A digital image watermarking system based upon block classification

Generally speaking, the human eye is less sensitive to changes in colour for vari-coloured images. As for an image with high colour intensities, people find it difficult to perceive any change in colour if the colour intensities of some pixels are adjusted by a small quantity. Based on these two observations, this paper classifies the original image into blocks of three types, which are complex blocks, white blocks and smooth blocks. Thus, when watermarking takes place, the colours of the pixels are varied depending on the block type; as a result, someone can take good care of the quality of both the embedded image and the extracted watermark. The experimental results show that the proposed watermarking system has high robustness against a variety of aggressive image processing, including blurring, sharpening, cropping and JPEG lossy compression.