DCT-based color digital image blind watermarking method with variable steps

In this paper, a blind watermarking method for color digital image based on DCT domain with variable steps is proposed to solve the copyright protection of color digital image. In this method, partial DCT coefficients of the image block transformed by two-dimensional discrete cosine transform (2D-DCT) are selected in the transform domain firstly, then these selected DCT coefficients at different positions are quantized by different quantization steps, and the embedding and blind extraction of digital watermark are completed. This method used color digital image as watermark image instead of gray image or binary image, and the color host image used in this scheme is selected from two public image databases (CVG-UGR and USC-SIPI). The experimental result shows that this scheme embedded color digital image watermark into host image successfully not merely has high invisibility, but also has strong robustness, which is suitable for digital image copyright protection.