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3D display
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=== 3D glasses === ==== Active shutter systems ==== {{Main|Active shutter 3D system}} [[File:Xpand LCD shutter glasses.jpg|thumb|A pair of LCD shutter glasses used to view XpanD 3D films. The thick frames conceal the electronics and batteries.]] With the eclipse method, a shutter blocks light from each appropriate eye when the converse eye's image is projected on the screen. The display 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.<ref name="Amazing15-16">Amazing 3D by Hal Morgan and Dan Symmes Little, Broawn & Company (Canada) Limited, pp. 15–16.</ref><ref name="3dmovingpictures.com">{{cite web |url=http://www.3dmovingpictures.com/chopper.html |title="The Chopper", article by Daniel L. Symmes |publisher=3dmovingpictures.com |access-date=2010-10-14 }}</ref> 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 cinema, television or computer screen, using the concept of [[alternate-frame sequencing]]. This is the method used by nVidia, [[XpanD 3D]], and earlier [[IMAX]] systems. A drawback of this method is the need for each person viewing to wear expensive, electronic glasses that must be synchronized with the display system using a wireless signal or attached wire. The shutter-glasses are heavier than most polarized glasses, though lighter models are no heavier than some sunglasses or deluxe polarized glasses.<ref>{{Cite web|url=http://www.berezin.com/3d/samsung_3d.htm|title=Samsung 3D|website=www.berezin.com|access-date=2017-12-02}}</ref> However these systems do not require a silver screen for projected images. Liquid crystal light valves work by rotating light between two polarizing filters. Due to these internal polarizers, LCD shutter-glasses darken the display image of any LCD, plasma, or projector image source, which has the result that images appear dimmer and contrast is lower than for normal non-3D viewing. This is not necessarily a usage problem; for some types of displays which are already very bright with poor grayish [[black level]]s, LCD shutter glasses may actually improve the image quality. ==== Anaglyph ==== {{main|Anaglyph 3D}} [[File:Anaglyph glasses.png|thumb|The archetypal 3D glasses, with modern red and cyan color filters, similar to the red/green and red/blue lenses used to view early anaglyph films]] In an anaglyph, two images are [[superimposed]] in an [[additive color|additive light]] setting through two filters, one red and one cyan. In a [[subtractive color|subtractive light]] setting, the two images are printed in the same [[complementary color]]s on white paper. Glasses with colored filters in each eye separate the appropriate image by canceling the filter color out and rendering the complementary color black. 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, in 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. ==== Polarization systems ==== [[File:REALD.JPG|thumb|Resembling sunglasses, RealD circular polarized glasses are now the standard for theatrical releases and theme park attractions.]] {{Main|Polarized 3D system}} To present a stereoscopic picture, two images are projected superimposed onto the same screen through different [[polarizing filter]]s. The viewer wears eyeglasses which also contain a pair of polarizing filters oriented differently (clockwise/counterclockwise with circular polarization or at 90 degree angles, usually 45 and 135 degrees,<ref>Make Your own Stereo Pictures Julius B. Kaiser The Macmillan Company 1955 [http://www.digitalstereoscopy.com/kaiser/m270n271.htm page 271] {{Webarchive|url=https://web.archive.org/web/20110226041039/http://www.digitalstereoscopy.com/kaiser/m270n271.htm |date=2011-02-26 }}</ref> with linear polarization). As each filter passes only that light which is similarly polarized and blocks the light polarized differently, each eye sees a different image. This is used to produce a three-dimensional effect by projecting the same scene into both eyes, but depicted from slightly different perspectives. Additionally, since both lenses have the same color, people with one dominant eye, where one eye is used more, are able to see the colors properly, previously negated by the separation of the two colors. Circular polarization has an advantage over linear polarization, in that the viewer does not need to have their head upright and aligned with the screen for the polarization to work properly. With linear polarization, turning the glasses sideways causes the filters to go out of alignment with the screen filters causing the image to fade and for each eye to see the opposite frame more easily. For circular polarization, the polarizing effect works regardless of how the viewer's head is aligned with the screen such as tilted sideways, or even upside down. The left eye will still only see the image intended for it, and vice versa, without fading or crosstalk. Polarized light reflected from an ordinary motion picture screen typically loses most of its polarization. So an expensive [[silver screen]] or [[aluminized screen]] with negligible polarization loss has to be used. All types of polarization will result in a darkening of the displayed image and poorer contrast compared to non-3D images. Light from lamps is normally emitted as a random collection of polarizations, while a polarization filter only passes a fraction of the light. As a result, the screen image is darker. This darkening can be compensated by increasing the brightness of the projector light source. If the initial polarization filter is inserted between the lamp and the image generation element, the light intensity striking the image element is not any higher than normal without the polarizing filter, and overall image contrast transmitted to the screen is not affected. ==== Interference filter technology ==== {{Main|Anaglyph 3D#Interference filter systems}} [[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 screen]]s 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. It is also known as '''spectral comb filtering''' or '''wavelength multiplex visualization''' The Omega 3D/[[Panavision 3D]] system also uses this technology, though with a wider spectrum and more "teeth" to the "comb" (5 for each eye in the Omega/Panavision system). The use of more spectral bands per eye eliminates the need to color process the image, required by the Dolby system. Evenly dividing the visible spectrum between the eyes gives the viewer a more relaxed "feel" as the light energy and color balance is nearly 50–50. Like the Dolby system, the Omega system can be used with white or silver screens. But it can be used with either film or digital projectors, unlike the Dolby filters that are only used on a digital system with a color correcting processor provided by Dolby. The Omega/Panavision system also claims that their glasses are cheaper to manufacture than those used by Dolby.<ref>"Seeing is believing""; Cinema Technology, Vol 24, No.1 March 2011</ref> In June 2012, the Omega 3D/Panavision 3D system was discontinued by DPVO Theatrical, who marketed it on behalf of Panavision, citing "challenging global economic and 3D market conditions".{{citation needed|date=May 2019}} Although DPVO dissolved its business operations, Omega Optical continues promoting and selling 3D systems to non-theatrical markets. Omega Optical’s 3D system contains projection filters and 3D glasses. In addition to the passive stereoscopic 3D system, Omega Optical has produced enhanced anaglyph 3D glasses. The Omega’s red/cyan anaglyph glasses use complex metal oxide thin film coatings and high quality annealed glass optics. ==== Other ==== {{main|Stereoscopy}} The [[Pulfrich effect]] is a [[psychophysics|psychophysical]] [[percept]] wherein [[:wikt:lateral|lateral]] motion of an object in the field of view is interpreted by the [[visual cortex]] as having a depth component, due to a relative difference in signal timings between the two eyes. [[Prism (optics)|Prismatic]] glasses make cross-viewing easier as well as over/under-viewing possible, examples include the [[KMQ viewer]].
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