Green/Blue Screen Help
 

My team (25), is working on a team project involving the use of a blue and/or green screen. So far, we have built the screen needed, we have the digital video cameras, and we have some software provided by other team members. Does anyone have any experience using blue/green screens? We are having some trouble getting this to work. Also, and recommendations on software to use, and how to go about using it? Thanks in advance.

Re: Green/Blue Screen Help
 

Couple of things:

1. Adobe Premiere is a good candidate to do your editing/

2. Make sure your background screen is evenly lit. Uneven lighting can cause color variations and the software will see it as a different color.

3. Try to avoid harsh shadows on the background screen.

4. If you are planning on inserting your talent on a background plate, make sure your lighting matches the background plate. (I.E. look at the shadows for clues on the direction of the light source and try to match the shadows of the talent to it.)

I would recommend experimenting first and see what the results are...

Re: Green/Blue Screen Help
 

Obvious, but make sure your actors aren't wearing something the same color as the screen unless it's absolutely intentional. Someone being partly invisible cause of a green shirt under a jacket isn't cool.

Also, try to have your subject lit very well or you'll end up with a greenish cast from the light reflected off the green screen.

Re: Green/Blue Screen Help
 

I'll be honest, greenscreening ain't easy. I have a greenscreen studio setup in my basement; it works... but not great. The best advice I can provide is light evenly! Get some powerful work lights from the Home Depot or Lowes and and set them up at all different angles to make sure the screen is evenly lit.

Also make sure you have a sufficient DV camera. A cheap 1-chip camera will not work well. At the very least, I'd recommend a Canon GL2. However, even that is vulnerable to the 4:1:1 problem. You can read more about the problem and potential solutions here: http://www.neopics.com/bluescreen/

As for software... depends. I use Apple Shake, but it only runs on Linux and Mac OS X. For PC, check out After Effects. It has some pretty effective compositing tools. If you want a dirt cheap compositing program, check out Chromonator at fxhome.com . It's tailored for low budget compositing.

Here are a few other useful resources I've stumbled across over the years:

http://www.philipwilliams.com/greenscreen.aspx
http://www.channel101.com/tutorials/...tutorial_id=19
http://www.jushhome.com/Bluescreen/Bluescreen.html

Best of luck with your greenscreening. If you need any help, feel free to send me an email at av11d@mac.com; I have a lot of experience with cheap compositing techniques.

Re: Green/Blue Screen Help
 

The exact process you are asking about in video is called "chroma key". It requires that the camera either output an RGB or component video and that you have an actual chroma key generator to make it all work in real time. You can make it sort of work with a device that will split the video from composite back to component, but that usually add noise that becomes part of the chroma key process. As to the flat light of the background, this is essential as well as it being a flat paint, not gloss or semigloss. Green is a better choice as the video signal in US TV is more green signal than anything else. Blue is the least amount and therefore has the greatest noise when seperated out. There should be no abrupt changes in the geometry, i.e. a green wall and green floor in the background won't work that well. You must back light the subject, to get them to stand out from the background and you must add light as needed to prevent the green or blue background from reflecting onto the subject from behind which will cause unpredictable results.

Re: Green/Blue Screen Help
 

The best solution is to use Adobe After Effect's for Chroma Keying. In terms of which matte color to use, use red, green, or blue, but it's actually up to what colors are being used in the frame. You obviously want to avoid a color that is being used by another screen object.

Re: Green/Blue Screen Help
 

Stay away from red, it is too close to fleshtone.

Re: Green/Blue Screen Help
 

Unless, of course, you're trying to do something that isn't a person.

Re: Green/Blue Screen Help
 

For greenscreening, one technique I've used is this special grey cloth (I forget what it's called) made just for this that hangs behind the actors/objects. Then a ring of 50 or so super bright green LEDs goes around the camera lense and points at whatever you are shooting with the camera. On the camera, this fabric reflects back green and shows up PERFECTLY EVEN with no shadows or anything, and the people don't look green at all. It actually gives them nice color. The only thing is it is kind of hard for the actors to stare into this ring of really bright LEDs around the camera lense.

Re: Green/Blue Screen Help
 

What you are describing here is the Chromatte system. This is a pretty good system, however the screen can very easily reflect your key lighting and screw up your matte.

Speaking as someone who has to light chroma-key stuff at least twice a month for network television, I can give you a few pointers.

Number one, is not to actually light your background. You want to concentrate your lighting on your subject, and make sure they have ample backlight. Your backlight should be almost as strong as your key lighting (front lighting) The screen itself just needs a little bit of a wash. Also seperate your subject from the screen as much as possible.
A good setup is to have two keylights, 45 degrees from your subject both in the horizontal and vertical axes. Then have two backlights, mirroring your key lights. If need be, add some lower powered side-fill, and put a wash on the screen. Lighting is really the key to getting a good chroma key.
Also, make sure there are no wrinkles in the green screen.
Personally, I like using after-effects for keying, but there are lots of options.