Author : Al Mehdi Saadat Chowdhury, M. Shahidur Rahman [ Volume No.:V, Issue No.II-Mar 2016] [Page No : 609-614] [2016]

This paper proposes an image enhancement technique using Tri-histogram equalization defined in terms of minimum and maximum intensity. Traditionally for image contrast enhancement, histogram equalization technique is used extensively. However, histogram equalization tends to change the mean brightness of any image to the middle gray level of the dynamic range, which often results in over or under enhancement and introduce some annoying artifacts. To overcome such problems, several bi-histogram based techniques and one tri-histogram based technique has been proposed. While bi-histogram based techniques divides the histogram of any image into two sub-histograms and equalize them independently, tri-histogram based technique divides the histogram into three sub histograms. This paper presents a novel tri-histogram based enhancement approach where two intensity values which are used to divide the histogram into three parts can be found by computing the minimum and maximum pixels per intensity count. After dividing the histogram into three parts, each of the parts are equalized individually and then combined together to produce the final enhanced image. The simulation results show that the proposed method outperforms other conventional bi-histogram and tri-histogram based techniques in terms of brightness preservation, structural similarity and PSNR.