Green Screen Advice

Jameson_Prod wrote on 1/5/2005, 5:36 AM
I am getting ready to start a project where I would like to interview a subject (sitting on a stool in front of a green screen) and then chroma key it and overlay it on top of a video. (The subject will be explaining what is happening in the video...probably placed in one of the corners...head and shoulder shot) I have made a green screen with neon green fabric and purchased the work lights (2 - 500 watt haolgens) as suggested by several on here from Lowes. My experiments have been OK...acceptable...but not as professional as I would like and have seen posted by others here(like Chanimal's video with his kids).

What I am displeased with are the edges of the face and hair and the loss of color (a faded look as if the opacity had been lowered on the track) in the subject when the key is applied. I believe my problems are due to:

1. green screen having a few wrinkles in it
2. distance lights are from the green screen and placement (creating faint shadows)
3. placement of the subject in relation to the green screen (creating faint shadows)
4. Obviously lack of experience!!!!!

I would appreciate any advice or tips & tricks on setup that you have used to make this work best. Sugesstins on distance of lights from the screen, where they are placed in reference to the subject (90 degrees, 45 degeres, head level, above the subject pointing down, etc.), and distance the subject is from the screen, etc. Also any comments on chroma key values used in Vegas and any thing else I may be missing or need.

Any and all commments welcomed.

Thanks in advance for your time.

Comments

Orcatek wrote on 1/5/2005, 6:46 AM
When you key it, adjust the sliders for low and high threshold while the mask only box is checked, you may be keying out more than needed.

Also use the secondary color corrector Before the chromakey to fix all the green to an even shade by using it to "replace" the wrong green with the right. Once again work by showing the mask till you get a good correction.

These two steps should help alot. Check out billybob's site on the secondary color corrector if you need help with it.

ScottW wrote on 1/5/2005, 6:47 AM
Some of the tricks I've picked up here - have the subject at least as far away from the screen as their height. Even lighting is important and it's not something you're going to get with just 2 lights. Don't use Vegas to do your keying. Use something designed specifically for this that will work in situations where you have uneven lighting.

For the budget minded, www.fxhome.com - I've used this and it does a good job for the price. It's a little slow during renders but you sure can't beat the price.

If you've got the money, www.seriousmagic.com - Ultra is faster, also does an excellent job (once you figure out how to work the various knobs) and has additional features such as support for virtual sets (and some sets are included in the base package).

Both Chromanator and Ultra do a great job of dealing with uneven lighting.

--Scott
Fleshpainter wrote on 1/5/2005, 7:45 PM
Two 500’s sounds like way too much direct light, shadows will be a nightmare. Try flipping them around and bouncing them off of white walls or something. The best setup that I have ever had used numerous tungsten reflector bulbs on the screen, and separate defused lamps on the subject. Record some 30 second tests using different setups. Then, in Vegas, start with the “pure green screen” template, and mess around with the sliders as mentioned above. It's easier if you place a red or magenta solid color (generated media) on the next track so you can see what you are doing.
Nat wrote on 1/5/2005, 8:10 PM
When doing greenscreening we usually place the lights quite high and between the subject and the set, this will usualy solve the shadow problem. With some good quality shots vegas does a good job at chormakeying. You can try the chroma blur filter or put a tiny amount of gaussian blur on the green channel only, it can help for the jaggy edges.
Jameson_Prod wrote on 1/6/2005, 5:28 AM
Thanks for all the advice and suggestions. I appreciate everyones time.
logiquem wrote on 1/6/2005, 6:36 AM
1. have a maximum distance between your subject and screen to avoid green cast on the subject.
2. light your subject with large soft screens (or any kind of diffusors) to avoid hard shadows on the screen.
3. you can light the screen with common daylight fluos. Use 1 or two units wide on the floor and the same on the celling (same width as the screen if possible, and about 2 ' from it) Use cardboard pannels as big reflectors to get even screen lighting.

I had a great succes with this approach myself.

Vegas Chroma smoother effect is really wonderfull for fine keying, altough extremely slow on rendering ...