Chromakeys

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Chromakeying is a technique that is used to remove a color from an image and show a different image in place of that color. In this article different quality and speed optimized techniques will be shown regarding how one can make color keying in software.

And the popular cure-all seems to be the proper lighting of your Chromakey wall (or back-drop). Not just a wimpy little 100 watt light aimed somewhere in the general direction of the background, but a host of lights that literally flood the background.

We’re talking a minimum of two 250 watt quartz halogens aimed at the backdrop from high and off to each side so that they will not inadvertently cast any shadows from your key subject (who should be standing at least three feet out from the backdrop).

The key subject should be illuminated with it’s own key light (another 250 watt plus) that is preferably diffused with either an umbrella or a diffusion filter.

If your camera and Panasonic MX-50 video mixer will not recognize your background as a solid, evenly lit blue, then the Chroma Keying will go crazy trying to determine where the background ends and the key subject begins.

Hence, the “jaggies.”

Every now and then, the background color of blue will reflect back onto the key subject. And this, of course, will cause background video to be keyed in onto the key subject, which you don’t want to do.

This reflected blue can be mostly eliminated by placing light colored amber gels over your background lights (the two lights that flood your backdrop). More specifically, ask for “bastard amber” at your local photo shop when purchasing these gels. They’ll know what you’re talking about.

As for the key subject light, place it about three or four feet off to one side or the other of the camera so as not to cast any direct shadows onto the background.

Once you have adjusted your “hue” and “slice” control on the Panasonic WJ-MX50 for optimum Chroma-key effect that you view on your monitor, slight adjustments of the angle and location of all of your lights will make the effect that much better.