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HDTV Terminology
Definition of Terms Associated with Television Technology
1080p
1080p is a high-definition video format with resolution of 1920 x 1080 pixels. The number 1080 represents 1,080 lines of vertical resolution, while the letter p stands for progressive scan, which means that each video frame is transmitted as a hole in a single sweep.
1080p is considered an HDTV video mode. The term usually assumes a widescreen aspect ratio of 16:9, providing a horizontal display resolution of 1920 dots (pixels) across and a frame resolution of 1920 x 1080 or 2,073,600 pixels.
ALiS
ALiS (Alternate Lighting of Surfaces) is a type of high-definition plasma panel designed for optimum performance when displaying 1080i material. On a conventional progressive-scan plasma TV, all pixels are illuminated at all times. With an ALiS plasma panel, alternate rows of pixels are illuminated so that half the panel's pixels are illuminated at any moment (somewhat similar to interlaced-scanning on a CRT-type TV). ALiS panels offer bright, clear picture quality, reduced power consumption, and extended panel life.
Analog TV
Analog technology has been in use for the past 50 years to transmit conventional TV signals to consumers. Most current television transmissions are received through analog television sets. Analog signals vary continuously, creating fluctuations in color and brightness.
Anamorphic video
Video images that have been "squeezed" to fit a video frame when stored on DVD. These images must be expanded (un-squeezed) by the display device. An increasing number of TVs employ either a screen with 16:9 aspect ratio, or some type of "enhanced-for-widescreen" viewing mode, so that anamorphic and other widescreen material can be viewed in its proper proportions. When anamorphic video is displayed on a typical TV with 4:3 screen size, the images will appear unnaturally tall and narrow.
Artifacts
Unwanted visible effects in the picture created by disturbances in the video transmission or processing. Examples include "dot crawl" or "hanging dots" in analog pictures, or "pixelation" in digital pictures.
Aspect ratio
The ratio of width to height for an image or screen. The North American NTSC television standard uses the squarish 4:3 (1.33:1) ratio. More and more direct-view and projection TVs (especially digital TVs) use the wider 16:9 ratio (1.78:1) to better display widescreen material like anamorphic DVDs and HDTV broadcasts.
ATSC
Advanced Television Standards Committee. Formed to establish technical standards for the U.S. digital television system.
Bitrate
Measured as "bits per second," and used to express the rate at which data is transmitted or processed. The higher the bitrate, the more data that is processed and, typically, the higher the picture resolution. Digital video formats typically have bitrates measured in megabits-per-second (Mbps). (One megabit equals one million bits.) The maximum bitrate for DVD playback is 10 Mbps; for HDTV it's 19.4 Mbps.
Black level
Describes the appearance of darker portions of a video image. Black is the absence of light, so to create the black portions of an image, a display must be able to shut off as much light as possible. Displays with good black level capability not only produce deeper blacks, but also reveal more details and shading in dark or shadowy scenes.
Burn-in
Screen burn-in can damage displays that rely on a phosphor coating on the screen — plasma TVs and rear-projection CRT-based TVs are the most vulnerable to burn-in, and it's less likely, but possible with direct-view CRT TVs. Burn-in can occur when a static image such as a video game, stock or news ticker, or station logo remains on-screen for an extended period. Over time, these images can become etched into the phosphor coating, leaving faint but permanent impressions on-screen. In recent years, makers of plasma TVs have refined the panel technology and included anti-burn-in features which substantially reduce the chances of burn-in. Plasma owners can further reduce the risk by properly adjusting the TV's brightness and contrast settings.
Contrast ratio
Measures the difference between the brightest whites and the darkest blacks a display can show. The higher the contrast ratio, the greater the ability of a display to show subtle color details and tolerate ambient room light. Contrast ratio is an important spec for all types of TV display, but especially for front projectors.
CRT (Cathode-Ray Tube)
A CRT ("picture tube") is a specialized vacuum tube in which images are created when an electron beam scans back and forth across the back side of a phosphor-coated screen. Each time the beam makes a pass across the screen, it lights up a horizontal line of phosphor dots on the inside of the glass tube. By rapidly drawing hundreds of these lines from the top to the bottom of the screen, images are created.
The regular "direct-view" TVs most people grew up watching have a single large picture tube, while CRT-based rear-projection and front-projection TVs use three CRTs: one each for the red, green, and blue primary colors.
De-interlacing (also called line-doubling)
The process of converting an interlaced-scan video signal (where each frame is split into two sequential fields) to a progressive-scan signal (where each frame remains whole). De-interlacers are found in digital TVs and progressive-scan DVD players. More advanced de-interlacers include a feature called 3-2 pulldown processing. For TVs, de-interlacing is often referred to as "line-doubling" or "upconversion."
