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From: ISSLTC@NUSVM.BITNET (Lim Thye Chean)
Newsgroups: comp.sys.apple2
Subject: GS PALETTE AND 320/640 MODE
Message-ID: <9106100316.AA18481@apple.com>
Date: 10 Jun 91 03:14:57 GMT
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X-Unparsable-Date: Mon, 10 Jun 91 10:19:18 SST

Thanks for the answer I got from my question of GS palettes. I have
actually does some work on them, and have some discoveries and surprise
here and there. Below are my story...

In order to solve the colour incompatibility between 320 and 640 mode,
I write a paint program, called GS Paint, with one aim: The picture
created in 320 or 640 mode must be able to convert the other mode,
WITHOUT ANY LOSS OR DISTORTION in colour details.

So the first thing I do is to design a set of palette which is almost
identical to 640 mode dithered palette. I means ALMOST because I really
hate some of the colours after dithering, like Red. So my 320 mode
palette have a much richer and nicer red. Besides, everything is identical.

The surprise comes in when I am designing the interface. No, I don't want
the GS to switch to 320-mode menu and dialog box when I am switching to
320-mode, just like all other paint programs. Instead, out of curiousity,
I remain the window and menu in 640 mode, and remapped line 13 to 200
to 320 modes. The result is fantastic and surprising. The shaston 8 fonts
is actually readable in 320 mode (although it is only half the size). And
it is also the same as for other fonts. Besides, I can use all DA's that
were designed with 640-mode in mind (like Control-Panel...I like the plane
that flies) with one exception: all of their colour becomes rich and
pretty.

It is no surprise if you know what is anti-aliasing, it is exactly the
opposite of dithering. In 640-mode, we use dithering to get more colour
at the expense of resolution. In 320-mode, we can actually get more
resolution at the expense of colours. Since the only colours that will
appeared correctly in 640-mode are black and white without dithered,
so we only need to anti-aliase black and white. When two pixels close
to each others are black and white, we can represent it as grey.

What is nice is that by using the palette as in 640-mode, the grey will
be at the exact location for anti-aliasing to occurs. So, no extra works
need to be done.

Now, in my beta version of my paint program, I can switch to any
resolution I want, without any distortion. Yes, the characters might be
a little blur at 320-mode, but they are readable. I plan to make the
part that do the palette conversion an NDA, so I can switch to 320-mode
while I am working on any 640-mode applications, that required little
text but lots of graphics (Page layout and AWGS graphics module for
example).

Anybody interested can mail me.


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                      *** Apple IIGS Forever ***

 An Apple IIGS lover from Malaysia. A software engineer from Singapore.
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                      Contact me at ISSLTC@NUSVM

       Lim Thye Chean - Lim is my surname. My name is Thye Chean.
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