Contrast enhancement algorithm using partially overlapped sub-block histogram equalization

Abstract

In this paper, an advanced histogram equalization algorithm for contrast enhancement is presented. Histogram equalization is the most widely used algorithm for contrast enhancement due to its effectiveness and simplicity. To overcome the brightness distortion of histogram equalization, brightness preserving bi-histogram equalization (BBHE) method was presented. But original histogram equalization and BBHE enhance image contrast according to its global histogram information, so sufficient contrast cannot be obtained for many cases. For higher contrast, local histogram equalization was developed. Using this method, higher contrast can be achieved, but it takes too long time because sub-block histogram equalization must be performed for each pixel to eliminate blocking effect. As a solution, to get high contrast of local histogram equalization and simplicity of global histogram equalization without blocking effect, partially overlapped sub-block histogram equalization (POSHE) is proposed. In this method, sub-blocks for local histogram equalization is partially overlapped, typically 2 ~ 64 times. So its computation complexity reduced about 1 over few hundreds times compared to that of local histogram equalization with high contrast. The proposed algorithm targets commercial purposes.