Digital audio output
A connection found on HDTVs and HDTV tuners for sending the Dolby Digital audio of HDTV broadcasts to an A/V receiver with Dolby Digital decoding. The two most common types of digital output are coaxial and Toslink optical.
Direct-view TV
A general term for non-projection types of TVs, which include conventional tube TVs and flat-panel plasma and LCD TVs.
DLP™ (Digital Light Processing)
A projection TV technology developed by Texas Instruments, based on their Digital Micromirror Device (DMD) microchip. Each DMD chip has an array of tiny swiveling mirrors which create the image. Depending on the TV's resolution, the number of mirrors can range from several hundred thousand to over two million. DLP technology is used in both front- and rear-projection displays.
There are two basic types of DLP projector: "single-chip" projectors use a single DMD chip along with a spinning color wheel, while much more expensive "3-chip" projectors dedicate a chip to each primary color: red, green, and blue.
Downconversion
A term used to describe the format conversion from a higher resolution input signal number to a lower display number, such as 1080i input to 480i display. Some HDTV tuners are able to downconvert digital HDTV signals for display on a regular analog TV.
DTV (Digital Television)
General term for America's digital broadcast TV standard, which began operation in late 1998, and is scheduled to completely replace the 60-year-old analog NTSC broadcast system by Feb. 17, 2009. DTV comes in two basic flavors: widescreen, near-film-quality HDTV (High-Definition Television) with Dolby Digital audio, and medium-quality SDTV (Standard-Definition TV).
DVI (Digital Visual Interface)
A multi-pin computer-style connection intended to carry high-resolution video signals from video source components (some HD-capable satellite and cable boxes, and upconverting DVD players) to HD-capable TVs with a compatible connector. Most (but not all) DVI connections use HDCP (High-bandwidth Digital Content Protection) encryption to prevent piracy. In consumer electronics products, DVI connectors are rapidly being replaced by HDMI connectors, which carry both video and audio.
EDTV (Enhanced-Definition Television)
A designation applied to televisions that can not only display signals in 480-line progressive (480p) mode, but which can also accept 480p signals from video sources such as progressive-scan DVD players. 480p picture quality is superior to standard analog TV (480i), but not as sharp as true HDTV (1080i or 720p). EDTVs are generally either plasma or flat-panel LCD models.
Field
In interlaced-scan video, each complete frame is split into 2 sequential fields, each of which contains half the scanning lines of the frame. One field contains the odd scanning lines, and the other field the even lines.
Flat-panel TV
Any ultra-thin, relatively lightweight TV — especially those which can be wall-mounted. Current flat-panel TVs use either plasma or LCD screen technology.
Frame
A complete, individual picture in a movie film. In a video signal, a frame contains all of the picture's scanning lines. The frame rate of a progressive-scan format is twice that of an interlaced-scan format.
Frame rate
The rate at which frames are displayed. The frame rate for movies on film is 24 frames per second (24 fps). In regular NTSC video, the frame rate is 30 fps. The frame rate of a progressive-scan format is twice that of an interlaced-scan format. Example: the frame rate for 480i DVD is 30 fps (or 60 interlaced fields per second); for progressive-scan DVD at 480p, it's 60 fps.
Front-projection TV
A 2-piece display system consisting of a separate projector (typically placed on a table or ceiling-mounted) and screen. Front-projection systems can display images up to 20 feet across, or larger. The traditional large, expensive CRT-based front projectors have mostly been replaced by compact, lightweight digital projectors using DLP, LCD or LCoS technology. These digital projectors are usually much more affordable, too.
Gain
Measures the light-reflecting ability of a projection screen. The higher the number, the greater the amount of light reflected back to the viewer(s).
HDCP (High-Bandwidth Digital Content Protection)
HDCP encryption is used with high-resolution signals over DVI and HDMI connections and on D-Theater D-VHS recordings to prevent unauthorized duplication of copyrighted material.
HDTV (High-Definition Television)
Often mistakenly used as a generic description of all digital television, HDTV specifically refers to the highest-resolution formats of the 18 total DTV formats. Although there still isn't 100% agreement among manufacturers, retailers, journalists, etc., true HDTV is generally considered to be 1,080-line interlaced (1080i) or 720-line progressive (720p).
HDTV-ready
Term used to describe TVs which can display digital high-definition TV formats when connected to a separate HDTV tuner. These TVs generally have built-in tuners for receiving regular NTSC broadcasts, but not digital. An HDTV-ready TV may also be referred to as an "HDTV monitor."
Interlaced scan
In a television display, interlaced scan refers to the process of re-assembling a picture from a series of video signals. The "standard" NTSC system uses 525 scanning lines to create a picture (frame). The frame/picture is made up of two fields: The first field has 262.5 odd lines (1,3,5...) and the second field has 262.5 even lines (2,4,6...). The odd lines are scanned (drawn on the screen) in 1/60th of a second, and the even lines follow in the next 1/60th of a second. This presents an entire frame/picture of 525 lines in 1/30th of a second.
