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Date Posted: 15:26:47 09/03/04 Fri
Author: Phil Gregory
Subject: Re: unsupported compression tag 6
In reply to: R.Nelson 's message, "unsupported compression tag 6" on 05:18:50 08/24/04 Tue

>unsupported compression tag 6.

I've run into the same thing. Here's what I've found:

Revision 6.0 of the TIFF specification allowed for using JPEG compression on the image. It assigned that compression scheme to compression type 6. Several years later, they updated the specification and altered the way that JPEG compression was handled. They used compression type 7 for the new JPEG scheme and recommended that the previous implementation be phased out. The Envision components do not have support for the older method, somewhat understandibly.

I (and, apparently, you) have an existing tool that generates old-style JPEG compression. I'm not sure what I can do about this--I already have a history of data encoded in this manner. I haven't been able to find a workaround. If I'm to read this, it will need to be added to the Envision code, at probably no small investment of time.

On top of that, the Envision developer doesn't seem to be around on this forum. Does anyone know when the many problems mentioned here will be addressed?


For reference:
TIFF Specification, revision 6.0: <a rel=nofollow target=_blank href="http://partners.adobe.com/asn/developer/pdfs/tn/TIFF6.pdf">http://partners.adobe.com/asn/developer/pdfs/tn/TIFF6.pdf</a>
TIFF Technical Note #2: <a rel=nofollow target=_blank href="http://www.remotesensing.org/libtiff/TIFFTechNote2.html">http://www.remotesensing.org/libtiff/TIFFTechNote2.html</a>

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