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After shelling out quite a lot for green screen cloth, which you'd think was woven with golden threads for what they charge for it, I ran across-- actually ran into --a substitute that cost less, is more versatile, easier to hang and I found it, of all places, at the local Wal-Mart. Those of you with school age kids might have figured this out already, or if not it's been staring you in the face for a long time.

Green screen cloth: $149.00 plus shipping

Wal-Mart blue screen: $21.60 including tax and transportation back.

Being able to bend, cut and tape your blue screen to match specific shots without costing a lot of money: Priceless

In case you're really to new to video green or blue screens are often used behind a subject that you want to appear as being somewhere else. In post production you will composite the two shots by subtracting the background color from the behind the subject. You've probably seen this every day on the news. Your local weather man is not standing in front of a giant weather map, he or she is usually standing in front of a blue or green screen looking at a monitor that's out of frame to one side or the other and the two shots are composited (or composted as I like to call it) before the signal is sent to your TV set.

In video the technique, known as Chroma Keying, keying, blue screening or green screening and is used extensively. The Chroma Key process is based on a color channel. Everything of a particular color is "keyed out" and replaced by another image or color. I've seen it used on computer screens, control panels, and more often windows when they want the view out the window to be elsewhere. They'll blue screen behind the windows and replace the view with waving palm trees, exploding volcanoes or whatever is appropriate to the scene.

Why blue and green? Historically color cameras have been more sensitive to blue light, though that is less true today. Blue is also on the complimentary side of flesh tones, often the main subject, so it works unless the talent is wearing blue which can lead to some really interesting results. And no matter how many times or how loud you say, "DON'T WEAR BLUE OR GREEN." I can almost guarantee someone is going to walk in wearing one or both of the wrong colors. Fortunately just about any color can be used these days, if you happen to have a wide selection of solid color backgrounds to pick from.

It takes a bit of practice to get the lighting just right and doing it really well is an art from by itself. One of the challenges is when the background color reflects back on to the subject creating a fringe called blue spill. This can be minimized with careful lighting and gels or camera filters. Hair is one of those areas that give me trouble. If a subject has big hair, like my wife, and it's wispy at the ends the background will show through just enough to give me blue spill. It takes time to learn, the good news is now you can experiment without burning a lot of cash.

The item I ran into at Wal-Mart were display boards kids use to build science displays. They come in a variety of colors including, you guessed it, blue. $4.97 each. And the odd thing about this blue is it's nearly the perfect shade for blue screen work. Since these are cardboard displays, the surface is slightly shiny compared to blue screen fabric but not bad. And they are creased so the panels will fold over, protecting the surface and making them easy to transport. Initially I was worried the creases would show, but when tacked or taped flat to the wall the creases are barely visible and don't show in video composites I've tried.

For my test I put four of them on the wall with double-sided tape. Worked perfect. But be careful if you're doing this on a painted wall. I got tape that was made for hanging posters. If you get the wrong kind of tape it will pull off chunks of paint when you take it down. Also found I could use push pins or small nails if I wasn't worried about leaving holes behind. A small tub of joint compound made short work of those.

I was so excited I had to call one of my buddies in the local video club and let him know. "Oh, we already knew about that," he informed me after a few patient minutes listening to my excited rambling. "Except we use colored foam core." Apparently everyone in town knew about this trick except me. "And we just painted one wall and part of the floor in the studio." Okay, fine, nobody likes a show off. As you can see there are a number of ways to do green or blue screen on the cheap, this is just one of many.

If you don't have a Wal-Mart near by that stocks the boards I found, you can start your hunt online at www.sciencehunt.com.

I got four of the 36 x 48 variety. And I know a bunch of you are going to jump in with other tricks, so bring it on. Let's hear what else you clever devils have fashioned for your green screen shots.

Object to Chroma Key	Blue Board
Object - Background + Blue Board = Burried Ruin