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Definition of HDTV related terms



1080i

The highest possible HDTV resolution of 1920x1080 with interlaced scan. Widescreen aspect ratio of 16:9.

1080p

The highest possible HDTV resolution of 1920x1080 with progresive scan. 1080p resolution is not used today and currently there are no 1080p broadcasts.

480i

SDTV resolution of 640x480. Interlaced scan. This is digital television, but it is NOT HDTV, no matter what the salesperson from your cable/satellite provider is trying to tell you.

480p

EDTV resolution of 852x480. Progressive scan. Again, although EDTV is digital television, it is NOT HDTV, no matter what your cable/satellite provider is telling you.

720p

The minimum resolution that qualifies as "High Definition". TV set supporting 720p and better is a true HDTV. 720p is 1280x720 and has a widescreen aspect ratio of 16:9.

Aspect ratio

Aspect ratio specifies the relative size of the screen width and height. For example, the aspect ratio of 4:3 means that the screen height is 3 units of length and the screen width is 4 units of length. The aspect ratio of 4:3 is used in analog television (NTSC) and also in some digital television standards such as SDTV and EDTV (although EDTV may have 16:9 aspect ratio as well). HDTV has widescreen aspect ratio 16:9 supported in both 720p and 1080i resolutions. Widescreen ratio is ideal for watching HD DVDs as the movies are typically recorded in a widescreen format. Aspect ratio of 16:9 allows you to get rid of the horizontal black stripes on the TV screen top and bottom when watching widescreen movies.

ATSC

Advanced Television System Committee defined DTV television standards including HDTV standards.

Comb filter

Buit-in device needed to display analog television on fixed-pixel screens. The analog television transmits a composite signal, i.e. a signal with overlapped luminance and chrominance (brightness and color) information. The comb filter separates brightness and color from the incoming signal. Cheaper and less effective are analog comb filters. More expensive and better quality are 3D digital comb filters.

CRT

Cathode-ray tube is the oldest TV monitor type. Cathode-ray tube consists of an electron gun capable of generating high speed electron beam and a fluorescent screen. When the electron beam hits the screen coated with a phophorescent material, the affected screen area is illuminated. The electron beam is manipulated using a magnetic field to scan the entire screen line by line creating a complete TV image. Being gradually replaced by flat LCD and plasma screens, CRTs are still widely used in televisions. CRTs are bulky and awkward but they do have advantages comparing to the modern technologies. One of the most prominent advantages is their low price, CRT HDTVs are much cheaper than LCD and plasma HDTVs. Another advantage is much better color rendering and easy adaptation to various resolutions.

De-interlacer

Converts interlaced scan into progressive scan image. Similar to line doubler but instead of merely repeating each line twice some sort of interpolation may be applied for further image smoothing.

DCR HDTV

Digital Cable Ready HDTV. Has a built-in tuner and a card slot eliminating the need for a set-top box with cable TV.

DTV

Digital Television. Widely used DTV standards are SDTV, EDTV and HDTV.

EDTV

Enhanced Definition TV. Lower than HDTV resolution of 480p (852x480) pixels. EDTV is progressive scan. It can be widescreen and can be not.

Field

Part of the TV image containing either only odd or only even lines of the image. The field is half of the frame and contains half of the frame lines (or pixels) number. In interlaced scan the full frame is never shown on the screen, and two fields are alternated on the screen at twice the frame rate. In analog TV 60 fields per second are shown.

Fixed-pixel display

Fixed-pixel display always displays the image in one fixed resolution called native resolution. HDTV may support numerous resolutions but finally all of them are scaled into native resolutio. LCDs, plasma, DLPs are all fixed-pixel displays.

Frame

Full TV image. Made up of two fields. In analog TV 30 frames per second are shown. In HDTV the frame rate may be as high as 60 frames per second.

HDTV antenna (aka HD antenna)

TV antenna that has been optimized for optimum HD signal reception.

