An advanced gradient histogram and its application for contrast and gradient enhancement

This paper proposes an image contrast and gradient enhancement method based on advanced gradient histogram equalization (AGHE). We first define a novel advanced gradient histogram (AGH). Unlike the traditional intensity histogram which only contains intensity information, the AGH contains both gradient and intensity information of image. This character enables AGH to alleviate high peaks and thus avoid over enhancement in AGHE. Moreover, it's proved that AGHE can increase the mean of absolute gradients (MAG) which is a measurement of image gradient. Then we present a sine function histogram correction (SHC) to control the enhancement level of AGHE. By modifying AGH using SHC before equalization, both the contrast and gradient enhancement levels can be controlled effectively. Simulation results demonstrate that AGHE with SHC (SAGHE) can improve the image subjective quality effectively by enhancing both the contrast and gradient of image.