Rear-projection television
Encyclopedia
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
display technology. Up until the mid-2000s, most of the relatively affordable consumer large screen TVs up to 100 in (254 cm) used rear-projection technology. A variation is a video projector
Video projector
A video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other...
, using similar technology, which projects onto a screen
Projection screen
A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed, as in a movie theater; painted on the wall; or semi-permanent or mobile, as in a conference room...
.
Modern rear-projection television has been commercially available since the 1970s, but at that time could not match the image sharpness of the CRT
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
. Current models are vastly improved, and offer a cost-effective HDTV large-screen display. While still thicker than LCD and plasma flat panel
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
s, modern rear-projection TVs have a smaller footprint than their predecessors. The latest models are light enough to be wall-mounted.
However, the projection technique is much older than this. Projection systems were used in the very early 1950s when it was still impossible to manufacture CRTs with a screen size much over 12 inches. Utilising a 2 inch monochrome CRT driven at a very high accelerating voltage for the size (typically 25 kV), the tube produced an extremely bright picture which was projected via a schmitt lens and mirror assembly onto a semi translucent screen of typically 17 to 19 inches in size. The resultant picture was darker than with a direct view CRT and had to be watched in subdued lighting. The degree to which the tube was driven meant that the tube had a relatively short life. Details of a specific TV set with its optical system can be found here.
Three types of projection systems are used in projection TVs. CRT rear-projection TVs were the earliest, and while they were the first to exceed 40", they were also bulky and the picture was unclear at close range. Newer technologies include DLP (reflective micromirror chip), LCD projector
LCD projector
An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector...
s, and LCoS
Liquid crystal on silicon
Liquid crystal on silicon is a "micro-projection" or "micro-display" technology typically applied in projection televisions. It is a reflective technology similar to DLP projectors; however, it uses liquid crystals instead of individual mirrors. By way of comparison, LCD projectors use...
, has been capable of 1080p
1080p
1080p is the shorthand identification for a set of HDTV high-definition video modes that are characterized by 1080 horizontal lines of resolution and progressive scan, meaning the image is not interlaced as is the case with the 1080i display standard....
resolution, and examples include Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
's SXRD
SXRD
SXRD is Sony's proprietary variant of liquid crystal on silicon, a technology used mainly in projection televisions and video projectors. In the front and rear-projection television market, it competes directly with JVC's D-ILA and Texas Instruments' DLP...
(Silicon X-tal Reflective Display), JVC
JVC
, usually referred to as JVC, is a Japanese international consumer and professional electronics corporation based in Yokohama, Japan which was founded in 1927...
's D-ILA (Digital Direct Drive Image Light Amplifier), and MicroDisplay Corporation's Liquid Fidelity
Liquid Fidelity
Liquid Fidelity is a "microdisplay" technology applied in high-definition televisions. It incorporates Liquid Crystal on Silicon technology capable of producing true 1080p resolution with two million pixels on a single display chip....
.
While popular in the early 2000s as an alternative to more expensive LCD
Liquid crystal display television
Liquid-crystal display televisions are television sets that use LCD display technology to produce images. LCD televisions are thinner and lighter than cathode ray tube of similar display size, and are available in much larger sizes...
and plasma
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
flat panels
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
, the falling price and improvements to LCDs have led to Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
, Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
, Toshiba
Toshiba
is a multinational electronics and electrical equipment corporation headquartered in Tokyo, Japan. It is a diversified manufacturer and marketer of electrical products, spanning information & communications equipment and systems, Internet-based solutions and services, electronic components and...
and Hitachi
Hitachi, Ltd.
is a Japanese multinational conglomerate headquartered in Marunouchi 1-chome, Chiyoda, Tokyo, Japan. The company is the parent of the Hitachi Group as part of the larger DKB Group companies...
planning to drop rear-projection TVs from their lineup. Currently, Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...
, Mitsubishi
Mitsubishi
The Mitsubishi Group , Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese multinational conglomerate company that consists of a range of autonomous businesses which share the Mitsubishi brand, trademark and legacy...
, ProScan
ProScan
Proscan is one of the American brand divisions of Thomson Consumer Electronics, with products competing with higher-end electronics. The ProScan name is owned by RCA. The company created television and video products to compete with Sony's Trinitron XBR, Pioneer's Elite, and other electronics brand...
, RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
, Panasonic
Panasonic
Panasonic is an international brand name for Japanese electric products manufacturer Panasonic Corporation, which was formerly known as Matsushita Electric Industrial Co., Ltd...
and JVC
JVC
, usually referred to as JVC, is a Japanese international consumer and professional electronics corporation based in Yokohama, Japan which was founded in 1927...
remain in the market. The bulk of earlier rear-projection TVs meant that they cannot be wall-mounted, and while most consumers of flat-panels do not hang up their sets, the ability to do so is considered a key selling point. On June 6, 2007, Sony did unveil a 70" rear-projection SXRD model KDS-Z70XBR5 that was 40% slimmer than its predecessor and weighed 200 lbs, which was somewhat wall-mountable, however on December 27, 2007, Sony decided to exit the RPTV market. Mitsubishi began offering their LaserVue line of wall mountable rear-projection TVs in 2009.
Types of rear-projection technologies
A projection television uses a projector to create a small image from a video signal and magnify this image onto a viewable screen. The projector uses a bright beam of light and a lens system to project the image to a much larger size. A front-projection television uses a projector that is separate from the screen, and the projector is placed in front of the screen. The setup of a rear-projection television is in some ways similar to that of a traditional television. The projector is contained inside the television box and projects the image from behind the screen.The following are different types of projection televisions, which differ based on the type of projector and how the image (before projection) is created:
- CRT projectorCRT projectorA CRT projector is a video projector that uses a small, high-brightness CRT as the image generating element. The image is then focused and enlarged onto a screen using a lens kept in front of the CRT face. Most modern CRT projectors are color and have three separate CRTs , and their own lenses to...
: Small cathode ray tubeCathode ray tubeThe cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
s create the image in the same manner that a traditional CRT television does, which is by firing a beam of electrons onto a phosphor-coated screen and then the image is projected to a large screen. This is done to overcome the limit of size of cathode ray tube which is about 40 inches which is the maximum size a normal CRT television set (see image). Normally 3 CRTs are used, one red, one green and one blue, aligned so the colors mix correctly on the projected image.
- LCD projectorLCD projectorAn LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector...
: A lamp transmits light through a small LCD chip made up of individual pixels to create an image. The LCD projector uses mirrors to take the light and create three separate red, green, and blue beams, which are then passed through three separate LCD panels. The liquid crystals are manipulated using electric current to control the amount of light passing through. The lens system takes the three color beams and projects the image.
- Digital Light Processing (DLP) projectorVideo projectorA video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. All video projectors use a very bright light to project the image, and most modern ones can correct any curves, blurriness, and other...
: A DLP projector creates an image using a digital micromirror deviceDigital micromirror deviceA digital micromirror device, or DMD, is an optical semiconductor that is the core of DLP projection technology, and was invented by Dr. Larry Hornbeck and Dr. William E. "Ed" Nelson of Texas Instruments in 1987....
(DMD chip), which on its surface contains a large matrix of microscopic mirrors, each corresponding to one pixel in an image. Each mirror can be rotated to reflect light such that the pixel appears bright, or the mirror can be rotated to direct light elsewhere and make the pixel appear dark. The mirror is made of aluminum and is rotated on an axle hinge. There are electrodes on both sides of the hinge controlling the rotation of the mirror using electrostatic attraction. The electrodes are connected to an SRAM cell located under each pixel, and charges from the SRAM cell drive the movement of the mirrors. Color is added to the image-creation process either through a spinning color wheel (used with a single-chip projector) or a three-chip (red, green, blue) projector. The color wheel is placed between the lamp light source and the DMD chip such that the light passing through is colored and then reflected off a mirror to determine the level of darkness. A color wheel consists of a red, green, and blue sector, as well as a fourth sector to either control brightness or include a fourth color. This spinning color wheel in the single-chip arrangement can be replaced by red, green, and blue light-emitting diodes (LED). The three-chip projector uses a prism to split up the light into three beams (red, green, blue), each directed towards its own DMD chip. The outputs of the three DMD chips are recombined and then projected.
- Laser video display (LVD)
See also
- Silk screen effectSilk screen effectSilk Screen Effect is a visual phenomenon seen in rear-projection televisions. SSE is described by viewers as seeing the texture of the television screen in front of the image. SSE may be found on all rear-projection televisions including DLP and Liquid Crystal on Silicon . The effect is most...
- Screen-door effectScreen-door effectThe screen-door effect or fixed-pattern noise is a visual artifact of the projection technology used in digital projectors, where the fine lines separating the projector's pixels become visible in the projected image...
- DLP
- Large screen television technology