Problems with Dark Edges

by Dyske Suematsu  •  October 5, 2006

When shooting against a green screen, you want the edges of the foreground subject to have as much contrast as possible. In this example below, we have two major problems. 1. The green screen is under-lit. 2. There is a shadow all around the edge of the subject.

Exhibit A

This footage was shot using Chromatte which is a chroma-key backdrop system that uses a specialized fabric and a ring of LED lights around the camera lens. With this system, you do not need to light the background at all; you just have to worry about lighting the foreground subject, which saves a lot of time and effort. However, unfortunately, there are some drawbacks with it.

Firstly, it creates a shadow around the edge of the subject. This happens because the source of the green color is the LED ring on the camera; it has to hit the backdrop and come back to the camera. The subject unavoidably blocks some of the light, and thus creates shadows.

Secondly, if the subject is wearing something reflective, like glasses, you literally end up seeing the green LED lights (as you can see in Exhibit A).

Exhibit B

Exhibit B is a result of using ordinary settings in Ultimatte (AdvantEdge). As you can see, it is unable to clean up the edges. It is especially visible around the left side of the neck. If I push the parameters to clean it up, what happens is Exhibit C.

Exhibit C

The hair of the subject falls apart. And, even at these settings, the edges are still not clean. You also notice the holes created by the reflections on the glasses. If you look carefully, you would also notice that the whites of the eyes are reflecting the green, causing them to show through some of the background color (in this case red).

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