I did the following experiment. There is a huge plane of the white color and a point like light source 1m above. The camera is very far away (I used the orthographic luxrender camera). It is easy to get the analytic solution for this setup. The visible intensity distribution across the plane is given by (1+x^2)^(-3/2), where x is proportional to the distance from the light source. I rendered the image with bidir and sppm methods and used linear tonemapping with gamma=1. As expected bidir gives right answer and sppm doesn't. The difference for sppm is in the power, instead of -3/2 we get -2. Maybe it can give someone a hit where to look for this extra 1/2 power in the code.
Rom1 wrote:I remember a fix from guibou few month ago
17d0510aeb9a) SPPM: fix normalisation issue
guibou wrote:Could you do the same experiment with sppm but changing the number of photon per pass please ?
Vutshi wrote:EDIT: Ooops, something is emerging for 5M... Why does it make any difference?
Rom1 wrote:When the search radius is reduce ?
is there some kind of mechanism to "reset" the search radius ?
I use a mix material with 0.5% matte to have the sppm working on my glass product, and 150 as maxpath value.
At each pass I have a very small amount of chance to have interesting contribution with my specular path. So if I missed them in the first pass, do i have chance to find them on the other pass ? Or is there only a refinement of my existing contribution ?
guibou wrote:I'm not sure I fully understand your graph. What are the units of it ?
guibou wrote:About the test with a different number of photon per pass, It was because previously this was an influence, so I wanted to be sure it was not a regression introduced by late patches.
As far as i know, the difference of 50M may come from the bias introduced by so much photon per pass. It should disappears with a smaller starting radius.
guibou wrote:Is your plane having infinite extends ? (Or is the visible area convolved by the searching radius is still contained inside the plane ?) It may comes from boundary effect of the density estimation.
Ie, if your plane is 1*1 and your search radius is 1.5, you get a small part of your search radius which is outside the plane, so cannot gather light, so leads to less light.
But this is in contradiction with the 50M curve, because a bigger starting radius leads to more boundary effects hence to less ligh, and your 50M curve have more light than the 500K, if I understand correctly the graph
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