A Novel Watermarking Method Based on Sub-band Coefficient Encoding in DCT Domain

This paper presented a novel watermarking method to embed a watermark into an image. To improve the transparency and robustness of watermark embedding, a visual model was employed to calculate the block based just noticeable difference (JND), and the three sub-bands of coefficient matrix in the medium frequencyof block discrete cosine transform (BDCT) were defined to embed objects. Firstly, an original watermark file was transferred into a binary watermark sequence, which was encoded by redundant encoding method and scrambled randomly if necessary. Then, two neighboring image blocks were selected each time from the host image by Hilbert scanning order, and transformed by BDCT. According to the JND and the watermark bit, the BDCT sub-band coefficients at same region of two neighboring blocks were adjusted to embed the watermark. Lastly, the inverse BDCT was executed to get the embedded image. The experiments show that the embedded watermark is invisible, and the algorithm is robust to common image processing operations.