Re: A Cheap Scan Line Doubler!

[mjmahon@aol.com (Michael J. Mahon)]

Scott Alfter replied:

>In article <c6ucnWOKtJWZj7ajXTWc3Q@comcast.com>, Vector <abuse@aol.com>
>wrote:
>>http://www.scancom.ltd.uk/products/vd-300.htm
>>
>>Only �64.00 ...  Anyone tried this one with an Apple II?
>
>I wouldn't expect great results from it.  If it always assumes that the
>incoming signal is color, 80-column text will look nasty.

This is exactly what happens.  I have one of these boxes, and the
results are OK for games (but with different color artifacts than a
composite monitor) but not usable beyond 40 columns.

>>Also, is it possible to wire the IIgs RGB port into an S-Video plug for even
>>better results?
>
>I've not seen that done.  There would be some signal degradation
>involved...you could go from RGB to component video (like your DVD player
>puts out) with very little loss, but S-video mashes Cb and Cr together
>somehow into a single C signal.  (The Y signal (which also carries sync) is
>the same for both component video and S-video.  Composite video combines all
>three together.)

S-video multiplexes the chroma signals on a subcarrier, so they are not
baseband signals.  Since an S-video monitor doesn't have to filter the
subcarrier to separate it from a composite signal, the luminance signal's
bandwidth is not compromised, making for crisper displays.  But the
bandwidth is still limited much more than with an RGB display.

>That said, it might still be good enough.  I noticed a big difference when I
>switched my TiVo from composite to S-video...its menus look much cleaner. 
>Maybe converting RGB video from the IIGS to component video or S-video might
>be doable for hooking up a TV and still getting readable results...the only
>trick left would be to find a reasonably small TV that supports those
>inputs, as you mainly find them only on larget TVs.  It would be a solution
>to fewer and fewer compatible monitors being available.

Component video might be a solution.  It could be done from RGB using
only passive matrixing (with resistive mixing) followed by three video buffers,
which would be a very simple solution.  A small complication is that the
sync signal should not be present on the Cr Cb signals.

Has anyone here done this?
-michael

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