JP2009239419A - Profile preparation method, profile preparation apparatus, profile preparation program and printing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prepare a profile for achieving high color reproducibility. <P>SOLUTION: When preparing a profile specifying the correspondence relation between a camera RGB space and a CIELAB space used by a DSC 20, on the basis of the correspondence relation between the colorimetric XYZ values of a plurality of color patches CPs and a camera RGB value obtained by inputting the color patches CPs through the image DSC 20, a multigrid 3D-LUT specifying the correspondence relation between the camera RGB space and the CIELAB space is prepared. Then, the multigrid 3D-LUT is referred to and the multigrid 3D-LUT is adjusted so as to reduce the color difference ΔE between a converted XYZ value and colorimetric XYZ value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a profile creation method, a profile creation apparatus, a profile creation program, and a printing apparatus.

A method has been proposed in which a device-dependent color space used in a digital still camera is converted into an independent space, and a profile for performing color correction for each scene is created (see Patent Document 1).
According to the profile created by such a method, color correction can be performed simultaneously with the conversion to the independent space, and the processing can be made efficient.
JP 2007-258868 A

When color correction is not performed, it is desirable that the color photographed by the digital still camera matches the color in the independent space converted by the profile. However, in the above-mentioned document, there has been a problem that high color reproducibility cannot be realized because it has not been verified whether the color converted by the profile has changed from the original color.
SUMMARY An advantage of some aspects of the invention is that it provides a profile creation method, a profile creation apparatus, a profile creation program, and a printing apparatus that create a profile that achieves high color reproducibility.

  In order to solve the above-described problems, the present invention provides a colorimetric value of a plurality of color patches when creating a profile that defines a correspondence relationship between an input color space used by an image input device and a predetermined target color space. And a correspondence relationship between the color patch and an input value input by the image input device. Then, a lookup table that defines the correspondence between the input color space and the target color space is created based on the correspondence. A conversion value is obtained by converting the input value with reference to the lookup table, and the lookup table is adjusted so as to reduce a deviation between the conversion value and the colorimetric value. The profile is created based on the look-up table adjusted in this way. Since the look-up table is adjusted so as to reduce the deviation between the conversion value and the colorimetric value, high color reproducibility can be realized by the profile. The deviation may be an index of a color difference, and for example, a color difference can be used.

  Further, as an example of a specific method of the adjustment, the hue and saturation are adjusted while maintaining the lightness of the color value in the target color space corresponding to the vertex of the input color space defined in the lookup table. It may be. That is, by adjusting only the hue and the saturation while maintaining the brightness of the color value in the target color space, the brightness adjustment can be performed individually. Further, by limiting the adjustment target to the color values corresponding to the vertices of the input color space, the adjustment work can be facilitated.

  Further, in order to facilitate the adjustment work, the deviation and the distribution of the converted value and the colorimetric value may be displayed for each brightness area in a predetermined color space. In this way, it is possible to easily grasp what tendency the deviation has in each brightness range, and preferable adjustment can be performed. For example, it is possible to make adjustments so that the lightness range where the deviation is conspicuous or the lightness range which is frequently used is emphasized.

  In creating the lookup table based on the correspondence between the colorimetric value and the input value, first, the input color space and the target color are based on the correspondence between the colorimetric value and the input value. You may make it produce the matrix which prescribes | regulates the correspondence with space. For example, a matrix that fits the correspondence between the colorimetric values and the input values may be calculated by a matrix least square method. Further, the lightness of each color value of the target color space defined in the lookup table is normalized based on the white lightness obtained by converting the white point of the input color space using the created matrix. . By doing so, it is possible to limit the range that the brightness value of each color value of the target color space can take in the look-up table, and for example, it is possible to prevent overexposure due to excessive brightness. Since this normalization causes an adverse effect that the brightness is shifted as a whole, it is desirable to reduce the adverse effect by adjusting the brightness with a tone curve.

