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Posted by nobody special on 01/20/06 05:12
Technically, you can chromakey with any single shade of color: orange,
purple, whatever. Blue was the most common choice because it has less
than any other color of the reddish shades that are in human skin,
making it easier to key a face and body. The green came later, after
the pigmenting process for that color was perfected, and obviously,
nobody wears THAT shade of green, not since the early 70's, so it's
easier to use if you wear blue jeans or whatnot. (Yes I come from a
time in the dim past before "neon" or "floursecent" color pigments were
commonplace. And they had chromakey then!)
If you were wearing a lot of yellow, Blue BG would work much better, as
it's directly opposite on the color wheel and yellow is right next to
green. In Hollywood, for a brief time the preferred BG color for matte
work was a kind of bloody orange, but I have not seen that for a long
time, I think it was a custom deal that only worked with a particular
film stock and process. As to other reasons for blue preferred over
green; if you get spill or fringing, the blue fringe is much more
attractive to the eye than neon lime green; sometimes the blue spill or
fringe isn't even noticed in the final comp, where it would stick out
like a sore thumb using green. And as I said before, the blue wall can
also be used *without* keying, as just a pleasant neutral BG on it's
own. Nice to get double-duty out of a setup.
There is a technical reason for "digital green" to be preferred these
days: Dv cameras get their green info off the luminance channel, so
theoretically at least, you get a slight improvement in color
resolution with the additional green/luma combination. I think it can't
help any extra unless your gear is specifically set up to use that
difference. Meanwhile, Dv cameras with a 4:1:1 color space tend to make
inferior keys to analog, which has more chroma information. Sometimes,
going retro in your tech actually gives better results.
One other tip, Alex, try turning down the detail control in your
cameras a little: these Dv camcorders are often set preternaturally
high by the factory and people who think over-amping the detail makes
things look sharper or "crisper". That will also add some ringing and
tearing on your edges from over-modulating at the line between matte
and fill channels. Turn the detail down to "normal" or even a skosh
lower, and the key will actually look better/sharper, with less
ailiasing.
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