JP2521182B2 - Color correction device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a color correction device, and more particularly to a color correction device that facilitates accurate color reproduction and correction of color correction values.

[Prior art]

For example, a three-dimensional color signal generated by a color television camera, a color image scanner, or other image reading device is displayed on a color display device as a soft copy of a color image, or a color image is displayed.
When obtaining a color image as a hard copy by a printer, the color image displayed on the display surface of the display or the color image of the printed hard copy is made into a desired good color reproduction state. Must be By the way, a color display device or a color display device in which a color signal of a specific color system generated by the image reading device requires a color signal of a color system different from the color signal of the specific color system described above. As a matter of course, a color image in a desired good color reproduction state cannot be reproduced by supplying it to a printer or the like. Therefore, various color signal conversion methods for converting a multidimensional color signal corresponding to the color of the first color system into a multidimensional color signal corresponding to the color of the second color system have been conventionally proposed. It has been done. As the color signal conversion method described above, a multi-dimensional color signal corresponding to a color of the first color system is subjected to a matrix calculation process using a first-order polynomial or a second-order polynomial, and the second color system is converted. A color signal conversion method by a calculation method for converting a multi-dimensional color signal corresponding to a color, and a look-up table (LU) for data of a multi-dimensional color signal corresponding to a color of the first color system.
T) as an address signal for lookup
Conventionally, two methods, a color signal conversion method by a direct mapping table method that obtains data of a multidimensional color signal corresponding to a color of the second color system directly from a table, are two typical ones. Are known.

[Problems to be Solved by the Invention]

However, the color correction apparatus configured by applying the color signal conversion method based on the above-described calculation method has an advantage that the correction condition can be easily changed by changing the coefficient, but the color reproducibility is improved. In order to do so, it is necessary to use a multi-order polynomial expression with a cross term as an expression used for calculation, so that a color correction device that can obtain correct color reproduction is realized by a color correction device with a simple configuration. It's difficult to do
The color correction device configured by applying the color signal conversion method based on the table method has an advantage that good color reproduction can be easily realized. However, when changing the correction conditions, the look-up table based on the memory configuration is used. Must be prepared, or the contents of the rewritable look-up table must be rewritten, but in any of the above cases, a large amount of memory is required, which is a problem. .

[Means for Solving the Problems]

According to the first aspect of the present invention, a color signal to be corrected is subjected to color correction by performing a matrix operation of a first-order polynomial.
When the data of the bit group of the upper digit in the color signal of the color signal to be corrected is supplied as the address signal, the corrected color signal data and the lower digit of the color signal data to be corrected described above. The achromatic condition between the input and output color signals is maintained as the interpolation calculation coefficient data in the equations of the first and second terms used for the calculation performed on the data of the bit group of A look-up table capable of outputting interpolation calculation coefficient data that minimizes the error due to the least squares method when changed, and the lower digit bit group data in the correction target color signal data and The interpolation calculation coefficient data is input to calculate and output the interpolation data, the corrected color signal data, and the interpolation data. The providing cascade manner provided a color correction apparatus comprising a second color correction circuit which is configured to include an adder for outputting the sum.

[Action]

By the first color correction circuit configured to perform the color correction by subjecting the color signal to be corrected to the matrix calculation of the first-order polynomial, the color correction according to the light source change at the time of image reading or the original condition, or the image When the data of the upper digit bit group in the color signal data output from the first color correction circuit is supplied as an address signal after performing the color correction of The achromatic color condition between the input and output color signals is maintained and the respective color signals are respectively used as the interpolation operation coefficient data in the expressions of the first and second terms used in the operation performed on the data of the digit bit group. Including a look-up table and a calculation unit capable of outputting the coefficient data for interpolation calculation that minimizes the error due to the least squares method when changing independently. When the second color correction circuit that has been formed performs color correction according to the characteristics of the output device, or when the data of the upper digit bit group of the color signal data to be corrected is supplied as an address signal. ,
The achromatic color condition between the input and output color signals is used as the interpolation calculation coefficient data in the expressions of the first and second terms used in the calculation performed on the corrected color signal data and the data of the bit group of the lower digit. And a look-up table and a calculation unit capable of outputting the interpolation calculation coefficient data that minimizes the error due to the least squares method when each color signal independently changes. After performing the color correction by assuming that the output device has the standard characteristic by the generated second color correction circuit, the characteristic of the difference between the actual characteristic of the output device and the standard characteristic is calculated by the matrix of the first-order polynomial. Is corrected by the first color correction circuit configured to perform the color correction and is supplied to the output device.

