How does UnpackBits work?

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Article #16587

#16587

From: Marc Russell Pawliger
Date: Fri, 29 May 1987 20:01

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1128 bytes

I have been trying to implement UnpackBits in c with mediocre success.  As I
understand it, packbits does the following:
	
Read a byte called control
	control  < 128?
		Next control+1 bytes are straight bitmap
	control  >= 128?
		The next byte in the input stream is repeated 256-control
times
		(2s complement of control times)

I am able to read in a file I made that consists of straight lines of bitmap,
however when I have to read a compressed file (a MacPaint file), the routine
gets messed up.

Any code fragments greatly appreciated.

			Marc Pawliger
			mp1w+@andrew.cmu.edu
			mp1w@cmuccvma.bitnet

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Path: arc1-ca.pugleaf.net!utzoo!mnetor!seismo!rochester!pt.cs.cmu.edu!andrew.cmu.edu!mp1w+
From: mp1w+@andrew.cmu.edu (Marc Russell Pawliger)
Newsgroups: comp.sys.mac
Subject: How does UnpackBits work?
Message-ID: <UUjSY6y00Vs4AKo08H@andrew.cmu.edu>
Date: Fri, 29-May-87 16:01:10 EDT
Article-I.D.: andrew.UUjSY6y00Vs4AKo08H
Posted: Fri May 29 16:01:10 1987
Date-Received: Sat, 6-Jun-87 15:48:26 EDT
Organization: Carnegie Mellon University
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