Hi,
You can do this 2 way. When you are doing the georeferencing, you can select
"use 0 for transparency when needed." This can sometimes give good results but
can leave some transparent pixels in the map depending on the image.
Another way is to right click on the layer in the layer panel, to select layer
properties, than to go to transparency. You can add a temporary no data value
or play with the custom transparency options.
The no data entered here is temporary and will not be used in the raster math
for example. It is for the screen rendering only.
Nicolas
> Le 12 avr. 2017 à 10:17, scott.madry [via OSGeo.org]
> <ml-node+s1560n5317021...@n6.nabble.com> a écrit :
>
> Hello, QGIS gurus and friends.
>
>
> Some of my students are georeferencing historical maps in QGIS, and want to
> remove the black edge areas that appear after the raster arrays are warped,
> or at least make these and only these black areas completely transparent.
> Seems a simple task? Thanks- Scott Madry, UNC Chapel Hill, USA
>
>
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