Green screen effects are very popular now, especially as the technology needed to get a good key is no longer limited to high end VFX companies. However, whilst software such as After Effects can produce great results the key to getting a good, er, key is in the actual setting up of the lighting for the shots.
Here is a shot I’ve been struggling with.
As you can see there are bright and dark areas and also parts of the umbrella that are also green. These shadows and highlights will cause problems because their colour is closer to black and white than green so the chroma key effect will not recognise them. There are tools to compensate in After Effects but if this was a consistent shade of green the key would be much easier to achieve and cleaner.
When lighting for a key try to pull the subject forward of the background to soften harsh shadows and reduce spill (the reflection of the green colour on the subject). Also try and use a diffuse light (LEDs and Kino Flows work well, spotlights are too harsh without diffusion paper). Also try and use a fill light to illuminate the screen behind the subjects (but make sure this is even with no hotspots).
Also be aware that any green in the shot will be keyed out unless we use a mask on that area. The problem is tracking a mask can be very time consuming.
As I alway say, the extra 5 minutes spent setting up a shoot can save hours in post production.
Here’s something I shot which keyed out nicely. There are a couple of green items on the table but because the table is static and the shot was done using a tripod I had no problem masking them.