Estimation of point light source parameters for object-based coding

摘要

In this paper, the source model of moving rigid 3D objects of an object-based analysis-synthesis coder (OBASC) is extended from diffuse to non-diffuse illumination introducing the explicit illumination model of a distant point light source and ambient diffuse light. For each image of a real image sequence containing moving objects, first, shape and 3D motion parameters describing the objects are estimated assuming an ellipsoid-like smooth shape. Then, the illumination parameters are estimated by a fast iterative maximum-likelihood Gauβ-Newton estimation method. Typically, the illumination parameters converge after very few images close to the true ones. The accurateness depends on the amount of object rotation and the correctness of the shape assumptions. For a real image sequence showing a textured ball covering 20% of image area, rotating about 10 ° per frame, and illuminated by spot and ambient light, the extension of the source model reduces the model failures from 9.9% of the image area to 6.7%. In the area of model failures, the image synthesized from the source model parameters differ significantly from the real image. In this early experiment, source model parameters are coded losslessly. Since model failures are expensive by means of bit-rate, a significant reduction of bit-rate can be expected.