Jean-Francois Delaigle

Circular interpretation of bijective transformations in lossless watermarking for media asset management

The need for reversible or lossless watermarking methods has been highlighted in the literature to associate subliminal management information with losslessly processed media and to enable their authentication. The paper first analyzes the specificity and the application scope of lossless watermarking methods. It explains why early attempts to achieve reversibility are not satisfactory. They are restricted to well-chosen images, strictly lossless context and/or suffer from annoying visual artifacts. Circular interpretation of bijective transformations is proposed to implement a method that fulfills all quality and functionality requirements of lossless watermarking. Results of several bench tests demonstrate the validity of the approach.

Watermarking algorithm based on a human visual model

This paper presents an additive watermarking technique for grey-scale pictures. It consists in secretly embedding copyright information (a binary code) into the picture without degrading its quality. Those bits are encoded through the phase of maximal length sequences (MLS). MLS are binary sequences with good correlation properties. The result of the autocorrelation is much greater than crosscorrelations, i.e; correlations made with shifted versions of this sequence. The embedded bits are retrieved from the result of the correlations. The core of the embedding process is underlaid by a masking criterion that guarantees the invisibility of the watermark. It is combined with an edge and texture discrimination to determine the embedding level of the MLS, whose bits are actually spread over 32 x 8 pixel blocks. Eventually, some results are presented, which analyze the efficiency of the retrieval as well as the resistance of the watermark to compression and its robustness against malevolent manipulation

Psychovisual approach to digital picture watermarking

In this paper, we wish to present a process enabling us to mark digital pictures with invisible and undetectable secret information. This so-called watermarking process is intended to be the basis of a complete copyright protection system. It consists of constructing a band-limited image from binary sequences with good correlation properties and in modulating some randomly selected carriers. The security relies on the secrecy of these carrier frequencies, which are deduced from a unique secret key. Then the amplitude of the modulated images is modified according to a masking criterion based on a model of the Human Visual System. The adding of the modulated images to the original is supposed to be invisible. The resulting image fully identifies the copyright owner since he is the only one able to detect and prove the presence of the embedded watermark thanks to his secret key. This paper also contains an analysis of the robustness of the watermark against compression and image processing

Human visual system features enabling watermarking

Digital watermarking consists of hiding subliminal information into digital media content, also called host data. It can be the basis of many applications, including security and media asset management. In this paper, we focus on the imperceptibility requirement for image watermarking. We present the main features of the human visual system (HVS) to be translated into watermarking technology. This paper highlights the need for dedicated inputs from the human vision community. The human visual system (HVS) is very complex and able to deal with a huge amount of information. Roughly speaking, it is composed of a receiver with a pre-processing stage, the eye and the retina, a transmission channel, the optic nerve, and a processing engine, the visual cortex. Mainly because of our lack of knowledge about brain behavior, i.e. about the way a stimulus is processed through its huge neural network, the large effort to understand and model the HVS behavior has partly remained fruitless. The aim of this paper is not to provide a thorough description of the HVS. For complete HVS models and more specific details, the reader is referred to existing literature. Here, we only try to understand, in a synthetic way and from an engineering perspective, the HVS features on which the designer of a watermarking algorithm can rely, i.e. its sensitivity and masking capabilities.

Compensation of geometrical deformations for watermark extraction in the digital cinema application

In this paper, we investigate the restoration of geometrically altered digital images with the aim of recovering an embedded watermark information. More precisely, we focus on the distorsion taking place by the camera acquisition of an image. Indeed, in the cinema industry, a large part of early movie piracy comes from copies made in the theater itself with a camera. The evolution towards digital cinema broadcast enables watermark based fingerprinting protection systems. The first step for fingerprint extraction of a counterfeit material is the compensation of the geometrical deformation inherent to the acquisition process. In order to compensate the deformations, we use a modified 12-parameters bilinear transformation model which closely matches the deformations taking place by an analog acquisition process. The estimation of the parameters can either be global, either vary across regions within the image. Our approach consist in the estimation of the displacement of a number of of pixels via a modified block-matching technique followed by a minimum mean square error optimization of the parameters on basis of those estimated displacement-vectors. The estimated transformation is applied to the candidate image to get a reconstruction as close as possible to the original image. Classical watermark extraction procedure can follow.

