Budget stereoscopic filter glasses with colored lenses—red/cyan or green/magenta—separating color data per eye. Cheap to produce; standard giveaway for classic 3D cinema screenings.
Anaglyph glasses work on an astonishingly simple principle: two colored filters—classically red and cyan, less often green and magenta—control which image information each eye receives. The left filter blocks everything in its complementary color, the right filter does the same. On set or in editing, this means you shoot or composite two slightly offset images on top of each other, each in one of the filter colors. For the viewer, the glasses separate these color channels again—the brain recombines them into spatial depth.
The practical advantage in the analog era was immense: the glasses cost cents in mass production, can be easily distributed to thousands of viewers, and the necessary camera technology is minimal. You don't need expensive polarization filters, 48fps synchronization, or special screens. That's why anaglyph glasses were the method of choice for B-movies and sensational cinema in the 1950s—"Creature from the Black Lagoon," "House of Wax." Audiences tolerated the compromises.
But herein lies the technical catch: color separation by red/cyan creates massive color shifts and ghosting effects—especially with movement. A white shirt develops red and cyan double outlines. Skin tones appear distorted. Looking for a long time causes headaches. The glasses don't really filter two separate images, but rather subtract color channels from the monoscopic source material. This isn't a true stereoscopic 3D impression, but an optical illusion with a high discomfort factor.
Today, we only use anaglyph glasses as a last resort—for previews in the edit suite when no polarized system is available, or as a demo tool. In professional 3D cinema, they have long been replaced by polarizing filters and active shutter technology. But the trick itself lives on: in VR and for mass distribution of 3D material over the internet, the anaglyph principle occasionally resurfaces—because it remains the cheapest method to pack spatial information into a 2D signal. You just have to know that you are demanding a real visual sacrifice from the viewer.