JP2739345B2 - Color correction method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color correction method for improving color reproduction characteristics of a color printer or the like.

[Summary of the Invention] The present invention reduces the capacity of a table memory when performing color correction processing of a color printer or the like by a table memory method,
In addition, in order to perform high-precision color correction processing, by storing data of a color correction result of a combination of smaller high-order n bits corresponding to the number of color reproduction gradations and using an interpolation method according to a certain algorithm, Achieve the goal.

[Conventional technology]

As a color correction method of a color printer, a color masking process is known. For example, the first order masking operation is And the secondary masking operation is Is represented by The input data (C, M, Y) is corrected to (C ', M', Y ') by a masking operation. As a method of realizing color correction, the calculation result of the expression (1) or (2) or the output data directly associated with the input data is used for all gradations of the input data (C, M, Y). There is a method of storing the combinations in the table memory. However, this method requires a large amount of memory of 2 ²⁴ × 3 bytes if the input data of each of C, M, and Y is 8 bits.
The cost of the equipment will increase significantly. As a method for improving this point, Japanese Patent Publication No. 52-16403 discloses a method of reducing the capacity of a table memory and interpolating a combination of input data that does not have a table memory.

[Problems to be solved by the invention]

In the interpolation method, for example, when calculating output data C 'for input data (C, M, Y), the interpolation calculation is performed by paying attention only to the value of C, so that the accuracy of the interpolation calculation is very poor. The table corresponding to the input data (C, M, Y) is (Cr, M
r, Yr), and the table one level higher than the input data is (C _{r + 1} , M _{r + 1} , Y _{r + 1} ), the interpolation calculation is performed for C, Cr and Cr _{+ 1.}
Seeking from the relationship. Therefore, the input data M and Y are Mr.
In the range of ≦ M ≦ Mr _{+ 1} , Yr ≦ Y ≦ Yr _{+ 1} , all values are the same. The same applies when M 'and Y' are obtained.

Further, a multiplier is required to calculate the ratio of C to Cr _{+ 1} , which makes the device expensive.

[Means for solving the problem]

The present invention has been made to solve the above problems,
Only the correction result by the combination of the upper n bits smaller than the number of bits of the input data of three colors is stored in the table memory, and several combinations of the input data not stored in the table memory are stored in the table memory according to an algorithm. To generate interpolation data by calculating the several types of data, that is,
The color separation input data C, M, and Y of the color image are provided as a table memory with color-corrected output data C ', M', and Y 'of a combination of upper n bits (m> n) for each m hits of each color. , C, M, and Y, two types of data are read from the table memory according to the combination of the lower (mn) bits of the input data of each color, and an intermediate value between the two data is calculated.
The same procedure is repeated a maximum of 2 ^(mn) -1 times to generate interpolation data.

[Action]

According to the present invention, even with a combination of input data that does not exist in the table memory, only a table memory of a combination of input data of the upper n bits of each color is generated by calculating several types of data read from the table memory to generate interpolation data. At least, the color correction process can be performed with substantially the same accuracy as in the case where the table memory has all the combinations of m bits of each color input data.

〔Example〕

FIG. 1 is a flow chart for explaining the present invention. In this embodiment, when m = 8, n = 6, that is, in the table memory, the color correction result of the combination in which the lower 2 bits are 00 among the combinations of the input data of 8 bits (0 to 255) for each of C, M, and Y is stored. The case in which it is performed will be described. FIG. 2 is a spatial coordinate diagram of a combination of input data stored in the table memory.

When 8 bits (0 to 255) of input data are divided into upper 6 bits (0 to 63) and lower 2 bits (0 to 3), the input data becomes C = 4C ₁ + i (C ₁ : 0 to 63, i: _{0~3) M = 4M 1 + j} (M 1: 0~63, j: 0~3) Y = 4Y 1 + k (Y 1: 0~63, k: can be placed and 0-3). Where C ₁ , M ₁ , and Y ₁ are the upper 6 bits,
i, j, k are the values of the lower two bits. If i = j = k = 0, the data stored in the table memory may be read. For other combinations of i, j, and k, data is generated by the following interpolation method.

