JP6734566B2 - Lattice point group generation method, lattice point group generation program, and lattice point group generation device - Google Patents

Description

The present invention relates to a grid point group generation method and a grid point group generation program for generating a group of grid points before color conversion in a color conversion table for converting a color of a color space of three channels into a color of another color space. And a grid point group generation device.

Conventionally, as a color conversion table for converting a color in a color space of three channels into a color in another color space, a color conversion table for converting a color in an RGB color space into a color in a CMYK color space is known ( See, for example, Patent Document 1.). When the image data in the RGB format is input, the image forming apparatus converts the image data in the RGB format into the image data in the CMYK format via the color conversion table, and then prints based on the image data in the CMYK format. Execute.

Many conventional color conversion tables have a cubic grid arrangement of grid points before color conversion, as shown in FIG. In the color conversion table in which the arrangement of grid points before color conversion is a cubic grid, the number of grid points per side of the cubic grid should be selected according to the capacity of the memory that stores the grid point information. However, it is usually determined in consideration of the required accuracy of the quality of the output image, the cost of parts for the image forming apparatus, and the like. The number of grid points required for the color conversion table in which the grid points are arranged in a cubic grid before color conversion is N^3, where N is the number of grid points per side of the cubic grid. Increases with the cube of N.

The RGB space and the CMYK space have different color gamut shapes, and moreover, the relationship between them is often non-linear. Therefore, when calculating the intermediate data between the grid points of the color conversion table by interpolation using linear interpolation, the spacing between the grid points becomes smaller as the number of grid points increases. It is possible to reduce the error from the intermediate data. That is, the greater the number of grid points in the color conversion table, the higher the accuracy of the quality of the output image by the image forming apparatus.

The upper limit of the capacity of the memory that stores the information on the grid points is determined according to the cost of parts to be mounted on the image forming apparatus. Then, the upper limit of the number of grid points of the color conversion table is determined according to the upper limit of the capacity of the memory that stores the information of the grid points. Hereinafter, the upper limit of the number of grid points that is determined according to the upper limit of the capacity of the memory that stores information on grid points is referred to as Smax. As described above, the number of grid points required for the color conversion table in which the grid points are arranged in a cubic grid before color conversion is N^3, but this rarely 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 grid points before color conversion are arranged in a cubic grid is an integer that does not exceed the cube root of Smax as in the following formula. Is set to.
Nmax = Floor [Smax^(1/3)]

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

Here, the upper limit of the number of grid points in the color conversion table in which the grid points before color conversion are arranged in a cubic grid is Nmax to the third power. Therefore, when Nmax is 10, the upper limit of the number of grid points in the color conversion table in which the grid points before color conversion are arranged in a cubic grid is 1000.

Therefore, the memory for storing the information on the grid points does not use the capacity corresponding to 1200-1000 = 100 grid points. Therefore, when using a color conversion table in which the arrangement of grid points before color conversion is a cubic grid, compare with the case of storing the maximum number of grid point information in the memory that stores the grid point information. As a result, the accuracy of the quality of the output image by the image forming apparatus becomes low.

As described above, when the arrangement of the grid points before the color conversion is a cubic grid, the accuracy of the quality of the output image by the image forming apparatus is sufficiently high under the condition that the component cost of the image forming apparatus is limited. There is a problem that it may not be secured.

Conventionally, as a grid point group generation method in which a group of grid points before color conversion in a color conversion table is not arranged in a cubic grid pattern, a group of grid points before color conversion in a color conversion table is generated by using a van der Corput sequence. A grid point group generation method is known (see, for example, Patent Documents 2 and 3). According to the grid point group generation methods described in Patent Documents 2 and 3, the number of grid points in the color conversion table can be increased under the condition that the capacity of the memory that stores grid point information is limited. Therefore, the accuracy of the quality of the output image via the color conversion table can be improved.

JP, 2005-088968, A JP, 2017-050617, A JP, 2017-050618, A

The color reproducibility in the output image via the color conversion table may be greatly affected by the reproducibility of a specific color. However, in the color conversion table generated by the grid point group generation method described in Patent Documents 2 and 3, the arrangement of the grid points before color conversion is substantially uniform, and the reproducibility of a specific color is high. There is almost no.

Therefore, it is an object of the present invention to provide a grid point group generation method, a grid point group generation program, and a grid point group generation device that can improve color reproducibility in an output image via a color conversion table. ..

A grid point group generation method of the present invention is a grid point group generation method for generating a grid point group before color conversion in a color conversion table for converting a color of a color space of three channels into a color of another color space. And a sequence generating step for generating a van der Corput sequence and a lattice point generating step for generating lattice points, wherein the sequence generating step is performed from the maximum number of lattice points that can be allocated for the color conversion table. A step of generating three van der Corp. sequences in which a quotient obtained by dividing a number obtained by subtracting a specific number by a divisor that is either 6 or 12 has the same number of terms and a basis is a positive integer of 2 or more In the grid point generating step, in each of 6 patterns in which each of the three van der Corp. sequences is associated with each of the three channels, the terms of the same order of the three van der Corp. sequences are included. On the outermost shell as a grid point existing on the outermost shell in the color space of the three channels and not at any of the eight corners. In the step of generating grid points, the number of grid points on the outermost shell generated by the grid point generation step is a remainder obtained by dividing the maximum number by subtracting the specific number by the divisor, The number is less than or equal to the total number with the specific number.

With this configuration, the grid point group generation method of the present invention positively secures the grid point on the outermost shell as the grid point before color conversion in the color conversion table, so that the high saturation color in the output image via the color conversion table is obtained. The reproducibility of can be improved.

In the grid point group generation method of the present invention, the grid point generation step includes an inter-angle line as a grid point existing on a line segment between any two of the eight corners in the color space of the three channels. It may be a step of generating a minute grid point as at least one of the outermost shell grid points.

With this configuration, the grid point group generation method of the present invention positively secures the grid point on the inter-angle line segment as at least one of the grid points on the outermost shell. When calculation is performed by interpolation, the accuracy of calculation of intermediate data on a line segment between two adjacent corners in the color space before color conversion or in the vicinity of this line segment can be improved.

In the grid point group generation method of the present invention, the grid point generation step may be a step of generating grid points on inter-angle line segments on the line segment at equal intervals.

With this configuration, the grid point group generation method of the present invention can generate grid points on inter-angle line segments by a simple calculation, so that grid points on inter-angle line segments can be easily generated.

In the grid point group generation method of the present invention, the grid point generation step is a step of generating the grid point on the inter-line segment with some of the terms of the van der Corp. sequence generated in the sequence generation step as coordinates. You can have it.

With this configuration, the grid point group generation method of the present invention does not need to change existing grid points on inter-angle line segments when a new grid point on inter-angle line segments is added. Lattice points can be easily generated.

In the grid point group generation method of the present invention, in the grid point generation step, the grid points on the outermost shell surface as grid points existing on the surface of the outermost shell in the color space of the three channels are the outermost shells. It may be a step of generating at least one of the upper grid points.

With this configuration, the grid point group generation method of the present invention positively secures the grid point on the outermost shell surface as at least one of the grid points on the outermost shell, so that the intermediate data between the grid points in the color conversion table is obtained. When is calculated by interpolation, the accuracy of calculation of intermediate data on the surface of the outermost shell in the color space before color conversion or in the vicinity of this surface can be improved.

In the grid point group generation method of the present invention, the grid point generation step may be a step of generating the grid points on the outermost shell surface at equal intervals on the surface.

With this configuration, the grid point group generation method of the present invention can generate the grid points on the outermost shell surface by a simple calculation, so that the grid points on the outermost shell surface can be easily generated.

In the grid point group generation method of the present invention, the grid point generation step includes the outermost shell surface in which two van der Corput sequences generated in the sequence generation step have the same order of terms as a part of coordinates. It may be a step of generating upper lattice points.

With this configuration, the grid point group generation method of the present invention does not need to change already existing outermost shell surface lattice points when adding a new outermost shell surface lattice point, so Lattice points on the shell surface can be easily generated.

In the grid point group generation method of the present invention, the number sequence generation step may be a step of generating the two van der Corp. sequences having different bases.

With this configuration, the grid point group generation method of the present invention improves the uniformity of the arrangement of the grid points on the outermost shell surface in which the terms of the same order in the two van der Corput sequences are part of the coordinates. The uniformity of the accuracy of the quality of the output image via the color conversion table can be improved.

In the grid point group generation method of the present invention, the grid point generation step is a step of generating angular grid points as grid points corresponding to the eight corners of the color space of the three channels. The total number of the grid points on the outermost shell and the square grid points generated by the step may be equal to or less than the total number of the remainder and the specific number.

With this configuration, since the grid point group generation method of the present invention generates grid points corresponding to eight corners of the color space before color conversion, intermediate data between grid points of the color conversion table is calculated by interpolation. In this case, it is possible to improve the accuracy of calculation of the intermediate data near the corner of the color space before color conversion.

In the grid point group generation method of the present invention, the grid point generation step generates a grid point on the gray axis as a grid point existing on the gray axis in the color space of the three channels and being neither white nor black. In the step, the total number of the outermost shell lattice points, the corner lattice points and the gray axis lattice points generated by the lattice point generation step is the sum of the remainder and the specific number. It may be less than or equal to a number.

With this configuration, the grid point group generation method of the present invention positively secures a grid point on the gray axis, that is, an achromatic grid point as a grid point before color conversion in the color conversion table. It is possible to improve the reproducibility of an achromatic color and a color close to the achromatic color, which has a large influence on the color reproducibility of the output image through the output image. Therefore, the grid point group generation method of the present invention can improve the color reproducibility in the output image via the color conversion table.

In the grid point group generation method of the present invention, the grid point generation step generates a grid point on the gray axis as a grid point existing on the gray axis in the color space of the three channels and being neither white nor black. And the total number of grid points on the outermost shell and the grid points on the gray axis generated by the grid point generation step is equal to or less than the total number of the remainder and the specific number. Is also good.

With this configuration, the grid point group generation method of the present invention positively secures a grid point on the gray axis, that is, an achromatic grid point as a grid point before color conversion in the color conversion table. It is possible to improve the reproducibility of an achromatic color and a color close to the achromatic color, which has a large influence on the color reproducibility of the output image through the output image. Therefore, the grid point group generation method of the present invention can improve the color reproducibility in the output image via the color conversion table.

In the grid point group generation method of the present invention, the sequence generation step may be a step of generating the three van der Corp. sequences having different bases.

With this configuration, the grid point group generation method of the present invention improves the uniformity of the layout of grid points with the terms having the same order in the three van der Corp. columns as coordinates, and therefore outputs through the color conversion table. The uniformity of image quality accuracy can be improved.

