JP2008109403A - Display device, program for color calibration of display device, and method of generating three-dimensional lookup table - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device having an improved precision of an output signal value (parameter) of a three-dimensional lookup table. <P>SOLUTION: When an output signal value of a target point cannot be calculated by tetrahedral interpolation, the three-dimensional lookup table for color conversion provided in the display device obtains candidates of the output signal value of the target point by using output signal values of first lattice points P2, P3, and P4 near the target point P0 and output signal values of second lattice points P6, P8, and P10 which are on virtual lines going near the target point through the first lattice points and are adjacent to the first lattice points, and takes an average value of these candidates of the output signal value as an output signal value of the target point. Since the output signal value of the target point can be determined in consideration of changes of the output signal value along a virtual line, the precision of the output signal value of the three-dimensional lookup table is improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a display device such as a liquid crystal display device, a color calibration program for the display device, and a method for creating a three-dimensional lookup table, and in particular, a three-dimensional lookup table for color conversion provided in the display device. Relating to the technology to create.

Conventionally, devices such as printers and scanners with color spaces of cyan (C), magenta (M), yellow (Y), and black (K) perform color gamut conversion using a three-dimensional lookup table. I came. On the other hand, a display device such as a liquid crystal display device has high color reproducibility due to its properties, so that display is performed without any operation or a method according to color reproduction theory (for example, a matrix method). ) Has been used. However, in the method according to the color reproduction theory, the performance depends on the quality of the display device. Recently, more accurate color control has been required for display devices. Since the color space is a three-dimensional representation such as RGB, L ^* a ^* b ^* , XYZ, etc., pursuing accuracy requires control by a three-dimensional lookup table.

  Specifically, since a display device such as a liquid crystal display device has color characteristics (also referred to as “color gamut”) unique to the device, for example, the same red (r), green (g), and blue (b) It is known that even if the input signal is given, the colors displayed on the screen will not be the same if the devices are different. In order to eliminate such a color-specific difference in the display device, a three-dimensional lookup table for color conversion is used. As is well known, a three-dimensional lookup table for color conversion is a search table in which input signal values (r, g, b) and output signal values (R, G, B) are associated with each other. Specifically, the input signal values (r, g, b) constitute a three-dimensional cubic lattice, and output signal values (R, G, B) are set at the lattice points of the cubic lattice. Hereinafter, the output signal value (R, G, B) set at each grid point of the three-dimensional lookup table is also referred to as “parameter” of the three-dimensional lookup table.

  Now, assuming that the three-dimensional lookup table is 8 bits (256 gradations for each color), the displayable colors (number of parameters) are about 16.77 million colors. If all these color conversion data are provided, the data amount of the three-dimensional lookup table becomes enormous. Therefore, each color of the input signal value (r, g, b) is roughly sampled, for example, in 9 steps. In this case, 729 colors can be displayed. The other colors are obtained by interpolation.

The output signal value (parameter) of the three-dimensional lookup table is determined as follows.
First, the ideal characteristics of the display device are determined. This ideal characteristic is obtained by setting the target display color in the XYZ or Lab color system at each lattice point of the cubic lattice represented by the input signal value (r, g, b). It is.

  Next, actual measurement characteristics of the display device are obtained. This measured characteristic is obtained by setting the measured display color in the XYZ or Lab color system at each lattice point of the cubic lattice represented by the input signal value (r, g, b). It is.

Based on the data of the four actual measurement points (T1, T2, T3, T4) surrounding each ideal lattice point (hereinafter also referred to as “target point (T0)”), the color of the target point (T0) is determined. The output signal value (R, G, B)) to be given is obtained. The output signal value is determined by so-called tetrahedral interpolation. In this way, all output signal values of the three-dimensional lookup table are obtained (for example, see Patent Document 1).
JP 2000-251054 (paragraphs 0086 to 0101, FIG. 6)

However, the conventional example having such a configuration has the following problems.
That is, according to the output signal value determination method of the three-dimensional lookup table by the conventional tetrahedral interpolation method, when there is a target point that is not surrounded by the four actual measurement points, the output signal value related to the target point is expressed as follows: I ask for it. Hereinafter, a description will be given with reference to FIG.

  In FIG. 10, symbols T1 to T4 are actual measurement points at which display colors are actually measured. The symbol T0 is a target point that is not surrounded by four actual measurement points. According to the conventional method, a perpendicular line is drawn from the target point T0 to a line segment connecting two measured points T1 and T2 close to the target point T0, and the intersection T0 ′ is obtained. Then, the display colors of the two actual measurement points T1 and T2 are proportionally distributed according to the distance between the actual measurement point T1 and the intersection point T0 ′ and the distance between the lattice point T2 and the intersection point T0 ′, and output the target point T0. The signal value is estimated.

  As described above, according to the conventional method, when there is a target point that is not surrounded by the four actual measurement points, the display color of the two adjacent actual measurement points is linearly interpolated as an output signal value related to the target point. Therefore, there is a problem that the consistency with the output signal values of other lattice points obtained by the tetrahedral interpolation method is poor, and as a result, the accuracy of the three-dimensional lookup table is poor.

The present invention has been made in view of such circumstances, and an object thereof is to provide a display device in which the accuracy of an output signal value of a three-dimensional lookup table is increased.
It is another object of the present invention to provide a color calibration program for a display device and a method for creating a three-dimensional lookup table that can increase the accuracy of the output signal value of the three-dimensional lookup table.

