JP2019118089A - Color conversion method, color conversion program, and color conversion device - Google Patents

Abstract

To provide a color conversion method, a color conversion program, and a color conversion device that can improve reproducibility of colors.SOLUTION: In a color conversion method including a color conversion table creation step of creating a color conversion table for converting colors, and a color conversion step of converting colors by using the color conversion table created in the color conversion table creation step, the color conversion table creation step is a step in which creating the color conversion table only with a specific cubic lattice point group as a specific group of cubic lattice points (S622) and creating the color conversion table by adding a non-cubic lattice point group that is not a group of cubic lattice points to the specific cubic lattice point group (S624 or S625) can be switched to each other.SELECTED DRAWING: Figure 33

Description

  The present invention relates to a color conversion method, a color conversion program, and a color conversion device for converting color using a color conversion table for color conversion.

  Conventionally, there is known an image forming apparatus that converts input image data in RGB format into image data in CMYK format using a color conversion table, and then executes printing based on the image data in CMYK format ( See, for example, Patent Document 1).

  As a conventional color conversion table, as shown in FIG. 40, there are many cases in which the arrangement of grid points before color conversion is a cubic grid. And, in the color conversion table in which the arrangement of lattice points before color conversion is cubic lattice, the number of lattice points per side of the cubic lattice is selected depending on the capacity of the memory for storing the information of the lattice points In general, the accuracy of the required quality of the output image, the cost of parts applied to the image forming apparatus, etc. are considered and determined. The number of lattice points required for a color conversion table in which the arrangement of lattice points before color conversion is a cubic lattice is N ^ 3, where N is the number of lattice points per side of the cubic lattice. Increases in proportion to the cube of N with the increase of.

Unexamined-Japanese-Patent No. 2015-088968

  However, when the arrangement of grid points before color conversion is a cubic grid, under the condition that the cost of parts of the image forming apparatus is limited, sufficient accuracy of the quality of the output image by the image forming apparatus can be ensured. There is a problem that there is something that can not be done.

  The RGB space and the CMYK space differ in the shape of the color gamut, and furthermore, the relationship between the two is often non-linear. Therefore, when calculating intermediate data between grid points of the color conversion table by linear interpolation, the larger the number of grid points, the smaller the distance between the grid points. Therefore, actual intermediate data and intermediate data calculated by interpolation are used. The error of can be reduced. That is, as the number of lattice points in the color conversion table is larger, the accuracy of the quality of the output image by the image forming apparatus is higher.

The upper limit of the capacity of the memory for storing lattice point information is determined according to the cost of parts applied to the image forming apparatus. The upper limit of the number of lattice points in the color conversion table is determined according to the upper limit of the capacity of the memory storing the information of the lattice points. Hereinafter, the upper limit of the number of grid points determined according to the upper limit of the capacity of the memory storing the grid point information is referred to as Smax. As described above, although the number of lattice points required for the color conversion table in which the arrangement of lattice points before color conversion is a cubic lattice is N ^ 3, it hardly coincides with Smax. Therefore, the upper limit Nmax of the number N of grid points per side of the color conversion table in which the arrangement of grid points before color conversion is a cubic grid is an integer not exceeding the cube root of Smax, as in the following equation Set to
Nmax = Floor [Smax ^ (1/3)]

For example, when Smax is 1200 in terms of parts cost, Nmax of the color conversion table in which the arrangement of lattice points before color conversion is a cubic lattice is 10 as in the following equation.
Nmax = Floor [1200 ^ (1/3)] = 10

  Here, the upper limit of the number of lattice points of the color conversion table in which the arrangement of lattice points before color conversion is cubic lattice is the cube of Nmax. Therefore, when Nmax is 10, the upper limit of the number of lattice points of the color conversion table in which the arrangement of lattice points before color conversion is cubic lattice is 1000.

  Therefore, the memory for storing the grid point information will not use the capacity equivalent to 1200-1000 = 200 grid points. Therefore, when using a color conversion table in which the arrangement of grid points before color conversion is a cubic grid, comparison with the case where maximum number of grid point information is stored in a memory storing grid point information Therefore, the accuracy of the quality of the output image by the image forming apparatus is reduced.

  Then, this invention aims at providing the color conversion method, the color conversion program, and the color conversion apparatus which can improve the reproducibility of a color.

  The color conversion method according to the present invention includes a color conversion table generation step of generating a color conversion table for color conversion, and a color conversion method using the color conversion table generated by the color conversion table generation step. Generating the color conversion table using only a specific cubic lattice point group as a specific group of cubic lattice points, and a non-cubic lattice that is not a cubic lattice point group. It is characterized in that it is possible to switch between adding a point group to the specific cubic lattice point group and generating the color conversion table.

  With this configuration, when the color conversion method of the present invention generates a color conversion table by adding a non-cubic lattice point group to a specific cubic lattice point group, the color conversion table is generated using only the specific cubic lattice point group As compared with the above, the number of lattice points in the color conversion table can be increased under the condition that the capacity of the memory for storing the information of lattice points is limited, so that the color reproducibility can be improved. Further, the color conversion method of the present invention is compared to the case where a color conversion table is generated by adding a non-cubic grid point group to a specific cubic grid point group when generating a color conversion table using only a specific cubic grid point group. Thus, it is possible to facilitate the use of the functions and applications prepared on the assumption of the color conversion table generated only by the cubic grid point group.

  In the color conversion method according to the present invention, the color conversion table generation step may be a step which can switch a lattice point group for a natural image and a lattice point group for a non-natural image as the non-cubic lattice point group. good.

  According to this configuration, the color conversion method of the present invention adds a grid point group for a natural image to a specific cubic grid point group to generate a color conversion table, and a grid for a non-natural image on a specific cubic grid point group. Since it is possible to switch between adding a point cloud and generating a color conversion table, colors can be converted by the color conversion table suitable for the image to be converted, and color reproducibility is improved. be able to.

  In the color conversion method according to the present invention, the color conversion table generation step includes the lattice point group for the natural image and the lattice point group for the non-natural image as an image of a color conversion target in the color conversion step. The step may be switchable as the non-cubic lattice point group based on

  According to this configuration, the color conversion method of the present invention adds a grid point group for a natural image to a specific cubic grid point group to generate a color conversion table, and a grid for a non-natural image on a specific cubic grid point group. Since it is possible to switch between adding a point group and generating a color conversion table based on an image of a color conversion target, convenience can be improved.

  A color conversion program according to the present invention includes color conversion table generation means for generating a color conversion table for color conversion, and color conversion using the color conversion table generated by the color conversion table generation means. Making a computer implement conversion means, said color conversion table generation means generating said color conversion table only with a specific cubic lattice point group as a specific group of cubic lattice points, and not a cubic lattice point group It is possible to switch between adding a non-cubic lattice point group to the specific cubic lattice point group to generate the color conversion table.

  According to this configuration, when a computer executing the color conversion program of the present invention adds a non-cubic lattice point group to a specific cubic lattice point group to generate a color conversion table, the color conversion table is generated using only the specific cubic lattice point group. Since the number of grid points in the color conversion table can be increased under the condition that the capacity of the memory for storing grid point information is limited as compared with the case of generating the color reproducibility, color reproducibility is improved. be able to. In addition, when a computer that executes the color conversion program of the present invention generates a color conversion table using only a specific cubic lattice point group, a non-cubic lattice point group is added to the specific cubic lattice point group to generate a color conversion table As compared with the case where it does, the utilization of the function and application which are prepared supposing the color conversion table generated only with cubic lattice point group can be facilitated.

  The color conversion device according to the present invention converts a color using color conversion table generation means for generating a color conversion table for converting colors, and the color conversion table generated by the color conversion table generation means. Generating the color conversion table using only a specific cubic lattice point group as a specific group of cubic lattice points, and a non-cubic lattice that is not a group of cubic lattice points. It is possible to switch between adding a point group to the specific cubic lattice point group and generating the color conversion table.

  With this configuration, when the color conversion device of the present invention generates a color conversion table by adding a non-cubic lattice point group to a specific cubic lattice point group, the color conversion table is generated using only the specific cubic lattice point group As compared with the above, the number of lattice points in the color conversion table can be increased under the condition that the capacity of the memory for storing the information of lattice points is limited, so that the color reproducibility can be improved. The color conversion device of the present invention is also compared to the case where a color conversion table is generated by adding a non-cubic grid point group to a specific cubic grid point group when generating a color conversion table using only a specific cubic grid point group. Thus, it is possible to facilitate the use of the functions and applications prepared on the assumption of the color conversion table generated only by the cubic grid point group.

  The color conversion method, the color conversion program, and the color conversion apparatus of the present invention can improve color reproducibility.

