Here are some tips and tricks for optimizing your greenscreen shots when shooting with the gh2.
Since I have the gh2, I use it side by side with a red one when doing greenscreen shootings for TV Vfx.
As the gh2 isn´t capable of recording raw and doesn´t have the same lattitude as the red, I figured out the following techniques
to take the gh2 greenscreen shots to a level where you can really intercut them with the red material on broadcast programs.
Which I regularily did and do, and nobody ever realized, that that material wasn´t all shot with the red.
Try this with the 5d MK2 and you´d be completly lost.

Lets assume you build a little greenscreen set, maybe 5x3 metres, shooting somebody standing in front and on green cloth.
As money is short you buy no pro greenscreen cloth but just green cloth from ebay or so. Thats fine.

Try to get the cloth as wrinklefree as possible, some wrinkles won´t be a big problem.

If you have very dark (Black) shadows on the foor or elsewhere in the greenscreen try to brighten them up with bounced light - styrofoam will do.
It´s not necessary to get a perfectly even lit screen, just avoid deep black shadows and blown out white spots.

If you can control the brightness of the screen by adding light with lamps or bouncecards, or subtracting light with black cloth here´s how you can find the perfect sweet spot for the brightness, the greenscreen should have:
You need a greycard which has a square of 90% white in it and a Kodak Wratten No. 99 Filter. Both together shouldn´t be over 100$ but it really makes the difference.
Light your actor in front of the screen and the screen itself.
Set the exposure on your camera.
Hold the 90 % white card in front of the greenscreen, so it catches the light the actor would usually catch.
Look thru the No.99 (green) filter. If the the 90% white looks darker green than your greenscreen you have to brighten the greenscreen,
if it looks brighter try to darken the greenscreen. Your setup is perfect when the 90% white seen thru the green filter looks more or less like your greenscreen. If you´ve done that a few times you get a feeling for it.
This technique really helps getting an easy good key with gh2 material.

If you have a lot of action creating lots of motionblur in your image, you´ll get problems. The blur against green gets quite ugly and tends to produce
black edges. If you can afford Reelsmart Motionblur (an After Effects Plugin), you should double your shutter speed during shooting (1/100 for 25 frames or 1/120 for 30 frames). You´ll get cleaner and sharper motion. Use Reelsmart Motionblur to generate Motionblur on your greenscreen footage right after the keyer before merging with the background. Select "Images are premultiplied" if you encounter fringes.

I found the following GH2 settings best for me:
Smooth, contrast -1, sharpness -1, color saturation -1, noise reduction -1

Always prefer greenscreen to bluescreen, cause the green channel is much cleaner.

If you are short on light, and you have too much noise in your shot, even if you don´t see it a first glance (zoom in and you´ll find it),
denoise your shots with neatvideo before keying. It´s the best denoiser by far. In my opinion it gives you the opportunity to push one stop further than you would normally do. Push the iso up to the extend, that you would normally say "Okay thats one step too much, now I see more noise that I can accept" . Using neatvideo gets you back to the quality of one Iso down most of the time.

Use 5DtoRGB to transfer your clips before compositing. It helps you get a "smoother gamma", saving more color information in dark parts of your greenscreen.

Although all this works with a unhacked gh2 (I did a broadcast job with it before the hack), using the higher bitrate of the hack greatly enhances your results. I use the 66mb setting.

Last tip, if you have serveral keyers or keying plugins, always test them all quickly without heavy tweaking on your shot.
In most cases one keyer will work obviously better than the others, and thats really not always keylight. Choose the one that performed best, and refine.

Hope that helps you to tackle greenscreen shots easier in the future.
It´s clear that you can´t follow all that tips in most cases, just try to use as many of them as possible.

Regards
Holger Neuhaeuser