Unified Sampling + FG for Rendering Interiors?

Discussions about rendering in SOFTIMAGE©
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Unified Sampling + FG for Rendering Interiors?

Post by shushens » 11 Jun 2014, 22:58

After a long leave from hobbyist CG activities, I wanted to take XSI out for a spin again. I suppose I will not have to worry about keeping up with new feature for too long :p =(( But anyway, after being heckled by the importon + FG problem, I started wondering about unified sampling. I do not understand how lighting is supposed to look 'natural' with it, but I guess that is also a part of the question.

So I have a real simple scene here:
I am using the river road HDR+LDR set to light it. I have set up the reflection/refraction and visible background with my pass like so:
This contributes nothing to the FinalGathering. I have used the low resolution HDRI with the user_ibl_env shader with the following settings:
I have tried to match my render options closely to Nox's, as mentioned here.

And I have gotten a really grainy test render, like so:


So, I am in need of some education here. What are my options? I am not entirely sure what FG is doing here. Should I try to use GI still? Raising area light samples to 15x15 or 20x20 shows marginal change in the noise level. Raising ibl samples slows the render down drastically.
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Re: Unified Sampling + FG for Rendering Interiors?

Post by Kzin » 25 Jun 2014, 23:50

user_ibl is a pure brute force ibl lighting solution which means there is no precompute stage which bakes information of the hdr to make the ibl lighting faster. better choise would be to use builtin_ibl thru string options if you have xsi 2015.

as a general note, lighting an interior thru an ibl light is not a good idea because, like you wrote, the performance hit to get nice and clean result is really big.

best way is to go with portal lights without an ibl light. place them in your windows and lit your room with these lights. put one hdr in the envslot and let the portal lights do the rest.
and fg for indirect should give you good results.

and if you are using an ibl light mental ray will not use fg rays from environment because that would double the light energy which is wrong.