It is a block diagram of a color conversion table generation device concerning a 1 embodiment of the present invention. FIG. 6 is a block diagram of an MFP storing a color conversion table generated by the color conversion table generation device shown in FIG. 1; It is a flowchart of operation | movement of the color conversion table production | generation apparatus shown in FIG. 1 in the case of producing | generating a color conversion table. It is a flowchart of the lattice point group generation process shown in FIG. (A) It is a perspective view of the cubic lattice point group which the number of lattice points of 1 side produced | generated by the color conversion table production | generation apparatus shown in FIG. 1 is six. (B) It is a perspective view of the cubic lattice point group shown to Fig.5 (a) at the time of observing in the direction which goes to a black point from a white point. 5 is a flowchart of a natural image lattice point group generation process shown in FIG. 4; It is a flowchart of important lattice point generation processing shown in FIG. It is a figure which shows the gray axis by which a grid point is produced | generated in the gray on-axis grid point production | generation process shown in FIG. FIG. 8 is a flow chart of gray on-axis grid point generation processing shown in FIG. 7 in the case of generating grid points at equal intervals on the gray axis; FIG. It is a flowchart of a gray on-axis grid point generation process shown in FIG. 7 in the case of generating a grid point having coordinates of a term of van der Corput column. It is a flowchart of the outermost shell upper lattice point generation process shown in FIG. FIG. 12 is a flowchart of inter-corner line segment grid point generation processing shown in FIG. 11; FIG. It is a figure which shows the line segment of the largest saturation in which a lattice point is produced | generated in the largest saturation line segment upper lattice point production | generation process shown in FIG. FIG. 13 is a flowchart of maximum saturation line segment upper lattice point generation processing shown in FIG. 12 in the case of generating lattice points at equal intervals on the maximum saturation line segment; FIG. FIG. 13 is a flowchart of a maximum saturation line segment grid point generation process shown in FIG. 12 in the case of generating a grid point in which a coordinate of the van der Corput column is a part of coordinates. It is a figure which shows the skyline by which a grid point is produced | generated in the on-skyline grid point production | generation process shown in FIG. FIG. 13 is a flowchart of on-skyline grid point generation processing shown in FIG. 12 in the case of generating grid points at equal intervals on the skyline. FIG. 13 is a flowchart of on-skyline grid point generation processing shown in FIG. 12 in the case of generating a grid point whose partial coordinates are terms of van der Corput column; FIG. It is a figure which shows the bottom line in which a lattice point is produced | generated in the bottom line top lattice point production | generation process shown in FIG. 13 is a flowchart of a bottom line on-grid point generation process shown in FIG. 12 in the case of generating grid points at equal intervals on the bottom line. FIG. 13 is a flowchart of a bottom line on-grid point generation process shown in FIG. 12 in the case of generating a grid point whose partial coordinates are terms of the van der Corput column. It is a flowchart of the outermost shell surface lattice point generation process shown in FIG. 11 in the case of generating lattice points at equal intervals on the outermost shell surface. FIG. 12 is a flowchart of outermost shell on-plane grid point generation processing shown in FIG. 11 in the case of generating grid points in which the coordinate of the same order of two types of van der Corput sequences is taken as a part of coordinates. FIG. 7 is a flowchart of color gamut internal grid point generation processing shown in FIG. 6; FIG. It is a flowchart of the lattice point allocation process shown in FIG. (A) It is a perspective view of an example of the lattice point group produced | generated in the lattice point group production | generation process for natural images shown in FIG. (B) It is a perspective view of the lattice point group shown to Fig.26 (a) at the time of observing in the direction which goes to a black point from a white point. (A) It is a perspective view of an example of the lattice point group produced | generated in the lattice point group production | generation process for non-natural images shown in FIG. (B) It is a perspective view of the lattice point group shown to Fig.27 (a) at the time of observing in the direction which goes to a black point from a white point. 5 is a flow chart of the general conversion steps of the color conversion process performed by the MFP shown in FIG. It is a flowchart at the time of making the conversion step shown in FIG. 28 into a single step. It is a flowchart which shows the color conversion process which outputs "color space JCH in of an input device" used for production | generation of the conversion step shown in FIG. FIG. 29 is a flow chart showing a color conversion process of outputting “color space JCH out of output device” used to generate the conversion step shown in FIG. 28. 5 is a flowchart of the operation of the MFP shown in FIG. 2 when printing is performed. It is a flowchart of a use color conversion table production | generation process shown in FIG. (A) It is a perspective view of an example of the lattice point group determined in S624 shown in FIG. (B) It is a perspective view of the lattice point group shown to Fig.34 (a) at the time of observing in the direction which goes to a black point from a white point. (A) It is a perspective view of an example of the lattice point group determined in S625 shown in FIG. (B) It is a perspective view of the lattice point group shown to Fig.35 (a) at the time of observing in the direction which goes to a black point from a white point. It is a flowchart of the color conversion process shown in FIG. It is a flowchart of the correspondence search process shown in FIG. It is a flowchart of the interpolation process shown in FIG. FIG. 39 is a flowchart of included tetrahedron search processing shown in FIG. 38. FIG. It is a figure which shows the conventional color conversion table.

  Hereinafter, an embodiment of the present invention will be described using the drawings.

  First, the configuration of the color conversion table generation device according to the present embodiment will be described.

  FIG. 1 is a block diagram of a color conversion table generation apparatus 10 according to the present embodiment. FIG. 2 is a block diagram of an MFP (Multifunction Peripheral) 20 storing the color conversion table generated by the color conversion table generation device 10.

  As shown in FIG. 1, the color conversion table generation device 10 includes an operation unit 11 which is an input device such as a mouse and a keyboard to which various operations are input, and an LCD (Liquid Crystal Display) which displays various information. A display unit 12 that is a display device, a communication unit 13 that is a communication device that communicates with an external device via a network such as a LAN (Local Area Network) or the Internet, an HDD that stores programs and various data A storage unit 14 that is a storage device such as a hard disk drive) and a control unit 15 that controls the entire color conversion table generation device 10 are provided. The color conversion table generation device 10 is configured by, for example, a computer such as a PC (Personal Computer).

  The storage unit 14 includes a cubic grid point color conversion table 14a as a color conversion table generated by a cubic grid point group to convert colors in the RGB color space to colors in the CMYK color space, and a cubic grid point color conversion table 14a. Table for natural images as a color conversion table for natural images, and a non-natural image as a color conversion table for non-natural images to be added to the cubic grid point color conversion table 14a An additional table 14c can be stored.

  The control unit 15 includes, for example, a central processing unit (CPU), a read only memory (ROM) storing programs and various data in advance, and a random access memory (RAM) used as a work area of the CPU of the control unit 15. And). The CPU of the control unit 15 is configured to execute a program stored in the ROM of the control unit 15 or the storage unit 14.

  Next, the configuration of MFP 20 shown in FIG. 2 will be described.

  FIG. 2 is a block diagram of MFP 20 as a color conversion apparatus according to the present embodiment.

  As shown in FIG. 2, the MFP 20 reads an image, an operation unit 21 which is an input device such as a button to which various operations are input, a display unit 22 which is a display device such as an LCD to display various information, A scanner 23 that is a reading device, a printer 24 that is a printing device that executes printing on a recording medium such as paper, and a fax device that performs fax communication via a communication line such as an external facsimile machine (not shown) and a public telephone line And a communication unit 26 which is a communication device for communicating with an external apparatus via a network such as a LAN or the Internet, a semiconductor memory storing various data, a storage device such as an HDD, etc. A storage unit 27 and a control unit 28 that controls the entire MFP 20 are provided.

  The storage unit 27 is a cubic grid point color conversion table 27a as a color conversion table generated by a cubic grid point group to convert colors in the RGB color space to colors in the CMYK color space, and a cubic grid point color conversion table 27a. Table for natural images as a color conversion table for natural images, and a non-natural image as a color conversion table for non-natural images to be added to cubic grid point color conversion table 27a An additional table 27c can be stored.

  The storage unit 27 stores a color conversion program 27 d for converting an RGB-format input image into a CMYK-format output image. The color conversion program 27d may be installed in the MFP 20 at the manufacturing stage of the MFP 20, or may be additionally installed in the MFP 20 from an external storage medium such as a USB (Universal Serial Bus) memory, or from the network 20 It may be installed additionally.

  The storage unit 27 is a color conversion table in which a grid point group included in any one of the natural image addition table 27b and the non-natural image addition table 27c is added to the grid point group included in the cubic grid point color conversion table 27a. Can be stored as lattice point addition / presence information 27e indicating whether to generate.

  The control unit 28 includes, for example, a CPU, a ROM storing programs and various data, and a RAM used as a work area of the CPU of the control unit 28. The CPU of the control unit 28 executes a program stored in the ROM of the control unit 28 or the storage unit 27. That is, the MFP 20 is a computer.

  The control unit 28 executes a color conversion program 27 d stored in the storage unit 14 to convert color images of RGB format into output images of CMYK format, and colors to generate a color conversion table. And conversion table generation means 28b.

  Next, the operation of the color conversion table generation device 10 will be described.

  FIG. 3 is a flowchart of the operation of the color conversion table generation device 10 in the case of generating the cubic grid point color conversion table 14a, the natural image addition table 14b and the non-natural image addition table 14c.

  As shown in FIG. 3, the control unit 15 generates grid point group groups for generating grid points before color conversion in the cubic grid point color conversion table 14a, the natural image additional table 14b, and the non-natural image additional table 14c. A process is performed (S101).

  FIG. 4 is a flowchart of the lattice point group generation process shown in FIG.

  As shown in FIG. 4, the control unit 15 obtains the maximum number Smax of lattice points that can be allocated for the color conversion table in terms of capacity of the storage unit 27 of the MFP 20 (S121).

  Next, the control unit 15 generates a group of cubic lattice points as a lattice point group of the cubic lattice point color conversion table 14a within a range not exceeding the maximum number Smax obtained in S121 (S122).

Note that the lattice point group generated by the control unit 15 in S122 is, for example, as shown in Equation 1 and FIG. 5 when the number of lattice points on one side is six when the maximum number Smax is 300. It becomes a good grid point group. FIG. 5A is a perspective view of a cubic lattice point group in which the number of lattice points on one side is six. FIG. 5 (b) shows the cube shown in FIG. 5 (a) when observed from the point of white {1, 1, 1} to the point of black {0, 0, 0}. It is a perspective view of a lattice point group. The cubic lattice point group shown in Equation 1 and FIG. 5 is a group of 6 × 6 × 6, ie, 216 lattice points. When the maximum number Smax is 300 and the number of lattice points of the cubic lattice point color conversion table 14a is 216, the lattice points of the natural image additional table 14b and the non-natural image additional table 14c are respectively at maximum It is 84 pieces.

Further, the lattice point group generated by the control unit 15 in S122 is, for example, a lattice point as shown in Equation 2 when the number of lattice points on one side is five when the maximum number Smax is 300. It becomes a group. The cubic lattice point group shown in Equation 2 is a group of 5 × 5 × 5, ie, 125 lattice points. When the maximum number Smax is 300 and the number of lattice points of the cubic lattice point color conversion table 14a is 125, the lattice points of the natural image additional table 14b and the non-natural image additional table 14c are respectively at maximum It is 175 pieces.

  As shown in FIG. 4, when the process of S122 is completed, the control unit 15 executes a natural image lattice point group generation process for generating a lattice point group for the natural image additional table 14b (S123).

  FIG. 6 is a flowchart of the natural image lattice point group generation process shown in FIG.

  As shown in FIG. 6, the control unit 15 exists on the gray axis grid point as a grid point existing on the gray axis and not white or black in the RGB color space, and on the outermost shell in the RGB color space One or more lattice points (hereinafter referred to as "important lattice points") with the lattice points on the outermost shell as lattice points that do not have any of eight corners (hereinafter referred to as "important lattice points") The important grid point generation process generated as a part is executed (S141).

  Note that the grid point on the line segment between the corners as a grid point existing on the line segment between any two corners of the eight corners in the RGB color space is the grid point on the outermost shell, and the grid point in the RGB color space A lattice present on the surface of the outer shell, that is, the surface of r = 0, the surface of r = 1, the surface of g = 0, the surface of g = 1, the surface of b = 0, and the surface of b = 1 There is an outermost shell lattice point as a point.

  In the inter-corner line segment grid point, a line segment of maximum saturation, ie, a line segment between red and yellow, a line segment between yellow and green, a line segment between green and cyan, between cyan and blue There is a grid point on the line segment of, the line segment between blue-magenta, and the line segment between magenta-red. In addition, a line segment between white and primary colors, that is, a line segment between white-red, a line segment between white-green, and white-blue Between the grid point on the line segment between and the line segment between white and secondary color, that is, the line segment between white-cyan, the line segment between white-magenta, and between white-yellow There are grid points on the line segment of. In addition, a line segment between black and a primary color, that is, a line segment between black-red, a line segment between black-green, and black-blue Between the grid point on the line segment between and the line segment between black and secondary color, ie, the line segment between black and cyan, the line segment between black and magenta, and the line between black and yellow There are grid points on the line segment of.

