Extract an alpha matte from a ID-Pass to be used as a mask
How to use :
Select one or more color to be keyed.If the color is not an exact match, or if you use 8bits images for the ID pass, then increase the tolerance factor.
Note that pure Black color is ignored (to avoid unnecessary calculations) , but if you need to key black color you can still set the key color to a very very low gray value and increase a bit the tolerance factor)
The screenshot below doesn't show the tolerance slider that has been added after.