Low cost spatial watermarking

This paper presents a block-based spatial watermarking method. The main interest of this method is that it attempts to realise a good compromise between robustness performance, quality of the embedding and computational cost. This method is based on elementary perceptual criterion and adapts the embedding with regards to the content of the blocks. The paper ends with results deduced from many perceptual tests. The robustness towards lossy compression is also deeply analysed

Analyses of error correction strategies for typical communication channels in watermarking

Abstract Most watermarking techniques rely on redundancy where signature bits are encoded in a sufficiently large amount of sites for robustness against distortions and attacks while the watermark energy is kept low enough to remain imperceptible. The goal of this paper is to explore some strategies for exploiting this redundancy using error correcting codes. In some watermarking techniques bits are extracted via hard-decisions leading to a binary symmetric channel model while in others the extraction is carried out with soft-decisions leading to a additive Gaussian channel model. First, we consider error correcting codes for very high error rates of the watermarking channel where the trade-offs of Bose–Chaudury–Hocquenheim (BCH) and repetition codes are investigated. We also present the performance and a fast implementation of soft-decoders. We give two potential realizations of soft-decoding, namely, Viterbi decoder for convolutional codes and a new algorithm for soft-BCH decoding.

Secure delivery of images over open networks

We present architectures for the secure delivery of images over open networks, such as the Internet or broadcast networks. Those systems integrate access control mechanisms and tracking procedures, once the pictorial material has been accessed. We show how these architectures have been tested in the context of the connection of cultural databases to the Internet (AQUARELLE system) and in the context of broadcasting of high-value TV programs (OCTALIS system used during the football World Cup). This work shows the interest for a global integrated design of delivery systems in which watermarking, monitoring, and public key infrastructures based on trusted third parties are designed according to coherent functional models.

Low-cost perceptive digital picture watermarking method

This paper presents an additive watermarking technique for grey scale pictures, which can be extended to video sequences. It consists of embedding secretly a copyright information (a binary scale) in the picture without degrading its quality. Those bits are encoded through the phase of Maximal Length Sequences (MLS). MLS are sequences having good correlation properties, which means that the result of the autocorrelation is far greater than crosscorrelations, i.e. correlations made with shifted version of this sequence. This embedding is performed line by line going from the top to the bottom of the picture as the objective was to implement a low cost and real time embedding method able to work for common video equipments. The very embedding process is underlain by a masking criterion that guarantees the invisibility of the watermark. This perceptive criterion, deduced from physiological and psychophysic studies, has already proved its efficiency in a previously presented paper. It is combined with an edge and texture discrimination to determine the embedding level of the MLS, whose bits are actually spread over 32 by 8 pixel squares. Eventually, some preliminary results are presented, which analyze the efficacy of the decoding as well as the resistance of the watermark towards compression and robustness against malevolent treatments.

Improving data hiding by using convolutional codes and soft-decision decoding

This paper presents an other way of considering watermarking methods, which are analyzed from the point of view of the Information Theory. Watermarking is thus a communication problem in which some information bits have to be transmitted through an additive noise channel subjected to distortions and attacks. Designing watermarking methods in such a way that this channel is Gaussian can be profitable. This paper shows to what extent error protection techniques extensively studied for digital communication through Gaussian channels can be used advantageously for watermarking. Convolutional codes combined with soft-decision decoding are the best example. Especially, when soft-decision Viterbi decoding is employed, this kind of coding schemes can achieve much better performance than BCH codes, at comparable levels of complexity and redundancy, both for still and moving images.