Frank Bossen

Digital signature of color images using amplitude modulation

Watermarking techniques, also referred to as digital signature, sign images by introducing changes that are imperceptible to the human eye but easily recoverable by a computer program. Generally, the signature is a number which identifies the owner of the image. The locations in the image where the signature is embedded are determined by a secret key. Doing so prevents possible pirates from easily removing the signature. Furthermore, it should be possible to retrieve the signature from an altered image. Possible alternations of signed images include blurring, compression and geometrical transformations such as rotation and translation. These alterations are referred to as attacks. A new method based on amplitude modulation is presented. Single signature bits are multiply embedded by modifying pixel values in the blue channel. These modifications are either additive or subtractive, depending on the value of the bit, and proportional to the luminance. This new method has shown to be resistant to both classical attacks, such as filtering, and geometrical attacks. Moreover, the signature can be extracted without the original image.

Digital watermarking of color images using amplitude modulation

Keywords: LTS1 Reference LTS-ARTICLE-1998-011doi:10.1117/1.482648View record in Web of Science Record created on 2006-06-14, modified on 2016-08-08

Dynamic approach to visual data compression

This paper presents the Swiss Federal Institute of Technology (EPFL) proposal to MPEG-4 video coding standardization activity. The proposed technique is based on a novel approach to audio-visual data compression entitled dynamic coding. The newly born multimedia environment supports a plethora of applications which cannot be covered adequately by a single compression technique. Dynamic coding offers the opportunity to combine several compression techniques and segmentation strategies. Given a particular application, these two degrees of freedom can be constrained and assembled in order to produce a particular profile which meets the set of specifications dictated by the application. The basic principles of this approach are presented together with the data representation system. The major characteristics of dynamic coding are reviewed, along with simulation results showing the performance of such an approach in a very low bit-rate video coding environment.

Shape compression of moving objects using context-based arithmetic encoding

This paper deals with an approach to the compression of 2-D shape information. Specifically, the approach utilises a block-based context-based arithmetic encoding method to exploit both spatial and temporal redundancy in sequences of shapes. The method is shown to be highly efficient in comparative tests. In addition, it is demonstrated that context-based arithmetic encoding is easily extended for the coding of interlaced shape sources and for encoding any source in a scalable and/or error resilient manner. The application of the technique is in the compression of video object shapes within the framework of object-based video coding. The proposed algorithm is part of the MPEG-4 video specification.

Efficient compression of non-manifold polygonal meshes

We present a method for compressing non-manifold polygonal meshes, i.e. polygonal meshes with singularities, which occur very frequently in the real-world. Most efficient polygonal compression methods currently available are restricted to a manifold mesh: they require a conversion process, and fail to retrieve the original model connectivity after decompression. The present method works by converting the original model to a manifold model, encoding the manifold model using an existing mesh compression technique, and clustering, or stitching together during the decompression process vertices that were duplicated earlier to faithfully recover the original connectivity. This paper focuses on efficiently encoding and decoding the stitching information. By separating connectivity from geometry and properties, the method avoids encoding vertices (and properties bound to vertices) multiple times; thus a reduction of the size of the bit-stream of about 10% is obtained compared with encoding the model as a manifold.

Shape representation and coding of visual objets in multimedia applications — An overview

Emerging multimedia applications have created the need for new functionalities in digital communications. Whereas existing compression standards only deal with the audio-visual scene at a frame level, it is now necessary to handle individual objects separately, thus allowing scalable transmission as well as interactive scene recomposition by the receiver. The future MPEG-4 standard aims at providing compression tools addressing these functionalities. Unlike existing frame-based standards, the corresponding coding schemes need to encode shape information explicitly. This paper reviews existing solutions to the problem of shape representation and coding. Region and contour coding techniques are presented and their performance is discussed, considering coding efficiency and rate-distortion control capability, as well as flexibility to application requirements such as progressive transmission, low-delay coding, and error robustness.RésuméLes besoins en matière de fonctionalité orientées objet dans les communications audioviduelles sont apparus récemment avec l’émergence d’application nouvelles telles que la video conférence, les vidéophones et la vidéo interactive. Alors que les normes de compression existantes traitent la scène audio-visuelle au niveau de la trame, il est maintenant nécessaire de traiter séparément les différents objet présents, permettant ainsi une transmission échelonnable aussi bien que la recomposition de la scène par le receveur. La future norme MPEG-4 a pour but de proposer des outils de compression offrant ces nouvelles fonctionalités. Contrairement aux standards orientés trame existants, les schémas de codage correspondants doivent intégrer l’information de forme. Cet article présente un certain nombre de solutions existantes au problème de la représentation et du codage des formes. Différentes techniques de codage deformes et de contours sont présentées et leurs performances sont analysées en considérant l’efficacité du codage et la capacité de régulation débit/distortion, ainsi que la flexibilité vis-à-vis des besoins de l’application, tels que la transmission progressive, le codage à court délai, et la résistance aux erreurs.

Scalable shape representation for content based visual data compression

Two major classes of shape coding methods are reviewed, namely bitmap coding and contour coding, and in particular their scalable extensions. In addition to their absolute compression efficiency, we analyze their performance in the framework of a complete image/video coding scheme, and show that they bring complementary functionalities depending on the targeted application.