Novel Reversible Pixel-Value-Ordering Technique for Secret Concealment

This work is to preserve the distortion of marked image from the original image, that is, to improve the Peak Signal-to-Noise Ratio (PSNR) and to improve the Embedding Capacity (EC). Pixel-Value-Ordering (PVO) is the technique used for ensuring reversibility in Reversible Data Hiding (RDH). The difference-value is calculated from ordered pixel blocks. From the difference-value histogram, the rough bins are shifted to vacate place for concealing secret whereas the smooth bins are expanded to conceal secret. The proposed Novel Reversible Pixel-Value-Ordering Technique (RPVOT) is the containment of two schemes: Novel Difference Computation (DC) and Novel Histogram Shifting (HS). Firstly, for DC, the existing approaches compute the difference between first two (or, last two) pixel values of an ordered block whereas, the novel DC technique picks up the first two pixel values (or, last two pixel values) from an ordered block and the rounded mean of pixel values in minimum and maximum position subtracted from a pixel value in minimum position is computed. This novel DC makes eligible more number of blocks for secret concealment than other existing approaches by which more secret bits can be concealed and visual worth of the marked image is conserved as well. Secondly, novel HS is proposed which break the rule of shifting all the blocks that are not meant for embedding by shifting some blocks using naturally occurring empty bins in the histogram. This novel HS prevents many blocks from unnecessary alteration in their pixel values and hence, visual worth of the marked image is improved further. Both novel DC and novel HS are combined together to form novel RPVOT which significantly improves the Embedding Capacity (EC) along with Peak Signal-to-Noise Ratio (PSNR).