Path: utzoo!utgpu!watmath!clyde!att!rutgers!mailrus!cornell!uw-beaver!uoregon!markv From: markv@uoregon.uoregon.edu (Mark VandeWettering) Newsgroups: comp.graphics Subject: Re: raytracing in || (supersampling speedup) Keywords: 4 rays per pixel Message-ID: <3266@uoregon.uoregon.edu> Date: 30 Nov 88 17:31:13 GMT References: <9700001@datacube> <3148@uoregon.uoregon.edu> <1351@umbc3.UMD.EDU> <5263@cbmvax.UUCP> <5548@thorin.cs.unc.edu> <7034@watcgl.waterloo.edu> Reply-To: markv@drizzle.UUCP (Mark VandeWettering) Organization: University of Oregon, Computer Science, Eugene OR Lines: 32 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. And also super-ungood. Better than not doing it, but hardly satisfactory. You may as well do it as a post process. The problem really arises from sampling on a regular grid. You can have drop outs (small objects dissappear) and other problems as well. >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). Correct. The fact that you have gained no more information about the picture (haven't cast more rays) means that you aren't really going to improve on the quality of the imae over the unfiltered case. >The technique used by Sweeney in 1984 (while here at Waterloo) compares the four >pixel-corner rays and if they are not in close agreement subdivides the pixel. >The recursion terminates either when the rays from the subpixel's corners are >in close agreement or when some max depth is reached. The subpixel values are >averaged to form the parent pixel intensity (though a more general convolution >could be used in gathering up the subpieces). This is common, and nice. I have been planning on doing an adaptive antialiaser for my raytracer, but.... ahh....to have free time again. Mark VandeWettering