Cycles image filter weird behavior

Hi,

i just tried to increase film filter in Cycles but i got extremely weird behavior. Pretty much any mainstream renderer blurs the image using filter to reduce noise and aliasing artifacts. So you basically get trade off between noise and blurriness. But cycles for some reason applies filtering only on the base shading, and not actual raytracing effects. So even with huge filter of 10, I am still getting quite noisy image. Here’s an example:


As you can see, noise remains ultra-sharp and unfiltered. I think Cycles could use actual correct image filtering, because noise management seems to be priority with Cycles these days.

It’s been noted: http://wiki.blender.org/index.php/Dev:2.6/Source/Render/Cycles/Optimization/Notes#Antialiasing

(see the last bullet in that section)

Cycles has a rather weird pixel filter, IIRC it is based on this paper: http://lgdv.cs.fau.de/publications/publication/Pub.2006.tech.IMMD.IMMD9.filter/

FIS is supposed to reduce noise on practical scenes, and comes with the side benefit on not rendering pixels along tile borders twice. Which is why Cycles in CPU mode often gets speed improvement from tile sizes like 32x32 or even 16x16, whereas with something like Arnold or Mental Ray sizes like 64x64 are usually closer to the sweet spot.

Whether it’s really a net gain or not is up for debate, hence why its in the optimization notes.

I do not think those problems are completely tied together. Even with buckets, filtering should not cause much of a problem. I can’t understand why anyone would do this at rendertime. Filtering should always be sort of a post processing effect. Not really after entire frame finishes, but a last thing before bucket draws, on top of everything. When doing progressive rendering, filtering can be refreshed once each given number of passes.

My point is, in current form, it is basically useless, because it doesn’t do what filtering should be doing. It’s a couple of buttons currently occupying UI space for no reason whatsoever.