[gdal-dev] gdal_translate, exporting "Byte - Eight bit unsigned integer" single band tiff to gpkg using -ot Byte results in 4 bands raster with changed values

[Even Rouault]

On mercredi 2 décembre 2020 15:16:44 CET Nicolas Cadieux wrote:
> Hi,
> 
> This follows a discussion in the qgis-user mailing list.  We are using
> gdal_translate (and QGIS "export as") on a 8bit unsigned single band
> tiff to a .gpkg.  When using no -ot switch or when using -ot Byte, this
> results in a 4 band .gpkg raster with the wrong values.  (Values in band
> 1 to 3 are similar but off the mark). Band 4 is set at 255 as expected. 
> Looks like some type of compression is going on in the band 1 to 3).
> 
> When saving using the -ot Int16 or Float32 switch, all is well and the
> result has one band with the correct values.
> 
> ex: gdal_translate -ot Int16 -of GPKG "E:/Users/Nicolas/Google Drive
> Nicolas/Partage_temporaire/qgis/int16.gpkg" "E:/Users/Nicolas/Google
> Drive Nicolas/Partage_temporaire/qgis/int16.gpkg"
> 
> Is this a possible problem with the driver or is the problem sitting 18
> inches in front of the screen? Problem similar on a Mac running QGIS
> 3.10.1-A with GDAL 3.0.2 and QGIS3.16 on Windows running GDAL 3.1.4.
> 
> Test files are found here:
> https://drive.google.com/drive/folders/1fMl9odowUFFRQFK61rTxgHeom_D8ymN6?usp
> =sharing
> 

The answer is there:
https://gdal.org/drivers/raster/gpkg.html#tile-formats

For Byte input (that isn't recognized as to be used by the tiled gridded 
coverage data), the default tile format will use JPEG lossy compression for 
tiles with a fully opaque channel.

-co TILE_FORMAT=PNG will use lossless compression

GeoPackage raster aim was initially for visualisation purposes, hence this 
default. The more analytic side was a later addition to the format, and 
actually an extension

Even

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com