Saturday, March 15, 2008

HDTV sources

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. A HDTV compatible television set will not improve the quality of SDTV channels. To display a superior picture, high definition televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

  • Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal a HD tuner is required. Most newer high definition televisions have a HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.
  • Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.
  • Satellite-based TV companies, such as DirecTV and Dish Network (both in North America), Sky Digital (in the UK and Ireland), Bell ExpressVu and StarChoice (both in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.
  • HD programming can be located by ZIP code and by provider at this site:
  • Video game systems, such as the Xbox, Playstation 3, and Xbox 360, and digital set-top boxes that rely on an Internet connection, such as the Apple TV, can output a HD signal. The Xbox Live Marketplace, iTunes, and Playstation Network services offer HD movies, TV shows, movie trailers, and clips for download, but at lower bitrates then Blu-ray or HD-DVD.
  • Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to a HDTV.
  • Two optical disc standards, Blu-ray Disc (25GB-50GB) and HD DVD (15GB-30GB), can provide enough digital storage to store hours of HD video content.[9]


HDTV broadcast systems are defined threefold, by:

  • The scanning system: progressive scanning (p) or interlaced scanning (i). Progressive scanning simply draws a complete image frame (all the lines) per image refresh, whereas interlaced scanning draws a partial image field (every second line) during a first pass, then fills-in the remaining lines during a second pass, per image refresh. Interlaced scanning requires significantly lower signal/data bandwidth, but an interlaced signal loses half of the vertical resolution and suffers "combing" artifacts when showing a moving subject on a progressive display (although the worst effects can be mitigated by suitable image post-processing known as 'deinterlacing'). As some compensation, however, interlaced mode provides finer time-sampling, giving two (half-resolution) image samples in the same time interval as one (full-resolution) image sample in progressive mode.
  • The number of frames per second or fields per second.

The 720p60 format is 1280 × 720 pixels progressive scanning with 60 fields per second (60 Hz). The 1080i50 format is 1920 × 1080 pixels (ie 2 MP) interlaced scanning with 50 fields per second. Sometimes interlaced fields are called half-frames, but they are not, because two fields of one frame are temporally shifted. Frame pulldown and segmented frames are special techniques that allow transmitting full frames via an interlaced video stream.

For commercial naming of the product, either the frame rate or the field rate is often dropped, e.g. a "1080i television set" label indicates only the image resolution.[10] Often, the rate is inferred from the context, usually assumed to be either 50 or 60 Hz, except for 1080p, which denotes 1080p24, 1080p25, and 1080p30, but may include 1080p50 and 1080p60 in the future.

A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second, and 50i means 25 interlaced frames per second consisting of 50 interlaced fields per second. Most HDTV systems support some standard resolutions and frame or field rates. The most common are noted below.

Standard Display Resolutions

Standard Definition usually refers to 480 vertical lines of resolution or more.

Resolution (W×H) Active Frame (W×H) Canonical Name(s) Pixels (Advertised Megapixels) Display Aspect Ratio (X:Y) Pixel Aspect Ratio - Standard "4:3" (X:Y) Pixel Aspect Ratio - Widescreen "16:9" (X:Y) Description
720×480 710.85×486 480i/p 345,600 (0.3) 3:2 4320:4739 10:11 5760:4739 40:33 Used for 525-line/ (60 * 1000/1001) Hz video, e.g. NTSC-M
720×576 702×576 576i/p 414,720 (0.4) 5:4 128:117 12:11 512:351 16:11 Used for 625-line/50 Hz video, e.g. PAL-I

When resolution is considered, both the resolution of the transmitted signal and the (native) displayed resolution of a TV set are taken into account. Most HDTV sets contain video scalers and will "upscale" or "upconvert" the transmitted signal to that of the set's native format.

Sometimes the progressive versions of these video formats are referred to as EDTV, or "Enhanced Definition Television." This is slightly misleading, for although a progressive frame contains double the image information as that of an interlaced frame, Standard Definition is already capable of displaying progressive frames, for example in MPEG video with the appropriate "Progressive" flag set. Despite this, 480p/576p signals are not currently broadcast.

