Re: Apple IIgs Color Dither Problem

[Tony Kavadias]

On 2009-09-19 23:02:34 +1000, Immortal Nephi <Immortal_Nephi@hotmail.com> said:

> What do you mean "dithering algorithms used by Apple IIgs emulators
> are too simplistic"?  KEGS probably does not have dithering algorithm
> to hide vertical strip.  There has to be another way.  Like I said
> color dithering translation table may be needed to prevent from
> showing dithering on the screen.

I use an emulator called Sweet 16, which is a Mac OS X "version" of an older
emulator called Bernie ][ The Rescue for Mac OS 8 and higher.  While I could
argue that this is the best Apple IIGS emulator ever written for the Macintosh
to date, there are some shortcomings... one of them is its "AppleColor 
RGB Monitor
mode".

What this does is combine the colours of even-odd adjacent pixels for 
pixels that
are not black nor white in order to come up with a way to display cleaner
640-resolution graphics.

However, in my opinion, I find that while the algorithm does the job in killing
the vertical stripes of adjacent colours on 640 displays, it does so by
killing the accuracy (fidelity) of the picture, particularly since while black
and white even-odd pixel pairs are not blended to make grey, other colours
do not get the same treatment, so if there was a picture that relied on 
coloured
edges to define a picture, those edges would be distorted by the software
dithering process.

However, to make a "smarter" dithering algorithm would mean to be able to
identify where to blend colours and where not to, and this would require a
degree of artificial intelligence to do the job... something I'd rather not
apply anyway (I disable "AppleColor RGB Monitor mode" and just put up with
the vertical stripes!).

You mentioned using KEGS... I noticed that it does not have software dithering
like Bernie does.  If you can, you might like to try Bernie/Sweet 16 to see if
they can help you achieve the graphics results you're looking for:

http://www.sheppyware.net/downloads/downloads-mac/files/Sweet16%202.1.3.dmg

(The above link is only useful for Mac OS X only.)

Cheers!


-- tonza