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From: skinner@saber.UUCP
Newsgroups: net.graphics
Subject: Re: Color dither (ordered vs. error propagation)
Message-ID: <1963@saber.UUCP>
Date: Mon, 21-Apr-86 12:47:03 EST
Article-I.D.: saber.1963
Posted: Mon Apr 21 12:47:03 1986
Date-Received: Wed, 23-Apr-86 21:35:18 EST
References: <1664@sdcsvax.UUCP> <396@cit-vax.Caltech.Edu> <1679@sdcsvax.UUCP>
Organization: Saber Technology, San Jose, CA
Lines: 40

> <I really dislike inclusions>
> 
> In article <396@cit-vax.Caltech.Edu> jon@cit-vax.UUCP (Jonathan P. Leech) writes:
> >In article <1664@sdcsvax.UUCP> hutch@sdcsvax.UUCP (Jim Hutchison) writes:
> >>... By using an ordered color dither, I get a reasonable image, and
> >>maintain a static map configuration.
> >>...
> >>Any suggestions?  What I have now is very pleasantly displaying the 24bit
> >>images we have received from USC (mandrel, milk drop, faces, peppers, park).
> >
> >    You might try Floyd-Steinberg dither (I believe this is also known
> >as 'minmized average error' dither. It works basically like this:
> >...
> >    My implementation of this is ~ 3x as slow  as  ordered  dither  on
> >Suns and HP bobcats - enough to be quite annoying.
> >-- 
> 

I also implemented the Floyd-Steinberg dither, first in true floating point
(quite slow on a workstation), then in integer (not much faster, due
to extra precision to prevent truncation errors).  Then, I finally
realized that the quantization value and the error terms could be
pre-computed and stored in a look-up table.  The resulting program is
about 4x as fast as the floating point version.  

If anyone is interested, I will post the code.  It has some
limitations, such as dithering to a destination of at most 8 bits, but
the 8 can be any combination of red, green, or blue bits.  It also
handles less than 8 bits well, as would be needed with an 8 color
printer.  Of course it still exibits the problems of F-S dither.

------------------------------------------------------------------------------
"You know something people?  I'm not black,
 But there's a whole lots of times I wish I could say I'm not white"

Name:	Robert Skinner
Snail:	Saber Technology, 2381 Bering Drive, San Jose, California 95131
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