[Gimp-developer] TIFF Deflate compression method writes proprietary/deprecated tag to file

[Federico <federicotg gmail com>]

Hi.
I noticed GIMP 2.8.4 is writing the proprietary ZIP/Flate compression code
(0x80b2) when exporting images in TIFF format and selecting deflate
compression.
According to the TIFF Revision 6.0, Supplement 2 (
http://partners.adobe.com/public/developer/en/tiff/TIFFphotoshop.pdf) the
value for the Compression tag should be 0008.

I can confirm Gimp is writing the proprietary tag by exporting a deflated
tiff and running

tiffdump 1.tif | grep Compression
Compression (259) SHORT (3) 1<32946>

If I use imagemagick's mogrify to create the tiff
mogrify -path /home/user/ -compress Zip -depth 8 -format tif fotografía7.tif

I get
tiffdump /home/user/fotografía7.tif | grep Compression
Compression (259) SHORT (3) 1<8>

The compression algorithm is the same, only the code is changed for a
standard value. As TIFF is used for long term archiving, the generating the
files with the standard value is important for future implementations that
may not understand the proprietary tag.

Should I file a bug? Do you think it is important?

Here's a section of the spec:

"Note:
A proprietary ZIP/Flate compression code (0x80b2) has been used by some
software vendors. This code
should be considered obsolete. The compression used by the obsolete code is
identical to that defined
above. We recommend that TIFF implementations recognize and read the
obsolete code, but only write the
official compression code (8)."