Embedding color watermarks in color images

Abstract

Robust watermarking with oblivious detection is essential to practical copyright protection of digital images. Effective exploitation of characteristics of human visual perception helps to develop a watermarking scheme that fulfills the requirement. An oblivious watermarking scheme is proposed that embeds color watermarks in color images. Through color quantization, the color watermark is embedded by modifying the quantization index of each color pixel without perceivable color distortion. Only very little information including the specification of color gamut and quantizer stepsize as private key is required to extract color watermarks. Experimental results promisingly show that the proposed watermarking scheme is computationally simple and quite robust in face of various attacks such as cropping, low-pass filtering, white noise addition, rotation, scaling, and JPEG lossy compression with the compression ratio as high as 27.5.