Liquid crystal shutter glasses (also called LC shutter glasses[1] or active shutter glasses.[2]) are glasses used in conjunction with a display screen to create the illusion of a three dimensional image, an example of stereoscopy. Each eye's glass contains a liquid crystal layer which has the property of becoming dark when voltage is applied, being otherwise transparent. The glasses are controlled by an infrared, radio frequency, DLP-Link or Bluetooth transmitter that sends a timing signal that allows the glasses to alternately darken over one eye, and then the other, in synchronization with the refresh rate of the screen. Meanwhile, the display alternately displays different perspectives for each eye, using a technique called alternate-frame sequencing, which achieves the desired effect of each eye seeing only the image intended for it.
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LC shutter glasses mostly eliminate "ghosting" which is a problem with other 3D display technologies such as linearly polarized glasses. Moreover, unlike red/cyan colour filter 3D glasses, LC shutter glasses are colour neutral enabling 3D viewing in the full colour spectrum.
Flicker can be noticeable except at very high refresh rates, as each eye is effectively receiving only half of the monitor's actual refresh rate. Most modern LC glasses however generally work in higher refresh rates and mostly eliminate this problem.
Until recently, the method only worked with CRT monitors; some modern flat-panel monitors now support high-enough refresh rates to work with some LC shutter systems.[3]
LC shutter glasses are shutting out light half of the time; moreover, they are slightly dark even when letting light through, because they are polarized. This gives an effect similar to watching TV with sunglasses on, which causes a darker picture perceived by the viewer. However, this effect can produce a higher perceived display contrast when paired with LCD displays because of the reduction in backlight bleed.
Frame rate has to be double that of an ordinary stream 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 of the equipment. This is especially noticeable when the image stream is interactively generated in real time by 3D hardware on computers.
In addition, shutter glasses tend to be much more expensive than other forms of stereoscopic glasses. Whereas most anaglyph, ChromaDepth, and polarized 3D glasses can be purchased at very low prices (less than US$1 as of 2010, with anaglyph filters being the least expensive), shutter glasses feature far more advanced technology and usually sell for two orders of magnitude higher than paper anaglyphs and one order over paper ChromaDepth and polarized glasses, with most models selling for well over US$100, particularly for the standard wireless models.
Shutter glasses are also matched to the TV so it may not be possible to use your shutter glasses with a different brand 3DTV. However, efforts are being made to create a Universal 3D Shutter Glass.
In March 2011 Panasonic Corporation, together with XPAND 3D, have formulated the M-3DI Standard, which aims to provide industry-wide compatibility and standardisation of LC (Active) Shutter Glasses. This movement aims to bring about compatibility among manufacturers of 3D TV, computer, notebook, home projection, and cinema with standardised LC (Active) Shutter Glasses that will work across all 3D hardware seamlessly.
There are many sources of low-cost 3D glasses. IO glasses are the most common glasses in this category. XpanD 3D is a manufacturer of shutter glasses, with over 1000 cinemas currently using XpanD glasses.[4] With the release of this technology to the home-viewer market as of 2009, many other manufacturers are now developing their own LC shutter glasses, such as Unipolar International Limited, Accupix Co., Ltd, Panasonic, Samsung, and Sony.
The M-3DI Standard, announced by Panasonic Corporation together with XPAND 3D in March 2011, aims to provide industry-wide compatibility and standardisation of LC (Active) Shutter Glasses.
Samsung has developed Active 3D glasses that are 2 ounces and utilize lens and frame technology pioneered by Silhouette who creates glasses for NASA.[5]
Nvidia makes a 3D Vision kit for the PC; it comes with 3D shutter glasses, a transmitter, and special graphics driver software. A certified 120 Hz monitor is required to use the 3D Vision; standard LCD monitors run at 60 Hz.
Liquid crystal shutter glasses were first invented by Stephen McAllister of 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, but E&S was a very early adopter of third-party glasses such as the StereoGraphics CrystalEyes in the mid-1980s.
In 1982, Sega's arcade video game SubRoc-3D came with a special 3-D eyepiece,[6] which was a viewer with spinning discs to alternate left and right images to the player's eye from a single monitor.[7]
In 1984, the Vectrex released the 3D Imager, a primitive form of active shutter glasses that used a motorized rotating disc with transparencies as physical shutters. Although bulky and crude, they used the same basic principle of rapidly alternating imagery that modern active shutter glasses still use.
Sega released the SegaScope 3-D for the Sega Master System in 1987 for Japan and in 1989 for North America, where it was the first known electronic device to use LCD Active Shutter glasses. Only eight 3D compatible games were ever released. Nintendo's Famicom also featured a similar Famicom 3D System, which was an LCD shutter headset, released in 1987 only for Japan.
In 1999-2000, a number of companies created stereoscopic LC shutter glasses kits for the Windows PCs which worked with application and games written for Direct3D and OpenGL 3D graphics APIs. These kits only worked with CRT computer displays and employed either VGA pass-through, VESA Stereo or proprietary interface for left-right synchronization.
The most prominent example was the ELSA Revelator glasses, which worked exclusively in NVidia cards through a proprietary interface based on VESA Stereo. Nvidia later bought the technology and used it in its stereo driver for Windows.
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 graphic card, so a high-end device was needed. Visual glitches were common, as many 3D game engines relied on 2D effects which were rendered at the incorrect depth, causing disorientation for the viewer. Very few CRT displays were able to support 120 Hz refresh rate at common gaming resolutions of the time, so high-end CRT display was required for flicker-free image; and even with capable CRT monitor, many users reported flickering and headaches.
