1. A device for synthesizing a high dynamic range image based on per-pixel exposure mapping, comprising: an image-capturing module, for obtaining a plurality of source images each having a unique exposure value; an image-processing module, for performing an exposure-value modulating means to exposure values of pixels on an identical location in two said source images that have similar said exposure values so as to achieve exposure synthesis of the pixels and form synthesis images; and a recursive control module, for sending the formed synthesis images back to the image-processing module for reprocessing until the image-processing module generates only one said synthesis image.