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Okay, I know that 720p & 1080i are true High Def and from what I can gather 480i & 480p are considered Enhanced Def.


What was regular TV considered then before all of this? Was it 480 or was it an even lower resolution?
 

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No, 480i (which is regular old analog NTSC interlaced TV format) is called Standard Definition (SD) - the newer 480p (output from progressive DVD players) is Enhanced Definition (ED). 1080i and 720p are HD.
 

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The digital 480i signals are also 640 horizontal lines (480x640). The old analog NTSC signals are 525 vertical lines but since many of those are used for retrace the actual vertical lines is 486. This is close to the digital 480 so no one would notice the difference. The NTSC horizontal resolution is 330 (486x330) which is half that of digital 480i that has 640 horizontal lines. Thus a digital 480i signal COULD be twice as detailed as an analog signal. Hense it is enhansed definition.


Rick R
 

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Quote:
Originally posted by Rick_R
Thus a digital 480i signal COULD be twice as detailed as an analog signal. Hense it is enhansed definition.
480i is standard digital TV (SDTV), 480p is now called enhanced digital TV (EDTV).


Originally both 480i & 480p were SDTV, but a few years back the CEA decided to give 480p a different label.
 

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Quote:
Originally posted by Rick_R
The NTSC horizontal resolution is 330 (486x330) which is half that of digital 480i that has 640 horizontal lines. Thus a digital 480i signal COULD be twice as detailed as an analog signal. Hense it is enhansed definition.
This topic never seems as cut and dry to me as you'd first think it would be. For one thing, I don't believe it is correct to say that NTSC is limited to 330 lines of horizontal resolution, though I do believe that is true of OTA analog NTSC transmissions. Laserdisc and DVD can provide higher horizontal resolution in an NTSC signal (around 425 and 480, respectively). The issue is further complicated by the fact that TV resolution has traditionally been counted based on aspect ratio rather than total lines of resolution. So for a traditional 4x3 set receiving an OTA analog NTSC signal, you'd multiply that 330 x 1.33 and get approx. 440 total lines across the screen width. If I'm not mistaken, digital TV standards have tended to follow the same semantics as the computer industry.... in other words, a 1080x1920 HD 16x9 resolution is 1080x1920 pixels (or counting HD in the old per picture height standard, it'd be 1080x1080). The horizontal resolution is NOT counted per picture height like it used to be. So to be fair, you'd compare analog at 440 horizontal lines to digital at 640.


Of course, that's all assuming a pristine analog OTA signal, which is rarely achieved. It also doesn't take in to account perceived resolution due to mpeg compression, etc. The point being, it's not quite as cut & dry as it should be, and when comparing digital resolution to analog, you have to compensate for the fact that analog was counted per picture height, while digital is total lines across picture width (at least I THINK that's right).
 

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Since NTSC is analog-era standard, the number of pixels in a line is irrelevant. All that matters is the number of horizontal lines. The TV just cuts off lines at the appropriate frequency and whatever detail is there gets shown on the screen with as much detail as the TV can handle, which probably varies TV to TV.
 

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It is my understanding that the number of horizontal lines across the OTA NTSC screen os 330 (not 330x1.33). This is of course limited by the 4.2 mhz video signal in the 6 mhz channel. Laser disks and DVDs are not limited by the OTA channel size and can have better horizontal resolutuion.


Rick R
 

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Nevertheless peter0302 is correct - the NTSC signal commonly called 480i is an analog domain signal and has no defined pixel counts. Resolution in analog signals used a "lines of resolution" standard based on test patterns - the final figure necessarily reflected the overall system bandwidth including source, transmission or media, playback system and display performance.


Laserdisks are an analog recording media and the bandwidth and "lines of resolution" measurements apply. DVDs are digital media and the data is encoded in "odd" and "even" fields of 240linesX720pixels/line. You can play this back as recorded after digital/analog conversion as 480i or combine the fields while still in the digital domain, perform D/A conversion, and play it back as 480p at twice the bandwidth (480i has 15.75Khz bandwidth, 480p has 30.1Khz bandwidth).


Note that once you have converted the digital source to a video signal, it is analog in nature unless you are using DVI or another digital standard. Thus there are 1080i, 720p, and 480p analog video signals driving most HD displays.


Gary
 
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