Green Screen

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Green Screen is a method used for creating mattes.  A foreground person or object is videotaped with a green background.  Through a matting process, the green essentially becomes ‘transparent’ and allows a background to be seen instead.

Quicktime Video: Clearasil Times Square

I’ve heard people say that HDV is no good for creating green screen mattes.  This Clearasil test spot is an example of green screen matting in HDV.  In fact, all foreground and background elements were shot with the Sony Z1 HDV canera (even the shiny clearasil product tube was shot with the Z1 in front of a green screen.

A few things to remember when shooting for a green screen matte:

Stay away from the background!
When you keep a minimum of 10’ between your subject and the green background, it minimizes green ‘spill’ from the backdrop.  Less green spill = a cleaner matte!

Cover unseen green areas
Seems like a no-brainer, but if it’s not needed for the matte, it doesn’t need to be there bouncing green spill around the room!  To be doubly safe, cover those unseen green areas with light pink sheets (the pink minimizes green.)

Add edge and back lights
This is particularly true when shooting full length shots, since light coming back at the subject from the green screen must be counteracted, plus edge lights will probably help make your subject look like they are ‘lit in the real world’
In fact, adding a light minus-green (magenta) gel, such as a 1/8 or 1/4, will help counteract any green that your edge light is working to overcome!

Don’t use fluorescents to light your subject.
Virtually all fluorescent tubes emit a ‘spike’ in the green area.  If you don’t believe me, go look at the spectral analysis curves at the Kino-Flo website.  Using fluorescents is, however, an excellent way to light your green background.

Be careful of your wardrobe!
A surprising number of materials are reflective enough to ruin an otherwise perfect matte.  Particularly watch out for items like shiny black boots (sure to pick up green reflections.)
Also be careful of ‘blue’ jeans.  In many ‘pre-washed’ styles, the blue of the jeans has faded to reveal a yellow-green tinge!  In general, watch out for not only greens, but yellows as well, since many yellow shades contain quite a bit of green.

Pull your matte from the highest resolution, earliest generation original you have.
Seems like another no-brainer, but remember that every time you transcode or go another generation, or even worse move to a compressed editing format, you are lising resolution and color information that may be the difference between a marginal and a great matte.

Use the best matting program available - and LEARN IT!.
I recently talked with an editor who had just moved to Final Cut Pro from a more hardware-based system.  He was shocked by how poorly it created its native mattes within the program.  He was ready to go back to his old system.
Instead he went out and bought Boris Effects.  He still feels that FCP deals with mattes in a backwards way, but after spending a day learning how to use Boris properly for mattes, he was able to do matting ‘100 times better’ than with the native FCP system.
There are other fine software-based matting programs, such as Ultra2 and Ultimatte.  Each one has its advantages, but every program NEEDS TO BE LEARNED FULLY!

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