[Qgis-user] Geo Raster Background

[Charles Dixon-Paver]

There's not really any way for a GIS system to automatically differentiate
between black background pixels and black data pixels. QGIS supports users
setting custom pixel values to render as transparent pixels, but it's left
up to users to ensure that their data and background values are different.

>From my view, there are a couple of options when it comes to fixing this
issue in your data. One is to use an image processing tool like GIMP or
Photoshop effectively, but that requires retaining the geographic
information and knowing how to reprocess the raster accordingly.

The simplest solution I'm aware of is probably to follow this workflow in
QGIS:

   - Start a new QGIS project
   - Set all black pixels to transparent in the transparency tab of the
   raster layer properties
   - Digitize a "bounding area" - you can do this with a memory layer
   - Move your vector layer to render underneath the raster
   - Give the vector a simple black symbology
   - Use the "Convert map to raster" tool from the processing toolbox

There are a wide number of variations on that workflow that are possible of
course, but I think that's the easiest to get started.

Regards



On Fri, 1 Oct 2021 at 09:28, L.W. <eaglelw at gmx.de> wrote:

> Hi,
>
> how to change the backgroundcolor of a georeferenzed raster image?
>
> When a raster image is rotated by qgis after setting all points the
> backgroundcolor is black RGB(0,0,0).
>
> Set black to transparent is difficult when there is black text.
>
> regards
>
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