[alkonaut]

This. Doing “physical” SSS means shooting rays stochastically into the medium (skin, milk, marble) and having them bounce around inside, emerging at a random location, but more likely close to where it entered.

That type of tracing will simply not produce a reasonable result in a reasonable time. You have to cheat.

[berkut]

That's not completely true - at least in the VFX industry we've been doing brute-force SSS (with multiple scattering) for more than two years now in some cases. Yeah, it can be slow depending on the MFP, but it's usable...

Cheats like Dipole/Dwivedi are still used when they can be, but they often have artefacts and aren't completely correct, so they're starting to be avoided now.

[pixel_fcker]

Dwivedi is brute force. It’s just a sampling strategy.

[berkut]

True, but it's biased, which still causes trouble with some edge cases, depending on how/where you bias towards - biasing towards point-of-entry isn't always better than not biasing depending on where the lights are, and it's cumbersome to set up for artists (depending on where you bias towards).

[alkonaut]

Interesting, any particular renderers that do this?