  Furthermore, the technical idea of the present invention can be implemented not only by a specific profile creation method but also by a profile creation apparatus. That is, the present invention can be specified as a profile creation apparatus having means corresponding to each step performed by the profile creation method described above. Of course, when the above-described profile creation apparatus reads the program to implement each of the above-described means, the technical features of the present invention can be applied to a program for executing a function corresponding to each of the means and various recording media on which the program is recorded. It goes without saying that the idea can be embodied. Needless to say, the profile creation apparatus of the present invention can be distributed not only by a single apparatus but also by a plurality of apparatuses. Further, the profile creation method of the present invention may be realized in a printing apparatus such as a printer or an image input apparatus such as a digital still camera, or a printing apparatus or digital device using a profile created by the profile creation method of the present invention. The effect of the present invention can also be exhibited in an image input device such as a still camera.

Hereinafter, embodiments of the present invention will be described in the following order.
1. Configuration of profile creation device:
2. Profile creation process:
3. Variations:

1. Configuration of Profile Creation Device FIG. 1 shows the configuration of a computer that specifically implements a profile creation device according to an embodiment of the present invention. In FIG. 1, a computer 10 includes a CPU 11, a RAM 12, a ROM 13, a hard disk drive (HDD) 14, a general purpose interface (GIF) 15, a video interface (VIF) 16, an input interface (IIF) 17, and a bus 18. The bus 18 implements data communication between the elements 11 to 17 constituting the computer 10, and communication is controlled by a chip set (not shown). The HDD 14 stores program data 14a for executing various programs including an operating system (OS), and the CPU 11 executes calculations according to the program data 14a while expanding the program data 14a in the RAM 12. . Further, the HDD 14 stores a conversion profile 14b that defines color conversion rules between non-device-dependent color spaces. According to the conversion profile 14b, the XYZ space, the CIELAB space, and the sRGB space can be mutually converted.

  The GIF 15 provides an interface conforming to the USB standard, for example, and connects an external digital still camera (DSC) 20 and a colorimeter 30 to the computer 10. The VIF 16 connects the computer 10 to an external display 40 and provides an interface for displaying an image on the display 40. The IIF 17 connects the computer 10 to an external keyboard 50a and a mouse 50b, and provides an interface for the computer 10 to acquire input signals from the keyboard 50a and the mouse 50b.

  FIG. 2 shows a software configuration of a program executed in the computer 10. In the figure, an operating system (OS) PG1, a profile creation application (APL) PG2, and a colorimeter driver PG3 are executed. The OS PG1 provides an interface between the programs, and the colorimeter driver PG3 executes a process for controlling the colorimeter 30. APL_PG2 includes a UI unit PG2a, a colorimetric value acquisition unit PG2b, an input value acquisition unit PG2c, a matrix generation unit PG2d, a 3D-LUT generation unit PG2e, a 3D-LUT adjustment unit PG2f, a tone curve generation unit PG2g, and a memory color correction unit PG2h. And a profile creation unit PG2i. Details of processing executed by each of the modules PG2a to PG2i constituting the image processing application PG2 will be described together with a flow of image processing described later.

2. Profile Creation Processing FIG. 3 shows the flow of profile creation processing according to this embodiment. The profile creation processing of this embodiment defines the correspondence between RGB values (hereinafter referred to as camera RGB values) defined in the input color space depending on the DSC 20 and the non-device-dependent target color space. This is a process for creating a profile. The DSC 20 outputs image data in which the color of each pixel constituting the photographed image is represented by a camera RGB value (in this embodiment, each RGB channel is represented by 8 bits), and the profile is This is necessary to convert the color indicated by each pixel of the image data into a color value in a non-device-dependent color space. In particular, since the DSC 20 is an image input device, the profile is called a source ICC profile. Of course, the profile creation method of the present invention can also be applied when creating a profile for other image input devices such as a scanner, a film scanner, and a digital video camera. .

  First, in step S100, the DSC 20 is caused to photograph a predetermined color chart CC, and the colorimeter 30 is caused to measure the color of the color chart CC. At this time, the color chart CC photographed by the DSC 20 and the color chart CC colorimetric by the colorimeter 30 are the same, and the environment light source for photographing and colorimetry is the same. In this embodiment, it is assumed that photographing and colorimetry are performed under a CIE_D55 light source as a standard natural light source. The color chart CC is composed of a plurality of color patches CP each showing a different color, and it is desirable to use a color that each color patch CP indicates covers the entire color space without being biased.

