[gdal-dev] GDAL translate 16 bit to 8 bit

[Cleo Drakos]

thanks Hanlie.

cleo


On Fri, Aug 22, 2014 at 9:01 PM, Hanlie Pretorius <
hanlie.pretorius at gmail.com> wrote:

> Hi Cleo,
>
> I used
>
> -scale 0 4095 0 255
>
> The reason for the 4095 is that the images actually use only the first
> 12 bits of the 16 bits (according to the documentation) and 2^12 =
> 4096.
>
> If it was a true 16 bit image I would use 65535 for the 'max from' value.
>
> Regards
> Hanlie
>
>
>
> 2014-08-22 13:56 MGT+02:00, Cleo Drakos <cleo21drakos at gmail.com>:
> > hi Hanlie,
> > can you tell me what value you put for -scale to convert into 8 bit?
> >
> > cleo
> >
> >
> > On Fri, Aug 22, 2014 at 7:02 PM, Hanlie Pretorius <
> > hanlie.pretorius at gmail.com> wrote:
> >
> >> Hi Even,
> >>
> >> Yes, I quoted the exact message, but it displays in the QGIS interface.
> >>
> >> I tried gdal_translate with the -ot and -scale parameters on the
> >> multispectral image and that worked much better, thanks.
> >>
> >> Regards
> >> Hanlie
> >>
> >> 2014-08-21 20:33 MGT+02:00, Even Rouault <even.rouault at spatialys.com>:
> >> > Le jeudi 21 août 2014 08:57:32, Hanlie Pretorius a écrit :
> >> >> Hi,
> >> >>
> >> >> I'm working with a 16 bit SPOT 6 image that I want to convert from 16
> >> >> bit pixel depth to 8 bit pixel depth. I say 16 bit, but if I load the
> >> >> file into Envi, it reports that uses only 12 bits. However gdalinfo
> >> >> reports 16 bit (see below).
> >> >>
> >> >> I've manage to do so on the multispectral image, but the result is
> >> >> poor colour wise.
> >> >>
> >> >> So I split the image into its four bands that is, I now have one
> image
> >> >> per
> >> >> band.
> >> >>
> >> >> When I now try to convert to 8 bit, I get a message that says:
> >> >> "Warning 742327101_R1C1_band1_8bit.TIF not created".
> >> >
> >> > Are you quoting the exact message ? I can't find any trace of it in
> the
> >> > relevant parts of the source code. Did you check that you have write
> >> > permissions in the directory where you launch the command ?
> >> >
> >> > Anyway for what you want to do you likely need to explore the -scale
> >> option
> >> > of
> >> > gdal_translate. But that's unrelated to the error
> >> >
> >> >>
> >> _______________________________________________
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> >> http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >>
> >
>
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