HDTV
From Fusselman.org
The Digital TV Revolution is here! Over there, actually... No, wait... Revolution?!
Point is, neither "Digital TV" or "HDTV" are really anything much but buzzwords these days. Here's how I understand them:
Digital TV means any television signal (that is, live or prerecorded video content) sent in a digitized format. This doesnt mean that it was originated in a digital format, but that the transmission of it is digital. This is how "It's a Wonderful Life" can be "Digitally Remastered". Digital TV can be transmitted either wirelessly (in the case of OTA or Satellite) or wired, in the sense of digital cable.
HDTV means any video signal that's better than the standard 480i of old broadcast television (Most VCRs are even worse). HD signal grades have 2 components: the number (typically 480, 720, or 1080), which represents the number of lines of vertical pixels on the screen and the letter (either I for interlaced or P for progressive). Interlaced means that the image is built half a frame at a time (odd lines and then even, back and forth), while progressive indicates that each frame is painted top to bottom, every time.
Given that most sources say that 720 is what it takes to be "really HD", computer monitors have been HD for a very long time. A standard XGA setup (1024x768) would be called 768p in HDTV marketing speak. It should be noted that most monitors don't conform to any of the standard HD resolutions, or even aspect ratios.
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