In order to achieve such an object, the present invention has the following configuration.
In other words, the invention according to claim 1 includes a three-dimensional grid point corresponding to an input signal value, and each grid point stores an output signal value corresponding to the input signal value. A display device comprising a dimensional look-up table and configured to give an output signal value color-converted by the three-dimensional look-up table to a display;
The three-dimensional lookup table stores an output signal value corresponding to an input signal value obtained as follows.
(1) A three-dimensional grid characteristic corresponding to an input signal value is provided, and a three-dimensional ideal characteristic in which an ideal display color of the display unit with respect to the input signal value is stored at each grid point is obtained.
(2) A three-dimensional lattice characteristic corresponding to an input signal value is provided, and a three-dimensional actual measurement characteristic in which an actual display color measured by the display unit with respect to the input signal value is stored in each lattice point is obtained.
(3) It is determined whether or not the ideal characteristic value related to the target point for which the output signal value is to be obtained is surrounded by the measured characteristic value related to the three-dimensional measured characteristic among the lattice point group of the three-dimensional lookup table. ,
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The output signal value of the target point is obtained by three-dimensional interpolation,
(5) When the ideal characteristic value related to the target point is not surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the first grid in the vicinity of the target point in the grid point group of the three-dimensional lookup table The output signal value of the point and the output signal value of at least the second grid point adjacent to the first grid point among the grid points on the virtual line passing through the first grid point toward the target point. To find a candidate for the output signal value of the target point,
(6) The processing of (5) above is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is determined as the output signal of the target point. It is characterized by a value.

The operation and effect of the invention described in claim 1 are as follows.
The method of determining the output signal value with respect to the input signal value of the three-dimensional lookup table differs depending on whether or not the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic. When the ideal characteristic value related to the target point is surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the target characteristic point is measured using the actual measurement characteristic value of each lattice point of the three-dimensional actual measurement characteristic surrounding the target point. Since the point output signal value is obtained by three-dimensional interpolation, the target point output signal value can be obtained with relatively high accuracy.

  On the other hand, when the ideal characteristic value related to the target point is not surrounded by the measured characteristic value related to the three-dimensional actual measurement characteristic, the output of the grid point in the vicinity of the target point in the lattice point group of the three-dimensional lookup table If the output signal value of the target point is obtained using only the signal value, the accuracy is deteriorated. Hereinafter, a description will be given with reference to FIG. In FIG. 7, symbol P0 is a target point, and P1 to P10 are lattice points of a three-dimensional lookup table for which output signal values have already been obtained. Assume that the output signals at the grid points P2, P3, and P4 are “10”, for example, and the output signal values at the grid points P6, P8, and P10 are “8”, for example. In such a case, when the output signal value of the target point P is obtained as an average value using only the output signal values of the adjacent grid points P2, P3, and P4, the value of the target point is “10”. However, considering each value of the grid points P6, P8, and P10, the value gradually increases from the grid point P6 through the grid point P2 toward the target point P (P6 “8” → P2). “10” → P0 “12”). Similarly, it is considered that the value gradually increases from P8 → P3 → P0 and from P10 → P4 → P0. In view of this, it is preferable to estimate that the value of the target point is “12”.

  Therefore, in the first aspect of the invention, when the ideal characteristic value related to the target point is not surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the output signal of the first grid point in the vicinity of the target point Value and the output signal value of the second grid point adjacent to the first grid point among the grid points on the virtual line passing through the first grid point toward the target point. The candidate of the output signal value of the point is obtained, the above processing is repeated for a plurality of grid points in the vicinity of the target point to obtain each candidate of the output signal value, and the average value of these output signal value candidates is obtained as the target The output signal value of the point. When the output signal value of the target point is obtained in this way, the change in the output signal value along the virtual line is reflected in the output signal value of the target point. It can be obtained with improved properties.

  Since the display device according to the first aspect of the present invention sets the output signal value of the three-dimensional lookup table for color conversion as described above, the color conversion can be performed with high accuracy.

According to a second aspect of the present invention, in the display device according to the first aspect, the device further includes:
Provided on the input side than the three-dimensional lookup table, the input side lookup table for arbitrarily setting the γ characteristics of the display device,
An output side look-up table that is provided on the output side of the three-dimensional lookup table and cancels the γ characteristic of the display so as to substantially linearize the γ characteristic.

The operation of the second aspect of the invention is as follows.
Since the output side lookup table cancels the γ characteristic of the display and the γ characteristic is substantially linearized, the γ characteristic set in the input side lookup table becomes the γ characteristic of the display device. In other words, the γ characteristic of the display device can be arbitrarily set by changing the characteristic of the input side lookup table. Although it is possible to give such a value for γ characteristic setting to a three-dimensional lookup table for color conversion, setting of the γ characteristic becomes complicated and an attempt is made to set the γ characteristic with high accuracy. Then, the data amount of the three-dimensional lookup table becomes enormous. According to the second aspect of the present invention, since the lookup table for setting the γ characteristic is provided individually, it is easy to set the γ characteristic and avoid an increase in the data amount of the three-dimensional lookup table. Can do.

  According to a third aspect of the present invention, in the display device according to the first or second aspect, the three-dimensional interpolation of the process (4) is tetrahedral interpolation. When the ideal characteristic value related to the target point is surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the value can be obtained with high accuracy when the output signal value of the target point is obtained by tetrahedral interpolation.

  According to a fourth aspect of the present invention, in the display device according to any one of the first to third aspects, a noise component is removed from an output signal value of each lattice point obtained by the processing of (6), and the three-dimensional The look-up table stores output signal values from which noise components have been removed. Since the output signal value is obtained by using the actually measured three-dimensional measurement characteristic, a noise component may be included in the measurement process. According to the invention of claim 4, since noise components are removed from the output signal value of each grid point obtained by the processing of (6), the accuracy of the output signal value of the three-dimensional lookup table is further improved. be able to.

