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Anaglyphic 3D, an old trick
An anaglyph is composed of two superimposed images of complementary colors, presenting the same scene with a slightly shifted point of view: most often the « left eye » view is in red and the « right eye » view in cyan.
By filtering the light for each eye in an adequate way, a 3D view of the scene can be restored for a spectator possessing an approximately « normal) sight), i.e. possessing two eyes with an innate perception of depth.
The principle was described in 1853 by Wilhelm Rollmann in Germany. Charles Joseph d’Almeida seized on this knowledge, spoke about it at the Paris Academy of Sciences in 1858. Louis Ducos du Hauron perfected the technique, and finished developing it in 1891. It was he who gave the anaglyph name to the method.
The anaglyphic process reaches the cinematograph, adapted by Louis Lumière in 1936. This will however remain slightly used, special glasses being necessary, increasing the cost of projections.
Anaglyphs were widely used at the beginning of the 20th century for tourism (3D monuments), education, leisure, and advertising. Today, improved versions are still used for example in space research, with phase-shifted digital images in anaglyphic mode from the surface of Mars during the Mars Exploration Rover and Phoenix missions.
The depthmap
While doing my research, I realized that a technique is often used by cinema: films are shot normally, then 3D is added afterwards! Technicians use what is called a depthmap for each image.
The depthmap is a grayscale version of an image. The levels of gray are distributed in such a way as to represent the depth of the original image. The most widely used standard says that light colors are close, and dark colors are far (neutral gray is position 0).
From this depthmap, which therefore indicates a distance from the eye of the observer, we can do simple mathematical calculations to create an image slightly shifted relative to the first. Imagine if this offset reflects the distance between two eyes...
Let’s say that the original image is the one that corresponds to the left eye. By calculating the shifted image that would correspond to the right eye, we simply obtain the basis of anaglyphic 3D.
The process is very time-consuming: each image must first be cut into depth zones, which is a manual operation. Then you need to calculate the shifted image (Photoshop’s Dispersion plugin is perfect for this), and recombine the two sides « left » and « right ».
The cropping of the image is such a painful operation that I tried several techniques:
- manually: requires a graphics tablet and a lot of patience
- the masking plugins under Photoshop: I tried them all, none is precise enough to obtain a correct rendering in 3D
- the use of artificial intelligence: the progress made in deep learning in recent years is promising, and I am still studying the question
Know that I spend about four hours per photo to process, cutting and testing, before producing the final image.
3D photo formats used on this site
In my photo galleries where you can find 3D versions of images, you can encounter the following formats. Here is how to visualize them:
- the original photo: it is here so you can compare with the other versions
- the depthmap: represents the distance in greyscale of the objects in the original photo
- red and blue anaglyph: you need red and cyan anaglyph glasses (red for the left eye) to visualize the photo with depth
- cross-eyed anaglyph: for people who don’t own anaglyph glasses. To perceive depth, no need for them: you have to cross your eyes and control them, to try to mix the left and right parts in the « middle ». It requires a bit of training, and can cause strain to the eyes. The advantage is that the colors are not distorted.
For more explanations and training, you can follow this article.
Softwares like StereoPhotoMaker let you visualize these files, and convert them to other formats
- Animated: computing several positions allows to create a video giving the impression of depth without glasses. Videos are in aPNG format: if you don’t see anything moving, please update your internet browser! Only recent releases of Firefox, Chrome and Safari can read them
To create the videos, I’m using a heavily modified script given back to Ugo Capeto’s site for the oldest photos, and my own tools that you can find on GitHub for the latest ones.
Enjoy my photos in 3D!
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