Adnan M. Alattar

Reversible watermark using difference expansion of quads

A reversible watermarking algorithm with very high data hiding capacity has been developed for colored images. The algorithm allows the watermarking process to be reversed to restore the original image exactly. The algorithm hides triplets of bits in the difference expansion of quads of adjacent pixels. The necessary difference expansion transform and its inverse is derived for quads. Also, the necessary conditions to avoid under- and overflow are derived. The algorithm can also be applied recursively, to maximize the amount of data that can be hidden into an image. Simulation results show that the algorithm can hide a bit-rate as high as 3.3 bits/colored pixel while maintaining an image quality level of 33.5 dB.

Watermarking electronic text documents containing justified paragraphs and irregular line spacing

In this paper, we propose a new method for watermarking electronic text documents that contain justified paragraphs and irregular line spacing. The proposed method uses a spread-spectrum technique to combat the effects of irregular word or line spacing. It also uses a BCH (Bose-Chaudhuri-Hocquenghem) error coding technique to protect the payload from the noise resulting from the printing and scanning process. Watermark embedding in a justified paragraph is achieved by slightly increasing or decreasing the spaces between words according to the value of the corresponding watermark bit. Similarly, watermark embedding in a text document with variable line spacing is achieved by slightly increasing or decreasing the distance between any two adjacent lines according to the value of the watermark bit. Detecting the watermark is achieved by measuring the spaces between the words or the lines and correlating them with the spreading sequence. In this paper, we present an implementation of the proposed algorithm and discuss its simulation results.

Evaluation of selective encryption techniques for secure transmission of MPEG-compressed bit-streams

Total encryption of MPEG-I compressed bit-streams requires a large processing time. To reduce this processing time, Spanos and Maples (1996) propose encrypting only the data in the Intracoded frames. In this paper, experimental results are presented which indicate that Spanos and Maples method does not provide an adequate level of security. A better method that calls for encrypting all the Intra-coded macroblocks (I-MBs) in all frames is then presented. Although this method achieves a 69% reduction in the processing time over total encryption, the motion content of the video sequence is apparent. Therefore, another method that calls for encrypting the headers of all predicted, macroblocks (MBs) in addition to encrypting the data in all I-MBs is presented. Simulation results for this method show that the decoded video is fully disguised, but at the expense of decreasing the savings in the processing time to 21-60% of the processing time of total encryption.

Watermark re-synchronization using log-polar mapping of image autocorrelation

Many watermarking algorithms embed the watermark into the image as contiguous non-overlapping tiles. This tiling structure forms an implicit synchronization template that can be revealed through autocorrelation. This template is composed of a set of weak peaks, replicating the relative position of the watermark tiles. Hence, synchronization can be resolved by comparing the actual locations of these peaks to the theoretical ones to determine the scaling factor and the orientation angle of the tiles. Unfortunately, these peaks are very weak and measuring their locations directly is not easy. In this paper, a log-polar mapping of the synchronization template is computed to convert the scaling factor and the rotation angle of the template into vertical and horizontal shifts. These shifts are then detected using a Phase-Only-Matched filter (POM), which concentrates the weak energy from all peaks into a single peak that is much easier to detect. The scaling factor and orientation angle are determined from the location of this peak. Simulation results of this method have shown that this method is very effective and produces accurate results.

High-capacity invertible data-hiding algorithm for digital audio

A high-capacity, data-hiding algorithm that lets the user embed a large amount of data in a digital audio signal is presented in this paper. The algorithm also lets the user restore the original digital audio from the watermarked digital audio after retrieving the hidden data. The hidden information can be used to authenticate the audio, communicate copyright information, facilitate audio database indexing and information retrieval without degrading the quality of the original audio signal, or enhance the information content of the audio. It also allows secret communication between two parties over a digital communication link. The proposed algorithm is based on a generalized, reversible, integer transform, which calculates the average and pair-wise differences between the elements of a vector composed from the audio samples. The watermark is embedded into the pair-wise difference coefficients of selected vectors by replacing their least significant bits (LSB) with watermark bits. Most of these coefficients are shifted left by one bit before replacing their LSB. The vectors are carefully selected such that they remain identifiable after embedding and they do not suffer from overflow or underflow after embedding. To ensure reversibility, the locations of the shifted coefficients and the original LSBs are appended to the payload. Simulation results of the algorithm and its performance are presented and discussed in the paper.

