1. An image processing apparatus comprising: a determining unit that determines, in image data formed by a plurality of packs each formed by a plurality of pixels and serving as a unit, a monotonic pack formed by a plurality of pixels equal to a preceding pixel precedently subjected to image processing and a normal pack other than the monotonic pack; a pixel row forming unit that forms a pixel row including a plurality of pixels obtained from the normal pack and arranged in a line, while deleting the plurality of pixels included in the monotonic pack; a pixel row processing unit that processes the pixel row formed by the pixel row forming unit, by inputting the pixel row to an image processing unit; and a supplementing unit that supplements 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 obtained from the normal pack, to thereby obtain an image processing result of the image data.