Apply multiple keys to a single subject
In some instances, it may be difficult to key an entire subject with a single keying filter while retaining fine details. For example, uneven lighting or background color might mean that the best settings to key a subject’s hair may not work elsewhere. In such cases, you can use masks to isolate different parts of a subject, and then apply different keying settings to each area.
Segment a subject into separate keying zones
Create a group and place the layer you’re keying in the new group.
Duplicate the layer you’re keying until you have a separate duplicate for each part of the image you want to key separately.
Use a mask tool to mask each part of the subject in the duplicate layers.
Note: For more about using the mask tool, see Masks and transparency overview.
Make sure the masks overlap, so there are no gaps in the foreground.
Note: If the foreground subject is moving, you might need to animate the overlapping masks.
Apply the relevant keying filter to the isolated parts of the subject, then adjust each filter’s settings.
Eventually, you may find you can achieve an optimal key for each part of the subject. Furthermore, with all duplicates nested in a single group, you can continue to manipulate the subject as a single object.