Image processing apparatus, and color correction method and lookup table

• US 20040126010A1
• Filed: 12/17/2003
• Published: 07/01/2004
• Est. Priority Date: 12/18/2002
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Yamazoe, Manabu
• Granted Patent: US 7,599,552 B2
• Time in Patent Office: Days
• US Class Current: 382/162
• CPC Class Codes: H04N 1/6005 with luminance or chrominance signals, e.g. LC1C2, HSL or YUV
• CPC Class Codes: H04N 1/646 Transmitting or storing colour television type signals, e.g. PAL, Lab; Their conversion into additive or subtractive colour signals or vice versa therefor H04N1/642, H04N1/644 take precedence

Abstract

In a color conversion method of inputting at least two color difference values and obtaining a corresponding saturation value, a main lookup table which stores the saturation value for the color difference values, and a sub-lookup table for obtaining an address for accessing the main lookup table are created. The address of the main lookup table is determined on the basis of the sub-lookup table and the difference between the two color difference values, in correspondence with two arbitrary color difference values. A saturation value corresponding to the two color difference values is obtained from the determined address of the main lookup table.

Claims

1. A color conversion method of inputting at least two color difference values and obtaining a corresponding saturation value, comprising steps of:

creating a main lookup table which stores saturation value for the color difference values, and a sub-lookup table for obtaining an address for accessing the main lookup table;

determining the address of the main lookup table in correspondence with two color difference values on the basis of the sub-lookup table and a difference between the two color difference values; and

obtaining a saturation value corresponding to the two color difference values from the address determined in said determining step.

2. The method according to claim 1, wherein the main lookup table has a smaller number of entries than the number of all possible combinations of the two color difference values by utilizing symmetry of the saturation value for the color difference values.

3. The method according to claim 1, wherein the sub-lookup table stores an address of an entry in which the two color difference values are the same.

4. A lookup table for obtaining an output value defined for an input value, comprising:

a main lookup table adapted to, when a definition of an output value has or is regarded to have symmetry for a plurality of input values, or when a combination of the plurality of input values is limited by a specific existence condition, store the output values for the plurality of input values in consideration of at least one of the symmetry and the specific existence condition; and

a sub-lookup table adapted to store an address of an entry in which the plurality of input values are the same,

wherein an address of said main lookup table is determined on the basis of said sub-lookup table and a difference between the two input values, in correspondence with two arbitrary input values.

5. The table according to claim 4, wherein the specific existence condition includes a color space.

6. The table according to claim 4, wherein the output value includes a saturation in a color space determined in advance.

7. An image processing apparatus for inputting image data and obtaining a corresponding saturation value, comprising:

calculation means for calculating a color difference value of each pixel of the input image data;

a main lookup table adapted to store saturation values for the color difference values;

a sub-lookup table adapted to obtain an address for accessing said main lookup table in correspondence with the color difference value;

determination means for determining the address of said main lookup table in correspondence with two color difference values of pixels calculated by said calculation means, on the basis of said sub-lookup table and a difference between the two color difference values; and

read means for accessing said main lookup table on the basis of the address determined by said determination means and reading out a corresponding saturation value.

8. The apparatus according to claim 7, wherein said main lookup table has a smaller number of entries than the number of all possible combinations of the two color difference values by utilizing symmetry of the saturation value for the color difference values.

9. The apparatus according to claim 7, wherein said sub-lookup table stores an address of an entry in which the two color difference values are the same.