Patent ID: 8107772

Claim:
An image processing apparatus comprising: a tone converting section, in a computer processor, to convert a tone level of a target pixel in multi-level image data based on a threshold value of the tone level so that the number of tone levels is reduced; a resolution converting section, in a computer processor, to output a pixel block consisting of a predetermined number of pixels according to the tone level obtained in the tone converting section with respect to each target pixel, so as to generate image data with higher resolution than the multi-level image data; and an error diffusing section, in a computer processor, to diffuse an error between the tone levels before and after the tone conversion in the tone converting section to a surrounding pixel of the target pixel, based on a diffusion coefficient pattern; and wherein when the converted tone level of the target pixel is a first predetermined value or lower, the resolution converting section refers to an output sequence category of a black pixel used in a pixel block of a surrounding pixel above and on the left of the target pixel, selects an output sequence pattern of a black pixel belonging to an output sequence category in which a black pixel in a pixel block of the target pixel and a black pixel in a pixel block of the surrounding pixel are adjacent so as to concentrate a black pixel in a pixel block of the target pixel and a black pixel in a pixel block of the surrounding pixel, and outputs a pixel block corresponding to the selected output sequence pattern.