The invention described in claim 5 is provided with a three-dimensional grid point corresponding to an input signal value, and an output signal value corresponding to the input signal value is stored in each grid point. A color calibration program for a display device configured to provide a display with an output signal value color-converted by the three-dimensional lookup table,
The following procedure is performed on the computer to which the display device is connected, that is,
(1) A procedure for obtaining a three-dimensional ideal characteristic having a three-dimensional lattice point corresponding to an input signal value, and storing each display point as an ideal display color for the input signal value at each lattice point;
(2) A procedure for obtaining a three-dimensional actual measurement characteristic having a three-dimensional grid point corresponding to an input signal value, and storing the actual display color measured by the display unit for the input signal value at each grid point; ,
(3) It is determined whether or not an ideal characteristic value related to a target point for which an output signal value is to be obtained is surrounded by an actual measurement characteristic value related to a three-dimensional actual measurement characteristic among lattice point groups of the three-dimensional lookup table. Procedure and
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The procedure for obtaining the output signal value of the target point by three-dimensional interpolation,
(5) When the ideal characteristic value related to the target point is not surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the first grid in the vicinity of the target point in the grid point group of the three-dimensional lookup table The output signal value of the point and the output signal value of at least the second grid point adjacent to the first grid point among the grid points on the virtual line passing through the first grid point toward the target point. To find a candidate for the output signal value of the target point,
(6) The processing of (5) above is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is determined as the output signal of the target point. A procedure with values,
(7) A procedure of giving output signal values obtained for all grid points of the three-dimensional lookup table to the three-dimensional lookup table;
To update the output signal value corresponding to the input signal value of the three-dimensional lookup table.

  According to the invention according to claim 5, when the computer executes the procedures (1) to (6), the output signal value of each lattice point of the three-dimensional lookup table is obtained, and according to the procedure (7), Since the contents of the three-dimensional lookup table are updated, color calibration of the display device can be performed with high accuracy.

  According to a sixth aspect of the present invention, in the color calibration program for a display device according to the fifth aspect, the three-dimensional interpolation of the process (4) is tetrahedral interpolation. According to tetrahedral interpolation, the output signal value of the target point can be obtained with high accuracy.

  According to a seventh aspect of the invention, in the color calibration program for a display device according to the fifth or sixth aspect, the noise component is removed from the output signal value of each grid point obtained in the processing of (6), Step (7) is executed. According to the seventh aspect of the invention, the accuracy of the output signal value of the three-dimensional lookup table can be further increased.

The invention according to claim 8 is provided with a three-dimensional grid point for color conversion, comprising a three-dimensional grid point corresponding to an input signal value, and storing an output signal value corresponding to the input signal value at each grid point. A table creation method,
The output signal value corresponding to the input signal value obtained through the following process is stored in the three-dimensional lookup table.
(1) A process of obtaining a three-dimensional ideal characteristic having a three-dimensional lattice point corresponding to an input signal value, and storing an ideal display color of the display unit with respect to the input signal value at each lattice point;
(2) A process of obtaining a three-dimensional actual measurement characteristic in which a three-dimensional grid point corresponding to an input signal value is provided, and each grid point stores a measured actual display color of the display unit for the input signal value;
(3) It is determined whether or not an ideal characteristic value related to a target point for which an output signal value is to be obtained is surrounded by an actual measurement characteristic value related to a three-dimensional actual measurement characteristic among lattice point groups of the three-dimensional lookup table. Process,
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The process of obtaining the output signal value of the target point by three-dimensional interpolation,
(5) When the ideal characteristic value related to the target point is not surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the first grid in the vicinity of the target point in the grid point group of the three-dimensional lookup table The output signal value of the point and the output signal value of at least the second grid point adjacent to the first grid point among the grid points on the virtual line passing through the first grid point toward the target point. Using the process of obtaining candidate output signal values at the target point,
(6) The processing of (5) above is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is determined as the output signal of the target point. It is characterized by the process of value.

  According to the eighth aspect of the invention, the output signal value of each lattice point can be obtained with high accuracy.

  According to a ninth aspect of the present invention, in the method for creating a three-dimensional lookup table according to the eighth aspect, the three-dimensional interpolation of the process (4) is tetrahedral interpolation. According to tetrahedral interpolation, the output signal value of the target point can be obtained with high accuracy.

  A tenth aspect of the present invention is the method of creating a three-dimensional lookup table according to the eighth or ninth aspect, wherein a noise component is removed from an output signal value of each lattice point obtained by the processing of (6), The output signal value from which the noise component has been removed is stored in a three-dimensional lookup table. According to the invention described in claim 10, the accuracy of the output signal value of the three-dimensional lookup table can be further improved.

The invention described in claim 11 is provided with a three-dimensional grid point corresponding to an input signal value, and an output signal value corresponding to the input signal value is stored in each grid point. A table creation method,
The output signal value corresponding to the input signal value obtained through the following process is stored in the three-dimensional lookup table.
(1) A process of obtaining a three-dimensional ideal characteristic having a three-dimensional lattice point corresponding to an input signal value, and storing an ideal display color of the display unit with respect to the input signal value at each lattice point;
(2) A process of obtaining a three-dimensional actual measurement characteristic in which a three-dimensional grid point corresponding to an input signal value is provided, and each grid point stores a measured actual display color of the display unit for the input signal value;
(3) It is determined whether or not an ideal characteristic value related to a target point for which an output signal value is to be obtained is surrounded by an actual measurement characteristic value related to a three-dimensional actual measurement characteristic among lattice point groups of the three-dimensional lookup table. Process,
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The process of obtaining the output signal value of the target point by three-dimensional interpolation,
(5) A process of removing a noise component from the output signal value of each lattice point obtained in the process of (4).

  According to the eleventh aspect of the present invention, the noise component mixed in the process of obtaining the three-dimensional actual measurement characteristic can be removed, so that the accuracy of the output signal value of the three-dimensional lookup table can be further improved.

  According to the present invention, the ideal characteristic value related to the target point for which the output signal value is to be obtained is not surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic in the lattice point group of the three-dimensional lookup table. Includes an output signal value of a first grid point in the vicinity of the target point and a grid point on a virtual line passing through the first grid point toward the target point and adjacent to at least the first grid point. The output signal value at the second grid point is used to obtain an output signal value candidate for the target point, and the above processing is repeated for a plurality of grid points near the target point to obtain an output signal value candidate. Since each is obtained and the average value of these output signal value candidates is used as the output signal value of the target point, the output signal value of each grid point in the three-dimensional lookup table is obtained with improved continuity with other points. Can do. As a result, the color characteristics unique to the apparatus are corrected, and a natural display can be obtained.

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of the display device according to the first embodiment.
The display device according to this embodiment is a liquid crystal display device, and includes an input side lookup table (LUT) 1, a three-dimensional lookup table (LUT) 2, and an output side lookup table ( LUT) 3 and a liquid crystal display 4 are provided.

