PROCEEDINGS ARTICLE | June 22, 2004
Proc. SPIE. 5306, Security, Steganography, and Watermarking of Multimedia Contents VI
KEYWORDS: Transparency, Image compression, Digital image processing, Visualization, Image processing, Digital watermarking, Image quality, Quantization, Visual system, Image classification
A robust, invisible watermarking scheme is proposed for digital images, where the watermark is embedded
using the block-based Lapped Orthogonal Transform (LOT). The embedding process follows a spread spectrum
watermarking approach. In contrast to the use of transforms such as DCT, our LOT watermarking scheme allows
larger watermark embedding energy while maintaining the same level of subjective invisibility. In particular, the
use of LOT reduces block artifacts caused by the insertion of the watermark in a block-by-block manner, hence
obtaining a better balance between invisibility and robustness. Moreover, we use a human visual system (HVS)
model to adaptively adjust the energy of the watermark during embedding. In our HVS model, each block is
categorized into one of four classes (texture, fine-texture, edge, and plain-area) by using a feature known as the
Texture Masking Energy (TME). Blocks with edges are also classified according to the edge direction. The block
classification is used to adjust the watermark embedding parameters for each block.