In the grid point group generation method of the present invention, in the sequence of steps, the quotient obtained by dividing a number obtained by subtracting the specific number from the maximum number by 12 as the divisor is the same as the number of terms van der. The grid point generating step is a step of generating a Corp. sequence, and in each of the 6 patterns, after generating grid points whose coordinates are terms in the same order of the three van der Corp. It may be a step of generating grid points of complementary colors of points.

With this configuration, the grid point group generation method of the present invention improves the uniformity of the grid point arrangement, and thus improves the uniformity of the accuracy of the quality of the output image via the color conversion table.

The grid point group generation program of the present invention is a grid point group for generating a group of grid points before color conversion in a color conversion table for converting a color of a color space of three channels into a color of another color space. The generation program is a computer that realizes a sequence generation unit that generates a van der Corput sequence and a lattice point generation unit that generates a lattice point, and the sequence generation unit is a grid that can be assigned to the color conversion table. Three van der Corputs with the same number of terms as the quotient obtained by subtracting a specific number from the maximum number of points by a divisor that is either 6 or 12, and the number of terms is a positive integer greater than or equal to 2 A row is generated, and the grid point generating means, in each of 6 patterns in which each of the three van der Corp. rows is associated with each of the three channels, has the same order of the three van der Corp. rows. The grid point generating means generates grid points whose coordinates are, and the grid point generating means is a grid point on the outermost shell as a grid point existing on the outermost shell and not at any of the eight angles in the color space of the three channels. The number of grid points on the outermost shell that generate points and are generated by the grid point generating means is the remainder obtained by dividing the maximum number by the specific number by the divisor, and the specific number. Is less than or equal to the total number of and.

With this configuration, the computer that executes the grid point group generation program of the present invention positively secures the grid points on the outermost shell as the grid points before color conversion in the color conversion table, and therefore outputs through the color conversion table. It is possible to improve the reproducibility of highly saturated colors in an image.

A grid point group generation device of the present invention is a grid point group generation device that generates a group of grid points before color conversion in a color conversion table for converting a color of a color space of three channels into a color of another color space. And a sequence generating unit for generating a van der Corpus sequence and a lattice point generating unit for generating lattice points, wherein the sequence generating unit determines the maximum number of lattice points that can be allocated for the color conversion table. Generate three van der Corput sequences with the same number of terms as the quotient obtained by dividing the number minus a specific number by a divisor that is either 6 or 12, and the basis is a positive integer greater than or equal to 2, The grid point generation means, in each of 6 patterns in which each of the three van der Corp. sequences is associated with each of the three channels, sets the terms of the same order of the three van der Corp. sequences as coordinates. The grid point generating means generates a grid point on the outermost shell as a grid point existing on the outermost shell in the color space of the three channels and being neither of the eight angles, The number of the outermost shell lattice points generated by the lattice point generation means is the total number of the remainder obtained by dividing the maximum number minus the specific number by the divisor and the specific number. It is characterized by the following.

With this configuration, the grid point group generation device of the present invention positively secures the grid point on the outermost shell as the grid point before color conversion in the color conversion table, so that the high saturation color in the output image via the color conversion table is obtained. The reproducibility of can be improved.

The grid point group generation method, grid point group generation program, and grid point group generation device of the present invention can improve color reproducibility in an output image via a color conversion table.

It is a block diagram of a color conversion table generation apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of an MFP that stores a color conversion table generated by the color conversion table generating device shown in FIG. 1. 3 is a flowchart of the operation of the color conversion table generation device shown in FIG. 1 when generating a color conversion table. 4 is a flowchart of a grid point group generation process shown in FIG. 3. It is a flowchart of the normal grid point generation process shown in FIG. It is a figure which shows the gray axis by which a grid point is produced|generated in the grid point production|generation process on a gray axis shown in FIG. 5 is a flowchart of a gray-axis grid point generation process shown in FIG. 4 when grid points are generated at equal intervals on the gray axis. 5 is a flowchart of a grid point generation processing on a gray axis shown in FIG. 4 when a grid point having a term of a van der Corput sequence as coordinates is generated. 5 is a flowchart of the outermost shell lattice point generation process shown in FIG. 4. 10 is a flowchart of a grid point generation process on an inter-angle line segment shown in FIG. 9. It is a figure which shows the line segment of the maximum saturation with which a grid point is produced|generated in the grid point production|generation process on the maximum saturation line segment shown in FIG. 11 is a flowchart of the maximum saturation line segment grid point generation processing shown in FIG. 10 when grid points are generated at equal intervals on the maximum saturation line segment. 11 is a flowchart of the maximum saturation line segment grid point generation processing shown in FIG. 10 in the case of generating a grid point in which the terms of the van der Corput sequence are a part of the coordinates. It is a figure which shows the skyline where a grid point is produced|generated in the grid point production|generation process on a skyline shown in FIG. 11 is a flowchart of the on-skyline grid point generation processing shown in FIG. 10 when grid points are generated at equal intervals on the skyline. FIG. 11 is a flowchart of the skyline on-grid point generation processing shown in FIG. 10 in the case of generating a grid point in which the terms of the van der Corp. It is a figure which shows the bottom line by which a grid point is produced|generated in the grid point production|generation process on a bottom line shown in FIG. 11 is a flowchart of the bottom line grid point generation processing shown in FIG. 10 when grid points are generated at equal intervals on the bottom line. FIG. 11 is a flowchart of the bottom line on-grid point generation processing shown in FIG. 10 in the case of generating a grid point having a part of coordinates in the van der Corput sequence. 10 is a flowchart of a grid point generation process on the outermost shell surface shown in FIG. 9 when grid points are generated at equal intervals on the outermost shell surface. 10 is a flowchart of the outermost shell surface grid point generation processing shown in FIG. 9 in the case of generating a grid point in which terms of the same order of two types of van der Corput sequences are part of the coordinates. FIG. 3A is a perspective view of a grid point group generated by the color conversion table generation device shown in FIG. 1 when three types of van der Corp. sequences having bases of 2, 3, and 5 are generated. FIG. 23B is a perspective view of the grid point group shown in FIG. 22A when observed in the direction from the white point to the black point. FIG. 3A is a perspective view of a grid point group generated by the color conversion table generation device shown in FIG. 1 when three types of van der Corp. sequences having bases of 2, 3, and 7 are generated. FIG. 23( b) is a perspective view of the lattice point group shown in FIG. 23( a) when observed in the direction from the white point to the black point. 3 is a flowchart of general conversion steps of a color conversion process executed by the MFP shown in FIG. 25 is a flowchart when the conversion step shown in FIG. 24 is a single step. 25 is a flowchart showing a color conversion process for outputting the “input device color space JCH in” used for generating the conversion step shown in FIG. 24. 25 is a flowchart showing a color conversion process for outputting the “color space JCH out of the output device” used for generating the conversion step shown in FIG. 24. FIG. 23A is a perspective view of the tetrahedral group plotted with respect to the lattice point group shown in FIG. 22, when observed from the same viewpoint as that in FIG. 22A. FIG. 29B is a perspective view of the tetrahedral group shown in FIG. 28A, when observed from the same viewpoint as that in FIG. 22B. 23A is a perspective view of the tetrahedral group plotted with respect to the lattice point group shown in FIG. 23, when observed from the same viewpoint as that in FIG. 23A. FIG. 29( b) is a perspective view of the tetrahedral group shown in FIG. 29( a) when observed from the same viewpoint as that in FIG. 23( b ). 3 is a flowchart of the operation of the MFP shown in FIG. 2 when executing printing. It is a flowchart of the color conversion process shown in FIG. 32 is a flowchart of the correspondence search process shown in FIG. 31. 33 is a flowchart of the interpolation processing shown in FIG. It is a flowchart of the inclusion tetrahedron search process shown in FIG. It is a figure which shows the conventional color conversion table.

An embodiment of the present invention will be described below with reference to the drawings.

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

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

As shown in FIG. 1, the color conversion table generation device 10 includes an operation unit 11 that is an input device such as a mouse and a keyboard to which various operations are input, and an LCD (Liquid Crystal Display) that displays various information. A display unit 12 which is a display device, a communication unit 13 which is a communication device that communicates with an external device via a network such as a LAN (Local Area Network) and the Internet, and an HDD (which 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 a computer such as a PC (Personal Computer).

The storage unit 14 can store a color conversion table 14a for the MFP 20 (see FIG. 2) for converting a color in the RGB color space into a color in the CMYK color space.

The storage unit 14 stores a grid point group generation program 14b for generating a grid point group before color conversion in the color conversion table 14a. The grid point group generation program 14b may be installed in the color conversion table generation device 10 at the manufacturing stage of the color conversion table generation device 10, or may be a CD (Compact Disk), a DVD (Digital Versatile Disk), or a USB (Universal Serial). It may be additionally installed in the color conversion table generating device 10 from an external storage medium such as a Bus memory, or may be additionally installed in the color conversion table generating device 10 from the network.

The control unit 15 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores programs and various data in advance, and a RAM (Random Access Memory) used as a work area of the CPU of the control unit 15. ) And. The CPU of the control unit 15 is adapted to execute a program stored in the ROM of the control unit 15 or the storage unit 14.

The control unit 15 executes a lattice point group generation program 14b stored in the storage unit 14 to generate a sequence generating unit 15a that generates a van der Corput sequence and a lattice point generating unit 15b that also generates a lattice point. Realize.

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

FIG. 2 is a block diagram of the MFP 20 according to this embodiment.

As shown in FIG. 2, the MFP 20 reads an image with an operation unit 21 that is an input device such as a button for inputting various operations, a display unit 22 that is a display device such as an LCD that displays various information, and an image. A scanner 23 that is a reading device, a printer 24 that is a printing device that prints on a recording medium such as paper, and a fax device that performs fax communication with an external facsimile device (not shown) via a communication line such as a public telephone line. A fax communication unit 25, a communication unit 26 that is a communication device that communicates with an external device via a network such as a LAN or the Internet, and a storage device such as a semiconductor memory or an HDD that stores various data. A storage unit 27 and a control unit 28 that controls the entire MFP 20 are provided.

The storage unit 27 can store a color conversion table 27a for converting a color in the RGB color space into a color in the CMYK color space.

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

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

FIG. 3 is a flowchart of the operation of the color conversion table generation device 10 when generating the color conversion table 14a.

As shown in FIG. 3, the control unit 15 executes a grid point group generation process for generating a group of grid points before color conversion in the color conversion table 14a (S101).

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

As shown in FIG. 4, the sequence generator 15a of the control unit 15 obtains the maximum number Smax of grid points that can be allocated for the color conversion table 14a in terms of capacity of the storage unit 27 of the MFP 20 (S111).

