An image processing apparatus includes a division-conversion unit and a composing unit. The division-conversion unit extracts data representing N pixels (N is an integer of two or greater) from image data, divides the extracted data into k (2≦k≦N) divided data elements such that at least one pixel is described in each of the k divided data elements, and converts each of the k divided data elements into a single piece of data by using a conversion table. The conversion table is provided in accordance with the number of pixels described in each of the k divided data elements and is used for converting the corresponding k divided data element into the single piece of data by performing conversion processing. The composing unit combines the single pieces of data so as to generate one-pixel output data which is reduced from the extracted N-pixel data with a reduction ratio of 1/N.