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A front projection effect is an in-camera visual effects process in film production for combining foreground performance with pre-filmed background footage.
Working
In contrast to rear projection, in front projection the background image is projected on to both the performer and the background screen. This is achieved by having a screen made of Scotchlite, a product of the 3M company that is also used to make screens for movie theatres. Scotchlite is made from millions of glass beads cut in half and affixed to the surface of the cloth. These glass beads reflect light back only in the direction in which it came, far more efficiently than any common surface. In fact, Scotchlite is 1000 times more reflective than the human body.
The actor (or horse or spaceship, etc.) performs in front of the Scotchlite with a movie camera pointing straight at him. In front of the movie camera is a one-way mirror angled at 45 degrees. At 90 degrees to the camera is a projector which casts a faint image of the background on to the one-way mirror which then reflects the image back at the performer and the Scotchlite; the image is too faint to appear on the actor but will show up clearly on the Scotchlite. In this way, the actor becomes his own matte. The combined image is then reflected back through the one-way mirror and is recorded by the camera.
A Space Odyssey (film) is commonly believed to be the first movie to make use of front projection for the “Dawn of Man” sequence. The 1967 monster film Equinox made use of it first. The actors in ape suits were filmed on a stage at Elstree and combined with footage of Africa. (The effect is almost flawless except for the glowing cheetah's eyes reflecting back the light.)
Zoptics
Front projection was chosen as the main method for shooting Christopher Reeve's flying scenes in The Movie. However, they still faced the problem of having Reeve actually fly in front of the camera. Yugoslav effects wizard Zoran Perisic devised a new refinement to front projection that involved placing a zoom lens on both the movie camera and the projector. These zoom lenses were synched by computer so as the camera zooms in, the projector zooms out, or vice versa. The background grows smaller and the actor grows bigger; thus Superman flies towards the camera. Perisic called this technique Zoptics. The process was also used in the three Superman sequels, The Movie and Perisic's sole film as director Sky Bandits (also known as Gunbus.)
IntroVision
In Front projection, light from the projector that travels through the one-way mirror is “soaked up” by black velvet. In IntroVision, the black velvet is replaced by another Scotchlite screen that reflects the image back towards another scotchlight screen placed before the performer. Thus, the same image appears from two different sources and lands on two different screens creating a “3D” effect. IntroVision was first used in Outland to combine star Sean Connery with models of the Io mining colony. It was also used in Under Siege, Army of Darkness and The Fugitive, where it seemed to place Harrison Ford on top of a model bus that was then rammed by a model train.
Front projection phased out
Front projection had several advantages over its main rival bluescreen. It didn't have the thick black outlines that sometimes appear on bluescreen films. It was less time consuming - and therefore less expensive - than the long process of optically separating and combining the background and foreground images using an optical printer. It allowed the director (if not necessarily the actors) to see the background and call out necessary adjustments (“Jump now, Harrison!”). And, especially with Zoptics, it was a more flexible system that allowed for more complex sequences that could be attempted at the time with bluescreen. However, advancements in green screen and CGI animation have rendered front projection obsolete. The last major blockbuster to extensively use front projection was the Sylvester Stallone action thriller Cliffhanger.
See also
"Front projection effect"