FCP-L: Re: [FCP-L] Best way to Matte White Screen

Saturday, October 24, 2009

Re: [FCP-L] Best way to Matte White Screen

On Oct 24, 2009, at 3:36 PM, Robin S. Kurz wrote:

> You will NEVER pull a usable matte based on WHITE unless of course
> your foreground plate is *completely* black. Not without a massive
> amount of garbage mattes that is, in which case you might as well
> roto.

This is simply not true.

It is quite possible to pull a usable procedural matte by keying off
the contrast in individual color channels of the original image. You
can use the resulting hicon matte as a holdout matte for the FG, which
allows you to concentrate on just getting the edges keyed out decently.

Of course, this will generally not work for hair or any sort of detail
that requires fine transparency. And if you're dropping the keyed FG
onto a dark BG plate, you're in for a world of pain as well. But I've
done this sort of thing often enough to know that depending on the
cricumstances it's totally possible to pull things like this off. Far
from ideal, of course, but also not impossible.

If you're willing to get down and dirty in a dedicated compositing app
like Shake, you can get even better results by using the keyed white
fringing to your advantage as an edge matte to comp in the original
color of hair using color solids (similar to how greenscreen spill
suppressors work. albeit in a much more brute-force way)

Keying is NEVER a one-click process, even on professionally shot green-
screen plates. You will almost always have to do some roto,
articulated g-mattes and multiple key passes in order to get a great
key.

Never say "never"!

--
Mel Matsuoka

http://twitter.com/melorama
http://twitter.com/hawaiifcpug
http://twitter.com/LiftGammaGain

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