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Re: IIgs RGB to VGA experiment

js@cimmeri.com wrote:

Follow up.

- Re Highway RGB/VGA converter -- no further progress here yet until I
can order an LM1881.   Haven't completely eliminated this option.

- Re Component 480i YPbPr TV inputs.  Scott Alfter made the excellent
suggestion of trying a YPbPr Component input on HDTV monitors.  So, I
tried connecting my IIgs composite out to the Y jack on both a Samsung
Sync Master 192MP LCD/TV and a Toshiba 50" RPTV at work.   Both worked
perfectly and rock steady in 40col, 80col, GSOS desktop, albeit in
monochrome.    Strangely, IIgs to the same monitors' composite ins
really performed quite poorly, with or without color.


Actually, that would be expected.

It would be quite unusual to detect the absence of the color burst
and then expand the processing bandwidth of the video signal (as the
Applecolor //e monitor does).

The Y component input, however, is known not to contain a chroma
subcarrier, and so can be uniformly processed with high bandwidth.


   I do note that regardless of the size of the TV, the output still
looked great.. even at 50".   Others have expressed the concern that a
SMALL screen is required.   Apparently not true -- these TVs are
*sturdying up* the lines and making them look good at large sizes.


The lines *really are* that wide.  The effect is just one of
"magnification".  If you don't mind the relatively low pixel
count, then it will look fine--crisp but coarse.


  Now, remember.. these tests were from the gs COMPOSITE output to
Component Y.   Since the RGB port is more direct (skips MC1377),  I am
wondering what the RGB port can produce -- so I am now considering
buying an RGB->Component YPbPr converter to further examine the
Component approach.   They appear simple to build, but I don't have the
time to do that.


It should work perfectly.  I proposed this a while back, but I don't
think anyone actually tried it.


   For this test, I some need some advice: what is the minimum
resolution needed to correctly display all IIgs modes, up to SuperHires
640x200?

>

Since there's a border even at 640x200, I assume more horizontal "dots"
are needed than a mere 640.   Is the correct resolution needed more
like 912?  (Or in standard LCD width, 1024?).   The LCD monitor above
is native 1280 across; the Tosh HDTV, likely even higher (=>1900?).   I
note, though, from the IIgs RGB manual, a resolution of only 640x200 is
noted.   So I don't know if the IIgs RBG actually had more dots than
640x200 or not.  How could I determine this?  It's too damn small to
count the dots with a ruler (quite aggravating -- try it).

   My current thinking is that an LCD or CRT monitor of at least 1080i
HDTV resolution is needed to get a true 912(?) dots.


The real answer will have more to do with the interpolation/scaling
algorithm of the TV than the native resolution, since any digital
display, even a CRT one, will pixellate the display.

Since it is *very* unlikely that the TV will attempt to lock to the
Apple dot clock, results may be a little unstable unless the TV pixels
provide more than 2:1 oversampling of the Apple video--which would be
a *very* high end display.  ;-)


   As an experiment to determine the minimum, I also tried the Y input
on a standard resolution Toshiba CRT TV w/480i input, which has (I
counted) about 360 aperture grill lines horizontally and about 260
lines vertically on that tube .   While the image was rock steady and
functional, mono looked ok, all displays were just too fuzzy, and 80col
text was legible but headache inducing.


That has been my experience as well.  Just not a fine enough shadow
mask...


Thanks, all.

p.s.  I scanned through the archives and saw that this IIgs
RGB/VGA/Other? topic has been going on a LONG time.. in fits and
starts.   Tough problem.   I'm also needing this solution for my TRS-80
CoCo3 with the same kind of RGB output.


Yes, it's a perennial favorite.  ;-)

-michael

Parallel computing for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."