  The input value acquisition unit PG2c acquires shooting data generated by the DSC 20 shooting the color chart CC via the OS_PG1 and the GIF 15. The photographing data is image data in which the color of each pixel is expressed by a camera RGB value (input value), and each color patch is designated by designating a pixel position corresponding to the position of each color patch CP in the color chart CC. The camera RGB value obtained by photographing can be acquired. The camera RGB values are acquired by performing a decoding process (not shown) on the photographic data. On the other hand, the colorimetric value acquisition unit PG2b causes the colorimeter 30 to sequentially measure the color patches of the color chart CC via the colorimeter driver PG3 and the GIF 15, and obtains the colorimetric values of the color patches CP. Acquire sequentially. In the present embodiment, it is assumed that the colorimetric values of each color patch are obtained as XYZ values in the XYZ space. Hereinafter, the XYZ value obtained by the color measurement is expressed as a color measurement XYZ value.

FIG. 4 schematically illustrates the state of step S100. As shown in the figure, the color chart CC is composed of a plurality of color patches CP, and the camera RGB values (input values) are obtained by performing shooting with the DSC 20 and colorimetry with the colorimeter 30 for each color patch CP. And the colorimetric XYZ values (colorimetric values) are obtained. The correspondence relationship between the camera RGB value and the colorimetric XYZ value obtained here is stored in the RAM 12 or the HDD 14 as measurement data MD. As described above, when the correspondence between the camera RGB values and the colorimetric XYZ values is obtained for each color patch CP, the matrix creation unit PG2d determines the correspondence between the camera RGB values and the XYZ values described above in step S105. A prescribed matrix M is calculated. The correspondence relationship between camera RGB values and XYZ values defined by the matrix M is expressed by the following equation (1).

In the above equation (1), a _{11 to} a ₃₃ represent matrix elements constituting the matrix M. In the present embodiment, the square error between the correspondence between the camera RGB values and the colorimetric XYZ values obtained in step S100 and the correspondence between the camera RGB values and the XYZ values defined by the matrix M is minimized. Is calculated by the matrix least squares method. When the matrix M is obtained as described above, the 3D-LUT creation unit PG2e creates a 3DLUT in steps S110 to S112.

  FIG. 5 schematically shows a 3D-LUT creation procedure in steps S110 to S112. First, 8 vertices of a cubic color space of camera RGB values expressed in 8 bits [K (Black), R (Red), G (Green), B (Blue), C (Cyan), M (Magenta), Y ( (Yellow), W (White)] are sequentially substituted into the above equation (1), and XYZ values corresponding to these are calculated. When the XYZ values corresponding to the eight vertices are obtained, an eight-vertex 3D-LUT (shown in the upper part of FIG. 5) storing the correspondence with the camera RGB values for the eight vertices is created, and the eight-vertex 3D-LUT is stored in the RAM 12. Or it memorize | stores in HDD14 (step S110). In the next step S112, a multi-grid 3D-LUT is created by equally dividing the 8-vertex 3D-LUT by a large number of grid points (lookup table creation means). Specifically, 17 × 17 × 17 (4 × 4 × 4 in the figure for simplification) uniform orthogonal lattices are generated for each RGB channel of the camera RGB values, and the lattice points on the uniform orthogonal lattice are generated. XYZ values corresponding to the camera RGB values are calculated by performing tetrahedral interpolation while referring to the 8-vertex 3D-LUT. Then, a multi-grid 3D-LUT (shown in the lower part of FIG. 5) storing the camera RGB values on the grid points and the calculated XYZ values is stored in the RAM 12 or the HDD 14. In the present embodiment, the conversion is performed by combining the 3D-LUT with tetrahedral interpolation, but other linear interpolation such as hexahedral interpolation may be applied.