The output side look-up table 3 is for canceling the γ characteristic of the liquid crystal display 4 and linearizing the γ characteristic (γ = 1), and the input signal values (R ₂ , G ₂ , It is a one-dimensional lookup table provided individually according to B ₂ ). On the other hand, the input side look-up table 1 is for arbitrarily setting the γ characteristic of the display device on the assumption that the γ characteristic of the liquid crystal display 4 is canceled in the output side look-up table 3. , A one-dimensional lookup table provided individually according to input signal values (R ₀ , G ₀ , B ₀ ).

The three-dimensional lookup table 2 is used for color conversion, and includes three-dimensional grid points corresponding to input signal values (R ₁ , G ₁ , B ₁ ), and each grid point has an input signal value (R ₁ , output signal values (R ₂ , G ₂ , B ₂ ) corresponding to ₁ , G ₁ , B ₁ ) are stored. The method for determining the output signal value (parameter) of the three-dimensional lookup table 2 that is a feature of this embodiment will be described in detail later.

According to the present embodiment, the input signal value (R ₀ , G ₀ , B ₀ ) of the number of bits corresponding to the liquid crystal display 4, for example, 8 bits or 10 bits, respectively, is given to the input side lookup table 1. The input signal value (R ₀ , G ₀ , B ₀ ) is converted by an arbitrary γ characteristic stored in advance in the input side lookup table 1 and output as a signal value (R ₁ , G ₁ , B ₁ ). The This signal value (R ₁ , G ₁ , B ₁ ) is given to the three-dimensional lookup table 2. The three-dimensional lookup table 2 converts input signal values (R ₁ , G ₁ , B ₁ ) with preset color conversion characteristics and outputs signal values (R ₂ , G ₂ , B ₂ ). . The signal values (R ₂ , G ₂ , B ₂ ) are converted by the output side look-up table 3 with characteristics opposite to the γ characteristics of the liquid crystal display 4. The output signal values (R ₃ , G ₃ , B ₃ ) are given to the liquid crystal display 4.

  As described above, according to the apparatus of the present embodiment, the output side lookup table 3 cancels the γ characteristic of the liquid crystal display 4, so that display is performed with an arbitrary γ characteristic set in the input side lookup table 1. Can do. In addition, since arbitrary color conversion can be performed by the three-dimensional lookup table 2, color reproduction can be performed without being influenced by the unique color characteristics of the liquid crystal display 4. The functions of the input / output look-up tables 1 and 3 can also be given to the three-dimensional look-up table 2. However, the data amount of the three-dimensional look-up table 2 becomes enormous. In this embodiment, since the input / output lookup tables 1 and 3 are provided separately from the three-dimensional lookup table 2, the data amount of the three-dimensional lookup table 2 can be kept low.

  Next, a method for determining the output signal value of the three-dimensional lookup table 2 will be described with reference to the flowchart of FIG.

Step S1: Calculation of ideal characteristics First, an ideal characteristic of a display device representing what kind of color reproduction is desired for an input signal value (R, G, B) is calculated. The ideal characteristic includes a three-dimensional grid point corresponding to the input signal value, and an ideal display color of the display unit for the input signal value is stored in each grid point. In this embodiment, the display color is represented by the tristimulus values (X, Y, Z) of the XYZ color system, but may be represented by the Lab system. A specific example for calculating the ideal characteristic will be described below.

Between the input signal value (R, G, B) and the red, green, and blue tristimulus values (X, Y, Z) of the XYZ color system, there is a relationship represented by the following equation (1). .

Therefore, first, the transformation matrix M in the equation (1) is calculated. Specifically, the _first XYZ color system tristimulus values (X, Y, Z) when a red input signal (R ₁ = 255, G1 = 0, B1 = 0) is given. Get the relational expression. The values of the tristimulus values (X, Y, Z) can be known from the device characteristics (characteristics of the display 4) described in the ICC profile. It should be noted that the tristimulus values (X, Y, Z) may be determined from the actually measured characteristics of the display 4 or the tristimulus values (X , Y, Z) may be determined. The second relational expression when the “green” input signal (R = 0, G = 255, B = 0) is given in the same manner as when the “red” input signal is given, and the “blue” input signal. A third relational expression is obtained when (R = 0, G = 0, B = 255) is given. Based on the first to third relational expressions, each element (m00, m01,..., M22) of the conversion example M is determined.

Once the transformation matrix M is calculated, the transformation matrix M and the γ characteristic (luminance characteristic) set in the input side lookup table 1 are used to specify an arbitrary input signal (R ₀ , G ₀ , B ₀ ). The tristimulus values (X, Y, Z) of the lattice points, that is, ideal display colors are calculated. A specific calculation procedure will be described below.

First, an arbitrary input signal Vi as shown by the following equation (2) is set.

Next, the signal R _0i ′ taking into account the γ characteristic set in the input side look-up table 1.
G _0i ′ and B _0i ′ are obtained. Assuming that γ characteristics of R, G, and B are γ _r , γ _g , and γ _b , signals R _0i ′, G _0i ′, and B _0i ′ are obtained by the following equation (3).

Using the signals R _0i ′, G _0i ′, B _0i ′ in consideration of the γ characteristics and the transformation matrix M obtained previously, the tristimulus values (X, Y, Z) of each lattice point of the ideal characteristics are It calculates | requires by Formula (4). By executing the above calculation for all arbitrary inputs (grid points), the ideal characteristic of the display device is obtained.

Step S2: Acquisition of actual measurement characteristics An arbitrary input signal (see the equation (2)) is given to the display device, the color displayed on the liquid crystal display 4 at that time is measured, and the actually measured tristimulus values (X _i , Y _i , Z _i ). The three-dimensional actual measurement characteristic obtained by measuring all the grid points includes a three-dimensional grid point corresponding to the input signal value, and each grid point has an actual display color (measured by the display unit for the input signal value). In this embodiment, tristimulus values (X _i , Y _i , Z _i )) are stored.

