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Tuesday, August 12, 2008

Television program

A television program (U.S.), television programme (UK), or television show (U.S) is something that people watch on television. . It may be a one-off broadcast or, more usually, part of a periodically recurring television series.

A television series that is intended to be broadcast a finite number of episodes is usually called a miniseries or serial (although the latter term also has other meanings). North Americans call a short run lasting less than a year a season; People of the United Kingdom and the Republic of Ireland call this a series. This season or series usually consists of 6–26 installments in the USA, but in the UK there is no defined length. U.S. industry practice tends to favor longer seasons than those of some other countries.

A single instance of a program is called an episode, although particularly in the USA this is sometimes also called a "show", and in the UK a "programme" and the USA a "program". A one-off broadcast may, again particularly in the USA and USA-influenced countries, be called a "special", or particularly in the UK a "special episode". A television movie or in the UK a television film ("made-for-TV" movie) is a film that is initially broadcast on television rather than being released in cinemas or direct-to-video, although many successful television movies are later released on DVD.

Today, advertisements play a role in most television programming, such that each hour of programming can contain up to 15 minutes of advertisements in some countries. By contrast, being publicly funded, the BBC in the United Kingdom does not run advertisements, except to advertise its own programmes. Its promotions appear between and near the end of programmes but not in the middle of them, much like the Public Broadcasting Service (PBS) in the United States and the Australian Broadcasting Corporation (ABC) in Australia. The number of commercial interruptions can also vary, for instance Japanese television tends to prefer fewer and longer commercial breaks while American television has several spread throughout the program. This has an impact on the writing of the show; in order to provide a smooth transition as well as keep the audience from switching channels. With rise of internet video clips, there is serious debate about where the future of television programs is going.

Program content


The content of television programs may be factual, as in documentaries, news, and reality television, or fictional as in comedy and drama. It may be topical as in the case of news and some made-for-television movies or historical as in the case of such documentaries or fictional series. It may be primarily instructional as in the case of educational programming, or entertaining as is the case in situation comedy, reality TV, or game shows, or for income as advertisements.

A drama program usually features a set of actors in a somewhat familiar setting. The program follows their lives and their adventures. Many shows, especially before the 1980s, maintained a status quo where the main characters and the premise changed little. If some change happened to the characters lives during the episode, it was usually undone by the end. (Because of this, the episodes could usually be watched in any order.) Since the 1980s, there are many series that feature progressive change to the plot, the characters, or both.

Common TV program periods include regular broadcasts (like TV news), TV series (usually seasonal and ongoing with a duration of only a few episodes to many seasons), or TV miniseries which is an extended film, usually with a small pre-determined number of episodes and a set plot and timeline. Miniseries usually range from about 3 to 10 hours in length, though critics often complain when programs hit the short end of that range and are still marketed as "minis." In the UK, the term "miniseries" is only usually used in references to imported programmes, and such short-run series are usually called "serials".

Older American television shows began with a Pilot title sequence, showed opening credits at the bottom of the screen during the beginning of the show, and included closing credits at the end of the show. However, beginning in the 1990s some shows began with a "cold open," followed by a title sequence and a commercial break. Many serialistic shows begin with a "Previously on..." (such as 24) introduction before the teaser. And, to save time, some shows omit the title sequence altogether, folding the names normally featured there into the opening credits. The title sequence has not been completely eliminated, however, as many major television series still use them in 2007.

While television series appearing on TV networks are usually commissioned by the networks themselves, their producers earn greater revenue when the program is sold into syndication. With the rise of the DVD home video format, box sets containing entire seasons or the complete run of a program have become a significant revenue source as well. Many of the prime-time comedy shows and Saturday morning cartoons will be digitally remastered for United States television around mid-May 2008, as there will be more original and re-issued DVD sets of television programs containing either entire seasons or complete series runs to come in the future.


Friday, August 8, 2008

Rear-projection television

Rear projection is a type of large-screen television display technology. Most very large screen TVs (to 100 inches [254 cm] or more) use rear projection. A variation is a video projector, using similar technology, which projects onto a screen.

