[gdal-dev] GPKG : how to save tile into 1-band 8-bit PNG

[Philippe Ghesquiere]

Dear all,

*Some context*
In our system, we convert elevation data into Geopackage in order to use
them with mapcache/mapserver.
For our display needs, we save two layers in a GPKG file :

   - a color-relief layer  : saved as RGBA 8-bit PNG tiles
   - a hillshade layer : saved as RGBA 8-bit PNG tiles

*My environment*
GDAL V3.8.4

*My question :*
Since a hillshade image is a gray-scale image, isn't it possible to save
tiles in 1-band 8-bit PNG + Alpha band, instead of RGB, into a PKG database?

I have tried several options with either gda_translate (-b 1, -ot Byte,
TILE_FORMAT=PNG or PNG8)  or gdalwarp, with no success.

Thanks for any hints you could give me.

Sincerely
Philippe
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