yes, maybe to orange, a color that is not in the original image, so I
can do this color transparent.
Am 01.10.2021 um 18:25 schrieb David Strip:
When georeferencing, aren't the areas outside the original image, eg,
the "triangles" resulting from rotation, treated as no data? Wouldn't
this issue be resolved by setting the no data value to something other
than black?
Just guessing here, obviously.
On 10/1/2021 2:36 AM, L.W. wrote:
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.
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