Steps S3 and S4: Determination of whether or not tetrahedral interpolation is possible. Of the lattice point group of the three-dimensional lookup table 3, an ideal characteristic value related to a target point for which an output signal value is to be obtained is an actual measurement measurement related to a three-dimensional actual measurement characteristic Determine if it is surrounded by values. The procedure will be described in detail below.

  First, in the lattice point group of the three-dimensional lookup table 3, the coordinates in the color space of the ideal characteristic value relating to the target point for which the output signal value is to be obtained are referred to as P0 (hereinafter referred to as “target point P0”). To do. Then, one actual measurement point P1 closest to the target point P0 is found among the actual measurement points corresponding to the respective grid points of the three-dimensional actual measurement characteristics (this actual measurement point is also expressed by coordinates in the color space).

  Hereinafter, a description will be given with reference to FIG. A hexagonal pyramid having P1 as a vertex, that is, a tetrahedron (P1, P2, P3, P4) is assumed for the hexahedron including the target point P0 with the found actual measurement point P1 as one vertex (reference numerals in FIG. 3). Tetrahedron indicated by A). Then, using the plane equation, it is determined whether or not the target point P0 is surrounded by the tetrahedron (P1, P2, P3, P4). Specifically, the determination is made according to the following procedure.

  First, equations are obtained for all planes of the tetrahedron (P1, P2, P3, P4). Then, the positional relationship between the target point P0 and each plane is examined. If it is determined that all the target points P0 are located in the positive direction with respect to the four planes, the target point P0 is a tetrahedron (P1, P2, P3). , P4).

The plane equation can be obtained as follows. Please refer to FIG. For example, an actual measurement point (P1, P2, P3) is taken as an example. This plane equation is
ax + by + cz + d = 0
, The coefficients a, b, and c are obtained as an outer product of the vector V1 from the point P1 to P2 and the vector V2 from the point P1 to P3 (see Expression (5)).

However, it is d = -1 × (a × V1 x + b × V1 y + c × V1 z).
The point P4 is set to be in the positive direction (s ≧ 0) of the plane (P1, P2, P3).
Here, a _{s = a × P4 x + b} × P4 y + c × P4 z + d.
When the point P4 is located in the negative direction with respect to the obtained plane equation, (-1) is multiplied by (a, b, c, d).

  If it is determined that the target point P0 is not surrounded by the tetrahedron (P1, P2, P3, P4) after the above determination, the measured point P1 is sandwiched between the planes (P2, P3, P4). To move to the actual measurement point P1 ′ on the opposite side, and similarly determine whether or not the target point P0 is surrounded by tetrahedrons (P1 ′, P2, P3, P4) (indicated by symbol B in FIG. 3).

  If the target point P0 is not surrounded by the tetrahedron (P1 ′, P2, P3, P4), and the target point P0 is outside (in the negative direction) the plane (P1 ′, P2, P3), the target point P0 Is surrounded by tetrahedrons (P1 ′, P2, P3, P4 ′) (indicated by symbol C in FIG. 3). On the other hand, if the target point P0 is outside the plane (P1 ′, P2, P4), the target point P0 is in a tetrahedron (P1 ′, P2, P3 ′, P4) (indicated by reference sign D in FIG. 3). It will be surrounded. If the target point P0 is outside the plane (P1 ′, P3, P4), the target point P0 is in a tetrahedron (P1 ′, P2 ′, P3, P4) (indicated by symbol E in FIG. 3). It will be surrounded.

Step S5: Parameter calculation by tetrahedral interpolation When the presence of the tetrahedron surrounding the target point P0 is confirmed as described above, the output signal values (R ₂ , G ₂ , B ₂₎ a determined by tetrahedral interpolation. Hereinafter, a description will be given with reference to FIG. Now, it is assumed that the target point P0 is surrounded by tetrahedrons (P1, P2, P3, P4). This tetrahedron (P1, P2, P3, P4) is further divided into four tetrahedrons v1, v2, v3, v4 having the target point P0 as a vertex. Then, using each volume of these tetrahedra v1 to v4, calculates an output signal value of the target point according to the following equation _{(6) (R 2, G} 2, B 2).
RGB (P0) = (RGB (P1) × V1 + RGB (P2) × V2 + RGB (P3) × V3 + RGB (P4) × V4) / V (6)
In the equation (6), RGB (P0) is an output signal value (R ₂ , G ₂ , B ₂ ) corresponding to the target point P0 of the three-dimensional lookup table 2. RGB (P1) to RGB (P4) are input signal values (R, G, B) corresponding to the actual measurement points P1 to P4 of the three-dimensional actual measurement characteristics. Furthermore, V1 to V4 are volumes of tetrahedrons v1 to v4. V is the volume of the tetrahedron (P1, P2, P3, P4).

  In this embodiment, when the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the output signal value of the target point is obtained by tetrahedral interpolation. In addition to tetrahedral interpolation, spline interpolation, triangular prism (prism) interpolation, hexahedral (cubic) interpolation, pyramid interpolation, volume interpolation, and the like can be used.

  Returning to the flowchart of FIG. If it is determined in step S4 that there is no tetrahedron surrounding the target point P0, the process proceeds to step S6.

Step S6: Estimation of output signal value When the ideal characteristic value related to the target point is not surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the vicinity of the target point in the lattice point group of the three-dimensional lookup table Among the output signal values of the first grid point at and the grid points on the virtual line passing through the first grid point toward the target point, at least the second grid point adjacent to the first grid point Using the output signal value, a candidate output signal value at the target point is obtained. Then, this process is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is set as the output signal value of the target point.
Hereinafter, a specific description will be given with reference to FIGS. 6 and 7.

  In FIG. 6, the grid point group in the region indicated by the symbol A is a grid point group of the three-dimensional lookup table 2 whose output signal value is obtained by tetrahedral interpolation. On the other hand, since the ideal characteristic values related to these lattice points are not surrounded by the actual measurement characteristic values related to the three-dimensional actual measurement characteristics, the output signal value is obtained by tetrahedral interpolation. This is a lattice point group that could not be obtained. Now, a case where the output signal value of the target point P0 in the region B is obtained will be described. First, a first grid point in the vicinity of the target point P0 is extracted. When considering a three-dimensional grid, there are 26 neighboring grids surrounding the target point. Among these, the grid point whose output signal value is obtained by the tetrahedral interpolation in step S5 is set as the first grid point.

