The traditional histogram equalization is unable to keep the input image brightness

when enhancing the image details. Based on partially overlapped sub-block histogram equalization algorithm (POSHE)

recursive separateness method is used in the process of sub-block histogram equalization. An advanced partially overlapped local histogram equalization algorithm is proposed. The sub-block image is separated recursively into different sub-images with the cumulative density function (CDF). Then each sub-image histogram is equalized within its respective gray range

and all the sub-images are incorporated into the equalized sub-block. Both linear and bilinear interpolation are used in the equalized sub-block based on step size avoiding the generation of the blocking effects and the influence on the image details. The simulation results show that the local details are enhanced

and the input image brightness is also preserved effectively. Finally

the influence on the image details is eliminated by avoiding the blocking effects

and more natural visual impression can be seen in the equalized image.