it would help to know how you went about keying.. which effects, techniques, etc…
if it is just green spill, you might try the spill supressor effect…
but, i can tell you that there is really no sure fired way to get a great key every time, but there are techniques that can help. there are tutorials here at the cow that can help.
one is aharon rabinowtz’s supertight junk mattes, which is a techniques that will reduce the amount of area that you are keying and generally helps in createing better keys.
barend onneweer has an older tutorial for precedural matte creation that is still a very solid way to produce a key using the concept of core and edge mattes.
if you are using keylight, you can actually use 2 instances of the effect in a similar procedure to the technique that barend shows. the details are in the manual for keylight.
i often use aharon’s super tight junk matte to ‘crop out’ the extra green screen area, then paste the masks back onto the layer to key, shrink it in (via the mask expansion setting) and maybe feather it a bit. then using keylight, set that mask as the ‘inside mask’ with in key light. this creates a core matte similar to barend’s and similar to the method outlined in keylight manual, but it render’s more quickly.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW