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Lcd Projector



DLP (Digital Light Processing) technology uses micro-mirrors to project images from a monitor onto a large screen. DLP is seen in standalone projection units, in rear projection TVs, and in a majority of digital cinema projection. LCD (Liquid Crystal Display) video projectors send light from a metal-halide lamp through a prism to display video, images, or computer data on a screen or flat surface.




lcd projector



The ideal choice for your projector depends upon several factors: whether you want it for a home theater or office presentations; whether it has a dedicated spot or will be used when traveling often; and, of course, budget. Other factors like sharpness, clarity, picture quality, etc. are constant, and non-negotiable. This video guides you on what factors to consider before you buy a projector:


DLP projectors rely primarily on a DLP chip, or digital micromirror device (DMD), which comprises up to two million tiny mirrors, each mirror one-fifth the width of a human hair. Each of these mirrors can independently move toward or away from a light source to create a dark or light pixel. The color is fed to the DMD by a beam of light from a light lamp source, which then passes through a spinning color wheel before it reaches the chip, and the image is fed through the lens and onto the projection screen.


A DLP projector with three-chip architecture can deliver up to 35 trillion colors. A three-chip DLP projector uses a prism to split light from the lamp, and each primary color of light is routed to its own DLP chip, then recombined and routed out through the lens. Three-chip systems are in higher-end home theater and large venue projectors, and DLP Cinema projection systems in digital movie theaters.


LCD projectors use 3 LCD technology systems with the same LCD displays as those used to create images in watches and other electronic devices. This system combines three liquid crystal displays, where an image is created in a multi-step process. A light source provides a beam of white light, which is passed to three mirrors (or dichroic mirrors) specially shaped to reflect only a certain wavelength of light.


DLP technology is 'reflective'. Instead of passing a light source through a LC material, light is reflected off the DMDs. In a single-chip DLP projector, light from the lamp enters a reverse-fisheye, passes through a spinning color wheel, crosses underneath the main lens, and reflects off a front-surfaced mirror, where it is spread onto the DMD. From there, light either enters the lens or is reflected off the top cover down into a light-sink to absorb unneeded light.


LCD projectors use transmissive LCD, which allows light to pass through the liquid crystal. In LCD projectors there are always three LCD panels, and they are always light transmissive devices rather than reflective or direct view displays


Being light-source agnostic, DLP technology can effectively use a variety of light sources. Typically, the main DLP light source is a replaceable high-pressure xenon arc lamp unit. Alternatively, ultra-small or pico DLP projectors use high-power LEDs or lasers. For LCD projectors, Metal-halide lamps are used given their outputting an ideal color temperature and a broad spectrum of color. Smaller metal-halide lamps make LCD projectors smaller, hence more portable than most other projection systems.


Motion-picture projectors have come a long way since their hand-cranked progenitors over a century ago. For the first half of their history, they relied exclusively on film to provide moving images that were projected onto a screen, and that technology continued to be used in commercial cinemas until around 2000.


Meanwhile, cathode-ray tube-based video projectors were developed in the 1950s using red, green, and blue CRTs to project electronic video images onto a screen. Many home-theater buffs remember those huge, heavy boxes with the bulging red, green, and blue eyes.


The first digital-projection technology was LCD (liquid crystal display). It was conceived by Gene Dolgoff in 1968, but LCD technology was not sufficiently developed to be practical in a projector at the time; that would have to wait until the mid-1980s.


In some LCD projectors, the light source is a blue laser. With most laser projectors, some of the blue light from the laser hits a spinning wheel coated with phosphor that emits yellow light, which is then split into its red and green components using dichroic mirrors (Fig. 2). The rest of the blue laser light is directed to the blue imager.


Some home-theater LCD projectors with 1080p imagers simulate UHD resolution with a pixel-shifting technique. The pixel-shifting in Epson's models is part of a technology suite Epson calls 4K PRO-UHD. In this process, an optical refracting plate oscillates back and forth, shifting the final image diagonally by half a pixel once per frame (Fig. 4). Because the LCD cells can be switched to different levels of transparency much faster than any current frame rate, each set of shifted pixels is independently controllable, doubling the effective number of pixels on the screen. In addition, the pixels overlap, so the pixel grid is more dense, further reducing the screen-door effect.