When the multi-lattice 3D-LUT can be created as described above, in step S115, the UI unit PG2a and the 3D-LUT adjustment unit PG2f display a UI screen for adjusting the multi-lattice 3D-LUT on the display 40. Here, first, the camera RGB values stored in the measurement data MD (camera RGB values obtained by photographing in step S100) are converted into XYZ values by performing tetrahedral interpolation while referring to the multi-grid 3D-LUT. The converted XYZ value is expressed as a converted XYZ value. A color difference ΔE between the converted XYZ value and the colorimetric XYZ value stored in the measurement data MD (the XYZ value obtained by the colorimetry in step S100) is calculated. In the present embodiment, the color difference ΔE is calculated by a color difference formula of CIE_Δ1994. The converted XYZ value and the colorimetric XYZ value are converted into L ^* a ^* b ^* values by the conversion profile 14b, and the color difference ΔE is calculated. The color difference ΔE is calculated for each color patch CP. When the color difference ΔE is calculated for each color patch CP, the UI unit PG2a outputs a UI screen displaying the color difference ΔE. Here, it is only necessary to evaluate the color shift indicated by the converted XYZ value and the colorimetric XYZ value, and the Euclidean distance in the XYZ space may simply be used instead of the color difference ΔE.

  FIG. 6 shows an example of the UI screen displayed in step S115. In the figure, an area A1 for displaying a patch color difference is provided, and a color difference ΔE (character indicating the color difference) is displayed for each color patch CP in each cell formed in the area A1. The arrangement of the cells may be according to the arrangement of the color patches CP in the color chart CC, or may be arranged according to the color. In addition, although not shown, each cell is colored in accordance with the magnitude of the color difference ΔE. For example, as the color difference ΔE increases, the color may be divided from blue to yellow to red. Further, the average color difference ΔE (characters indicating) of all the color patches CP is displayed at the bottom of the area A1.

Below the area A1, there is provided an area A2 in which graphs G1 to G7 in which converted XYZ values and colorimetric XYZ values of each color patch CP are plotted in the CIELAB space are displayed. Each of the graphs G1 to G7 shows an a ^* b ^* plane obtained by slicing the CIELAB space with a plurality of different lightness L ^* values, and L ^* a ^{* of} converted XYZ values and colorimetric XYZ values existing in the vicinity of each slice plane ^. The b ^* value conversion coordinates are plotted. In the example of FIG. 6, the L ^* a ^* b ^* values converted coordinate transformation XYZ values indicated by ●, it shows a L ^* a ^* b ^* values converted coordinates of the colorimetric XYZ values ×. There are check boxes that allow you to select conversion values and colorimetric values. If only conversion values are checked, only ● is plotted, and if only colorimetric values are checked, only × Plot. When both the conversion value and the colorimetric value are checked, both of the “x” are plotted. In addition, you may display the line | wire which connects ● or x. Radio buttons that can be alternatively selected by the mouse 50b are provided above the graphs G1 to G7, and the selected graphs G1 to G7 can be enlarged and displayed in the area A2a. Yes.

  Further, the UI screen is provided with a region A3. In the region A3, six vertices excluding B and W among the eight vertices described above in the multi-grid 3D-LUT [R, G, B, C, A text box for adjusting an XYZ value associated with [M, Y] is provided. A text box for adjusting the hue adjustment amount (ΔH value) and the saturation adjustment amount (ΔC value) is provided for each of the eight vertices, and the desired ΔH value and ΔC value amount can be input. It has become. The UI unit PG2a monitors the input of numerical values to the text box. If there is a change in the numerical value input to the text box (step S120), the 3D-LUT adjustment unit PG2f has eight vertices in step S125. Perform 3D-LUT adjustment.

  The 3D-LUT adjustment unit PG2f acquires the XYZ values associated with the six vertices of the current 8-vertex 3D-LUT, and performs adjustments corresponding to the ΔH value and the ΔC value specified for the XYZ values. Since the ΔH value and the ΔC value mean the adjustment amount in the HCV space, the XYZ values at the six vertices of the eight vertex 3D-LUT are adjusted after being converted into the adjustment amount of the XYZ value. When the XYZ values of the six vertices are adjusted, the 3D-LUT adjustment unit PG2f performs camera RGB for the adjusted six vertices [R, G, B, C, M, Y] and the two vertices [K, W]. The 8-vertex 3D-LUT in which the correspondence between the value and the XYZ value is defined is stored in the RAM 12 or the HDD 14, and the process returns to step S112. Then, the 3D-LUT creation unit PG2e calculates the XYZ values corresponding to the camera RGB values on the lattice points by the uniform orthogonal grid for each RGB channel of the camera RGB values while referring to the recreated 8-vertex 3D-LUT. Calculated by performing body interpolation. Then, a multi-grid 3D-LUT storing the camera RGB values and the calculated XYZ values on the grid points is created as an adjusted multi-grid 3D-LUT (lookup table adjusting means).

