In-camera VFX via live rear-projection during shooting — predecessor to green screen. Star Trek's Roddenberry swore by it for photorealistic backgrounds.
The Introvision technique utilizes an illuminated rear projection screen behind the actors—the background material is projected live from behind onto a translucent surface during the shoot. The camera films through the screen. The result: performers and background are created in a single take, without separate compositing work. No green screen, no matte paintings in post-production, no layering logistics. Everything happens on set, in real-time—that's the crucial point.
Roddenberry made Introvision the standard solution for Star Trek (1966–1969). Spaceship bridges, alien planet sets, space scenes—projected while the actors spoke their lines. The advantage was clear: movement in the background appeared lively, the camera could zoom or pan minimally, and the production flow remained tight. It didn't require an elaborate matte painting department or layer-by-layer optical work in the printing lab. However, there were drawbacks: the rear projection screen had to be extremely brightly lit to be visible, which caused spill and light halos around the figures. Depth of field was critical—focus had to be precisely between the actors and the screen. And the available projectors were sluggish; rapid cuts or dynamic camera movements could lead to artifacts.
After the 1970s, the method slowly died out. Digital compositing and later green screen allowed for more precise control, better mattes, and eliminated light halos. Yet, Introvision was ingenious for its time: it provided television productions and low-budget films a way to create complex visual environments without overloading the optical department. Some documentaries about 1960s-70s sci-fi still mention camera operators manually controlling projectors to synchronize live with camera movement. That was practical VFX choreography.
Today, Introvision is a textbook chapter. But anyone analyzing old Star Trek episodes will immediately recognize the characteristic flatness and haloing around the performers—not bad, just different. The method shows: before digital simulation came optical-mechanical real-time solutions. And they worked.