Theater ad for one of the first commercial 3D films, Ouch, which used a subtractive anaglyph process developed by Ives and Leventhal. Subtractive anaglyphs store the left and right channels as colored images on the film itself; Ives and Leventhal glued together two strips of film, one yellow and the other cyan. The film was then projected through a single projector. Additive anaglyphs, on the other hand, project two strips of film through color filters using two projectors.