  Quaternion singular value decomposition (QSVD) is a robust technique of
digital watermarking which can extract high quality watermarks from watermarked
images with low distortion. In this paper, QSVD technique is further
investigated and an efficient robust watermarking scheme is proposed. The
improved algebraic structure-preserving method is proposed to handle the
problem of "explosion of complexity" occurred in the conventional QSVD design.
Secret information is transmitted blindly by incorporating in QSVD two new
strategies, namely, coefficient pair selection and adaptive embedding. Unlike
conventional QSVD which embeds watermarks in a single imaginary unit, we
propose to adaptively embed the watermark into the optimal hiding position
using the Normalized Cross-Correlation (NC) method. This avoids the selection
of coefficient pair with less correlation, and thus, it reduces embedding
impact by decreasing the maximum modification of coefficient values. In this
way, compared with conventional QSVD, the proposed watermarking strategy avoids
more modifications to a single color image layer and a better visual quality of
the watermarked image is observed. Meanwhile, adaptive QSVD resists some common
geometric attacks, and it improves the robustness of conventional QSVD. With
these improvements, our method outperforms conventional QSVD. Its superiority
over other state-of-the-art methods is also demonstrated experimentally.
