An image forming apparatus for compressing image data, includes: a compression unit that reduces data into a predetermined bit number per band of image data so as to satisfy a condition related to a predetermined compression and compresses the reduced data; a specifying unit that specifies a minimum bit number among the predetermined bit numbers applied to the bands and specifies bands which are not compressed by the minimum bit number; and a re-compression unit that performs re-compression on the specified bands so that the data is compressed by the minimum bit number.