Frédéric Jordan

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

Using fractal compression scheme to embed a digital signature into an image

With the increase in the number of digital networks and recording devices, digital images appear to be a material, especially still images, whose ownership is widely threatened due to the availability of simple, rapid and perfect duplication and distribution means. It is in this context that several European projects are devoted to finding a technical solution which, as it applies to still images, introduces a code or watermark into the image data itself. This watermark should not only allow one to determine the owner of the image, but also respect its quality and be difficult to revoke. An additional requirement is that the code should be retrievable by the only mean of the protected information. In this paper, we propose a new scheme based on fractal coding and decoding. In general terms, a fractal coder exploits the spatial redundancy within the image by establishing a relationship between its different parts. We describe a way to use this relationship as a means of embedding a watermark. Tests have been performed in order to measure the robustness of the technique against JPEG conversion and low pass filtering. In both cases, very promising results have been obtained.

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.

Fast hybrid block/region-based algorithm for object tracking

This paper presents a technique to segment and track a region of interest in a video sequence. The presented technique starts with a spatio-temporal contour extraction. This contour extraction is performed by mixing information from a spatial gradient and a temporal differentiator. A block segmentation is then applied on the image, and within each block the contour part is approximated by a straight line segment. These contour approximations are then further quantized by a vector quantization technique, using a predefined codebook. In order to close and smooth the region of interest contour, an interpolation based on hermite polynomials is performed on the set of discrete quantized contour parts. Finally, the tracking process is performed using an addition-removal of blocks containing contour parts by testing their possible belonging to the polynomial contour. This testing is done by using a blurred version of the polynomial contour in order to be able to track deformations in the object. The initial guess for tracking is given manually by an end-user.