edwin@cwi.nl (Edwin Blake) (02/05/91)
In article <1991Feb1.082556.8553@agate.berkeley.edu> deadman@garnet.berkeley.edu (Ben Haller) writes: > What is involved in human perception besides physics??!? > ... but if the photons coming into a human eye >are the same for a real scene and for a computer-generated copy of that >real scene, how could the human possibly tell them apart? What else do you >think is involved? So. And when has any reproduction ever reproduced quantum mechanical reality for anything more complex than a single hydrogen atom? So what about a teapot? It takes Nature 24 hours to simulate a quantum mechanical day exactly. No computer is going to simulate the events on a medium sized pool table in less than the age of the Universe. In any realistic graphical simulation a great deal else is involved beyond physics and all of these things can only be understood by an appeal to human perception. E.g., 25 frames flickering 75 times a second, reduced contrast, smaller colour ranges, limited spatial resolution ... In the case of video the "photon reproduction" has been reduced to the discrete glow of three kinds of phosphors! So where is the physical reality now? Even perspective projection is only right from one single viewpoint. Yet all of us have the cultural training (thanks to the Renaissance) to note the picture frame and undo the distortion. This process becomes unconcious to such an extent that a movie screen truly appears to be a window on a world to many people. > Perfect simulation of reality is necessary if, for example, you want to >be able to go to a movie and *not* be able to tell your non-graphics-savvy >friends which parts of the movie were artificially generated and which >parts weren't. This view, that graphics needs physics, only physics and nothing but, is deep-rooted but wrong. (Physics needs graphics, but that is another story). I trace it back to the debate on faking vs. physical realism, that is, to Reeves vs. Greenberg -- to introduce a bit of controversy perhaps -- but see Comm. ACM vol 31 (1988) pp. 166-117 and 123-129,151 and also SIGGRAPH'87, pp. 116-117. I think we need a new catch phrase: Subjective Graphics (!), to emphasize the human orientation of the subject. "Subjective Graphics", because computer graphics depends for its effects more on Human Perception than on any Simulation of Physics. Subjective Graphics, if seriously pursued, will provide a theory of faking and be a fertile field for fast algorithms. Edwin Blake, edwin@cwi.nl CWI -- Centre for Mathematics and Computer Science, Department of Interactive Systems, Kruislaan 413, 1098 SJ Amsterdam, The Netherlands. Phone: +31 20 5924009