Re: DHGR Correction for KEGS32 & AppleWin

[Andy McFadden <fadden@fadden.com>]

mdj <mdj.mdj@gmail.com> wrote:
> If the emulators appear to be mapping the colours incorrectly, I'd
> venture that it's because the emulators choose to more closely mimic
> the composite video signals produced by all Apple II's. Remember, the
> IIGS's RGB output is only an approximation of the quasi-NTSC signal
> produced by the composite video out. You are probably correct that the
> IIGS approximation is 'wrong', it is after all only 4 bits of
> resolution per colour channel.

I did an experiment once with a Magnavox monitor attached to my IIgs.  I
don't recall the monitor's model number, but it was the kind that
A2-Central used to sell.  The nifty thing about it is that it would select
from multiple inputs with switches on the back.

So, I connected both the RGB and composite outputs from the IIgs to the
monitor, cranked up Dazzle Draw, and flipped back and forth between the
two inputs.

As you might expect, there were significant differences between the two.
Not just in color, but in how the pixels blur together.

My goal was to accurately reproduce the IIgs RGB output in DHGR for the
CiderPress conversion, but I found a lot of combinations that didn't make
sense -- every pixel depends on the current color and the previous color,
but sometimes it's more dependent than others.  Rather than try to reverse-
engineer the signal that was being emulated/generated/mangled, I punted
on it and implemented something close.  (Actually, I implemented 4 different
modes: one that works the way the //e tech note describes, one that looks
like the IIgs display, one that does an ideal 140x280 screen, and one B&W.
The colors I just mapped to the usual IIgs values.)

I also didn't implement the weird standard hi-res stuff that gets you
browns and yellows.  I don't think most emulators to that either.

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