[NTLUG:Discuss] re: tv resolution

[Steve Baker]

Fred wrote:

> On Sat, 16 Apr 2005 Jack Snodgrass <mylinuxguy at gmail.com>
> wrote:
> "My 32" TV is set up as the 2nd monitor. Seems to work so
> far... not 100% crisp and clear... need to see if there are
> any special TV settings I can use to make it clearer. "
> 
> Jack:
> 
> Max resolution of NTSC tv approx 350 lines.

No - the vertical resolution of a single NTSC field is 262 and
a half scanlines.  Remember that TV is "INTERLACED".  The system
only displays half of the scanlines every 60th of a second.  So
over 1/30th of a second, you see 525 scanlines.

A poorly setup PC will probably display the same 262 scanlines
in both fields.  A properly set up PC should display all 524,
sending half the scanlines out every alternate field.  Generally,
the messy half line at the end if the display will be ignored.

The horizontal resolution is impossible to define because NTSC
is an analog system. However, if you push the resolution too
high, you'll get weird colour shifting effects.  640 horizontal
pixels is probably as good as you can reasonably hope for.

However, your PC (if properly set up) should be able to produce
graphics at least as good as broadcast TV.  But using a PC tuner
to grab images - then display them on the TV may not produce such
good images because of inevitable losses in the NTSC->RGB->NTSC
conversion process.

Using an NTSC TV as a monitor is usually a disasterous idea.
The interlacing (if properly set up at 524 lines) produces
'interlace flicker' when a single pixel high feature is
only showing up at 30Hz instead of 60Hz.  Working at only
262 lines gets you around that problem - but a 262 line display
is only going to show maybe a 20th of the amount of information
as a normal 2048x1280 PC monitor...it's hardly worth bothering with.

You also get peculiar colour artifacts on NTSC because of the
way colour is encoded onto the monochrome signal...put a magenta
rectangle to the left or right of a green rectangle and see the
interesting black or white line running between them.

Those things can be eliminated by going into the TV through
component video cables (thereby avoiding NTSC altogether).

Up-market TV's have an actual computer monitor port which
allows you to send PC displays to them directly...and if they
have enough resolution (as would be the case with an HDTV),
then it might make a pretty good monitor.

However, if you are using a TV (of any kind), do make sure
you have a PROPER screen saver installed - ie one that actually
stands a chance of saving your screen from damage rather than
just being eye-candy.  TV's are more susceptible to burn-in
than PC monitors and if you regularly run (say) your browser
on your TV, you'd better get used to seeing the MOZILLA logo
floating ghost-like over all your TV programs after a while!

> Of course, you might mess around with the contrast and
> brightness controls. There might even be a focus control on
> the chassis, but after all the work you will figure out why
> Apple II computers only had 40 character lines.

Yes!  And how they came up with such a weird set of colours
and why the Apple ][ I owned (in England where we have PAL
instead of NTSC) showed a totally different set of colours!

---------------------------- Steve Baker -------------------------
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HomePage : http://www.sjbaker.org
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