JP2006345112A - Method for making color separation table and image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a good recording image by preventing generation of a false outline in the center of a color space on a color separation table for performing color separation processing. <P>SOLUTION: A control line for making a color separation table is set (S601). Based on a control line, a cube of color separation table is divided into six tetrahedrons (S602), and each tetrahedron is further divided into triangles (S603). When the interior of the triangle is interpolated, weighting is calculated (S605) and lattice point data is determined. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color separation table creation method and an image processing apparatus, and more particularly to a color separation table creation method and an image processing apparatus for converting color signals constituting image data into color signals of a color material such as ink used for printing. Is.

  In the process of converting the color signal of image data into the color signal of a color material such as ink used in a printing apparatus such as a color printer, a color separation table is generally used. This color separation table is, for example, Y (yellow), M (magenta), C (cyan), K (black), which are ink color signals at grid points defined by the values of R, G, and B color signals. ) Ink value (ink amount) is stored as grid point data.

  As a method of generating this color separation table, a cube composed of grid points in the RGB color space is divided into six tetrahedrons each having four vertices of the vertices of the cube, and each tetrahedron is configured. The ink amount (grid point data) is determined in advance for the grid points on each side forming the four triangles, and the interpolation process based on the ink amount of the grid points on this side is used to calculate the points in the tetrahedron other than these sides. A method for obtaining the ink amount at a lattice point is known.

  FIG. 1 is a diagram illustrating six divided tetrahedrons. When creating the color separation table, eight vertices, W (white), C, M, Y, R, G, B, and K, in which lattice point data is determined in advance are determined, and vertices C, M, The line is divided into six parts using a line passing through Y, R, G, and B to the vertex K and seven lines connecting the vertex W and the vertex K.

  For example, in Patent Document 1, for example, in the tetrahedron shown in FIG. 1A, first, an interpolation method related to the interior of the six tetrahedrons is divided into a plurality of triangles parallel to the triangle WRK. A method using peak values and contour lines of ink values on three sides of a triangle is described.

  FIG. 2 is a diagram illustrating an example of interpolating divided triangles. In the triangle ABC, when the ink values (1) for the side AB, (2) for the side AC, and (3) for the side BC are given, the ink values of (1) and (2) After the vertex A and the vertex I of the ink value of (3) are connected and the side AI is interpolated, interpolation is performed for the triangle ABI and the triangle ACI, respectively. Interpolation creates contour lines from the ink values on each side and uses the contour lines as a guide. After such interpolation is performed for each ink color, a tetrahedron is formed as a collection of triangles, and the six tetrahedrons are combined to create a cubic color separation table.

JP 2002-033930 A

  However, in the conventional example, each of the six tetrahedrons defines one triangle among the four triangles constituting the tetrahedron, and performs interpolation by dividing the triangle into a plurality of triangles parallel to the triangle. For this reason, in a cubic color separation table created by combining six tetrahedrons, the ink values of grid points across the tetrahedron boundary may not change smoothly. As a result, a pseudo contour may occur in an image output using the color separation table. That is, the direction of division into a plurality of triangles differs according to the triangles defined for each tetrahedron during division. For this reason, in the interpolation inside the triangle, as described with reference to FIG. 2, if the interpolation according to the ink value distribution of each side is simply performed, the internal interpolation of the different triangles in the adjacent tetrahedron is performed. In some cases, the ink values at the lattice points across the boundary surface of the tetrahedron do not change smoothly.

  The present invention has been made to solve the above-described problems, and the object of the present invention is to create a color separation table even if the direction of dividing a triangle differs for each tetrahedron. It is an object of the present invention to provide a color separation table creation method and an image processing apparatus that do not generate a pseudo contour in an image output using the.

  In order to achieve the above object, the present invention provides a method for creating a color separation table for converting a color signal of a predetermined color space into a color material value signal of a color material color space for performing image output, A step of setting a plurality of control lines obtained by connecting predetermined grid points in a solid consisting of grid points defined by color signals of a predetermined color space, and four of the set control lines A step of setting a plurality of tetrahedrons by a combination of the control lines, a step of setting a plurality of triangles parallel to the triangle facing the vertex for each of the set of tetrahedrons, and the plurality of triangles For each of the three vertices of the triangle, for each grid point on the grid line parallel to the opposite side of the vertex, use the color material values of the grid points on the two sides where the grid line intersects. The same grid point that is obtained for three vertices by weighting the color material value of the obtained grid point with a greater weight as the distance from the vertex of the grid line is closer. And calculating the average of the weighted color material values, and setting the average value to the color material value of the grid point.

