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<p>Hi,</p>
<p>nope this isn't what I want ... it is the same as setting
transparent color manually.</p>
<p>I am using PDF and TIF for georeferencing.</p>
<p>Regards</p>
<p>Without no-data-0 or transparent-color:<br>
</p>
<p><img src="cid:part1.95BBC6D3.3DA0F456@gmx.de" alt=""></p>
<p>Set transparent-color to 0,0,0 or use no-data-0:<br>
</p>
<p><img src="cid:part2.AB2DB736.4AF229FD@gmx.de" alt=""></p>
<p><br>
</p>
<div class="moz-cite-prefix">Am 01.10.2021 um 19:26 schrieb Charles
Dixon-Paver:<br>
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<blockquote type="cite"
cite="mid:CAK2KqicgxUWu=Vv04hmZA3JhEJWbfyyEg=8b_BoVcJt+CeA7EA@mail.gmail.com">
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<div dir="ltr">I just loaded an unreferenced png with black
content into qgis, then set the nodata value to 99999, then did
a fake georeference with arbitrary coordinates, and the result
seemed to be rotated without any background pixels. Using 3.20
on Windows. The geoereferencer has a checkbox for setting nodata
to 0, so uncheck that first. Otherwise, if you're still unable
to get the "triangles" to change, my previous messages should
still apply.</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, 1 Oct 2021 at 18:27,
L.W. <<a href="mailto:eaglelw@gmx.de"
moz-do-not-send="true">eaglelw@gmx.de</a>> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>yes, maybe to orange, a color that is not in the original
image, so I can do this color transparent.</p>
<p><br>
</p>
<div>Am 01.10.2021 um 18:25 schrieb David Strip:<br>
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<blockquote type="cite">
<div>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?<br>
Just guessing here, obviously.<br>
<br>
<br>
On 10/1/2021 2:36 AM, L.W. wrote:<br>
</div>
<blockquote type="cite">
<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>Am 01.10.2021 um 09:50 schrieb Charles Dixon-Paver:<br>
</div>
<blockquote type="cite">
<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.</div>
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