Video projector
A video projector is an
to provide the illumination required to project the image. Most modern projectors can correct any curves, blurriness and other inconsistencies through manual settings.Video projectors are used for many applications such as conference room presentations, classroom training,
Overview
A video projector, also known as a digital projector, may project onto a traditional reflective projection screen, or it may be built into a cabinet with a translucent rear-projection screen to form a single unified display device.
Common
(1920×1080 pixels), 4K UHD (3840×2160), as well as 16:10 aspect ratio resolutions including WXGA+ (1280×800 pixels) and WUXGA (1920×1200 pixels).If a blue laser is used, a phosphor wheel is used to turn blue light into white light, which is also the case with white LEDs. (White LEDs do not use lasers.) A wheel is used in order to prolong the lifespan of the phosphor, as it is degraded by the heat generated by the laser diode. Remote fiber-optic RGB laser racks can be placed far away from the projector, and several racks can be housed in a single, central room. Each projector can use up to two racks, and several monochrome lasers are mounted on each rack, the light of which is mixed and transmitted to the projector booth using optical fibers.[2][3][4] Projectors using RB lasers use a blue laser with a phosphor wheel in conjunction with a conventional solid-state red laser.
The cost of a projector is typically driven by its base technology, features, resolution and light output. A projector with a higher light output (measured in lumens) is required for a larger screen or for a room with more ambient light.[5] For example, a light output of approximately 1500 to 2500 ANSI lumens is suitable for small screens viewed in rooms with low ambient light; approximately 2500 to 4000 lm is suitable for medium-sized screens with some ambient light; over 4000 lm is needed for very large screens or use in rooms with no lighting control such as conference rooms. High brightness large-venue models are increasingly common in boardrooms, auditoriums and other high-profile spaces, and models up to 75,000 lm[6] are used in large staging applications such as concerts, keynote addresses and displays projected on buildings. Video projectors can have a mechanism similar to local backlight dimming to achieve higher contrast ratios by using 6 DLP chips: 3 for display, and 3 for local dimming.[7][8]
A few camcorders have a built-in projector suitable to make a small projection; a few more powerful "pico projectors" are pocket-sized, and many projectors are portable.
Projection technologies
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- LCD light gates. This is the simplest system, making it one of the most common and affordable for home theaters and business use. Common problems include a visible “screen door” or pixelation effect, and the LCD panels deteriorating from heat and from UV degradation, leading to discolored spots or holes in the image, although recent advances have reduced the severity of these issues in some models.
- DLP projector using Texas Instruments’ DLP technology. This uses one to three microfabricated light valves called digital micromirror devices (DMDs). The single- and double-DMD versions use rotating color wheels in time with the mirror refreshes to modulate color. The most common problem with the single- or two-DMD varieties is a visible “rainbow” which some people perceive when moving their eyes. More recent projectors with higher speed (2× or 4×) and otherwise optimized color wheels have lessened this effect. 3-chip DLP projectors do not have this problem, as they display each primary color simultaneously, and offer higher light output and more accurate color reproduction, however the cost is significantly higher and thus 3-chip DLP technology is typically used in large venue, high brightness models, as well as Digital Cinema projectors.
- LCoS projectors (liquid crystal on silicon). Such projectors often process light in the Fourier domain, which enables correction of optical aberrations using Zernike polynomials.[9] Some commercially available technologies include:
- D-ILAJVC’s Direct-drive Image Light Amplifier based on LCoS technology.
- SXRDSony’s proprietary variant of LCoS technology.
- LEDprojectors use one of the above-mentioned technologies for image creation, with a difference that they use an array of Light Emitting Diodes as the light source, negating the need for lamp replacement.
- Hybrid LED and laser diode system developed by Casio. Uses a combination of Light Emitting Diodes and 445 nm laser diodesas the light source, while image is processed with DLP (DMD) chip.
- MEMSlaser beam-steering technology, whereas Aaxa Technologies uses laser diodes + LCoS.
- Laser projectors are now available from most projector manufacturers, including Barco, Canon, Christie Digital, Dell, Epson, Hitachi, NEC, Optoma, Panasonic, Sony, Viewsonic and many others. These units use a monochrome blue laser light source to excite a yellow phosphor medium creating a broad spectrum light (instead of incandescent or mercury vapor lamps used to create the broad spectrum light). This broadband spectrum light is then split into the primaries with a color wheel and are used with most common projection technologies, including single & 3-Chip DLP, LCD and LCoS.[10] They offer numerous advantages, including eliminating the high cost and downtime of replacing lamps, variations in brightness and color that occur as lamps age and improved color fidelity. Typical laser light sources used in projectors are rated for 20,000 hours before the light output is reduced to 50%, whereas lamps lose brightness quickly and need to be replaced after as little as 1000–2000 hours.
Obsolete technologies
- cathode ray tubes. Once dominated the video projection market, but given their limited light output, size, weight and need for complex alignment, they have since been displaced by digital projectors and are no longer being made.
- Eidophor oil-film projectors.
- LIA (light image amplifier) light valves.
- Kloss Video.
- Talaria oil-film projectors.
Do-it-yourself video projectors
Some
See also
- 3LCD
- Comparison of display technology
- Digital cinema
- Digital divide
- Digital Light Processing (DLP)
- Handheld projector
- Holographic screen
- Inflatable movie screen
- Large-screen television technology
- Live event support
- Projection screen
- Project Ariana
- Projector (disambiguation)
- Screen door effect
- Video designer
References
- ^ Charles Proctor (January 18, 2007). "Christmas is a time for taking -- from schools". Los Angeles Times. Retrieved 2010-11-26.
- ^ "Christie 6P laser lights CGV's biggest screen in South Korea". Retrieved 2023-12-28.
- ^ "Christie RGB laser projection" (PDF). Retrieved 2023-12-28.
- ^ "Novel laser sources for large-venue projection markets".
- ISBN 978-0-240-80703-4.
- ^ "Barco XDL-4K75 DLP Projector".
- ^ "Christie to Sell Breakthrough Eclipse HDR Projector for Home Theaters".
- ^ "Best Home Theater Projector of All Time? Meet the Christie Eclipse".
- S2CID 24142134.
- ^ "What's the difference between laser phosphor and RGB laser?". www.barco.com. Retrieved 2023-06-24.
- ^ DIY Perks. "Building a TRUE 4k home cinema projector". Youtube. Retrieved 23 August 2023.
- ^ Völkel, Frank (November 14, 2004). "Supersize Your TV for $300: Build Your Own XGA Projector!". Tom's Hardware. Archived from the original on 2010-12-29. Retrieved 2022-12-27.
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