The trick to pulling a great key in post is to ensure you setup your shoot correctly. Here are a couple of tips to ensure you get a better result.
My Green Screen Tips
Have your talent standing in front of the chroma screen with a minimum distance of 2 metres. This minimises the chances of your talent casting shadows back onto the chroma screen. It also helps minimise the amount of reflection from the chroma screen back onto the edge of the talent.
Make sure you light correctly. Your back lights need to light the chroma screen evenly, no hot spots and no shadow areas, not too bright and not too dark. Have a rim light for your talent, this really helps crisp up the edges. Your main light or key light needs to evenly light your talent and use a fill light or reflector for the other side.
Flip your camera. If you're filming a presenter then flip your camera to the horizontal. By doing this you get almost twice the size image and twice the amount of pixels. In post just flip the image around and scale down, this really helps minimize those little jaggies on the edges of your talent when you're using 4:2:0 colour space (which most mid-range cameras do).
Think about getting your hands on an external recorder like the Atomos Ninja or the Blackmagic HyperDeck Shuttle. External recorders like these allow you to record in ProRes 4:2:2 (as well as other highres codecs). The extra colour space from these codecs makes a universe of difference in pulling a key in post. In fact at Incubate Productions, we won't do a chroma shoot without one.
Be careful when using a DSLR camera! As fantastic as DSLR's are they have one major floor, moire. Moire is that horrible swimming effect that occurs when you film tight, intricate patterns and once you've filmed it it's nigh on impossible to get rid of it. As a rule you should always check that your talents isn't wearing anything that could cause moire. We always do a test shot and play it back on the large screen to check (it's saved our bacon on a couple of occasions).
Finally and most obviously, ensure that your talent doesn't wear anything the same colour as your chroma screen. Sounds obvious, I know, but we've seen it happen on a few occasions.
Charles Meadows is a Director, DoP and owner of Incubate Productions in Johannesburg, South Africa. He has produced, filmed and director more commercials and corporate films than he can remember.