[Bf-cycles] Antialiasing overbright areas in Cycles

[Mike Farnsworth]

You can pre-clamp pixel sample brightness before any averaging/compositing,
as long as you're okay with a bias (toward dark) in the final pixel
result.  Sometimes it can really do the trick for hot spec aliasing.
You'll find this problem more or less prevalent with caustic-like paths and
with hot specs in motion blur.  You especially will see the problem with
any pixel filters with negative lobes, but Cycles just uses Gaussian so
this shouldn't be a problem.  The other thing to do is find the source of
the hot sample further down the ray path, and deal with it there; often you
can do that in a more energy-preserving way if it's in an indirect bounce.
I'll leave it up to your imagination what form these can take on.  Cycles
already has the caustic avoidance, which is a bit of a blunt hammer, but
there are similar things that can be done that keep some of the energy (and
thus reduce bias).

-Mike



On Sun, Mar 3, 2013 at 8:11 AM, Brecht Van Lommel <
brechtvanlommel at pandora.be> wrote:

> I'd like to investigate a solution here, we can in principle support
> FSA, and there's some other tricks that I'd like to try. But for now
> the only way to solve this is to handle a high resolution and scale
> down afterwards.
>
> Brecht.
>
> On Sun, Mar 3, 2013 at 3:24 PM, Ton Roosendaal <ton at blender.org> wrote:
> > Hi,
> >
> > There's a very practical reason why you cannot anti-alias it.
> >
> > You perceive aliasing *only* after putting it on a clamped display. If
> your screen would show values > 1.0 anti-aliasing would work. :)
> >
> > So the proper way to antialias is to first clamp colors of samples to
> display range, then merge all samples to average them. This is why Blender
> Internal "FSA" does a good job. So you can composite (per sample) the high
> dynamic range, then it clamps, and then merges the colors values.
> >
> > For Cycles this trick is not so obvious to add, since it takes 100s of
> samples per pixel...
> >
> > -Ton-
> >
> > ------------------------------------------------------------------------
> > Ton Roosendaal  Blender Foundation   ton at blender.org    www.blender.org
> > Blender Institute   Entrepotdok 57A  1018AD Amsterdam   The Netherlands
> >
> > On 3 Mar, 2013, at 14:40, Adriano Oliveira wrote:
> >
> >> Is there a way do better antialiasing overbright areas?
> >>
> >> PS: I don't want to clamp the highlights.
> >>
> >> Adriano A. Oliveira
> >>
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