For simplicity of explanation, it is assumed that there are three first grid points P2, P3, and P4 in the vicinity of the target point P0 as shown in FIG. Hereinafter, the description will be focused on the first grid point P2. A second grid point P6 adjacent to the first grid point on the virtual line passing through the first grid point P2 toward the target point is extracted. A vector V (P2-P6) from the second grid point P6 toward the first grid point P2 is assumed. This vector V (P2-P6) is translated to assume a vector V (P2-P6 + P2) with P2 as a base point, and a target point candidate _P01 is at the tip of the vector V (2 × P2-P6). Estimated. Then, the output signal value RGB (P ₀₁ ) of the first target point candidate P ₀₁ is obtained by the following equation (7) using the output signal values RGB (P 2) and RGB (P 6) of the lattice points P 2 and P 6. be able to.
RGB (P ₀₁ ) = 2 × RGB (P 2) −RGB (P 6) (7)

Similarly, the output signal value RGB (P ₀₂ ) of the second candidate P ₀₂ of the target point is obtained from the first grid point P 3 and the second grid point P 8 adjacent thereto by the following equation (8). Can do.
RGB (P ₀₂ ) = 2 × RGB (P 3) −RGB (P 8) (8)
Further, the output signal value RGB (P ₀₃ ) of the third candidate P ₀₃ as the target point can be obtained from the first lattice point P 4 and the second lattice point P 10 adjacent thereto by the following equation (9). .
_{- RGB (P 03) = 2} × RGB (P4) -RGB (P10) ··· (9)
A symbol P0 ′ illustrated in FIGS. 6 and 7 indicates a set of first to third candidates P _{01 to} P ₀₃ of target points.

The target point candidate points P ₀₁ , P ₀₂ , and P ₀₃ obtained as described above reflect changes in the output signal value generated from the grid point P 6 toward P 2 to the candidate point P _01. Similarly, the change in the output signal value generated from the grid point P8 toward P3 is set as the candidate point _P02 , and the change in the output signal value generated from the grid point P10 toward P4 is set as the candidate point _P03 . Each is reflected. Therefore, as the output signal value RGB (P ₀ ) of the final target point, as shown in the following equation (10), the output signal values of these candidate points P ₀₁ , P ₀₂ , P _03,. The average value may be taken.
RGB (P ₀ ) = (RGB (P ₀₁ ) + RGB (P ₀₂ ) + RGB (P ₀₃ ) +.
+ RGB (P _0N )) / N (10)
Here, N is the number of first lattice points.

  In this embodiment, candidate output signals for target points are obtained using the output signal value of the first grid point and the output signal value of the second grid point adjacent to the first grid point on the virtual line. However, the output signal value of the third grid point adjacent to the second grid point on the virtual line may be further considered.

  Returning to the flowchart of FIG. When the output signal value of the target point is estimated in step S6, the process proceeds to the next step S7, and it is determined whether or not the output signal value has been calculated for all grid points in the three-dimensional lookup table 2, and all grid points are determined. Steps S3 to S6 are repeated until an output signal value is obtained for.

Step S8: Removal of noise components When the output signal values are obtained for all the lattice points, the process proceeds to step S8, and the noise included in the output signal value group is removed. That is, in order to obtain the output signal value of the grid point of the three-dimensional lookup table 2, the color displayed on the liquid crystal display 4 is measured as described in step S2. In such a display color measurement process, a noise component may be mixed into the actually measured three-dimensional measurement characteristic. As a result of this noise component being mixed into the output signal value at the lattice point of the three-dimensional lookup table 2, the change in the output signal value at the lattice point becomes discontinuous. Since the output signal value at the lattice point is inherently expected to be continuous, the noise component is removed using a Laplacian filter or a median filter.

  As described above, the output signal values of all the lattice points in the three-dimensional lookup table 2 can be determined. According to this embodiment, among the lattice point groups of the three-dimensional lookup table, the ideal characteristic value related to the target point for which the output signal value is to be obtained is not surrounded by the measured characteristic value related to the three-dimensional measured characteristic. In this case, the output signal value of the first grid point in the vicinity of the target point and a virtual line passing through the first grid point toward the target point and adjacent to the first grid point. Using the output signal values of the two grid points, candidate output signal values for the target point are obtained, and the above processing is repeated for a plurality of grid points near the target point to obtain respective output signal value candidates. Since the average value of these output signal value candidates is used as the output signal value of the target point, the output signal value of each lattice point in the three-dimensional lookup table can be obtained with high accuracy.

  The second embodiment relates to a color calibration program for a display device. FIG. 8 is a block diagram illustrating a schematic configuration of a computer that executes a color calibration program for a display device and a display device that is a target of color calibration.

  Since the display device 10 has the same configuration as that described in the first embodiment, a description thereof is omitted here. The computer 20 includes a central processing unit (CPU) 21, a data read-only memory (ROM) 22, and a random access memory (RAM) 23 for primary storage of data. Connected through. A CD-ROM driver 26 for driving a compact disc (CD) ROM 25 is connected to the bus 24 via a controller 27. Further, a hard disk driver 29 for driving the hard disk 28 is connected to the bus 24 via the controller 30. A keyboard 31 and a mouse 32 as operating devices are connected to the bus 24 via the controller 33. The display device 10 is also connected to the bus 24 via the controller 34.

  The operation of the second embodiment will be described below with reference to the flowchart of the color calibration program for the display device shown in FIG.

  The color calibration program for the display device according to the present embodiment is provided by, for example, the CD-ROM 25 as a storage medium and is taken into the computer 20, and the program is stored in the hard disk 28. The color calibration program may be provided by communication using the Internet or the like. At the time of color calibration, the CPU 21 reads the color calibration program in the hard disk 28 and executes the processing.

