Embedding color watermark image to color host image based on 2D-DCT

Abstract

For protecting the copyright of color image, a blind watermarking algorithm for color digital images is proposed in this paper. First, affine transform and Arnold transform are successively used in the pre-processing stage to encrypt watermark information twice, which greatly improves security of watermarking algorithm. Then, the different embedding coefficients in the different image blocks and the different quantization steps in the different image layers are selected to modify part of the middle-frequency coefficients after two-dimensional discrete cosine transform (2D-DCT) for embedding the color digital watermark, which helps to improve the invisibility and robustness of watermark. Finally, the relationship between coefficient pairs of 2D-DCT is used to realize the blind extraction of the watermark information. By comparing the proposed algorithm to other relevant watermarking algorithms after many experiments, we can see that the proposed watermarking algorithm has better invisibility, stronger robustness, larger capacity and higher security.