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Re: S-Video on ThinkPad T42 with Debian Jessie - can't get above 800x600



On Sun, 13 Apr 2014 20:57:46 +1000
Chris Angelico <rosuav@gmail.com> wrote:

> On Sun, Apr 13, 2014 at 1:39 AM, Chris Angelico <rosuav@gmail.com>
> wrote:
> > On Fri, Apr 11, 2014 at 12:50 AM, Chris Angelico <rosuav@gmail.com>
> > wrote:
> >> I've just converted a laptop from Windows XP to Debian Jessie, with
> >> the expectation that I'd be able to do everything at least as well
> >> as before. That's been mostly true, but I'm stuck on a problem
> >> with the S-Video output: whatever I do, the TV shows only 800x600.
> >
> > In the interests of experimentation, I live-booted AntiX on that
> > same hardware. The result is exactly the same; xrandr says the
> > S-video output is in its only mode of 800x600 60Hz, and telling it
> > to go 1024x768 just results in the top left 800x600 being visible.
> 
> Further experimentation has revealed a rather interesting result. It
> seems that Windows was claiming that it was driving the S-video at
> 1024x768, but was actually stretching it down to 800x600. Short of
> reinstalling Windows (which I will not do!), I have no way to prove
> this, but anecdotal evidence is that text is a bit more readable now.
> So it's looking like 800x600 is all we really get anyway. Everything's
> working other than that, so I'm basically going to consider the matter
> closed, unless anyone has fancy ideas to try.
> 

I was waiting for someone more knowledgeable to answer, as I've never
used S-Video with computers, but downconversion does seem likely.

I did wonder what was going on, because as far as I knew S-Video is
defined only for PAL and NTSC, 576i/50 and 480i/60 in modern
terminology. The point of it is that analogue luminance and chrominance
are carried on separate channels, thus avoiding some of the nastiness
inherent in encoding colour into a luminance signal. It really is a TV
signal, and an analogue standard definition one at that.

It would seem that the Linux driver doesn't control the video card
downconversion process properly, but as you say, a downconversion from
1024x768 isn't going to give you better results than from 800x600.

Mr Google says that JVC first used S-Video in 1987, but it would have
been around 1981 that I modified a Hitachi SK-81 camera to provide
separate Y and C outputs to feed a portable U-Matic, modified by
Roderick Snell who was then working at Brighton Polytechnic.

-- 
Joe


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