Color Image Blind Watermark Algorithm Based on Spread Spectrum Modulation and Visual Masking
基于扩频调制和视觉掩蔽的彩色图像盲水印算法

In order to better protect the copyright of the color image, this paper explained theoretically why the green color image component should be chosen to embed into a watermark, and thus proposed a new blind watermark algorithm for a color image. First, the green component of the original image was divided block by block with size 8×8 pixels, and transformed with discrete cosine transformation (DCT). Second, the binary watermark image was spread spectrum modulated by two uncorrelated random sequences. At last, in order to maximize the enhanced watermark strength without affecting transparency, human visual masking factor was imported. And the modulated watermark with different intensities was embedded in mid-frequency region coefficients of DCT domain based on visual masking factor magnitude. The watermark was extracted by comparing the relativity between two random sequences with watermarked image, and the process did not need the original image, which means a blind watermark algorithm. Experimental results demonstrated that this method was invisible and robust against some usual attacks such as JPEG compression, cropping, adding noise, and embedding watermark in a green component is more robust against lossy compression than embedding watermark in a red or blue component.