Next, the sequence generator 15a calculates the quotient n and the remainder 1 by dividing the number obtained by subtracting the specific number p from Smax obtained in S111 by 12, as in the following equation (S112).
n = Floor[(Smax-p) / 12]
l = Smax-12n

Here, the specific number p is the eight corners of the RGB color space as the color space before color conversion by the color conversion table 14a, that is, red (red), green (green), blue (blue), cyan (cyan). ), magenta, yellow, black and white as grid points, and grid points that exist on the gray axis in the RGB color space and are neither white nor black. Is the total of the required number of grid points on the gray axis and the required number of grid points on the outermost shell that are on the outermost shell in the RGB color space and are not any of the eight angles.

The grid points on the outermost shell are the grid points on the inter-angle line segment as grid points existing on the line segment between any two of the eight corners in the RGB color space, and the outermost shell in the RGB color space. Planes, that is, r=0 plane, r=1 plane, g=0 plane, g=1 plane, b=0 plane, and lattice points existing on the b=1 plane There exists a grid point on the outermost shell surface of.

The grid point on the inter-angle line segment has a maximum saturation line segment, that is, a line segment between red-yellow, a line segment between yellow-green, a line segment between green-cyan, and a line between cyan-blue. , A line segment between blue-magenta, and a grid point on the line segment between magenta-red. In addition, at the grid point on the inter-angle line segment, a line segment between white and the primary color, that is, a line segment between white-red, a line segment between white-green, and a white-blue line segment. Between the grid points on the line segment between and the white and the secondary color, that is, the line segment between white-cyan, the line segment between white-magenta, and the white-yellow And a grid point on the line segment of. In addition, at the grid point on the inter-angle line segment, a line segment between black and the primary color, that is, a line segment between black-red, a line segment between black-green, and a black-blue line segment. Between the black point and the secondary color, that is, the line segment between black-cyan, the line segment between black-magenta, and the line segment between black-yellow and There is a grid point on the line segment of.

The required number of grid points on the gray axis, the required number of grid points on the line segment of maximum saturation, the required number of grid points on the line segment between the white and the primary colors, and the white and secondary colors The required number of grid points on the line segment between them, the required number of grid points on the line segment between black and the primary color, and the required number of grid points on the line segment between black and the secondary color , The required number of grid points on the outermost shell surface is determined by the designer of the color conversion table 14a.

After the processing of S112, the control unit 15 is a grid point that is not any of the grid points corresponding to the eight corners of the RGB color space, the grid points on the gray axis, and the grid points on the outermost shell (hereinafter referred to as “normal grid”). A normal grid point generation process for generating a "point") as a part of the grid point group of the color conversion table 14a is executed (S113).

FIG. 5 is a flowchart of the ordinary grid point generation processing shown in FIG.

As shown in FIG. 5, the sequence generator 15a generates three types of van der Corp. sequences having the same number of terms as n calculated in S112 and a basis of a positive integer of 2 or more (S131). The van der Corp. sequence is a sequence in which the number of each term is larger than 0 and smaller than 1.

After the processing of S131, the lattice point generation means 15b of the control unit 15 nests the three types of van der Corput columns generated in S131 and performs matrix conversion to obtain an array of "n rows and 3 columns". The same number of three-dimensional point groups as the quotient n is generated (S132).

Next, the grid point generation unit 15b generates 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 S132, as a part of the grid point group of the color conversion table 14a. (S133).

Next, the grid point generation means 15b generates a grid point group of complementary colors of the grid point group generated in S133 as a part of the grid point group of the color conversion table 14a (S134). For example, if the grid points generated in S133 are {r, g, b}, the grid point generation means 15b sets {1-r, 1-g, 1-b} as a grid point group of complementary colors. To generate.

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It should be noted that as the van der Corp. sequence generated by the sequence generating unit 15a in S131, for example, any of the following van der Corp. sequences can be adopted.
Van der Corp. sequence when the base is 2

Van der Corp. sequence when the base is 3

The van der Corput sequence when the base is 5.

Van der Corp. sequence when base is 7

Van der Corput sequence when the base is 9

For example, when three types of van der Corp. sequences having bases of 2, 3, and 5 are generated in S131 by the sequence generation unit 15a, the grid point generation unit 15b generates the three-dimensional point group shown in Formula 6 in S132. To generate. Here, the RGB color space has three channels of R value, G value, and B value, and the combination (exchange) patterns of the three channels are {r,g,b}, {r,b,g}. , {G,r,b}, {g,b,r}, {b,r,g}, {b,g,r} exist. Therefore, when the grid point generation unit 15b associates the pattern of {r,g,b} with the three-dimensional point group shown in Expression 6 in S133, the mapping point group {r,g,b} shown in Expression 6 It is generated as a part of the grid point group of the conversion table 14a. When the grid point generation unit 15b associates the pattern of {r,b,g} with the three-dimensional point group shown in Formula 6 in S133, the mapping point group {r,g,b} shown in Formula 7 It is generated as a part of the grid point group of the conversion table 14a. When the grid point generation unit 15b associates the pattern of {g,r,b} with the three-dimensional point group shown in Formula 6 in S133, the mapping point group {r,g,b} shown in Formula 8 It is generated as a part of the grid point group of the conversion table 14a. Further, when associating the pattern of {g,b,r} with the three-dimensional point group shown in Expression 6 in S133, the grid point generation means 15b changes the mapping point group {r,g,b} shown in Expression 9 into It is generated as a part of the grid point group of the conversion table 14a. Further, when associating the pattern of {b,r,g} with the three-dimensional point group shown in Expression 6 in S133, the grid point generation means 15b changes the mapping point group {r,g,b} shown in Expression 10 into It is generated as a part of the grid point group of the conversion table 14a. Further, when associating the pattern of {b,g,r} with the three-dimensional point group shown in Expression 6 in S133, the grid point generation means 15b changes the mapping point group {r,g,b} shown in Expression 11 into colors. It is generated as a part of the grid point group of the conversion table 14a. That is, the grid point generation means 15b has 6 patterns in which each of the three types of van der Output sequences generated in S131 by the sequence generation means 15a is associated with each of the three channels of R value, G value and B value. In each of the above, a grid point having coordinates of terms of the same order in the three types of van der Corp. sequences is generated.

Here, the van der Corp. sequence expanded into a multidimensional prime number is called a Halton sequence. Therefore, the three-dimensional point cloud generated in S132 based on the three types of van der Corp. sequences whose bases are prime numbers, etc. The three-dimensional point cloud is a Halton sequence. The Halton sequence is preferable because it has high randomness and can improve the uniformity of arrangement of lattice points. However, even if the randomness deteriorates and the crystal structure appears in the arrangement of the lattice points, the lattice point generation means 15b exchanges the channel information of the coordinates of the lattice points in the process of S133, thereby making each of the six basic hues different. Since the grid point groups are arranged so as to be symmetric with respect to the hue plane, and the grid point group of the complementary color of the grid point group arranged in the process of S133 is also arranged in the process of S134, the uniformity of the arrangement of the grid points is uniform. Can be secured. Therefore, the bases of the three types of van der Corput sequences generated in S131 may not be prime numbers. For example, the bases of the three types of van der Corp. sequences generated in S131 may be 2, 3, and 9, respectively.

After the processing of S134, the control unit 15 ends the normal grid point generation processing shown in FIG.

As shown in FIG. 4, when the normal grid point generation processing of S113 is completed, the grid point generation means 15b has eight corners of the RGB color space, that is, {r, g, b} are values shown in Expression 12, respectively. A certain grid point is generated as a part of the grid point group of the color conversion table 14a (S114).

Next, the control unit 15 executes the gray-axis on-grid point generation processing for generating the gray-axis on-grid points as a part of the grid point group of the color conversion table 14a (S115).

FIG. 6 is a diagram showing a gray axis on which grid points are generated in the grid point generation processing on the gray axis shown in FIG.

In the gray-axis on-axis grid point generation processing shown in FIG. 4, grid points on the gray-axis on the gray axis shown in FIG. 6, that is, gray-axis on-grid points are generated.

As a method of generating grid points on the gray axis, for example, a method of generating grid points at equal intervals on the gray axis, that is, a method of generating grid points at a linear position, a method of generating grid points at a non-linear position on the gray axis, van Various methods can be adopted, such as a method of generating a lattice point whose coordinates are terms in the der Corp. sequence.

FIG. 7 is a flowchart of the grid point generation processing on the gray axis shown in FIG. 4 when grid points are generated at equal intervals on the gray axis.

As shown in FIG. 7, the grid point generation means 15b determines the number Ca of grid points on the gray axis (S141). Here, the number Ca of grid points on the gray axis is basically the required number of grid points on the gray axis used in S112. However, as the number Ca of grid points on the gray axis, at least a part of the remainder l calculated in S112 may be added. For example, when the grid point generation means 15b determines the number Ca of grid points on the gray axis by adding at least a part of the grid residue on the gray axis to the required number of grid points on the gray axis, The number obtained by subtracting 6 from the remainder l may be added to the required number of grid points on the gray axis, or when the remainder l is less than 6, all the remainder l are added to the required number of grid points on the gray axis. May be. In addition, the number Ca of grid points on the gray axis is generated in the normal grid point generation processing of S113 when the number of grid points actually generated in the normal grid point generation processing of S113 is smaller than the planned number of grid points. At least a part of the difference between the planned number of grid points and the number of grid points actually generated in the normal grid point generation processing of S113 may be added.

After the processing of S141, the grid point generating means 15b obtains a sequence of numerical values that equally divides the range from 0 to 1 by (Ca+1) (S142), and removes the columns obtained by excluding 0 and 1 from the sequence obtained in S142. Ask (S143).

Next, the grid point generation means 15b finds grid points on the gray axis by substituting the numerical values of the same term in the column found in S143 into each channel of the RGB color space (S144).

For example, when the number Ca of grid points on the gray axis is 3, the grid point generation unit 15b sets 0, 1/4 as a sequence of numerical values that equally divides the range from 0 to 1 into (Ca+1). 2/4, 3/4, 1 are obtained in S142, and 1/4, 2/4, 3/4 are obtained in S143. Therefore, the grid point generation means 15b obtains grid points whose {r, g, b} are the values shown in the equation 13 in S144.

After the processing of S144, the grid point generation means 15b generates the group of grid points on the gray axis obtained in S144 as a part of the grid point group of the color conversion table 14a (S145), and then the gray point shown in FIG. The on-axis grid point generation processing ends.

FIG. 8 is a flowchart of the grid point generation processing on the gray axis shown in FIG. 4 in the case of generating a grid point whose coordinates are the terms of the van der Corput sequence.

As shown in FIG. 8, the grid point generation unit 15b determines the number Ca of grid points on the gray axis, similarly to the processing of S141 (S151).

Next, the sequence generator 15a generates a van der Corp. sequence in which the number of terms Ca is the same as the number Ca determined in S151 and the basis is a positive integer of 2 or more (S152).