【Example】

Hereinafter, specific contents of the color correction apparatus of the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 are block diagrams showing an embodiment of a color correction apparatus of the present invention, FIG. 3 is a block diagram showing a configuration example of a first color correction circuit, and FIG. 4 is a second color correction circuit. 5 is a block diagram showing an example of the configuration of an arithmetic unit used in the second color correction circuit, FIG. 6 is a block diagram showing an example of the configuration of an arithmetic unit used in the second color correction circuit, and FIG. A diagram illustrating the stored contents of the up table,
FIG. 7 is a diagram showing a color space for explanation. 1 and 2 showing an embodiment of the color correction apparatus of the present invention, 1, 2 and 3 are input terminals of the color signal to be corrected, and 4,5 and 6 are output terminals of the color correction apparatus. , CCC1 is a first color correction circuit, and CCC2 is a second color correction circuit. The first color correction circuit CCC1 is configured to perform a color correction by subjecting a color signal to be corrected to a matrix operation of a first-order polynomial. An example of the structure is shown in FIG. In the first color correction circuit CCC1 shown in FIG. 3, 7, 8, 9
Are input terminals for the color signal to be corrected, and 10, 11, 12 are terminals of the first color correction circuit CCC1. In the first color correction circuit CCC1 shown in FIG. 3, 19 is a multiplication coefficient generation read-only memory for generating the multiplication coefficients rk, gk, bk and supplying them to the multipliers 20 to 22, and 23 to 25 are It is an adder. Multiplication coefficient generation The multiplication coefficients rk, gk, bk generated in the read-only memory 19 are as follows. rk: rk1, rk2, rk3 gk: gk1, gk2, gk3 bk: bk1, bk2, bk3 And the first color correction circuit CCC1 shown in FIG. 3 has a color signal R for its input terminals 7-9. , G, B are supplied, the color signals Rout, Gout, Bo output to the output terminals 10 to 12 are output.
ut looks like this: Rout = rk1 * R + gk1 * G + bk1 * B Gout = rk2 * R + gk2 * G + bk2 * B Bout = rk3 * R + gk3 * G + bk3 * B Multiplication coefficient generation The multiplication coefficients rk, gk, bk generated in the read-only memory 19 are as described above. rk: rk1, rk2, rk3 gk: gk1, gk2, gk3 bk: bk1, bk2, bk3, so even if there are 100 types of corrections to be made in the first color correction circuit CCC1, multiplication The coefficient generation read-only memory 19 has a large storage capacity.
900 bytes is enough. For example, when the white balance of the color signal to be corrected is changed by the color correction in the first color correction circuit CCC1 shown in FIG. 3, the multiplication coefficients rk1, gk2,
It is only necessary to change bk3, and in the case of changing the saturation of red for the correction target color signal, for example, the multiplication coefficient rk1 described above may be increased, and the multiplication coefficients rk2 and rk2 may be negative. , For example, to make red in the magenta direction, the multiplication coefficient rk1 described above is increased, and the multiplication coefficient rk2 is set to zero or negative,
Make rk3 positive. Next, when the data of the upper digit bit group in the color signal data to be corrected is supplied as the address signal, the second color correction circuit CCC2 corrects the corrected color signal data and the lower digit bit. The achromatic condition between the input and output color signals is maintained as the interpolation calculation coefficient data in the expressions of the first and second terms used in the calculation performed on the group data, and each color signal changes independently. FIG. 4 is a block diagram of a configuration including a lookup table and a calculation unit capable of outputting the coefficient data for interpolation calculation that minimizes the error due to the least squares method when It is shown in. In the second color correction circuit CCC2 shown in FIG. 4, 13, 14,
Reference numeral 15 is an input terminal for the color signal to be corrected, and 16, 17, 18 are output terminals of the second color correction circuit CCC2. 26 is a look-up table, 27 is a calculation unit, 28 to 30
Are adders, and 16 to 18 are output terminals of three-dimensional color signals (color signal data) corresponding to the colors of the second color system. In FIG. 4, the first color signal processing target
Input terminal as a three-dimensional color signal corresponding to the color of the color system of
It is said that the color signal data supplied to 13 to 15 are red signal data R, green signal data G, and blue signal data B, and 3 corresponding to the color of the second color system. The color signal data output to the output terminals 16 to 18 as three-dimensional color signals (color signal data) are also considered to be the red signal data Rout, the green signal data Gout, and the blue signal data Bout. In FIG. 4, red signal data R and green signal data supplied to the input terminals 13 to 15 as three-dimensional color signal data corresponding to the color of the first color system to be subjected to color signal processing. The G and blue signal data B are n (n = 8 in the following description) bit color signal data, and are also supplied to the look-up table 26 as address signals. 3 corresponding to the color of the first color system input to the arithmetic unit 27 and the upper X bits in the data of the three-dimensional color signal corresponding to the color of the color system of
