[Qgis-user] Geo Raster Background

[L.W.]

Thanks for answering, but I think this is not the way I want to go ...

Or, I do not have written detailed.

I have a raster image e.g. a white rectangle, after setting the points,
QGIS rotats this image, let's say, by 45 degrees.

The corners of the imported image are now black triangles.

I do want to have e.g. red triangles ...

Regards


Am 01.10.2021 um 09:50 schrieb 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
> <mailto: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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