See-through panel behind actors — glass or printed screen showing background. Faster setup than greenscreen for static scenes.
On set, I envision transparencies as the classic solution when time is tight and the actor is meant to stand relatively still in front of a background. You mount a printed or projected surface — glass, acrylic, sometimes even a high-resolution canvas — directly behind the performer. The advantage over greenscreen lies in its immediacy: no keying session in post-production, no color correction of the matte, no fringing issues. What you see in the viewfinder is essentially the finished composite — at least optically.
In practice, however, things are more nuanced. A good transparency requires precise lighting: the background must be lit evenly, but it must not spill onto the performer or create flares. I work with separate lights for the transparency layer — often T12s or LED panels — to decouple it from the key light on the actor. The distance between the performer and the transparency is critical: too close and the lighting becomes flat, too far and the background appears spatially disconnected. I usually maintain a distance of 1.5 to 2.5 meters.
Limitations become apparent with camera movements. A panning camera quickly reveals the flatness — parallax disappears, the background moves unnaturally. Therefore, I primarily use transparencies for static or very minimally moving shots: portraits in an office, drivers behind a windshield (here as a projection), figures in waiting areas. For dolly shots or pan movements, I opt for greenscreen or a real location much faster.
Material and size also influence the lighting technology. A real glass pane is expensive, causes scratches, and is cumbersome to transport. Modern printed plastic transparencies are more manageable but less sharp. High-resolution digital projection transparencies (e.g., with a projector and a screen) offer flexibility — I can switch backgrounds live — but require absolutely stable equipment and darkness on set.
In a historical context, transparency was the standard composite technique before digital — matte paintings were used in real-time behind actors. Today, I use it as a pragmatic tool: fast, visible, forgiving. It remains useful when light control on set is possible and the scene does not demand complex motion architecture.