The lower Z bits in the dimensional color signal data are each 4 bits (X = Z = 4). In the look-up table 26, the four higher ranks in the three-dimensional color signal data (red signal data R, green signal data G, and blue signal data B) corresponding to the colors of the first color system are respectively included. Color obtained by converting the three-dimensional color signal corresponding to the color of the first color system extracted corresponding to the bits rx, gx, bx into the three-dimensional color signal corresponding to the color of the second color system Signal data Rx, Gx, Bx {8-bit main data in FIG. 6}
And the calculation coefficient data kr, kg, kb to be used in the calculation of the color signal processing performed in the calculation unit 27 (each (8 × 3) -bit calculation coefficient data kr, kg, kb in FIG. 6). }
And are remembered. Then, the upper 4 bits of data rx, in each of the three-dimensional color signal data R, G, B corresponding to the color of the first color system subjected to the color signal processing supplied to the input terminals 13 to 15, rx,
gx and bx are lookup tables 2 as address signals
When supplied to 6, the color signal converted into a three-dimensional color signal corresponding to the color of the second color system stored at the address specified by the address signal in the look-up table 26. Data Rx, Gx, Bx and the calculation coefficient data kr, kg, kb to be used in the calculation of the color signal processing are read. The color signal data Rx, Gx, Bx converted into the three-dimensional color signal corresponding to the color of the second color system read from the look-up table 26 are added via the transmission lines 34 to 36. 28-30
Data kr, kg, kb supplied to the arithmetic unit 27 via the transmission lines 37 to 39, and the arithmetic coefficient data kr, kg, kb to be used in the arithmetic operation of the color signal processing read from the look-up table 26.
Is supplied to. In the arithmetic unit 27, the three-dimensional color signal data R, G, B data corresponding to the color of the first color system, which is the target of color signal processing supplied to the input terminals 13 to 15, are respectively included. Since the low-order 4 bits of data rz, gz, bz are supplied via the transmission lines 31 to 33, the operation coefficients supplied from the look-up table 26 via the transmission lines 37 to 39 as described above. Data kr, kg, kb and the lower 4 bits of the three-dimensional color signal data R, G, B data corresponding to the color of the first color system to be subjected to the color signal processing described above. Data rz, gz, bz of the predetermined operation, that is, Interpolation data Rz, G is calculated by performing the calculation as in the above equation (1).
z, Bz is generated and is supplied to the adders 28-30 described above via the transmission lines 40-42. In FIG. 4, the interpolation coefficients kr1, kr2, kr3 are collectively represented by the interpolation coefficient kr, and the interpolation coefficients kg1, kg2, kg3 are collectively represented by the interpolation coefficient kg, and similarly, the interpolation coefficients kb1, kb2, kb3.
Are collectively represented by the interpolation coefficient kb, and the interpolation coefficient may be kr, kg, kb in the description corresponding to the above. FIG. 5 is a block diagram of an example of the configuration of the arithmetic unit 27 that performs the arithmetic operation represented by the equation (1). In FIG. 5, 43 to 45 are multipliers and 46 to 48 are parallel series. The conversion circuits and 49 to 51 are adders. In the adders 28 to 30, the color signal data Rx, Gx, Bx converted into the three-dimensional color signals corresponding to the colors of the second color system read from the look-up table 26, and the calculation unit 27. Add the interpolation data Rz, Gz, Bz output from Rout = Rx + Rz, Gout = Gx + Gz, Bout = Rx + Bz and output the output signal data Rout, Gout, Bout processed by the color signal to the output terminals 16 to 18. . In the second color correction circuit shown in FIG. 4, the lookup table 26 stores the upper 4 bits in the data R, G, B of the three-dimensional color signal corresponding to the color of the first color system. 3 corresponding to the color of the first color system extracted correspondingly
Color signal data Rx, Gx, Bx obtained by converting three-dimensional color signal data R, G, B into a three-dimensional color signal corresponding to the color of the second color system
And calculation coefficient data kr {kr1, kr2, kr to be used in the calculation of the color signal processing performed in the calculation unit 7.
3}, kg {kg1, kg2, kg3}, kb {kb1, kb2, kb3} are stored, but the above-mentioned calculation coefficient data kr {kr1, kr2, kr
3}, kg {kg1, kg2, kg3}, kb {kb1, kb2, kb3} are used to interpolate color signal data using the interpolation data Rz, Gz, Bz obtained by the calculation result performed by the calculation unit 27. As a result, in order to obtain an image in which the white balance is perfect and the color jump is minimal, it is possible to easily and easily obtain the image by the above-mentioned arithmetic operation for the color signal processing operation. Coefficient data kr {kr1, kr2, kr3}, kg {kg
