Clamp Indirect 0:
Clamp Indirect 10:
Setting it to 0 by default would really solve a lot of unintended issues (I’m constantly getting reports about that).
Here’s the difference between the previous two renders:
In my opinion, default clamps, both direct and indirect, and filter glossy should be set to zero. Yes, it may cause fireflies, but otherwise it may lead to more horrible results, for example manipulation with really bright light sources, which power exceeds clamp values, will have no difference in the viewport. Some old demo files have low clamp values.
This problem is more confusing for a user to identify or describe, than just handling fireflies. Low clamp values may be described as “I do everything I can and nothing happens to my lights”, while fireflies are googled easily with a simple and obvious search request “blender bright pixels”.
And with introduction of nishita sky this issue of preset clamp values comes back in a new flavour. As I figured out in my personal tests, nishita sun disk brightness is roughly equal to sun power of 100, and the sky is dimmer by one order of magnitude, and both effectively make default clamp values absolutely useless.
Personally I tend to just turn off clamping (but not filter glossy) anyways. Since the denoisers are in, there’s also less reason for this.
@brecht if you think it should be more discussed then please let me know what the reasons are to keep the Clamp Indirect default value to 10 instead of 0, otherwise, here is the patch.
I think scenes where I actually had trouble with unclamped light before could still get away with far higher values as well. 10 is awfully low if it’s to be turned on by default at all.
The scenes where I saw it happening usually involved a very high brightness light source very close to some very light-colored material so basically a large amount of the light in the scene would be defined by this complicated indirect light. In that case it helps to set Indirect Clamping to something in the hundreds or thousands iirc. Definitely far higher than just 10.
So one option could also be to just way crank up that value.
But I think I’d prefer it to be off by default and then it should tell you in the tool tip “if you have a lot of fireflies try setting this value to something greater than 0. Start high, work your way down” or something.
FWIW the reason I’m less concerned about filter glossy is that this only is a hotfix of sorts for the difficult lightpaths a regular pathtracer can’t deal with anyway. Caustics, in so far as they appear at all, will look incorrect (or just a noisy non-convergent mess) anyway.
If Cycles did something cleverer with certain difficult paths (such as Reflective Diffuse Reflective paths), that option wouldn’t be needed, but as it stands it’s still necessary, I think.
