Reversible Contrast Enhancement by Histogram Specification and Very Low Distortion Data Hiding

This paper deals with reversible contrast enhancement (RCE). Image enhancement is achieved by histogram specification, the most popular contrast enhancement technique. A low bitrate procedure for inverting histogram specification is developed. The data for original image recovery is reversibly embedded into the contrast enhanced version. Very low distortion RDH schemes that exploit the sparse histogram of the contrast enhanced images are also proposed. Their major novelties are: embedding only into the histogram bins that provide room without any pixel shifting or overflow/underflow control, and encoding of embedded data sequence with fewer bits of “1”. The newly proposed RDH can exceed 1 bpp at average square errors per embedded bit between 0.375 and 0.5. It should be stressed that one gets reversibility at the distortion of least significant bit substitution algorithms. Experimental results are presented. With the proposed RCE-HS, reversibility is obtained without any visual distortion.