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{{Short description|Method of displaying stereoscopic 3D images}}
[[Image: CrystalEyes shutter glasses.jpg|thumb|A pair of CrystalEyes shutter glasses]]
[[File:Active-3d-shutter-technology.gif|thumb|Functional principle of active shutter 3D
systems]]
An '''active shutter 3D system''' (a.k.a. '''alternate frame sequencing''', '''alternate image''', '''AI''', '''alternating field''', '''field sequential''' or '''eclipse method''') is a technique
Modern active shutter 3D systems generally use liquid crystal shutter glasses (also called "LC shutter glasses"<ref>[http://portal.acm.org/citation.cfm?id=11215 "LC shutter glasses provide 3-D display for simulated flight"], [[Society for Information Display|Information Display Magazine]], Vol. 2, Issue 9, September 1986</ref> or "active shutter glasses"<ref>[http://www.physorg.com/news173082582.html "Active Shutter 3D Technology for HDTV"], [[PhysOrg]], September 25, 2009</ref>). Each eye's glass contains a [[liquid crystal]] layer which has the property of becoming opaque when [[voltage]] is applied, being otherwise [[Transparency (optics)|transparent]]. The glasses are controlled by a timing signal that allows the glasses to alternately block one eye, and then the other, in synchronization with the [[refresh rate]] of the screen. The timing synchronization to the video equipment may be achieved via a wired signal, or wirelessly by either an [[infrared]] or [[radio frequency]] (e.g. [[Bluetooth]], DLP link) transmitter. Historic systems also used spinning discs, for example the [[Teleview]] system.
Active shutter 3D systems are used to present [[3D film]]s in some theaters, and they can be used to present 3D images on [[Cathode
== Advantages and disadvantages ==
Although virtually all ordinary unmodified video and computer systems can be used to display 3D by adding a plug-in interface and active shutter glasses, disturbing levels of flicker or ghosting may be apparent with systems or displays not designed for such use. The rate of alternation required to
===Advantages===
* Unlike [[Anaglyph image|red/cyan color filter (anaglyph) 3D glasses]], LC shutter glasses are color neutral, enabling 3D viewing in the full
* Unlike in a [[Polarized 3D system]], where the (usually) horizontal spatial resolution is halved, the active shutter system can retain full resolution ([[1080p]]) for both the left and right images. Like any system, manufacturers of televisions may choose not to implement the full resolution for 3D playback but use halved vertical resolution (540p) instead.<ref>[https://web.archive.org/web/20160313043030/http://www.digitalversus.com/tv-television/investigation-active-3d-tvs-full-hd-3d-guaranteed-a1467.html Investigation: Active 3D TVs, Full HD 3D Guaranteed?] Digitalversus.com. 5 December 2011. (Archived.)</ref>
===Disadvantages===
* Flicker can be noticed except at very high refresh rates, as each eye is effectively receiving only half of the monitor's actual refresh rate. However, modern LC glasses generally work in higher refresh rates and eliminate this problem for most people.
*
* LC shutter glasses are shutting out light half of the time; moreover, they
* When used with LCDs, esp. early ones, extreme localized differences between the image to be displayed in one eye and the other may lead to [[crosstalk]], due to LCD panels' pixels sometimes being unable to fully switch, for example from black to white, in the time that separates the left eye's image from the right one.
* Frame rate has to be double that of a non-3D, anaglyph, or [[polarized 3D system]]s to get an equivalent result. All equipment in the chain has to be able to process frames at double rate; in essence this doubles the hardware requirements.
* Despite a progressive fall in prices, due to the intrinsic use of electronics, they remain more expensive than anaglyph and polarized 3D glasses.
* Because of their integrated electronics and batteries, early shutter glasses were heavy and expensive. However, design improvements have resulted in newer models that are cheaper, lightweight, rechargeable and able to be worn over prescription lenses.
* From brand to brand, shutter glasses use different synchronization methods and protocols. Therefore, even glasses that use the same kind of synchronization system (e.g. infrared) will probably be incompatible across different makers.
* Alternated viewing of left and right views leads to an effect of time parallax, if there are side moving objects in the scene: they are seen as in front or behind their actual location, according to the move direction.
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==Standards==
The '''M-3DI Standard''' was a cross-manufacturer standardization initiative to increase compatibility of [[LC Shutter Glasses|LC (Active) Shutter Glasses]] led by the [[Panasonic]] in partnership with XpanD 3D and announced in March 2011.<ref name=panasonic_announcement>{{cite web|url=http://www.panasonic.co.uk/html/en_GB/News/Latest+News/Cross-Industry+3D+Active+Shutter+Eyewear+Technology/7280037/index.html |title=M-3DI Standard Announcement |publisher=panasonic.co.uk |access-date=2011-04-05}}</ref> It aimed to increase acceptance of 3D products by consumers by extending the agreement to various manufacturers of 3D TV, computers, notebooks, home projectors, and cinema hardware.<ref name=panasonic_announcement /> As of April 2011, the agreement was joined by [[Hitachi]], [[Changhong]], [[Funai]], [[Hisense]], [[Mitsubishi Electric]], [[Epson]], [[ViewSonic]], and SIM2 Multimedia S.p.A.<ref name=panasonic_announcement /><ref name="Di Felice">{{cite web |last1=di Felice |first1=Gian Luca |title=Occhiali 3D: standard unico in arrivo! |url=https://www.avmagazine.it/news/televisori/occhiali-3d-standard-unico-in-arrivo_6495.html |website=www.avmagazine.it |access-date=13 May 2024 |language=it |date=31 August 2011}}</ref>
In August of the same year, M-3DI was superseded by another agreement, named "'''Full HD 3D Glasses Initiative'''", formed between Panasonic, [[Samsung]], [[Sony]], [[Sharp Corporation]], [[TCL Technology]], [[Toshiba]] and [[Philips]].<ref name="Di Felice" /> The standardization agreement comprised consumer products including televisions, computers and projectors, also based on XpanD 3D's technology. The press release in the announcement said, "Universal glasses with the new IR/RF protocols will be made available in 2012, and are targeted to be backward compatible with 2011 3D active TVs."<ref>{{cite web |last1=Hannaford |first1=Kat |title=The Manufacturers Are Finally Standardizing 3D Glasses...Together |url=https://gizmodo.com/5828667/the-manufacturers-are-finally-standardizing-3d-glassestogether |website=Gizmodo |access-date=13 May 2024 |language=en |date=8 August 2011}}</ref>
Field Sequential has been used in video games, VHS and VHD movies and is often referred to as HQFS for DVDs, these systems use wired or wireless LCS glasses.
