Digital Television Definitions and Terms

Analog TV
Analog technology has been in use for the past 50 years to transmit conventional TV signals to consumers. "Standard" television broadcasts in analog TV. Analog signals vary continuously, creating fluctuations in color and brightness.

Aspect Ratio
A numerical expression of the relationship of width to height of a TV screen. 4:3: This numerical sequence refers to the aspect ratio of the National Television Systems Committee (NTSC) TV screen, with "4" unit width corresponding to "3" unit height, proportionally, regardless of the actual size of the screen. 16:9: This numerical sequence refers to the aspect ratio of wide screen DTV formats for all HDTV and some SDTV (Standard Definition) video. A "16" unit width corresponds to "9" unit height proportionally, regardless of the actual size of the screen. The widescreen 16:9 numerical sequence provides a viewing experience very similar to that of 35 mm movies.

ATSC: An acronym for advanced television systems committee, and the name of the DTV system used by broadcasters in the U.S.

Barn Doors
A term used in television production to describe the effect that occurs when a 4:3 image is viewed on a 16:9 screen. When this happens, viewers see black bars on the sides of the screen or "barn doors."

This term is short for "Coder-decoder." A codec is a device that converts analog video and audio signals into a digital format for transmission. It also converts received digital signals back into an analog format.

Compression refers to the reduction of the size of digital data files by removing redundant and/or non-critical information ("data" being the elements of video, audio and other "information"). Digital TV in the U.S. would not be possible without compression.

Computer Input
Some HDTV sets have an input like SVGA or VGA that allows the TV sets to be connected to computers.

Also known as "enhanced TV." Datacasting is the act of providing enhanced options offered with some digital programming to provide additional program material or non-program related resources. This allows viewers the ability to download data (video, audio, text, graphics, maps, services, etc.) to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.

See "codec." A device or program that translates encoded data into its original format (i.e., it decodes the data.)

Digital Cable
A service provided by many cable providers, digital cable offers viewers more channels. Contrary to many consumers' beliefs, digital cable is not the same as High-Definition Television or digital television; rather digital cable simply offers cable subscribers the options of paying for more services.

Digital Monitor
DTV monitors are televisions that can display a digital signal but lack an integrated tuner (unlike an integrated digital set), and thus cannot receive a digital broadcast signal without an additional set-top box.

Digital Television (DTV)
Digital TV is the umbrella term encompassing High-definition Television and several other applications, including Standard Definition Televison, datacasting, multicasting and interactivity.

Digital Tuner
A digital tuner serves as the decoder required to receive and display digital broadcasts. It can be included inside TV sets or via a set-top box.

Down Converting
Process by which a high-definition signal is converted to a standard definition picture.

Enhanced TV
Also known as "datacasting." This term is used for certain digital on-air programming that includes additional resources downloaded to viewers. Some forms of enhanced TV allow live interaction; other forms are not visible on-screen until later recalled by viewers. Producers add these options to some digital programming to enhance program material -- allowing viewers the ability to download related program resources to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.

This acronym stands for "Enhanced Definition Television." It refers to a complete products/system with at least a digital receiver display scanning format, and Dolby Surround Sound audio output capabilities.

HDTV: "High-definition Television."

This is the most superior video picture available in Digital TV. In the U.S., the 1080i and 720p formats in a 16:9 aspect ratio are the two acceptable HDTV formats. HDTV is a component of DTV.

Interactive Television
This is when TV programming features interactive content and enhancements, blending traditional TV viewing with the interactivity of a personal computer.

Letterbox refers to the image of a wide-screen picture on a standard 4:3 aspect ratio television screen, typically with black bars above and below. It is used to maintain the original aspect ratio of the original source (usually a theatrical motion picture of 16:9 aspect ratio or wider).

The option to multicast was made possible by digital technology to allow each digital broadcast station to split its bit stream into 2, 3, 4 or more individual channels of programming and/or data services. (For example, on channel 7, you could watch 7-1, 7-2, 7-3 or 7-4.)

NTSC is the acronym that stands for National Television Systems Committee"and the name of the current analog transmission standard used in the U.S., which the committee created in 1953.

Pixel is actually two words jammed together ( ¾ picture and element). A pixel is a tiny sample of video information, the "little squares" that make up an overall picture.

Pixels Per Inch
Pixels per inch (PPI) is a measure of the sharpness (that is, the density of illuminated points) on a television display screen.

The level of resolution directly affects picture quality. The higher the resolution, the more picture detail there is. Many things affect picture quality, including number of bits, pixel count, format, receiver quality, cameras, lenses and lighting used for live or taped programming. Resolution is measured by the number of pixels displayed. One of the high-definition picture formats is composed of 1080 active lines, and each line is composed of 1920 active pixels. Therefore, each frame has over 2 million (1080x1920=2,073,600) color pixels creating the image. By way of contrast, today's typical analog television is roughly equivalent to 480 active lines, with each line holding about 440 pixels. So, each frame has a little over 200,000 color pixels in use creating the image.

This is the digital process by which analog information is measured, often millions of times per second, in order to convert analog to digital.

Standard Definition TV Format (SDTV)
There are two main digital formats - HDTV and SDTV. SDTV typically does produce better quality images than that of traditional analog TV and pictures somewhat akin to digital cable. However, its images are not nearly as sharp as the images from the ultimate form of digital television ¾ High-definition TV (HDTV).

Set-top Converter Box
This unit sits on top of the viewer's analog TV, receives the Digital TV signal, converts it to an analog signal, and then sends that signal on to the analog TV.

This acronym is short for the "Super Video Graphics Array" display mode. SVGA resolution is 800 x 600 pixels.

Terrestrial Broadcasting
This is a broadcast signal transmitted "over-the-air" to an antenna.

Process by which a standard definition picture is changed to a simulated high-definition picture.

This acronym is short for the "Video Graphics Array" display mode. VGA resolution is 640 x 480 pixels.

Wide screen
A term given to picture displays with a wider aspect ratio than NTSC 4:3. Digital HDTV or SDTV is referred to as "16:9 wide screen." Most motion pictures also have a 16:9 wide screen aspect ratio. Most Digital TVs have a screen that is wider than it is tall (if a Digital TV screen is nine inches high, it's 16 inches wide.) When watching a show recorded in the wide screen format on a Digital TV, viewers see more of the movie, while when viewing wide screen format on an analog TV, cropped edges are evident