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From: olson@endor.harvard.edu (Eric Olson)
Newsgroups: comp.sys.mac
Subject: Re: Looking for Dithering Algorithms
Message-ID: <2879@husc6.UUCP>
Date: Fri, 25-Sep-87 10:22:24 EDT
Article-I.D.: husc6.2879
Posted: Fri Sep 25 10:22:24 1987
Date-Received: Sat, 26-Sep-87 20:16:51 EDT
References: <3320020@hpcid.HP.COM>
Sender: news@husc6.UUCP
Reply-To: olson@endor.UUCP (Eric Olson)
Organization: Aiken Computation Lab Harvard, Cambridge, MA
Lines: 29

In article <3320020@hpcid.HP.COM> cnc@hpcid.HP.COM (Chris Christensen) writes:
>I am looking for information about dithering algorithms.
>
>I often see images on the Mac that were dithered with an algorithm with
>which I am unfamiliar.
>
>I am familiar with contrained average (checkerboard like patterns) and 
>pseudo-optical screening (various size dots), but the algorithm I speak
>of looks like it uses a pseudo random screen. It is grainy in apperence
>but has fewer "dithering artifacts" than either of the above algorithms.
>
>For anyone with Hypercard, the picture of the baby in the photo album stack
>uses the algorithm to which I refer.

That is the dither generated by the Koala MacVision slow-scan video 
digitizer.  I believe its called "Floyd Steinberg Dither": this is what
it is called in a very old version of GrayPaint (a/k/a The Realist a/k/a
The Image Studio, now by Letraset).  I don't know anything else about it.
The MacVision was relatively inexpensive, and a very popular digitizer.  I
don't think it's available anymore.

The baby in the Hypercard Slide Show stack is Bill Atkinson's daughter,
Laura.

-Eric



Eric K. Olson		olson@endor.harvard.edu		harvard!endor!olson