Reducing resolution loss in two-pass rendering by optimal view directions and display-surface partitioning

We describe a method for reducing the amount of aliasing or resolution loss in two-pass rendering for distortion and alignment correction of a projector-based display. Resolution loss is caused by the fact that the second rendering pass must resample the result of the first rendering pass, and the two procedures in general have sampling rates that vary differently. We show that for a flat display surface, it is possible to choose a viewing direction for the first-pass render so that its sampling-rate variations cancel with variations of the second-pass sampling rate. This means that the first-pass effectively samples the projector frame-buffer evenly, so an appropriate resolution for the first-pass render will provide uniformly low aliasing over the entire framebuffer. We also show that, for flat display surfaces, this choice of view direction can be combined with an appropriate first-pass intrinsics matrix to eliminate the need for a second pass. The resulting single-pass rendering algorithm is very similar to existing single-pass techniques, but has a few advantages that we discuss. For a non-flat display surface, relative sampling cannot be made perfectly uniform, but the optimal view direction for a best-fit plane provides an approximate solution when the display surface is almost flat. Although the approximation is poor when the display surface differs radically from a plane, we describe a technique for those cases, which automatically subdivides the display surface into partitions that are approximately planar. In common display-surface configurations, great improvements in rendering quality are obtained by using two or three partitions, which causes only modest rendering overhead.