An image processing apparatus, which performs an error diffusion on M-value image data with an error weight matrix into N-value image data, includes: a corrected-value calculating unit that calculates a corrected value by adding a first value and a second value to a pixel value corresponding to a processing-target color component of a pixel of interest, the first value being obtained by multiplying an error for each quantized pixel of the processing-target color component by the matrix, and the second value being obtained by multiplying an error for each quantized pixel of a different color component by the matrix; a quantizing unit that compares the corrected value with a quantization threshold, and outputs N-value image data; and an error diffusion unit that calculates an error at the pixel of interest by subtracting a quantization threshold from a value obtained by adding the first value to the pixel value.