Green Screen

[Todd Reid]

Chroma keying in FCP is still a bit tricky, but doable.

You didn’t mention what format you will shoot on, the theme here is….
the less compression you add, the better your outcome.

Capture your footage at the highest quality possible, cause the more your signal gets compressed, the worse its going to look.
Input your footage with the least amount of compression your system will allow.
Spend the most time on your lighting. Evenly lit greenscreens go a lot faster in post.

You may want to look into 3rd party apps for the compositing Boris, dvmatte, shake, AE. A google search will provide many options.

The internal FCP chroma might work if footage is carefully shot/lit, but I’ve always
relied on zmatte for keying in the dv world.

[Jeff Carpenter]

A common mistake with green screen, I think, is that people try to make the green really bright. You want good color saturation, but making the screen as bright as you can will result in more green spill on your subjects and make for a harder keying job in general, I think.

Light and expose for your talent first and then light the green. You should aim for about 50% – 60% on the IRE scale. If you’re not using a scope, you can still estimate something that’s well lit but not super-bright. The screen shouldn’t be brighter than the talent.

Also, subject back lights should have some kind of color gel, like gold or amber, that helps seperate their edges more than plain white light would.

[Mark Suszko]

With green screen, the backlight used for spill suppression would be magenta, amber backlight is used with BLUE screen. You’re picking the color farthest opposite on the color wheel from the key color. Depending on the software used, a colored backlight for spill suppression hurts rather than helps, i.e. for Ultimatte it is a bad choice generally, because Ultimatte works on a different principle. There are chromakeyers in Motion too, don’t forget. They have their own spill suppressors.

One thing green screening outside has going for it is, if the green screen and talent catches the sun at the same angle, everything is going to stay more or less evenly-lit, but if you have any clouds, you’re hosed. Also, the sun continually moves so if you shoot for any length of time you get continuity errors.

Even lighting is “key”. Also, separate your talent from the green screen by their body height plus two feet, to reduce the risk of spill contamination as well as shadows hitting the screen. If you don’t have a scope on the set (and you should when keying) the next best cheat is to activate camera zebra bars and use them to see if zebras set at something like 60 IRE appear evenly across the screen. Correct until they do. I light the screen first, then turn it off and light the talent according to what is needed to match the backgrounds to be inserted, i.e. make sure the light is motivated and from the same direction, etc. Then turn on both lighting sets and make final tweaks if they interact at all.

I find a little reduction in the detail setting helps especially when shooting 4:1:1 DV.

A friend told me of the horrible problems he had when he shot the green elements in a different frame rate and codec than the rest of the program. Don’t mix 24-frame and 30- frame in the keying project for example. The cross-conversions really take down overall quality.

[Kenyon Blower]

Everybody’s tips on lighting is the key to getting a good key. I use Boris Continuum for my keying. One last tip. if you are getting a fairly good key but seeing a litte tearing around the subject, I apply a slight gaussian blur to the alpha channel.

Kenyon Blower
Vide-Post / San Diego
Dual 2.5 G5
3 Gig Ram
Medea 2TB Fibre Raid
Medea 640 gig SCSI
FCP 5.1
KONA LH

[Liam Lawyer]

And if you are shooting on DV another good tip is to use plug ins like Natress G Nicer that will clean up the color signal (in effect making it 4:2:2) before you chroma key it – makes a noticeable difference on the edging for sure..

I have been using the Color Keyer instead of the chroma keyer as well – much easier to tweak I find.. and even quicker to deal with then Boris plugins too.

This is definitely an area that FCP could use some improvement on…