1, kg2, kg3}, kb {kb1, kb2, kb3}, that is, the primary 2 performed on the detailed signal portion of each color signal in the three-dimensional color signal corresponding to the color of the first color system. The achromatic color data obtained as a result of the calculation of the calculation coefficients kr, kg, kb in the above equations when the respective color signals change by the same value is the color of the second color system read from the storage device. Is provided on the achromatic color axis in the data of the three-dimensional color signal corresponding to, and it is determined to give an interpolation coefficient that minimizes the error by the least square method when each color signal changes independently. Of. The above points will be specifically described in detail. FIG. 7 is an explanatory diagram of a three-axis color space used to display a three-dimensional color (color signal) of an arbitrary color system, and each figure shows the three axes of the color space.
It is said to be the color space of the RGB color system with R, G, and B. In FIG. 7, 0 is the origin of the three axes R, G, B of the color space, and the origin 0 and the points equidistant from the origin 0 are ΔR, ΔG,
A space surrounded by eight points of ΔB, ΔC, ΔY, ΔM, and ΔW forms a cubic color space. When the cube color space shown in FIG. 7 is divided into N equal parts for each edge, it is shown as being composed of N ³ small cube color spaces. ^The cube color space, which is configured as an aggregate of ^three small cube color spaces, has three-dimensional color signal data R, G, and B corresponding to the colors of the RGB color system, where N = This indicates the color space in the case of data of n bits each represented by the relationship of 2 ⁿ . Therefore, if the data of the three-dimensional color signal according to the RGB color system is 8 bits (n = 8), the above-mentioned 7th
The color space of the cube surrounded by the eight points in the figure is composed of 256 ³ small cubes obtained by equally dividing each of its edges by 2 ⁸ (= 256). It will be represented as being in the state of being. By the way, when the data of the three-dimensional color signal according to the RGB color system is each 8 bits (n = 8) as described above, it is described above by the upper 4 bits (X = 4) of the data of each color signal. The small cube formed in the cubic color space surrounded by the eight points in Fig. 7 was obtained by equally dividing 2 ⁴ (= 16) for each edge of it. ³ (= 4096) small cubes, which means that the small cube formed by the lower 4 bits (Z = 4) in the data of each color signal is: Each of the small cubes formed by the upper 4 bits of the data of each color signal described above is divided into 2 ⁴ (= 16) equal parts for each edge of the small cube. ³ (= 4096 It is as well known that are made as the condition being constituted by a number of small cubes. By the way, as described above, each of the n supplied to the input terminals 13 to 15 in FIG. 4 as three-dimensional color signal data corresponding to the color of the first color system to be subjected to color signal processing. Out of the red signal data R, the green signal data G, and the blue signal data B of the bits, the upper X bits (4 bits in the above example) of each color signal data are addressed to the look-up table 26. By being supplied as a signal, the main data stored in advance in the look-up table 26 by the address signal, that is, the data of the three-dimensional color signal corresponding to the color of the first color system (red signal The three-dimensional color signal corresponding to the color of the first color system extracted corresponding to the upper X bits in each of the data R, the green signal data G, and the blue signal data B} is converted into the second color system. 3 corresponding to the color of Data Rx color signals converted to the original color signals, Gx, Bx {main data of each 8 bits in FIG. 6}
And calculation coefficient data kr, kg, kb to be used in the calculation of the color signal processing performed in the calculation unit 27 {calculation coefficient k shown as each (8 × 3) bit in FIG. 6).
r, kg, kb} are read from the look-up table 26 and correspond to the colors of the first color system to be subjected to color signal processing at the input terminals 13 to 15 in FIG. Of the n-bit red signal data R, the green signal data G, and the blue signal data B supplied as three-dimensional color signal data, the lower Z bits of each of the color signal data (the above-mentioned example 4 bits) rz, gz, bz are supplied to the arithmetic unit 27, and the arithmetic coefficient data described above is calculated in the arithmetic unit 27.
By performing the operation as shown in the above-mentioned equation (1) with kr, kg, kb, the data rz, gz, bz of the lower Z bits in the data of each color signal are used. As described above, the interpolation data Rz, Gz, Bz are obtained. Then, the main data stored in advance in the look-up table 26, that is, the upper X in the data of the three-dimensional color signal corresponding to the color of the first color system, respectively.
