Abstract: An object of the invention is to provide an image memory system capable of efficiently reading out image data also in case of consecutively reading out image data from an image memory along a direction other than the direction in which a burst access can be performed. In case that a bit-map image is partitioned into square or rectangular blocks and image data of pixels contained in one block are made to correspond to one row space, row spaces respectively corresponding to two blocks being adjacent to each other with a common side between them are made to belong to different synchronous DRAMs without fail and all of row spaces respectively corresponding to four blocks having commonly one vertex are made to belong to different banks.

Abstract: Disclosed is an image synthesis method in which image are synthesized so as not to create mach band. Primary differential of brightness of an image to be synthesized changes continuously (a). When the brightness of the image to be synthesized changes in this manner, primary differential of brightness of a synthesized image by superposing is also continuous, thus the brightness does not change suddenly and mach band does not occur (b).