  FIG. 7 is a flowchart of the important grid point generation process shown in FIG.

  As shown in FIG. 7, the control unit 15 determines the necessary number of on-gray on-axis grid points determined by the designer of the natural image additional table 14b as the number on-gray on-axis lattice points Ca (S161) .

  Next, the control unit 15 executes a gray on-axis grid point generation process that generates a gray on-axis grid point as part of the grid point group of the natural image addition table 14b (S162). Note that the control unit 15 does not generate a grid point that overlaps with the grid point generated in S122 in the on-gray-axis grid point generation process.

  FIG. 8 is a diagram showing gray axes at which grid points are generated in the on-gray grid point generation process shown in FIG. 7.

  In the on-gray on-axis lattice point generation process shown in FIG. 7, on-gray on-axis lattice points shown by thick lines in FIG. 8, that is, on-gray on-axis lattice points are generated.

  As a method of generating the on-gray grid points, for example, a method of generating grid points at equal intervals on the gray axis, that is, linear positions, a method of generating grid points at non-linear positions on the gray axis, van Various methods may be employed, such as a method of generating a grid point whose coordinates are terms in the column of the Der Corput column.

  FIG. 9 is a flowchart of the on-gray grid point generation process shown in FIG. 7 in the case of generating grid points at equal intervals on the gray axis.

  As shown in FIG. 9, the control unit 15 obtains a string of numerical values equally dividing the range from 0 to 1 by (Ca + 1) (S181), and obtains a string excluding 0 and 1 from the string obtained in S181. (S182).

  Next, the control unit 15 substitutes the numerical value of the same term of the column determined in S182 into each channel of the RGB color space to determine a grid point on the gray axis (S183).

For example, when the number Ca of grid points on the gray axis is 3, the control unit 15 sets the range from 0 to 1 to (Ca + 1), that is, 0, 1/4, 2 as a string of numerical values equally divided by 4. / 4, 3/4, 1 are determined in S181, and 1/4, 2/4, 3/4 are determined in S182. Therefore, the control unit 15 obtains lattice points in which {r, g, b} are values shown in Equation 3 in S183.

  After the process of S183, the control unit 15 generates the group of on-gray axis lattice points obtained in S183 as a part of the lattice point group of the natural image additional table 14b (S184), and the gray shown in FIG. End the on-axis grid point generation process.

  FIG. 10 is a flowchart of the on-gray grid point generation process shown in FIG. 7 in the case of generating a grid point having coordinates of a term of van der Corput column.

  As shown in FIG. 10, the control unit 15 generates a van der Corput sequence having the same number of terms and the number Ca of on-gray axis lattice points, and the base being a positive integer of 2 or more (S201). The van der Corput sequence is a sequence in which the number of each term is greater than zero and smaller than one.

  Next, the control unit 15 substitutes the numerical value of the same term of the van der Corput sequence generated in S201 into each channel of the RGB color space to obtain a grid point on the gray axis (S202).

For example, when the number Ca of on-gray grid points is 16, if the basis is 2, the van der Corput sequence generated in S201 is as shown in Expression 4, and the on-gray grid points obtained in S202 Becomes as shown in equation 5. When the number Ca of on-gray-axis grid points is 16, if the basis is 3, the van der Corput row generated in S201 is as shown in Eq. 6, and the on-gray-axis grid points obtained in S202 Is as shown in Equation 7.

  After the process of S202, the control unit 15 generates the group of on-gray axis lattice points obtained in S202 as a part of the lattice point group of the natural image additional table 14b (S203), and the gray shown in FIG. End the on-axis grid point generation process.

  As shown in FIG. 7, when the gray-on-grid point generation process in S162 is completed, the control unit 15 generates the outermost on-shell grid point as a part of the grid point group of the natural image addition table 14b. An on-shell grid point generation process is executed (S163).

  FIG. 11 is a flowchart of the outermost shell grid point generation process shown in FIG. 7.

  As illustrated in FIG. 11, the control unit 15 generates an inter-corner line grid point generation that generates an inter-corner line grid point lattice point among the outermost shell grid points as a part of the grid point group of the natural image additional table 14 b. The process is executed (S221).

  FIG. 12 is a flowchart of the inter-corner line segment lattice point generation process shown in FIG.

  As shown in FIG. 12, the control unit 15 determines the required number of grid points on the line segment of maximum saturation, determined by the designer of the natural image additional table 14b, The number of points Cb is determined (S241).

  Next, the control unit 15 generates a grid point on the maximum saturation line segment that generates a grid point on the line segment of maximum saturation among the grid points on the line segment between corners as a part of the grid point group of the natural image additional table 14b. A point generation process is executed (S242). Note that the control unit 15 does not generate grid points that overlap with the grid points generated in S122 in the maximum saturation line segment upper lattice point generation process.

  FIG. 13 is a diagram showing a line segment of maximum saturation at which lattice points are generated in the maximum saturation line segment upper lattice point generation process shown in FIG.

  In the maximum saturation line segment upper lattice point generation process shown in FIG. 12, lattice points on the line segment of maximum saturation indicated by thick lines in FIG. 13 are generated.

  As a method of generating grid points on a line segment of maximum saturation, for example, a method of generating grid points at equal intervals on a line segment of maximum saturation, that is, linear positions, on a line segment of maximum saturation Various methods can be employed, such as a method of generating grid points at nonlinear positions in, and a method of generating grid points whose partial coordinates are terms in the van der Corput column.

  FIG. 14 is a flowchart of maximum saturation line segment upper lattice point generation processing shown in FIG. 12 in the case of generating lattice points at equal intervals on the maximum saturation line segment.

  As shown in FIG. 14, the control unit 15 obtains a string of numerical values equally dividing the range from 0 to 1 by (Cb / 6 + 1) (S261), and excludes 0 and 1 from the string obtained in S261. (S262).

  Next, the control unit 15 uses grids obtained in S262 to obtain lattice points arranged at equal intervals on each line segment of maximum saturation (S263).

For example, when the number Cb is 18, the control unit 15 sets the range from 0 to 1 to (Cb / 6 + 1), that is, 0, 1/4, 2/4, 3 as a string of numerical values equally divided by 4. / 4, 1 are determined in S261, and 1/4, 2/4, 3/4 are determined in S262. Then, the control unit 15 sets lattice points arranged at equal intervals on a line segment between red: {1, 0, 0} and yellow: {1, 1, 0} connecting red-yellow, Lattice points whose values {r, g, b} are shown in equation 8 are determined in S263. The control unit 15 sets a line segment between yellow and green, a line segment between green and cyan, a line segment between cyan and blue, a line segment between blue and magenta, and a line between magenta and red. The grid points on the minute are also determined in S263 in the same manner as the grid points on the line segment between red and yellow.

  After the process of S263, the control unit 15 generates the group of lattice points on the line segment of maximum saturation obtained in S263 as a part of the lattice point group of the natural image additional table 14b (S264) The grid point generation process on the maximum saturation line segment shown in FIG. 14 ends.

  FIG. 15 is a flowchart of the maximum saturation line segment on-grid point generation process shown in FIG. 12 in the case of generating a grid point whose partial coordinates are terms of the van der Corput column.

  As shown in FIG. 15, the control unit 15 has the same number as the quotient obtained by dividing the number Cb of lattice points on the line segment of maximum saturation by 6 and the number of terms is the same number, and the base is a positive integer of 2 or more. The van der Corput column is generated (S281).

  Next, the control unit 15 obtains grid points on each line segment of maximum saturation using the van der Corput sequence generated in S281 (S282).

For example, when the number Cb of lattice points on the line segment of maximum saturation is 24, when the basis is 2, the van der Corput sequence generated in S281 becomes as shown in Equation 9, and is obtained in S282 , Grid points on the line segment between red and yellow are as shown in equation 10. The control unit 15 sets a line segment between yellow and green, a line segment between green and cyan, a line segment between cyan and blue, a line segment between blue and magenta, and a line between magenta and red. The grid points on the minute are also determined at S 282 similarly to the grid points on the line segment between red and yellow.

  After the processing of S282, the control unit 15 generates the group of lattice points on the line segment of maximum saturation obtained in S282 as a part of the lattice point group of the natural image additional table 14b (S283). The maximum saturation line segment upper lattice point generation process shown in FIG. 15 ends.

  As shown in FIG. 12, when the maximum saturation line segment upper lattice point generation process of S 242 is completed, the control unit 15 determines white, the primary color, and 2 determined by the designer of the natural image additional table 14 b. The necessary number of grid points on a line segment between the next color and the next color (hereinafter referred to as "skyline") is determined as the number Cc of grid points on the skyline (S243).

  Next, the control unit 15 executes an on-skyline grid point generation process of generating grid points on the skyline as a part of the grid point group of the natural image addition table 14b among the on-square line point grid points (S244) . Note that the control unit 15 does not generate grid points that overlap the grid points generated in S122 in the on-skyline grid point generation process.

  FIG. 16 is a diagram showing a skyline in which grid points are generated in the on-skyline grid point generation process shown in FIG. 12.

  In the on-skyline lattice point generation process shown in FIG. 12, lattice points on the skyline shown by thick lines in FIG. 16 are generated.

  As a method of generating grid points on the skyline, for example, a method of generating grid points at equal intervals on the skyline, that is, at linear positions, a method of generating grid points at nonlinear positions on the skyline, van der Corput Various methods may be employed, such as generating grid points whose column coordinates are part of the coordinates.

  FIG. 17 is a flowchart of on-skyline grid point generation processing shown in FIG. 12 in the case of generating grid points at equal intervals on the skyline.

  As shown in FIG. 17, the control unit 15 obtains a sequence of numerical values equally dividing the range from 0 to 1 by (Cc / 6 + 1) (S301), and removes 0 and 1 from the sequence obtained in S301. Are determined (S302).

  Next, the control unit 15 uses grids obtained in S302 to obtain grid points arranged at equal intervals on each skyline (S303).

For example, when the number Cc is 12, the control unit 15 sets the range from 0 to 1 to (Cc / 6 + 1), that is, 0, 1/3, 2/3, 1 as a string of numerical values equally divided by 3. Are determined in S301, and 1/3 and 2/3 are determined in S302. Then, the control unit 15 sets grid points arranged at equal intervals on a line segment between white: {1, 1, 1} and red: {1, 0, 0}, and white-red. Lattice points whose values {r, g, b} are shown in Equation 11 are determined in S303. The control unit 15 is a line segment between white-green, a line segment between white-blue, a line segment between white-cyan, a line segment between white-magenta, and a line between white-yellow. The grid points on the minute are also obtained in S303 similarly to the grid points on the line segment between white and red.

