QMC | External illumination only, small GI portals

GI Bounces: 3, GI-Gamma 2.2, Geometry AA
Scenario: External illumination only, small GI portals

The illumination of the sky material had to be 10 times higher to compensate the brightness for the small amount of light coming in.

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This is a good proof that scenes with small but intense lights (the GI portal in this case) need way higher settings which is why 4096 samples worked good for the previous pic but not sufficiently for this one.
By making the GI Portals smaller on one hand and increasing the brightness from outside on the other hand this scene carries a much larger contrast in it. Thus chances of a shadingpoint sampling very different brightness values increases giving an overall grainier look. To smoothen it out even more samples would be necessary. (Rendertimes getting out of hand now but we'll get to the optimization later)
Also the Gamma2.2 setting comes more into play here in darker corners in terms of more grain since this scene is generally darker.