolation using the output gradation values of the six grids surrounding the color point to be converted. You can also.

C16. Modification 16:
As in the above-described embodiment, the modification amount of the gradation value of the HSB color system in the tone adjustment (see FIG. 14A) is a value determined in advance for each gradation value of the HSB color system. There may be. Further, a calculation formula may be determined in advance, and the modification amount may be calculated by substituting each gradation value of the HSB color system into the calculation formula. The latter mode is also included in the mode in which the size is changed by a “predetermined amount” according to the gradation value. Note that the “predetermined amount” according to the gradation value may be zero.

C17. Modification 17:
In the embodiment described above, the end of the range in which the hue (H), saturation (S), and brightness (B) are modified in the HSB color system, which is a color system including lightness gradation (FIG. 14 (a)). The three-dimensional lookup table 104c is determined so that the points on the color space of the sRGB color system corresponding to the combinations of H1, H4, S1, S4, B1, and B4) are grids. However, when generating an n-dimensional lookup table that is referred to during color adjustment, the following input gradation value is determined as the input gradation value of the original lookup table 104c ′, and n It is also preferable to generate a dimension lookup table 104a. The gradation value is the maximum value or the minimum value (H2, H3, S2, S3, B2 in FIG. 14A) in a range in which a certain amount of modification is performed in a converted color system such as the HSB color system. , B3) is a combination of gradation values corresponding to the combination of gradation values c9 to c16 having the gradation value of each component. c9 to c16 are shown in FIG.

c9: (H, S, B) = (H2, S2, B2)
c10: (H, S, B) = (H2, S2, B3)
c11: (H, S, B) = (H2, S3, B2)
c12: (H, S, B) = (H2, S3, B3)
c13: (H, S, B) = (H3, S2, B2)
c14: (H, S, B) = (H3, S2, B3)
c15: (H, S, B) = (H3, S3, B2)
c16: (H, S, B) = (H3, S3, B3)

  FIG. 19 is a diagram illustrating points pc9 (Vcr9, Vcg9, Vcb9) to pc16 (Vcr16, Vcg16, Vcb16) on the sRGB space corresponding to the points c9 to c16 on the HSB space. In the aspect of the modified example 17, the points pc1 to pc16 are grids of the three-dimensional lookup tables 104c 'and 104a. That is, the input tone values of the points pc1 to pc16 become the input tone values of the respective color components of the three-dimensional lookup tables 104c 'and 104a. With such an aspect, it is possible to use an accurate output gradation value at a boundary portion where the color modification method changes. In addition to the above-described aspects, the amount of color modification, that is, the boundary portion where the calculation formula applied when determining the modification amount of the output gradation value changes, or after modification to the output gradation value before modification. For the boundary part where the color modification method changes widely, such as the boundary part where the ratio of the output gradation value changes, the combination of gradation values corresponding to the color on the boundary is the input gradation value (grid) of the lookup table It is preferable that

C18. Modification 18:
The n-dimensional lookup table can be in the following manner. That is, the n-dimensional lookup table does not have output tone values for all combinations of input tone values, but has output tone values for some combinations of input tone values. . Then, when the n-dimensional lookup table is referred to, a plurality of output gradation values possessed by the n-dimensional lookup table are read out, and interpolation processing is performed using them to perform image processing. used. In such an aspect, as described above, it is particularly preferable to determine the input tone value of the lookup table based on the color range in which the color is changed.

C19. Modification 19
In the above embodiment, a part of the configuration realized by hardware may be replaced with software, and conversely, a part of the configuration realized by software may be replaced by hardware. For example, a part of the function of the printer driver 96 (see FIG. 2) can be executed by a hardware circuit.

  A computer program for realizing such a function is provided in a form recorded on a computer-readable recording medium such as a floppy disk or a CD-ROM. The host computer reads the computer program from the recording medium and transfers it to the internal storage device or the external storage device. Alternatively, the computer program may be supplied from the program supply device to the host computer via a communication path. When realizing the function of the computer program, the computer program stored in the internal storage device is executed by the microprocessor of the host computer. Further, the host computer may directly execute the computer program recorded on the recording medium.

