[Bf-compositor] [ENH] Sampling

[Troy Sobotka]

Nice to see Sebastian bringing up the subject of sampling. Apologies
for giving it its own thread, but I feel the importance is huge in
quality imaging. Many discussions previously have ended up in the dust
pile sadly, so a tremendous thanks to Sebastian for rekindling the
discussion.

Sampling is quite horrific in Blender due to only the cubic b being
implemented by default for the higher quality interpolations. While
this might all sound too techy, anyone that has dealt with purely
creative output probably has slammed into this issue.

While sharper, Lanczos[1] and other such approaches tend to result in
halos during stair / repeated applications.

Having the ability to apply particular sampling approaches per node
might be worth considering. Perhaps a node input to determine type
given the plethora of contextual needs?

I would implore everyone to have a peek at the prefilter applied to
cubic b. I've done up a few attempts at nodes that are likely out of
date, but sadly require a much lower level integration in the current
compositor because of the need for a separate image buffer[2][3].

The interpolation was first brought to my attention via Matthias
Fauconneau ages ago. I do not believe this interpolation approach has
landed in any mainstream imaging applications, but as any individual
interested in imaging would likely attest after having experimented
with it, it is one of best baseline interpolations available,
suffering from none of the hyper sharpening / blurring. It also offers
perhaps the most organic looking interpolation available.

[1] http://en.wikipedia.org/wiki/Lanczos_resampling
[2] http://www.youtube.com/watch?v=nfhTET86kdE (watch in HD to see the
perceptual sharpness results)
[3] http://wiki.blender.org/index.php/User:Sobotka/Cubic_B-Spline_Scaling_Algorithm