SSS is affected by Skylight. Shouldn't be.
Subsurface Scattering shows when it's hit with direct light. I.E:
In UE4 However, I've setup a scene using only a skylight, with flat lighting or ambient lighting, you should only see the diffuse color, not SSS. BUT:
SSS Intensity = 1
SSS Intensity = 10
Skylight influences the SSS way too much!
Engine version: 4.15.1 Repro Steps: 1. Create a new map. 2. Remove pre-baked lighting. 3. Remove directional light. 4. Add Skylight. 5. Add PPV, disable auto exposure (just so you see the issue easier). 6. Add a SSS material to a mesh and change the SSS multiplier.
SSS shouldn't make a visible difference while in flat ambient lighting condition.
I've entered a bug to see what the developers say regarding this issue. You can track and vote on the issue by following the link below.
answered May 09 '17 at 07:03 PM
So I asked around to confirm what you are saying, but Skylights are expected to affect Subsurface Scattering. This is because Skylights are still emitting photons whether direct or indirect, it makes no difference. Now, the actual phenomenon in real life outside of video games, the effect can be more visible and pronounced with direct lighting; however, in Unreal we are dealing with calculating emitted photons from all light sources. There is no difference between Skylight photons and Directional Light photons, and in reality there is no difference between direct and indirect light, its only a term we use in rendering since direct lighting is much easier to calculate.
I ran some tests on my end just to see for myself, and its outcome is clear and expected.
As you can see I used a completely black input for my base color. I also exposed the opacity input as this determines the amount of simulated light scattered to show the SS effect.
I also made sure to rebuild my lighting before viewing any of my results. You want to make sure you discard all the old indirect lighting.
Movable Skylight with Cubemap
Movable Skylight Captured Scene
In summary the results I am getting are expected because the Skylight is still emitting photons which is going to be picked up by the Subsurface Color. Thanks for taking the time to test the issue, but this is not a bug and just how subsurface scattering works with lighting in the engine.
answered Apr 27 '17 at 04:21 PM
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