Next, the grid point generation unit 15b obtains grid points on the gray axis by substituting the numerical values of the same term of the van der Corp. sequence generated in S151 into each channel of the RGB color space (S153).

For example, when the number Ca determined in S151 is 16, when the base is 2, the van der corp. sequence generated in S152 is as shown in Equation 14, and the gray-axis on-grid point obtained in S153 is It becomes as shown in Expression 15. Further, when the number Ca determined in S151 is 16, when the basis is 3, the van der Corp. sequence generated in S152 becomes as shown in Equation 16, and the gray-axis on-axis lattice point obtained in S153 is It becomes as shown in Formula 17.

After the processing of S153, the grid point generation unit 15b generates the group of grid points on the gray axis obtained in S153 as a part of the grid point group of the color conversion table 14a (S154), and then the gray point shown in FIG. The on-axis grid point generation processing ends.

As shown in FIG. 4, when the gray-axis on-grid point generation processing of S115 ends, the control unit 15 generates the outer-most-shell grid points as a part of the grid point group of the color conversion table 14a. Lattice point generation processing is executed (S116).

FIG. 9 is a flowchart of the outermost shell lattice point generation processing shown in FIG.

As shown in FIG. 9, the control unit 15 performs the inter-angle line segment upper grid point generation processing of generating the inter-angle line segment upper grid points among the outermost shell upper grid points as a part of the grid point group of the color conversion table 14a. Execute (S161).

FIG. 10 is a flowchart of the inter-angle line segment upper grid point generation processing shown in FIG. 9.

As shown in FIG. 10, the control unit 15 generates the maximum saturation line that generates the grid point on the line segment with the maximum saturation among the grid points on the inter-angle line segment as a part of the grid point group of the color conversion table 14a. The minute grid point generation processing is executed (S171).

FIG. 11 is a diagram showing line segments of maximum saturation at which grid points are generated in the grid point generation processing on the maximum saturation line segment shown in FIG.

In the maximum saturation line segment grid point generation processing shown in FIG. 10, grid points on the maximum saturation line segment shown by the bold line in FIG. 11 are generated.

As a method of generating grid points on the maximum saturation line segment, for example, a method of generating grid points at equal intervals on the maximum saturation line segment, that is, at linear positions, on the maximum saturation line segment Various methods can be adopted, such as a method of generating a lattice point at a non-linear position, a method of generating a lattice point in which a term of the van der Corp. sequence is a part of coordinates, and the like.

FIG. 12 is a flowchart of the maximum saturation line segment grid point generation processing shown in FIG. 10 when grid points are generated at equal intervals on the maximum saturation line segment.

As shown in FIG. 12, the grid point generation means 15b determines the number Cb of grid points on the line segment having the maximum saturation (S181). Here, the number Cb of grid points on the line segment of maximum saturation is basically the required number of grid points on the line segment of maximum saturation used in S112. However, the number Cb of grid points on the line segment having the maximum saturation is not limited to the remainder 1 calculated in S112, even if at least a part of the number not used in the grid point generation processing on the gray axis in S115 is added. good. For example, when the grid point generation means 15b adds at least a part of the remainder l to the required number of grid points on the line segment having the maximum saturation to determine the number Cb, the remainder l is on the gray axis of S115. When the number not used in the grid point generation processing is 6 or more, 6 of the remainder l may be added to the required number of grid points on the line segment having the maximum saturation. If the number of grid points Cb on the line segment having the maximum saturation is less than the planned number of grid points actually generated in the normal grid point generation processing of S113, the normal grid point generation processing of S113 is performed. Of the difference between the number of grid points scheduled to be generated in S3 and the number of grid points actually generated in the normal grid point generation processing of S113, which is used in the gray axis grid point generation processing of S115 You may add at least one part of the number which is not done.

After the processing of S181, the grid point generation means 15b obtains a sequence of numerical values that equally divides the range from 0 to 1 by (Cb/6+1) (S182), and excludes 0 and 1 from the sequence obtained in S182. A row is obtained (S183).

Next, the grid point generation means 15b uses the row found in S183 to find grid points arranged at equal intervals on each line segment of maximum saturation (S184).

For example, when the number Cb is 18, the grid point generation means 15b sets 0, 1/4, 2/4 as a sequence of numerical values that divide the range from 0 to 1 into (Cb/6+1), that is, 4 3/4, 1 are obtained in S182, and 1/4, 2/4, 3/4 are obtained in S183. Then, the grid point generation means 15b arranges grid points arranged at equal intervals on a line segment between red-yellow connecting red:{1,0,0} and yellow:{1,1,0}. As a result, grid points having {r, g, b} each having the value shown in Expression 18 are obtained in S184. The grid point generation means 15b includes a line segment between yellow-green, a line segment between green-cyan, a line segment between cyan-blue, a line segment between blue-magenta, and a line between magenta-red. The grid points on the line segment of are also obtained in S184 similarly to the grid points on the line segment between red and yellow.

After the processing of S184, the grid point generation means 15b generates the group of grid points on the line segment having the maximum saturation obtained in S184 as a part of the grid point group of the color conversion table 14a (S185). The grid point generation processing on the maximum saturation line segment shown in FIG.

FIG. 13 is a flowchart of the maximum saturation line segment grid point generation processing shown in FIG. 10 in the case of generating a grid point in which the terms in the van der Corput sequence are a part of the coordinates.

As shown in FIG. 13, the grid point generation means 15b determines the number Cb of grid points on the line segment having the maximum saturation, similarly to the processing of S181 (S191).

Next, the sequence generator 15a generates a van der Corpse sequence in which the quotient obtained by dividing the number Cb determined in S191 by 6 is the same as the number of terms, and the base is a positive integer of 2 or more (S192).

Next, the grid point generation unit 15b uses the van der Corp. sequence generated in S192 to obtain grid points on each line segment having the maximum saturation (S193).

For example, when the number Cb determined in S191 is 24, when the base is 2, the van der Corp. sequence generated in S192 becomes as shown in Formula 19, and the red-yellow range between red-yellow calculated in S193 is obtained. The grid points on the line segment are as shown in Expression 20. The grid point generation means 15b includes a line segment between yellow-green, a line segment between green-cyan, a line segment between cyan-blue, a line segment between blue-magenta, and a line between magenta-red. The grid points on the line segment of are also obtained in S193 similarly to the grid points on the line segment between red and yellow.

After the processing of S193, the grid point generation means 15b generates the group of grid points on the line segment having the maximum saturation obtained in S193 as a part of the grid point group of the color conversion table 14a (S194). , The grid point generation processing on the maximum saturation line segment shown in FIG. 13 ends.

As illustrated in FIG. 10, when the maximum saturation line segment upper grid point generation processing of S171 is completed, the control unit 15 determines that the white and the primary color and the secondary color are included in the inter-angle line segment upper grid points. The grid point on the skyline (hereinafter referred to as "skyline") is generated as a part of the grid point group of the color conversion table 14a (S172).

FIG. 14 is a diagram showing a skyline in which grid points are generated in the skyline grid point generation processing shown in FIG.

In the skyline grid point generation processing shown in FIG. 10, grid points on the skyline shown by thick lines in FIG. 14 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, a method of generating grid points at a non-linear position on the skyline, a van der corp Various methods can be adopted, such as a method of generating grid points in which a column term is a part of coordinates.

FIG. 15 is a flowchart of the on-skyline grid point generation processing shown in FIG. 10 when grid points are generated at equal intervals on the skyline.

As shown in FIG. 15, the grid point generation means 15b determines the number Cc of grid points on the skyline (S201). Here, the number Cc of grid points on the skyline is basically the required number of grid points on the skyline used in S112. However, the number Cc of grid points on the skyline is used in both the gray axis on-axis grid point generation processing of S115 and the maximum saturation line segment grid point generation processing of S171 of the remainder l calculated in S112. You may add at least one part of the number that does not exist. For example, when the grid point generation means 15b adds at least a part of the remainder l to the required number of grid points on the skyline to determine the number Cc, of the remainder l, the grid point generation processing on the gray axis in S115 and When the number not used in any of the maximum saturation line segment grid point generation processing in S171 is 6 or more, 6 of the remainder l may be added to the required number of grid points on the skyline. Further, the number Cc of grid points on the skyline is generated in the normal grid point generation processing of S113 when the number of grid points actually generated in the normal grid point generation processing of S113 is smaller than the planned number of grid points. Of the difference between the planned number of grid points and the number of grid points actually generated in the normal grid point generation processing of S113, the gray-axis grid point generation processing of S115 and the maximum saturation line of S171. At least a part of the number not used in any of the minute grid point generation processing may be added.

After the processing of S201, the grid point generation means 15b obtains a sequence of numerical values that equally divides the range from 0 to 1 by (Cc/6+1) (S202), and excludes 0 and 1 from the sequence obtained in S202. A column is calculated (S203).

Next, the grid point generation means 15b uses the columns found in S203 to find grid points arranged at equal intervals on each skyline (S204).

For example, when the number Cc is 12, the grid point generation unit 15b sets 0, 1/3, 2/3 as a sequence of numerical values that divide the range from 0 to 1 into (Cc/6+1), that is, 3 1 is obtained in S202, and 1/3 and 2/3 are obtained in S203. Then, the grid point generation means 15b arranges grid points arranged at equal intervals on a line segment between white-red that connects white:{1,1,1} and red:{1,0,0}. As a result, grid points having {r, g, b} each having the value shown in Expression 21 are obtained in S204. The grid point generation means 15b includes 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 line segment of are also obtained in S204 similarly to the grid points on the line segment between white-red.

After the processing of S204, the grid point generation means 15b generates the group of grid points on the skyline obtained in S204 as a part of the grid point group of the color conversion table 14a (S205), and is shown in FIG. The grid point generation processing on the skyline ends.

FIG. 16 is a flowchart of the skyline on-grid point generation processing shown in FIG. 10 in the case of generating a grid point whose coordinates are some of the terms in the van der Corput sequence.

As shown in FIG. 16, the grid point generation means 15b determines the number Cc of grid points on the skyline, as in the process of S201 (S211).

Next, the sequence generator 15a generates a van der Corpus sequence in which the quotient obtained by dividing the number Cc determined in S211 by 6 has the same number of terms and the basis is a positive integer of 2 or more (S212).

Next, the grid point generation means 15b obtains grid points on each skyline by using the van der Corp. sequence generated in S212 (S213).

For example, when the number Cc determined in S211 is 18, when the base is 2, the van der Corput sequence generated in S212 becomes as shown in Formula 22, and the range between white-red obtained in S213 is obtained. The grid points on the line segment are as shown in equation 23. The grid point generation means 15b includes 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 line segment of are also obtained in S213 similarly to the grid points on the line segment between white-red.

