US Patent 7822272 Adaptive histogram equalization for images with strong local contrast

The present invention relates to a method, apparatus and computer program product for contrast enhancement of images based on adaptive histogram equalization. In particular it relates to preventing adaptive histogram equalization from causing fading artifacts and object extension artifacts. An adaptive histogram equalization method is provided comprising the steps of dividing an image into regions of pixels, determining structures of local pixel value differences of a predefined strength of the image, building for every region a histogram of the pixel values based on the determined structures of local pixel value differences and mapping pixel values of each region based on the histogram corresponding to the region.