Isolating pure primary colors without white?

[Aharon Rabinowitz]

A limit on chroma keyers is that they generally don’t handle whites and blacks well. That’s why there’s a Luma Keyer – however, I don’t know if there are any 3rd party keyers that are geared towards this – I’ve only worked with Blue and green screen.

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Aharon Rabinowitz
aharon(AT)yahoo(DOT)com
http://www.allbetsareoff.com
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Creative Cow Master Series DVD
particleIllusion Fusion Volume 1
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[Ryan Hill]

There is the channel arithmetic filter. For the red layer, use the red channel minus the green and blue channels.

For white, desaturate and threshold.

But this is with the understanding that the colours are really “pure,” and seems so obvious that there must be something I’m missing.

I have the long-term goal of learning to write plug-ins, and then I can make my own keying formulas.