binarycortex wrote:Dade, is there a way other than a small startradius or small alpha to get the tight caustics?
binarycortex wrote:Here are my findings when dealing with SPPM, can you confirm/deny these Dade.
1. To get the picture to clean up faster you need a larger start radius with a larger alpha. The defaults (startradius 2 and alpha 0.7) work pretty good for this. However it produces muted caustics.
2. For tighter caustics you need a small photon search radius (startradius of 0.1 and alpha 1.0), or a larger startradius and small alpha (startradius 2.0/1.0 and alpha 0.05/0.1).
3. If you use the small startradius of 0.1 with an alpha of 1.0 there will be a lot of noise and convergence is very very slow. This is because the photon search radius is so small that the photons don't overlap and won't flll in very fast.
binarycortex wrote:3. If you use a larger startradius of 1.0 and a smaller alpha of 0.1 it will converge slightly faster because there is more photon overlap but due to the small alpha it will become noisy and still take a long time to converge.
4. Larger startradius increases the photon pass time, but improves convergence at the cost of caustics. Conversely, a smaller startradius decreases photon pass time, but improves caustics at the cost of convergence time.
5. The alpha setting controls the eventual size of the photon search radius. Larger settings have better convergence rates, again, at the cost of caustics.
6. When dealing with a small startradius or an eventually small search radius due to a small alpha setting, more photons per pass is more efficient/better convergence rate. At the cost of the speed of the photon pass.
7. The speed of the eye pass is controlled by the size of the image.
binarycortex wrote:Other questions.
Does the search radius ever get reset to the startradius setting? If not it seems to me that this would help convergence.
binarycortex wrote:Is there any advantage to using hybridhashgrid over the hashgrid?
binarycortex wrote:Can you confirm that the kdtree lookupaccel option is currently non functional?
alpha must be less than 1 otherwise the search radius won't be reduced and the precision won't increase, if the value is too small the radius will shrink so fast that soon the probability of a photon hitting it will be negligible.
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