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.
In the Layers list, create a new group, then drag the image layer you’re keying into that group.
In the Layers list, Control-click the image layer, then choose Duplicate from the shortcut menu.
Create a duplicate for each part of the image that you want key separately.
Use a mask tool to mask each part of the subject in the duplicate layers.
Make sure the masks overlap, so there are no gaps in the foreground.
Note: If the foreground subject is moving, you may 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.