[Digikam-devel] [Bug 211758] Saving TIFF-16 compressed using exiv2 0.18 shows odd results

[Andreas Huggel]

https://bugs.kde.org/show_bug.cgi?id=211758





--- Comment #33 from Andreas Huggel <ahuggel gmx net>  2010-04-07 04:55:59 ---
Re comment #32: 

> - do you "recommend" that we remove Exif.Thumbnail.* when saving a TIFF with our TIFF loader?

Yes, that way it will also work with older versions of exiv2.

> - is there a workaround for the Predictor tag in our TIFF loader

If the TIFF is written as an 'Adobe deflated' compressed TIFF, i.e., the TIFF
image written by libtiff has an Exif.Image.Compression tag with a Short value 8
then digiKam can add (or prevent deletion of) the Predictor tag. It seems to
have a Short value of 2 (but I've only determined that empirically with just a
few TIFFs, so not sure if it's really always 2 - I'm not into TIFF image data
compression algorithms).

More general, when older versions of exiv2 are in use, digiKam could prevent
modifications to the image tags of TIFF images itself, similar to what exiv2 is
doing in Exiv2::Internal::TiffHeader::isImageTag() -
http://dev.exiv2.org/repositories/entry/exiv2/trunk/src/tiffimage.cpp#L1643
(this is the newer version, IIRC you once implemented something like this based
on the previous code)

I believe this issue is also related to bug #183171 and may go away once that
bug is fixed.

Andreas

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