Color image watermarking in the Karhunen-Loeve transform domain

In the field of image watermarking, research has been mainly focused on gray scale image watermarking; the extension to the color case still represents one of the open issues watermarking researchers are faced with. To solve the problem of the correlation among image color bands, a new approach is proposed here which is based on the exploitation of the de-correlation property of the Karhunen-Loeve transform (KLT). The KLT is applied to the red, green, blue components of the host image, then watermarking is performed independently in the discrete Fourier transform (DFT) do- main of the KL-transformed bands. In order to preserve watermark invisibility, embedding is achieved by modifying the magnitude of mid-frequency DFT coefficients according to an additive- multiplicative rule. In detection, KL de-correlation is exploited to de- sign an optimum watermark decoder. In particular, based on the Neyman-Pearson criterion, the watermark presence is revealed by comparing a likelihood function against a threshold. Experimental results are presented proving the robustness of the algorithm against the most common image manipulations, and its superior performance with respect to techniques based on luminance watermarking. © 2002 SPIE and IS&T. (DOI: 10.1117/1.1426383)