[NTLUG:Discuss] OT - re: tv resolution

[Steve Baker]

Fred wrote:
> On Sun, 17 Apr 2005 Steve Baker <sjbaker1 at airmail.net> wrote:
> 
>>No - the vertical resolution of a single NTSC field is 262
>>and a half scanlines.  
> 
> Pardon me. The standard for video resolution is TVL, or
> horizontal lines. That is how many vertical stripes can be
> resolved by a tv display, not how many scan lines there are
> in a picture.

The number of scanlines defines the vertical resolution - and
that is what I was responding to.  It's a hard number written
down in the NTSC specification.  You said:

 > Max resolution of NTSC tv approx 350 lines.

...and it's not.  It's 262.5 or 525 depending on whether you
count them as interlaced or not.

There are applications (such as video games - and perhaps
the video surveillance systems you work with) where fewer
scanlines are used for one reason or another - and applications
where NTSC is extended or adapted - but the maximum in the
standard is 525 lines.

30 seconds of Googling will convince you I'm right.

>>The horizontal resolution is impossible to define because
>>NTSC is an analog system. 
> 
> Not true. You measure it with a test card.

You can measure how well a particular analog signal with
certain bandwidth characteristics looks on a particular TV
set - but the horizontal resolution that you program your
computer to generate isn't defined by the NTSC standard
because it's an analog standard.  You can feed a TV with 480
pixels, 512 pixels or 640 or even 800 pixels per scanline and
it'll work.  Whether you can actually *SEE* all of that
information depends on a lot of analog stuff between the digital
world of the PC and the screen of the TV.  There isn't a standard
for that.  All you have is an analog bandwidth number - and even
that may be exceeded by many modern TV's and graphics cards - and
not reproduced accurately by other supposedly NTSC compatible
systems such as VCR's.   Not only that - but the bandwidth of
the color difference signals is much less than the monochrome
part of the signal - so defining a "Horizontal Resolution" is
a patchy business at best.

> I regularly watch dvds on my computer and they look better 
> there than on my tv, so I would say that the computer
> graphics are better than broadcast TV, IF the software is right. 

Yes. The monitor is higher resolution (by far) than your
TV - and DVD's can hold higher resolution images than an
NTSC television can display.  So certainly, your computer
will display DVD's better than your TV when you go from a
digital source to the computer's monitor.  However, going from
a computer's tuner card via the PC and out to a TV set via the
graphics card will significantly degrade the image versus simply
watching that TV show directly on the TV.  Scan conversion,
attempts at de-interlacing, color-difference to RGB conversions
and conversions back the other way - all cause loss of precision
which ultimately means worse image quality.

---------------------------- Steve Baker -------------------------
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