Portals with HDRI lighting?

[JohannesL]

Sorry if this has been covered already, couldn't find any post answering my question.

I'm trying to keep render times down for interiors with corners of rooms that are far from the windows, in other word a pain to get noise free. Thought portals could help me out, only to realize that portals actually makes things worse.

See attached image. Left one is with portals (plane normal facing inwards), and no glass in the windows. Right one is without portals. As you can see, the result is not visibly different, can't see any difference at all BUT, with portals, the render time actually increases with 24% (in this case).

Does portals not work at all with HDRI lighting, or what am I doing wrong here? When reading the diagram post about portals on this forum, it seems that portals would be a real life saver, but obviously it's the opposite.

[mbetke]

You may read this article. Its useable for Octane Render too: http://blog.maxwellrender.com/tips/phot ... r-renders/

Using Cooherent ratio, lowrering Gi-samples to 5 and higher path termination power drops down the render times. last but ot least you could drop the glossy/difuse depth but not to much because glass will get dark then. An external denoiser helps a lot too. I use Neat Image. Saves me 2000-3000 samples on some scenes.

I never use portals. I think it is broken or so.

[Goldisart]

then why do we need the portal ?!?!?!?

[mbetke]

You don't need a portal. As far as I understand it is just a tool to guide light. But I never investigated if it drops render times so much. For me a come along very fine without.