Date   : Thu, 03 Apr 2008 18:00:19 +0200
From   : kortink@... (John Kortink)
Subject: Monitors

On Thu, 03 Apr 2008 15:56:02 +0200, francis@... wrote:

>>Hi all,
>>
>>What are you guys using for BBC monitors these days?
>
>I'm using an Acorn AKF18 (14" multisync monitor supplied with
>some 32-bit Acorns), and a cable that I made with resistors
>on the R,G, and B lines and with the BBC's Csync output wired
>to Hsync on the monitor (possibly with a resistor, I can't
>remember).

I presently use a TV card in a PC, hooked up to the
BBC via composite or S-video (my last low linerate
accepting monitor, I think an Eizo 9060S, died some
time ago).

Not too bad, just a bit of colour crawl left (at least
on S-video). And there are pieces of software that can
do some useful realtime post-processing of the analogue
video, like thresholding (e.g. DScaler), which should
provide some additional improvement (haven't tried yet).

Suitably wired SCART (with a few resistors) to LCD TV
works very well too, but IMO a TV is not ideal for BBC
activity (too big, awkward placing).

>I'm sure the AKF18 won't last forever, so what I'd
>ideally like is a scan-converter type piece of
>hardware that upscaled to 1280x1024.  Because
>1280x1024 is a multiple of 640x256 and the other
>beeb resolutions there'd be no blurring when
>displaying this on a 1280x1024 LCD (and it'd
>also look nice on CRTs).  Unfortunately I'm not
>really a hardware person so I have no idea how
>difficult it would be to make such a piece of
>hardware.

The main problem is upping the line rate, and the
horizontal pixel rate as well. I suppose somewhat
arbitrary scaling would be best, to be able to suit
a number of common native resolutions, not only
1280 x 1024. Perhaps output letterboxed to
widescreen. Etc. De-interlacing is somewhat
trivial, since both frames are from the same
source pixels anyway, just displaced in time.

One could probably make do with storing two source
lines, one to store a new source line, the other to
replicate a previous one, then swap between the two
every source line. Perhaps some averaging between
subsequent output lines for a smoothing effect.

And, of course, split composite sync into hsync and
vsync digitally (and perhaps draw a separate line
to the 6845 pixel clock for accurate pixel sampling,
but this is obviously less than ideal, and a bit of
oversampling will probably suffice).

Ideally, output not (only) to VGA but to DVI (which
probably requires a standard to-DVI chip due to the
reasonably high pixel rates involved).

All doable with only a bit of realtively cheap
hardware. But in requires a lot of careful design,
and maybe some considerable effort to make it a
little programmable (e.g. being able to switch
between unscaled, scaled, letterboxed etc.).


John Kortink

-- 

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