Quote: "Greenscreens and bluescreens are used in live action films for backdrops which will be digitally filled in with images."
This is a process called cromakeying. The key is the area to be remapped and cromanance being a component part of all colours that determines where it is on the colour spectrum. (cromanance, luminence, intensity etc).
The video underlay is not necessarily digital, infact the technique was invented long before computers where used to render anything in films using a device called a cromakey genlock.
Blue screen matting is the most common for playing back of live video underlay and is used because blue is at the week end of the televisual spectrum, because blue has the weekest cromanance value it creates less bleed over.
Green is more commonly used for computer rendered backdrops because it is in the middle of the televisual colour spectrum, green is stronger. Choosing red (which has the highest cromanance) may cause the CGI image to appear matted because of the croma strength of the colour.
Quote: "They're green or blue because that uniform color can be found and replaced easily by computers"
Hope i've cleared that up.
Quote: "though why they don't use pinkscreens (a far rarer color) is beyond me."
Pink would be a bad choice because it is a combination of red and blue, pink also tends to be pastel (else you would describe it as magenta, purple etc) and pastel colours have a high "intensity". High intensity have stronger bleed effects that would create a thick ghosting effect between the two layers of video because intensity tends to adjust in a smoothed effect across video, the individual red and blue components of pink would also cause mayhem in trying to cromokey it which would most likely cause a speckling effect of the two layers.
There is an algorythm to define what colours can be used for cromakeying, but I forget what it is exactly as I haven't done any for over a decade now.
You can use numerous shades of red green or blue with varying intensities, the most common choice though is a shade referred to as croma-blue which if you really really really want to know, I could look up for you from some old projects.
An additional problem that sometimes leads to the choice of green is the fashion popularity of the colour black and leathers. Picture a scene from Mission Impossible or Matrix and it is hard to imagine the characters not wearing something leather at some point, the problem with leather is under reflection it can often appear to have a blue-black shade, this can create holes in the overlay that show speckled backdrop video through Keanu Reaves trench coat...
There are two solutions to this, either buff the leather gently with brown polish so it reflects red, or use greenscreen matting instead.
Finally there are other forms of genlocking too, for example linear keying is used by teletext/ceefax services to overlay that blocky text on your screen. Linear genlocks allow for video overlay (rather than video underlay as in screen matting described above). In teletext genlocks they use colour 0,0,0 - the absense of colour - to key over the video, but this can be set to anything.
Linear keying typically results in higher quality results, however do not sabotage your television thinking you've got the ultimate industry genlock in there... That's a little 8 bit chip that has been in existence longer than your oldest ancestors grave, it can just about cope with the concept of inserting 11 lines of blocky text into each field in the display (there are two fields on the television screen - actually, dont get me started this subject you'll be here all night).
Quote: "I watched monsters inc. "
The second most powerful computer network in the world is owned by Industrial Light & Magic, a division of Lucus Arts. My understanding is that their highly specialised custom software are actually just Max plugins.
In the case of Monsters Inc it appears from above that Pixar use Maya.
Some other sudios use Lightwave (Babylon 5 for instance).
In short, we're using the same tools but to achieve a different effect. The computer networks they have are purely for rendering and a few machines to output the finished streams to video. My rig can do that too, just not to the same level of broadcast quality as the big boys.
They dont have any magic wands, or any highly customised tool that we dont have access too.
At the end of the day it just comes down to talent. They have it. And we pay them millions to watch the results.
God created the world in 7 days, but we're still waiting for the patch.
