1920s camera trick — moving backdrop behind transparent foreground object. Precursor to rear projection; allowed real-time compositing and double exposure in a single pass.
Pomeroy Process
As early as the 1920s, solutions were needed for composites without a process screen and multiple exposures — and this is precisely where the Pomeroy Process comes in. A moving screen is placed behind a transparent or semi-transparent foreground object, while the camera captures both layers simultaneously. The result: actors in front of a window, a moving car in the background, all recorded in a single take, without later matting or optical compositing.
The technique works pragmatically: a screen — often white or light-colored — runs behind glass, silk, or another translucent material. The foreground layer remains relatively static or moves in a controlled manner, while the background screen simulates the movement of the background. Lighting direction is essential — the background projection must appear flatter than the foreground, otherwise the separation will look incorrect. In contrast to later Rear Projection (projection onto a screen from behind), Pomeroy worked with physical movement and optical layering.
On set, the limitations quickly become apparent: camera movements are severely restricted — a pan can destroy the entire setup because the perspective relationship between the foreground and the moving screen is incorrect. However, for static setups, such as an actor at a window while a street passes by outside, Pomeroy was economical and reliable. No elaborate shooting day on a real location was necessary, no multiple exposures that are tedious to time.
Historically, the process marks a transition: early special effects techniques were montage-heavy, Pomeroy brought live compositing to the stage — albeit primitive. Later, Rear Projection and digital keying replaced these mechanical solutions, but the conceptual approach — multiple image layers simultaneously in front of the lens — remains fundamental. Anyone using green screens today is working on the same logistical principle, only that the separation takes place digitally. The Pomeroy Process was the hardware version of this idea.