A 3-D film or S3D film is a motion picture processed to include the illusion of depth perception. Derived from stereoscopic photography, a specifically designed motion picture camera is used record the subject from two perspectives and hardware is setup to playback the video and its illusion of space using unique displays and/or eyewear. 3-D films are not limited to feature film theatrical releases; Television broadcasts and direct-to-video films have also used incorporated similar methods to draw attention to their content.
3-D films have existed in some form in since 1890 but largely relegated to a niche in the motion picture industry because of the costly hardware and processes required to produce and playback a 3-D film and the lack of a stereoscopic format for all levels the entertainment business. Nonetheless, 3-D films were prominently featured in the 1950s and 1980s in American cinema and currently experiencing a resurgence at the start of 21st century coinciding with the development of computer-generated imagery and introduction of high-definition video standards.
Techniques
Stereoscopic motion pictures can be produced through a variety of different methods. Over the years the popularity of various systems being widely employed in movie theaters has waxed and waned. Though anaglyph was sometimes used prior to 1948, during the early "Golden Era" of 3-D cinematography of the 1950s the polarization system was used for every single feature length movie in the United states, and all but one short film. In the 21st century, polarization 3-D systems have continued to dominate the scene though during the 60s and 70s some classic films which were converted to anaglyph for theaters not equipped for polarization and were even shown in 3D on TV! In the years following the 90s some movies were made with short segments in anaglyph 3D. Following are some of the technical details and methodologies employed in some of the more notable 3-D movie systems that have been developed:
Anaglyph
Anaglyph images were the earliest method of presenting theatrical 3-D and the one 3-D method most commonly associated with stereoscopy by the public at large, mostly because of non theatrical 3D media such as comic books and 3D TV where polarization doesn't work. They were made popular because of the ease of their production and exhibition. Though the earliest theatrical presentations were done with this system, most 3D movies from the 50s and 80s were originally shown polarized.
In an anaglyph, the two images are either superimposed in an additive light setting through two filters, one red and one cyan. In a subtractive light setting, the two images are printed in the same complementary colors on white paper. Glasses with colored filters in either eye separate the appropriate images by canceling the filter color out and rendering the complementary color black.
Anaglyph images are much easier to view than either parallel sighting or crossed eye stereograms, although the latter types offer bright and accurate color rendering, particularly in the red component, which is muted, or desaturated with even the best color anaglyphs. A compensating technique, commonly known as Anachrome, uses a slightly more transparent cyan filter in the patented glasses associated with the technique. Process reconfigures the typical anaglyph image to have less parallax.
An alternative to the usual red and cyan filter system of anaglyph is ColorCode 3-D , a patented anaglyph system which was invented in order to present an anaglyph image in conjunction with the NTSC television standard, to which the red channel is often compromised. ColorCode uses the complementary colors of yellow and dark blue on-screen, and the colors of the glasses' lenses are amber and dark blue.
The anaglyph 3-D system was the earliest system used in theatrical presentations and requires less specialized hardware, but the polarization 3-D system has been the standard for theatrical presentations since it was used for Bwana Devil in 1952, though early Imax presentations were done using the eclipse system and in the 60s and 70s classic 3D movies were sometimes converted to anaglyph for special presentations. The polarization system has better color fidelity and less ghosting than the anaglyph system.
In the post 50s era, anaglyph has been used instead of polarization in feature presentations where only part of the movie is in 3D such as in the 3D segment of Nightmare on Elmstreet 6: Freddy's dead and the 3D segments of Spy kids 3D .
Eclipse method
With the eclipse method, a mechanical shutter blocks light from each appropriate eye when the converse eye's image is projected on the screen. The projector alternates between left and right images, and opens and closes the shutters in the glasses or viewer in synchronization with the images on the screen. This was the basis of the Teleview system which was used briefly in 1922.
A variation on the eclipse method is used in LCD shutter glasses . Glasses containing liquid crystal that will let light through in synchronization with the images on the computer display or TV, using the concept of alternate-frame sequencing. This is the method used by XpanD
Lenticular or barrier screens
In this method, glasses are not necessary to see the stereoscopic image.
Both images are projected onto a high-gain, corrugated screen which reflects light at acute angles. In order to see the stereoscopic image, the viewer must sit within a very narrow angle that is nearly perpendicular to the screen, limiting the size of the audience. Lenticular was used for theatrical presentation of numerous shorts in Russia from 1940-1948 and in 1954 for the feature length films Crystal , Machine 22-12 and The Pencil on Ice .
Though it's use in theatrical presentations has been rather limited lenticular has been widely used for a variety of novelty items and has even been used in amateur 3d photography!
Interference Filter Technology
Dolby 3D Uses specific wavelengths of red, green, and blue for the right eye, and different wavelengths of red, green, and blue for the left eye. Eyeglasses which filter out the very specific wavelengths allow the wearer to see a 3D image. This technology eliminates the expensive silver screens required for polarized systems such as RealD, which is the most common 3D display system in theaters. It does, however, require much more expensive glasses than the polarized systems.
Pulfrich
The Pulfrich effect is based on the phenomenon of the human eye processing images more slowly when there is less light, as when looking through a dark lens.
Imagine a camera which starts at position X and moves left to right to position Y as shown by the arrow. If a viewer watches this segment with a dark lens over the left eye, then when the right eye sees the image recorded when the camera is at Y, the left eye will be a few milliseconds behind and will still be seeing the image recorded at X, thus creating the necessary parallax to generate right and left eye views and 3D perception, much the same as when still pictures are generated by shifting a single camera. The intensity of this effect will depend on how fast the camera is moving relative to the distance to the objects, greater speed creates greater parallax. A similar effect can be achieved by using a stationary camera and continuously rotating an otherwise stationary object. If the movement stops, the eye looking through the dark lens (which could be either eye depending on the direction the camera is moving) will "catch up" and the effect will disappear.
Of course, incidental movement of objects will create spurious artifacts, and these incidental effects will be seen as artificial depth not related to actual depth in the scene. Unfortunately, many of the applications of pulfrich involve deliberately causing just this sort of effect and this has given the technique a bad reputation. When the only movement is lateral movement of the camera then the effect is as real as any other form of stereoscopy, but this seldom happens except in highly contrived situations.
Though pulfrich as has been used often on TV and in computer games, it is rarely if ever used in theatrical presentations.
Pseudo-stereoscopic systems
Alternative systems, such as Chromadepth exist, but fall under the realm of "pseudo-stereoscopic" in that two, separate records are not recorded or projected.
Systems without glasses
Several other less popular 3-D systems exist which also do not require the use of special viewing glasses. These systems are referred to as Autostereoscopic displays.
Polarization systems
In stereoscopy, two forms of polarization
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