Sushil K. Bhattacharjee

Towards second generation watermarking schemes

The digital watermarking schemes of today use pixels (samples in the case of audio), frequency or other transform coefficients to embed the information. The drawback of such schemes is that the watermark is not embedded in the perceptually significant portions of the data. We refer to such techniques as first generation watermarking schemes. In this paper we introduce the concept of second generation watermarking schemes which, unlike first generation watermarking schemes, employ the notion of data features. We propose a scheme based on point features in images using a scale interaction technique based on 2D continuous wavelets. The features are used to compute a Voronoi partition of the image. The watermark is embedded in each segment using spread spectrum watermarking. In the recovery process the same features are detected, and again used to partition the image. Then the watermark is extracted from each segment separately.

Compression tolerant image authentication

It is straightforward to apply general schemes for authenticating digital data to the problem of authenticating digital images. However, such a scheme would not authenticate images that have undergone lossy compression, even though they may not have been manipulated otherwise. We propose a scheme for authenticating the visual content of digital images. This scheme is robust to compression noise, but will detect deliberate manipulation of the image-data. The proposed scheme is based on the extraction of feature-points from the image. These feature-points are defined so as to be relatively unaffected by lossy compression. The set of feature-points from a given image is encrypted using public key encryption, to generate the digital signature of the image. Authenticity is verified by comparing the feature-points of the image in question, with those recovered from the previously computed digital signature.

Spatio-temporal segmentation based on region merging

This paper proposes a technique for spatio-temporal segmentation to identify the objects present in the scene represented in a video sequence. This technique processes two consecutive frames at a time. A region-merging approach is used to identify the objects in the scene. Starting from an oversegmentation of the current frame, the objects are formed by iteratively merging regions together. Regions are merged based on their mutual spatio-temporal similarity. We propose a modified Kolmogorov-Smirnov test for estimating the temporal similarity. The region-merging process is based on a weighted, directed graph. Two complementary graph-based clustering rules are proposed, namely, the strong rule and the weak rule. These rules take advantage of the natural structures present in the graph. Experimental results on different types of scenes demonstrate the ability of the proposed technique to automatically partition the scene into its constituent objects.

Orientation radiograms for image retrieval: an alternative to segmentation

For content based image retrieval using shape descriptors, most approaches so far extract shape information from a segmentation of the image. Shape features derived based on a specific segmentation are not suitable for images containing complex structures. Further, static segmentation based approaches are useful only for a small set of queries. In this paper we discuss the limitations of such boundary based shape features, and propose an alternative shape characterization technique based on orientation radiograms. A working image retrieval system based on this approach is described and sample results are presented for a full-image query.

Shot detection tools in digital video

Tools for detecting scene-changes in digital video are discussed in this paper. We describe tools useful for raw video-data as well as for MPEG-2 compressed bit-streams. Our approach for finding shot-boundaries in raw-data is based on comparisons of color histograms. We provide a comparison of several histogram-similarity measures that have been proposed by other researchers. We also propose the use of the cosine measure which outperforms the other measures discussed here. An algorithm for detecting shot boundaries in MPEG-2 compressed sequences is also described. It extends the work presented in [1] by processing P-frames and B-frames in addition to I-frames.

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.

Robust region merging for spatio-temporal segmentation

A region merging technique for spatio-temporal segmentation of scenes is presented. The proposed technique is a bottom-up method and expects an initial set of regions. These regions are compared on the basis of a similarity measure that integrates both spatial and temporal information. The unsupervised merging procedure is based on a weighted, directed graph that is updated dynamically. Two graph based clustering rules are presented. These rules are used to cluster regions into ensembles that represent meaningful objects present in the scene. Experimental results demonstrate the efficiency of the proposed method.

End-stopped wavelets for detecting low-level features

In this paper, we present two filters that simulate the behavior of biological end-stopped cells. Both are zero-mean filters, and are well located in the spatial as well as frequency domains, that is, these filters are admissible wavelets. We refer to the two filters as ES1 and ES2. The ES1 filter responds to ends of linear structures which have a specific orientation, and the ES2 filter responds to line- segments which have a specific orientation, and which have a length within a specific range. We show sample results to demonstrate the behavior of the proposed wavelets, and we also discuss the scale-space behavior of these wavelets briefly.

MPEG-4 video verification model : a solution for interactive multimedia applications

Keywords: LTS1 Reference LTS-ARTICLE-1998-005View record in Web of Science Record created on 2006-06-14, modified on 2017-05-10

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.