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DV Chromakeys

From the magical CGI composites of Hollywood to the meteorologist pointing to an animated map, the one essential element that links them is the key. Perhaps you'd like to make your two-year old child appear like Godzilla on top of a neighborhood of unsuspecting barbecue dads. In the olden days, that kind of composite was an expensive and time-consuming process of optical printing, re-photographing film images and hand-drawing mattes to replace the previously photographed foreground object, one frame at a time. We know an easier way.

Same as it Ever Was

When the consumer DV format came out in 1995, it truly was a milestone. 500-line resolution and far clearer color than analog S-VHS and Hi-8, all on a tiny tape that could be digitally copied or captured to a computer through a single FireWire cable, edited and dubbed back to the camcorder without losing any quality. Indeed, with the advent of faster processors, higher-speed hard-drives and ever increasing memory, not to mention hardware-accelerator boards, computers have risen to the challenge of video editing with a ferocity that leaves even a so-called "state-of-the-art" 500MHz Pentium II from 1998 in the dust. Despite all this technological prowess, when it comes to chromakeying, we're still confined to the basics: replacing the background key color with a new background. The trick is to leave the foreground subject intact as a clean, pure composite, with no telltale hint that the foreground subject is even part of a composite, making the illusion complete. Pre-CGI (computer generated graphics), filmmakers grappled with these same issues. Even post-CGI filmmakers have to be careful when photographing their actors against blue or green screen to ensure that their actors will composite cleanly into the yet-to-be-produced FX backgrounds in post. The process of creating clean composites is as much an art as a science, and demands tight quality control over every element seen in the frame.

Chromakeying is the process of selecting a color (or small range of colors) in a video signal and making that color transparent. You place your foreground subject against some type of plain-color background, blue or green being the color backgrounds commonly used. After your software makes the color transparent, you can put anything you want into the backg…