Image processing apparatus, and color correction method and lookup table

• US 7,599,552 B2
• Filed: 12/17/2003
• Issued: 10/06/2009
• Est. Priority Date: 12/18/2002
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Yamazoe, Manabu
• Primary Examiner(s): Strege; John B
• Application Number:
  US10/736,498
• Publication Number:
  US 20040126010A1
• Time in Patent Office: 2,120 Days
• Field of Search: 382162-167, 382/293, 345/589, 345/604, 358518-540
• US Class Current: 382/167
• 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. An address to be used in accessing 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 first and second color difference values and obtaining a corresponding saturation value, comprising steps of:

creating a main lookup table which stores saturation values for color difference values, and a sub-lookup table for obtaining a value corresponding to the first color difference value for accessing the main lookup table, wherein the first color difference value is equal to or less than the second color difference value;

accessing the sub-lookup table with the first color difference value to obtain the value corresponding to the first color difference value;

determining an address of the main lookup table in correspondence with the first and second color difference values on the basis of the value obtained in the accessing step and a difference between the first and second color difference values; and

obtaining a saturation value corresponding to the first and second color difference values by accessing the main lookup table with the address determined in the determining step,

wherein the main lookup table has a smaller number of entries than the number of all possible combinations of the first and second color difference values by utilizing symmetry of the saturation value for the first and second color difference values.

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

3. 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 a value corresponding to a first color difference value being equal or less than a second color difference value, for accessing the main lookup table in correspondence with the first color difference value;

determination means for accessing the sub-lookup table with the first color difference value to obtain the value corresponding to the first color difference value and for determining an address of the main lookup table in correspondence with the first and second color difference values of pixels calculated by the calculation means, on the basis of the value corresponding to the first color difference value obtained by the sub-lookup table and a difference between the first and second color difference values; and

read means for accessing the main lookup table with the address determined by the determination means and reading out a saturation value corresponding to the first and second color difference values,

wherein the main lookup table has a smaller number of entries than the number of all possible combinations of the first and second color difference values by utilizing symmetry of the saturation value for the first and second color difference values.

4. The apparatus according to claim 3, wherein the sub-lookup table stores the address of an entry in which the first and second color difference values are the same.