PURPOSE: An error diffusion halftone method is provided to judge whether one dot among plural colors is to be printed or not by comparing addition of total values generated by combining plural color gradation and accumulative error of plural colors by pixels with a threshold level. CONSTITUTION: Gradation levels of different colors of a CMY image formed by converting a printer RGB color image into a CMY space by a simple method are discriminated for specified pixels to be processed and each gradation of CMY is calculated. When C(cyan) and M(magenta) planes are of dependent type, the input sum of a range between zero to 510 of C and M gradation levels is generated. The input sum of the pixels to be processed is judged whether or not it is smaller than a 100% paint-out threshold, i.e., a full intensity threshold 255 or not, and when the gradation of the pixel is 255 or more, the dot is printed for the pixel. And the present total values are compared for C and M and it is judged whether C or M dot must be printed or not.
TONE DEPENDENT PLANE DEPENDENT ERROR DIFFUSION HALFTONING