  When the multi-lattice 3D-LUT is adjusted as described above, the UI screen displayed on the display 40 by the UI unit PG2a is updated in step S115. Here, the process for displaying the UI screen described above is executed based on the adjusted multi-lattice 3D-LUT. That is, by performing tetrahedral interpolation with reference to the adjusted multi-grid 3D-LUT, the camera RGB values stored in the measurement data MD (camera RGB values obtained by the imaging in step S100) are converted into XYZ values. Convert. Then, a color difference ΔE between the converted XYZ value and the colorimetric XYZ value stored in the measurement data MD (the XYZ value obtained by the colorimetry in step S100) is calculated and reflected on the UI screen described above. That is, by repeatedly executing the processing of steps S112 to S125, the multi-lattice 3D-LUT can be adjusted, and the change in the color difference ΔE according to the adjustment can be confirmed on the UI screen.

Therefore, it is possible to search for the XYZ values of the six vertices [R, G, B, C, M, Y] that reduce the color difference ΔE. Further, on the UI screen, the converted XYZ values and the L ^* a ^* b ^* value conversion coordinates of the colorimetric XYZ values existing in the vicinity of each slice surface of the lightness L ^* values are plotted, so that the color difference ΔE for each lightness region. The tendency of can be grasped. Therefore, it is also possible to adjust the XYZ values at the six vertices [R, G, B, C, M, Y] so as to reduce the color difference ΔE particularly in the lightness region that is frequently used in the image. . Further, when adjusting the XYZ values of the six vertices [R, G, B, C, M, Y], the adjustment amount is indicated by the ΔH value that represents the hue adjustment amount and the ΔC value that represents the saturation adjustment amount. Therefore, the brightness of the six vertices [R, G, B, C, M, Y] can be prevented from changing. An adjustment completion button is provided on the UI screen, and clicking of the adjustment completion button by the mouse 50b is monitored by the UI unit PG2a (step S130).

When the click of the adjustment completion button is detected, the 3D-LUT adjustment unit PG2f acquires the adjusted multi-grid 3D-LUT, and at the multi-grid 3D-LUT, white vertices [W Y _W value associated with] to obtain the (white brightness) (step S135). In the XYZ space, the Y value takes a value between 0 and 1, but the Y _W value is a value calculated by the matrix M in the above equation (1), so it can be considered that it exceeds 1. This is because the matrix M is calculated without considering the dynamic range of the image sensor of the DSC 20. The Y value associated with each lattice point is normalized to 0 to 1 by uniformly dividing each Y value associated with each lattice point of the multi-grid 3D-LUT by the whiteness value Y _W.

  FIG. 7 schematically shows the normalization in step S135. In the figure, before and after normalization of the Y value associated with the grid point on the gray axis where the camera RGB value is R = G = B is compared. At the grid points in the high brightness area, the Y value before normalization exceeds 1, but by normalization, the Y values at each grid point fall within the range of 0-1. By doing so, it is possible to prevent overexposure when the Y value of the converted XYZ value converted by the multi-lattice 3D-LUT exceeds 1. However, since the brightness is corrected downward as a whole, the converted XYZ value converted by the multi-grid 3D-LUT shows a darker color than the original.

  In step S140, the XYZ values associated with the normalized multi-lattice 3D-LUT are converted into RGB values in the sRGB space that are easy to adjust (hereinafter referred to as sRGB values). Note that the XYZ values are converted into sRGB values using the conversion profile 14b. As a result, the multi-lattice 3D-LUT shows the correspondence between the camera RGB space and the sRGB space. In step S145, the input value acquisition unit PG2c captures a plurality of color patches CP showing gray gradation with the DSC 20 under the D55 light source, and captures data indicating the imaging result via the OS_PG1 and the GIF 15 as a tone curve generation unit. PG2g acquires.

