Patent ID: 7342684

Claim:
An image processing apparatus for quantizing multilevel color image data containing at least two kinds of color components, comprising: error addition means for adding a quantization error value distributed from a neighboring pixel for each color component to each of a plurality of color components contained in a target pixel; a threshold table which stores a quantization threshold for each of the color components in accordance with a combination of color component values of pixels; modulation amount determination means for determining a threshold modulation amount of each color in accordance with a combination of color component values of pixels including the target pixel; and quantization means for acquiring a threshold for each color component from said threshold table in accordance with a combination of color components of the target pixel, determining a threshold modulated by adding the modulation amount to the threshold for each color, and quantizing the target pixel in accordance with a relationship in magnitude between the modulated threshold and a value of each color component to which an error value is added by said error addition means.