Brightness Preserving Image Contrast Enhancement using Weighted Mixture of Global and Local Transformation Functions

Hasanul Kabir1, Abdullah Al-Wadud2, and Oksam Chae1 ‎
‎1Department of Computer Engineering, Kyung Hee University, Korea
‎2Industrial and Management Engineering Division, Hankuk University of Foreign Studies, Korea

Abstract: 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. ‎

Keywords: Contrast enhancement, global transformation function, local transformation function, and intensity pair.‎