An Automatic Method to Evaluate the Imperceptibility of Digital Watermark

Since human eyes are liable to be tired and fail to distinguish tiny distinctions when evaluating watermark imperceptibility, this paper presents an automatic evaluation method. In the method, the pixel distribution of the differential images between original image and watermark-embedded images are calculated to construct several comparative sequences; meanwhile, a reference sequence is formed through analyzing the ideal distribution of the pixels in the differential images. Next, an overall imperceptibility index is achieved through the grey relational degrees between the two kinds of sequences. Pilot experiments show that the evaluation results not only agree with human visual system, but also basically consist with theoretical analysis.