Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!sdd.hp.com!spool.mu.edu!snorkelwacker.mit.edu!bloom-beacon!eru!hagbard!sunic!mcsun!hp4nl!charon!edwin From: edwin@cwi.nl (Edwin Blake) Newsgroups: comp.graphics Subject: Viewer-Centered Graphics (nee Psycho-, nee Subjective-,nee Turing Test) Summary: Graphics IS more than physics Keywords: perception, perspective, Leonardo, realism, physics Message-ID: <3118@charon.cwi.nl> Date: 6 Mar 91 09:44:22 GMT References: <91Feb20.131305est.6899@neat.cs.toronto.edu> Sender: news@cwi.nl Organization: CWI, Amsterdam Lines: 52 Soft sciences argue endlessly about terminology to the disgust of (us) physicists. To continue the tradition, this note is about a viewer- centered (centred?) approach to computer graphics -- psycho-graphics being too scientific/Hitchcock like -- one wants room for both art and science in graphics. The discussion was, as you recall, about physics not providing the sole underlying basis for graphics. A dismissive definition of realism in graphics is "like a photograph". In an overblown form this even becomes `the Turing test for computer graphics'. Shall we agree that perspective projection lies at the heart of such realism? This `realism' has grave problems as many others have noted, at least since Leonardo da Vinci, if not Plato. Perspective as you or I normally see it is very seldom correct since one inevitably has to unscramble an off-centre view (head-mounted displays or peepholes of anamorphic art are exceptional). Yet the realism of photographs is taken as unproblematic enough to become the definitive example of realism. Please note: this not an attack on physics, photographs or perspective or anything. I am trying to provide a lever for breaking loose fixed ideas. The fact is that that off-centre perspective view IS realistic, i.e., convinces us, the viewers, that it is a window on a scene in some environment. But it also enables us to adopt other encodings of perspective. Even with photography, alternative perspectives are available. David Hockney's joiners (composite photographs) provide a very good example. I reproduce an example of his work in my paper called "The natural flow of perspective: reformulating perspective projection for computer animation" Leonardo (1990), Vol 23, no 4, pp. 401-409 & Color plate A. I work these ideas out further in that. Seeing (perception) is more than just the retinal interface. A picture can quite legitimately directly address higher level cortical representations -- and in that sense one can get modern art which is more convincing (realistic) than `window'-art. Consider two planes flying overhead in parallel straight lines from one horizon to another. How do you `picture' their paths in your mind? Straight lines? Converging at one end only as in perspective?! Converging at both ends in some curvilinear fashion? (A related topic: what sort of metric does Cyberspace have?) Edwin Blake, edwin@cwi.nl Phone: +31 20 5924009 Centre for Mathematics and Computer Science (CWI) Department of Interactive Systems, Kruislaan 413, 1098 SJ Amsterdam, The Netherlands