[gdal-dev] palette file format doc ?

[Even Rouault]

Michael,

Le 20/03/2024 à 21:38, Michael Sumner via gdal-dev a écrit :
> Is the palette_file  .txt format documented?
>
> https://gdal.org/programs/gdalattachpct.html
>
> It's mentioned in a few utilities, and created by tests but I couldn't 
> find an existing example or a description (I guessed, incorrectly at 
> first, leaving out the index column). I

The initial attachpct.py script only worked with a GDAL raster as the 
source for the palette. The support for text formats, or qml, qlr seems 
to be a later addition by Idan Miara, and the best doc is probably the 
code: 
https://github.com/OSGeo/gdal/blob/master/swig/python/gdal-utils/osgeo_utils/auxiliary/color_palette.py 
. You may also have a look at autotest/pyscripts/test_gdal_utils.py 
which has tests for this color palette reading code. Looking a bit at 
it, I suspect the GDAL text format refered is the one actually used by 
gdaldem color-relief: 
https://gdal.org/programs/gdaldem.html#color-relief , which is itself 
derived from the one used by GRASS r.colors . But the Python code (only 
Python) and the one used by gdaldem (only C++) are different, so I 
wouldn't exclude there might be some differences.

| take it that it is 0-255 range values, but is index 0-based or 1?

0-based, as (unsigned) raster values are

> And, can index be *value* in any contexts?

If you use a raster with a signed data type, that could be negative 
values (assuming I understand your question)

Even

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