A Blind Watermarking Algorithm Based on Block DCT for Dual Color Images

A dual color image blind watermarking algorithm is proposed based on block discrete cosine transformation (DCT). Firstly, the original watermark image and the original host image in RGB color space are converted to YCbCr color space, and the block DCT is implemented on their Y, Cb and Cr layer respectively. Secondly, the low frequency coefficients of each quantization sub-block of the watermark image are extracted to encode into a new one dimensional binary sequence, and the watermark sequence is obtained by the operations of spread spectrum and scrambling on the binary sequence, which is embedded into the middle and low frequency coefficients of Y Cb and Cr layer of the original host color image, and a new watermarked image can be generated by reverse DCT and color space transformation. Finally, the watermark can be robustly extracted according to error-correcting bits. The experimental results show that the proposed watermarking scheme is invisible and robust.