Analog NTSC video uses interlaced scanning, as do several digital television formats. Formats that include an "i" (1080i, 480i) use interlaced scanning. See also progressive scan.
LCD (Liquid Crystal Display)
Liquid Crystal Display technology is one of the methods used to create flat-panel TVs. Light isn't created by the liquid crystals; a light source (bulb) behind the panel shines light through the display. The display consists of two polarizing transparent panels and a liquid crystal solution sandwiched in between. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal acts like a shutter, either allowing light to pass through or blocking the light. The pattern of transparent and dark crystals forms the image.
LCD technology is used in flat-panel, rear-projection, and front-projection TVs.
LCoS (Liquid Crystal on Silicon)
A projection TV display technology that sandwiches a layer of liquid crystal between a cover glass and a highly reflective, mirror-like surface patterned with pixels that sits on top of a silicon chip. These layers form a microdisplay that can be used in rear-projection and front-projection TVs. Manufacturers use different names for their LCoS-based technologies. JVC uses D-ILA™ or HD-ILA™, while Sony uses SXRD™.
Letterboxed video
A method for displaying the entire picture as seen in a movie theater. The resulting image width is much greater than its height. On a TV screen with standard aspect ratio (4:3), letterboxed videos appear with horizontal black bars above and below the image.
Light output
Measures the amount of light produced by a projection display, and is an especially important spec for front projectors. Expressed in "lumens" or "ANSI lumens," with a higher number indicating greater light output.
Lumen
The unit of measure for light output of a projector. Different manufacturers may rate their projectors' light output differently. "Peak lumens" is measured by illuminating an area of about 10% of the screen size in the center of the display. This measurement ignores the reduction in brightness at the sides and corners of the screen.
The more conservative "ANSI lumens" (American National Standards Institute) specification is made by dividing the screen into 9 blocks, taking a reading in the center of each, and averaging the readings. This number is usually 20-25% lower than the peak lumen measurement.
Luminance
The brightness or black-and-white component of a color video signal. Determines the level of picture detail.
MHz (Megahertz)
Equal to one million Hz. Video signal bandwidth is typically expressed in megahertz.
Microdisplay
A general term covering several different technologies used in digital rear-projection and front-projection TVs. These displays produce large images; the "micro" refers to the postage stamp-sized image chips that create the images. Microdisplay types include DLP, LCD, and LCoS
MPEG-2
The video compression standard used for digital television, DVD, and small-dish satellite TV. This adaptive, variable bitrate process is able to allocate more bits for complex scenes involving a lot of motion, while reducing the bits in static scenes. MPEG stands for Moving Picture Experts Group.
MTS (Multichannel Television Sound)
The method of broadcasting stereo sound over ordinary analog TV channels. MTS reception capability is built into virtually all stereo TVs and HiFi VCRs.
Pixel
Short for "picture element." The smallest bit of data in a video image. The smaller the size of the pixels in an image, the greater the resolution.
Pixel response time
Response time refers to the amount of time it takes for a single pixel in a video display to switch from active to non-active; it is measured in milliseconds (ms). If a display's response time is too slow, faint motion trails may be visible following fast-moving onscreen objects. For smooth, accurate playback of high-quality video material, look for a response time of 12 ms or less.
Plasma
Gas-plasma technology is one of the methods used to create flat-panel TVs. Besides enabling thin, lightweight TVs that can be hung on the wall, plasma offers other advantages. The display consists of two transparent glass panels with a thin layer of pixels sandwiched in between (think of this layer as containing around one million tiny fluorescent bulbs — the pixels). Each pixel is composed of three gas-filled cells or sub-pixels (one each for the red, green and blue primary colors). A grid of tiny electrodes applies an electric current to the individual cells, causing the gas to ionize. This ionized gas (plasma) emits high-frequency UV rays which stimulate the cells' phosphors, causing them to glow, which creates the TV image.
Progressive scan
Some digital television broadcast formats (720p, 480p), and most DVD players, use a type of video signal known as progressive scan. Instead of splitting each video frame into two sequential fields like standard interlaced NTSC video, progressive-scan video displays the entire frame in a single sweep. For example, where standard NTSC video displays 30 frames (60 fields) per second, progressive scan displays 60 full frames per second.
Displaying progressive-scan video requires more bandwidth (there's twice as much vertical information) and a faster horizontal scan frequency than interlaced video. Progressive-scan picture quality is more filmlike, with more fine detail and less flicker. For progressive-scan viewing, you'll need a TV that's HDTV-ready.
