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Stereoscopic 3D (S3D) is a method of giving depth perception that exploits uses the binocular disparity [[depth cue]] to produce the illusion of depth. It can be used in still or moving images. It produces an illusion of depth by displaying two slightly different images left and right eyes[[eye]]s.<ref name=”1”> Techopedia. 3-D Stereo Technology (S3-D). Retrieved from https://www.techopedia.com/definition/81/3d-stereo-technology-s3d</ref>. This ability is based on the characteristics of the human visual system.
The eyes, being positioned horizontally in the head, receive two views of the visual scene - one for the left-eye and another for the right-eye. The views overlap but differ slightly since they originate from two distinct perspectives. The visual system interprets and processes the information gathered from the two images to produce stereoscopic depth. The binocular system is very good at coordinating the movement of the eyes, which move constantly even during fixation. From a functional point of view, the images of both eyes fall on the fovea when fixating binocularly on a point. The fovea is the part of the back of the eye that has the highest acuity. According to Tam et al. (2011), “an object fixated binocularly is imaged on the same relative coordinates in the left-eye and right-eye views and it is perceived as a single percept, i.e., it is seen as a single object.” <ref name=”2”> Tam, J. A., Speranza, F., Yano, S., Shimono, K. and Ono, H. (2011). Stereoscopic 3D-TV: Visual Comfort. IEEE Transactions on Broadcasting, 57(2)</ref>
[[File:Anaglyph lenses.jpg|thumb|Figure 3. Red and blue anaglyph 3D glasses (Image: amazon.com)]]
There are several techniques available used to create the illusion of a 3D image with the use of lenses. 3D displays use the same guiding principles as the visual system to exhibit depth. In each eye, slightly different perspectives are presented so that the brain uses the differences between them to give the sense of depth .<ref name=”7”> Hurricane Media (2011). Stereoscopic 3D filming and graphics, how 3D works [Video]. Retrieved from https://www.youtube.com/watch?v=IYm3BmnyVrg</ref> <ref name=”8”> Techopedia. 3-D Stereo Technology (S3-D). Retrieved from https://www.techopedia.com/definition/81/3d-stereo-technology-s3d</ref> <ref name=”9”> Gouraud, G. (2011). A Developer's Guide To Stereoscopic 3D In Games. Retrieved from http://www.gamasutra.com/view/feature/134827/a_developers_guide_to_.php?print=1</ref>.
One of the techniques is polarization 3D, that can use active or passive polarized lenses (figure 1 and 2). Anaglyph 3D uses passive red cyan lenses or chromatically opposite colors. These can be considered the classic-type 3D glasses and are a type of passive lenses (figure 3). Head-mounted displays also provide S3D using a separate display optic very close to the eyes. Finally, autostereoscopic 3D is a technique that allows for 3D depth without glasses .<ref name=”2”></ref> <ref name=”8”></ref>.
Passive glasses do not require the use of batteries and do not need to be electronically linked to the display mechanism. They use optical filters to selectively sort the right and left images to the correct eye. Newer versions of this technology work by interlacing the left and right images together using a unique screen made of two emitting filters on top of one another. Gouraud (2011) wrote that “each image is displayed using a property of light called polarization. This allows the passive-polarized glasses to then selectively filter out light between two images using the corresponding polarized films. Therefore, each eyepiece must be polarized in a different direction, allowing separate images to be delivered to each eye. In this manner, a 3D effect is achieved.” <ref name=”9”></ref>
Active shutter has been the primary technology used in home entertainment systems. The mechanism takes advantage of the high frame rates that are available in LED and plasma TVs (120 Hz and above). The TV displays two high definition pictures at a high refreshment frequency (>60 Hz) to achieve temporal multiplexing. The shutter glasses sync with the TV to actively filter the corresponding frames so that each eye only receives the intended image .<ref name=”9”></ref>.
With the autostereoscopic display technology (also referred to as parallax barrier), there is no requirement for the users to wear glasses to achieve a three-dimensional effect. The technology relies on an optical filter which divides the images and enables it to direct light to each eye. This allows the viewer to perceive a coherent left and right image. The Nintendo 3DS uses this type of display technology .<ref name=”9”></ref> The Nvidia Quadro FX 4500 graphics cards compatible with the original 2006 Mac Pro have a stereoscopic 3D output port.<ref>Apple Unveils New Mac Pro Featuring Quad 64-bit Xeon Processors. Apple Newsroom.https://www.apple.com/newsroom/2006/08/07Apple-Unveils-New-Mac-Pro-Featuring-Quad-64-bit-Xeon-Processors/</ref>
===Historical context===
Stereoscopic vision has evolved during millions of years. It is a common feature between humans and many animals, generally predators. In these, two parallel aligned eyes deliver different perspectives of the same scene. Stereoscopic vision is an important sense that is vital for the survival of the animals who possess it .<ref name=”10”> Stereo3d. Basics/Quick-Info. Retrieved from http://www.stereo3d.com/3dhome.htm</ref>.
Charles Wheatstone first developed the stereoscope in 1938. His research demonstrated that the brain processes the images from each eye into a single three-dimensional object. When two stereoscopic images were viewed side by side through a stereoscope, a sense of depth and immersion was created. The design principles of the stereoscope are still applied today in things like the Google Cardboard and low budget VR HMDs for mobile phones .<ref name=”11”> Virtual Reality Society. History Of Virtual Reality. Retrieved from https://www.vrs.org.uk/virtual-reality/history.html</ref>.
The popular View-Master stereoscope was patented in 1939, and was used for “virtual tourism”. In 1949 David Brewster suggested the use of lenses, giving rise to the lenticular stereoscope. The cinematographer Morton Heilig developed the Sensorama in the mid-1950s. It was an arcade-style theatre cabinet that stimulated all the senses. It had stereoscopic 3D display, stereo speakers, fans, smell generators, and a vibrating chair with the objective of immersing the viewer in the film. Heilig created six short films for the Sensorama. He was also responsible for the Telesphere Mask, that was patented in 1960. It was the first example of a HMD - although without motion tracking and for use with non-interactive film medium. This headset provided S3D and wide vision with stereo sound .<ref name=”11”></ref>.
==Devices==
==Stereoscopic 3D benefits and visual discomfort==
When compared to standard 2D TV, the S3D-TV technology enhances has been claimed to increase the entertainment value of television programs. While the main benefit of 3D-TV is the has greater depth perception, there is evidence that stereoscopic television and it could also enhance the perception of sharpness, sense of presence, and naturalness. According to some surveys, it seems that people would rather view S3D images than 2D, provided that there are no uncomfortable side effects <ref name=”2”></ref>.
In games, the use of stereoscopy seemed to increase immersion and spatial presence. Although the effects differed between games, it seems that the use of S3D allows for a more natural and engaging experience <ref name=”3”></ref>.
One of the concerns regarding S3D technology relates to is visual comfort. This has been a long-standing problem in stereoscopic research. It refers to the subjective sensation of discomfort associated with the viewing of stereoscopic images. This issue is not recent; in the past (mainly in the early 1950’s1950s), there were some attempts to popularize 3D movies. These did not succeed due to the limited stereoscopic technology available at the time and due to visual discomfort (2). Current stereoscopic displays with a fixed screen plane can cause several human visual cues to conflict with each other, mainly accommodation and convergence. This leads to a negative experience associated with symptoms of visual fatigue like sore eyes, eye strain, headache, and blurred vision. In HMDs this effect also occurs. It has to be noted that the presence and intensity of the visual discomfort vary from person to person <ref name=”3”></ref>.
==References==