As I've said before, doing a great green screen key is one of the most difficult effects you can pull off. It's amazing that so many people attempt it as their first effect, only to be frustrated at the results. Unlike broadcast, most people shoot with MiniDV or HDV, which, by default, are compressed formats. 
Not to worry, though...read on and you'll get the shot you're after.

First Off: What Screen is Right for You?

If you have a big enough budget, you can pretty much skip most of this (and most of the headaches) by buying a green screen kit that utilizes a reflective background and a light ring. Two examples of this are Reflecmedia's Chromatte and Datavideo's CKL-100. The CKL-100 has five important features:

1) Used properly, it can match the output of the Chromatte system.
2) Minor wrinkles tend not to be an issue, unlike typical green screen cloth.
3) Since it's a reflective cloth, you can drape it over people, objects, etc.
4) It comes with both blue and green lights on one ring, making it easy to switch keys.
5) Feature for feature, it is less than 1/5 of the cost of a comparable Chromatte package.

Basically, for the price of a cheap pro light kit (just under $1000), you can have hollywood-level green screen effects.

If you're doing something that is going to be a studio-based perminent install, or if you just don't have a big enough budget, no worries - you'll still get amazing results by building your own green screen wall.

Blue vs. Green

Back in the early days, there was no such thing as a green screen. Films would use blue screens to do special effects with actors because it was easy to key out. It also is the only color that is not used in skin tones, so you're almost guaranteed that you won't take the color out of your talent by keying for blue.

Unlike film, both HDV and DV are compressed formats. With film, it wouldn't matter what color you keyed for, because there was plenty of information. Nowadays, green is used because for DV and HDV, the green channel preserves the most color information. Blue is still used rarely if your talent has blonde hair, but you can key a blonde on green if you use a hair light as detailed below.

Location, Location, Location

Where you set up your screen makes a difference. If you are in tight quarters, such as a small office or garage with white walls, you may have a issue with your talent looking a little green under the gills. This is because all those nearby surfaces are acting like giant white cards, bouncing the light and basking your talent in an eerie, sci-fi glow.

If you have to set up a permanent tight space, you might consider painting the walls with a flat black to absorb the light, or if you are on set, move to a larger location or use straw/tan gels over your lights to help neutralize the effect.

Making / Painting Your Wall

For reference, here's some cheap paints that have been used to create green screen walls. When buying, make sure to specify that you need an interior flat paint. You would never want to get anything that would reflect light, like a gloss or semi-gloss…lighting a green screen wall is hard enough without it shining back on you.

Paint Colors (some from personal experience, others from the web)

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Sherwin Williams:
a) Irish Green
b) Straightforward Green
c) Color match from Green Screen:
103-4Y 113-1Y 1145Y32 Base 4
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Glidden (Home Depot):
a) Fresh Melon Green
b) Color match from Green Screen:
Base 2 (HD9012)
COLORANT 0Z 48 96
AX PERM YELLOW 01 31 01
B LAMP BLACK 00 01 00
D THALO GREEN 01 04 00
KX WHITE 00 11 00
*********************
Behr (Home Depot):
S-G-440 "Green Acres"
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Valspar (Lowe's):
a) Reptar Green (Nickolodeon Paints, Rugrats Collection)
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Also, keep in mind the smoothness of the wall. If you're going off a standard interior wall, just make sure it's nice and smooth. If you've got a wall in your garage that's made up of cinder blocks, remember that every crack gives the light another place to bounce off of, so use a good primer and lots of coats of your paint. Another trick is to just lean a couple of large sheets of a smooth wood (such as MDF) against the wall and paint them instead, which will result in a lot less work.

Remember, if you're going to do a full body shot, it goes without saying that you'll also need a green floor with some additional lighting. Just keep it in mind, it can be accomplished much in the same way mentioned above (woodfloor, or straight to surface if in a garage). You may want to get a greenscren cloth for the floor via ebay and color match the paint to it.

IMPORTANT: After painting your screen, do not touch it if at all possible! The only way to ensure that you get back a consistent color is by keeping it clean. If you do mess it up, the only real way to get it back to where it was is to repaint the entire surface, so be careful.