The camera RGB values acquired by the tone curve generation unit PG2g are converted into sRGB values by performing tetrahedron interpolation with reference to the normalized multi-grid 3D-LUT, and the sRGB values are further converted using the conversion profile 14b. Are converted to L ^* a ^* b ^* values (hereinafter referred to as converted L ^* a ^* b ^* values) in the CIELAB space. Further, the colorimetric value acquisition unit PG2b causes the colorimeter 30 to perform colorimetry on the same color patch CP under the D55 light source via the colorimeter driver PG3 and GIF15. The tone curve generation unit PG2g acquires the colorimetric value from the L ^* a ^* b ^* value in the CIELAB space (hereinafter referred to as the colorimetric L ^* a ^* b ^* value). In step S145, the tone curve generation unit PG2g creates a tone reproduction tone curve TC.

FIG. 8 shows the relationship between the converted L ^* value (vertical axis) and the colorimetric L ^* value (horizontal axis) obtained by colorimetry / photographing in step S145. The converted L ^* value tends to be smaller than the actual colorimetric L ^* value. This is because the converted L ^* value is obtained by the conversion by the multi-grid 3D-LUT normalized by the white lightness Y _W. Therefore, a tone curve is created so that the converted L ^* value approaches the original colorimetric L ^* value. First, on the low brightness side from the control point CP1, the tone reproduction tone curve TC is linear so as to follow the colorimetric L ^* value. In this linear portion, the output value and the input value have a proportional relationship of the gradient obtained by dividing the colorimetric L ^* value by the converted L ^* value. On the other hand, on the higher brightness side than the control point CP1, the tone reproduction tone curve TC is formed as a spline curve connecting the control point CP1 and the maximum brightness L _W ^* . The shape of the spline curve connecting the control point CP1 and the maximum brightness L _W ^* can be uniquely determined by the position of the control point CP2 existing between them. The control point CP2 is set to be a spline curve that does not cause gradation unevenness or early saturation.

  The 3D-LUT adjustment unit PG2f uniformly applies the tone reproduction tone curve TC created as described above to the sRGB values associated with the lattice points of the multi-grid 3D-LUT (Step S3). S150). That is, the sRGB value associated with each grid point of the multi-grid 3D-LUT is adjusted by the tone reproduction tone curve TC. That is, the multi-lattice 3D-LUT once has a dark reproducibility by the above-described normalization, but by applying the tone reproduction tone curve TC, it can be brought close to the original tone reproduction. However, on the high brightness side, the upward correction by the tone reproduction tone curve TC is suppressed by the spline curve, so that the occurrence of overexposure can be prevented. As described above, the adjustment to the multi-grid 3D-LUT that ensures the gradation reproducibility is completed. In the next memory color correction unit PG2h step S155, memory color correction is performed.

  FIG. 9 schematically shows a state of memory color correction (sky blue correction). In the memory color correction, the color gamut to be subjected to the memory color correction is specified in the sRGB space, and the grid points to which the associated sRGB values belong to the color gamut are extracted from the multi-grid 3D-LUT. For example, grid points belonging to the sky blue or flesh color gamut are extracted from the multi-grid 3D-LUT. Then, the sRGB values associated with the grid points belonging to the color gamut are adjusted so as to approach the ideal memory color. For example, the sRGB value of the grid point belonging to the sky blue is adjusted to be brighter than the original value. As described above, when conversion is performed using the multi-grid 3D-LUT in which the sRGB values are adjusted, sRGB values considering the memory color correction can be obtained as a conversion result. In the present embodiment, an example of performing memory color correction is illustrated, but it goes without saying that a multi-grid 3D-LUT including elements of brightness correction, contrast correction, white balance correction, and color balance correction may be created. .

In step S160, the sRGB values associated with the respective grid points of the current multi-grid 3D-LUT are converted into L ^* a ^* b ^* values in the CIELAB space using the sRGB values using the conversion profile 14b (profile). Creating means). As a result, a multi-grid 3D-LUT in which the correspondence between the camera RGB value and the L ^* a ^* b ^* value is defined for each grid point is created. In step S165, the profile creation unit PG2i stores the multi-lattice 3D-LUT as the created profile in the HDD 14, and the process ends.

