Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!cornell!batcomputer!itsgw!imagine!rpics!kyriazis From: kyriazis@rpics (George Kyriazis) Newsgroups: comp.graphics Subject: Re: raytracing in || (supersampling speedup) Keywords: 4 rays per pixel Message-ID: <1899@imagine.PAWL.RPI.EDU> Date: 30 Nov 88 17:48:55 GMT References: <9700001@datacube> <3148@uoregon.uoregon.edu> <1351@umbc3.UMD.EDU> <5263@cbmvax.UUCP> <5548@thorin.cs.unc.edu> <7034@watcgl.waterloo.edu> Sender: news@imagine.PAWL.RPI.EDU Reply-To: kyriazis@turing.cs.rpi.edu (George Kyriazis) Organization: RPI CS Dept. Lines: 41 In article <7034@watcgl.waterloo.edu> awpaeth@watcgl.waterloo.edu (Alan Wm Paeth) writes: >In article <5548@thorin.cs.unc.edu> brown@tyler.UUCP (Lurch) writes: >> >>From what I understand, the way to achieve 4 rays per pixel is to sample at >>vertical resolution +1, horizontal resolution +1, and treat each ray as a >>'corner' of each pixel, and average those values. This is super cheap compared >>to sampling at twice vertical and horizontal. > >This reuses rays, but since the number of parent rays and number of output >pixels match, this has to be the same as low-pass filtering the output >produced by a raytracer which casts the same number of rays (one per pixel). > By sampling the image at points homogeneously spaced, ray tarcing becomes a point sampling technique, and inevitably you get aliasing effects. You can stransform there sample points into gaussian distributions, sampling somewhere inside the pixel and weighting the color of the pixel accordingly. Since this has a randomness effect into it, the eye does not perceive it as aliasing but as noise. By taking more that one sample per pixel, you actually spread out the gaussians merging them with the rest of the pixels. That merging gives a continuity of color. That technique was described in a paper by Rob Cook (I don't rememeber the title). >This approach means that the subpixel averaging takes place adaptively in >regions of pixel complexity, as opposed to globally filtering the entire >output raster (which the poster's approach does implicitly). Unfortunately I always have to take several samples per pixel :-( > > /Alan Paeth > Computer Graphics Laboratory > University of Waterloo George Kyriazis kyriazis@turing.cs.rpi.edu kyriazis@ss0.cicg.rpi.edu ------------------------------