Patent ID: 8279489

Claim:
An image processing apparatus for converting multi-level image data to binary image data using an error diffusion method, comprising: an update unit configured to add an error, diffused to a position of multi-level pixel data as a subject of binarization, to said pixel data, thereby update said pixel data; a determiner configured to determine whether current pixel data belongs to a highlight portion, a dark portion or an intermediate portion, by comparing a value of the current pixel data updated by said update unit with predetermined threshold values Ts and Th; a highlight portion processor configured to, when said determiner determines that said current pixel data belongs to said highlight portion, refer to already-binarized results in a range determined in accordance with the value of said current pixel data, and determine a value of binary pixel data corresponding to said current pixel data; a dark portion processor configured to, when said determiner determines that said current pixel data belongs to said dark portion, refer to the already-binarized results in the range determined in accordance with the value of said current pixel data, and determine the value of the binary pixel data corresponding to said current pixel data; an intermediate portion processor configured to, when said determiner determines that said current pixel data belongs to said intermediate portion, compare a threshold value T monotonously increasing in accordance with the value of said current pixel data with the value of said current pixel data, thereby determine the value of the binary pixel data corresponding to said current pixel data; and a diffuser configured to diffuse a difference between the value of said current pixel data and the value of the binary pixel data determined by said highlight portion processor, said dark portion processor or said intermediate portion processor, to unbinarized pixel positions in the neighborhood of the pixel position of said current pixel data.