As described above, in the present embodiment, when creating a profile that defines the correspondence between the camera RGB space and CIELAB space used by the DSC 20, the colorimetric XYZ values of a plurality of color patches CP and the color patch CP. A multi-grid 3D-LUT that defines the correspondence between the camera RGB space and the CIELAB space is created based on the correspondence with the camera RGB values input by the image DSC 20. Then, the multi-grid 3D-LUT is adjusted so as to reduce the color difference ΔE between the converted XYZ value obtained by converting the camera RGB value with reference to the multi-grid 3D-LUT and the colorimetric XYZ value. According to the multi-lattice 3D-LUT created in this way, the camera RGB values of each pixel of the photographing data photographed by the DSC 20 are converted into L ^* a ^{* in} the CIELAB space (target color space) independent of the DSC 20 ^. An ICC profile that can be converted to a b ^* value can be provided. In particular, the color difference ΔE of the conversion result is reduced by adjusting the six vertices [R, G, B, C, M, Y] of the multi-grid 3D-LUT, so that the color reproducibility before and after the conversion is also ensured. be able to.

  Note that by not adjusting the two vertices [K, W] on the gray axis of the multi-grid 3D-LUT, it is possible to prevent an unnecessary color from being generated in the achromatic color. In the present embodiment, a UI screen on which the change of the color difference ΔE can be confirmed is displayed, and designation of the hue adjustment amount ΔH value and the saturation adjustment amount ΔC value is accepted, but the six vertexes [R, G, B, C , M, Y], the CPU 11 may calculate the optimum hue adjustment amount ΔH and saturation adjustment amount ΔC. For example, using the average value of the color difference ΔE as an objective function, an optimal solution of the hue adjustment amount ΔH and the saturation adjustment amount ΔC for six vertices that minimize the objective function may be calculated by a known numerical optimization method. Good. Further, the above-described normalization can prevent over-exposure in the conversion result, and the gradation reproducibility can be ensured without causing over-exposure by the adjustment based on the above-described gradation reproduction tone curve TC. Note that a link profile may be created by further combining an ICC profile of an output device such as a printer with the created multi-lattice 3D-LUT.

3. In the above, an example in which a multi-grid 3D-LUT is finally created as an ICC profile has been exemplified, but not all conversion / adjustment rules are defined by the LUT, and conversion / adjustment of the present invention Part or all of the rules may be defined by a conversion formula or a matrix. For example, in the case of a device having a small storage capacity such as a general printer, it is desirable to store a conversion formula or a matrix rather than storing a multi-grid 3D-LUT. By using a matrix that can be converted equivalent to the multi-lattice 3D-LUT after normalization in step S135 of the profile creation process described above, and a conversion formula corresponding to the tone reproduction tone curve TC in step S150, the above-described process is used. A conversion result (excluding memory color correction) similar to that of the multi-grid 3D-LUT of the embodiment can be obtained. According to the matrix and the conversion formula, even in a device having a small storage capacity such as a printer, the same conversion can be performed without squeezing the storage capacity. Since only linear processing is performed until normalization in step S135, a matrix capable of conversion equivalent to the multi-grid 3D-LUT can be calculated.

  FIG. 10 shows the configuration of the printer 110 having the above matrix and conversion formula. In the figure, the printer 110 is composed of a CPU 121, a RAM 112, a ROM 113, a memory card slot 114, a printing unit 115, and a bus 118. The ROM 113 stores a matrix 113b that can be converted in the same way as the multi-lattice 3D-LUT after normalization in step S135 of the profile creation process described above, and a conversion formula 113c corresponding to the tone reproduction tone curve TC in step S150. In addition, an output profile 113 d that defines the correspondence between the sRGB values and the amounts of CMYK ink used by the printing unit 115 of the printer 110 is stored. The printer 110 executes a print control process for printing the shooting data shot by the DSC 20 based on the program data 113 a stored in the ROM 113.

  The memory card slot 114 stores shooting data shot by the DSC 20, and the CPU 111 acquires the shooting data. Then, the CPU 111 sequentially applies the matrix 14b and the conversion formula 113c to the camera RGB values of each pixel included in the shooting data, thereby adjusting the sRGB values of the sRGB space (target color space) in which the adjustment by the tone reproduction tone curve TC is reflected. Is calculated. Further, the output profile 113d is used to convert the sRGB values into CMYK ink amounts, and halftone processing and rasterization processing are sequentially performed on the CMYK ink amounts, and finally a drive signal for driving the printing unit 115. Is generated. The printing unit 115 of this modification includes an inkjet printing mechanism, and controls the ejection of each ink from the print head, the drive of the print head, and the control of the paper feed system according to the drive signal.

