Patent ID: 8736865

Claim:
An image processing method, executed by an image processing apparatus, for performing a quantization process of multivalued image data into a lower level N-value (N is an integer equal to or more than 2) by an error diffusion process, the image processing method comprising: inputting multivalued image data of an image; an obtaining step of adding an error from a peripheral pixel to the multivalued image data of a target pixel of an image to obtain a correction value; a setting step of, from a threshold value matrix configured such that different values are arrayed in a row array and in a column array, selecting one value according to a pixel position of the target pixel in the image to set a threshold value for comparing with the correction value, the row consisting of pixels corresponding to values in the row array and the column consisting of pixels corresponding to values in the column array intersecting; a quantization step of, according to a result of comparing the threshold value set in the setting step with the correction value obtained in the obtaining step, outputting N-value data; a diffusion step of diffusing an error between the correction value and the N-value data, the error occurring in association with the quantization step, in a peripheral pixel position where the quantization step has not been performed; and outputting a value indicating printing or non-printing of the target pixel, wherein in the threshold value matrix, average values in respective rows or average values in respective columns are almost a same value.