Information hiding based on gray relation and contourlet transform

Today, the mainly spatial domain algorithm in the field of information hiding is Tian's differential expansion algorithm, on this basis, the improved algorithm is proposed. The main advantages of the space domain algorithm are simple implementation, large embedded capacity, but poor robustness. This chapter begins to describe another important technique to achieve information hiding, which is to hide the information in the transform domain. The principle of transform domain algorithm is mainly the first digital image transform, such as DCT transform, DWT transform, and then embed the watermark into the transformed coefficients, and finally through the corresponding inverse transform to embed the watermark. Under the condition of selecting proper embedding intensity, the transform domain algorithm can still maintain good invisibility, and the robustness is greatly improved. Therefore, the transform domain algorithm has been widely used in daily applications.