  According to the above configuration, in the internal interpolation of the triangle divided for each tetrahedron, the internal interpolation is performed in each of the three directions determined by the vertices of the triangle, and the weighted average of the ink values obtained in each of these three directions To create a color separation table. Thus, the ink value of each grid point obtained as a result of interpolation of each triangle and the formation of the tetrahedron using this result is such that the grid point closer to the control line constituting the tetrahedron is closer to the grid point on that control line. The value is close to the ink value. As a result, it is possible to obtain a color separation table in which the ink values at the lattice points sandwiching the boundaries of the tetrahedrons do not change greatly, change smoothly, and suppress pseudo contours.

Embodiments of the present invention will be described below in detail with reference to the drawings.
(Embodiment 1)
FIG. 3 is a block diagram showing a schematic configuration for executing creation of a color separation table for performing color separation processing in the printing system according to the embodiment of the present invention.

  In the figure, reference numeral 301 denotes a control line setting unit, which sets at least seven control lines connecting the color points and black points of the first color space according to the color separation table. For example, a line from the vertex W through the vertices C, M, Y, R, G, and B to the vertex K and a line connecting the vertex C and the vertex K are set. Reference numeral 302 denotes a tetrahedron creation unit that selects four lines from the control lines set in 301 and creates a tetrahedron in the first color space. Reference numeral 303 denotes an interpolation direction determining unit that determines the interpolation direction of the tetrahedron, and 304 denotes a triangle forming unit that forms a plurality of triangles parallel to one surface of the tetrahedron according to the interpolation method determined in 303. Is a triangle interpolation means for interpolating the triangle formed by 304, 306 is a means for determining the weight of the reference line using the interpolation direction determined in 303, and 307 is a value interpolated in 305. And means for determining the signal value of the lattice point using the weight determined in 306, respectively.

  FIG. 4 is a diagram showing a specific configuration of the computer system used in the present embodiment.

  In the figure, 401 indicates an image input signal device such as a spectrophotometer, 402 indicates a computer such as a personal computer, 403 indicates a display for displaying image signal information and the like, and 404 indicates a recording device such as a printer. The computer 402 edits the image signal read by the spectrophotometer 401 and stores data.

  FIG. 5 is a block diagram showing a main part used for processing in the present embodiment in the computer system shown in FIG.

  Reference numeral 502 denotes a computer system, reference numeral 513 denotes an input device such as a mouse or a keyboard for inputting an instruction from the outside such as a user, 401 denotes an image input signal device such as a spectrophotometer, 403 denotes display of an image to be processed, A display device for displaying a message to the operator, 404 a recording device such as a color printer, 514 a transmission device such as a modem or a network card capable of transmitting and receiving various data from an external device, and 515 an external device External line input devices such as a microphone for inputting audio data are shown respectively. In the computer system 502, a CPU 503 executes a program recorded in the inside or an externally input program, controls the color separation system, and performs processing for creating a color separation table to be described later. 504 is a ROM that stores image processing and the like in advance, 505 is a RAM that temporarily stores programs and image data to be processed, 506 is a display control device that controls the display device 403, and 508 is a program or Reference numeral 510 denotes an external storage device for storing image data before and after image processing, 510 denotes a compact disk drive, and 511 denotes a floppy (registered trademark) disk drive. The ROM 504 and the external recording device 508 store a program for creating a color separation table to be described later.

  Reference numerals 501, 502, 507, 509, and 512 denote interfaces that connect the input device 513, spectrophotometer 401, recording device 404, transmission device 509, external input device 515, and computer system 502, respectively.

  FIG. 6 is a flowchart showing processing for creating a color separation table for use in color separation processing.

First, a control line for creating a color separation table is set (S601).
FIG. 7A is a diagram schematically showing the configuration of the color separation table. The color separation table corresponds to each grid point of the color signal R′G′B ′ and is a set of (C′M′Y′K ′) that is a signal of each ink of CMYK that is the color material of this embodiment. It is stored as grid point data.

