experiments with using variance ontop of lowdiscrepancy

[Radiance]

Hey,

Last night i did some experiments with a modification to the lowdiscrepancy sampler.

My aim is to try to be able to render a decent resolution complex animation frame from a professional animation,
in an acceptable time for production.

I added a usevariance param to lowdiscrepancy, which resamples pixels based on variance.
This seems to do a good job.
I've still got some normalization issues as i'm opting to use per screen based normalization and therefore
need to prescale the contributions before splatting to the film.

I've managed to get down to 2.5 hours for a 1440x810 frame.

I think once my normalization is correct, and some more optimization/tweaks, together with an ICC build i should be able
to get this frame rendered to an acceptable output quality in 2-3 hours.

Once this is done i'd like to render a scene from 'elephants dream' as a test.

I've still to tweak the scene a bit, and adding some better variance construction estimate is also something to investigate.
the scene is not yet luxified so there's still no decent materials and some normal issues.

greetz,
radiance

[droid]

FYI... I've also dabbled with this concept and it does give EXCELLENT results for some scenes. Areas where the variance changes slowly and suddenly leaps up can be tricky (e.g. low probability specularly-viewed caustics) but I guess such effects are the last thing on people's minds when rendering animations.

Ian.

[zsouthboy]

I think you should shoot for a scene of BBB instead of elephant's dream, but I like the idea

[dougal2]

hmm, a scene is like a minute ? 30 frames/sec for 3 hrs? Plus export time ? hmm.... it might be ready for christmas

[Radiance]

hmmm, yeah well it's just a test eh,
we can render for a couple of weeks together with dade's machines or something.

i gues 20-30 seconds should be enough

if we render it a PAL resolution it should be 3x faster

Radiance

[Dade]

we can render for a couple of weeks together with dade's machines or something.

I'm working on the project of a deskside cluster built of diskless-headless nodes (only q6600+motherboard+2GB ram) with an hand-built case. The price of the single node is quite low (under 250 euro + VAT) so I'm playing with the idea to build a 4xNodes box (16 cores). I'm going to post some more information in the off topic forum soon

[Karl vom Berge]

Hey,
I added a usevariance param to lowdiscrepancy, which resamples pixels based on variance.
This seems to do a good job.

Great!

This is a classical adaptive sampling technique in Monte Carlo integration. However, adaptive sampling can introduce bias, depending on how you have implemented this. I just want to point that out.

Ref. Veach PhD thesis, chapter 2, section 2.7.1.

Adaptive sampling just based on variance is a great technique, but it is not perfect in the sense that on some areas of scenes you actually can allow for quite a lot of noise (e.g. highly textured objects, or very complex shadows (e.g. from tree canopies), generally: on high frequent signals in the image). Perceptual heuristics can be used here in order to determine if the renderer needs to refine pixels or not. These techniques avoid computing stuff a human can't see.

See my post in this thread: http://www.luxrender.net/forum/viewtopic.php?f=8&t=451

Karl

[Dade]

I'm working on the project of a deskside cluster built of diskless-headless nodes (only q6600+motherboard+2GB ram) with an hand-built case. The price of the single node is quite low (under 250 euro + VAT) so I'm playing with the idea to build a 4xNodes box (16 cores). I'm going to post some more information in the off topic forum soon

Ahah, found someone brave enough to have already built what I have in mind (however his system is not diskless): http://helmer.sfe.se/

It is funny, his exotic "case" it is available from my local Ikea store too: http://www.ikea.com/it/it/catalog/products/00107874

[dougal2]

That's a very neat casing solution! (not so hot on cable management though)

[Radiance]

Ha,

perfect for winter dade,
you can grab a pair of nice, warm socks in the morning

Radiance