Lattice codes and quantization-based techniques have received considerable attention as a method of digital watermarking
with side information. However, these algorithms are also recognized to be highly sensitive to common
signal processing primitives such as valuemetric scaling, e.g. changes in volume of a song, or re-quantization,
e.g. JPEG compression. Hence, it is reasonable to investigate alternative codes which may offer the potential
for superior performance. In previous work, we designed a new class of codes, called dirty paper trellis codes
(DPTC), which are by construction immune to valuemetric scaling. Although DPTC have shown themselves to
be resistant to certain classes attacks, the trellises were generated randomly, thus leading to suboptimal codes.
In this paper, Ungerboeck's work on trellis coded modulation (TCM) is exploited to significantly improve the
performance of the DPTC. Experimental results show that the resulting trellises significantly outperform the
original design.
KEYWORDS: Digital watermarking, Sensors, Fourier transforms, Databases, Signal to noise ratio, Image registration, Pattern recognition, Image processing, Signal processing, Signal detection
Many electronic watermarks for still images and video content are sensitive to geometric distortions. For example, simple rotation, scaling, and/or translation (RST) of an image can prevent detection of a public watermark. In this paper, we propose a watermarking algorithm that is robust to RST distortions. The watermark is embedded into a 1-dimensional signal obtained by first taking the Fourier transform of the image, resampling the Fourier magnitudes into log-polar coordinates, and then summing a function of those magnitudes along the log-radius axis. If the image is rotated, the resulting signal is cyclically shifted. If it is scaled, the signal is multiplied by some value. And if the image is translated, the signal is unaffected. We can therefore compensate for rotation with a simple search, and for scaling by using the correlation coefficient for the detection metric. False positive results on a database of 10,000 images are reported. Robustness results on a database of 2,000 images are described. It is shown that the watermark is robust to rotation, scale and translation. In addition, the algorithm shows resistance to cropping.
We describe psychophysical experiments conducted to study PicHunter, a content-based image retrieval (CBIR) system. Experiment 1 studies the importance of using (a) semantic information, (2) memory of earlier input and (3) relative, rather than absolute, judgements of image similarity. The target testing paradigm is used in which a user must search for an image identical to a target. We find that the best performance comes from a version of PicHunter that uses only semantic cues, with memory and relative similarity judgements. Second best is use of both pictorial and semantic cues, with memory and relative similarity judgements. Most reports of CBIR systems provide only qualitative measures of performance based on how similar retrieved images are to a target. Experiment 2 puts PicHunter into this context with a more rigorous test. We first establish a baseline for our database by measuring the time required to find an image that is similar to a target when the images are presented in random order. Although PicHunter's performance is measurably better than this, the test is weak because even random presentation of images yields reasonably short search times. This casts doubt on the strength of results given in other reports where no baseline is established.
KEYWORDS: Digital watermarking, Image compression, Image processing, Video, Computer programming, Electronic filtering, Optical filters, Signal processing, Interference (communication), Signal to noise ratio
A watermark embeds an imperceptible signal into data such as audio, video and images, for a variety of purposes, including captioning and copyright control. In this paper, we first outline the desirable characteristics of digital watermarks. Previous work in digital watermarking is then reviewed. Early work identified redundant properties of an image (or its encoding) that can be modified to encode watermarking information. The early emphasis was on hiding data, since the envisioned applications were not concerned with signal distortions or intentional tampering that might remove a watermark. However, as watermarks are increasingly used for purposes of copyright control, robustness to common signal transformations and resistance to tampering have become important considerations. Researchers have recently recognized the importance of perceptual modeling and the need to embed a signal in perceptually significant regions of an image, especially if the watermark is to survive lossy compression. However, this requirement conflicts with the need for the watermark to be imperceptible. Several recent approaches that address these issues are discussed.
Conference Committee Involvement (5)
Security, Steganography, and Watermarking of Multimedia Contents IX
29 January 2007 | San Jose, CA, United States
Security, Steganography, and Watermarking of Multimedia Contents VIII
16 January 2006 | San Jose, California, United States
Security, Steganography, and Watermarking of Multimedia Contents VII
17 January 2005 | San Jose, California, United States
Security, Steganography, and Watermarking of Multimedia Contents VI
19 January 2004 | San Jose, California, United States
Security and Watermarking of Multimedia Contents V
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