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> It's not meaningless at all, it's a close approximation of light absorption that happens to be measurably and perceptually indistinguishable from the physical

> It's not meaningless at all, it's a close approximation of light absorption that happens to be measurably and perceptually indistinguishable from the physical spectral absorption process, save for a few corner cases that are being worked on. If the result is 99.9% accurate physically, and 100% perceptually indistinguishable to humans, then it's a valid predictive physical model. > Subsurface scattering, for example, is modeling absorption more phyically, and replacing the simple multiplication with a simulation process, because we now have the computational power to do so. Surely everyone has to accept that whatever we do here is always going to be an approximation to arrive at a similar looking result to reality that won't be following what's really going on to a low level? We're not going to be able to model individual photons, atoms, electrons, quantum effects etc. so it's always going to be an approximation/abstraction. The goal should be whether it looks indistinguishable not if it is indistinguishable.

dahart 9y ago
Yes absolutely - If the metric for realism isn't perceptually indistinguishability, then we might need to rethink what the word "realism" means. I don't think anyone here is arguing against that though. I think @sillysaurus3 is saying that the approximations we make in our simulations will always have large errors that cause visible artifacts, that the unrealistic CG will always be perceptually distinguishable from real video. Modeling individual photons is happening in research rendering code, just not on the same scale as reality. Path tracing renderers using spectral colors & modern shading models are getting there. We might use a few million photons at a time to render a room instead of the quadrillions that reality uses. People are thinking about modeling individual atomic interactions, electrons, and quantum effects. There might even be experimental renderers already that do this, I wouldn't be the least bit surprised. If not, it'll happen pretty soon. BTW, there is no super distinct line when you're talking about the simulation of atomic interactions and electromagnetism, even for the 100% full simulation of all subatomic particles individually. I'm not sure that's possible yet, but I am pretty sure its unnecessary for "realism" in the context of film making. There are shading models that account for electromagnetic & atomic effects. Physically based shaders obey Helmholtz reciprocity and energy conservation, among other things. Some of them account for multiple atomic level reflections. This is a statistical way of accounting for atomic effects, just like color multiplication is a statistical way of accounting for spectral absorption. New shading models every year are accounting for smaller and smaller margins of error from the previous approximations. Check out this crazy shading model from 25 years ago that is based on electromagnetism theory and accounts for atomic level shadowing & masking: http://www.graphics.cornell.edu/pubs/1991/HTSG91.pdf http://www.graphics.cornell.edu/pubs/1991/HTSG91.pdf I think this paper still wins the award for most equations in a Siggraph paper. It didn't win any realism awards though. :P

dahart 9y ago

Yes absolutely - If the metric for realism isn't perceptually indistinguishability, then we might need to rethink what the word "realism" means. I don't think anyone here is arguing against that though. I think @sillysaurus3 is saying that the approximations we make in our simulations will always have large errors that cause visible artifacts, that the unrealistic CG will always be perceptually distinguishable from real video. Modeling individual photons is happening in research rendering code, just not on the same scale as reality. Path tracing renderers using spectral colors & modern shading models are getting there. We might use a few million photons at a time to render a room instead of the quadrillions that reality uses. People are thinking about modeling individual atomic interactions, electrons, and quantum effects. There might even be experimental renderers already that do this, I wouldn't be the least bit surprised. If not, it'll happen pretty soon. BTW, there is no super distinct line when you're talking about the simulation of atomic interactions and electromagnetism, even for the 100% full simulation of all subatomic particles individually. I'm not sure that's possible yet, but I am pretty sure its unnecessary for "realism" in the context of film making. There are shading models that account for electromagnetic & atomic effects. Physically based shaders obey Helmholtz reciprocity and energy conservation, among other things. Some of them account for multiple atomic level reflections. This is a statistical way of accounting for atomic effects, just like color multiplication is a statistical way of accounting for spectral absorption. New shading models every year are accounting for smaller and smaller margins of error from the previous approximations. Check out this crazy shading model from 25 years ago that is based on electromagnetism theory and accounts for atomic level shadowing & masking: http://www.graphics.cornell.edu/pubs/1991/HTSG91.pdf http://www.graphics.cornell.edu/pubs/1991/HTSG91.pdf I think this paper still wins the award for most equations in a Siggraph paper. It didn't win any realism awards though. :P