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<p>Thanks for answering, but I think this is not the way I want to
go ...</p>
<p>Or, I do not have written detailed.<br>
</p>
<p>I have a raster image e.g. a white rectangle, after setting the
points, QGIS rotats this image, let's say, by 45 degrees.</p>
<p>The corners of the imported image are now black triangles.</p>
<p>I do want to have e.g. red triangles ...</p>
<p>Regards<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">Am 01.10.2021 um 09:50 schrieb Charles
Dixon-Paver:<br>
</div>
<blockquote type="cite"
cite="mid:CAK2KqidN6RU469NhC2Rgw=DhiNZbdEe9J24J-VUXN_X4022w6A@mail.gmail.com">
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<div dir="ltr">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.<br>
<br>
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.<br>
<br>
The simplest solution I'm aware of is probably to follow this
workflow in QGIS:<br>
<ul>
<li>Start a new QGIS project</li>
<li>Set all black pixels to transparent in the transparency
tab of the raster layer properties</li>
<li>Digitize a "bounding area" - you can do this with a memory
layer</li>
<li>Move your vector layer to render underneath the raster</li>
<li>Give the vector a simple black symbology</li>
<li>Use the "Convert map to raster" tool from the processing
toolbox</li>
</ul>
<div>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.<br>
<div><br>
</div>
<div>Regards</div>
<div><br>
</div>
</div>
</div>
<div dir="ltr"><br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, 1 Oct 2021 at 09:28,
L.W. <<a href="mailto:eaglelw@gmx.de" target="_blank"
moz-do-not-send="true">eaglelw@gmx.de</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
how to change the backgroundcolor of a georeferenzed raster
image?<br>
<br>
When a raster image is rotated by qgis after setting all
points the<br>
backgroundcolor is black RGB(0,0,0).<br>
<br>
Set black to transparent is difficult when there is black
text.<br>
<br>
regards<br>
<br>
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