[Qgis-user] Raster layer opacity expression - how does it work?

[Ujaval Gandhi]

I assume you are trying to set the opacity to 50% outside of a polygon
layer. This can be done using the 'Inverted Polygon' renderer. See this
screenshot https://ibb.co/Sf5HySf

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Ujaval Gandhi
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On Sun, Dec 5, 2021 at 5:12 PM Jonathan Schultz <jonathan at schultz.la> wrote:

> Hello,
>
> I'm trying to use opacity on a raster layer to highlight an area of
> interest. So, for example, I would use opacity 100 for an area (defined
> in another layer), and 50 for anywhere outside that area. But I can't
> seem to even find basic documentation on how the Renderer opacity values
> work. If I enable the Assistant I get a bunch of fields: Source (an
> expression), Values from and to, plus a checkbox "Apply transform curve"
> with its own set of fields.
>
> When I google words like "Renderer opacity" all I get are references to
> the source code but no documentation or examples.
>
> This is QGIS version 3.22.0-Białowieża running on Linux/Debian.
>
> Does anyone know how this stuff works, or how I could find out?
>
> Thanks!
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