FIG. 3 shows (C, M, Y) = (80, 4) from the spatial coordinates of FIG.
(0,12) and (C, M, Y) = (84,44,16) are extracted from the tables and illustrate the following specific examples. i, j, k
Is 2, C = 4 (C ₁ +1) and M = 4 (M ₁ +
1) Select a table in which Y = 4 (Y ₁ +1), a table in which i = j = k = 0, and a table in which i = j = k = 0.
An intermediate value between the two table data is calculated. For example, if (C, M, Y) = (82,42,16), the table (80,40,1)
6) and the tables (84, 44, 16) are selected, data is read from the two tables, and an intermediate value of the read data is calculated. FIG. 4 shows a selection table when i, j, k is 2. Next, when i, j, k is 1, the calculation result when i, j, k is 2 is obtained by the above method when i, j, k is 2, and the calculation result and i = An intermediate value of the table data when j = k = 0 is calculated. When i, j, k is 3, C = 4 (C ₁ +1), M = 4 (M ₁ +1), and Y = 4, respectively.
An intermediate value between the table value (Y ₁ +1) and the calculation result when i, j, k is 2 is calculated.

For example, when the input data is (C, M, Y) = (83, 42, 13), it can be set to (4 × 20 + 3, 4 × 10 + 2, 4 × 3 + 1). First, when the processing in the case where i, j, k is 1 or 3 is performed by the above method, the value of (4 × 20 + 2, 4 × 10 + 2, 4 × 3) − and (4
It is sufficient to calculate an intermediate value between the values of (21, 4 × 10 + 2, 4 × 3 + 2) −. Next, the values for performing the processing in the case where i, j, k is 2 are as shown in the table (80, 40, 12) and the table (84, 44, 12).
Can be obtained from the table data of Table (84, 40, 12) and Table (84, 44, 16). Further, the color correction data of the input data (83, 42, 13) can be obtained by calculating an intermediate value between the two.

If the interpolation method of the present invention is used, the lower 3 bits of the 8-bit input data for each of C, M, and Y are set to 0 using the same algorithm.
The color correction processing is performed with almost the same accuracy as when all the color correction results of the combination of 8 bits for each color are stored in the table memory simply by storing the color correction result of the combination of 00 and the combination of the lower 4 bits of 0000 in the table memory. It can be performed.

〔The invention's effect〕

The present invention uses the interpolation method as described above,
Significantly reduced table memory capacity, and each color m
Each correction process can be performed with approximately the same accuracy as when a table memory is provided for all combinations of bit input data.

Furthermore, when the present invention is implemented in hardware, the present invention can be configured without using a multiplier, thereby preventing an increase in the cost of the apparatus.

[Brief description of the drawings]

FIG. 1 is a flowchart, FIG. 2 is a spatial coordinate diagram, FIG.
FIG. 4 is a spatial coordinate diagram of a specific example, and FIG. 4 is an explanatory diagram showing a selection table.

Claims (3)

(57) [Claims] 1. An m bit of each color when the value of lower (mn) bits is 0 for higher n (m> n) bits for each m bits of color separation input data of three colors of a color image. (2 ⁿ ) ^three color correction result data corresponding to the combination corresponding to each value of the input data are represented on spatial coordinates consisting of three axes corresponding to each color of the input data, with the origin being (0,0,0). Is provided as a table memory, and when the input data includes a value whose lower (mn) bit is not 0 for any of the coordinate values, for each coordinate value of the input data in the table memory, The color correction result data of the table memory at each coordinate point determined by a combination of a value when the value of the lower (mn) bit is 0 and a value obtained by incrementing the value of the upper n bits with respect to the value is read out. Intermediate value of color correction result data of each coordinate point , And using the intermediate value to generate interpolation data. 2. The color separation input data C, M, and Y of a color image. For each m bits of each color, each color when the value of the lower (mn) bits is 0 for the upper n (m> n) bits. (2 ⁿ ) ³ corresponding to the combination (C, M, Y) corresponding to each value of m bits
The color correction result data (C ′, M ′, Y ′) is set to the origin (0,
(0,0) is provided as a table memory on the spatial coordinates of the C axis, M axis, and Y axis, and the input data (C, M, Y) is C, M, Y.
When the value of the lower (mn) bit includes a value other than 0 for any of M and Y, in the table memory,
For each coordinate value of C, M, and Y, the value of each coordinate point determined by a combination of a value when the value of the lower (mn) bit is 0 and a value obtained by incrementing the value of the upper n bits with respect to the value Reading the color correction result data from the table memory, calculating an intermediate value of the color correction result data (C ′, M ′, Y ′) at each coordinate point, and generating interpolation data using the intermediate value. Color correction method. 3. Computing an intermediate value between the intermediate value and the color correction result data of each of the coordinate points or an intermediate value between the intermediate values at a maximum of 2 ^(mn) -1 times at maximum, thereby interpolating the interpolation data. The color correction method according to claim 1, wherein the color correction is generated.