Re: RGB to VGA monitor

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

Supertimer wrote:

>Ok, I'd like to put my IIGS back in service.  It no longer has a color
>monitor.  I would like to use something other than a Second Sight
>card because the display of that card isn't identical to what is
>displayed on the normal IIGS RGB monitor.  Is there a cheap scan
>converter that would take a video RGB signal and transform it into
>a PC VGA signal?

O.K., I've just had a chance to try out my NTSC to VGA converter
with an Apple //e, with mixed results.

The converter is the "Video Cheese Box" (!) and it actually looks
like about a half-pound of cartoon cheese--you know, the kind that
has "holes" about as big as a nickel.  Of course, none of the "holes"
actually vents the case, just provides "chunks" out of the edges, etc.

When used with a VGA monitor and an Apple //e, is does an excellent
impression of a TV set--replete with color fringes on everything, even in
text mode.  Interestingly, if I put the Apple in a "mixed" graphics/text
mode, the text looks much better:  still colored, but with much less
fringing.  This suggests to me that the "box" has AGC on the color
burst, and when it goes away suddenly at the end of the graphics
portion of the screen, the color is attenuated.

Also readily apparent is the large Apple II "overscan allowance".
Since the Apple II was designed to interface with a TV as a monitor,
and most TVs overscan the screen by 5%-25% so that no black
edge is visible around the picture, the Apple's active scan line is
limited to 40-microsecond vs. NTSC's 55 or so to ensure that all
the displayed video is actually visible.  As a result, when viewing
the scan-converted video on a 15" VGA monitor, the edges of
the Apple II screen are 7.5" wide and 6" tall--a lot of wasted
screen real estate.  (By comparison, the blue screen that the
box displays when no video is present is 9.5" wide by 7.25" high--
and a _lovely shade of blue!)  Of course, the VGA monitor is
actually underscanned, so no edge info is off the screen.

The display would be quite satisfactory for a game, but is hard to
put up with for 40-column text and is useless for 80-column text.

It would be interesting to see how other "scan doubler" boxes do,
particularly on monochrome inputs, like the text display.  It would
be possible (though not particularly likely) to provide a "width"
adjustment on the scan doubler to select how much of the NTSC
input line is captured and doubled, so that the full VGA raster
could be utilized.  I would really like to see a box that killed the
color when the burst was absent (as it should).

What say?  Any other user reports?  It would be nice to find
a really good one for Apple II use, considering how cheap (free)
and ubiquitous VGA displays are.

-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/