High-definition television Notation

HDTV broadcast systems are defined threefold, by:

• The number of lines in the vertical display resolution.

• 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.

[edit] 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
					ITU-R BT.601	MPEG-4	ITU-R BT.601	MPEG-4
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.

http://en.wikipedia.org/wiki/High-definition_television