Embedding color image watermark in color image based on two-level DCT

Abstract

With the widespread use of color images in many areas, the colorful logo or mark is gradually used as watermark to protect the copyright in recent years. Since the color image watermark has more bit information, it is a challenging work to design a robust color watermarking scheme. By utilizing the two-level DCT, a novel watermarking algorithm is proposed to embed the color image watermark in the direct current (DC) coefficients and the alternating current (AC) coefficients of the color host image. Firstly, the host image is divided into $$8 \times 8$$ non-overlapping blocks, and these blocks are transformed by one-level DCT. Secondly, its upper-left $$4 \times 4$$ coefficients are further transformed by two-level DCT, and the transformed coefficients are ordered by zigzag arrangement. Thirdly, according to human visual system (HVS), the digital watermarks are embedded into the DC coefficient and the first seven AC coefficients of these blocks, respectively. Experimental results show that the proposed watermarking algorithm is robust to many common image processing attacks and geometric attacks, and the performance of the proposed method outperforms other color watermarking methods considered in this paper.