Stereoscopic displays: Anaglyph process
2023-02-16
Introduction to glasses-based processes
The glasses-based processes are the most widespread variants of stereoscopic displays today, which can be attributed to the sometimes excellent perceptual results that outweigh the disadvantage of the need for special 3D glasses in most situations 5 .
Regardless of the specific implementation, the physical separation of the eyes into two separate optical devices as well as perception centers is always exploited to selectively show them different partial images with the help of glasses 5 / 20 / 21 / 22 .
The glasses can generally be divided into active models, in which electronics necessary for the function of the system, usually powered by a button cell, are located in each pair of glasses, and passive models, which do without such electronics and use only optical conditions for the exclusive selection of individual images 5 .
Thus, unlike in glasses-free methods, the physical distance of the eyes from each other and thus their slightly different perspectives are not exploited for image selection 5 / 22 .
Overview
The so-called anaglyph process is one of the oldest stereoscopic processes that is suitable for displaying changeable motifs or films. It was first described in 1853 by W. Rollmann in his article "Two new stereoscopic methods" in the journal "Annalen der Physik" and uses passive glasses with different, complementary color filter foils in front of the left and right eye 20 / 22 / 23 (see Fig. 6 ).
Classically, the complementary color combinations red-cyan or green-magenta, which use all three RGB primary colors, are used for this purpose 5 / 21 / 22 . However, combinations of only two primary colors such as red-blue or red-green are also possible 18 / 21 / 22 , with the latter variant being considered below.
Functioning
The color filters used are tinted, semi-transparent glass panels for use with the black-and-white projectors commonly used in the past, or thin plastic color films for use in the glasses themselves 22 . The glass color filters can be omitted today due to the easy availability of color-capable displays that can perform color filtering without additional or sometimes duplicate hardware 22 .
The red filter only allows waves in the range of the wave spectrum perceived as red to pass, which results in a color shift of the entire perception and means that the red partial representation can no longer be distinguished from the background by the viewer, while the blue partial representation becomes visible as black due to absorption of these wavelengths 5 / 18 / 20 / 22 . The blue filter, in turn, fades out the blue partial representation in a complementary manner to the red filter and makes the red partial representation visible as black 5 / 18 / 20 / 22 . Figure 7 illustrates this effect.
Consequently, the use of color to implement the stereoscopic effect only enables black and white perception in full quality, since the color filters cause considerable color distortion and shifting 5 / 6 and, in the long run, the colors are suppressed by the brain in favor of pure brightness perception for most people 21 / 22 .
Benefits and drawbacks
The biggest advantage of the anaglyph process is the simplicity of the technique used and thus the low cost, since it can be implemented with any current color screen/projector or, in the past, with 2 black-and-white projectors plus the various color filters and extremely inexpensive paper-color-foil glasses without much reduction in the usable resolution 5 / 22 .
In return, however, one must also come to terms with severely limited display options that are restricted to black and white 5 / 21 / 22 , which is why the development of newer, color-capable methods occurred, which have largely supplanted the anagylph process today.
Appendix
Fig. 6: Red-green anaglyph glasses
Fig. 7: Red-green anaglyph image
Sources
Text
- Rollmann, Wilhelm: Zwei neue stereoskopische Methoden, in: Annalen der Physik vol. 166 (1853), p. 186 ff..
- Grimm, Paul, Broll, Wolfgang, Herold, Rigo, Reiners, Dirk, and Cruz-Neira, Carolina: VR/AR-Ausgabegeräte, in: Dörner, Ralf, Broll, Wolfgang, Grimm, Paul, and Jung, Bernhard: Virtual und Augmented Reality (VR/AR). Grundlagen und Methoden der Virtuellen und Augmentierten Realität, 2. edition, Berlin 2019, p. 201 – 211.
- Grasnick, Armin: Grundlagen der virtuellen Realität. Von der Entdeckung der Perspektive bis zur VR-Brille, Berlin 2020, p. 239 – 249.
- Grasnick, Armin: 3D ohne 3D-Brille. Handbuch der Autostereoskopie, Berlin 2016, p. 61 – 69.
Appendix
- Based on: GeoTrinity: 3d-Brille 1978.jpg, https://commons.wikimedia.org/wiki/File:3d-Brille_1978.jpg , 14.02.2023.
- Based on: LosHawlos: Mh stereogramm anaglyphentechnik.png, https://commons.wikimedia.org/wiki/File:Mh_stereogramm_anaglyphentechnik.png , 14.02.2023.
