Patent ID: 8335018

Claim:
An image forming apparatus comprising: a storage unit configured to store a divisor matrix including at least two kinds of divisor values; and a changing unit configured to change M (M>N) gradation image data into N (N>3) gradation image data, wherein the changing unit is configured to divide a pixel value of a target pixel of the M gradation image data by a divisor value corresponding to a pixel position of the target pixel to change the M gradation image data into the N gradation image data, wherein the storage unit is configured to store a basic dither matrix including basic dither values that are variable for respective positions in the matrix, and wherein the changing unit is configured to subtract a basic dither value corresponding to the pixel position of the target pixel from the pixel value of the target pixel of the M gradation image data, and to divide the subtracted pixel value of the target pixel of the M gradation image data by a divisor value corresponding to the pixel position of the target pixel, to change the M gradation image data into the N gradation image data.