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In recent decades, the availability of lightweight optoelectronic shutters has led to an updated revival of this display method. Liquid crystal shutter glasses were first invented by Stephen McAllister of [[Evans and Sutherland|Evans and Sutherland Computer Corporation]] in the mid-1970s. The prototype had the LCDs mounted to a small cardboard box using duct tape. The glasses were never commercialized due to [[Ghosting (television)|ghosting]], but E&S was a very early adopter of third-party glasses such as the [[StereoGraphics]] [[CrystalEyes]] in the mid-1980s.
[[Matsushita Electric]] (now Panasonic) developed a [[3D television]] that employed active-shutter technology in the late 1970s. They unveiled the television in 1981, while at the same time adapting the technology for use with the first [[stereoscopic video game]], [[Sega]]'s arcade game ''[[SubRoc-3D]]'' (1982).<ref name="GM185">{{cite magazine|title=
In 1985 3D [[Video High Density|VHD]] players became available in Japan from manufacturers such as Victor ([[JVC]]), [[National (brand)|National]] ([[Panasonic]]), and [[Sharp Corporation|Sharp]]. Other units were available for field sequential VHS tapes including the Realeyes 3D. A few kits were made available to watch field sequential DVDs. Sensio released their own format which was higher quality than the High Quality Field Sequential (HQFS) DVDs.
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The method of alternating frames can be used to render modern 3D games into [[true 3D]], although a similar method involving alternate fields has been used to give a 3D illusion on consoles as old as the [[Master System]] and [[Nintendo Entertainment System|Family Computer]]. Special software or hardware is used generate two channels of images, offset from each other to create the stereoscopic effect. High frame rates (typically ~100fps) are required to produce seamless graphics, as the perceived frame rate will be half the actual rate (each eye sees only half the total number of frames). Again, LCD shutter glasses synchronized with the graphics chip complete the effect.
In 1982, [[Sega]]'s [[Arcade game|arcade]] video game ''[[SubRoc-3D]]'' came with a special 3D eyepiece,<ref name=KLOV>{{KLOV game|9856|SubRoc-3D}}</ref> which was a viewer with spinning discs to alternate left and right images to the player's eye from a single monitor.<ref name=Perron>Bernard Perron & Mark J. P. Wolf (2008), ''Video game theory reader two'', [https://books.google.com/books?id=oe0zNalKkTgC&pg=PA158 p. 158], [[Taylor & Francis]], {{ISBN|0-415-96282-X}}</ref> The game's active shutter 3D system was jointly developed by Sega with [[Panasonic|Matsushita]] (now Panasonic).<ref>{{Cite web|url=http://flyers.arcade-museum.com/?page=thumbs&db=videodb&id=1106|title=The Arcade Flyer Archive - Video Game Flyers: Subroc-3D, Sega}}</ref>
In 1984, [[Milton Bradley Company|Milton Bradley]] released the 3D Imager, a primitive form of active shutter glasses that used a motorized rotating disc with transparencies as physical shutters, for the [[Vectrex]]. Although bulky and crude, they used the same basic principle of rapidly alternating imagery that modern active shutter glasses still use.
In 1993 [[Pioneer Corporation|Pioneer]] released the [[LaserActive]] system which had a bay for various "PAC's" such as the Mega LD PAC and LD-ROM² PAC. The unit was 3D capable with the addition of the LaserActive 3D goggles (GOL-1) and the adapter (ADP-1).
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The glasses kits came with driver software which intercepted API calls and effectively rendering the two views in sequence; this technique required twice the performance from the [[graphics processing unit|graphic card]], so a high-end device was needed. Visual glitches were common, as many 3D [[game engine]]s relied on 2D effects which were rendered at the incorrect depth, causing disorientation for the viewer. Very few CRT displays were able to support a 120 Hz [[refresh rate]] at common gaming resolutions of the time, so high-end CRT display was required for a flicker-free image; and even with a capable CRT monitor, many users reported flickering and headaches.
These CRT kits were entirely incompatible with common LCD monitors which had
The USB-based [[Nvidia 3D Vision]] kit released in 2008 supports CRT monitors capable of 100, 110, or 120 Hz refresh rates, as well as 120 Hz LCD monitors.
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==Therapeutic alternating occlusion==
{{Main|Alternating occlusion training}}
In [[vision therapy]] of [[amblyopia]] and of intermittent central [[Suppression (eye)|suppression]], liquid crystal devices have been used for purposes of enhanced occlusion therapy. In this scenario, the amblyopic patient wears electronically programmable liquid crystal glasses or goggles
==See also==
*[[Digital 3D]]
*[[Teleview]]
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[[Category:Liquid crystal displays]]
[[Category:3D imaging]]
[[Category:
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