[gdal-dev] Trouble with GPKG and colors

[Idan Miara]

Hi Even,

Thanks for you prompt answer!

Could you please point out a valid example on how to read/write a single
byte raster dataset (preferably with a color table) in GPKG with any
supported setup (tiling, format, padding etc)?

GTiff also can store different band count, padding, etc, but there isn't a
similar problem with it. I'm not sure I understand the difference.
So I'm not sure I understand the RGBA expansion you were talking about, do
you have a link to more info on that matter?

Kind regards,
Idan

On Mon, 29 Oct 2018 at 14:29, Even Rouault <even.rouault at spatialys.com>
wrote:

> On lundi 29 octobre 2018 14:19:12 CET Ben Avrahami wrote:
> > Hello, I'm trying to save a byte raster to a geopackage. I ran into a
> > problem that the geopackage raster driver does not behave as expected
> when
> > working with bytes and color tables. I have written a python script that
> > explains the issue (attached):
> >
> > The script creates 4 rasters in similar ways but prints different
> outputs:
> >
> > GTIFF(no palette):  Minimum=0, Maximum=9, Color Table=False, band count=1
> > GTIFF(palette):  Minimum=0, Maximum=9, Color Table=True, band count=1
> > GPKG(no palette):  Minimum=0, Maximum=9, Color Table=False, band count=4
> > GPKG(palette):  Minimum=0, Maximum=255, Color Table=False, band count=4
> >
> > The problem is that even though we set a color table in the geopackage
> when
> > writing, it reads as having no color table when reading. Worse yet, the
> > original raster values are lost when written with a color table.
> >
> > Is there any workaround or fix for this? We want to be able to keep
> > non-image byte data with a palette to geopackage.
> >
>
> Change
> ds = gdal.OpenEx(path, gdal.OF_READONLY)
> to
> ds = gdal.OpenEx(path, gdal.OF_READONLY, open_options=['BAND_COUNT=1'])
>
> if you know that all the tiles have a color table. Note: that will not
> work if
> your raster is made of a single tile that has some padding (which seems to
> be
> the case in your demo code), because the driver has to expand to RGBA to
> be
> able to fill transparent pixels.
>
> The fact that you don't get excatly the characteristics of the input
> dataset
> comes from the fact that GPKG can store tiles of different formats, band
> count, etc, so the driver defaults to exposing at RGBA as a safe setting
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
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