  After the process of S303, the control unit 15 generates the group of lattice points on the skyline obtained in S303 as a part of the lattice point group of the natural image addition table 14b (S304), as shown in FIG. Finish the on-skyline grid point generation process.

  FIG. 18 is a flow chart of the on-skyline grid point generation process shown in FIG. 12 in the case of generating a grid point whose partial coordinates are terms of the van der Corput column.

  As shown in FIG. 18, the control unit 15 has the same number of terms and the quotient of dividing the number Cc of grid points on the skyline by 6, and the base is a positive integer of 2 or more. It generates (S321).

  Next, the control unit 15 obtains grid points on each skyline using the van der Corput row generated in S321 (S322).

For example, if the number Cc of grid points on the skyline is 18, when the basis is 2, the van der Corput sequence generated in S321 becomes as shown in Equation 12, and is obtained in S322, white-red The grid points on the line segment between are as shown in Equation 13. The control unit 15 is a line segment between white-green, a line segment between white-blue, a line segment between white-cyan, a line segment between white-magenta, and a line between white-yellow. The grid points on the minute are also determined in S322 similarly to the grid points on the line segment between white and red.

  After the process of S322, the control unit 15 generates the group of lattice points on the skyline obtained in S322 as a part of the lattice point group of the natural image addition table 14b (S323), as shown in FIG. Finish the on-skyline grid point generation process.

  As shown in FIG. 12, when the on-skyline grid point generation process of S244 is completed, the control unit 15 determines the black and the primary and secondary colors determined by the designer of the natural image additional table 14b. The required number of grid points on the line segment between them (hereinafter referred to as "bottom line") is determined as the number Cd of grid points on the bottom line (S245).

  Next, the control unit 15 performs bottom-bottom on-grid point generation processing that generates grid points on the bottom line among inter-corner line segments on top grid points as part of the grid point group of the natural image addition table 14b S246). Note that the control unit 15 does not generate grid points that overlap with the grid points generated in S122 in the bottom line grid point generation process.

  FIG. 19 is a diagram showing a bottom line on which grid points are generated in the bottom line on-bottom grid point generation process shown in FIG. 12.

  In the bottom line on-grid point generation process shown in FIG. 12, grid points on the bottom line indicated by thick lines in FIG. 19 are generated.

  As a method of generating grid points on the bottom line, for example, a method of generating grid points at equal intervals on the bottom line, that is, linear positions, a method of generating grid points at nonlinear positions on the bottom line, Various methods can be adopted, such as a method of generating a grid point whose partial coordinates are terms of van der Corput sequence.

  FIG. 20 is a flowchart of a process of generating grid points on the bottom line shown in FIG. 12 in the case of generating grid points at equal intervals on the bottom line.

  As shown in FIG. 20, the control unit 15 obtains a string of numerical values obtained by equally dividing the range from 0 to 1 by (Cd / 6 + 1) (S341), and a string obtained by excluding 0 and 1 from the string obtained in S341. (S342).

  Next, the control unit 15 uses grids obtained in S342 to obtain lattice points equally spaced on each bottom line (S343).

For example, when the number Cd is 12, the control unit 15 sets the range from 0 to 1 to (Cd / 6 + 1), that is, 0, 1/3, 2/3, 1 as a string of numerical values equally divided by 3. Are determined in S341, and 1/3 and 2/3 are determined in S342. Then, the control unit 15 sets grid points arranged at equal intervals on a line segment between black: {0, 0, 0} and red: {1, 0, 0} and black-red, The lattice points whose values {r, g, b} are shown in Equation 14 are determined in S343. The control unit 15 sets a line segment between black and green, a line segment between black and blue, a line segment between black and cyan, a line segment between black and magenta, and a line between black and yellow. The grid points on the minute are also obtained in S343 similarly to the grid points on the line segment between black and red.

  After the process of S343, the control unit 15 generates the group of lattice points on the bottom line obtained in S343 as a part of the lattice point group of the natural image addition table 14b (S344). The bottom line on-grid point generation process shown is ended.

  FIG. 21 is a flowchart of the bottom line on-grid-point generation process shown in FIG. 12 in the case of generating a grid point whose partial coordinates are terms of the van der Corput column.

  As shown in FIG. 21, the control unit 15 has the same number as the quotient obtained by dividing the number Cd of lattice points on the bottom line by 6 and the number of terms is the same number, and the base is a positive integer of 2 or more. Are generated (S361).

  Next, the control unit 15 obtains lattice points on each bottom line using the van der Corput row generated in S361 (S362).

For example, when the number Cd of grid points on the bottom line is 18, when the basis is 2, the van der Corput sequence generated in S361 becomes as shown in Equation 12, and is determined in S362, black-red The grid points on the line segment between are as shown in Equation 15. The control unit 15 sets a line segment between black and green, a line segment between black and blue, a line segment between black and cyan, a line segment between black and magenta, and a line between black and yellow. The grid points on the minute are also obtained in S362 similarly to the grid points on the line segment between black and red.

  After the process of S362, the control unit 15 generates the group of lattice points on the bottom line obtained in S362 as a part of the lattice point group of the natural image addition table 14b (S363). The bottom line on-grid point generation process shown is ended.

  As shown in FIG. 12, when the bottom line on-grid point generation process at S246 is completed, the control unit 15 ends the on-square line point on-grid point generation process shown in FIG.

  As shown in FIG. 11, when the inter-square line grid point generation processing in S221 is completed, the control unit 15 needs the grid points on the outermost shell surface determined by the designer of the natural image additional table 14b. The number is determined as the number Ce of lattice points on the outermost shell surface (S222).

  Next, the control unit 15 executes an outermost shell upper lattice point generation process of generating an outermost shell upper lattice point among the outermost shell upper lattice points as a part of the lattice point group of the natural image additional table 14b. (S223). Note that the control unit 15 does not generate grid points that overlap with the grid points generated in S122 in the outermost shell surface lattice point generation processing.

  As a method of generating the outermost shell surface lattice points, for example, a method of generating lattice points at equal intervals on the outermost shell surface, that is, linear positions, lattice points at the nonlinear position on the outermost shell surface A variety of methods can be adopted, such as a method of generating H.sub.x, and a method of generating lattice points whose partial coordinates are terms in the same order of two van der Corput sequences.

  FIG. 22 is a flowchart of the outermost shell surface lattice point generation process shown in FIG. 11 in the case of generating lattice points at equal intervals on the outermost shell surface.

  As shown in FIG. 22, the control unit 15 obtains a string of numerical values equally dividing the range from 0 to 1 by ((Ce / 6) ^ (1/2) +1) (S 381), and obtains in S 381 A row excluding 0 and 1 from the row is determined (S 382).

  Next, the control unit 15 uses grids obtained in S382 to obtain lattice points arranged at equal intervals on each outermost shell surface (S383).

For example, when the number Ce is 54, the control unit 15 sets the range from 0 to 1 to ((Ce / 6) ^ (1/2) +1), that is, 0 as a series of numerical values equally divided by 4. 1/4, 1/2, 3/4, 1 are determined in S381, and 1/4, 1/2, 3/4 are determined in S382. Then, in step S383, the control unit 15 obtains lattice points whose values {r, g, b} are shown in Equation 16 as lattice points arranged at equal intervals on the plane of r = 0. The control unit 15 sets the r = 1 plane, the g = 0 plane, the g = 1 plane, the b = 0 plane, and the lattice points on the b = 1 plane also on the r = 0 plane. It obtains in S383 similarly to the grid point of.

  The grid point on the line segment between white and primary color and the grid point on the line segment between black and secondary color are on the skyline grid point generation process in S244 and on the bottom line in S246, respectively. As it is generated in the lattice point generation process, it may be excluded from the lattice points obtained in S383.

  After the process of S383, the control unit 15 generates the group of lattice points on the outermost shell surface obtained in S383 as a part of the lattice point group of the natural image addition table 14b (S384). The outermost shell surface lattice point generation process shown in 22 is ended.

  FIG. 23 is a flowchart of the outermost shell on-plane grid point generation process shown in FIG. 11 in the case of generating grid points whose partial coordinates are terms of the same order in two van der Corput sequences.

  As shown in FIG. 23, the control unit 15 has the same number of terms and the square root of the quotient obtained by dividing the number Ce of lattice points on the outermost shell surface by 6, and the base is a positive integer of 2 or more. Two types of van der Corput sequences are generated (S401).

  Next, the control unit 15 obtains lattice points on each outermost shell surface using the two types of van der Corput sequences generated in S401 (S402).

For example, when generating the van der Corput sequence of base 2 and the van der Corput sequence of base 3 when the number Ce of lattice points on the outermost shell surface is 150, the basis generated in S401 The van der Corput sequence of 2 and the van der Corput sequence of base 3 are as shown in Eqs. 17 and 18, respectively, and the lattice points on the plane of r = 0 determined in S402 are Eq. It will be shown. The control unit 15 sets the r = 1 plane, the g = 0 plane, the g = 1 plane, the b = 0 plane, and the lattice points on the b = 1 plane also on the r = 0 plane. It obtains in S402 similarly to the grid point of.

  The grid point on the line segment between white and primary color and the grid point on the line segment between black and secondary color are on the skyline grid point generation process in S244 and on the bottom line in S246, respectively. As it is generated in the lattice point generation process, it may be excluded from the lattice points determined in S402.

  After the processing of S402, the control unit 15 generates the group of lattice points on the outermost shell surface obtained in S402 as a part of the lattice point group of the natural image addition table 14b (S403). The outermost shell surface lattice point generation process shown in FIG.

  In the outermost shell surface lattice point generation process shown in FIG. 23, the process of arranging the lattice point group of complementary color is not included, but the control unit 15 is 1/1 of the square root of the quotient of dividing the number Ce by 6. A complementary color grid point group may be added in S402 by generating two types of van der Corput sequences having the same number of terms as 2 and the base is a positive integer of 2 or more in S401.

  As shown in FIG. 11, when the outermost shell surface lattice point generation processing of S223 is completed, the control unit 15 ends the outermost shell upper lattice point generation processing shown in FIG.

  As shown in FIG. 7, when the outermost shell upper lattice point generation process of S163 ends, the control unit 15 ends the important lattice point generation process shown in FIG.

  As shown in FIG. 6, when the important grid point generation process of S141 is completed, the control unit 15 sets grid points corresponding to eight corners of the RGB color space, a grid point on gray axis, and a grid point on the outermost shell. The color gamut internal grid point generation processing is performed to generate grid points (hereinafter referred to as "color gamut internal grid points") which are not any of the above as part of the grid point group of the natural image additional table 14b (S142). Note that the control unit 15 does not generate lattice points overlapping the lattice points generated in S122 in the color gamut internal lattice point generation processing.