High-Definition Display Resolutions

High Definition usually refers to 720 vertical lines of video format resolution or more.

Pixel Resolution (W×H) Video Format Supported Pixels (Advertised Megapixels) Aspect Ratio (X:Y) Description
Image Pixel
1024×768 HD Ready 786,432 (0.8) 16:9 4:3 Typically a computer resolution XGA; also exists as a standardized "HD-Ready" TV size on the Plasma display with non-square pixels.
1248×702 720p Clean Aperture 876,096 (0.9) 16:9 1:1 Used for 750-line video with raster artifact/overscan compensation, as defined in SMPTE 296M.
1280×720 720p 921,600 (0.9) 16:9 1:1 Typically a computer resolution WXGA, also used for 750-line video, as defined in SMPTE 296M, ATSC A/53, ITU-R BT.1543, Digital television, DLP, LCD and LCOS projection HDTV displays.
1366×768 720p/1080i, HD Ready 1,049,088 (1.0) 683:384
(Approx 16:9)
Typically a TV resolution WXGA; also exists as a standardized "HD-Ready" TV size. HDTV common pixel resolution, that used on LCD HDTV displays.

1280×1080 HD Ready 1080p 1,382,400 (1.4) 32:27
(Approx 16:9)
3:2 Non-standardized "HD-Ready" TV size. Used on HDTV Plasma display.
1440×1080 HDCAM/HDV 1080i 1,555,200 (1.6) 4:3 4:3:1 Used for anamorphic 1152-line video in the HDCAM and HDV formats introduced by Sony and defined (also as a luminance subsampling matrix) in SMPTE D11.
1888×1062 1080p Clean Aperture 2,001,280 (2.0) 16:9 1:1 Used for 1152-line video with raster artifact/overscan compensation, as defined in SMPTE 274M.
1920×1080 1080i/1080p, HD Ready 1080p, Full HD 2,073,600 (2.1) 16:9 1:1 Used for 1152-line video, as defined in SMPTE 274M, ATSC A/53, ITU-R BT.709. HDTV common pixel resolution, that used on LCD HDTV displays.
3840×2160 2160p 8,294,400 (8.3) 16:9 1:1 Quad HDTV, (there is no HD Ready 2160p Quad HDTV format).

It should be noted that the numbers used for "HD-Ready" image resolutions do not constitute acceptable 750- or 1152-line video signals in most standards-compliant hardware; in this respect terms such as "720p" and "1080p" are mostly used for advertising, though that does not necessarily mean that HD-Ready TVs labeled in this manner are incapable of accepting those formats as input.

Additionally, the "Clean Aperture" numbers are almost always contained within the frames of their respective "Production Aperture" numbers (e.g., a 1888×1062 rectangle would be contained within a 1920×1080 frame). This is to maintain compatibility with analogue signals, which can often become distorted close to the edge of the frame. It also increases the chance that a digital signal being played on overscan-enabled equipment will display the entire picture visibly.

A common pixel resolution used in HD Ready LCD TV panels is 1366 x 768[11] pixels instead of the ATSC Standard 1280 x 720 pixels. This is due to maximization of manufacturing yield and resolution of VGA, VRAM that comes with a 768 pixel format. Hence, LCD manufacturers adopt the 16:9 ratio compatible for the HD Ready 1080p video standard. Nevertheless, every HDTV has an overscan processing chipset to fix resolution scaling and color rendering, eg LG XD Engine, SONY BRAVIA Engine. Only when viewing 1080i/1080p HD contents under HD Ready 1080p where there is true pixel-for-pixel reproduction, and for HD ready LCD TV, do some signals undergo a scaling process which results in a 3-5% loss of picture.

Standard frame or field rates

  • 23.976p (allow easy conversion to NTSC)
  • 24p (cinematic film)
  • 25p (PAL, SECAM DTV progressive material)
  • 30p (29.97p in drop frame) (NTSC DTV progressive material)
  • 50p (PAL, SECAM DTV progressive material)
  • 60p (59.94p in drop frame) (NTSC DTV progressive material)
  • 50i (PAL & SECAM)
  • 60i (59.94i in drop frame) (NTSC, PAL-M)

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