Tiff color table component values seem wrong (minus one from what they should be) about gdal HOT 3 OPEN

@slesim Can you attach such a file ? I believe the root cause is that TIFF color table entries are expressed as values in the [0,65535] range, and not [0,255], so software has to do remapping. GDAL uses division by 257 and truncation to do the conversion from [0,65535] to [0,255]. Other software might have slightly different approaches. The TIFF specification doesn't specify how to do that remapping

Current behaviour dates back to this changeset eeec5b6 that went in GDAL 2.3.0. Previously division by 256 was done.

from gdal.

Tifffile does not do any conversion or remapping. tif.pages[0].tags['ColorMap'].value is a numpy array of dtype uint16.

The conversion in the example code is int.from_bytes(r[i]), which is wrong in general but happens to give expected results for multiples of 256.

from gdal.

Thanks for your answers, it helps my understanding.
Here is a sample file :
rugoIndex.zip

from gdal.