Color signal data Rx obtained by converting the three-dimensional color signal corresponding to the color of the first color system extracted corresponding to the bit into the three-dimensional color signal corresponding to the color of the second color system, For Gx and Bx {8-bit main data in Fig. 6}, select an appropriate means from the actual measurement and various other means that have been conventionally used when implementing the direct mapping table method. The data Rx, Gx, Bx of the color signal of the second color system obtained by the above are used. Now, assuming that the upper X bits in the data of the three-dimensional color signal corresponding to the color of the first color system are the upper 4 bits of the color signal data of 8 bits respectively, The color signal data of the second color system stored in the look-up table 26 is surrounded by the eight points in FIG. 7 described above by the upper 4 bits of the data of each color signal. Each edge of a cube formed in a cube-shaped color space
2 ⁴ (= 16) 16 ³ (= 409)
6) Each piece of data in the second color system is represented by eight vertex positions for each of the small cubes. Therefore, the data of each color signal of the second color system read from the look-up table 26 is determined in correspondence with the upper 4 bits of each color signal data of 8 bits to be output from the color signal processing device. The coarse one, that is,
In the cube-shaped color space surrounded by the eight points in FIG. 7, each edge of the cube is 2 ⁸ (= 25
6) It is not selected from the data of each vertex position in 256 ³ small cubes obtained in the equally divided state, but for each edge of the cube surrounded by 8 points in Fig. 7, respectively. It is selected from the data of each vertex position in 16 ³ (= 4096) small cubes obtained by equally dividing 2 ⁴ (= 16). That is, the main data obtained from the look-up table 26 is obtained by deleting the data of the detailed signal portion determined in correspondence with the lower 4 bits (Z = 4) in the data of each 8-bit color signal. It is supposed to be in the state of being. {It should be noted that the data of the detailed signal portion which is determined in correspondence with the lower 4 bits (Z = 4) in the data of each 8-bit color signal which is omitted in the main data as described above is If it is assumed that they are located in the above-mentioned color space, a small cube and individual ones that are determined in correspondence with the upper 4 bits in the data of each 8-bit color signal described above, and for each individual edge of that cube,
2 ⁴ (= 16) 16 ³ (= 409)
6) It is represented as being located at each vertex position in a smaller cube. Therefore, the data missing from the main data obtained from the lookup table 26, that is, each of the above 8
Lower 4 bits (Z =
The data of the detailed signal portion determined corresponding to 4) indicates the detailed signal portion of each color signal in the three-dimensional color signal corresponding to the input color of the first color system. It is interpolated by the interpolation data generated from the data of the bit (when Z = 4). Since the actual color space is often distorted, it is not easy to perform correct interpolation. Therefore, paying attention to the fact that white balance occupies an important element in human vision, the result of interpolation shows that at least only white balance is in a correct state and gradation skipping does not occur. In addition, it is possible to obtain interpolation data that minimizes color skipping in the state where the white balance is properly maintained, that is, the first
In the case where each color signal changes by the same value, the calculation coefficient in the expressions of the first and second terms performed on the detailed signal portion of each color signal in the three-dimensional color signal corresponding to the color of the color system The achromatic color data obtained as a result of calculation is on the achromatic color axis in the data of the three-dimensional color signal corresponding to the color of the second color system read from the look-up table 26, and each color is The interpolation data Rz, Gz, and Bz are set so that the error due to the least squares method when the signal changes independently can be minimized. First, the achromatic color data obtained as a result of calculation when each color signal changes by the same value as described above corresponds to the color of the second color system read from the look-up table 26. The condition for being on the achromatic color axis in the data of the three-dimensional color signal and for preventing gradation skipping is: This is represented by the above equation (2). Calculation coefficients kr1, kr2, kr that satisfy the above equation (2)
As already described using 3, kg1, kg2, kg3, kb1, kb2, kb3 (1)
Expression, ie According to the above, for example, when the calculation is performed for the case where each color signal changes by the same value, the achromatic color data obtained as a result of the calculation is inevitably present on the achromatic color axis. Is continuously moved. The achromatic color axis described above is represented by, for example, a straight line connecting the origin 0 and the vertex 0W in FIG. However, in order to satisfy the above formula (2), the calculation coefficient