  FIG. 24 is a flowchart of the color gamut internal grid point generation process shown in FIG.

As shown in FIG. 24, the control unit 15 calculates the number q of cubic lattice points generated in S122 and the number p of important lattice points generated in S141 from Smax obtained in S121 as in the following equation A quotient n and a remainder l are obtained by dividing the subtracted number by 12 (S421).
n = Floor [(Smax-q-p) / 12]
l = (Smax-q-p)-12n

  Next, the control unit 15 generates three types of van der Corput sequences whose number of terms is the same as n calculated in S421 and whose base is a positive integer of 2 or more (S422).

  After the processing of S422, the control unit 15 nests the three types of van der Corput sequences generated in S422 and performs matrix transformation to obtain an array of “n rows and 3 columns”, thereby obtaining the same number of quotients of 3 A dimensional point group is generated (S423).

  Next, the control unit 15 generates, as a part of the grid point group of the natural image addition table 14b, a mapping point group in which the channels of the RGB color space are exchanged and combined with respect to the three-dimensional point group generated in S423. (S424).

  Next, the control unit 15 generates the lattice point group of the complementary color of the lattice point group generated in S424 as a part of the lattice point group of the natural image additional table 14b (S425). For example, assuming that the grid points generated in S424 are {r, g, b}, the control unit 15 generates {1-r, 1-g, 1-b} as a lattice point group of its complementary color. .

基底が３の場合のｖａｎ ｄｅｒ Ｃｏｒｐｕｔ列

基底が５の場合のｖａｎ ｄｅｒ Ｃｏｒｐｕｔ列

基底が７の場合のｖａｎ ｄｅｒ Ｃｏｒｐｕｔ列

基底が９の場合のｖａｎ ｄｅｒ Ｃｏｒｐｕｔ列

As the van der Corput sequence generated by the control unit 15 in S422, for example, any of the following van der Corput sequences can be adopted.
Van der Corput column with base 2

Van der Corput column for base 3

Van der Corput column for base 5

Van der Corput column for base 7

Van der Corput column with base 9

For example, when three types of van der Corput sequences whose bases are 2, 3 and 5, respectively, are generated by the control unit 15 in S422, the control unit 15 generates a three-dimensional point group shown in Formula 25 in S423. Here, in the RGB color space, there are three channels of R value, G value, and B value, and a combination (exchange) pattern of three channels is {r, g, b}, {r, b, g} There are six patterns: {g, r, b}, {g, b, r}, {b, r, g}, {b, g, r}. Therefore, when the control unit 15 associates the pattern of {r, g, b} with the three-dimensional point group shown in Eq. 25 in S424, the mapping point group {r, g, b} shown in Eq. It is generated as part of the grid point group of the additional table 14b. In addition, when the control unit 15 associates the pattern of {r, b, g} with the three-dimensional point group shown in the equation 25 in S424, the mapping point group {r, g, b} shown in the equation 26 is used for the natural image. It is generated as part of the grid point group of the additional table 14b. In addition, when the control unit 15 associates the pattern of {g, r, b} with the three-dimensional point group shown in equation 25 in S424, the mapping point group {r, g, b} shown in equation 27 is used for natural image It is generated as part of the grid point group of the additional table 14b. In addition, when the control unit 15 associates the pattern of {g, b, r} with the three-dimensional point group shown in equation 25 in S424, the map point group {r, g, b} shown in equation 28 is used for natural image It is generated as part of the grid point group of the additional table 14b. Further, when the control unit 15 associates the pattern of {b, r, g} with the three-dimensional point group shown in the equation 25 in S424, the mapping point group {r, g, b} shown in the equation 29 is used for the natural image. It is generated as part of the grid point group of the additional table 14b. Further, when the control unit 15 associates the pattern of {b, g, r} with the three-dimensional point group shown in the equation 25 in S424, the mapping point group {r, g, b} shown in the equation 30 is used for natural image It is generated as part of the grid point group of the additional table 14b. That is, the control unit 15 causes each of the three types of van der Corput sequences generated by the control unit 15 in S422 to correspond to each of the three channels of R value, G value, and B value respectively. Create grid points whose coordinates are in the same order of three van der Corput sequences.

  Here, the van der Corput sequence expanded in multiple dimensions into prime numbers is called Halton sequence. Therefore, it is generated in S 423 based on the three van der Corput sequences whose bases are prime, such as the three-dimensional point group generated in S 423 based on the three van der Corput sequences whose bases are prime respectively The three-dimensional point group is a Halton sequence. Halton columns are preferable because they are highly random and can improve the uniformity of the arrangement of grid points. However, even if the randomness drops and the crystal structure appears in the arrangement of grid points, the control unit 15 exchanges the channel information of the coordinates of the grid points in the process of S424, so that each hue plane of the basic six hues Since the lattice point group is arranged to be symmetrical with respect to the lattice point group, and the complementary color lattice point group of the lattice point group arranged in the process of S424 is also arranged in the process of S425, the uniformity of the arrangement of lattice points is ensured. can do. Therefore, the bases of the three van der Corput sequences generated in S422 may not be prime numbers. For example, the three van der Corput sequences generated in S422 may have bases 2, 3, and 9, respectively.

  After the process of S425, the control unit 15 ends the color gamut internal grid point generation process shown in FIG.

  As shown in FIG. 6, when the color gamut internal grid point generation process of S142 is completed, the control unit 15 determines the number of cubic grid points generated in S122 and the number of important grid points from Smax obtained in S121. It is determined whether the number obtained by subtracting the number of color gamut internal lattice points generated in S142 (hereinafter referred to as the "surplus number") is greater than 0 (S143).

  If the control unit 15 determines in S143 that the surplus number is larger than 0, the control unit 15 executes a lattice point allocation process of allocating the surplus lattice points to the important lattice points (S144).

  FIG. 25 is a flowchart of the lattice point allocation process shown in FIG.

  As shown in FIG. 25, the control unit 15 determines whether to add a grid point on the gray axis (S 441). For example, when the number Ca of on-gray grid points is less than the upper limit value determined by the designer of the natural image additional table 14b, the control unit 15 determines to add a on-gray grid point, and the gray axis If the number Ca of the upper grid points is the upper limit value determined by the designer of the natural image additional table 14b, it may be determined that the gray on-grid point is not added.

  The control unit 15 updates the number Ca of on-grey on-grid points so as to become the number after adding on-grey on-grid points if it is judged in S441 that the on-grey on-grid points are added (S442). Here, the number Ca of on-gray-axis grid points is updated in the range equal to or less than the upper limit value determined by the designer of the natural image additional table 14b.

  Next, the control unit 15 executes the on-gray axis grid point generation processing as in S162 (S443), and determines whether the surplus number is greater than 0 (S444).

  If the control unit 15 determines in S441 that no grid point on gray axis is added or determines in S444 that the surplus number is greater than 0, it determines whether to add a grid point on the line segment of maximum saturation. To do (S445). For example, when the number Cb of lattice points on the line segment of maximum saturation is less than the upper limit value determined by the designer of the natural image addition table 14b, the control unit 15 determines on the line segment of maximum saturation. If it is determined that a grid point is to be added and the number Cb of grid points on the line segment of maximum saturation is the upper limit value determined by the designer of the natural image additional table 14b, the line segment on maximum saturation is It may be determined not to add grid points.

  If the control unit 15 determines that the grid point on the line segment of maximum saturation is added in S445, the number of grid points on the line segment of maximum saturation is the number after the addition of grid points on the line segment of maximum saturation. The number Cb of lattice points is updated (S446). Here, the number Cb of lattice points on the line segment of maximum saturation is updated in the range equal to or less than the upper limit value determined by the designer of the natural image additional table 14b.

  Next, the control unit 15 executes the maximum saturation line segment grid point generation process as in S242 (S447), and determines whether the surplus number is greater than 0 (S448).

  The control unit 15 determines in S445 that the grid point on the line segment of maximum saturation is not added, or determines in S448 that the surplus number is greater than 0, determines whether to add the grid point on the skyline. (S449). For example, when the number Cc of grid points on the skyline is less than the upper limit value determined by the designer of the natural image additional table 14b, the control unit 15 determines to add grid points on the skyline, and If the number Cc of grid points of is an upper limit value determined by the designer of the natural image addition table 14b, it may be determined that grid points on the skyline are not added.

  The control unit 15 updates the number Cc of grid points on the skyline so as to become the number after adding grid points on the skyline when judging in S449 that the grid points on the skyline are added (S450). Here, the number Cc of lattice points on the skyline is updated in the range equal to or less than the upper limit value determined by the designer of the natural image addition table 14b.

  Next, the control unit 15 executes on-skyline grid point generation processing as in S244 (S451), and determines whether the surplus number is greater than 0 (S452).

  If the control unit 15 determines in S449 that no grid point on the skyline is to be added or if it determines in S452 that the surplus number is greater than 0, it determines whether to add a grid point on the bottom line (S453) . For example, when the number Cd of grid points on the bottom line is less than the upper limit value determined by the designer of the natural image additional table 14b, the control unit 15 determines to add grid points on the bottom line, If the number Cd of grid points on the bottom line is the upper limit value determined by the designer of the natural image addition table 14b, it may be determined that grid points on the bottom line are not added.

  The control unit 15 updates the number Cd of lattice points on the bottom line so as to become the number after the addition of lattice points on the bottom line, when judging in S453 that the lattice points on the bottom line are added (S454). Here, the number Cd of grid points on the bottom line is updated in the range equal to or less than the upper limit value determined by the designer of the natural image addition table 14b.

  Next, the control unit 15 executes a bottom line grid point generation process as in S246 (S455), and determines whether the surplus number is larger than 0 (S456).

  The control unit 15 determines in S453 that no grid point on the bottom line is added, or determines whether to add a grid point on the outermost surface if it is determined in S456 that the surplus number is greater than 0. (S457). For example, when the number Ce of lattice points on the outermost shell surface is less than the upper limit value determined by the designer of the natural image addition table 14b, the control unit 15 adds the lattice points on the outermost shell surface If it is determined that the number Ce of lattice points on the outermost shell surface is the upper limit value determined by the designer of the natural image additional table 14b, it is determined that the lattice points on the outermost shell surface are not added. It is good.

  If the control unit 15 determines that the grid point on the outermost shell surface is to be added in S457, the number Ce of grid points on the outermost shell surface is set so as to become the number after adding the grid points on the outermost shell surface. Update (S458). Here, the number Ce of lattice points on the outermost shell surface is updated in the range equal to or less than the upper limit value determined by the designer of the natural image addition table 14b.

