Most of the really good keying apps look at the difference in color values between two adjacent pixels to determine the key. When you select your green background in Keylight, it compares the RGB values of that selected color to every pixel in your frame to determine what should be keyed out and what should stay. Any pixel that falls too far outside of your selected BG color stays while everything else is keyed out. Therefore, applying color correction (of any sort) to the footage before keying will NOT change your situation in the slightest. If you boost the blues, all pixels shift toward blue and their relationship stays the same. This applies to any type of color treatment.
Your best bet might be to do one or all of the following:
- Follow Aharon Rabinowitz's brilliant
Super Tight Junk Mattes tutorial. This will limit the amount of poorly lit blue/greenscreen background that Keylight must deal with, allowing you to use milder settings that degrade your footage less.
- DV is notorious for chroma artifacts, which is probably the main reason for your troubles. Precompose your raw, un-keyed greenscreen footage. Within this new comp, create an adjustment layer above the footage, and apply the "Median" effect (Effects > Channel > Median). There is only one value to play with, change it to 3 or so. Put the adjustment layer in "Color" blending mode. This whole process will remove/smooth some of the artifacting in your footage and make for a better key. You will need to apply Keylight directly to this composition (nest it within another comp), NOT the source footage within the comp.
- To retain fine hair detail, you typically need much more delicate settings than are needed to key sleeves or pants, and one keyer setting applied to both will force you to compromise the quality of both.
For each area that should have its own specific settings you will need to duplicate your footage comp and use masks so that each layer represents one element. This way you have one layer that is just the head, one layer for the clothing etc. Then apply different keyer settings to each layer to suit its needs. You will need to animate these masks (depending on what happens in your shots) but again, this is how the pros do it and if you want the best results, this is a good place to start.
Brendan Coots
Splitvision Digital
www.splitvisiondigital.com
