Patent ID: 7679781

Claim:
A color image processing apparatus that generates output gray level values (c 4 , m 4 , y 4 , k 4 ) of four colors including black from input gray level values (c 1 , m 1 , y 1 ) of three colors of cyan, magenta and yellow, the color image processing apparatus comprising: a minimum value selection unit that selects a minimum value k 0 of the input gray level values (c 1 , m 1 , y 1 ); a first calculation unit that calculates a generation amount k 3 of black based on the minimum value k 0 ; a second calculation unit that calculates an under color removal amount u (k 0 ) which is a value relevant to the minimum value k 0 ; a third calculation unit that outputs a correction coefficient value f (k 0 ) which is a value relevant to the minimum value k 0 ; a subtraction unit that subtracts the under color removal amount u (k 0 ) from each of the input gray level values (c 1 , m 1 , y 1 ) to generate output (c 2 , m 2 , y 2 ); a multiplication unit that multiplies the output of the subtraction unit (c 2 , m 2 , y 2 ) by the correction coefficient value f (k 0 ) to obtain output (c 3 , m 3 , y 3 ); a significant bit selection unit that selects a significant bit of a multiplication result of the multiplication unit; and a gray level correction unit that makes a gray level correction to the generation amount k 3 of black and the output of the multiplication unit (c 3 , m 3 , y 3 ) to obtain the output gray level values (c 4 , m 4 , y 4 , k 4 ).