Rear projection television ( RPTV ) is a type of large screen television screen technology. Until about 2006, most of the relatively affordable consumer screen TVs up to 100% (250 cm) use rear projection technology. Variations are video projectors, using similar technology, which project to the screen.
Three types of projection systems are used in projection TV. CRT rear projection TVs are the earliest, and although they first exceed 40 ", they are also large and unclear images at close range.The newer technologies include: DLP (reflective micromirror chip), LCD projectors, Laser TV and LCoS They capable of 1080p resolution, and examples include Sony SXRD (Silicon X-tal Reflective Display), JVC D-ILA (Digital Direct Drive Image Light Amplifier), and Liquid Fidelity MicroDisplay Corporation.
Video Rear-projection television
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Modern rear projection televisions have been commercially available since the 1970s, but at that time can not match the sharpness of CRT images that are immediately visible. The current model is much better, and offers a large-screen HDTV screen that is cost-effective. Though still thicker than flat panel LCDs and plasma, modern rear projection TV has a smaller footprint than its predecessor. The latest models are light enough to be mounted on the wall.
However, the projection technique is much older than this. Popular projection systems began from 1946 to 1948 when it was still difficult to produce CRTs with a screen size of more than 12 inches. Using 3, 4 or 5 inch monochrome CRTs that are driven at very high acceleration voltages for size (typically 25-30 kV), the tube produces a very bright image projected through a Schmidt lens and a mirror assembly onto a semi-transparent screen. usually measuring 22.5 to 30 inches diagonally. The resulting image is darker than with a direct view CRT and should be watched with quiet lighting. The extent to which the tube is pushed means the tube has a relatively short life. Details of a particular TV set with its optical system can be found here.
Given their already large dimensions, projection TVs sometimes include larger speakers and more powerful built-in audio vs. direct-view CRTs and especially low-resolution flat panels, as well as basic surround sound processing or emulators such as Sound Retrieval System (SRS) by SRS Labs, similar to the sound bar.
Maps Rear-projection television
History
Although popular in the early 2000s as an alternative to more expensive LCD and plasma panels, price reductions and LCD enhancements led to Sony, Philips, Toshiba and Hitachi dropping rear projection TVs from their lineup. Samsung, Mitsubishi, ProScan, RCA, Panasonic and JVC came out of the market later when LCD televisions became the standard. Most of the previous rear projection TVs mean that they can not be mounted on the wall, and while most flat panel consumers do not close their devices, the ability to do so is considered a major selling point. On June 6, 2007, Sony introduced the SXRD rear projection model 70 " KDS-Z70XBR5 which is 40% thinner than its predecessor and weighs 200 pounds, which is somewhat wall-mountable.But on December 27, 2007, Sony decided to exit the RPTV market, Mitsubishi began offering their LaserVue line on wall-mounted rear projection TVs in 2009.
Type of rear projection technology
A projection television uses a projector to create a thumbnail or video of a video signal and enlarge this image onto a viewable screen. The projector uses bright rays and lens systems to project the image to a much larger size. A front projection television uses a projector separate from the screen and the projector is placed in front of the screen. The adjustment of rear projection television is in some ways similar to traditional television. The projector is inside a television box and projecting images from behind the screen.
The following are the different types of projection televisions, which differ by projector type and how the image (before the projection) is made:
- CRT projectors: Small cathode ray tubes make images in the same way as traditional CRT televisions, which by shooting electron beams onto a phosphor-coated screen and then the image is projected to large. screen. This is done to overcome the size limits of cathode ray tubes that are about 40Ã, "inches. Usually 3 CRTs are used, one is red, one is green and one is blue, aligned so the colors mix properly with the projected image.
- LCD Projector: The lamp transmits light through a small LCD chip composed of each pixel to create an image. The LCD projector uses a mirror to take light and make three separate red, green, and blue beams, which are then passed through three separate LCD panels. Liquid crystals are manipulated using an electric current to control the amount of light passing. The lens system takes three blocks of color and projects the image.
- Digital Lamp Projector (DLP): DLP projectors create images using digital micromirror devices (DMD chips), which on the surface contain a large matrix of microscopic mirrors, each corresponding to one pixel in an image. Each mirror can be rotated to reflect light in such a way that the pixels look bright, or the mirror can be rotated to direct light to another place and make the pixels look dark. The mirror is made of aluminum and is rotated on the hinge of the shaft. There are electrodes on both sides of the hinge controlling the rotation of the mirror using an electrostatic pull. The electrode is connected to an SRAM cell located below each pixel, and the charge of SRAM cells encourages the movement of the mirror. Color is added to the image-making process either through a rotating color wheel (used with a single chip projector) or a three-chip projector (red, green, blue). The color wheel is placed between the light source and the DMD chip so that the passing light is colored and then reflected off the mirror to determine the level of darkness. The color wheel consists of red, green, and blue sectors, as well as the fourth sector to control the brightness or include a fourth color. This rotating color wheel in a single chip arrangement can be replaced with red, green, and blue (LED) emitting diodes. The three-chip projector uses a prism to break the light into three blocks (red, green, blue), each directed to its own DMD chip. The output of the three DMD chips is recombined and then projected.
See also
- Silk screen effect
- The screen-door effect
- DLP
- Large screen television technology
- Laser video display (LVD)
References
Source of the article : Wikipedia
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