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<p>Hi,</p>
<p>It's quite simple, you just need to set the nodata value (what
you call the background-color) in the original file and then save
it. The complication is that this requires that the datatype for
the file accepts the no data value. This part is harder to figure
out for your not used to dealing with datatypes. Perhaps, what
should be asked for is a check to see if the nodata in the
translate tool check in compatibility with the datatype format.
Another possibility is to allow for setting the nodata value
(other than zero) in the Georeferencer tool (for both the input
file and the output file).<br>
</p>
<p>Nicolas<br>
</p>
<div class="moz-cite-prefix">On 2021-10-01 4:04 p.m., L.W. wrote:<br>
</div>
<blockquote type="cite"
cite="mid:31726384-91f6-049a-bf01-a99b92af3d67@gmx.de">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<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>
</div>
<blockquote type="cite"
cite="mid:3dc56dfb-36d3-0f00-87a2-90ff10421f46@gmail.com">
<meta http-equiv="Content-Type" content="text/html;
charset=UTF-8">
<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">
<meta http-equiv="Content-Type" content="text/html;
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.D57B7DAF.EB80F07F@gmail.com" alt=""
class=""></p>
<p>Set transparent-color to 0,0,0 or use no-data-0:<br>
</p>
<p><img src="cid:part2.F1F673EA.CC231F35@gmail.com" 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>
</blockquote>
</blockquote>
<br>
</blockquote>
</div>
</blockquote>
</div>
</blockquote>
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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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<pre class="moz-signature" cols="72">--
Nicolas Cadieux
<a class="moz-txt-link-freetext" href="https://gitlab.com/njacadieux">https://gitlab.com/njacadieux</a></pre>
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