Going Soft

Another way you can make a green screen is to buy a cloth. They do make pure green cloth, but to get the 'true green' cloth, you'll end up spending at least $100. Do yourself a favor - just go to Wal-Mart and get the brightest green you can. Most cloth stores sell ultra-bright (or 'party' green) for $1 a yard. I don't know about you, but $4-5 is a lot better than $100 any day, and it really works just as well.

The key is to keep it perfectly flat and smooth. When we used our backdrop, we would iron it, roll it, and place it gingerly into the bag. Once we were on location, we would take it out, attach it to a framework, and then go after it with a steamer to make sure it was perfectly smooth.

That's the trouble with cloth - it just wrinkles. If you want to go this route, it certainly is the cheapest, just make sure to build yourself a frame for it. I found a great tutorial on how to do that here:

http://www.kenrickparish.com/jgeerling/articles/photography/diy-greenscreen.html

Remember, if you want to do full body shots, make sure to buy an extra long run of cloth so that it will serve as a floor for your talent.

Importance of Lighting

No matter which green you go with, lighting is key! Keep it nice and even, and you won't have a problem using the chroma key filter of your choice to mask it out. Keep your subject pretty far away from the background to avoid casting shadows (about 10 ft should do for a full body shot). You can cheat a little bit if you are doing just a medium (half-body) or head shot, but I still wouldn't go any shorter than 5 ft between the subject and the screen.

Also, if you need to evenly light your screen, try using inexpensive long fluorecent bulbs, rated at 3000 K (degrees Kelvin, a measure of light temperature). If you're in a big box home improvement store, the color temperature should be marked on the box. If not, get one of the lighting professionals to help you.

They should blend well with standard lights, allowing you to use your expensive lighting kit on the subject, instead of the wall. Adding a keylight (or hairlight) that is set up near the wall and points towards your subject so that it splashes their back side with light will add separation and make your job keying later on a lot easier.

Mind Your Head

Make sure your subject's hairstyle of choice doesn't have a lot of 'fly-aways'. Tiny strands of hair tend to be lost in most keying attempts anyway. Blondes are especially troublesome, and if you find yourself getting too much of a green halo in your key, try using a blue background instead of green. Any bright blue should do the job, and a blue color cast is less noticeable on blonde hair in my experience. If you have a straw gel (light tan) to attach to your backof your hairlight, you should be able to neutralize the cast no matter what color you use.

Camera Command

This is the name of one of my favorite how-to videos. In short, camera command is all about knowing how to truly use your camera - especially your lens. With green screen shooting, if you have a rough wall, but you have a lens that allows for narrow depth of field (DoF), you're fine. As you bring your subject into focus, your background will blur, helping to smooth out minor inperfections and pitts in the surface. This will give you a smooth, rich green background, making your life easier once you get it into your program of choice.

For more information, google 'narrow depth of field video' or go buy Camera Command at www.cameracommand.com.

Watch the Results

Another trick you can employ is to use your laptop as a field monitor. After all, you won't be able to see in your camera's viewfinder if you are really getting a nice, sharp edge otherwise.

But no fret, with just a simple bit of software and a firewire cable, you can preview your footage on your laptop's big screen. It makes finding tricky spots and rough edges a lot easier. Adobe's OnLocation software for PC and Veescope Live for Mac are great because they have a ton of nice pro features, but I've heard that you can use VLC player to view the stream, minus the extras.

Of course, OnLocation takes the cake on PC laptops because, if you already have the Production Suite, you already have it!

Additional Resources

Check out the tutorials on digitaljuice.com. They had an excellent show about setting up a basic green room posted up on youtube:

http://www.youtube.com/watch?v=WC8zhFvJ-lc

Finally, Adobe also packages Ultra, which allows you to do virtual sets. What this means is that you can put your actor right in the middle of a virtual newsroom or office, and it comes off fairly well.

Wrapup

Hope this answers all your green screen questions. If you have any issues or know of a better way, let me know so that I can continue to improve this guide. Just leave comments below, and thanks!