Digital Image Steganography based on Seven Way Pixel Value Differencing

Background/Objectives: This paper presents a steganographic method by calculating the pixel value differences along seven directions using nine-pixel blocks. Methods/Statistical Analysis: The centrally located pixel in nine-pixel block is used to form seven pairs with its seven neighboring pixels. The eighth neighbor pixel is used as the indicator to identify whether a block suffers with Fall Off Boundary Problem (FOBP) or not. Findings: Seven pixel value differences are calculated and based on these differences embedding is done. After embedding, the central pixel value is normalized to have a single value for all the seven pairs by suitable adjustments. After adjustments if any pixel value in the block falls off boundary, then the entire block is exempted from embedding. This is noted at the eighth neighbor pixel, so that it can also be exempted during extraction. Furthermore, to increase the capacity and peak signal-to-noise ratio, the nine-pixel blocks which suffer with FOBP are embedded using Wu and Tsai’s PVD method. The extraction process is very simple and the secret message can be extracted from the stego-image without using the original cover image. Application/ Improvements: Without compromising the security and imperceptibility the hiding capacity is almost 50% increased as compared to Wu and Tsai’s Pixel Value Differencing (PVD) method.