Such projectors can accept and display a UHD video signal, but the actual number of pixels on the screen is only half of the 8.3 million pixels in the signal. Even so, by many reliable accounts, the image is much sharper and more detailed than a 1080p image. Can the best pixel-shifted 1080p subjectively deliver the same on-screen detail as a projector that renders the full UHD pixel count on the screen? This remains a subject of debate among manufacturers and enthusiasts. Along with the native resolution of the imagers, the level of detail perceived on-screen relies on the execution of the pixel-shifting technology and the associated optics, among other factors.


LCD imagers for projectors are made by Epson and Sony. Epson is the only major manufacturer of consumer-oriented LCD projectors, though it also makes models for business and educational applications as well as large venues. Sony makes a variety of LCD projectors for the business and education markets, and Panasonic offers models for large-venue and commercial installations. Other companies that make LCD projectors for various applications include Christie, Maxell, NEC, Ricoh, and Sharp.


Like LCD projectors, LCoS projectors separate light into its red, green, and blue components that are directed to three separate LCD-based imagers. But instead of light simply passing through the LCD cells, it is reflected off a shiny surface directly behind the cell array and passes back through the cells again (Fig. 5).


The light source in LCoS projectors is often a white lamp, but some use a blue laser and yellow phosphor wheel as the light source, a technology that JVC calls Blu-Escent and Sony calls Z-Phosphor. Either way, as with LCD projectors, the red, green, and blue light beams are directed to their respective imagers. The reflected light from the three imagers is then combined and projected onto a screen through the main lens (Fig. 6).


Commonly available LCoS imagers have reached a native resolution of 4K (4096x2160), and they are used in the JVC DLA-NX series and RS4500 as well as the Sony VPL-VW series and VPL-VZ1000ES ultra-short-throw projector. Sony also offers native 1080p resolution in the less-expensive VPL-HW series. In addition, JVC has created a native-8K (7680x4320) imager that's used for simulators and prototype large-venue demonstrations.


This doubles the number of pixels on the screen, though JVC claims it virtually quadruples the number of pixels, doubling them both vertically and horizontally. So, native 1920x1080 supposedly becomes 3840x2160. But in fact, there are only twice the number of independently controllable pixels on the screen, so 1920x1080 actually becomes 1920x1080x2. Like Epson projectors with 4K PRO-UHD, JVC projectors with 4K e-Shift can accept and display UHD video. In addition, signals with lower resolution, such as 1080p, are upscaled to 4K/UHD within the projector and split into two separate frames that are displayed alternately at 120 Hz.


JVC and Sony make LCoS imagers for their own projectors, which include home-theater models as well as larger units for professional simulators and digital cinema. Canon uses JVC imagers in its business projectors, and Wolf Cinema bases some of its home-theater models on JVC imagers as well.


The newest kid on the digital-projection block is DLP (Digital Light Processing). Originally developed in 1987 by Larry Hornbeck at Texas Instruments, the first DLP-based projector was introduced by Digital Projection in 1997. Since then, DLP has come to dominate digital cinemas with a market share of about 85%. It's also very popular for home theaters as well as business, education, commercial entertainment, and other applications.


Like all digital projectors, DLP models direct red, green, and blue light to the imagers. White light from a lamp can be separated into its red, green, and blue components, or a blue laser can excite a phosphor wheel to emit yellow light, which is then split into its red and green components while some of the blue light from the laser is used to create the blue portion of the image directly. Other approaches call for adding a second dedicated red laser to the blue, or to use separate red, green, and blue lasers, but this last approach is very expensive and not used except in digital-cinema projectors, super-high-end home theaters, and other color-critical professional applications. Red, green, and blue LEDs have also been used in a few models, but they are not as bright as lasers, so they aren't used much these days.


In any case, red, green, and blue light is directed to DLP imagers, which currently measure from 0.2 inches for small, portable devices to 1.38 inches for digital-cinema projectors; home-theater models today typically use imagers that measure 0.47-inch or 0.66-inch diagonally. However, they work quite differently from LCD or LCoS imagers. Instead of tiny LCD cells, a DLP imager is covered with an array of microscopic mirrors that correspond to the individual pixels (Fig. 10). This type of imager is called a Digital Micromirror Device (DMD). 041b061a72


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