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Re: RGB to VGA on a IIGS (again)

Michael J. Mahon wrote:

Lee Cremeans wrote:

Michael J. Mahon wrote:


mdj wrote:


On Jun 24, 12:18 am, "Bryan Parkoff" <nos...@nospam.com> wrote:


"mdj" <mdj....@gmail.com> wrote in message

1182580110.751279.80970@g37g2000prf.googlegroups.com">news:1182580110.751279.80970@g37g2000prf.googlegroups.com...





On Jun 23, 3:57 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:


mcph...@yahoo.com wrote:
I know this has been asked before, but I was wondering if there were 
any new RGB to VGA upscaling converters out that were particularly
good for this task. The XRGB-2 is no longer available (and was
pricey).




I would like to do RGB rather than composite to VGA with a GS and a
viewsonic LCD.




Right--if you start with composite, then the result can never be
any better than that, no matter what format you convert to.




The 'simple' solution is to use an LCD TV with a SCART input on it,
and use Roger's IIgs->RGB cable. The results will depend on the
quality of the TV.




I tried this a while back with my TV (A 32" model, a bit inconvenient
placing atop an Apple II) and the results were quite acceptable. On my 
Apple II though, I've now decided to regress to a green phosphor
monochrome display. For a non-gamer, this gives the best possible
results, but I would certainly like to find a small LCD TV that worked 
well.
I would be surprised to see Video (NTSC) to VGA Converter athttp://www.ramelectronics.net/html/video-vga-gvm-2000.html. I am sure 80 column is unreadable on VGA screen unless digital filter is used isntead of 
analog.  Do you agree?




I'd imagine pretty much all these converters use some form of digital
storage.



The issue is how the composite video is decoded, and what the bandwidth
of the resulting luminance signal is.  For NTSC decoding, it is almost
impossible to preserve a luminance bandwidth of more than 3.5MHz, which
isn't enough for good 80-column text.  Your monochrome monitor no doubt
has (luminance, of course!) bandwidth exceeding 10MHz.

The AppleColor Composite monitor, when in monochrome mode, switches its
luminance bandwidth to about 8MHz--a capability almost unique in
composite video processing, even in the digital age.


80 column text tends to look a little odd, with alternate scanlines
interpreting the pixel widths slightly differently. Readable, but not
particularly clear.



This is a result an interaction between the monitor's sampling of
what it thinks is an interlaced video signal, but isn't.


What's needed is a converter that can lock onto the Apple II's dot
clock...



Bingo!
Since this has come up again, I have to wonder: Why not use S-video for this, since practically everything supports it and it can do the higher luma bandwidths easily? This would be somewhat difficult on an original II or a IIc, since they're hardwired for analog, but the IIgs already has a RGB->NTSC converter in it (the MC1377P in the back) that could easily be tapped in the right places to get the raw luma and chroma out (IIRC chroma is on pin 9). (The Video Turtle, from what I can tell, was just a second MC1377P in a nice box that fit on the RGB port.)
I've been wanting to try it on my own IIgs, but I haven't had the time or the space in my room. 

I agree--S-video would be a very straightforward approach for the IIgs.
Note, though, that even S-video limits the bandwidth of chrominance
signals by subcarrier modulation.  This means that isolated color pixels
would lose saturation in comparison with RGB, but this would only be
noticeable in certain situations (like a colored starfield).
True...though in my case, I'd mainly be working with 80-column text and the SHR screen, where the colors aren't quite as important because there just aren't that many to begin with. (Then again, I also have KEGS set up on my Mac mini, which also helps, but sometimes you just have to play with the real hardware.) 


This is a good argument for HDMI, component video, or RGB, that any
home theater owner can appreciate!
I'd love to see someone finally make a proper YCrCb-out adapter for the IIgs (even though I wouldn't get much use out of it since my LCDs are computer monitors and can't do component). I know people have been talking about it for years, but is anyone doing it? 
-lee