Posted by Rick Merrill on 02/01/07 19:55

Andrew Rossmann wrote:
> In article <D_6wh.832427$5R2.679581@pd7urf3no>, stuart_miller@shaw.ca
> says...
>> <SFTVratings_troy@yahoo.com> wrote in message
>> news:1170274597.382084.36170@k78g2000cwa.googlegroups.com...
>>> For comparison other standards are:
>>> 240 - VHS (ditto Betamax)
>>> 330 - NTSC broadcast
>>> 425 - laserdisc (ditto S-VHS)
>>> 540 - DVD
>>>
>>> I was a bit surprised, but apparently the Electronics Industry
>>> Association measures the resolution differently than one might
>>> expect. They put a giant circle in the middle of the screen, count
>>> the number of visible pixels across, and arrive at a number like "425
>>> for laserdisc" or "540 for dvd". It seems counterintuitive, but
>>> that's how it's done.
>>>
>>> I imagine if the DVD is severely compressed, the quality would drop
>>> much lower than 540 (just as a VHS tape recorded in super-slow mode is
>>> only ~120 across). 540 is the ideal, not the norm.
>>>
>> Even in optimal situations, there are two resolutions to consider.
>> First is the signal. I had understood NTSC to be 525 each way, (for a video
>> camera)
>> Second is the display - there are regions of the signal ( top & bottom)
>> which are not displayed on the screen
>>
>> So what you actually see is less than what is recorded. The technical
>> sections of sites like digitalfaq explainm this properly.
>
> Don't confuse HORIZONTAL resolution with VERTICAL resolution.
>
> 525 is the VERTICAL resolution of NTSC. Of those 525, only 480 actually
> carry picture information. The rest are for sync, closed captioning, and
> other digital transmission features (parental control, XDS,
> TVGuideOnScreen, timecode for VCR's, etc...)
>
> The 240/330, etc mentioned above are rough HORIZONTAL resolutions.
>
> For reference, the HD resolutions are:
> 1280(h)x720(v)
> 1920(h)x1080(v)
>

Small nit: "only 480 actually carry picture information. The rest" are
for Vertical Retrace and get to carry CC, etc.

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