After the processing of S213, the grid point generation means 15b generates the group of grid points on the skyline obtained in S213 as a part of the grid point group of the color conversion table 14a (S214), and is shown in FIG. The grid point generation processing on the skyline ends.

As illustrated in FIG. 10, when the skyline upper grid point generation processing of S172 is finished, the control unit 15 selects a line segment (black line of the inter-angle line segment upper grid point) between the primary color and the secondary color. Hereinafter, a bottom line on-grid point generation process for generating grid points on the "bottom line") as a part of the grid point group of the color conversion table 14a is executed (S173).

FIG. 17 is a diagram showing a bottom line on which grid points are generated in the grid point generation processing on the bottom line shown in FIG. 10.

In the grid-on-bottom-line generation processing shown in FIG. 10, grid points on the bottom-line indicated by thick lines in FIG. 17 are generated.

As a method of generating grid points on the bottom line, for example, at equal intervals on the bottom line, that is, a method of generating grid points at a linear position, a method of generating grid points at a non-linear position on the bottom line, Various methods can be adopted, such as a method of generating lattice points in which the terms of the van der Corput sequence are a part of the coordinates.

FIG. 18 is a flowchart of the bottom line grid point generation processing shown in FIG. 10 when grid points are generated on the bottom line at equal intervals.

As shown in FIG. 18, the grid point generation means 15b determines the number Cd of grid points on the bottom line (S221). Here, the number Cd of grid points on the bottom line is basically the required number of grid points on the bottom line used in S112. However, the number Cd of grid points on the bottom line is the gray level on-axis grid point generation processing of S115, the maximum saturation line segment grid point generation processing of S171, and the skyline grid on S172 of the remainder l calculated in S112. At least a part of the number that is not used in any of the point generation processing may be added. For example, when the grid point generation unit 15b adds at least a part of the remainder l to the required number of grid points on the bottom line to determine the number Cd, the grid point generation processing on the gray axis in S115 of the remainder l is performed. , When the number not used in either the maximum saturation line segment grid point generation processing of S171 or the skyline grid point generation processing of S172 is 6 or more, 6 of the remainder l is set to the grid point on the bottom line. You may add to the required number of. Further, the number Cd of grid points on the bottom line is generated in the normal grid point generation processing of S113 when the number of grid points actually generated in the normal grid point generation processing of S113 is smaller than the planned number of grid points. Among the differences between the number of planned grid points and the number of grid points actually generated in the normal grid point generation processing of S113, the gray axis grid point generation processing of S115 and the maximum saturation of S171 At least a part of the number not used in both the line segment grid point generation processing and the skyline grid point generation processing in S172 may be added.

After the processing of S221, the grid point generation means 15b obtains a sequence of numerical values that equally divides the range from 0 to 1 by (Cd/6+1) (S222), and excludes 0 and 1 from the sequence obtained in S222. A row is obtained (S223).

Next, the grid point generation means 15b uses the row found in S223 to find grid points arranged at equal intervals on each bottom line (S224).

For example, when the number Cd is 12, the grid point generation means 15b defines a range of 0 to 1 as (Cd/6+1), that is, 0, 1/3, 2/3 as a sequence of numerical values equally divided by 3. 1 is obtained in S222, and 1/3 and 2/3 are obtained in S223. Then, the grid point generation means 15b is arranged at equal intervals on the line segment between black-red connecting black:{0,0,0} and red:{1,0,0}. As a result, the grid points where {r, g, b} are the values shown in Expression 24 are obtained in S224. The grid point generation means 15b uses a line segment between black-green, a line segment between black-blue, a line segment between black-cyan, a line segment between black-magenta, and a line segment between black-yellow. The grid points on the line segment of are also obtained in S224 similarly to the grid points on the line segment between black-red.

After the processing of S224, the grid point generation means 15b generates the group of grid points on the bottom line obtained in S224 as a part of the grid point group of the color conversion table 14a (S225), and then, in FIG. The process for generating lattice points on the bottom line shown is ended.

FIG. 19 is a flowchart of the bottom line on-grid point generation processing shown in FIG. 10 in the case of generating a grid point in which terms in the van der Corput sequence are a part of the coordinates.

As shown in FIG. 19, the grid point generation means 15b determines the number Cd of grid points on the bottom line, as in the processing of S221 (S231).

Next, the sequence generator 15a generates a van der Corpse sequence in which the quotient obtained by dividing the number Cd determined in S231 by 6 has the same number of terms and the basis is a positive integer of 2 or more (S232).

Next, the grid point generation means 15b obtains grid points on each bottom line using the van der Corp. sequence generated in S232 (S233).

For example, when the number Cd determined in S231 is 18, when the base is 2, the van der Corp. sequence generated in S232 becomes as shown in Formula 22, and the black-red range between black-red obtained in S233 is obtained. The grid points on the line segment are as shown in Expression 25. The grid point generation means 15b uses a line segment between black-green, a line segment between black-blue, a line segment between black-cyan, a line segment between black-magenta, and a line segment between black-yellow. The grid points on the line segment of are also obtained in S233 similarly to the grid points on the line segment between black-red.

After the processing of S233, the grid point generation means 15b generates the group of grid points on the bottom line obtained in S233 as a part of the grid point group of the color conversion table 14a (S234), and in FIG. The process for generating lattice points on the bottom line shown is ended.

As shown in FIG. 10, when the bottom line on-grid point generation processing of S173 is completed, the control unit 15 ends the inter-angle line segment on grid point generation processing shown in FIG.

As illustrated in FIG. 9, when the inter-angle line segment upper grid point generation processing in S161 ends, the control unit 15 sets the outermost shell surface grid points among the outermost shell grid points to the grid point group of the color conversion table 14a. A grid point generation process on the outermost shell surface generated as a part of is executed (S162).

As a method of generating the grid points on the outermost shell surface, for example, a method of generating grid points at equal intervals on the outermost shell surface, that is, linear positions, or a non-linear position on the outermost shell surface Various methods can be adopted, such as a method of generating a grid point having a part of coordinates of the same order terms of the two types of van der Corp. sequences.

FIG. 20 is a flowchart of the grid point generation processing on the outermost shell surface shown in FIG. 9 when grid points are generated at even intervals on the outermost shell surface.

As shown in FIG. 20, the grid point generation means 15b determines the number Ce of grid points on the outermost shell surface (S241). Here, the number Ce of lattice points on the outermost shell surface is basically the required number of lattice points on the outermost shell surface used in S112. However, the number Ce of grid points on the outermost shell surface is used in both the gray axis on-axis grid point generation processing of S115 and the inter-angle line segment grid point generation processing of S161 of the remainder l calculated in S112. Not at least some of the numbers may be added. For example, when the grid point generation unit 15b adds at least a part of the remainder l to the required number of grid points on the outermost shell surface to determine the number Ce, the grid point on the gray axis in S115 of the remainder l. When the number not used in both the generation processing and the grid point generation processing on the inter-angle line segment in S161 is 6 or more, add 6 of the remainder l to the required number of grid points on the outermost shell surface. Is also good. Further, the number Ce of grid points on the outermost shell surface is generated in the normal grid point generation processing of S113 when the number of grid points actually generated in the normal grid point generation processing of S113 is smaller than the planned number of grid points. Among the differences between the number of grid points that are scheduled to be performed and the number of grid points that are actually generated in the normal grid point generation processing of S113, the gray axis on-axis grid point generation processing of S115 and the corner interval of S161. At least a part of the numbers not used in any of the line segment grid point generation processing may be added.

After the processing of S241, the grid point generation means 15b obtains a sequence of numerical values that equally divides the range from 0 to 1 by ((Ce/6)^(1/2)+1) (S242), and obtains it in S242. A column in which 0 and 1 are excluded is obtained from the column (S243).

Next, the grid point generation unit 15b uses the row calculated in S243 to calculate grid points arranged at equal intervals on each outermost shell surface (S244).

For example, when the number Ce is 54, the grid point generation means 15b defines a range of 0 to 1 as ((Ce/6)^(1/2)+1), that is, a sequence of numerical values equally dividing by 4 0, 1/4, 1/2, 3/4, 1 are obtained in S242, and 1/4, 1/2, 3/4 are obtained in S243. Then, the grid point generation means 15b obtains grid points having {r, g, b} each of which is a value shown in Expression 26 as grid points arranged at equal intervals on the surface of r=0 in S244. The grid point generation unit 15b sets r=0 for the r=1 surface, the g=0 surface, the g=1 surface, the b=0 surface, and the grid point on the b=1 surface. Similar to the lattice points on the surface, it is determined in S244.

The grid points on the line segment between white and the primary color and the grid points on the line segment between the black and the secondary color are on the skyline grid point generation process of S172 and on the bottom line of S173, respectively. Since it is generated in the lattice point generation processing, it may be excluded from the lattice points calculated in S244. Then, the grid point generation means 15b uses at least some of the excluded grid points as grid points on the gray axis, grid points on the line segment having the maximum saturation, grid points on the skyline, and bottom points. It may be added to at least one of the grid points on the line and the grid points on the outermost shell surface.

After the processing of S244, the grid point generation means 15b generates the group of grid points on the outermost shell surface obtained in S244 as a part of the grid point group of the color conversion table 14a (S245), and the figure The outermost shell surface grid point generation processing shown in 20 is ended.

FIG. 21 is a flowchart of the outermost shell lattice point generation processing shown in FIG. 9 in the case of generating lattice points in which the terms of the same order of two types of van der Corput sequences are some coordinates.

As shown in FIG. 21, the grid point generation means 15b determines the number Ce of grid points on the outermost shell surface, as in the processing of S241 (S251).

Next, the sequence generator 15a generates two types of van der Corp. sequences having the same number of terms as the square root of the quotient obtained by dividing the number Ce determined in S251 by 6 and having a base as a positive integer of 2 or more. (S252).

Next, the grid point generation means 15b obtains grid points on each outermost shell surface using the two types of van der Corp. sequences generated in S252 (S253).

For example, when the number Ce determined in S251 is 150, when a van der Corpus sequence with a base of 2 and a van der Corpus sequence with a base of 3 are generated, a van der corp with a base of 2 is generated in S252. The Corput sequence and the van der Corpus sequence having a base of 3 are as shown in Formula 27 and Formula 28, respectively, and the lattice points on the surface of r=0 obtained in S253 are as shown in Formula 29. The grid point generation unit 15b sets r=0 for the r=1 surface, the g=0 surface, the g=1 surface, the b=0 surface, and the grid point on the b=1 surface. Similar to the lattice points on the surface, it is determined in S253.

The grid points on the line segment between white and the primary color and the grid points on the line segment between the black and the secondary color are on the skyline grid point generation process of S172 and on the bottom line of S173, respectively. Since it is generated in the lattice point generation processing, it may be excluded from the lattice points obtained in S253. Then, the grid point generation means 15b uses at least some of the excluded grid points as grid points on the gray axis, grid points on the line segment having the maximum saturation, grid points on the skyline, and bottom points. It may be added to at least one of the grid points on the line and the grid points on the outermost shell surface.