Even if kr1, kr2, kr3, kg1, kg2, kg3, kb1, kb2, kb3 are set, a large color skip may occur for each color depending on the distortion state of the color space. Therefore, in FIG. 7, six conditions excluding 0 and ΔW, that is, conditions for minimizing the error δr, δg, δb of the distance between the origin 0 and ΔR, ΔG, ΔB, ΔM, ΔC are set. The calculation coefficients kr1, kr2, kr3, kg1, kg2, kg3, kb1, kb2, kb3 calculated by the least squares method as shown in the following formulas (3) to (5) are calculated as shown in FIG. As a result, it is stored in the look-up table 26 as a pair with the above-mentioned main data. ^{δr = (kr1-Rr) 2} + (kr2-Rg) 2 + (kr3-Rb) 2 + (kr1 + kr2-Ry) 2 + (kr1 + kr3-Rm) 2 + (kr2 + kr3-Rc) 2 ... (3) δg = ( ^{kg1-Gr) 2 + (kg2} -Gg) 2 + (kg3-Gb) 2 + (kg1 + kg2-Gy) 2 + (kg1 + kg3-Gm) 2 + (kg2 + kg3-Gc) 2 ... (4) δb = (kb1-Br ) ² + (kb2-Bg) ² + (kb3-Bb) ² + (kb1 + kb2-By) ² + (kb1 + kb3-Bm) ² + (kb2 + kb3-Bc) ² (5) Each obtained as described above Calculation coefficient data kr1,
Look up kr2, kr3, kg1, kg2, kg3, kb1, kb2, kb3
The data stored in the table 26 and lacking in the main data obtained from the look-up table 26 are color signals in the three-dimensional color signal corresponding to the color of the input first color system. Lower 4 bits (when Z = 4) of data r, g, b showing the detailed signal portion of the above, and data kr1, kr2, kr3, kg1, kg2, kg3, kb1, kb2 of each operation coefficient described above. , kb3
And the interpolation data Rz, Gz, obtained by calculation by the calculation unit 27 having a simple configuration as illustrated in FIG.
By generating Bz and feeding it to the adders 28-30 via transmission lines 40-42 as shown in FIG.
At the output terminals 16 to 18, the three-dimensional color signal data Rout, Gout, Bout of the second color system in which the white balance is good, there is no gradation jump, and the color jump is minimum can be obtained. In the above description, the RG
Although the B color system has been described, it goes without saying that color conversion between any color systems can be performed, and the above description applies when the arithmetic expression is the first and third terms. However, any arithmetic expression may be used as long as it is an arithmetic expression having two or more first-order terms. For example, if an arithmetic expression of a multi-order polynomial is used, the error is reduced by that much. Of course. Referring to FIG. 1 showing an embodiment of a color correction apparatus of the present invention, a color correction target color signal is subjected to a matrix operation of a first-order polynomial to perform color correction.
The color signal corrected by the color correction circuit CCC1 according to the change of the light source at the time of image reading or the original condition is corrected by the second color correction circuit CCC2, that is, the first color correction circuit CCC1. When the data of the high-order bit group in the output color signal data is supplied as an address signal, the corrected color signal data,
As the interpolation calculation coefficient data in the equations of the first and second terms used for the calculation performed on the data of the bit group of the lower digit, the achromatic condition between the input and output color signals is maintained, and each color signal is A second color correction circuit CC configured to include a look-up table and a calculation unit capable of outputting interpolation calculation coefficient data that minimizes the error due to the least squares method when they change independently.
In FIG. 2 in which color correction is performed according to the characteristics of the output device by C2, and another embodiment of the color correction apparatus of the present invention is shown, first, the second color correction circuit is used.
CCC2, that is, when the data of the upper digit bit group in the data of the color signal to be corrected is supplied as the address signal, it is performed for the corrected color signal data and the lower digit bit group data. The achromatic condition between input and output color signals is maintained as the coefficient data for interpolation calculation in the first and second terms used in the calculation, and the error due to the least squares method when each color signal changes independently. With a second color correction circuit CCC2 configured to include a look-up table and a calculation unit capable of outputting the coefficient data for interpolation calculation that minimizes
After performing the color correction assuming that the output device has the standard characteristic, perform the color correction by subjecting the characteristic of the difference between the actual characteristic of the output device and the standard characteristic to the matrix calculation of the first-order polynomial. The color is corrected by the configured first color correction circuit CCC1 and supplied to the output device. As described above, according to the color correction apparatus of the present invention, the first condition is set according to the state of the signal supplied to the output device and the characteristics of the output device.
By using any of the color correction apparatuses having the configurations shown in FIGS. 2 and 2, it is possible to easily change and set the correction condition while maintaining the fidelity of color reproduction.

