Automatic adaptation of a face model in a layered coder with an object-based analysis-synthesis layer and a knowledge-based layer

摘要

The topic of investigation was the extension of a generic object-based analysis-synthesis coder (OBASC) using the source model of ‘moving flexible 3D objects’ for the encoding of moving images at very low data rates to a knowledge-based coder in case scene-specific knowledge can be acquired. According to the coding concept, the OBASC describes and encodes each moving object of an image sequence by three parameter sets defining its motion, shape and surface color. The parameter sets of each object are obtained by image analysis. Using the coded parameter sets, an image can be synthesized by model-based image synthesis. The coder switches to a knowledge-based coder as soon as scene-specific knowledge can be acquired. In the example given in this paper, an algorithm tries to detect faces within moving objects using template matching and feature extraction techniques. If a face is detected, the face model Candide is adapted to the image sequence and integrated into the 3D model object describing the moving object. Due to this knowledge of the scene, the head and shoulders scene can be more efficiently modeled and encoded. Furthermore, the knowledge of the scene contents is used for controlling the coder. When compared to OBASC, the knowledge-based coder reduces the bit-rate required for encoding head and shoulder scenes by 17%.