Evaluation of Watermarking Low Bit-rate MPEG-4 Bit Streams

A novel watermarking algorithm for watermarking low bit-rate MPEG-4 compressed video is developed and evaluated in this paper. Spatial spread spectrum is used to invisibly embed the watermark into the host video. A master synchronization template is also used to combat geometrical distortion such as cropping, scaling, and rotation. The same master synchronization template is used for watermarking all video objects (VOP) in the bit-stream, but each object can be watermarked with a unique payload. A gain control algorithm is used to adjust the local gain of the watermark, in order to maximize watermark robustness and minimize the impact on the quality of the video. A spatial and temporal drift compensator is used to eliminate watermark self-interference and the drift in quality due to AC/DC prediction in I-VOPs and motion compensation in P- and B-VOPs, respectively. Finally, a bit-rate controller is used to maintain the data-rate at an acceptable level after embedding the watermark. The developed watermarking algorithm is tested using several bit-streams at bit-rates ranging from 128-750 Kbit/s. The visibility and the robustness of the watermark after decompression, rotation, scaling, sharpening, noise reduction, and trans-coding are evaluated.

A high-capacity invertible data-hiding algorithm using a generalized reversible integer transform

A high-capacity, data-hiding algorithm that lets the user restore the original host image after retrieving the hidden data is presented in this paper. The proposed algorithm can be used for watermarking valuable or sensitive images such as original art works or military and medical images. The proposed algorithm is based on a generalized, reversible, integer transform, which calculates the average and pair-wise differences between the elements of a vector extracted from the pixels of the image. The watermark is embedded into a set of carefully selected coefficients by replacing the least significant bit (LSB) of every selected coefficient by a watermark bit. Most of these coefficients are shifted left by one bit before replacing their LSBs. Several conditions are derived and used in selecting the appropriate coefficients to ensure that they remain identifiable after embedding. In addition, the selection of coefficients ensures that the embedding process does not cause any overflow or underflow when the inverse of the transform is computed. To ensure reversibility, the locations of the shifted coefficients and the original LSBs are embedded in the selected coefficients before embedding the desired payload. Simulation results of the algorithm and its performance are also presented and discussed in the paper.

Watermarking low bit-rate Advanced Simple Profile MPEG-4 bitstreams

This paper presents a novel watermarking method for low bit-rate video that is compressed according to the Advanced Simple Profile of MPEG-4. A spatial spread spectrum watermark was embedded directly to the MPEG-4 bit-streams by adopting Hartungs approach of watermarking MPEG-2 compressed bitstreams. A synchronization template was employed to combat cropping, scaling, and rotation. A gain control algorithm adjusts the local strength of the watermark depending on local image characteristics, in order to maximize watermark robustness and to minimize the impact on the quality of the video. A drift compensator prevents the accumulation of watermark distortion and reduces inter-frame interference of watermark signals due to motion compensated prediction in inter-coded frames. The developed watermarking algorithm was tested at bit-rates ranging from 128-768 Kbit/s. The watermarks impact on visual quality as well as its robustness after decompression, scaling, rotation, sharpening, and noise reduction was evaluated.

Primitive-based image coding technique for still pictures

A new image coding technique for achieving an extremely high compression ratio while producing good image quality is described. The idea is analogous to that used in forensic applications when constructing a composite image of a criminal from a collection of images of facial features. The imput image is segmented into complicated primitives that are coded using previously constructed database of primitives. A duplicate database is used at the receiver to decode the primitives. The decoded primitives are assembled as in computer animation to produce a faithful reconstruction of the original image. The technique has been applied to head-and-shoulders images and compression ratios over 1000:1 have been achieved.<<ETX>>

A fast hierarchical watermark detector for real-time software or low-cost hardware implementation

In this paper, we develop a spread spectrum-based watermark algorithm for real-time software or low-cost hardware implementation. The developed detector is suitable for devices such as stand-alone watermark readers, cellular phones, and PDAs. These devices have primitive operating systems with limited processing power, memory, and system bandwidth. Our embedder tiles the watermark over the host image to let the watermark be detected from any region in the digital or printed watermarked image as the data is streamed through the device. It also adapts the watermark strength locally to maximize detection and minimize watermark visibility. Consequently, the watermark may be detectable only in few regions of the image that are not necessarily aligned with the original tile boundaries. To avoid a brute-force search, our detector uses a hierarchical search algorithm to quickly zoom into the region with the strongest watermark. This approach permits a real-time software implementation of the detector and reduces the necessary gate count, on-chip memory, and system bandwidth for a hardware implementation. Software simulation results of the developed algorithm indicate that the algorithm is very efficient and the detection results are better than those obtained using a sub-sampled brute-force search.