  In this specification, the host computer is a concept including a hardware device and an operation system, and means a hardware device that operates under the control of the operation system. The computer program causes such a host computer to realize the functions of the above-described units. Note that some of the functions described above may be realized by an operation system instead of an application program.

  In the present invention, the “computer-readable recording medium” is not limited to a portable recording medium such as a flexible disk or a CD-ROM, but an internal storage device in a computer such as various RAMs and ROMs, An external storage device fixed to a computer such as a hard disk is also included.

FIG. 2 is a block diagram illustrating a software configuration of the printing system according to the first embodiment. 7 is a flowchart showing processing in the LUT generation module 102. FIG. 5 is a view showing a part of the contents of a memory color table 105. 10 is a flowchart showing a procedure for determining a target memory color parameter representing the content of adjustment relating to a memory color. The flowchart which shows the production | generation procedure of the three-dimensional lookup table 104a in step S200 of FIG. The figure which shows an example of the production | generation method of the tone curve in step S220 of FIG. 6 is a flowchart showing a procedure for determining an input tone value of the three-dimensional lookup table 104a in step S230 of FIG. 6 is a flowchart showing a procedure for determining an input tone value of the three-dimensional lookup table 104a in step S230 of FIG. The figure which shows the method of determining the input gradation value of the three-dimensional lookup table 104a on the tone curve C1. The figure which shows the grid located on the plane of the blue input gradation value Vbi = 0 in the three-dimensional lookup table 104c by the black dot surrounded by the circle. The figure which shows the grid of the three-dimensional lookup table 104c defined by the input gradation value determined in step S350 of FIG. The flowchart which shows the procedure which modifies | changes about the output gradation value of the grid included in the range of a memory color among the three-dimensional lookup tables 104c. The figure which shows the range of a memory color among the three-dimensional lookup tables 104c. The figure which shows an example of the content of the modification of the gradation value in step S256. The figure which shows the memory color table 105. FIG. The flowchart which shows the procedure of the production | generation method of the tone curve in 2nd Example. The figure which shows an example of the production | generation method of the red tone curve in step S222 of FIG. The figure which shows an example of the modification method of the tone curve in step S224 of FIG. The figure which shows the points pc9 (Vcr9, Vcg9, Vcb9) to pc16 (Vcr16, Vcg16, Vcb16) on the sRGB space corresponding to the points c9 to c16 on the HSB space.

