(Mods: if this will do better in CS, please move with my apologies)
In visual media, there is a technique where a certain color is subtracted from the image so that another image can be substituted later in post-production.
In the old days (when I was a young’n), I remember reading an article about the old “Invisible Man” tv show (no, not the recent one where the guy got the “quicksilver” blob put into his brain, but the mid '70’s David McCallum show) where they described the “blue screen” technique: They would cover his “invisible parts” with blue and film him on a blue background, and then later replace everything that shade of blue with something else.
Lately, I’ve heard more of “green screen” (most recently in the Halloween episode of “Late Night with Conan O’Brien” which they did in “Skelevision”), where they put everything that was supposed to be invisible in the same shade of green so that they could subtract it out later and replace it with something else.
My questions: is there really a difference between “blue screen” and “green screen” techniques (other than the obvious color)? Is there a reason why one might work better than the other, and if so why? Has green replaced blue as the “invisible” color of choice for some reason, or are they both optimized for different applications?
I’d almost be inclined to guess that green might work better because it’s more to the center of the visible color spectrum, but that’s a total guess.
Nope. You could have red screen if you wanted, but it would interfere with skin tones. Green is just the least likely to be a part of costumes and such.
The technical term is Chromakey.
I think we’ve had a thread or two on this, but I could be thinking of another board.
While perusing the internet, I stumbled on the fact that Walt Disney, IIRC, pioneered this technique (quite common today) using a yellow screen. The process was much harder back then since there were no computers. It was all done by brute force, so to speak, and the end result was created in a photo lab., dark room, or wherever Hollywood folk went to develop their magic.
Just to make it clear that although similar techniques are used in both film and television production, the technical procedures are quite different.
Chromakey is the term for the technique used in television, as in the TV weatherman standing in front of an animated weather map. It’s done electronically (originally with analog circuitry, now with digital) in real-time, obviously.
In the film world, green screen or blue screen (those terms are used) was first done entirely optically, by using the green or blue areas to create a matte, an opaque area into which the new background image was subsequently printed. It was, obviously, not a real-time process.
Although I’m sure that there are labs out there still doing it that way, these days most special effects are done digitally: the original film is scanned to a digital file, and the green- or blue-screen processing is done in the computer, then the completed footage is recorded out to film again.
The digital process now used in film is probably very similar, technically, to that used in digital video switchers used in TV production, but it’s still not a real-time process, as it is for the weatherman.