After the processing of S253, the grid point generation means 15b generates the group of grid points on the outermost shell surface obtained in S253 as a part of the grid point group of the color conversion table 14a (S254), and the figure The outermost shell surface grid point generation process shown in 21 is ended.

The outermost shell surface grid point generation process shown in FIG. 21 does not include a process of arranging a grid point group of complementary colors, but the control unit 15 divides the number Ce by 6 by 1/square root of the quotient. A group of complementary color grid points may be added in S253 by generating two types of van der Corp. sequences in which the number of terms is the same as 2 and the basis is a positive integer of 2 or more in S252.

As shown in FIG. 9, when the outermost shell surface lattice point generation processing in S162 is completed, the control unit 15 ends the outermost shell surface lattice point generation processing shown in FIG.

As illustrated in FIG. 4, the control unit 15 ends the grid point group generation processing illustrated in FIG. 4 when the outermost shell on-grid point generation processing in S116 is completed.

In addition, when three types of van der Corp. sequences whose bases are 2, 3, and 5 are generated in S131 by the sequence generation unit 15a, the grids generated by the grid point generation unit 15b in the grid point group generation process of S101. The point group is, for example, the grid point group shown in FIG. Similarly, when three types of van der Corp. sequences whose bases are 2, 3, and 7 are generated in S131 by the sequence generation means 15a, they are generated by the lattice point generation means 15b in the lattice point group generation processing of S101. The grid point group is, for example, the grid point group shown in FIG.

FIG. 22A is a perspective view of the grid point group 31 generated when three types of van der Corp. sequences having bases of 2, 3, and 5 are generated. FIG. 22B shows the grid shown in FIG. 22A when observed in the direction from the white {1,1,1} point to the black {0,0,0} point. It is a perspective view of the point group 31.

FIG. 23A is a perspective view of a grid point group 31 generated when three types of van der Corp. sequences having bases of 2, 3, and 7 are generated. FIG. 23(b) shows the lattice shown in FIG. 23(a) when observed in the direction from the white {1,1,1} point to the black {0,0,0} point. It is a perspective view of the point group 31.

By exchanging the channel information of the coordinates of the grid points in the process of S133, the grid point group 31 is red (red), green (green), and blue as shown in FIG. 22(b) or FIG. 23(b). The basic six hues of (blue), cyan, magenta, and yellow are formed symmetrically with respect to each hue plane.

As illustrated in FIG. 3, when the grid point group generation process of S101 ends, the control unit 15 calculates an output value (CMYK value) corresponding to each grid point of the grid point group generated by the grid point group generation process. Yes (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) in which the relationship between the color value measured in advance and the colorimetric value is recorded”. Or a "color conversion LUT configured with a fine mesh created in advance".

First, the output value (CMYK value) corresponding to each grid point of the grid point group generated by the grid point group generation processing is calculated from the "LUT in which the relationship between the color value measured in advance and the colorimetric value is recorded". A method of obtaining by back calculation will be described.

The “LUT that records the relationship between the color values measured in advance and the colorimetric values” is a color patch in which CMYK values of various color values are set (may be a predetermined interval or random, but is usually Bk for stratification). Is a LUT obtained by printing a color patch in which CMYK values are set at predetermined discrete intervals in a form that is possible), measuring the color of the printed color patch, and converting it into an XYZ value (CMYK to XYZ conversion). .. The “LUT in which the relationship between the color values measured in advance and the colorimetric values is recorded” is an LUT used for developing the color conversion table 14a, not an LUT mounted on the MFP 20. Therefore, unlike the color conversion table 14a, the “LUT in which the relationship between the color values measured in advance and the colorimetric values is recorded” has no particular limitation on the capacity of the memory in which it is stored. The value includes a correspondence with the XYZ value.

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

Here, the XYZ value corresponding to each grid point (RGB value) of the grid point group generated by the grid point group generation processing can be recognized by the LUT (RGB to XYZ conversion). Therefore, each of the lattice point groups generated by the lattice point group generation processing is performed by combining the “LUT in which the relationship between the color values measured in advance and the colorimetric values is recorded” with the back-calculated LUT (XYZ to CMYK conversion). An output value (CMYK value) corresponding to a grid point 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 configured with a fine mesh created in advance" Will be described.

The “color conversion LUT formed by a fine mesh 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). The “color conversion LUT formed in advance with a fine mesh” is an LUT used for developing the color conversion table 14a, not an LUT mounted on the MFP 20. Therefore, unlike the color conversion table 14a, the "color conversion LUT configured with a fine mesh created in advance" has no particular limitation on the memory capacity in which it is stored. On the other hand, it includes the correspondence with the CMYK values.

The "color conversion LUT formed by a fine mesh created in advance" is subjected to a plurality of multi-stage LUT processes as shown in FIG. 24, or a part or all of these intermediate steps are shown in FIG. Such LUT processing is performed.

Here, the LUT process shown in FIG. 24 will be described.

FIG. 24 is a flowchart of general conversion steps of the color conversion process.

In the color conversion process shown in FIG. 24, the color space of the input color is rarely the CMYK format in the use of an office machine such as an MFP, but is basically the RGB format.

S261 is an F-DM (forward device model) conversion step, which is a step of converting the RGB format data into the CIE-XYZ space. For example, if the sRGB space is assumed as the RGB format, the conversion may be performed according to the definition.
(SRGB to XYZ conversion)

S262 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 environmental conditions) according to the definition of CIE-CAM02.
(XYZ to JCH conversion)

S263 is a GMA (gamut mapping algorithm) conversion step. Various methods have already been proposed by many companies or researchers, and it is only necessary to select and apply a suitable method from the purposes, conditions, preferences, characteristics of the output device, and the like.
(JCH to J'C'H' conversion)

S264 is a black amount generation step, in which the black amount is defined in accordance with the JCH value after the GMA conversion in S263, and is determined by calculation. Since many companies or researchers have already proposed various precedents, it is possible to select and apply a suitable one from the purposes, conditions, preferences, characteristics of the output device, and the like.
(J'C'H' to (J'C'H'+K) conversion)

S265 is a B (backward)-CAM conversion process, in which parameters are set and converted according to the output or the observation environment. It may be converted according to the definition formula of the color appearance model.
((J'C'H'+K) to (XYZ+K) conversion)

The order of S264 and S265 may be reversed, and there is such a conversion type. In the present invention, since the order of S264 and S265 is hardly influenced, the order of S264 and S265 does not matter.

S266 is a B-DM (backward device model) conversion step, and returns the device independent value (XYZ) to the output device value.
((XYZ+K) to (CMY+K) conversion)

In step S266, a patch in which m×m×m×m divisions are performed by dividing each channel of CMYK in advance by, for example, m is obtained, K-CMY to XYZ conversion data in a state of K layers is obtained, and this is K layer. It is sufficient to perform back calculation in another state to generate a K-XYZ to K-CMY LUT for each BK layer.

In the color conversion process shown in FIG. 24, the color space of the color output is in the CMYK format.

FIG. 24 schematically shows how each step is converted in multiple steps. However, some of the steps of S261 to S266 shown in FIG. 24 may be combined or separated, or by combining all the steps of S261 to S266, a single step (S271) may be performed at a stroke as shown in FIG. It may be an LUT for converting from RGB format to CMYK format.

A method of generating the color conversion process shown in FIG. 24 will be described.

The color conversion step shown in FIG. 26 outputs the “color space JCH in of the input device” by the same steps as S261 to S262 of the color conversion step shown in FIG.

The color conversion process shown in FIG. 27 is a color patch in which CMYK values of various color values are set (a predetermined interval or a random patch may be used, but in most cases, the CMYK values are set at predetermined discrete intervals so that Bk can be stratified. (Printed color patch) is printed by the MFP 20, the color of the printed color patch is measured and converted into an XYZ value (S291), and the XYZ value is measured using a color appearance model that matches environmental conditions. (S292), and outputs "color space JCH out of output device".

Then, the “input device color space JCH in” obtained through the color conversion process shown in FIG. 26 and the “output device color space JCH out” obtained through the color conversion process shown in FIG. An LUT for setting corresponding points and performing the conversion process (S263 in FIG. 24) and an LUT for setting Bk values when reproducing the corresponding points (S264 in FIG. 24) are obtained.

In general, the “input device color space JCH in” and the “output device color space JCH out” are different in size and shape. Therefore, many methods (GMA: Gamut Mapping Algorithm) have been proposed in the past for how to associate each point in the color space of the input device with 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, one of the many methods proposed in the past that is appropriate for the purpose, application, or condition is selected. Should be selected and adopted (S263 in FIG. 24).

Various methods have been proposed for black ink amount generation in the past, and an appropriate one may be selected and adopted from them according to the purpose, application, or condition (S264 in FIG. 24).

The color conversion process (S261 and S262) shown in FIG. 26, S263 and S264 obtained as described above, and the inverse conversion LUT (S265 and S266) by the inverse calculation (reverse search) of the color conversion process shown in FIG. 24 is shown in the figure from the input to the output.

As shown in FIG. 3, when the process of S102 ends, the control unit 15 divides the entire gamut before color conversion by the color conversion table 14a into tetrahedral groups (S103).

In S103, the tetrahedron of the tetrahedron group is formed by four adjacent lattice points among the lattice points of the lattice point group. In particular, when considering a circumscribing sphere of four selected lattice points, a tetrahedral group is formed by forming a set of tetrahedra so that no other lattice point enters inside the circumscribing sphere. good. For example, the tetrahedral group generated in S103 is a tetrahedral group formed by a three-dimensional Delaunay network. Here, for the generation of the three-dimensional Delaunay network, an appropriate method may be used from among known generation methods. That is, the tetrahedron group may be obtained by expanding it in a three-dimensional space in the same way as drawing a Delaunay diagram on a two-dimensional surface.

For example, when the tetrahedron group is plotted with respect to the lattice point group 31 shown in FIG. 22, it becomes as shown in FIG. FIGS. 28A and 28B are perspective views of the tetrahedron group 41 when observed from the same viewpoints as those in FIGS. 22A and 22B, respectively.

Further, when the tetrahedral group is plotted with respect to the lattice point group 32 shown in FIG. 23, it becomes as shown in FIG. 29A and 29B are perspective views of the tetrahedron group 42 when observed from the same viewpoints as those in FIGS. 23A and 23B, respectively.

As shown in FIG. 3, when the processing of S103 ends, the control unit 15 determines the grid point group generated in the grid point group generation processing of S101, the output value calculated in S102, and the tetrahedral group divided in S103. The color conversion table 14a including is generated (S104), and the operation illustrated in FIG. 3 ends.