Step T1: Acquisition of ideal characteristics In this step T1, a three-dimensional grid point corresponding to an input signal value is provided, and an ideal display color of the display for the input signal value is stored in each grid point. Get ideal characteristics. Specifically, this is the same as step S1 in the first embodiment. However, the operator inputs the RGB values and tristimulus values (X, Y, Z) that are used as a reference when calculating the conversion example M by operating the keyboard 31 or the like. When these values are input, the CPU 21 calculates the conversion example M based on the equation (1). Further, when the operator operates the keyboard 31 or the like to input the γ characteristic of the input-side lookup table 31, the CPU 21 uses the conversion example M calculated earlier and the γ characteristic to obtain the expression (4). Then, the tristimulus values (X, Y, Z) of each grid point of ideal characteristics are calculated. Note that the ideal characteristic may be acquired directly by the computer 20 instead of the above-described calculation.

Step T2: Acquisition of Actual Measurement Characteristics In this step T2, a three-dimensional grid point corresponding to the input signal value is provided, and the actual display color measured by the display unit for the input signal value is stored in each grid point. Acquire three-dimensional measured characteristics. Specifically, it is the same as step S2 of the first embodiment. However, the measured tristimulus values (X _i , Y _i , Z _i ) are input by the operator operating the keyboard 31 or the like.

Steps T3 and T4: Determination of whether or not tetrahedral interpolation is possible Here, the ideal characteristic value related to the target point for which the output signal value is to be obtained from the lattice point group of the three-dimensional lookup table by the CPU 21 is three-dimensionally measured. It is determined whether or not it is surrounded by measured characteristic values related to the characteristics. Specifically, since it is the same as steps S3 and S4 of the first embodiment, a description thereof is omitted here.

Step T5: Parameter calculation by tetrahedral interpolation Here, when the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the three-dimensional measured characteristic surrounding the target point is calculated. Using the measured characteristic value of each grid point, the output signal value of the target point is obtained by three-dimensional interpolation (for example, tetrahedral interpolation). Specifically, since it is the same as step S5 of the first embodiment, a description thereof is omitted here.

Step T6: Parameter Estimation Here, when the ideal characteristic value related to the target point is not surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the target point of the target point is determined in the lattice point group of the three-dimensional lookup table. Of the output signal value of the first grid point in the vicinity and the grid point on the virtual line passing through the first grid point toward the target point, at least the second grid point adjacent to the first grid point The output signal value candidate of the target point is obtained using the output signal value of. Then, this process is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is set as the output signal value of the target point. Specifically, since it is the same as step S6 of the first embodiment, a description thereof is omitted here.

Step T7:
When the output signal value of the target point is estimated in step T6, the process proceeds to the next step T7, and it is determined whether or not the output signal value (parameter) has been calculated for all the grid points of the three-dimensional lookup table 2. Steps T3 to T6 are repeatedly executed until output signal values are obtained for the grid points.

Step T8: Removal of noise components
When output signal values are obtained for all grid points of the three-dimensional lookup table, noise components included in the output signal value group are removed using a Laplacian filter or a median filter.

Step T9: Update of output signal value (parameter) After removing noise components from the output signal value group, these data are sent to the display device 10 via the controller 34, and the output signal value of the three-dimensional lookup table 2 is updated. To do. Note that the γ characteristics of the input side lookup table 1 and the γ characteristics of the output side lookup table 3 may also be updated using the computer 20.

  As described above, according to the second embodiment, the parameters of the three-dimensional lookup table 2 can be set with high accuracy, so that the color reproducibility of the display device can be maintained well.

  The noise component removal process described in the above embodiment can be suitably used when the output signal value of the three-dimensional lookup table is obtained using the three-dimensional actual measurement characteristic. A technique etc. are not specifically limited.

1 is a block diagram illustrating a schematic configuration of a display device according to a first embodiment. 3 is a flowchart showing a method for determining an output signal value (parameter) of a three-dimensional lookup table 2. It is a figure where it uses for description of tetrahedral interpolation. It is a figure where it uses for description of tetrahedral interpolation. It is a figure where it uses for description of tetrahedral interpolation. It is a figure where it uses for description of the process for estimating the output signal value of the target point which cannot perform tetrahedral interpolation. It is a figure where it uses for description of the process for estimating the output signal value of the target point which cannot perform tetrahedral interpolation. It is the block diagram which showed schematic structure of the display apparatus and computer which concern on 2nd Example. It is the flowchart which showed the procedure of the program for color calibration of a display apparatus. It is a figure where it uses for description of the determination method of the output signal value of the conventional three-dimensional lookup table.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Input side lookup table 2 ... Three-dimensional lookup table 3 ... Output side lookup table 10 ... Display apparatus 20 ... Computer

Claims (11)

