Embedding a Color Watermark into DC coefficients of DCT from Digital Images

In this paper, a secure watermarking framework based on Discrete Cosine Transform (DCT) for embedding a color watermark into digital images that provides robustness against JPEG compression and some other image processing attacks is presented. In the proposed algorithm, the RGB components of the color image have been separated, and then each component is selected to embed a color watermark. The images R, G and B are divided in 8 8 non-overlapped pixels blocks and each block is transformed to frequency domain using DCT. Next, with DC coefficient of each block a new block of 8x8 DC coefficients are arranged and a second DCT is applied. Later, Quantization Index Modulation (QIM) Dither Modulation (DM) is used as the embedding method to insert the color watermark into the 64 resultant coefficients. Meantime, the color watermark is transformed to YCbCr color space and a codification 4:2:0 is used to reduce the quantity of bits to represent it. The proposed watermarking scheme has demonstrated high resistance against various types of attacks in comparison with other state-of-art algorithms.