Explanation of symbols

21 ... CRT display 22 ... Printer 28 ... Print head 31 ... Carriage 32 ... Operation panel 41 ... CPU
42 ... ROM
DESCRIPTION OF SYMBOLS 90 ... Computer 91 ... Video driver 95 ... Application program 96 ... Printer driver 97 ... Resolution conversion module 98 ... Color conversion module 99 ... Halftone module 100 ... Rearrangement module 101 ... Reduced image generation module 102 ... LUT generation module (lookup table) Generation module)
DESCRIPTION OF SYMBOLS 103 ... Color tone adjustment module 104a, 104b ... Color conversion table 105 ... Memory color table 120 ... Keyboard 130 ... Mouse C1 ... Tone curve C1r ... Red tone curve C1p ... Temporary tone curve C1pr ... Red temporary tone curve Cbo ... Blue tone curve before modification Cbr ... Blue tone curve after modification Cgo ... Green tone curve before modification Cgr ... Green tone curve after modification Cm1 to CmM ... Color range of memory colors FNL ... Print image data Lrg ... (Red input gradation value Vri) = (Green input gradation value Vgi) straight line MID1 ... Image data obtained by converting the resolution of the image data PIDr MID2 ... Image data obtained by color-converting the image data MID1 MID3 ... Dot ON / Image data that is displayed with the image turned off Data (print image data)
MS: Head transport direction (main scanning direction)
O: Point where input gradation value and output gradation value are both the lowest value ORG: Original image data P ... Printing paper PID ... Initial image data PID2 ... Reduced image data PIDr ... Image data with adjusted color tone of initial image data Pmc ... Target memory color parameter SS ... Printing paper transport direction (sub-scanning direction)
Vcb1 to Vcb8: Blue gradation values at points pc1 to pc8 Vcg1 to Vcg8 ... Green gradation values at points pc1 to pc8 Vcr1 to Vcr8 ... Red gradation values at points pc1 to pc8 Vir1 ... Reference input floor of tone curve Tone value Vor1... Reference output tone value corresponding to reference input tone value Vir1 Vor1 '... Temporary output tone value corresponding to reference input tone value Vir1 Vir2... Tone curve reference input tone value Vor2. Reference output tone value Vor2 'corresponding to the input tone value Vir2 Temporary output tone value Vir3 corresponding to the reference input tone value Vir2 Reference input tone value Vor3 of the tone curve Vor3 ... Reference input tone value Vir3 Reference output tone value Vor3 ′ corresponding to the reference output tone value Vir3 Provisional output tone value Vri corresponding to the reference input tone value Vir3 Red input tone value Vg i ... Green input tone value Vbi ... Blue input tone value Vrr1 ... Red tone curve reference input tone value Vrr1 ... Red reference input tone value Vrr1 corresponding to the reference output tone value Vrr1 '... Red The provisional output tone value Vrr2 corresponding to the reference input tone value Vrr2 of the red tone curve Vrr2... The reference output tone value Vrr2 corresponding to the reference input tone value Vrr2 of red. Temporary output tone value Vrr3 corresponding to the red reference input tone value Vrir2 ... Reference input tone value Vror3 of the red tone curve Vror3 ... Reference output tone value Vror 3 'corresponding to the red reference input tone value Vrir3 ... Temporary output gradation value Vw corresponding to the red reference input gradation value Vrir 3 ... Output gradation corresponding to the input gradation value Vcbi Vcbro, Vcbgo, Vcbbo A quantity that defines the width of the range to be located within the pixel range Vy ... Lightness c1 to c8 ... A point that defines the range in which the color tone is adjusted in the HSB color space c1 to c16 ... in the HSB color space Points corresponding to the grid of the three-dimensional lookup table dB: Brightness (B) modification amount dc: Contrast adjustment parameter dcr: Red contrast adjustment parameter di: First candidate tone value interval dl: Brightness adjustment parameter dlr: average tone adjustment parameter for red dv _k ... difference in output tone value corresponding to input tone value having a predetermined interval p1 ... point corresponding to the first reference input tone value in the tone curve p2 ... tone curve Point corresponding to the second reference input tone value in p3... Corresponding to the third reference input tone value in the tone curve Points pc1 to pc8 ... Points that define the range of color tone adjustment in the sRGB color space pc1 to pc16 ... Points that become the grid of the three-dimensional lookup table in the sRGB color space pp1 to pp8 ... Color tone adjustment in the RG plane Pr1 ... Points corresponding to the first reference input gradation value in the red tone curve pr2 ... Points corresponding to the second reference input gradation value in the red tone curve pr3 ... Red tone curve Point corresponding to the third reference input gradation value pmax ... point corresponding to the maximum input gradation value Vmax in the tone curve σy ... standard deviation of brightness σr ... standard deviation of red gradation value

Claims (14)

