When an input image is shifted by 640 pixels from a test pattern with reference to the position of a nozzle, the remainder is obtained by dividing 640 pixels by pixels of the dither matrix in an x direction. For example, when the size of the dither matrix in the x direction is 256 pixels, the dither matrix is shifted by 128 pixels in a direction reverse to the x direction. In this manner, the phase of the dither matrix at the time of the quantization during test pattern printing matches the phase of the dither matrix at the time of the quantization during input image printing. Consequently, unevenness of the dither matrix at a position N becomes the same in both of the test pattern and the input image. The HS correction to density unevenness caused by the unevenness of the dither matrix becomes suitable for the input image.