maxxxmodelz opened this issue on Jun 07, 2012 · 636 posts
bagginsbill posted Sun, 01 July 2012 at 9:04 PM
Quoting myself from other threads due to lack of time.
IC is the source of artifacts in the white chair.
Quotes follow:
IDL with Irradiance Caching (IC) is a stochastic approximation. (Look up stochastic if it's not familiar. Without that word I'd have to say a hundred things.)
The more you rely on IC (for speed) the more error you should expect in the lighting. Since the error is stochastic, it's not the same error from one render to another.
Therefore, even if you're doing a still image, two renders in a row will not be the same.
IDL + IC contains artifacts, by definition. These artifacts will move in random ways, even if you change nothing.
It is possible to implement deterministic pseudo-randomness (repeatable, but still unpredictable), which would still have errors but they would not move around. I don't know why Poser is not implemented this way.
If you don't want stochastic approximation artifacts, set IC = 100. Prepare for very long renders.
IBL+AO is also stochastic.
The IC value represents the desired accuracy, which is inverse to how much the cache is used. When IC=100, you're saying you want 100% accuracy, which means 0% use of cached values. Lower values use the cache more, accepting less accuracy in exchange for greater speed.
When you lower the IC value, you're accepting huge inaccuracies, which predominantly express themselves as missing shadows in a lot of places. Which is another way to avoid shadows, right? So in a sense a very low IC does improve consistency, because it consistently fails to react to occlusion. This does not contradict anything I said, but does provide an alternative explanation to why you thought your results contradict what I said.
Basically you turn turn off small-scale occlusion when IC is set very low. If you elide all but the biggest and most obvious shadows, then yes it is very consistent. However, highly inaccurate.
Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)