  Next, the control unit 15 executes the outermost shell surface lattice point generation processing as in S223 (S459).

  The control unit 15 determines that the surplus number is 0 in S444, S448, S452 or S456, or does not add a grid point on the outermost shell surface in S457, or when the processing of S459 is completed, as shown in FIG. The lattice point allocation process shown in 25 is ended.

  As shown in FIG. 6, the control unit 15 determines in S143 that the surplus number is 0, or when the lattice point allocation process of S144 ends, ends the natural image lattice point group generation process shown in FIG. .

  In the above, the control unit 15 generates a grid point group on a gray axis, a grid point on a line segment with maximum saturation, a grid point on a skyline, and a bottom line in the natural image grid point group generation process. , Lattice point on the outermost shell, and gamut internal lattice point. However, in the natural image grid point group generation process, the control unit 15 generates a grid point on the gray axis, a grid point on the line segment of maximum saturation, a grid point on the skyline, and a grid point on the bottom line. It is not necessary to generate at least one of the outermost shell surface lattice point and the color gamut internal lattice point.

  As shown in FIG. 4, when the natural image grid point group generation process of S 123 is completed, the control unit 15 generates a grid point group for non natural image for generating a grid point group for the non natural image additional table 14 c. A generation process is performed (S124).

  The non-natural image lattice point group generation process of S124 is the same as the natural image lattice point group generation process of S123, and thus the detailed description will be omitted.

  The difference between the natural image grid point group generation process of S123 and the non-natural image grid point group generation process of S124 is that the grid point group generated in the natural image grid point group generation process is a non-natural image grid point It is the color conversion direction of the natural image in comparison with the lattice point group generated in the group generation process, and the lattice point group generated in the lattice point group generation process for non-natural image is generated in the lattice point group generation process for natural image It is a point that is a color conversion direction of a non-natural image as compared with the grid point group to be Here, natural images rarely include high-saturation colors and often contain low-saturation colors. Therefore, with the lattice point group in the color conversion direction of the natural image, lattice points are placed intensively in the RGB color space in order to enhance the reproducibility of the color after color conversion of the low saturation color. It is a lattice point group. On the other hand, non-natural images, such as abstract images such as graphics (Vector) and characters (Text), often contain highly saturated colors. Therefore, in order to improve the reproducibility of the color after color conversion of a high saturation color, the lattice points in the color conversion direction of the non-natural image are mainly arranged on the outermost shell of the RGB color space. Grid point group.

  For example, the lattice point group generated in the natural image lattice point group generation process is different from the lattice point group generated in the non-natural image lattice point group generation process on the gray on-axis lattice points and in the color gamut. The total number of lattice points may be large, or the number of at least one of the on-gray axis lattice points and the color gamut internal lattice points may be large. On the other hand, the lattice point group generated in the non-natural image lattice point group generation process is compared to the lattice point group generated in the natural image lattice point group generation process, and the lattice point on the line segment of maximum saturation. The total number of grid points on the skyline, grid points on the bottom line, and grid points on the outermost shell may be large, or grid points on the line segment of maximum saturation, and grid on the skyline The number of at least one of the points, the grid points on the bottom line, and the grid points on the outermost shell surface may be large.

  FIG. 26A is a perspective view of an example of a grid point group generated in the natural image grid point group generation process shown in FIG. 4. FIG. 26 (b) shows the grid shown in FIG. 26 (a) when observed from the point of white {1, 1, 1} to the point of black {0, 0, 0} It is a perspective view of a point cloud. In the example shown in FIG. 26, when the cubic lattice point group having the number of lattice points on one side of six is generated in S122, the on-gray axial lattice points and the maximum are determined in the natural image lattice point group generation process. Of the lattice points on the line segment of saturation, the lattice points on the skyline, the lattice points on the bottom line, the outermost lattice lattice point, and the gamut internal lattice point, only the gamut internal lattice point Is an example generated.

  FIG. 27A is a perspective view of an example of lattice point groups generated in the non-natural image lattice point group generation process shown in FIG. 4. FIG. 27 (b) shows the grid shown in FIG. 27 (a) when observed in the direction from the point of white {1, 1, 1} to the point of black {0, 0, 0}. It is a perspective view of a point cloud. In the example shown in FIG. 27, when a cubic lattice point group having six lattice points on one side is generated in S122, the on-gray axial lattice points in the non-natural image lattice point group generation process are generated. Of the lattice points on the line segment of maximum saturation, the lattice points on the skyline, the lattice points on the bottom line, the outermost lattice lattice point, and the gamut internal lattice point, on the outermost shell plane This is an example in which only grid points are generated.

  As shown in FIG. 4, when the non-natural image lattice point group generation process of S124 is completed, the control unit 15 ends the lattice point group generation process shown in FIG.

  As shown in FIG. 3, when the lattice point group generation process of S101 ends, the control unit 15 calculates an output value (CMYK value) corresponding to each lattice point of the lattice point group generated by the lattice point group generation process. (S102).

  The output value (CMYK value) corresponding to each grid point of the grid point group generated by the grid point group generation processing is “LUT (Lookup Table) recording the relationship between color value measured in advance and colorimetric value”. Or, it is calculated from "color conversion LUT composed of fine meshes created in advance".

  First, an output value (CMYK value) corresponding to each lattice point of the lattice point group generated by the lattice point group generation processing is obtained from “a LUT in which the relationship between the color value measured in advance and the colorimetric value is recorded”. A method of obtaining by inverse calculation will be described.

  “A LUT that records the relationship between color values measured in advance and colorimetric values” is a color patch that sets CMYK values of various color values (it may be a predetermined interval or random, but is usually separated by layers with Bk This is a LUT obtained by printing color patches in which CMYK values are set at predetermined discrete intervals in a form that can be performed by the MFP 20, and then measuring the colors of the printed color patches and converting them into XYZ values (CMYK to XYZ conversion) . “LUT recording the relationship between color values measured in advance and colorimetric values” is a LUT used for developing the cubic grid point color conversion table 14a, the natural image addition table 14b, and the non-natural image addition table 14c. This is not a LUT installed in the MFP 20. Therefore, “a LUT recording the relationship between color values measured in advance and colorimetric values” is different from the cubic grid point color conversion table 14a, the natural image addition table 14b, and the non-natural image addition table 14c, and Since there is no particular limitation on the capacity of the memory to be stored, the correspondence with the XYZ values is included for a very large number of CMYK values.

  An LUT obtained by back-calculating the “LUT in which the relationship between color values measured in advance and colorimetric values is recorded” is a LUT that converts XYZ values into CMYK values (XYZ to CMYK conversion).

  Here, XYZ values to which each lattice point (RGB value) of the lattice point group generated by the lattice point group generation processing corresponds can be recognized by the LUT (RGB to XYZ conversion). Therefore, each of the grid point groups generated by the grid point group generation process is combined with the LUT (XYZ to CMYK conversion) obtained by back-calculating the “LUT that records the relationship between color values measured in advance and colorimetric values”. Output values (CMYK values) corresponding to grid points can be obtained (RGB to CMYK conversion).

  Next, a method of obtaining an output value (CMYK value) corresponding to each grid point of the grid point group generated by the grid point group generation processing by “a color conversion LUT composed of fine meshes created in advance”. Will be explained.

  The “color conversion LUT composed of fine meshes created in advance” is an LUT indicating an output value (CMYK value) corresponding to an input value (RGB value) in the MFP 20 (RGB to CMYK conversion). “Color conversion LUT composed of fine meshes created in advance” is a LUT used for developing the cubic grid point color conversion table 14a, the natural image additional table 14b and the non-natural image additional table 14c. , It is not a LUT mounted on the MFP 20. Therefore, the “color conversion LUT composed of fine meshes created in advance” is stored differently from the cubic grid point color conversion table 14a, the natural image addition table 14b, and the non-natural image addition table 14c. There is no particular limitation on the capacity of the memory, and for a large number of RGB values, the correspondence with CMYK values is included.

  The “color conversion LUT composed of fine meshes created in advance” is shown in FIG. 29 where some or all of these intermediate steps are combined, or LUT processing of multiple stages as shown in FIG. 28 is performed. Perform such LUT processing.

  Here, the LUT processing shown in FIG. 28 will be described.

  FIG. 28 is a flowchart of a general conversion step of the color conversion process.

  In the color conversion process shown in FIG. 28, the color space of the input color is rarely the CMYK format in the application of the office machine such as MFP, but basically it is the RGB format.

S501 is an F-DM (forward device model) conversion step, which is a step of converting RGB format data into a CIE-XYZ space. For example, if an sRGB space is assumed as the RGB format, conversion may be performed according to the definition.
(SRGB to XYZ conversion)

S502 is an F-CAM (color appearance model) conversion step, for example, a step of converting from the CIE-XYZ space to the CIE-CAM02 space. Convert according to the definition of CIE-CAM02 (getting environmental conditions).
(XYZ to JCH conversion)

S503 is a GMA (gamut mapping algorithm) conversion process. A large number of companies or researchers have already proposed various methods, and among them, it is sufficient to select and apply a suitable one from the purpose, conditions, preferences, characteristics of output devices, and the like.
(JCH to J'C'H 'conversion)

S504 is a black amount generation step, in which the black amount is defined based on the JCH value after GMA conversion in S503, and is determined by calculation. Since various precedents have already been proposed by many companies or researchers, it is sufficient to select and apply one suitable from the purpose, conditions, preferences, characteristics of output devices, etc.
(J'C'H 'to (J'C'H' + K) conversion)

Step S505 is a B (backward) -CAM conversion step, in which parameters are set and converted according to the output or observation environment. It may be converted according to the definition expression of the color appearance model.
((J'C'H '+ K) to (XYZ + K) conversion)

  The order of S504 and S505 may go back and forth, and there are also such conversion types. Since the present invention is hardly affected by the order of S504 and S505, the order of S504 and S505 may be any.

S506 is a B-DM (backward device model) conversion process, and returns the device independent value (XYZ) to the output device value.
((XYZ + K) to (CMY + K) conversion)

  In step S506, a patch obtained by dividing each of the CMYK channels by, for example, m is divided by m in advance is measured to obtain K-CMY to XYZ conversion data in a state where K layers are separated, and this is used as the K layer. The BK stratified K-XYZ to K-CMY LUT may be generated by reverse calculation in another state.

  In the color conversion process shown in FIG. 28, the color space of the color to be output is in the CMYK format.

  FIG. 28 schematically shows how the conversion of each process is performed in multistage steps. However, a part of each step of S501 to S506 shown in FIG. 28 may be synthesized or separated, or by combining all the steps of S501 to S506, as shown in FIG. It may be a LUT for converting from RGB format to CMYK format.

  A method of generating the color conversion process shown in FIG. 28 will be described.