The color conversion table 14a generated in the operation illustrated in FIG. 3 is read from the color conversion table generation device 10 by some method such as communication via a network and stored in the MFP 20 as the color conversion table 27a.

Although the color conversion table 14a includes the tetrahedron group in the above description, the tetrahedron group may not be included in the color conversion table 14a. When the tetrahedron group is not included in the color conversion table 14a, the MFP 20 may generate the tetrahedron group based on the lattice point group included in the color conversion table 14a by the same process as S103.

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

FIG. 30 is a flowchart of the operation of the MFP 20 when executing printing.

As shown in FIG. 30, the control unit 28 of the MFP 20 executes color conversion processing for converting an input image in RGB format into an output image in CMYK format compatible with the printer 24a as an output device (S301).

FIG. 31 is a flowchart of the color conversion process in S301.

As shown in FIG. 31, the control unit 28 targets an RGB value that has not yet been targeted among the color values (RGB values) forming the input image in the RGB format (S331).

Next, the control unit 28 executes a correspondence relationship search process that searches for a correspondence relationship between the RGB values targeted in S331 and the CMYK values. (S332).

FIG. 32 is a flowchart of the correspondence search process in S332.

As shown in FIG. 32, the control unit 28 determines whether the target RGB value is a grid point before color conversion in the color conversion table 27a (S361).

When the control unit 28 determines in S361 that the target RGB value is the grid point before color conversion in the color conversion table 27a, it corresponds to the target RGB value among the grid points before color conversion in the color conversion table 27a. The conversion value (CMYK value) associated with the grid point is specified as the CMYK value corresponding to the target RGB value (S362), and the correspondence relationship search process shown in FIG. 32 ends.

When the control unit 28 determines in S361 that the target RGB value is not a grid point before color conversion in the color conversion table 27a, that is, a point between grid points, the conversion value (CMYK) corresponding to the target RGB value. Interpolation processing for converting the value) is executed (S363).

FIG. 33 is a flowchart of the interpolation processing in S363.

As shown in FIG. 33, the control unit 28 executes an inclusion tetrahedron search process of searching for a tetrahedron including the target RGB value from the tetrahedron group included in the color conversion table 27a (S401).

FIG. 34 is a flowchart of the included tetrahedron search process in S401.

As shown in FIG. 34, the control unit 28 targets a tetrahedron that is not yet a target among the tetrahedron group included in the color conversion table 27a (S431).

Next, the control unit 28 selects any two points (hereinafter, point A and point B) out of the four points (hereinafter, referred to as “point A, point B, point C, point D”) forming the target tetrahedron. Is selected) (S432).

Next, the control unit 28 sets the line segment formed by the two points (point A and point B) selected in S432 as the base, and the point of the target RGB value (hereinafter referred to as point X) and the target tetrahedron. 1 point other than the 2 points selected in S432 (hereinafter, referred to as point C) among the 4 points forming the target tetragon, and the remaining 1 point other than the 2 points selected in S432 among the 4 points forming the target tetrahedron. Normal vectors of three planes each including a triangle whose vertex is (hereinafter, referred to as point D) are calculated (S433). Here, the normal vector of a plane including a triangle is the outer product of two vectors of which one point is the start point and the other two points are the end points among the three points (for example, the three vertices of the triangle) forming the plane. It can be calculated by calculating.

Next, the control unit 28 determines whether the angle of the plane including the triangle having the point of the target RGB value as the vertex among the three angles calculated in S433 is between the angles of the remaining two planes. A determination is made (S434).

Next, the control unit 28 selects two points (point C and point D) that have not been selected in S432 from the four points (point A, point B, point C, point D) forming the target tetrahedron. (S435).

Next, the control unit 28 uses the line segment formed by the two points (point C and point D) selected in S435 as the base, and the point of the target RGB value (point X) and the four points forming the target tetrahedron. 1 point other than the 2 points selected in S435 (hereinafter referred to as point A), and the remaining 1 point other than the 2 points selected in S435 among the 4 points forming the target tetrahedron (hereinafter referred to as point B). The normal vectors of the three planes including the triangles each having the apex) are calculated (S436).

Next, the control unit 28 determines whether or not the angle of the plane including the triangle having the point of the target RGB value as the apex of the three angles calculated in S436 is between the angles of the remaining two planes. A determination is made (S437).

Next, the control unit 28 determines whether or not it is determined that both are in the determination in S434 and the determination in S437 (S438).

When the control unit 28 determines in S438 that it is determined not to be in between in at least one of the both determinations, the control unit 28 executes the process of S431.

When the control unit 28 determines in S438 that it is determined to be in-between in both determinations, the control unit 28 specifies the target tetrahedron as the tetrahedron including the target RGB values (S439), and includes the tetrahedron shown in FIG. The body search process ends.

The inclusion tetrahedron search process shown in FIG. 34 employs a method of searching for a tetrahedron containing the target RGB value based on the angle between the planes in the present embodiment. However, a method other than the method shown in FIG. 34 may be adopted as the inclusion tetrahedron search processing in S401. For example, by using the outer product with respect to the four planes forming the tetrahedron, it is determined whether or not the target RGB value point is on the front side of each plane, and it is on the front side on all the planes. On the condition of, the method of specifying the tetrahedron including the target RGB values may be adopted.

As shown in FIG. 33, after the inclusion tetrahedron search process of S401, the control unit 28 determines the target RGB value based on the ratio by which the points of the target RGB value volumetrically divide the tetrahedron searched in S401. A conversion value (CMYK value) corresponding to is calculated (S402).

For example, the control unit 28 sets the tetrahedron searched in S401 (hereinafter, configured by the point E, the point F, the point G, and the point H) to four triangles forming the tetrahedron searched in S401. Of four tetrahedrons (triangular pyramids) with the faces (ΔFGH, ΔEGH, ΔEFH, and ΔEFG) as the bottom, and the point of the target RGB value (point X) as the vertex, that is, tetrahedron X-FGH, Divide into X-EGH, X-EFH and X-EFG. If the volumes of the tetrahedrons X-FGH, X-EGH, X-EFH, and X-EFG are Ve, Vf, Vg, and Vh, respectively, and their sum, that is, the volume of the tetrahedron EFGH is Vs, the control unit 28 , The converted value (CMYK value) corresponding to the target RGB value can be calculated. In Expression 30, Xcmyk is a conversion value (CMYK value) corresponding to the target RGB value. Ecmyk, Fcmyk, Gcmyk, and Hcmyk are conversion values (CMYK values) corresponding to the points E, F, G, and H, respectively.

Note that Ve, Vf, Vg, and Vh may be obtained, for example, as shown in Expression 31, Expression 32, Expression 33, and Expression 34, respectively. Further, Vs may be calculated as the sum of Ve, Vf, Vg, and Vh, or may be calculated as shown in Formula 35, for example.

As shown in FIG. 33, the control unit 28 terminates the interpolation processing shown in FIG. 33 after the processing of S402.

Note that the interpolation processing shown in FIG. 33 is a tetrahedral interpolation method in this embodiment, but may be a method other than the tetrahedral interpolation method. For example, the interpolation processing may be a hexahedral interpolation method or a triangular prism interpolation method.

As shown in FIG. 32, the control unit 28 ends the correspondence search process shown in FIG. 32 after the interpolation processing of S363.

As shown in FIG. 31, the control unit 28 determines whether or not there is an RGB value which is not yet a target among the RGB values forming the input image in the RGB format after the correspondence relationship search processing in S332 ( S333).

When the control unit 28 determines in S333 that there is an RGB value that has not been targeted yet among the RGB values forming the input image in the RGB format, the control unit 28 executes the process of S331.

When the control unit 28 determines in S333 that there is no RGB value that has not yet been targeted among the RGB values forming the input image in the RGB format, the control unit 28 associates the RGB value and the CMYK value searched by the correspondence relationship search process of S332. Based on the relationship, the RGB format input image is converted into a CMYK format output image (S334), and the color conversion process shown in FIG. 31 is terminated.

As illustrated in FIG. 30, after the color conversion processing in S301, the control unit 28 causes the printer 24 to print on the recording medium based on the CMYK format output image generated in S301 (S302). The operation shown is ended.

As described above, since the color conversion table generation device 10 positively secures the outermost shell lattice point as the lattice point before color conversion in the color conversion table 14a (S116), the color conversion table 14a is used. It is possible to improve the reproducibility of the high saturation color in the output image. The color conversion table generating device 10 can improve the color reproducibility in an image that is not a natural image, such as an abstract image such as a graphic or a character image, by improving the reproducibility of highly saturated colors.

Since the color conversion table generation device 10 positively secures the inter-angle line segment grid point as at least one of the outermost shell grid points (S161), the intermediate data between the grid points of the color conversion table 14a is interpolated. When calculation is performed by interpolation (S363), the accuracy of calculation of intermediate data on a line segment between two adjacent corners in the RGB color space before color conversion or in the vicinity of this line segment can be improved. ..

The color conversion table generating device 10 generates inter-angle line segment lattice points at equal intervals on a line segment between any two of the eight angles in the RGB color space before color conversion (S181 to S185, S201). ~S205 and S221 to S225), since the inter-angle line segment upper grid points can be generated by a simple calculation, the inter-angle line segment upper grid points can be easily generated.

When the color conversion table generating device 10 generates inter-angle line segment grid points (S191 to S194, S211 to S214, and S231 to S234) in which the terms of the van der Corput sequence are part of the coordinates, the new inter-angle intervals are generated. When adding a grid point on a line segment, it is not necessary to change the grid point on the inter-line segment that already exists, so that the grid point on the inter-line segment can be easily generated.

The color conversion table generation device 10 does not have to include at least one of the grid point on the line segment having the maximum saturation, the grid point on the skyline, and the grid point on the bottom line in the color conversion table 14a. good.

Since the color conversion table generation device 10 positively secures the grid points on the outermost shell as at least one of the grid points on the outermost shell (S162), the intermediate data between the grid points of the color conversion table 14a is internally stored. When the calculation is performed by the interpolation (S363), the accuracy of calculation of the intermediate data on the surface of the outermost shell in the RGB color space before color conversion or in the vicinity of this surface can be improved.

When the color conversion table generating device 10 generates the outermost shell surface grid points on the surface of the outermost shell surface in the RGB color space before color conversion at equal intervals (S241 to S245), the outermost shell surface grid points. Can be generated by a simple calculation, so that the grid points on the outermost shell surface can be easily generated.

