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Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!usc!venera.isi.edu!raveling
From: raveling@venera.isi.edu (Paul Raveling)
Newsgroups: comp.windows.x,comp.sys.hp
Subject: Re: Converting RGB grey scale pictures into dithered patterns.
Message-ID: <9386@venera.isi.edu>
Date: 21 Aug 89 16:48:54 GMT
References: <19183@mimsy.UUCP>
Reply-To: raveling@venera.isi.edu (Paul Raveling)
Organization: Information Sciences Institute, Univ. of So. California
Lines: 30

In article <19183@mimsy.UUCP> preetham@chisti.umiacs.umd.edu (Preetham Gopalaswamy) writes:
>I am running HP-UX 6.5 on an HP Series 300 machine.  I would like to convert
>some grey scale pictures (running under X windows) into dithered patterns i.e.
>x black dots out of n dots represents (x/n)% grey.  I need this to display 
>black-white-grey images on a monochrome screen.  Are there any standard
>programs to do this or has any kind soul in netland already written it out for
>me to use :-)

	The imglib library functions available by anonymous FTP from
	venera.isi.edu include a routine that uses Floyd-Steinberg
	dithering to translate a color image to a monochrome image.

	It should be possible to adapt this routine easily or perhaps
	to use the imglib software as is.  Look at function color_to_mono
	in file imgcvt.c.  If your original data is purely grayscale
	you can eliminate the color-to-grayscale translation for each
	pixel that precedes dithering and error propagation.

	To get the imglib software, do an anonymous FTP login
	to venera.isi.edu and pick up pub/img.tar.Z.  To find
	images using the Img file format, check pub/img_ls-RAlF.Z
	and images/README.  README offers some tips for dealing
	with the fact that anonymous ftp refuses to show directory
	listings for the ~ftp/images hierarchy with the "dir" or "ls"
	commands.


----------------
Paul Raveling
Raveling@isi.edu