What is the most uncommon pigment in the phyiscal world?

My intuition on why Hollywood movies use a particular hue of blue for the background screen is because this pigment is not common in the real world. So a computer program would have an easy time replacing the blue background with computer generated graphics.

blue screen

I would like to use this particular blue color in a related fashion. In my Adobe Flash SWF, I would like set the stage background to this blue hue. A separate program will cut out the blue and replace it with a scenic background.

What is the exact hex value of the color used in blue screens on movie sets? Or if you know other pigments not common in the physical world, then feel free to share.

Answer

Chroma Keying (or Color Keying) comes from way back in the days of film, when it was originally called Blue Screen. It does not depend on an unusual pigment. You could, in theory, use almost any saturated color, the main point being that you’re dealing with a very limited color range that can be easily differentiated from the foreground subject. A green cube could be shot on a shocking pink background and would key perfectly well in Photoshop.

What makes chroma key most workable is to use a primary light color. Since red is the dominant skin tone, that leaves blue and green as the useful chroma key colors.

There’s a good article in the subject on Wikipedia that gives historical background and plenty of information. (Note in particular the section headed “Clothing”, which gives a great example of the kind of practical problem that can come up, and how it’s addressed.

There’s no EXACT hex value, because shadows and lighting create a range of values. When keying, you try to minimize those, but they are almost always there. Keying plug-ins and apps work with those ranges and have adjustment sliders specifically to handle them. The best plug-ins also take care of color spill (where a bit of green is reflected at the edges of the face or clothing, for example).

If you take a blue or green screen shot like your example and look at the individual channels in Photoshop, it will be immediately clear why an RGB primary is what works best for keying.

Attribution
Source : Link , Question Author : JoJo , Answer Author : Alan Gilbertson

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