Quote - Maybe it's a development of True Ambience (and the background process involved in that, which I suspect is some variation of final gather).

Well thats why i said a "decent" IBL implementation ;-) TA is old, unefficient, doesnt work as it should, and it produces too much noise.

TA seems to work with the rays that are already calculated in the scene during render, which is kinda unefficient.. It's kinda like rays trying to act like fotons. It's about as similar to FG as it is to GI or Radiosity, which means it's basically just another variation on the same topic, but as significantly different from either FG or GI or Radiosity as those three are different from each other.

FG works in a seperate render pass with a seperate set of FG-rays/samples which behave in a manner that is optimized for the desired FG effect. TA just uses the rays that are already there from the direct illumination (which is why it's hella noisy).

Lets let a real life example sketch the contrast:

In Mental Ray you rarely need to render with more then 500 FG samples for your entire scene.

In Bryce you can render your TA scene at 512 samples per pixel (!!) and STILL end up with a noisy image.

When using GI in you dont calculate Rays but Photons, which is apparently quite a different thing in renderland. Photon counts needed for GI can run into millions when scenes are more complex, so in that aspect the amount of samples is in less of a contrast compared to bryce's TA, but unlike TA rendering you can play around with photon radii and the way photon samples blend etc. etc. which allows u to reduce noise significantly. 

Most significantly better part about GI though is that it is (just like FG) calculated seperately from your raytracing passes and stores it's information in photon maps. Now once you've set up the right amount of fotons to represent the scene's complexity and calculated your photon map you can still tweak the radii and accuracy of the photons WITHOUT any need to rebuilt your photonmap! Which basically saves you lots of rendertime.

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