1. An image processing apparatus, comprising: a unit generating a multi-value code image by assigning first dot pattern code information to each of growth center pixels, which are growth centers of screen processing, in an image subjected to the screen processing by use of a dither matrix, the first dot pattern code information representing a dot pattern and obtained by encoding the dot pattern existing in an image area where dots grow around the growth center pixels; a unit performing an affine transformation on the multi-value code image; a unit assigning second dot pattern code information, which represents the dot pattern, to each of the growth center pixels before the affine transformation in the multi-value code image after the affine transformation according to the first dot pattern code information of at least one growth center pixel after the affine transformation, the at least one growth center pixel neighboring close to the growth center pixel before the affine transformation; and a unit developing the dot pattern for the image area at each of the growth center pixels before the affine transformation according to the second dot pattern code information.