【The invention's effect】

As is apparent from the above description in detail, the color correction apparatus of the present invention is configured to perform the color correction by applying the matrix calculation of the first-order polynomial to the color signal to be corrected. When the circuit and the data of the upper digit bit group in the color signal data to be corrected are supplied as the address signal, the corrected color signal data and the lower digit bit group in the correction target color signal data As the interpolation calculation coefficient data in the equations of the first and second terms used in the calculation performed on the data of 1, the achromatic condition between the input and output color signals is maintained, and each color signal changes independently. And a lookup table capable of outputting coefficient data for interpolation calculation that minimizes the error due to the least squares method, and the correction target color signal data described above. The data of the lower-order bit group and the above-described interpolation calculation coefficient data are input to calculate and output interpolation data, and the corrected color signal data and the interpolation data are added. According to the present invention, the state of the signal supplied to the output device, the state of the output device, and the second color correction circuit configured to include an adder for outputting are provided in series. By using any one of the color correction devices of the configurations shown in FIGS. 1 and 2 according to the characteristics, it is possible to easily set the modification conditions while maintaining the fidelity of color reproduction. The above-mentioned conventional problems can be well solved by the present invention.

[Brief description of drawings]

1 and 2 are block diagrams showing an embodiment of a color correction apparatus of the present invention, FIG. 3 is a block diagram showing a configuration example of a first color correction circuit, and FIG. 4 is a second color correction circuit. 5 is a block diagram showing an example of the configuration of an arithmetic unit used in the second color correction circuit, FIG. 6 is a block diagram showing an example of the configuration of an arithmetic unit used in the second color correction circuit, and FIG. FIG. 7 is a diagram showing an example of stored contents of the up table, and FIG. 7 is a diagram showing a color space for explanation. 1-3 Input terminals for color signals to be corrected, 4
~ 6 ... Output terminal of color correction device, CCC1 ... first color correction circuit, CCC2 ... is second color correction circuit, 7-9, 13-15 ...
Input terminal, 10 to 12, 16 to 18 ... Output terminal, 19 ... Multiplication coefficient generation read-only memory that generates multiplication coefficients rk, gk, bk and supplies them to the multipliers 20 to 22, 23 to 25 ... Addition Vessel, 26 ……
Look-up table, 27 …… Calculator, 28-30 ……
Adder, 37-39 …… Transmission line, 40-42 …… Transmission line, 43-45
…… Multiplier, 46 to 48 …… Serial parallel conversion circuit, 49 to 51 …… Adder,

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Claims (1)

(57) [Claims] 1. A first color correction circuit configured to perform a color correction by subjecting a color signal to be corrected to a matrix calculation of a first-order polynomial, and a high-order bit in data of the color signal to be corrected. When the group data is supplied as an address signal, the primary and secondary terms used for the operation performed on the corrected color signal data and the data of the lower digit bit group in the correction target color signal data. As the interpolation calculation coefficient data in the above equation, the achromatic condition between the input and output color signals is maintained, and the error by the least square method when each color signal changes independently is minimized. Look-up table capable of outputting calculation coefficient data, data of bit group of lower digit in correction target color signal data, and interpolation calculation coefficient A second calculation unit that receives the data and calculates and outputs interpolation data, and an adder that adds and outputs the corrected color signal data and the interpolation data. Color correction device in which a color correction circuit is provided in series