Rear-projection TV
Typically referred to as "big-screen" TVs, these large-cabinet TVs generally have built-in screens measuring at least 40". Up until a few years ago, all rear-projection TVs used three CRTs to create images. Using CRTs resulted in cabinets that were relatively heavy and bulky — nearly always designed as floorstanding TVs. Newer digital microdisplay rear-projection technologies, like DLP, LCD, and LCoS, make possible the more compact, lightweight "tabletop" big-screen TVs.
Resolution
The sharpness of a video image, signal or display, generally described either in terms of "lines of resolution," or pixels. The resolution you see depends on two factors: the resolution of your display and the resolution of the video signal. Since video images are always rectangle-shaped, there is both horizontal resolution and vertical resolution to consider.
Vertical resolution: The number of horizontal lines (or pixels) that can be resolved from the top of an image to the bottom. (Think of hundreds of horizontal lines or dots stacked on top of one another.) The vertical resolution of the analog NTSC TV standard is 525 lines. But, some lines are used to carry other data like closed-captioning text, test signals, etc., so we end up with about 480 lines in the final image, regardless of the source. So, all of the typical NTSC sources — VHS VCRs, cable and over-the-air broadcast TV (analog), non-HD digital satellite TV, DVD players, camcorders, etc. — have vertical resolution of 480 lines. DTV (Digital Television) signals have vertical resolution that ranges from 480 lines for SDTV, to 720 or 1080 lines for true HDTV.
Horizontal resolution: The number of vertical lines (or pixels) that can be resolved from one side of an image to the other. Horizontal resolution is a trickier concept, because while the vertical resolution of all analog (NTSC) video sources is the same (480 lines), the horizontal resolution varies according to the source. Some examples for typical sources: VHS VCRs (240 lines), analog TV broadcasts (330 lines), non-HDTV digital satellite TV (up to 380 lines), and DVD players (540 lines). DTV signals have horizontal resolution that ranges from 640 lines for SDTV, to 1280 lines (for 720p HDTV) or 1920 lines (for 1080i HDTV).
Scaler
Circuitry that converts a video signal to a resolution other than its original format. Scaling can involve upconversion or downconversion, and may also include a conversion between progressive- and interlaced-scan formats. A scaler can be built into a TV, HDTV tuner, or DVD player, or may be a standalone component.
SDTV (Standard-Definition Television)
A digital television format that is similar to current standards in picture resolution and aspect ratio. The picture and sound will be clearer than NTSC, and its digital nature will allow more than one program to be broadcast over the same bandwidth at the same time. Typical SDTV resolution is 480i or 480p.
Set-top box (STB)
Also called converter boxes, these receivers convert broadcasts (either analog cable, digital cable, or HDTV) for display on a television. HDTV-ready TVs (those without a built-in HDTV tuner) must be connected to a compatible HDTV tuner set-top box in order to receive digital television programs.
Upconversion
The term used to describe the conversion of a lower apparent resolution to a higher one. This process increases the number of pixels and/or frame rate and/or scanning format used to represent an image by interpolating existing pixels to create new ones at closer spacing. As an example, Sony TVs with Digital Reality Creation® can upconvert 480i video sources to 960i. Often referred to as "line-doubling."
V-Chip
For the past several years, the FCC (Federal Communications Commission) has required that TVs include "V-Chip" technology to block the display of television programs based on their rating. All sets with screens 13 inches or larger manufactured after January 1, 2000 must include the V-Chip. Broadcasters are required to encode an electronic signal in TV programs indicating the level of violence, language, and sexual content. Parents can program the TV with a rating so that when the the V-Chip reads a show's signal, it will prevent it from displaying if it is above the rating.
The rating system, known as "TV Parental Guidelines," was established by the National Association of Broadcasters, the National Cable Television Association and the Motion Picture Association of America. These ratings display on the TV screen for the first 15 seconds of rated programs.
Viewing angle
Measures a video display's maximum usable viewing range from the center of the screen, with 180° being the theoretical maximum. Most often, the horizontal (side to side) viewing angle is listed, but sometimes both horizontal and vertical viewing angles are provided. For most home theaters, horizontal viewing angle is more critical.
Widescreen
When used to describe a TV, widescreen generally refers to an aspect ratio of 16:9, which is the optimum ratio for viewing anamorphic DVDs and HDTV broadcasts.
Wobulation
A technique originally invented by Hewlett-Packard for its ink jet printers. Like interlacing, wobulation shows half the picture at a time, but displays the two halves so rapidly that our eyes combine the two parts into one. A 1080p DLP TV can display images with 1920 x 1080 pixels, yet its DMD (Digital Micromirror Device) image chip has 960 x 1080 mirrors. Half the image is displayed, then a separate pivoting reflective panel called an "actuator" shifts the display a half pixel's width to the side. This all happens fast enough to generate 60 full frames per second, for a clean progressive-scan image. It is also often referred to as "pixel-shifting."
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