Re: Double HIgh Resolution Question

[Andy McFadden <fadden@fadden.com>]

Eric Smith <eric-no-spam-for-me@brouhaha.com> wrote:
>> I should be able to convert from 560x192 to 280x192 by removing a pair
>> of dots each plot.  Each plot will only have one dot that will show 16
>> colors on 280x192 instead of 560x192.  It will look much neater than
>> 560x192 on emulator project.  What do you think?
> 
> Presumably you should do whatever makes the simulator[*] display look
> closest to the display of a real Apple.

Ay, there's the rub.

When working on CiderPress I spent a considerable amount of time trying
to make the display look right.  The trouble is that "right" is debateable,
because different "real" outputs look different.

I ended up with four modes:

 (1) Monochrome.  This looks exactly like a IIgs RGB monitor.  Easy.
 (2) Sliding window.  This looks very much like a composite monitor
  plugged into a IIgs, and probably looks about like a //e.  It has
  rather severe color fringing, but then so does the composite output.
  The algorithm used matches what is described in the DHR tech note.
 (3) Latched.  This looks a lot like IIgs RGB output, but there are a
  lot of funky quirks that I didn't try to emulate.  Mostly this is just
  "sliding window" with special handling of black/white transitions.
 (4) Ideal color.  Each pixel's color is determined by 4 bits, regardless
  of what comes before or after.  This doesn't resemble anything on a
  real Apple II.

The trouble with DHR is that you need a 12-bit lookup table to determine
the color of each pixel.  You have to consider the four bits that "should"
be determining the color, plus the previous 4 bits, plus the following 4
bits, because the color can be different depending on what came before or
after.  And there isn't a simple logic function that explains it.  (If
there is, it has eluded me.)

Actually, the *real* trouble with DHR is that what you see on composite
bears little resemblance to what you see on RGB, so even if you worked
out the whole 12-bit thing for RGB you're still "wrong" when compared
to composite.

Standard hi-res is easy by comparison -- assuming you don't want to
handle the oranges and browns that can appear if you do things just right.
(Somebody posted a test program on the net a while back; you can find the
program and its output on one of the CiderPress test images.  And, no, I
didn't try to handle that stuff.)

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