Bug with low opacity layer on transparent background?

[Ofnuts]

(04-16-2022, 09:54 AM)tmanni Wrote: The issue you are facing is due to the use of the opacity slider without a layer underneath.
This is a normal behavior: layer opacity determines how the layer is blend with the backdrop, not the alpha channel of the layer. So, with no backdrop, you lose this information when you export.
The way to do what you want (obtain this grey color when your exported image is put on a black background):
on the "Calque" layer :
- set the opacity slider to 100%
- either use Levels (or Curves) to decrease the Channel Alpha.
(or use a layer mask and set it's value to some dark grey)

Hmmm. If I create an image with a single layer, fill it with black, set the opacity to 50% and export this to PNG  I get this

   

While if the opacity is 100% I get this:

   

So the opacity slider applies anyway because Gimp exports a composite view of all layers so the opacities are taken in account (unless you use the file-*-save API which exports a single layer, without  taking its opacity in account).

And assuming you are right, the easiest way to have the opacity taken in account is to add a transparent layer under, then Gimp has something to blend into.