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Hi Matt,<br>
<br>
QGIS uses blend modes baked into qtpainter. So the qt library is
providing these blend modes. You would have to dig into the qt
source code to find out details. See
<a class="moz-txt-link-freetext" href="http://doc.qt.io/qt-4.8/qpainter.html#CompositionMode-enum">http://doc.qt.io/qt-4.8/qpainter.html#CompositionMode-enum</a> for a
starter.<br>
<br>
But I would assume that blend modes are well covered in computer
graphics literature and you could google some papers. They have been
around for many years now.<br>
<br>
Andreas<br>
<br>
<div class="moz-cite-prefix">On 10.09.2015 04:02, Matt Boyd wrote:<br>
</div>
<blockquote
cite="mid:CAFgHUGLA-njGzqUrddaKcQq5p57soExMuyRnOKiaw=tdGm8DTQ@mail.gmail.com"
type="cite">
<div dir="ltr">Thanks Nicolas,
<div>yes, I'm aware of those properties. What I'm trying to work
out is how QGIS does this so I can use it outside of QGIS in
another program. Some pointers to the sort of questions I
should be asking google on transparency would be handy.</div>
<div><br>
</div>
<div>Thanks</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Sep 10, 2015 at 10:33 AM,
Nicolas Cadieux <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:nicolas.cadieux@archeotec.ca" target="_blank">nicolas.cadieux@archeotec.ca</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<p dir="ltr">Hi,</p>
<p dir="ltr">In your raster properties, you can render
layers using various methods like add, multiply... It
works very well. Same options are available for vector
layer and objects.</p>
<p dir="ltr">Nicolas Cadieux M.Sc.<br>
Les Entreprises Archéotec inc. <br>
8548, rue Saint-Denis Montréal H2P 2H2<br>
Téléphone: <a moz-do-not-send="true"
href="tel:514.381.5112" value="+15143815112"
target="_blank">514.381.5112</a> Fax: <a
moz-do-not-send="true" href="tel:514.381.4995"
value="+15143814995" target="_blank">514.381.4995</a><br>
<a moz-do-not-send="true" href="http://www.archeotec.ca"
target="_blank">www.archeotec.ca</a></p>
<div class="gmail_quote">
<div>
<div class="h5">On Sep 9, 2015 7:51 PM, "Matt Boyd [via
OSGeo.org]" <<a moz-do-not-send="true"
href="http:///user/SendEmail.jtp?type=node&node=5223435&i=0"
rel="nofollow" link="external" target="_blank">[hidden
email]</a>> wrote:<br type="attribution">
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<blockquote style="border-left:2px solid #cccccc;padding:0
1em">
<div>
<div class="h5">
<div dir="ltr">Hi Group,
<div>this is possibly one of those questions about
a question. I'd like to create some blended
layers that look the same as layers in QGIS with
transparency applied.</div>
<div>I've another application that my data lives
in and they supply a calculator that's able to
do some fairly reasonable maths on different
grids and other types of data.</div>
<div><br>
</div>
<div>How does QGIS do transparency, and can I use
those equations / method elsewhere.</div>
<div><br>
</div>
<div>Thanks</div>
<div>Matt</div>
</div>
<br>
</div>
</div>
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