Help setting up PMC scene

[matej]

Hi guys!

I would like some advices on how to set up good quality PMC. I mainly avoided PMC the whole time, because I got (have) the impression PT produces less noise in a shorter time. I have compared the two with this renders:



Overall the PT render is better. PMC has more (blotchy) noise, random fireflies and noise (caustics??) on metal areas. SSS is just a tad better with PMC.

Any suggestions how could I improve the PMC settings? Ideally I would want to get the same noiseless DOF quality as PT, but without fireflies and at comparable render times.

[roeland]

The PMC settings look fine to me, I don't know why PMC is produces these fireflies. How is the scene illuminated?

You can expect that for some scenes pathtracing will work better, for others PMC will work better.

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Roeland

[matej]

Yes, I'm puzzled too about the fireflies. I did some more tests with PMC settings, to try to get a good solution for this scene. In this new setup the fireflies are even more expressed (the lighting is a bit more harsh - most of it comes from emitters). PT still fares better (even 2x better in render times), except in SSS noise where PMC does it better. I compared default settings with changes to PMC settings (those underlined in red were changed for the particular test):



I used a HDRI with low power, but the main lighting comes from a simple plane texture emitter from the left side and from the "candle flame" texture emitter. The candle material is a mix between diffuse & glossy, others are glossy. There is a glass plane in the picture frame (shouldn't matter).

I'm aware that PMC is not supposed to be the best solution for all problems. I'll have to investigate a bit more with different scenes, to get a better picture of PMC (haven't used it much till now)

[matej]

Another test with better results for PMC:



What I did here (compared to my second post) is:

- move the emiting plane 2x far and scale it 2x
- simplified the "flame" emitter geometry

Rendered to 512 samples all of them. PT is still better overall.

[matej]

I know now what was producing so many fireflies in the tests in my second post - I had a portal intersecting an emitter material. Sometimes I use portals to "remove" objects from the scene.

[roeland]

Did you uncheck the "enabled" checkbox on those portals?

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Roeland

[matej]

Did you uncheck the "enabled" checkbox on those portals?

No, that option was checked. If I disable it, then it does not produce fireflies, even if the geometries intersect, nice

What is the meaning of that option anyway? I dont see it mentioned in the manual.

[roeland]

If not checked the geometry is not treated as a portal anymore but just as fully invisible geometry.

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Roeland

[matej]

I see, thanks!