PROCEEDINGS ARTICLE | May 19, 2008
Proc. SPIE. 7000, Optical and Digital Image Processing
KEYWORDS: Lithium, Wavelet transforms, Image compression, Sensors, Digital filtering, Wavelets, Image resolution, Digital watermarking, Discrete wavelet transforms, Filtering (signal processing)
Watermarking using pixel-wise masking in the wavelet domain proves to be quite robust against common signal
processing attacks. Initially, in a system proposed by Barni et al., embedding is made only in the highest resolution level;
there are two disadvantages to this technique: the watermark information can be easily erased by a potential attacker and
embedding in the DWT is susceptible to geometric attacks, such as shifting. To enhance this watermarking method, we
use a modified perceptual mask that models the human visual system behavior in a better way, previously proposed by
the authors. The texture content is appreciated with the local standard deviation of the original image, which is further
compressed in the wavelet domain. Since the approximation image of the coarsest level contains too little information,
we appreciate the luminance content using a higher resolution level approximation sub-image. To increase the capacity
of the watermarking scheme the embedding is made in the HWT domain, using two strategies: in the real parts of the
HWT coefficients and in the absolute value of the HWT coefficients of the original image. The implementation of the
HWT is made using a new technique, recently proposed by the authors. Moreover, we make use of all the levels except
the coarsest one, for attack resilience. We use three types of detectors that take advantage of the hierarchical
decomposition. Tests were made for different attacks (JPEG compression, median filtering, resizing, cropping, gamma
correction, blurring, shifting and addition of white Gaussian noise), that prove the effectiveness of perceptual
watermarking in the HWT domain.