  In the color conversion step shown in FIG. 30, “the color space JCH in of the input device” is output by the same steps as S501 to S502 in the color conversion step shown in FIG.

  The color conversion process shown in FIG. 31 is a color patch in which CMYK values of various color values are set (a predetermined interval may be random or may be random, but in most cases, CMYK values are set at predetermined discrete intervals so as to be stratified by Bk) The printed color patch is printed by the MFP 20, and then the color of the printed color patch is measured and converted to an XYZ value (S541), and the lightness, saturation, and hue are matched with a color appearance model that matches the XYZ value to the environmental conditions. (S 542), and output “color space JCH out of output device”.

  Then, the “color space JCH in of the input device obtained through the color conversion process shown in FIG. 30” and the “color space JCH out of the output device obtained through the color conversion process shown in FIG. A corresponding point is set and a LUT (S503 in FIG. 28) for performing the conversion process and a LUT (S504 in FIG. 28) for setting a Bk value at the time of reproducing the corresponding point are obtained.

  Generally, the “input device color space JCH in” and the “output device color space JCH out” have different sizes and shapes. Therefore, many methods (GMA: Gamut mapping algorithm) have been proposed in the past as to how each point in the color space of the input device corresponds to the point in the color space of the output device. ing. Therefore, when associating each point in the color space of the input device with a point in the color space of the output device, among the many methods proposed in the past, it is appropriate according to the purpose, application, or condition Is selected and adopted (S 503 in FIG. 28).

  Various methods have been proposed in the past for the generation of the black ink, and therefore, an appropriate one may be selected and adopted in accordance with the purpose, application, or conditions (S 504 in FIG. 28).

  The color conversion process (S501 and S502) shown in FIG. 30, S503 and S504 obtained as described above, and the inverse conversion LUT (S505 and S506) by inverse calculation (inverse search) of the color conversion process shown in FIG. The illustration from input to output is as shown in FIG.

  As shown in FIG. 3, when the process of S102 is completed, the control unit 15 generates a color conversion table including the lattice point group generated in the lattice point group generation process of S101 and the output value calculated in S102. Then (S103), the operation shown in FIG. 3 ends. That is, the control unit 15 generates a cubic lattice point color conversion table 14a including the group of cubic lattice points generated in S122 and the output value calculated in S102 for this group, and for the natural image in S123. The natural image additional table 14b including the lattice point group generated in the lattice point group generation process and the output value calculated in S102 for this group is generated, and the lattice point group generation process for non-natural image is performed in S124. The non-natural image additional table 14c including the grid point group generated in step S2 and the output value calculated in step S102 for this group is generated.

  The combination of the cubic grid point color conversion table 14a, the natural image addition table 14b, and the non-natural image addition table 14c generated in the operation shown in FIG. 3 generates the color conversion table by any method, such as communication via a network. It is read from the apparatus 10 and stored in the MFP 20 as a combination of the cubic lattice point color conversion table 27a, the natural image addition table 27b and the non-natural image addition table 27c.

  Next, the operation of the MFP 20 will be described.

  First, the operation of the MFP 20 when the lattice point addition / non-existence information 27e is set will be described.

  When an instruction for setting the lattice point addition / non-existence information 27e is input through the operation unit 21 or the communication unit 26, the color conversion table generation unit 28b sets the lattice point addition / non-existence information 27e according to the input instruction. .

  Next, the operation of the MFP 20 in the case of executing printing based on an input image in RGB format will be described.

  FIG. 32 is a flowchart of the operation of the MFP 20 when printing is performed based on an input image in RGB format.

  As shown in FIG. 32, the color conversion table generation unit 28b executes a use color conversion table generation process for generating a color conversion table (hereinafter referred to as a "use color conversion table") used for the current printing (S601) .

  FIG. 33 is a flowchart of the used color conversion table generation process shown in FIG.

  As shown in FIG. 33, the color conversion table generating means 28b is included in the grid point group included in the cubic grid point color conversion table 27a in either one of the natural image addition table 27b and the non-natural image addition table 27c. It is judged based on the lattice point addition presence / absence information 27e whether to generate a color conversion table to which the lattice point group to be added is added (S621).

  The color conversion table generation unit 28b adds the grid point group included in any one of the natural image addition table 27b and the non-natural image addition table 27c to the grid point group included in the cubic grid point color conversion table 27a. If it is determined in S621 that the color conversion table is not generated, the grid point group included in the cubic grid point color conversion table 27a is determined as the grid point group included in the used color conversion table (S622), and the use shown in FIG. The color conversion table generation processing ends.

  The color conversion table generation unit 28b adds the grid point group included in any one of the natural image addition table 27b and the non-natural image addition table 27c to the grid point group included in the cubic grid point color conversion table 27a. If it is determined in S621 that a color conversion table is to be generated, it is determined whether the input image is a natural image (S623). Here, information on whether the input image is a natural image may be added to the input image by, for example, an operating system (OS) of the electronic device that has transmitted the input image to the MFP 20. When the information on whether the input image is a natural image is added to the input image, the color conversion table generation means 28b determines whether the input image is a natural image based on this information. It is good. The color conversion table generation unit 28b may determine whether the input image is a natural image by analyzing the color value distribution of the input image.

  When the color conversion table generation unit 28b determines in S623 that the input image is a natural image, the grid point group included in the cubic grid point color conversion table 27a and the grid point group included in the natural image additional table 27b are The grid point group included in the used color conversion table is determined (S624), and the used color conversion table generation process shown in FIG. 33 is ended.

  When the color conversion table generation unit 28b determines that the input image is not a natural image in S623, the grid point group included in the cubic grid point color conversion table 27a and the grid point group included in the non-natural image additional table 27c. Is determined as a lattice point group included in the use color conversion table (S625), and the use color conversion table generation process shown in FIG. 33 is ended.

  FIG. 34A is a perspective view of an example of the lattice point group determined in S624. FIG. 34 (b) shows the grid shown in FIG. 34 (a) when observed in a direction from the point of white {1, 1, 1} to the point of black {0, 0, 0}. It is a perspective view of a point cloud. The lattice point group shown in FIG. 34 is a lattice point group obtained by adding the lattice point group shown in FIG. 26 to the cubic lattice point group shown in FIG.

  FIG. 35A is a perspective view of an example of the grid point group determined in S625. FIG. 35 (b) shows the grid shown in FIG. 35 (a) when observed in the direction from the point of white {1, 1, 1} to the point of black {0, 0, 0}. It is a perspective view of a point cloud. The lattice point group shown in FIG. 35 is a lattice point group obtained by adding the lattice point group shown in FIG. 27 to the cubic lattice point group shown in FIG.

  As shown in FIG. 32, when the used color conversion table generation process of S601 ends, the color conversion means 28a uses conversion based on the grid point group included in the used color conversion table determined in S622, S624 or S625. The whole color gamut before color conversion by the table is divided into tetrahedron groups (S602).

  In S602, the tetrahedron of the tetrahedron group is formed of four adjacent lattice points among lattice points of the lattice point group. In particular, when considering a circumscribed sphere of four selected lattice points, a tetrahedron group is formed to form a tetrahedron group so that other lattice points do not enter inside the circumscribed sphere. good. For example, the tetrahedron group generated in S602 is a tetrahedron group configured by a three-dimensional Delaunay mesh. Here, for generation of the three-dimensional Delaunay network, an appropriate method may be used from among known generation methods. That is, it is sufficient to expand it in a three-dimensional space and obtain a tetrahedron group in the same way as drawing a Delaunay diagram on a two-dimensional surface.

  When the process of S602 is completed, the color conversion unit 28a performs a color conversion process of converting an input image in RGB format into an output image in CMYK format compatible with the printer 24 as an output device (S603).

  FIG. 36 is a flowchart of the color conversion process in S603.

  As shown in FIG. 36, the color conversion unit 28a targets RGB values not yet targeted among color values (RGB values) forming an input image in RGB format (S641).

  Next, the color conversion unit 28a executes a correspondence relationship search process for searching for the correspondence relationship between the RGB values targeted in S641 and the CMYK values. (S642).

  FIG. 37 is a flowchart of the correspondence relationship search process in S642.

  As shown in FIG. 37, the color conversion unit 28a determines whether the target RGB value is a grid point before color conversion in the use color conversion table (S661).

  When the color conversion means 28a determines that the target RGB value is the grid point before color conversion in the use color conversion table in S661, it corresponds to the target RGB value among the grid points before color conversion in the use color conversion table. The conversion value (CMYK value) associated with the grid point to be selected is specified as the CMYK value corresponding to the target RGB value (S662), and the correspondence search process shown in FIG. 37 is ended.

  If the color conversion means 28a judges that the target RGB value is not a grid point before color conversion in the used color conversion table, ie, a point between grid points in S661, a conversion value corresponding to the target RGB value ( Interpolation processing for converting CMYK values) is executed (S663).

  FIG. 38 is a flowchart of the interpolation process in S663.

  As shown in FIG. 38, the color conversion means 28a executes an inclusive tetrahedron search process for searching for a tetrahedron including the RGB value of interest from the tetrahedron groups generated in S602 (S681).

  FIG. 39 is a flowchart of included tetrahedron search processing in S681.

  As shown in FIG. 39, the color conversion means 28a targets tetrahedrons not yet targeted among the tetrahedron groups generated in S602 (S701).

  Next, the color conversion means 28a selects any two points (hereinafter, point A and point) of the four points (hereinafter, referred to as "point A, point B, point C, point D") that constitute the target tetrahedron. B) is selected (S702).

  Next, the color conversion means 28a uses the line segment formed by the two points (point A and point B) selected in S702 as the base, and points of the target RGB values (hereinafter referred to as point X), target four sides. Of the four points that constitute the body, one point other than the two points selected in S702 (hereinafter referred to as point C), and the remaining one other than the two points selected in S702, of the four points that constitute the target tetrahedron Normal vectors of three planes respectively including triangles whose apexes are points (hereinafter referred to as points D) are calculated (S703). Here, a normal vector of a plane including a triangle is an outer product of two vectors starting from one point and ending at the other two points among three points constituting the plane (for example, three vertices of a triangle) It can be calculated by calculating.

  Next, the color conversion unit 28a determines whether, among the three angles calculated in S703, the angle of the plane including the triangle having the point of the RGB value of interest as the vertex is between the angles of the remaining two planes. Is determined (S704).

  Next, the color conversion means 28a selects two points (point C and point D) not selected in S702 out of four points (point A, point B, point C and point D) constituting the target tetrahedron. (S705).

  Next, the color conversion means 28a sets the line segment formed by the two points (point C and point D) selected in S705 as the base, the point of the target RGB value (point X), and the target tetrahedron Of the points, one point other than the two points selected in S 705 (hereinafter referred to as point A), and the remaining one point other than the two points selected in S 705 among the four points constituting the target tetrahedron The normal vectors of three planes respectively including triangles whose apexes are B) are calculated (S706).