It is a block diagram which shows the hardware constitutions of a profile creation apparatus. It is a block diagram which shows the software structure of a profile creation apparatus. It is a flowchart which shows the flow of profile creation. It is a figure explaining the creation procedure of 3D-LUT. It is a figure explaining the creation procedure of 3D-LUT. It is a figure which shows an example of UI screen. It is a graph which shows the mode of normalization. It is a graph which shows the tendency of the brightness when image | photographing a gradation. It is a figure which shows the mode of memory color correction. It is a block diagram which shows the hardware constitutions of the printer concerning a modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Computer, 11 ... CPU, 12 ... RAM, 13 ... ROM, 14 ... HDD, 14a ... Program data, 14b ... Conversion profile, 15 ... GIF, 16 ... VIF, 17 ... IIF, 18 ... Bus, 20 ... DSC, 40 ... display, 50a ... keyboard, 50b ... mouse, PG1 ... OS, PG2 ... APL, PG2a ... UI unit, PG2b ... colorimetric value acquisition unit, PG2c ... input value acquisition unit, PG2d ... matrix creation unit, PG2e ... 3D- LUT creation unit, PG2f ... 3D-LUT adjustment unit, PG2g ... tone curve generation unit, PG2h ... memory color correction unit, PG2i ... profile creation unit, PG3 ... colorimeter driver.

Claims (8)

A profile creation method for creating a profile that defines a correspondence relationship between an input color space used by an image input device and a predetermined target color space,
A lookup table for defining a correspondence relationship between the input color space and the target color space based on a correspondence relationship between colorimetric values of a plurality of color patches and an input value obtained by inputting the color patch by the image input device; make,
Adjusting the lookup table so as to reduce the deviation between the conversion value obtained by converting the input value with reference to the lookup table and the colorimetric value;
A profile creation method, wherein the profile is created based on the adjusted lookup table.   The deviation is reduced by maintaining the lightness of the color value in the target color space corresponding to the vertex of the input color space defined in the lookup table and adjusting the hue and saturation. 2. The profile creation method according to 1.   3. The adjustment according to claim 1, wherein when the look-up table is adjusted, the deviation and the distribution of the converted value and the colorimetric value are displayed for each brightness region in a predetermined color space. The profile creation method described in any one. In creating the lookup table based on the correspondence between the colorimetric value and the input value, the input color space and the target color space are based on the correspondence between the colorimetric value and the input value. Create a matrix that defines the correspondence,
Normalizing the lightness of each color value of the target color space defined in the lookup table based on the white lightness obtained by converting the white point of the input color space using the matrix. The profile creation method according to any one of claims 1 to 3.   5. The profile creation method according to claim 4, wherein the brightness of each color value of the target color space defined in the look-up table is adjusted by a tone curve. A profile creation device that creates a profile that defines a correspondence relationship between an input color space used by an image input device and a predetermined target color space,
A lookup table for defining a correspondence relationship between the input color space and the target color space based on a correspondence relationship between colorimetric values of a plurality of color patches and an input value obtained by inputting the color patch by the image input device; A lookup table creation means to create;
Lookup table adjustment means for adjusting the lookup table so as to reduce the deviation between the conversion value obtained by converting the input value with reference to the lookup table and the colorimetric value;
A profile creation device comprising profile creation means for creating the profile based on the adjusted look-up table. A computer-readable profile creation program for causing a computer to execute a function of creating a profile that defines a correspondence relationship between an input color space used by an image input device and a predetermined target color space,
A lookup table for defining a correspondence relationship between the input color space and the target color space based on a correspondence relationship between colorimetric values of a plurality of color patches and an input value obtained by inputting the color patch by the image input device; A lookup table creation function to create,
A lookup table adjustment function for adjusting the lookup table so as to reduce a deviation between the conversion value obtained by converting the input value with reference to the lookup table and the colorimetric value;
A computer-readable profile creation program causing a computer to execute a profile creation function for creating the profile based on the adjusted lookup table.   The printing according to claim 1, wherein the image data input by the image input device is converted into image data of the target color space based on the profile according to claim 1, and printing is executed based on the converted image data. apparatus.

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