[Qgis-user] Displaying 16 bit per channel images

[Andre Joost]

Hello,

QGIS usually uses 24bit colours using three bands with values between 0 
and 255. An alpha channel can be added, if the file format supports it 
(JPG does not).

If you want to save bandwidth, you can use paletted colours with

Raster -> Conversion -> RGB to PCT

allowing 256 colours or less in one band with values between 0 and 255, 
and additional palette information (colour table) in the file header.

In GDAL, RGB2PCT.bat does the same, but not gdal_translate.
gdal_translate -expand rgb does only the other way round: from palette 
to three bands.

HTH,
André Joost

Am 13.02.2015 um 21:38 schrieb Gabriel Lema:
> Hello,
>
> I was wondering what QGIS does to display 16 bit per channel RGB
> images. I would like to covert them to 8 bit per channel normal PNG or
> JPG image, but when I save it using the "Save as..." in the "Project"
> menu, I get a low resolution image.
> If I could have access to the conversion from 16 bit to 8 bit that
> QGIS does, which makes a good looking RGB image, I could do that same
> conversion on any other software, and save it full resolution. Is it a
> gamma correction? I've tried many different, but haven't been
> successful so far.
> If I save it using gdal_translate I get a greenish looking image, that
> is very different from the good looking image that QGIS displays.
>
> Thank you for your help.
> Gabriel
>