An image processing apparatus,
A reduced image data generation unit that reduces the image of the first image data to be processed and generates second image data;
A lookup table generation unit that analyzes the second image data and generates a lookup table for performing conversion for modifying at least a part of the color of the image data based on the result of the analysis;
An image conversion unit that converts the first image data with reference to the lookup table. The apparatus of claim 1, comprising:
The first image data includes gradation values of n types (n is an integer of 2 or more) components of the first color system,
The lookup table is an n-dimensional color correction lookup table having a combination of n kinds of gradation values of the component as input values and output values, respectively.
The lookup table generator is
An n-dimensional lookup table having combinations of n kinds of gradation values of the components as input values and output values, respectively, and a color space of the first color system defined based on the result of the analysis Generating an original lookup table having, as input gradation values, gradation values determined according to a partial color range of
An image for generating the color correction lookup table by modifying a corresponding output gradation value for a first combination representing a color included in the color range among combinations of input gradation values of the original lookup table Processing equipment. The apparatus of claim 2, comprising:
The look-up table generation unit is configured to generate a first color system gradation representing a first reference point that is at least one point on a boundary of the color range in the color space of the first color system. An image processing apparatus that uses a combination of values as an input gradation value included in the original lookup table. The apparatus of claim 3, wherein
The lookup table generation unit, when modifying the output tone value of the original lookup table,
Converting a combination of output gradation values corresponding to the first combination of input gradation values into a combination of gradation values by a second color system having a component representing brightness;
Modifying the magnitude of the gradation values of at least some components of the combination of gradation values after the conversion,
The combination of the gradation values after the modification of the size is converted into the combination of the gradation values of the component of the first color system, and the modification of the output gradation value of the original lookup table An image processing apparatus. An apparatus according to claim 4, wherein
The lookup table generation unit targets gradation values within a first gradation value range determined according to the color range for gradation values of each component of the second color system, Modifying the size by a predetermined amount according to the size of the gradation value,
The first reference point is a point in the color space of the second color system, and is the maximum value or the minimum value of the first gradation value range of each component of the second color system. An image processing apparatus that corresponds to a point that is included as a gradation value of each component. The apparatus of claim 5, comprising:
The look-up table generation unit is configured to obtain gradation values of at least some components of the second color system.
The size is modified by a certain amount for a gradation value that is in a predetermined gradation value range and that is in a second gradation value range included in the first gradation value range. ,
For gradation values that are within the first gradation value range and not included in the second gradation value range, gradation values closer to the second gradation value range are closer to the fixed amount. An image processing apparatus that modifies the size by modifying the amount. The apparatus of claim 6, comprising:
The lookup table generation unit is a combination of gradation values of the first color system, and has the maximum value or the minimum value of the second gradation value range as the gradation value of each component. 2. An image processing apparatus, wherein a combination of gradation values corresponding to a combination of gradation values of two color systems is an input gradation value included in the original lookup table. The apparatus of claim 3, wherein
The color range is a range surrounded by a polyhedron having a plurality of color points as vertices in the color space represented by the first color system,
In the lookup table generation unit, the original lookup table has at least some combinations of gradation values among combinations of gradation values representing the plurality of color points as the first reference point. An image processing apparatus that uses an input gradation value. The apparatus of claim 2, comprising:
The look-up table generation unit selects a candidate color range having a largest area occupied by a color included in the candidate color range in the image of the second image data from among a plurality of predetermined candidate color ranges. An image processing apparatus that determines the color range. The apparatus of claim 9, comprising:
The image processing apparatus, wherein the candidate color range is a color range to be modified based on a memory color. The apparatus of claim 2, comprising:
The lookup table generator is
N tone curves having discrete tone values of the same type of component of the first color system as input values and output values, respectively, are generated based on the results of the analysis;
An image processing apparatus that generates the original look-up table for which at least one component has a smaller number of gradations of input values than the tone curve, based on the n tone curves. The apparatus of claim 11, comprising:
When generating the original lookup table, the lookup table generator generates a plurality of input gradation values of the tone curve that are predetermined as input gradation value candidates that the original lookup table should have. Are divided into a first group and a second group having a larger increase rate of the corresponding output gradation value than the first group, the input gradation values included in the second group are An image processing apparatus that determines at least a part of an input gradation value included in the original lookup table. An image processing method comprising:
(A) reducing the image of the first image data to be processed to generate second image data;
(B) analyzing the second image data;
(C) generating a lookup table for performing conversion to modify at least part of the color of the image data based on the result of the analysis of the second image data;
(D) converting the first image data with reference to the lookup table. A computer program for image processing,
A function of reducing the image of the first image data to be processed to generate second image data;
A function of analyzing the second image data;
A function of generating a look-up table for performing conversion for modifying the color of at least a part of the image data based on the result of the analysis of the second image data;
A computer program for causing a computer to realize a function of converting the first image data while referring to the lookup table.

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