A robust digital image watermarking algorithm based on Quadratic DCT transform

Robustness and invisibility are the two main indicators of the digital image watermarking system. In order to achieve the desired result, this paper presents a watermarking algorithm which based on the Quadratic DCT transform. This algorithm firstly conducts block DCT transform on the host image and selects the transformed DC coefficients in each block to form a new matrix; then conducts another block DCT transform on the new matrix. The high frequency coefficients of DCT coefficients are selected to embed the watermark. This algorithm which extracts the watermark without the original image achieves the blind detection. The simulation result shows that the algorithm has good invisibility, and as for down-sampling, noise, format conversion, filtering and other attacks, so it has strong robustness.