Reverse bluescreen

Reverse bluescreen is a visual effects technique pioneered by Jonathan Erland of Apogee Inc.(John Dykstra's company) for shooting the flying sequences in the film Firefox. Its objective is to enable the matting of subjects that confound the conventional process, such as those exhibiting reflective surfaces. It derives its name from the fact that it reverses, or inverts, the basic bluescreen process. Erland received a Scientific and Engineering Award from the Academy of Motion Picture Arts and Sciences for this technique.

Implementation

The patented technique is a variant of the traditional bluescreen traveling matte process for composite photography. The basic bluescreen process calls for filming a subject in front of the solid blue backing, which consists of a translucent blue plastic sheet in front of banks of fluorescent lights. This process poses a problem. A reflective surface on the subject being filmed would result in blue reflections visible to the camera. Since the compositing process entails converting blue in the image into some other background image, such reflections would result in holes in the foreground subject with the background scene showing through.

The reverse bluescreen process overcame this problem by coating the foreground subject with a clear fluorescent paint that was invisible under conventional visible light but fluoresced when illuminated by ultraviolet blacklight, thus inverting the process. The filmmakers shoot a subject, such as the glossy black jet fighter in the Warner motion picture Firefox, against a neutral (e.g., black) background lit with normal stage lights. Then, they reshoot exactly the same scene (using precise motion control photography), but with the normal stage lighting replaced with blacklight. The 360nm UV light causes the fluorescent paint to glow, transforming the plane from black to a glowing object. From this image a male and female traveling matte could be produced that enabled the plane to be composited into any background scene desired.