Dulce B. Ponceleon

Preconditioners for indefinite systems arising in optimization

Methods are discussed for the solution of sparse linear equations

Content awareness in a file system interface: implementing the “pile” metaphor for organizing information

Ky = z

Primal-dual methods for linear programming

, where K is symmetric and indefinite. Since exact solutions are not always required, direct and iterative methods are both...

CueVideo: a system for cross-modal search and browse of video databases

The pile is a new element of the desktop user interface metaphor, designed to support the casual organization of documents. An interface design based on the pile concept suggested uses of content awareness for describing, organizing, and filing textual documents. We describe a prototype implementation of these capabilities, and give a detailed example of how they might appear to the user. We believe the system demonstrates how content awareness can be not only used in a computer filing system, but made an integral part of the users experience.

Tracking subspace representations of face images

Many interior-point methods for linear programming are based on the properties of the logarithmic barrier function. After a preliminary discussion of the convergence of the (primal) projected Newton barrier method, three types of barrier method are analyzed. These methods may be categorized as primal, dual and primal—dual, and may be derived from the application of Newtons method to different variants of the same system of nonlinear equations. A fourth variant of the same equations leads to a new primal—dual method.In each of the methods discussed, convergence is demonstrated without the need for a nondegeneracy assumption or a transformation that makes the provision of a feasible point trivial. In particular, convergence is established for a primal—dual algorithm that allows a different step in the primal and dual variables and does not require primal and dual feasibility.Finally, a new method for treating free variables is proposed.

A real time software-only H.261 codec

The detection and recognition of events is a challenging problem in video databases. It involves cross-linking and combining information available in multiple modalities such as audio, video and associated text metadata. CueVideo is a system designed for the discovery and recognition of specific events called topics of discussion through advanced video summarization and cross-modal indexing. It supports search for relevant video content through several modes of video summarization including storyboards, moving storyboards and time-scale modified audio summarization. It also enables the recognition and indexing of topical events through cross-model search of audio and video content based on text and image queries respectively.

Performance of real-time software-only H.261 codec on the Power Macintosh

A small collection of successive frames of a video sequence of a talking person defines a subspace whose dimensionality is much less than the size of one frame. Any face image drawn from the video sequence can be associated with a subspace defined by itself and the frames close to it in time. Representing faces in their associated subspaces can reduce the complexity of further processing that is done on the faces. For a slowly varying video sequence, the subspace that a sliding window of frames will define will also be slowly varying. We describe one technique for efficiently tracking slowly varying subspaces. The method builds and updates the subspace of face images using an adaptation of the Gram-Schmidt orthogonalization procedure. We outline techniques for reducing the dimensions of the subspace while keeping the MSE small, and present one measure for dealing with the perceptual quality of the reconstructions. Finally, we consider subspace tracking in the context of video compression.<<ETX>>

Transform coding for low-bit-rate applications

Video and audio conferencing over networks is becoming increasingly popular due to the availability of video and audio I/O as standard equipment on many computer systems. So far, many algorithms have concentrated on playback only capability. This generally results in unacceptable real-time performance with respect to latency and encoder complexity. We describe a software-only system that allows full duplex video communication. For our analysis and implementation we chose a DCT based method that uses motion estimation and is modelled on the CCITT H.261 standard. We discuss the algorithm, followed by an analysis of the computational requirements for each major block. The results presented show the effect of computational simplifications on signal to noise ratio and image quality. We also examine the processing needs for full resolution coding and project when this will become available.

System for directing relevance-ranked data objects to computer users

The widespread use of teleconferencing as a major role of remote communication has until now been stymied by the costs associated with deploying specialized hardware required to achieve good performance. Another constraint has been the incompatibility among the various systems that are available. These facts coupled with the rapid increase in computational power available on desktop systems convinced us of the value of a standards-based software solution. Leveraging the performance of the PowerPC RISC processors, we have implemented a software-only realization of the CCITT H.261 video coding standard. In this paper, we will discuss the performance of the software codec which has been optimized for the Power Macintosh 8100. Over ISDN and loaded Ethernet, the codec provides good visual quality in terms of spatial quality and frame rate over a range of bit rates (less than 64 to 384 Kbits/s). We will outline the structure of the software codec and discuss its performance.

System for ranking the relevance of information objects accessed by computer users

Low bit rate image coding at 10 kbit/s and less is a difficult problem and does not appear possible with the current generation of block transform based methods. Current research efforts center around the use of transforms with less objectionable artifacts such as wavelets or model based methods. We examine a method that is transform based but captures specific features of the image to be represented. The transform uses principal component analysis to generate a basis set specific to the particular class of images to be coded. We present results from a transform designed for use in a `talking head sequence. Significant improvement in reconstructed quality is shown when perceptual weighting is used in generating the basis set. The appendix includes details of computationally efficient methods for deriving the basis set as well as a description of the weighting method.