Abstract
Robust watermarking with oblivious detection is essential to practical copyright protection of digital images. Effective exploitation of the characteristics of human visual perception to color stimuli helps to develop the watermarking scheme that fills the requirement. In this paper, an oblivious watermarking scheme that embeds color watermarks in color images is proposed. Through color gamut analysis and quantizer design, color watermarks are embedded by modifying quantization indices of color pixels without resulting in perceivable distortion. Only a small amount of information including the specification of color gamut, quantizer step-size, and color tables is required to extract the watermark. Experimental results 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, scaling, and JPEG compression with high compression ratios.
Highlights
Digital watermarking is a technique that hides a piece of information in an original media for the purpose of copyright protection, integrity checking, or captioning [1, 2, 3, 4, 5, 6, 7, 8, 9]
A color-image watermarking scheme that satisfies the requirements of transparency, robustness, and oblivious detection is proposed
Color watermarks are carried by the quantization indices of the host image in the uniform color space
Summary
Digital watermarking is a technique that hides a piece of information in an original media for the purpose of copyright protection, integrity checking, or captioning [1, 2, 3, 4, 5, 6, 7, 8, 9]. In the method of quantization index modulation [16], each of the host signal is quantized by one of a number of quantizers, of which indices are used to carry the watermark information. A watermarking scheme based on ordered color quantization is proposed in [17]. It is found that the color quantization and processing in most of these proposed techniques are not optimized by taking properties of human visual perception into account. To gain high robustness and transparency in color image watermarking, the knowledge of human visual perception of color stimuli must be well utilized in designing watermark embedding/extraction algorithms. Without resorting to the original image and with very little information as private key, the visually recognizable color watermarks can be detected by decoding each color pixel’s quantization index which is modified to carry the watermark signal in the embedding process. The color quantizer is so designed such that the quantization error and the distortion caused by the modification in quantization index will not be perceptible
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