  Next, the color conversion means 28a determines whether, among the three angles calculated in S706, the angle of the plane including the triangle having the point of the RGB value of interest as the vertex is between the angles of the remaining two planes. Is determined (S707).

  Next, the color conversion unit 28a determines whether or not it is determined that there is an interval between the determination in S704 and the determination in S707 (S708).

  If it is determined in S708 that the color conversion means 28a determines that there is not an interval between at least one of the determinations, the process of S701 is performed.

  If it is determined in S 708 that the color conversion means 28 a determines that there is an interval in both determinations, the color conversion means 28 a identifies the target tetrahedron as the tetrahedron including the target RGB value (S 709). End the tetrahedron search process.

  In the included tetrahedron searching process shown in FIG. 39, in the present embodiment, a method of searching for a tetrahedron including the target RGB value based on the angle between the planes is adopted. However, a method other than the method shown in FIG. 39 may be adopted as the inclusion tetrahedron search processing of S681. For example, it is determined whether or not the point of the RGB value of interest is on the near side of each plane by using the outer product with respect to the four planes constituting the tetrahedron, and is on the near side in all planes. Under the condition, a method of specifying a tetrahedron including the RGB value of the object may be adopted.

  As shown in FIG. 38, after the inclusive tetrahedron search processing of S681, the color conversion means 28a selects the target RGB based on the ratio at which the points of the target RGB values divide the tetrahedron searched in S681. A conversion value (CMYK value) corresponding to the value is calculated (S682).

For example, the color conversion means 28a is a four-sided tetrahedron searched for in S681 (hereinafter referred to as point E, point F, point G and point H) searched for in S681. Four tetrahedra (triangular pyramids) with triangle faces (ΔFGH, ΔEGH, ΔEFH and ΔEFG) as the base and points of the RGB values of interest (point X) as vertices, ie, tetrahedron X-FGH , X-EGH, X-EFH and X-EFG. Assuming that the volumes of tetrahedron X-FGH, X-EGH, X-EFH and X-EFG are Ve, Vf, Vg and Vh, respectively, and their sum, that is, the volume of tetrahedron EFGH is Vs, the color conversion means 28a 31 can calculate the conversion value (CMYK value) corresponding to the target RGB value. In Equation 31, X cm yk is a conversion value (CMYK value) corresponding to the target RGB value. Ecmyk, Fcmyk, Gcmyk, and Hcmyk are conversion values (CMYK values) corresponding to point E, point F, point G, and point H, respectively.

For example, Ve, Vf, Vg, and Vh may be determined as shown in Equation 32, Equation 33, Equation 34, and Equation 35, respectively. Further, Vs may be obtained as the sum of Ve, Vf, Vg and Vh, or may be obtained as shown in equation 36, for example.

  As shown in FIG. 38, the color conversion means 28a ends the interpolation process shown in FIG. 38 after the process of S682.

  Although the interpolation processing shown in FIG. 38 is a tetrahedron interpolation method in the present embodiment, it may be a method other than tetrahedron interpolation method. For example, the interpolation processing may be a hexahedron interpolation method or a triangular prism interpolation method.

  As shown in FIG. 37, the color conversion means 28a ends the correspondence relationship search process shown in FIG. 37 after the interpolation process of S663.

  As shown in FIG. 36, after the correspondence relationship search process of S642, the color conversion means 28a determines whether or not there are RGB values not yet targeted among the RGB values forming the input image in RGB format. (S643).

  The color conversion means 28a executes the process of S641 when judging in S643 that there is an RGB value not yet targeted among the RGB values forming the input image of RGB format.

  When the color conversion means 28a determines in S643 that there is no RGB value not yet targeted among the RGB values forming the input image in RGB format, the color conversion means 28a determines the RGB values and the CMYK values searched by the correspondence search process of S642. Based on the correspondence relationship, the input image in RGB format is converted into an output image in CMYK format (S644), and the color conversion process shown in FIG. 36 is ended.

  As shown in FIG. 32, after the color conversion processing of S603, the control unit 28 executes printing on the recording medium by the printer 24 based on the output image of the CMYK format generated in S603 (S604). End the operation shown.

  As described above, the MFP 20 includes the grid point group included in any one of the natural image addition table 27b and the non-natural image addition table 27c in the cubic grid point group included in the cubic grid point color conversion table 27a. When generating the use color conversion table by adding only the cubic grid point group included in the cubic grid point color conversion table 27a (YES at S621), and comparing with the case (NO at S621) Since the number of grid points in the used color conversion table can be increased under the condition that the capacity of the memory for storing grid point information is limited, color reproducibility can be improved.

  If the MFP 20 generates the use color conversion table only with the cubic lattice point group included in the cubic lattice point color conversion table 27a (NO in S621), the cubic lattice point group included in the cubic lattice point color conversion table 27a The cubic grid point group is compared with the case of generating the use color conversion table by adding the grid point group included in any one of the natural image addition table 27b and the non-natural image addition table 27c (YES in S621) It is possible to facilitate the use of functions and applications that are prepared on the assumption of a color conversion table generated by only the. For example, when the color of the existing device is simulated, the MFP 20 uses the color conversion table generated only by the cubic lattice point group when capturing or using the ICC profile, for color conversion. Calculation load can be reduced.

  The MFP 20 adds a grid point group included in any one of the natural image addition table 27b and the non-natural image addition table 27c to the cubic grid point group included in the cubic grid point color conversion table 27a. In the present embodiment, whether or not to generate a color conversion table is switched according to an instruction input via the operation unit 21 or the communication unit 26. However, the MFP 20 adds the grid point group included in one of the natural image additional table 27 b and the non-natural image additional table 27 c to the cubic grid point group included in the cubic grid point color conversion table 27 a Whether to generate a color conversion table may be switched based on an image to be subjected to color conversion.

  The MFP 20 adds a natural image grid point group included in the natural image additional table 27b to the cubic grid point group included in the cubic grid point color conversion table 27a to generate a use color conversion table, and It is possible to switch between generating the use color conversion table by adding the grid point group for non-natural image included in the non-natural image additional table 27c to the cubic grid point group included in the grid point color conversion table 27a Since (S623 to S625), the color can be converted by the color conversion table suitable for the image of the color conversion target, and the color reproducibility can be improved.

  The MFP 20 adds a natural image grid point group included in the natural image additional table 27b to the cubic grid point group included in the cubic grid point color conversion table 27a to generate a use color conversion table, and Adding a grid point group for non-natural image included in the non-natural image additional table 27c to a cubic grid point group included in the grid point color conversion table 27a to generate a use color conversion table Since switching is possible based on the image to be converted, convenience can be improved.

  The MFP 20 adds a natural image grid point group included in the natural image additional table 27b to the cubic grid point group included in the cubic grid point color conversion table 27a to generate a use color conversion table, and Adding a grid point group for non-natural image included in the non-natural image additional table 27c to a cubic grid point group included in the grid point color conversion table 27a to generate a use color conversion table; The switching may be performed according to an instruction input via the communication unit 21 or the communication unit 26.

  In the present embodiment, when the RGB value of the color conversion target in the used color conversion table is not a grid point before the color conversion in the used color conversion table, the MFP 20 calculates the CMYK value after the color conversion by interpolation. When the RGB value of the color conversion target in the used color conversion table does not exist inside the tetrahedron formed by the grid points before the color conversion in the used color conversion table, the MFP 20 displays a grid in the vicinity of the target RGB value. The CMYK values after color conversion may be calculated by extrapolation with a tetrahedron configured by points.

  The MFP 20 may have the function of the color conversion table generation device 10.

  When the MFP 20 has the function of the color conversion table generation device 10, the number of grids of the cubic grid point group included in the cubic grid point color conversion table 27a may be manipulated based on the image of the color conversion target or It may be changed according to the instruction input via the unit 21 or the communication unit 26. For example, the MFP 20 may set the number of cubic lattice point groups included in the cubic lattice point color conversion table 27a to zero.

  Further, when the MFP 20 has the function of the color conversion table generation device 10, the grid point on gray axis and the line segment of maximum saturation included in each of the natural image addition table 27b and the non-natural image addition table 27c. The number of grid points on the skyline, grid points on the skyline, grid points on the bottom line, grid points on the outermost shell, and color gamut internal grid points, based on the image of the color conversion target, or It may be changed according to the instruction input via the operation unit 21 or the communication unit 26.

  The color conversion table generation device 10 generates grid points using van der Corput sequences as quasi-random numbers in the present embodiment, but may generate grid points using quasi-random numbers other than van der Corput sequences. You may use pseudo-random numbers to generate grid points.

  The image forming apparatus using the color conversion table generated by the color conversion table generation apparatus 10 is an MFP in the present embodiment, but may be an image forming apparatus other than an MFP, such as a printer dedicated machine.

20 MFP (computer, color converter)
27a cubic grid point color conversion table 27b additional table for natural image 27c additional table for non-natural image 27d color conversion program 28a color conversion means 28b color conversion table generation means

Claims (5)

A color conversion table generation step of generating a color conversion table for color conversion;
A color conversion step of converting a color using the color conversion table generated by the color conversion table generation step;
The color conversion table generation step
Generating the color conversion table only with a specific cubic lattice point group as a specific group of cubic lattice points;
2. A color conversion method comprising the steps of: adding a non-cubic lattice point group which is not a cubic lattice point group to the specific cubic lattice point group to generate the color conversion table. The color conversion table generation step
Grid points for natural images,
The color conversion method according to claim 1, characterized in that the step is switchable as the non-cubic grid point group with a non-natural image grid point group. The color conversion table generation step
A grid point group for the natural image;
The grid point group for non-natural images is a step that can be switched as the non-cubic grid point group based on an image of a target of color conversion in the color conversion step. Description method of color conversion. Color conversion table generation means for generating a color conversion table for converting colors;
Causing a computer to realize color conversion means for converting colors using the color conversion table generated by the color conversion table generation means;
The color conversion table generation unit
Generating the color conversion table only with a specific cubic lattice point group as a specific group of cubic lattice points;
A color conversion program characterized by being switchable from adding a non-cubic lattice point group which is not a cubic lattice point group to the specific cubic lattice point group to generate the color conversion table. Color conversion table generation means for generating a color conversion table for converting colors;
Color conversion means for converting a color using the color conversion table generated by the color conversion table generation means;
The color conversion table generation unit
Generating the color conversion table only with a specific cubic lattice point group as a specific group of cubic lattice points;
A color conversion apparatus characterized by being switchable between generating a color conversion table by adding a non-cubic lattice point group which is not a cubic lattice point group to the specific cubic lattice point group.

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