Contrast Enhancement Scheme Integrating Global and Local Contrast Equalization Approaches

This paper proposes a new contrast enhancement scheme which integrates a global and a local contrast enhancement schemes to reduce the blocking and the washed-out effects at the same time. The proposed method executes a block-based histogram equalization on the temporary images which are obtained by dividing an input image into sub-blocks so that the sub-block of each temporary image may have a block size different from each other. In the next step, it calculates the contrast factors of all equalized temporary images and the temporary image having the largest contrast factor is selected to apply a global contrast enhancement algorithm. The global equalization function is extracted from the selected equalized temporary image and it is applied to the original image. The experiments have shown that the proposed algorithm produces a visually comfortable result image where the blocking and the washed-out effects cannot be detected.