Re: RGB to VGA on a IIGS (again)

[mdj <mdj.mdj@gmail.com>]

On Jun 24, 9:48 am, "Michael J. Mahon" <mjma...@aol.com> 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.

It's a lovely old Sanyo unit that looks wonderfully retro beside the
pinball machines downstairs :-) Bandwidth is 14Mhz, so yes it produces
a very clean picture.

> 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.

I love my AppleColor Composites too, but I'm finding my eyes are
starting to struggle with long exposure to anything less that pristine
text. Whether this is a function of getting old, or a side effect of
now spending so much time in front of higher quality displays I'm not
sure :-)

> > 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.

I figured it'd be something like that, or alternatively it's that the
upsampling algorithm is very simplistic and doesn't cope at all well
with the Apple II's slightly odd clock rate.

> > What's needed is a converter that can lock onto the Apple II's dot
> > clock...
>
> Bingo!
>
> -michael
>
> NadaNet file server for Apple II computers!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."