Data Hiding in Gray-Scale Images Using Pixel Value Differencing

Steganographic method for embedding secret messages into a gray-valued cover image is proposed. It uses the fact that. Human visual system is having low sensitivity to small changes in digital data. It modifies pixel values of image for data hiding. Cover images is partitioned into non-Overlapping blocks of two consecutive pixels. Difference between the two consecutive pixel values is calculated. These difference values are classified into number of ranges. Range intervals are selected according to the characteristics of human vision's sensitivity to gray value variations from smoothness to contrast. A small difference value indicates that the block is in a smooth area and a large one indicates that the block is in an edged area. The pixels in edged area can tolerate larger changes of pixel values than those in the smooth area. So. in the proposed method we can embed more data in the edged areas than the smooth areas. The difference value then is replaced by a new value to embed the value of a sub-stream of the secret message. The number of bits which can be embedded in a pixel pair is decided by the width of the range that the difference value belongs to. The method is designed in such a way that the modification is never out of the range interval. This method not only provides a better way for embedding large amounts of data into cover images with imperceptions, hut also offers an easy way to accomplish secrecy. This method provides an easy way to accomplish secrecy. This method provides an easy way to produce a more imperceptible result than those yielded by simple least-significant bit replacement methods. The embedded secret message can be extracted from the resulting stego-image without referencing the original cover image. Experimental results show the feasibility of the proposed method.