A three-dimensional look-up table for color conversion, in which a three-dimensional grid point corresponding to the input signal value is stored, and an output signal value corresponding to the input signal value is stored in each grid point, A display device configured to give an output signal value color-converted by an uptable to a display device,
The three-dimensional lookup table stores an output signal value corresponding to an input signal value obtained as follows.
(1) A three-dimensional grid characteristic corresponding to an input signal value is provided, and a three-dimensional ideal characteristic in which an ideal display color of the display unit with respect to the input signal value is stored at each grid point is obtained.
(2) A three-dimensional lattice characteristic corresponding to an input signal value is provided, and a three-dimensional actual measurement characteristic in which an actual display color measured by the display unit with respect to the input signal value is stored in each lattice point is obtained.
(3) It is determined whether or not the ideal characteristic value related to the target point for which the output signal value is to be obtained is surrounded by the measured characteristic value related to the three-dimensional measured characteristic among the lattice point group of the three-dimensional lookup table. ,
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The output signal value of the target point is obtained by three-dimensional interpolation,
(5) When the ideal characteristic value related to the target point is not surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the first grid in the vicinity of the target point in the grid point group of the three-dimensional lookup table The output signal value of the point and the output signal value of at least the second grid point adjacent to the first grid point among the grid points on the virtual line passing through the first grid point toward the target point. To find a candidate for the output signal value of the target point,
(6) The processing of (5) above is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is determined as the output signal of the target point. A display device characterized by a value. The display device of claim 1, wherein the device further comprises:
Provided on the input side than the three-dimensional lookup table, the input side lookup table for arbitrarily setting the γ characteristics of the display device,
A display device provided on the output side of the three-dimensional lookup table, the output side lookup table for canceling the γ characteristic of the display and making the γ characteristic substantially linear. The display device according to claim 1 or 2,
The display device in which the three-dimensional interpolation of the process (4) is tetrahedral interpolation. The display device according to any one of claims 1 to 3,
Removing a noise component from the output signal value of each grid point obtained in the process of (6),
The three-dimensional lookup table is a display device that stores output signal values from which noise components have been removed. A three-dimensional look-up table for color conversion, in which a three-dimensional grid point corresponding to the input signal value is stored, and an output signal value corresponding to the input signal value is stored in each grid point, A program for color calibration of a display device configured to give an output signal value color-converted in an uptable to a display device,
The following procedure is performed on the computer to which the display device is connected:
(1) A procedure for obtaining a three-dimensional ideal characteristic having a three-dimensional lattice point corresponding to an input signal value, and storing each display point as an ideal display color for the input signal value at each lattice point;
(2) A procedure for obtaining a three-dimensional actual measurement characteristic having a three-dimensional grid point corresponding to an input signal value, and storing the actual display color measured by the display unit for the input signal value at each grid point; ,
(3) It is determined whether or not an ideal characteristic value related to a target point for which an output signal value is to be obtained is surrounded by an actual measurement characteristic value related to a three-dimensional actual measurement characteristic among lattice point groups of the three-dimensional lookup table. Procedure and
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The procedure for obtaining the output signal value of the target point by three-dimensional interpolation,
(5) When the ideal characteristic value related to the target point is not surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the first grid in the vicinity of the target point in the grid point group of the three-dimensional lookup table The output signal value of the point and the output signal value of at least the second grid point adjacent to the first grid point among the grid points on the virtual line passing through the first grid point toward the target point. To find a candidate for the output signal value of the target point,
(6) The processing of (5) above is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is determined as the output signal of the target point. A procedure with values,
(7) A procedure of giving output signal values obtained for all grid points of the three-dimensional lookup table to the three-dimensional lookup table;
By executing the above, the output signal value corresponding to the input signal value of the three-dimensional lookup table is updated. In the color calibration program for a display device according to claim 5,
The three-dimensional interpolation of the process (4) is a color calibration program for a display device, which is tetrahedral interpolation. The program for color calibration of a display device according to claim 5 or 6,
A color calibration program for a display device that executes the procedure of (7) after removing a noise component from the output signal value of each grid point obtained in the process of (6). A method of creating a three-dimensional lookup table for color conversion, comprising a three-dimensional grid point corresponding to an input signal value, and each grid point storing an output signal value corresponding to the input signal value,
The output signal value corresponding to the input signal value obtained through the following process is stored in the three-dimensional lookup table.
(1) A process of obtaining a three-dimensional ideal characteristic having a three-dimensional lattice point corresponding to an input signal value, and storing an ideal display color of the display unit with respect to the input signal value at each lattice point;
(2) A process of obtaining a three-dimensional actual measurement characteristic in which a three-dimensional grid point corresponding to an input signal value is provided, and each grid point stores a measured actual display color of the display unit for the input signal value;
(3) It is determined whether or not an ideal characteristic value related to a target point for which an output signal value is to be obtained is surrounded by an actual measurement characteristic value related to a three-dimensional actual measurement characteristic among lattice point groups of the three-dimensional lookup table. Process,
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The process of obtaining the output signal value of the target point by three-dimensional interpolation,
(5) When the ideal characteristic value related to the target point is not surrounded by the actual measurement characteristic value related to the three-dimensional actual measurement characteristic, the first grid in the vicinity of the target point in the grid point group of the three-dimensional lookup table The output signal value of the point and the output signal value of at least the second grid point adjacent to the first grid point among the grid points on the virtual line passing through the first grid point toward the target point. Using the process of obtaining candidate output signal values at the target point,
(6) The processing of (5) above is repeated for a plurality of grid points in the vicinity of the target point to obtain respective output signal value candidates, and the average value of these output signal value candidates is determined as the output signal of the target point. A method of creating a three-dimensional lookup table, characterized by: The method for creating a three-dimensional lookup table according to claim 8,
The three-dimensional interpolation of the process (4) is a method of creating a three-dimensional lookup table that is tetrahedral interpolation. The method for creating a three-dimensional lookup table according to claim 8 or 9,
Removing a noise component from the output signal value of each grid point obtained in the process of (6),
A method for creating a three-dimensional lookup table, wherein an output signal value from which the noise component has been removed is stored in the three-dimensional lookup table. A method of creating a three-dimensional lookup table for color conversion, comprising a three-dimensional grid point corresponding to an input signal value, and each grid point storing an output signal value corresponding to the input signal value,
The output signal value corresponding to the input signal value obtained through the following process is stored in the three-dimensional lookup table.
(1) A process of obtaining a three-dimensional ideal characteristic having a three-dimensional lattice point corresponding to an input signal value, and storing an ideal display color of the display unit with respect to the input signal value at each lattice point;
(2) A process of obtaining a three-dimensional actual measurement characteristic in which a three-dimensional grid point corresponding to an input signal value is provided, and each grid point stores a measured actual display color of the display unit for the input signal value;
(3) It is determined whether or not an ideal characteristic value related to a target point for which an output signal value is to be obtained is surrounded by an actual measurement characteristic value related to a three-dimensional actual measurement characteristic among lattice point groups of the three-dimensional lookup table. Process,
(4) When the ideal characteristic value related to the target point is surrounded by the measured characteristic value related to the three-dimensional measured characteristic, the measured characteristic value of each lattice point of the three-dimensional measured characteristic surrounding the target point is used. The process of obtaining the output signal value of the target point by three-dimensional interpolation,
(5) A process of removing a noise component from the output signal value of each lattice point obtained in the process of (4).

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