  FIG. 7B shows the control line. In these lines, eight vertices W, C, M, Y, R, G, B, and K are defined in the cube shown in FIG. 7A, and vertices C, M, Y, and R are determined from the vertex W, respectively. , G, B to reach the vertex K, and a line connecting the vertex C and the vertex K. In S601, these lines are set as control lines, and a color conversion table is acquired. This table may be stored in a storage device such as an external recording device, a compact disk, a floppy (registered trademark) disk, or may be acquired via the transmission device 514.

  Next, using the control line set in S601, the cube shown in FIG. 7A is divided into six tetrahedrons shown in FIG. 1 (S602). The divided six tetrahedron data are stored in the RAM 505 and the external recording device 508.

  One of the divided tetrahedrons is divided into a plurality of triangles (S603). In the division, one of the four vertices of the tetrahedron is used as a reference and divided into a plurality of triangles for each lattice point parallel to the triangle on the bottom surface with respect to the reference vertex. It is divided into a plurality of planes parallel to one plane of the tetrahedron serving as a reference for the lattice points. As for the number of grid points, when an 8-bit RGB color separation table is created, the minimum value is 2, and the maximum value is 256. For example, in the tetrahedron shown in FIG. 1A, triangles parallel to the surface WRK are created toward the point M by the number of lattice points.

  For all the divided triangles, interpolation is performed based on the ink value of each side from the direction of each vertex (S604).

  FIG. 8 is a diagram illustrating an example of a triangular interpolation direction. When interpolation is performed in the direction from the vertex A to the side BC, the ink values of the side AB and the side AC and the grid line that is parallel to the opposite side of the vertex A and passes through the lattice points are used. The ink value of each lattice point inside the triangle with respect to the vertex A is obtained. That is, interpolation is performed to determine the ink value of each grid point from the ink value at the intersection of the grid line, side AB, and side AC, by the internal ratio of the distance between each intersection and the grid point. Similarly, grid lines corresponding to the ink values of the sides BA and BC are used for the direction from the vertex B to the side AC, and the ink values of the sides CA and CB are used for the direction from the vertex C to the side AB. Using grid lines, ink values are obtained for each grid point from each vertex.

The interpolated result is stored in a storage device such as the RAM 505 or the external storage device 508.
Next, the weight of each grid line is obtained (S605).

  FIG. 9 is a diagram illustrating an example of weighting. First, the weight of each grid line is calculated in the direction from the vertex A toward the side BC. The weight is a value obtained by dividing the number of grid lines counted from the side BC by the total number of grid lines parallel to the side BC to the sum of the sum S1 of the ink values of the side AC and the sum S2 of the ink values of the side AB. Multiply to find. In this way, the weight is a value that increases as it is closer to the vertex and decreases as it is farther from the vertex. Similarly, the weight of each grid line is calculated in the direction from the vertex B toward the side AC and the direction from the vertex C toward the side AB. For example, for grid point P in FIG. 9, the weight WA from vertex A is (8/8) × (S1 + S2), the weight WB from vertex B is (1/8) × (S2 + S3), and from vertex C The weight WC is (1/8) × (S1 + S3).

The calculated value is stored in a storage device such as the RAM 505 or the external storage device 508.
Next, signal values of lattice points inside the triangle are calculated based on the respective weights (S606). The signal value of the lattice point is obtained using the interpolation result obtained in S604 and the weight obtained in S605. Each signal value is obtained by multiplying the ink value obtained in the direction from the vertex A in S604 by the weight of the grid line from the vertex A obtained in S605 and the direction from the vertex B in S604. The number obtained by multiplying the ink value by the weight of the grid line from the vertex B obtained in S605, and the ink value obtained in the direction from the vertex C in S604 by the weight of the grid line from the vertex C obtained in S605. The number obtained by multiplying the number obtained by the multiplication is divided by the total weight of the grid lines from the vertices A, B, and C of the obtained grid points. The calculated value is stored in a storage device such as the RAM 505 or the external storage device 508. For example, the signal value of the grid point P shown in FIG. 9 is (WA × α + WB × β + WC × γ) / () where the ink values obtained in S604 are α from vertex A, β from vertex B, and γ from vertex C. WA + WB + WC). The processing from S604 to S606 is performed for all the divided triangles, and the signal values are obtained for all the grid points. The obtained signal value for each lattice point is stored in a recording device such as the RAM 505 or the external recording device 508 (S607).

