Illuminations: Mopping up Spills

Previous Image « » Next Image

Just as a flower growing where you don't want it is a weed, light splashing where you don't want it is a spill. Light spills cause all sorts of problems: they emphasize the wrong areas of the video image, they cause distracting highlights and reflections, and they give away the fact that the setting is lit artificially.

Preventing or removing light spills is fairly simple when you know some tricks of the trade, so here they are. Fundamentally, there's only one way to prevent a spill: by blocking the unwanted part of the light before it hits the spill surfaces. But as the Wicked Witch muses in The Wizard of Oz, "The question is, how to do it. These things must be done dehhhh-licately!"

Any masking will create a line where the light stops; so try to match the light edge to a natural line in the image, like an inside wall corner, a ceiling line, or a doorway. If you can't find a suitable straight-edge, make the light border as soft (diffused) as possible. Edge sharpness varies with the distance between the light and the flag or other mask: the farther apart they are, the sharper the edge. A hard edge works well with a natural set line; but if you have no obvious boundary, a soft edge will fade the light gradually and look more rea…