5.3 View Interpolation 5.1 the Back-buuer Algorithm 5.2 Radiosity Redistribution 4.3 Image Subdivision

An algorithm of hidden surface removal based on frame-to-frame coherence. In Post and Barth 25], pp. 261{273. stage. Furthermore, the algorithm is formulated for static scenes; to generalize it to scenes with moving objects, the trajectories of these objects must be known in advance, so images may be pre-rendered for diierent object locations. This would further increase the memory requirements. On the positive side, the time needed to interpolate an image is independent of the model complexity. Additionally, the entire model is not needed to compute the pixel motion vectors| only depth information is required. Therefore, the technique might also be used for walkthroughs of real environments photographed from several positions. The necessary depth information may be obtained by a depth-sensing camera or by photogrammetry. The back-buuer algorithm: An extension of the radiosity method to dynamic environments. A progressive ra-diosty approach to fast radiosity image generation. patch which radiates the most energy on the new object's center) is repeatedly found, its radiosity is shot to the patches on the new object, and the negative of its radiosity is shot to the patches in the new object's shadow (found using a shadow volume 24]). This continues until the most signiicant patch's radiosity is smaller than some threshold level. Finally, the radiosity changes found above are distributed to the rest of the scene by the usual progressive radiosity algorithm (slightly modiied to handle negative energies). Object deletion is handled similarly. A change in an object's position, geometry or surface properties is handled by deleting the object and re-inserting it with the new attributes. To handle changes in the model even before the updating of the radiosities due to previous changes has converged, the geometry changes in the scene must be maintained in a list. The list enable the algorithm to determine, for each patch whose radiosity has changed, the scene geometry relative to which the patch's old radiosity was calculated. This list is called a log in 12] and a geometry queue in 6]. The results of this technique show gradually diminishing inaccuracies in the calculated ra-diosities, compared to the converged values. George et al. reported 6.1{12.4 speedup, relative to progressive radiosity, for the addition of a new object, while Chen found 1.2{3.6 speedup for geometry changes and 1.1{21.8 speedup for luminance or reeectance changes. As mentioned at the beginning of Section 5, after the patch radiosities have been computed, walk-through sequences …