  When the vertex of the tetrahedron is used as a reference, it is divided into a plurality of triangles parallel to the triangle on the bottom surface with respect to the reference vertex, and the above-described processing from S603 to S607 is performed for each triangle. By repeating this process four times, which is the number of vertices of the tetrahedron, four types of signal values at one lattice point are given.

  Next, a tetrahedron is formed based on the tetrahedron lattice point data obtained by the above processing (S608). This formation includes, for example, a method of taking an average value of the four data obtained in S606 and a method of obtaining by calculating a weight from each vertex of the tetrahedron.

  The processes from S603 to S608 are performed on the six tetrahedrons forming the cube. The obtained signal value is stored in a storage device such as the RAM 505 or the external storage device 508.

  Finally, the tetrahedrons are combined to complete a cube, and a lookup table for use in color separation processing is created (S609).

  As described above, according to the present embodiment, in the internal interpolation of the triangle divided for each tetrahedron, the internal interpolation is performed in each of the three directions determined by the vertices of the triangle, and the ink obtained in each of the three directions is obtained. Find a weighted average of values. Then, the decomposition into a plurality of triangles is performed for the four vertices of the tetrahedron, and the color point data (ink value) obtained for each of the four obtained vertices is taken to obtain a weighted average. Create a decomposition table. Thus, the ink value of each grid point obtained as a result of interpolation of each triangle and the formation of the tetrahedron using this result is such that the grid point closer to the control line constituting the tetrahedron is closer to the grid point on that control line. The value is close to the ink value. As a result, the ink values at the lattice points sandwiching the boundaries of the tetrahedrons do not change greatly and change smoothly.

  In this embodiment, by repeating the processing from S603 to S607 four times, which is the number of vertices of the tetrahedron, four types of signal values of one lattice point are given. It may be divided into a plurality of triangles parallel to the bottom triangle with respect to the vertex, and one kind of signal value of one lattice point may be used, and is not restricted by the number of processing of S603 to S607.

  In the present embodiment, the present invention is not restricted by the triangle division direction, the order of the triangle interpolation directions, or the like. In the present embodiment, the process of dividing the triangle for each tetrahedron (S603) and the interpolation process (S604). , Weight calculation (S605), signal value calculation (S606), etc., all six tetrahedrons may be decomposed into triangles, and then interpolation processing may be performed for each triangle. It is not constrained by the unit or order of processing, such as obtaining weights after performing interpolation processing on triangles.

(Embodiment 2)
In the first embodiment, the weight is obtained by multiplying the sum of the ink values of the two sides by the value obtained by dividing the number of grid lines by the total number of grid lines (S605), but only the distance from the vertex is obtained. The weight may be a weight corresponding to only the sum of the ink values of each side. Also, the ink value of each side used for the interpolation process may be used as a reference for the weight, or the weight corresponding to the ink value of each side used for the interpolation process and the distance from the vertex may be used.

(Embodiment 3)
In the first and second embodiments, one of the divided tetrahedrons is divided into a plurality of triangles using each of the four vertices as a reference, but may be divided using two vertices or three vertices as a reference.

(Other)
The present invention is not limited to only the apparatus and method for realizing the above-described embodiment, and a software program for realizing the above-described embodiment is stored in a computer (CPU or MPU) in the system or apparatus. The above embodiment may be realized by supplying and operating the various devices by the computer of the system or apparatus according to the program.

  As a storage medium for storing such a program, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. .

  The computer controls various devices according to only the supplied program, so that not only the functions of the above embodiments are realized, but also the OS (operating system) on which the program is running on the computer, or The above embodiment may be realized in cooperation with other application software or the like.

  Further, after the supplied program is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, the CPU provided in the function expansion board or function storage unit based on the instructions of the program The above-described embodiment may be realized by performing part or all of the actual processing.

It is a figure which shows six divided tetrahedrons. It is a figure which shows the example which interpolates the divided | segmented triangle. It is a block diagram which shows schematic structure which the color separation table of Embodiment 1 of an invention produces. 1 is a diagram illustrating a specific configuration of a computer system used in Embodiment 1. FIG. FIG. 3 is a block diagram showing a main part of the computer system shown in FIG. 2. 6 is a flowchart illustrating processing for creating a color separation table according to the first exemplary embodiment. It is a figure which shows the structure of a color separation table typically, and the figure which shows the control line of a color separation table. It is a figure which shows the example of the interpolation direction of a triangle It is a figure which shows the example of weighting.

