Yes, the tools to create green screen composites have changed and, yes, it is cheaper and easier to produce green screen FX shots, but that doesn't mean it is simple or effortless to "sell" the shot to your audience.
It certainly isn't as easy as "just shoot against a green sheet and then drop a chromakey effect on the shot in Final Cut." There are several things in Pre-Production, Production, and Post-Production to keep in mind that will go a long way to selling your green screen shots.
Like Scotch Tape and Kleenex, names associated with cellophane tape and tissue paper respectively, green screen has become the go-to word to describe the filmmaking process where two images are composited together by replacing a solid color background in post-production with a background from a different location, or from something created in the computer. Practically every film or video made today, from Hollywood blockbusters and low-budget Indies to corporate and commercials, has some sort of green screen element. The reason for this rise in popularity can be summed up in one word: Digital.
The Early Days
Before digital technology, only big Hollywood films with big Hollywood budgets could do the types of effects that called for compositing two or more elements together in one shot. Back then, the chosen color was not green, it was blue (see sidebar). Although the general system had been in use since the 1930s, the true invention of the blue screen traveling matte process is credited to Lawrence Butler in 1940. Butler used the technique to create the Academy Award winning effects seen in The Thief of Bagdad. Bluescreen and the optical printer were the main tools of the special effects compositing world for decades, until computers and digital filmmaking.
There are countless reasons to shoot against green, but they all boil down to two categories: either you are trying to realistically place a subject into an environment or you are placing a subject in front of an abstract or graphically driven background. They both have challenges and specific criteria to follow, but I find the latter to be somewhat less interesting than the former. It's one thing when the subject is clearly keyed over a graphic background. You see that often in corporate interviews, reality TV, the local weathercast and things like that. The bigger challenge is to composite the foreground and background together so well that the audience thinks you got the shot on location.
Let There Be Light
One bad key can ruin the entire composite. A jagged buzz around the edges of the foreground, green fringe in the hair, colored spill on reflected surfaces - all these things destroy the illusion that the foreground and background were shot simultaneously. Preparation and proper lighting on the set will prevent these and other obstacles that can wreak havoc with a good composite.
First, realize that you must light the background and foreground separately. The green (or blue) should be lit as evenly as possible. Avoid wrinkles, seams, cracks or uneven paint on your background. Remember, that you only need to have the green around the foreground subject. There is no need to light a giant green-screen background if you're only going to be replacing a small portion of it. Also, place your foreground subject as far from the green background as possible. This will limit spill. Spill is when the background color reflects onto the foreground subject. Too much spill will make it difficult to pull a good key in Post and it may also spoil the illusion. Finally, as a general rule, make sure that the light level on the background is lower than the light level on the foreground and avoid a harsh backlight. Some other things to avoid on your subject are: frizzy hair, highly reflective jewelry, and clothing the same color as the background.
Lighting your foreground subject depends entirely on the background plate. Which segues nicely into the next topic.