Anaglyph
An anaglyph is a 3D picture made of two colored views, one per eye, seen through red-cyan glasses. Its history from silent film to Mars, and why colors shimmer.
What is an anaglyph?
An anaglyph is a stereo image shown as two overlapping views in contrasting colors, nearly always red for the left eye and cyan for the right. Without glasses it looks like a photo with colored fringes; through matching filter glasses each eye sees only its own view, and the picture gains depth.
It's the cheapest way to show 3D. You need one ordinary print or screen plus glasses made of cardboard and colored gel, and the same image works in a book, on a phone or projected on a wall. That's why it keeps coming back after more expensive systems fade out.
From silent film to Mars
The first 3D feature film, The Power of Love, premiered in Los Angeles in September 1922 and used red-green glasses. It had two endings, a happy one and a tragic one, and which you saw depended on the lens you looked through. The 3D version is now lost.
Most 3D films of the 1950s boom were projected with polarized light, which keeps natural color, but anaglyph took over printing. In 1953 St. John published a 3-D Mighty Mouse comic using a process by Joe Kubert and Norman Maurer, packed with paper glasses, and a short craze for 3D comics followed. Today NASA posts anaglyphs from the stereo camera pairs on its Mars rovers, so anyone with paper glasses can see the terrain in depth.
Why do anaglyphs make colors shimmer?
Each eye only gets part of the spectrum. The left eye sees the scene in red, the right in green and blue, and the brain has to merge two images that differ in brightness as well as position. A strong red looks bright to one eye and nearly black to the other, and the result flickers between the two. That's called retinal rivalry, and it's why anaglyphs work best on gray or muted pictures and why a red car or a deep blue sky loses its depth.
The color pairs changed over the years to reduce this. Early anaglyphs used red with green or with blue. Red and cyan became the standard because cyan carries green and blue together, so the right eye gets a fuller picture. Amber and blue systems such as ColorCode 3D keep color better and were used for 3D commercials during the 2009 Super Bowl.
Reading the fringes
The fringes tell you where things sit. Parts of the scene at screen depth have no fringe at all. Anything meant to float in front of the screen shows red on its right edge and cyan on its left, and anything behind the screen shows the reverse. If every edge in a picture has the same fringe, it was made with a plain color offset, which moves the whole flat image forward or back without giving it any depth.
Making an anaglyph from one photo
Anaglyph 3D Effect splits a single photo or video into red and cyan views and guesses depth from the picture itself. Because of rivalry, choose an image without large areas of pure red or cyan, and with a clear subject in front of a separate background. The page opens on the Deep preset; Depth source Edges suits outdoor scenes where brightness says little about distance, and Mode Colour split gives a fringe-only look for posters that nobody needs glasses for.
