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

Robin sez:
> Since this is getting *way* OT...

Not sure how editing technique is OT... if it is, Jim will step in.

Ed sez;
> Hmm, and all these years I thought YUV, YCbCr and YPbPr white is, in
> fact,
> *all* the colors, just as in RGB, add red, green, and blue
> together, and
> you get... white.

I'm with Ed. We edit in the additive world of light. In that world,
white is all colors. The subtractive world of CMYK is for printing
and not relevant here.

Mel sez:
> Keylight will *NOT* work for luma keying. It's a color-difference
> based keyer, so there needs to be color contrast in the RGB channels
> in order for it to generate a matte from something.

I just sat down with Keylight and a clip of a woman with a blue jacket
on with a white blouse under it. I keyed out the white, cut rough,
soft masks to hide the "defecation" ... and changed the blouse color
to pink. To your point, Mel... it must be a color key.

I sez:
For all the lovely discussion about theory, the simple fact remains
that "white keying" is NOT a practical form of keying to be used in
lieu of Blue or Green, as Shane pointed out. It's something I've used
in one very limited circumstance... keying multiple Interviews shot on
white seamless onto a clean, white BG for the purpose of creating a
clean, homogenous white background for all clips. I discovered it
after shooting interviews on white seamless in 5 different locations
and the slight variations in the white background were obvious cut-to-
cut. When I removed the FG white and replaced it with a clean, white
BG plate, all the things that were white stayed white... but
importantly, the SAME white. Yes, I cropped the subject tightly, had
to add a few masks on a few of them, the matte densities were anything
but "normal"... but it worked. Say what you want about theory, the
proof is in the link I posted.

Again, this is a cheat I discovered..., a trick, a technique that you
can stick in your bag and use if somebody walks in with a bunch of
stuff shot on white in different locations and wants the white to look
"cleaner". Use it or not.

Be well...
---
Bob
------
Robert Griffiths
http://www.FireDancer.tv

On Oct 25, 2009, at 8:36 AM, Robin S. Kurz wrote:

>
> On 25.10.2009, at 15:07, Ed Dooley wrote:
>
>> Hmm, and all these years I thought YUV, YCbCr and YPbPr white is, in
>> fact,
>> *all* the colors, just as in RGB, add red, green, and blue together,
>> and
>> you get...white
>
>
> No. Technically, pure white is *the absence of color*. In other words,
> you can't mix colors to create white. Therefore, white is the absence
> of color in the strictest sense of the definition. But it's one of
> those 'it's who you ask' things... and probably yet another otiose
> tangent at this point. ;-)
>
>
>> (unlike CMYK where you get black).
>
>
> No. With *K* you get black. CMY mixed together give a very dark grey,
> that's what the "K" is for, which is pure black (but also for the sake
> of saving ink when printing). The "K" in CMYK stands for "key" since
> in printing cyan, magenta, and yellow plates are "keyed" or aligned
> with the black key plate.
>
> - RK
>
>
>
> ------------------------------------
>
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>
>
>

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