Bi-directional Pixel-Value Differencing Approach for Steganography

A hybrid image steganographic approach has been proposed in this paper to enlarge the data hiding capability of cover image as well as to improve the quality of stego image. This research is a hybrid combination of cryptography, steganography and data compression. The basic building block of this approach is Wu and Tsai’s method (PVD), LZW compression scheme, Vernam cipher and gray code. In this approach, chunks of the secret data are embedded by altering the pixel values of the consecutive pixels in the cover image according to their hiding capacity. The hiding capacity of the two consecutive pixels depends on their difference value, which is calculated by pixel-value differencing technique (PVD). Two layer data hiding is the key feature of this approach that’s why it is called a Bi-Directional approach. Two layer data hiding approach improves the data hiding capacity and quality of stego image as well. In second layer data hiding we consider left pixel of the pixel pair as the right pixel and vive-versa. It improves the quality of stego image. In this technique stego image is totally indistinguishable from the original image by the human eye. It is also secure against the RS detection attack.