Abstract
A robust and geometric invariant digital watermarking scheme for gray-level images is proposed in this paper. The scheme carries out watermark embedding and extraction based on histogram in DWT domain. For watermark embedding, firstly, the original image is decomposed into the approximation and details sub-bands, of which, the approximation sub-band is used for watermark embedding. Pixels of the approximation subband are grouped into m blocks, each of which has the same number of gray-levels, thus the block histogram is generated; with the block histogram, the percentage of number of pixels in each block is calculated. Then some pixels in a block are moved to form a specific pattern in the gray-level histogram distribution, indicating the watermark. Finally, the embedded approximation sub-band and the other three details sub-bands are constructed into a watermarked image. For watermark extraction, firstly, the watermarked image is also decomposed into the approximation and details sub-bands; then the pixels in the approximation sub-band are grouped into blocks in the similar manner. According to the histogram distribution in each block, the watermark is extracted. Experimental results show that the proposed scheme is highly robust against JPEG compression, geometric attacks and some common signal processing, and it outperforms the existing methods in term of robustness.