Explanation of symbols

401 Image signal input device 402 Computer 403 Display 404 Printer 514 Transmission device 515 External input line

Claims (7)

A method of creating a color separation table for converting a color signal of a predetermined color space into a color material value signal of a color space for performing image output,
Setting a plurality of control lines obtained by connecting predetermined grid points in a solid composed of grid points defined by color signals of the predetermined color space; and
A step of setting a plurality of tetrahedrons by a combination of four control lines among the set control lines;
For each of the set tetrahedrons, setting a plurality of triangles parallel to the triangle facing the vertex;
For each of the plurality of triangles, for each of the three vertices of the triangle, for the grid points on the grid line parallel to the opposite side of the vertex, the color material values of the grid points on the two sides where the grid line intersects are used. A step of obtaining a color material value by interpolation;
The color material value of the obtained grid point is weighted as the distance from the vertex of the grid line is shorter, and the average of the weighted color material values of the same grid point obtained for the three vertexes is obtained. , Setting the average value to the color material value of the grid point;
A method for creating a color separation table. The step of setting a plurality of triangles parallel to the triangle facing the vertex sets a plurality of triangles parallel to the triangle facing the vertex for each of the four vertices;
In the step of setting the color material value, for each of the plurality of tetrahedrons, an average of four weighted averaged color material values of the same lattice point in the tetrahedron is obtained with respect to the four vertices of the tetrahedron. The color separation table creation method according to claim 1, wherein the average value is set as a color material value of the lattice point.   The step of obtaining an average of the weighted color material values is characterized in that the weight is determined using an amount of color material values of two sides having the vertex as an end with respect to each of the three vertices. The color separation table creation method according to claim 1 or 2. An image processing device that converts a color signal of a predetermined color space into a color material value signal of a color space for performing image output,
Means for setting a plurality of control lines obtained by connecting predetermined grid points in a solid consisting of grid points defined by color signals of the predetermined color space;
Means for setting a plurality of tetrahedrons by a combination of four control lines among the set control lines;
Means for setting a plurality of triangles parallel to the triangle facing the vertex for each of the set tetrahedrons;
For each of the plurality of triangles, for each of the three vertices of the triangle, for the grid points on the grid line parallel to the opposite side of the vertex, the color material values of the grid points on the two sides where the grid line intersects are used. Means for obtaining color material values by interpolation;
The color material value of the obtained grid point is weighted as the distance from the vertex of the grid line is shorter, and the average of the weighted color material values of the same grid point obtained for the three vertexes is obtained. , Means for setting the average value to the color material value of the grid point;
An image processing apparatus comprising: The means for setting a plurality of triangles parallel to the triangle facing the vertex sets a plurality of triangles parallel to the triangle facing the vertex for each of the four vertices,
The means for setting the color material value obtains, for each of the plurality of tetrahedrons, an average of four weighted averaged color material values of the same lattice points in the tetrahedron, which are obtained with respect to four vertices of the tetrahedron. The image processing apparatus according to claim 3, wherein the average value is set to a color material value of the lattice point.   The means for obtaining an average of the weighted color material values is characterized in that the magnitude of the weight is determined using the amount of color material values of two sides having the vertex as an end for each of the three vertices. The image processing apparatus according to claim 3 or 4. A program for causing a computer to execute image processing for creating a color separation table for converting a color signal of a predetermined color space into a color material value signal of a color material for performing image output, The image processing is
Setting a plurality of control lines obtained by connecting predetermined grid points in a solid composed of grid points defined by color signals of the predetermined color space; and
A step of setting a plurality of tetrahedrons by a combination of four control lines among the set control lines;
For each of the set tetrahedrons, setting a plurality of triangles parallel to the triangle facing the vertex;
For each of the plurality of triangles, for each of the three vertices of the triangle, for the grid points on the grid line parallel to the opposite side of the vertex, the color material values of the grid points on the two sides where the grid line intersects are used. A step of obtaining a color material value by interpolation;
The color material value of the obtained grid point is weighted as the distance from the vertex of the grid line is shorter, and the average of the weighted color material values of the same grid point obtained for the three vertexes is obtained. , Setting the average value to the color material value of the grid point;
The program characterized by having.

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