An Improvement of Embedding Color Watermarks in Color Images Based on Schur Decomposition

In this paper, three supplementary processes (namely, restitution., data jittering., and level-shifting) are introduced to remedy the deficiency of the Schur decomposition (SD)-based blind watermarking scheme for color images. A block structure for manipulation is formed by partitioning the host image into non-overlapping blocks of 4 ×4 pixels and applying SD to each block separately. A restitution process is used to recover the elements that should not be modified during watermarking to preserve the quality of the watermarked image. To enable the extraction of the embedded watermark based on SD, the pixel intensity in each block is shifted to another intensity level using data jittering and level-shifting processes. Experiment results indicate that the proposed scheme can be used to extract watermarks without errors when not under attack, and can withstand a variety of image processing attacks. Compared with the primitive scheme based on SD, the proposed method exhibits superior robustness and imperceptibility with the same payload capacity.