Hi Jukka, You are right. I have been misled by the size of the "hillshade only" GPKG compared to the color-layer one. It appears that the PNG compression efficiency depends a lot on the image content :
- the color-layer image is quite smooth and the compression factor is high, even if it's an RGB image - the hillshade image is "noisier", which yields to a lower compression factor. Thanks Philippe On Mon, Feb 16, 2026 at 10:27 AM Rahkonen Jukka < [email protected]> wrote: > Hi, > > I believe that what you want happens automatically. I made some tests > with GDAL version 3.13.0dev-a4cba2aeca, released 2026/02/04 and command > > gdal_translate -f gpkg -b 1 p4433h.tif 1band.gpkg -co tile_format=png > > gdalinfo reports only one band > > Band 1 Block=256x256 Type=Byte, ColorInterp=Gray > > I exported couple of the png blobs from the gpkg with spatialite-gui, and > the full png tiles seem to have single band, but the border tiles which > contain nodata area have also alpha band. > > The tile tables in geopackage can contain a mixture of different image > blobs, for example single band png tiles and single band + alpha png tiles. > Reporting the exact band type for such mixture is not possible. GDAL has > some rules and options for handling the case, see > https://gdal.org/en/stable/drivers/raster/gpkg.html#raster-gpkg-tile-formats > and open option "band_count". > > Probably everything works fine and GDAL saves the tiles automatically so > that no disk space is wasted. If you need to to be sure, study the blobs > directly and check what bit depth and color type they really have. > > -Jukka Rahkonen- > ________________________________________ > Lähettäjä: gdal-dev <[email protected]> käyttäjän Philippe > Ghesquiere via gdal-dev <[email protected]> puolesta > Lähetetty: Maanantai 16. helmikuuta 2026 8.41 > Vastaanottaja: gdal-dev <[email protected]> > Aihe: [gdal-dev] GPKG : how to save tile into 1-band 8-bit PNG > > Dear all,Some contextIn 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 tilesa hillshade layer : saved as RGBA 8-bit PNG tilesMy > environmentGDAL V3.8.4My 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.SincerelyPhilippeThe information in this e-mail is confidential. The > contents may not be disclosed or used by anyone other than the addressee. > Access to this e-mail by anyone else is unauthorised.If you are not the > intended recipient, please notify Airbus immediately and delete this > e-mail.Airbus cannot accept any responsibility for the accuracy or > completeness of this e-mail as it has been sent over public networks. If > you have any concerns over the content of this message or its Accuracy or > Integrity, please contact Airbus immediately.All outgoing e-mails from > Airbus are checked using regularly updated virus scanning software but you > should take whatever measures you deem to be appropriate to ensure that > this message and any attachments are virus free. The information in this e-mail is confidential. The contents may not be disclosed or used by anyone other than the addressee. Access to this e-mail by anyone else is unauthorised. If you are not the intended recipient, please notify Airbus immediately and delete this e-mail. Airbus cannot accept any responsibility for the accuracy or completeness of this e-mail as it has been sent over public networks. If you have any concerns over the content of this message or its Accuracy or Integrity, please contact Airbus immediately. All outgoing e-mails from Airbus are checked using regularly updated virus scanning software but you should take whatever measures you deem to be appropriate to ensure that this message and any attachments are virus free.
_______________________________________________ gdal-dev mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/gdal-dev
