Add support for variable length custom tags #173
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In libtiff, custom tags with variable length (eg, a binary blob) are indicated with the special constants TIFF_VARIABLE (-1) or TIFF_VARIABLE2 (-3). In such case, when reading a field the length is passed as first argument, and the data as a pointer as second argument. So far, some standard tags with such format were supported, but not custom tags. => Add support for such tags. Also fix the names of the attribute created automatically, which got broken in the switch from Python 2 to 3. What should have been named, for instance, TIFFTAG_CUSTOM, was named like TIFFTAG_b'CUSTOM', quotes included! Also fix the test cases, which were not working, mostly related to reading/writing tags.
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In libtiff, custom tags with variable length (eg, a binary blob) are indicated with the special constants
TIFF_VARIABLE(-1) orTIFF_VARIABLE2(-3). In such case, when reading a field, the length is passed as first argument, and a pointer to the data as second argument.So far, some standard tags with such format were supported, but not custom tags. We needed such tags to support reading metadata from some microscopes. We had to hack it by modifying directly
tifftags. You can see it here:https://github.com/delmic/odemis/blob/a025bc7d991a37b408adb031a2561c35c3b87d23/src/odemis/dataio/tiff.py#L95
This change allows to directly extend the custom tags, with
add_tags().Also fix the names of the automatically created attribute, which got broken in the switch from Python 2 to 3.
What should have been named, for instance,
TIFFTAG_CUSTOM, was named likeTIFFTAG_b'CUSTOM', quotes included!Also fix the test cases, which were not working, mostly related to reading/writing tags.
Now, all the tests pass, as run with:
python3 ./libtiff/libtiff_ctypes.py