I was looking at some screen caps of the remastered Mudd's Women over at Trekcore and, lo and behold, there are the equivalent of CGI matte lines around the asteroids (check out the block borders):
http://tos.trekcore.com/hd/albums/1x06hd/muddswomenhd024.jpg
No such thing around the Enterprise. Most odd!
http://tos.trekcore.com/hd/albums/1x06hd/muddswomenhd024.jpg
No such thing around the Enterprise. Most odd!


), FX houses can even go so far as to do each light source and the specular and diffuse elements as separate passes.