An image processing apparatus for subjecting input image data to a density conversion includes three dot isolation circuits which subject the pixels on each of a plurality of lines adjoining in the sub-scan direction to a density conversion in accordance with a different predetermined conversion characteristic (LUT) for each line. Though each dot separation circuit deals with a different number of lines of image data to undergo a density conversion, the predetermined conversion characteristics can be set in advance in such a manner that the density values of a plurality of pixels on adjoining line will be preserved if an overall view of the reproduced image is taken.