HDTV programming

High definition content provided by networks.

HDTV-ready

High definition TV that doesn't have built-in tuner. Without a tuner you can not receive free over-the-air HDTV broadcasts. If you have HDTV-ready TV and want to receive over-the-air broacasts you have to buy a HDTV tuner, a separate set-top box.

HDTV tuner

A tuner is needed to receive over-the-air broadcasts. HDTV tuner is built-in unless you have HDTV-ready TV. In this case you have to buy an external tuner in order to watch OTA HDTV.

Interlaced scan

In interlaced scan the frame (TV image) is made up of two fields. The first field contains the odd lines, and the second field the even lines of the image. At each time instant only one field is shown on a TV screen. Two fields of the frame are shown in succession. Although the fields alternation on the screen is done fast, minor image degradation is usually visible on analog TVs in the form of flickering.

LCD

Liquid Crystal Diode (LCD) flat-panel TV technology. LCD is a fixed-pixel display. In LCDs an image is produced on a matrix of crystal cells. The amount of light passing through each cell is controlled by the voltage applied to the crystal cell. Comparing to plasma, LCD HDTVs are lighter and typically have better native resolution. Currently LCDs are available only with small-to-medium screens, although the available LCD screen sizes are growing rapidly. For medium screen sizes LCDs are more expensive and have poorer color reproduction than plasma HDTVs.

Line doubler

DTV built-in device converting interlaced scan image into progressive scan image. This is done by displaying both image fields in each field interval of 1/60 seconds. Line doublers reduce the interlaced image flicker but of course can not improve the image resolution.

Native resolution

All fixed-pixel screens (LCD and plasma but not CRT) display picture in a single resolution, called native resolution. Native resolution should not be confused with supported resolutions and in fact, it does not have to match any of the HDTV resolutions, namely 720p or 1080i. HDTV may support 720p and 1080i but have different native resolutio. In this case it will rescale the TV images coming in one of the supported resolution into its native resolution before displaying the image on the screen. Number of pixels in native resolution must be at least that of 720p in order to render true HDTV. It is also important to understand that even in the most sophisticated rescaling process you never really "increase the resolution" of the image. You simply can not have more details in the scaled image than were present in the original image.

OTA HDTV

Over-the-air HDTV broadcasts. Other HDTV sources are satellite and cables HDTV programming.

Plasma HDTV

Flat-panel TV technology. Plasma screen is a fixed-pixel screen. For large screen sizes 37''-42'' plasma HDTVs are sligthly cheaper than LCDs and can provide somewhat better quality and wider viewing angle. For even bigger sizes LCDs are not available and plasma HDTV is the only flat panel choice. Typically, plasma HDTVs have lower native resolution, are heavier and thicker than LCDs of the same size.

Progressive scan

In progressive scan the whole frame (TV image) is shown at the same time on the screen. Another type of scan, interlaced scan, divide a frame into two fields and shows the image field-by-field.

Pulldown

Typical film camera has a frame rate of 24 fps, while HDTV frame rate is 30 fps or 60 fps. Pulldown (aka 3:2 pulldown) technique is applied to convert film movies from 24 fps to 30 fps prior to broadcast. This conversion causes some degradation of video quality, which can be corrected in HDTVs by a built-in reverse pulldown (aka pulldow processing) device.

Raster squeeze (aka anamorphic squeeze)

Raster squeeze is relevant to non-widescreen CRT HDTVs. The squeeze is necessary to watch widescreen HDTV on a non-widescreen display (one with aspect ratio 4:3).

Resolution

The term resolution is related to .

Scaler

Built-in device used to convert the TV image from one of the supported resolutions into the native resolution.

SDTV

Standard Definition TV format. The "low-end" digital television format, pretty far from HDTV quality. It is non-widescreen, interlaced format with resolution of 480i (640x480) pixels.

Widescreen HDTV

High Definition TV format with aspect ratio of 16:9.