Rear projection television has been commercially available since the 1970s, but at that time could not match the image sharpness of the CRT. Current models are vastly improved, and offer a cost-effective HDTV large-screen display. While still thicker than LCD and plasma flat panels, modern rear projection TVs have a smaller footprint than their predecessors and are light enough to be wall-mounted.[1]

Three types of projection systems are used in projection TVs. CRT projectors were the earliest, and while they were the first televisions to exceed 40", they were also bulky and the picture was unclear at close range. Newer technologies include DLP (reflective micromirror chip) and LCD projectors. A type of LCD projection technology, LCoS, has been capable of 1080p resolution, and examples include Sony's SXRD (Silicon X-tal Reflective Display), JVC's D-ILA (Digital Direct Drive Image Light Amplifier), and MicroDisplay Corporation's Liquid Fidelity.

While popular in 2005 and 2006 as an alternative to more expensive LCD and plasma flat panels, the falling price and improvements to LCDs have led to Sony, Philips, Toshiba and Hitachi planning to drop rear projection TVs from their lineup.[2][3] Currently, Samsung, Mitsubishi, RCA, Panasonic and JVC 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.[4] In the 1Q of 2008 a comparison of worldwide TV sales breaks down to 22.1 million for CRT, 21.1 million for LCD, 2.8 million for Plasma, and 124 thousand for rear-projection. [1]

Comparison of different 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 projector: Small CRT'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. The CRT's can be arranged in various ways. One arrangement is to use one tube and three phosphor (red, green, blue) coatings. Alternatively, one black-and-white tube can be used with a spinning color wheel. A third option is to use three CRT's, one for red, green, and blue.
  • LCD 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) Projector: A DLP projector creates an image using a digital micromirror device (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.

CRT projector

Advantages

  • Not restricted to fixed pixel resolutions, able to display varying resolutions
  • Achieves excellent black level and contrast ratio
  • Achieves excellent color reproduction
  • CRTs have generally very long lifetimes
  • Better viewing angles than those of LCD display

Disadvantages

  • Heavy and large, especially depth-wise
  • If one CRT fails the other two should be replaced as well to maintain color and brightness balance
  • Susceptible to burn-in because CRT is phosphor-based
  • Needs to be 'converged' about every year
  • Has focus problems

LCD projector

Advantages

  • Smaller than CRT projectors
  • LCD chip can be easily repaired or replaced
  • Is not susceptible to burn-in

Disadvantages

  • The Screen-door effect: Individual pixels may be visible on the large screen, giving the appearance that the viewer is looking through a screen door.
  • Possibility of defective pixels
  • Poor black level: Some light passes through even when liquid crystals completely untwist, so the best black color that can be achieved is a very dark gray, resulting in worse contrast ratios and detail in the image. Some newer models use an adjustable iris to help offset this.
  • Not as slim as DLP projection television
  • Uses lamps for light, lamps may need to be replaced
  • Fixed number of pixels, other resolutions need to be scaled to fit this
  • Limited viewing angles

DLP projector

Advantages

  • Slimmest of all types of projection televisions
  • Achieves excellent black level and contrast ratio
  • DMD chip can be easily repaired or replaced
  • Is not susceptible to burn-in
  • Better viewing angles than those of CRT projectors
  • Image brightness only decreases due to the age of the lamp
  • defective pixels are rare
  • Does not experience the screen-door effect

Disadvantages

  • Uses lamps for light, lamps need to be replaced on average once every year and a half to two years
  • Fixed number of pixels, other resolutions need to be scaled to fit this
  • The Rainbow Effect: This is an unwanted visual artifact that is described as flashes of colored light seen when the viewer looks across the display from one side to the other. This artifact is unique to single-chip DLP projectors.

Comparison

Advantages

  • Significantly cheaper than flat-panel counterparts
  • Front-projection picture quality approaches that of movie theater
  • Front-projection takes up very little space because a projector screen is extremely slim, and even a suitably-prepared wall can be used
  • Display size can be extremely large, up to hundreds of inches
  • Projectors that are not phosphor-based (LCD/DLP) are not susceptible to burn-in

Disadvantages

  • Front-projection more difficult to set up because projector is separate and must be placed in front of the screen, typically on the ceiling
  • Rear-projection televisions are much bulkier than flat-panel televisions
  • Lamp may need to be replaced after heavy usage
  • Rear-projection has smaller viewing angles than those of flat-panel displays
  • Rear-projection is susceptible to glare

From Wikipedia, the free encyclopedia