The color conversion table generation device 10 generates a new outermost shell in the case of generating the outermost shell lattice points having some coordinates of terms in the same order between the two van der Corput columns (S251 to S254). When adding the in-plane lattice points, the existing outermost shell surface lattice points do not need to be changed, so that the outermost shell surface lattice points can be easily generated. Here, since the color conversion table generation device 10 generates two van der Corp. sequences having different bases as the two van der Corp. sequences for generating the lattice points on the outermost shell surface (S252), 2 Since the uniformity of the arrangement of the grid points on the outermost shell surface having the terms of the same order in the two van der Corp. sequences as some coordinates is improved, the accuracy of the quality of the output image via the color conversion table 14a is improved. Uniformity can be improved. Note that the color conversion table generation device 10 may generate two van der Corp. sequences having the same basis in S252.

The color conversion table generation device 10 does not have to include the outermost shell surface lattice points in the color conversion table 14a.

Since the color conversion table generation device 10 positively secures grid points on the gray axis, that is, achromatic grid points as grid points before color conversion in the color conversion table 14a (S115), the color conversion table 14a is used. It is possible to improve the reproducibility of an achromatic color and a color close to the achromatic color, which greatly affects the color reproducibility of the output image. Therefore, the color conversion table generation device 10 can improve the color reproducibility in the output image via the color conversion table 14a. The color conversion table generation device 10 can improve the reproducibility of the color in the natural image by improving the reproducibility of the achromatic color and the color close to the achromatic color.

Note that the color conversion table generation device 10 does not have to include the gray-axis lattice points in the color conversion table 14a.

Regarding the outermost shell grid points and the gray axis grid points, the number of grid points may be increased or decreased by confirming the color reproducibility in the output image via the color conversion table 14a. That is, the gray-axis on-grid point generation processing and the outermost-shell-on-grid point generation processing may be re-executed multiple times.

Since the color conversion table generation device 10 generates grid points corresponding to eight corners of the RGB color space before color conversion (S114), the intermediate data between the grid points of the color conversion table 14a is calculated by interpolation. In the case of (S363), the accuracy of calculation of the intermediate data in the vicinity of the corner of the color space before color conversion can be improved.

Note that the color conversion table generation device 10 does not have to include the grid points corresponding to the eight corners of the RGB color space before color conversion in the color conversion table 14a.

Since the color conversion table generation device 10 generates the group of grid points before color conversion in the color conversion table 14a by using the van der Output sequence without arranging them in a cubic grid shape (S112 to S113), The number of grid points in the color conversion table 14a can be increased under the condition that the capacity of the memory for storing information is limited. Therefore, the color conversion table generation device 10 can improve the accuracy of the quality of the output image via the color conversion table 14a.

Since the color conversion table generation device 10 generates three van der Corp. sequences having different bases (S131), the uniformity of the arrangement of the grid points with the terms in the same order in the three van der Corp. sequences as coordinates. Can be improved. Therefore, the color conversion table generation device 10 can improve the uniformity of the accuracy of the quality of the output image via the color conversion table 14a. Note that the color conversion table generation device 10 may generate at least two three van der Corp. sequences having the same base in S131. When at least two bases generate three van der Corp. sequences having the same base, the randomness is reduced and the lattice structure has a crystalline structure as compared with the configuration in which three van der Corp. sequences having different bases are generated. Easy to appear. However, even if the randomness deteriorates and the crystal structure appears in the arrangement of the lattice points, the color conversion table generation device 10 exchanges the channel information of the coordinates of the lattice points in the process of S133, and thereby the basic 6 hue Since the grid point groups are arranged so as to be symmetrical with respect to each hue plane, and the grid point group of the complementary color of the grid point group arranged in the process of S133 is also arranged in the process of S134, the arrangement of the grid points is uniform. It is possible to secure the sex.

The color conversion table generating device 10 sets the terms of the same order in the three van der Corp. columns in each of the 6 patterns in which each of the three van der Corp. columns is associated with each of the three channels of the RGB color space. After the grid points to be the coordinates are generated (S133), the grid points of the complementary color of this grid point are also generated (S134), so that the uniformity of the arrangement of the grid points can be improved. Therefore, the color conversion table generation device 10 can improve the uniformity of the accuracy of the quality of the output image via the color conversion table 14a. The color conversion table generation device 10 does not have to execute the process of S134. When the process of S134 is not executed, the color conversion table generation device 10 may calculate the quotient n by dividing the number obtained by subtracting the specific number p from Smax by 6 in S112.

Although the image forming apparatus that uses the color conversion table generated by the color conversion table generating apparatus 10 is the MFP in the present embodiment, it may be an image forming apparatus other than the MFP, such as a printer dedicated machine.

10 color conversion table generator (grid point group generator, computer)
14a Color conversion table 14b Lattice point group generation program 15a Numerical sequence generation means 15b Lattice point generation means 27a Color conversion table 31, 32 Lattice point group (group of lattice points)

Claims (15)

A grid point group generation method for generating a group of grid points before color conversion in a color conversion table for converting a color of a color space of three channels into a color of another color space,
a sequence generating step for generating a van der Corp. sequence,
And a grid point generation step for generating grid points,
In the step of generating a number sequence, the quotient obtained by dividing a number obtained by subtracting a specific number from the maximum number of grid points that can be allocated for the color conversion table by a divisor that is either 6 or 12, and the number of terms are the same number. Generating three van der Corput sequences whose bases are positive integers greater than or equal to 2;
In the grid point generating step, in each of 6 patterns in which each of the three van der Corp. sequences is associated with each of the three channels, terms in the same order of the three van der Corp. sequences are set as coordinates. Is a step of generating grid points
The grid point generation step is a step of generating grid points on the outermost shell as grid points existing on the outermost shell in the color space of the three channels and being neither of the eight angles,
The number of the outermost shell lattice points generated by the lattice point generating step is the total number of the remainder obtained by dividing the maximum number minus the specific number by the divisor, and the specific number. Ri der below,
The specific number is 8, the required number of grid points on the gray axis as grid points existing on the gray axis in the color space of the three channels and being neither white nor black, and the outermost shell grid A method for generating a grid point group, which is a total of the required number of points. In the grid point generation step, an inter-angle line segment upper grid point as a grid point existing on a line segment between any two of the eight corners in the color space of the three channels is set on the outermost shell. 2. The grid point group generation method according to claim 1, which is a step of generating at least one of the grid points. The grid point group generation method according to claim 2, wherein the grid point generation step is a step of generating grid points on the inter-angle line segment at equal intervals on the line segment. The grid point generating step is a step of generating the grid point on the inter-angle line segment with some of the coordinates of the van der Corput sequence generated by the sequence generating step as some coordinates. The described grid point group generation method. In the grid point generating step, a grid point on the outermost shell surface as a grid point existing on the surface of the outermost shell in the color space of the three channels is generated as at least one of the grid points on the outermost shell. The grid point group generation method according to any one of claims 1 to 4, which is a step. The grid point group generation method according to claim 5, wherein the grid point generation step is a step of generating grid points on the outermost shell surface on the surface at equal intervals. The grid point generating step is a step of generating the grid point on the outermost shell surface having, as a part of coordinates, terms in the same order of the two van der Corp. sequences generated by the sequence generating step. The grid point group generation method according to claim 5. The grid point group generation method according to claim 7, wherein the sequence generation step is a step of generating the two van der Corp. sequences having different bases. The grid point generating step is a step of generating a corner grid point as a grid point corresponding to the eight corners of the color space of the three channels,
The total number of the grid points on the outermost shell and the square grid points generated by the grid point generation step is equal to or less than the total number of the remainder and the specific number. The grid point group generation method according to claim 8. The grid point generation step is a pre-Symbol generating a gray axis lattice points,
The total number of the outermost shell lattice points, the square lattice points and the gray axis lattice points generated by the lattice point generating step is equal to or less than the total number of the remainder and the specific number. 10. The grid point group generation method according to claim 9, wherein: The grid point generating step is a step of generating grid points on the gray axis as grid points existing on the gray axis in the color space of the three channels and being neither white nor black,
It is characterized in that the total number of the outermost shell lattice points and the gray axis lattice points generated by the lattice point generating step is equal to or less than the total number of the remainder and the specific number. The grid point group generation method according to any one of claims 1 to 8. 12. The grid point group generation method according to claim 1, wherein the sequence generation step is a step of generating the three van der Corp. sequences having different bases. The number sequence generating step is a step of generating the three van der Corp. sequences having the same number of terms as the quotient obtained by dividing the number obtained by subtracting the specific number from the maximum number by 12 as the divisor,
In the grid point generation step, in each of the six patterns, after generating grid points whose coordinates are terms in the same order of the three van der Corp. sequences, grid points complementary in color to the grid points are also generated. The grid point group generation method according to any one of claims 1 to 12, which is a step. A grid point group generation program for generating a group of grid points before color conversion in a color conversion table for converting a color of a color space of three channels into a color of another color space,
a sequence generating means for generating a van der Corp. sequence;
Let the computer realize the grid point generation means that generates the grid points,
The number sequence generating means has the same number of terms as the quotient obtained by dividing the number obtained by subtracting a specific number from the maximum number of grid points assignable for the color conversion table by a divisor that is either 6 or 12. Generate three van der Corput sequences whose bases are positive integers greater than or equal to 2,
The grid point generation means, in each of 6 patterns in which each of the three van der Corp. sequences is associated with each of the three channels, sets the terms in the same order of the three van der Corp. sequences as coordinates. Generate grid points
The grid point generation means generates grid points on the outermost shell as grid points existing on the outermost shell in the color space of the three channels and not at any of the eight angles,
The number of the outermost shell lattice points generated by the lattice point generation means is the total number of the remainder obtained by dividing the maximum number minus the specific number by the divisor and the specific number. Ri der below,
The specific number is 8, the required number of grid points on the gray axis as grid points existing on the gray axis in the color space of the three channels and being neither white nor black, and the outermost shell grid A grid point group generation program characterized by being the total of the required number of points. A grid point group generation device for generating a group of grid points before color conversion in a color conversion table for converting a color of a color space of three channels into a color of another color space,
a sequence generating means for generating a van der Corp. sequence;
And a grid point generation means for generating grid points,
The number sequence generating means has the same number of terms as the quotient obtained by dividing the number obtained by subtracting a specific number from the maximum number of grid points assignable for the color conversion table by a divisor that is either 6 or 12. Generate three van der Corput sequences whose bases are positive integers greater than or equal to 2,
The grid point generation means, in each of 6 patterns in which each of the three van der Corp. sequences is associated with each of the three channels, sets the terms in the same order of the three van der Corp. sequences as coordinates. Generate grid points
The grid point generation means generates grid points on the outermost shell as grid points existing on the outermost shell in the color space of the three channels and not at any of the eight angles,
The number of the outermost shell lattice points generated by the lattice point generation means is the total number of the remainder obtained by dividing the maximum number minus the specific number by the divisor and the specific number. Ri der below,
The specific number is 8, the required number of grid points on the gray axis as grid points existing on the gray axis in the color space of the three channels and being neither white nor black, and the outermost shell grid An apparatus for generating a grid point group, which is a total of the required number of points.

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