Brightness preserving image contrast enhancement using weighted mixture of global and local transformation functions

Transformation functions utilizing the global information content of an input image have been long serving contrast enhancement by stretching the dynamic range of intensity levels. Other transformation functions focus on local information content to correct image details, such as edges and texture. In this paper, an effective method for image contrast enhancement is presented with a mapping function, which is a mixture of global and local transformation functions that improve both the brightness and fine details of the input image. The final mapping function incorporates a local intensity-pair distribution generated expansion function from each image block to control the enhancement of image details that the global transformation function alone may fail to improve. Contribution from the global transformation function preserves the overall image brightness and contrast stretching. Experiments show that the proposed method competes well with the existing enhancement methods, both subjectively and quantitatively.