An image processing apparatus includes: a determining unit determining, in image data including packs each including pixels and serving as a unit, a monotonic pack including pixels equal to a precedently image-processed preceding pixel and a normal pack other than the monotonic pack; a pixel row forming unit forming a pixel row including aligned pixels of the normal pack, while deleting the pixels of the monotonic pack; a pixel row processing unit processing the formed pixel row by inputting the pixel row to an image processing unit; and a supplementing unit supplementing an image processing result of the pixel row output from the image processing unit with, as an image processing result of the deleted pixels of the monotonic pack, a result of image processing by the image processing unit on the preceding pixel of the normal pack, to thereby obtain an image processing result of the image data.