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<p>sounds like rocketscience ... for a simple task to set the
background-color ...</p>
<p>may be I am searching the web where I have to place my feature
request for this ...<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">Am 01.10.2021 um 21:39 schrieb Nicolas
Cadieux:<br>
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<blockquote type="cite"
cite="mid:3dc56dfb-36d3-0f00-87a2-90ff10421f46@gmail.com">
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<p>Hi,<br>
</p>
<p>Start by setting the nodata value in the input raster.
(raster/conversion/translate/Assign a specific nodata value to
output bands). Make sure you select a data type that allows
your nodata value. For example, if you select <span
style="color: rgb(0, 0, 0); font-family: Lato, 'Open Sans',
'Lucida Grande', 'Segoe UI', Arial, sans-serif; font-size:
14.399999618530273px; font-style: normal; font-variant-caps:
normal; font-weight: normal; letter-spacing: normal; orphans:
auto; text-align: start; text-indent: 0px; text-transform:
none; white-space: normal; widows: auto; word-spacing: 0px;
-webkit-tap-highlight-color: rgba(0, 0, 0, 0.4);
-webkit-text-stroke-width: 0px; background-color: rgb(255,
255, 255); display: inline !important; float: none;">Byte -
Eight bit unsigned integer, and a no data value of <b>-999</b>,
-999 does not exist in that data type so the nodata values
will be 0 therefore affecting all black pixels in the image.
Select something like int16 of float32... and a no data value
of -999 for the test. Load the new raster and in the layer
properties, make sure you have been successful changing the
nodata values.<br>
</span></p>
<p><span style="color: rgb(0, 0, 0); font-family: Lato, 'Open
Sans', 'Lucida Grande', 'Segoe UI', Arial, sans-serif;
font-size: 14.399999618530273px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; orphans: auto; text-align: start;
text-indent: 0px; text-transform: none; white-space: normal;
widows: auto; word-spacing: 0px; -webkit-tap-highlight-color:
rgba(0, 0, 0, 0.4); -webkit-text-stroke-width: 0px;
background-color: rgb(255, 255, 255); display: inline
!important; float: none;">Then, when georeferencing, make sure
you <b>DO NOT select "Use 0 for transparency when needed".</b>
The nodata from the georefrenced file will be taken from the
original file (-999). Therefore, pixels with the value 0 in
the image will not be affected.</span></p>
<p><span style="color: rgb(0, 0, 0); font-family: Lato, 'Open
Sans', 'Lucida Grande', 'Segoe UI', Arial, sans-serif;
font-size: 14.399999618530273px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; orphans: auto; text-align: start;
text-indent: 0px; text-transform: none; white-space: normal;
widows: auto; word-spacing: 0px; -webkit-tap-highlight-color:
rgba(0, 0, 0, 0.4); -webkit-text-stroke-width: 0px;
background-color: rgb(255, 255, 255); display: inline
!important; float: none;">Nicolas<br>
</span></p>
<p><span style="color: rgb(0, 0, 0); font-family: Lato, 'Open
Sans', 'Lucida Grande', 'Segoe UI', Arial, sans-serif;
font-size: 14.399999618530273px; font-style: normal;
font-variant-caps: normal; font-weight: normal;
letter-spacing: normal; orphans: auto; text-align: start;
text-indent: 0px; text-transform: none; white-space: normal;
widows: auto; word-spacing: 0px; -webkit-tap-highlight-color:
rgba(0, 0, 0, 0.4); -webkit-text-stroke-width: 0px;
background-color: rgb(255, 255, 255); display: inline
!important; float: none;"><br>
</span></p>
<div class="moz-cite-prefix">On 2021-10-01 2:33 p.m., L.W. wrote:<br>
</div>
<blockquote type="cite"
cite="mid:eb05aed0-f992-6244-eda9-3346417c8424@gmx.de">
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charset=UTF-8">
<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.F08FB9E5.96135E31@gmx.de" alt="" class=""></p>
<p>Set transparent-color to 0,0,0 or use no-data-0:<br>
</p>
<p><img src="cid:part2.CC8A359B.277E042F@gmx.de" alt="" class=""></p>
<p><br>
</p>
<div class="moz-cite-prefix">Am 01.10.2021 um 19:26 schrieb
Charles Dixon-Paver:<br>
</div>
<blockquote type="cite"
cite="mid:CAK2KqicgxUWu=Vv04hmZA3JhEJWbfyyEg=8b_BoVcJt+CeA7EA@mail.gmail.com">
<meta http-equiv="content-type" content="text/html;
charset=UTF-8">
<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>
</div>
<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>
</div>
<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>
</div>
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<pre class="moz-signature" cols="72">--
Nicolas Cadieux
<a class="moz-txt-link-freetext" href="https://gitlab.com/njacadieux" moz-do-not-send="true">https://gitlab.com/njacadieux</a></pre>
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