3D Colorspace Keyer for Fusion

While trying to find information about the math of Nuke’s IBK I rediscovered vfxwiki, formerly miafx.com. Its chapter on keying is quite a treasure trove of information.

I’ve implemented the formula for a 3D chroma keyer as a macro for Fusion. You can find it along with usage information on Vfxpedia.

The Keyer treats pixels as points in a three-dimensional space (HSV by default). The alpha channel is created by looking at each pixel’s distance from the reference color. Two formulas are implemented. The “Manhattan Distance” and the direct route as defined by the Pythagorean Theorem:

distance = sqrt( (r1-r2)^2 + (g1-g2)^2 + (b1-b2)^2 )

The latter results in a much softer matte that needs to be processed futher but which is perfect for semi-transparent areas or fine hair detail. Check out the example key, pulled from a free green screen plate by Hollywood Camera Work:

If green screens like this existed in real life… 🙂 I’m usually given dull cloth with wrinkles in it.

Download the macro or view the help page on vfxpedia.

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