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Date: Fri, 22 Mar 2002 00:56:46 -0500
To: tiff <tiff@olympiakos.com>
From: Jon Saxton <spam.free@verizon.net>
Reply-To: Jon Saxton <js@triton.vg>
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Subject: Re: Changing Orientation Tag
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** Reply to message from "Erika Nesse" <enesse@umich.edu> on Wed, 20 Mar 2002
11:37:49 -0500

> I was wondering if anyone knows of any software that changes the
> orientation of tiffs by toggling the orientation tag, instead of
> actually changing the order of the data?  

That's what I do in my cheque-processing software.  If a document is imaged
upside-down and the operator clicks the "invert" button, I just change the
orientation tag and leave the image unchanged.  Any viewer worth using should
interpret the orientation tag if it is present.  If it doesn't, you have a
crappy viewer.  (Of course I do flip the image on the screen so the user can see
it properly - I just don't bother reconstructing the image in the TIFF file.)

> The reason I'm asking is that I would like to convert some files which
> have a non-standard value for their orientation tag (due to the somewhat
> over-helpful scanner which created them) to the standard value, so that
> they do not show up in different orientations depending on whether the
> viewing software implements the orientation tag or not.  

Now I am confused.  This seems to contradict the question in the first
paragraph.  It seems like you do want to twiddle the pixels after all.  For each
image in a TIFF file the steps are:

	decompress
	rotate and/or mirror
	compress

Again, I assert that it is the viewer's responsibility to display the image
correctly.  This is especially so with modern operating systems supporting
virtualised graphics, because to display the image with the proper view is just
a matter of setting up the source and destination presentation spaces correctly.
The code is trivial; there are no transforms to be done on the pixel arrays at
all so failure to support all possible orientations is just a matter of
laziness, ignorance or pig-headedness on the part of the programmer.

IMNSHO, the "correct" answer is to get the vendor to fix the bug.

--
Jon Saxton <js@triton.vg> OS/2 software developer
U.S. agent for Triton Technologies International Ltd
http://www.triton.vg/


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