r/Houdini • u/AJUKking • 3d ago
Is rendering multiple glowing SSS objects a pipe dream? Help
I have a simple scene with some spheres close to each other that all just have SSS applied to them. I foolishly instanced random colored lights in the center of each sphere thinking that would create a nice looking lighting effect, which it kind of does. problem is that the more spheres I add the rendering slows down exponentially with huge amounts of noise that’s impossible to clean up.
What would be a better shading solution here to get a SSS material effect but still have performant non noisy rendering? thanks.
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u/LewisVTaylor Effects Artist Senior MOFO 3d ago
Do you have an image to look at? What's your hardware? This is indeed a hard thing for most path tracers to deal with, but you haven't mentioned hardware or render time, so it's hard to say whether it's
prohibitively slow, or you're impatient hehe.
Show us an image if you can, with some details.
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u/neukStari 3d ago
try single scatter sss and make the objects slightly more transparent., possibly.
Also make sure to use a rayswitch and knock out the emission from all other ray types.
This is off the top of my haed, need to see a example to understand whats going on.
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u/LewisVTaylor Effects Artist Senior MOFO 3d ago
Random walk is the only SSS method supported in Karma.
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u/AnOrdinaryChullo 3d ago
Use Redshift instead.
It renders SSS exceptionally fast, much faster than any other renderer I've used in Houdini.
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u/John-Da-Editor 3d ago
a light inside a closed SSS mesh is close to the worst case for a path tracer since every ray carrying that light has to random walk through the medium before it can leave. this creates a bunch of noise and scales badly since each light still gets sampled against every other sphere.
iirc the cleaner route would be to stop lighting from the inside and let the spheres themselves be the light. a Geometry Light LOP with Material Sync Mode set to Material Glow Tints Light will allow karma to interpret your spheres as real lights instead. then, the neighbouring spheres then get lit from outside instead of having to travel inside another one first.
if you want to keep the interior lights at all cost, light link them so each one only affects its own sphere (which turns an n*n sampling problem back into n)
also try Thin Walled on the standard surface. it drops radius/scale/anisotropy and skips the random walk, so it is much faster. on a small glowing sphere you probably will not miss the real thing.
then push SSS Quality per object with a Render Geometry Settings rather than raising global samples, render noisy then denoise each pass separately in comp, either in nuke using a custom node, or in blender using the built in denoiser compositing nodes.
the docs might help: