Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcso!hpfcdq!olsen
From: olsen@hpfcdq.HP.COM (John Olsen)
Newsgroups: comp.sys.amiga
Subject: Re: Neptune Voyager Pix directly viewable on Amiga
Message-ID: <4710003@hpfcdq.HP.COM>
Date: 6 Sep 89 14:50:04 GMT
References: <21728@cup.portal.com>
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 28

portuesi@tweezers.esd.sgi.com (Michael Portuesi) writes:
>In article <2497@pur-phy> murphy@pur-phy (William J. Murphy) writes:
> >  Although HAM will sacrifice some resolution,
> >  it will allow more gray scale approximations.
>No, it won't.  The Amiga has four bits of color resolution each for R,
>G and B.  It is limited to sixteen greyscales no matter what display
>mode you choose.  They can all be displayed in a high-res image.

Sorry, but you missed the word "approximations".  For example:
R G B
8 8 8 Medium gray
8 8 7 \
8 7 8  \  Approximately gray, and all between the 888 and 777.  The 
7 8 8   \ intensities may be very close, so you might want to only use
8 7 7   / two of the intermediate shades (one with a single 7 and one with
7 8 7  /  two sevens), but that still gives you 46 shades of near-gray
7 7 8 /   (two between each adjacent pair of true grays -> 30 extra colors).
7 7 7 Next true gray down

I've used this technique with good results, and I've spotted some of those
near-grays in some digitized images by looking really close.  If you use 
dithering with it, you can make really nice images.  Now dithering in HAM
is not exactly straightforward, and opens up a whole new can of worms which 
I don't want to worry about now.  :^)  I hope this helped a little.

John M. Olsen, Graphics Software Engineer
olsen@hpfcdq.HP.COM  -or-  ...!hplabs!hpfcdq!olsen
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