So, let's just say the difference between having an actual green screen and not having one was like night and day. The way that a green screen captures the light is so very different from a sheet or a tarp.
So, I set up the green screen, and that was great and all, but I still needed the answer to the big question. Would it edit? I shot my footage and popped it on to the computer. At first, I was not impressed. It was the best footage I had gotten so far, but I still had shadow problems. And when I tried to get rid of those, I was erasing my actress... So I changed the lighting and tried again. Same problem. Oh well, I was running out of time. I was just going to have to deal with the visual noise. So I continued with the edit, and other than the noise, the edit was going good. Until... I lost the project! My definition of not impressed changed a bit at that point.
I still had the footage, so I started over again. Surprisingly, having to start from scratch really turned out to be the best thing for the project. When I edited out the green screen, it actually went away like it was supposed to! Hardly any extra effort. So what was different? What had I changed between the original and the restart? The amount of shadow in my sample!
After that it was smooth sailing. I ended up with a good product and a good learning lesson.
Some tips I learned:
1) Use a non-textured, matte surface. Shiny surfaces produce highlights which are hard to key out. The general advice given if you have poor green screen footage, is to filter it multiple times. Having tried this, I can testify that the sharp highlights caused by a tarp do not come out this way. At least, not without wiping your talent from the screen.
2) You want your background to be as close to one solid color as possible. This way it's easier to key out without keying out the talent at the same time.
3) If the screen is dark, then find a way to light it up. Obviously, you need to do this without affecting the lighting on your talent. Depending on the thickness of the screen you can light it from behind, or from the front along the side, or the top. Do your best to avoid varying shades of green in your screen, and avoid shadows cast by your talent or anything else in front of the screen. Be careful to avoid "hotspots" if you're choosing to light from behind.
4) Obviously, a proper green muslin backdrop designed for this purpose is best.
5) When doing the actual edit, it's best to select the darker areas of shadow when keying out the green. Doing so makes it easier to hit the right spectrum of green to get rid of the shadows.
One final bit of advice that I learned too late, and so didn't get to try: Lower the ISO setting on your camera as far as you possibly can. The higher the ISO, the more noise or "snow" you get. So in theory, the lower your ISO the cleaner your green screening will be. I didn't get the chance to film this way. So I can't verify the accuracy. However in a little bit of experimentation, I did discover that lowering the ISO resulted in a much darker image on the camera. So I guess if you lower the ISO, it's doubly important to pay attention to the lighting.
All in all, it was a rewarding experience, and I was glad that I kept the talent far enough away from the screen to avoid the spill. (That's the reflected light from the screen around the edge of the talent.) As it was, I had a fair amount of spill anyway. Unfortunately I had to shoot (and edit) multiple times, but now I know from practical experience what to do. The Internet can only get you so far after all. ;)
--CGWise–––––––––––––––
aka Charlie Griffin
"To learn and not to do, is really not to learn. To know and not to do, is really not to know."
- Stephen Covey, The 7 Habits of Highly Effective People
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