Noisy Portals

[leandrooliveira]

Hi everybody!
The goal of using Portal Lights is get less noise in a indoor scene, right?
In my tests, it´s happening the opposite.
I´m using Blender 2.91.2.
Without and with portals, respectively:

[CarlG]

Well, the purpose is to guide rays towards a direction it is expected to find skylight/hdri (not sunlight). So it’s works best for small openings and skylight ports as a source of illumination, not for massive windows on multiple walls that uses translucent materials, sunlight, and small interior lights as well to mess things up. Direct sunlight on a bright floor, those spots aren’t a real competitor. In that situation, by random chance it is likely to find a lightsource anyway.

Portals are just a tool in your arsenal. If you find they makes things worse, then just don’t use them. It’s not a “it’s supposed to… they lied…” Now, I have the freedom of choice, and I usually render out interior lights (sometimes groups of lights) in isolation and add them together after. If a sharp intense sunlight is problematic, I reduce its strength and increase its size to make it more cloudy, or go for a dimly lit evening outside with no sun at all. Combining light sources and light sizes can really make the noise situation unbearable, and rendering out in passes is the solution.

[leandrooliveira]

Thank you, Carl! I´ll follow your advice. Thanks again!

[YAFU (English is not my native language)]

Portals stopped being very useful since the default settings of Multiple Importance Sampling changed in Blender:

Blender 2.8 Cycles rendering with portals

Just trying to understand why when Portals was implemented in 2.75, nobody doubted the advantages of this with respect to the lower noise (no lower render time). The advantage of Portals was clear in many user tests, obtaining much less noise. But then in new versions of Blender some users began to question the advantages of Portals in some interior scenes. The think is that in 2.75 default scenes were set in World tab by default: Settings > Multiple Importance=OFF (Map Resolution=256 if you en…

You will notice the noise reduction mainly when Multiple Importance Sampling=OFF (World tab > Settings > Surface > Sampling=None), or with low Map Resolution values.
And less noise reduction doesn’t always mean less render times with portals. Actually, nowadays I’m not sure if portals is useful.

[leandrooliveira]

Hi YAFU. Thanks for your answer. I agree with you, but I think, Portals will be more efficient in some cases. For example, take a look on the example scene test made by moony:

Blender 2.8 Cycles rendering with portals

Portals is definitely working in 2.8. I created a very difficult scene for a path tracer (a camera obscura). The only light in this scene is the environment HDRI that is leaking through the very small pinhole window on the right. This is the difference between portals and no portals - 500 samples: [untitled] [untitled2]