We consider the problem of camera pose estimation from a scene model obtained beforehand by a structure-from-motion (SfM) algorithm. The model is made of 3D points, each one of them being represented by its coordinates and a set of photometric descriptors such as SIFT, extracted from some of the input images of the SfM stage. Pose estimation is based on the matching of interest points from a test view with model points, using the descriptors. Descriptors having a limited invariance with respect to viewpoint changes, such an approach is likely to fail when the test view is far away from the images used to construct the model. Viewpoint simulation techniques, as ASIFT, have proved effective for wide-baseline image matching. This paper explores how these techniques can enrich a scene model by adding descriptors from simulated views, using either orthographic or pinhole virtual cameras. Viewpoint simulation permits pose estimation in situations where the approach based on the sole SIFT descriptors simply fails.

We are concerned about the problem of transmitting constant quality video over the B-ISDN. A gain in channel utilization is achieved when several variable bit rate video sources share a common ATM connection. To achieve such gain, the impact of cell losses on video quality degradation should be considered. Multi-layered video coding has been shown to tolerate more cell losses than non-layered video coding while maintaining negligible quality degradation. We exploit this cell loss tolerability in a multi-layered video coding scheme to improve multiplexing efficiency while preserving a constant video quality.

We present a rate control algorithm adapted to MPEG video coders ensuring that output conforms to the parameters of a leaky-bucket network access controller. The algorithm avoids unpredictable rate variations without the rigidity and systematic coding delay of constant bit-rate (CBR) coders, and makes possible resource provision for guaranteed quality of service. A relatively large burst tolerance parameter allows considerable scope for variation at GoP scale, and only restricts the natural rate when necessary to avoid long-term overloads. Possible multiplexing schemes are discussed distinguishing buffer provision for cell-scale and burst-scale congestion.