These CRT kits were entirely incompatible with common LCD monitors which had very high pixel response times, unlike CRT displays. Moreover, the display market swiftly shifted to LCD monitors and most display makers ceased production of CRT monitors in early 2000s, which meant that PC glasses kits shortly felt into disuse and were reduced to a very niche market, requiring a purchase of a used high-end, big diagonal CRT monitor.
SplitFish Eye FX 3D was a stereo 3D shutter glasses kit for the Sony PlayStation 2 released in 2005; it only supported standard-definition CRT TVs. The accessory included a pass-trough cable for the PS2 gamepad; when activated, the attached accessory would issue a sequence of rapidly alternating left-right movement commands to the console, producing a kind of "wiggle stereoscopy" effect additionally aided by the wired LC shutter glasses which worked in sync with these movements.[8] The kit arrived too late in the product cycle of the console when it was effectively replaced by the PlayStation 3, and only a few games were supported, so it was largely ignored by gamers.[9]
The USB-based Nvidia 3D Vision kit released in 2008 supports CRT monitors capable of 100, 110, or 120 Hz refresh rate, as well as 120 Hz LCD monitors.
In 2007, Texas Instruments introduced stereo 3D capable DLP solutions to its OEMs,[10] and Samsung and Mitsubishi introduced the first 3D ready televisions. These solutions utilize the inherent speed advantage of the Digital Micro-mirror Device (DMD) to sequentially generate a high refresh rate for the left and right views required for stereoscopic imaging.
DLP 3D technology uses the SmoothPicture wobulation algorithm and relies on the properties of modern 1080p60 DMD imagers. It effectively compacts two L/R views into a single frame by using a checkerboard pattern, only requiring a standard 1080p60 resolution for stereoscopic transmission to the TV. The claimed advantage of this solution is increased spatial resolution, unlike other methods which cut vertical or horizontal resolution in half.
The micromirrors are organized in a so-called "offset-diamond pixel layout" of 960×1080 micromirrors, rotated 45 degrees, with their center points placed in the center of "black" squares on the checkerboard. The DMD employs full-pixel wobulation to display the complete 1080p image as two half-resolution images in a fast sequence. The DMD operates at twice the refresh rate, i.e. 120 Hz, and the complete 1080p picture is displayed in two steps. On the first cadence, only half of the original 1080p60 image is displayed - the pixels that correspond to the "black" squares of the checkerboard pattern. On the second cadence, the DMD array is mechanically shifted (wobulated) by one pixel, so the micromirrors are now in a position previously occupied by the gaps, and another half of the image is displayed - this time, the pixels that correspond to the "white" squares.[11][12]
A synchronization signal is generated for LC shutter glasses worn by the viewer, using either a standard VESA Stereo plug to connect wired glasses or wireless emitters, or brief flashes of light on the viewing screen during the blanking interval (DLP Link). The LC shutter glasses process the signal and control the shutter for each eye to ensure that the correct left and right views are presented to the correct eye.
Plasma display panels are inherently high-speed devices as well, since they use pulse-width modulation to maintain the brightness of individual pixels, making them compatible with sequential method involving shutter glasses. Modern panels feature pixel driving frequency of up to 600 Hz and allow 10 bit to 12 bit color precision with 1024 to 4096 gradations of brightness for each subpixel.
Samsung Electronics launched 3D ready PDP TVs in 2008, a "PAVV Cannes 450" in Korea and PNAx450 in the UK and the US. The sets utilize the same checkerboard pattern compression scheme as their DLP TVs, though only at the native resolution of 1360x768 pixels and not at HDTV standard 720p, making them only usable with a PC.
Matsushita Electric (Panasonic) prototyped the "3D Full-HD Plasma Theater System" on CES 2008. The system is a combination of a 103-inch PDP TV, a Blu-ray Disc player and shutter glasses. The new system transmits 1080i60 interlaced images for both right and left eyes, and the video is stored on 50-Gbyte Blu-ray using the MPEG-4 AVC/H.264 compression Multiview Video Coding extension.
Liquid crystal displays have traditionally been slow to change from one polarization state to another. Users of early 1990s laptops are familiar with the smearing and blurring that occurs when something moves too fast for the LCD to keep up. This smearing can result in a completely unviewable image when using shutter glasses.
LCD technology is not usually rated by frames per second but rather the time it takes to transition from darkness to brightness and back to darkness, in milliseconds. In order to achieve an equivalent minimum refresh rate of 120 Hz, an LCD must be able to transition at a speed of not more than 8.33 ms. However, each frame is displayed for at most 8.33ms, and minimizing the response is key. For example: if it takes 8.33ms for the LCD to transition to the desired image, and a sequential black/white image is shown, the 8.33ms which should be displaying "white" will begin at black, and after 8.33ms finally achieve white. Similarly, the next 8.33ms which should be displaying "black" will begin as white, and after 8.33ms finally achieve black.
However, because pixel transition speed has become a strong selling point of LCD monitors, marketing hype has unfortunately obscured these speed-of-transition specifications with what some consider tortuous qualifying statements that make inadequate technology appear to be better than it really is (see PMPO for another example of such marketing distortions). While the average person attempting to buy a high quality LCD for normal home use might not notice these minor performance differences, a slowly transitioning LCD can have a severely negative impact on usability with shutter glasses. For stereoscopic applications, it is important that the LCD be truly capable of what is being claimed.
Generally, shutter glasses fit comfortably over prescription glasses.[13]
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