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From: alex@dartvax.UUCP (Alex Hartov)
Newsgroups: comp.graphics
Subject: CT image files format
Message-ID: <6949@dartvax.UUCP>
Date: Wed, 26-Aug-87 23:49:15 EDT
Article-I.D.: dartvax.6949
Posted: Wed Aug 26 23:49:15 1987
Date-Received: Sat, 29-Aug-87 14:17:15 EDT
Reply-To: alex@dartvax.UUCP (Alex Hartov)
Organization: Dartmouth College, Hanover, NH
Lines: 69

>Received: from obelix.liu.se by asterix.liu.se; Mon, 17 Aug 87 21:02:11 +0200
>Received: by obelix.liu.se; Mon, 17 Aug 87 21:01:13 SDT
>Date: Mon, 17 Aug 87 21:01:13 SDT
>From: P{r Emanuelsson <linus!harvard!seismo!enea!obelix.liu.se!p_e>
>Message-Id: <8708171901.AA25733@obelix.liu.se>
>To: alex
>Subject: Re: CT images conversion to VICOM format
>Newsgroups: comp.graphics,comp.sys.workstations
>In-Reply-To: <3285@ncoast.UUCP>
>Organization: University of Linkoping, Sweden
>Status: RO
>
>In article <3285@ncoast.UUCP> you write:
>> I would like to know if anyone has some information to share concerning
>>CT (aka CAT SCAN) file formats produced on GE systems.
>
>Well, is that something I would like to know! I have some tapes, but
>have never been able to decipher them. If you get any information, please
>forward them to me, or post in comp.graphics. Hope it's not proprietary :-(
>
>Cheers,
>
>/Per Emanuelsson


Per,                (also for the benefit of anyone interrested)

Your were the only person to answer my posting.  However I did find out a few
things concerning CT file formats.  First let me be more specific.  There are 
several manufacturers that make CT machines and each have their own way of 
doing things.  For my project I receive tapes made on a General Electric 
CT machine.  The format they use is the so-called GE8800 system, as opposed to 
the 9800 system which is more recent.  The computer they use is a Data 
General Eclipse equipped with an 800 bpi 1/2" tape drive.  The tapes are
transferred on a VAX unix machine using a program that swaps bytes (because
of DG's tape format).  From looking at the raw data and some trial and error 

I have been able to determine the following:

Tapes contain several files separated by EOF's.  The first 2 files do not 
contain image data and I do not use them.  The image data is contained in the
third and following files.  

There are several types of image files, so far I have only been able to display
images that were saved as 'screen dumps' or 'screen save'.  

The image data starts at the 3rd block of the image files, a block being 256
words or 512 bytes. 

In the case of screen saves, the images are squares of 320 pixels to the side.
The image data consists of 16 bit words (2 bytes) in integer format of 12 bits,
the 4 most significant bits being used for graphic overlays.  It is a simple 
matter to read the image data and pad it to a 512X512 image if that's what your
system uses. 

GE uses another type of images which are elliptic, apparently with x and y axes
that can be changed in scale.  I haven't been able to figure these out although
I have been able to show distorted images to convince myself that I was on
the right track.

Between images there is a block (256 words) of data that is some sort of image
header.

That's all I have..

			Alex.

--
P.S. The brain is in gear, the clutch is slipping...