Ubuntu-MATE 20.04 / GIMP 2.10.38 / G’MIC 3.4.0 with updated filters before screenshots
In Lights & Shadows > Slice Luminosity, the filter remove the alpha channel from the original image after being executed, is that normal?
On the screenshots below you will see that I speak also of > when selecting “in place”, it does not put in place but on a new layer, but while writing I found the suggestion > -fx_slice_luminosity which said it’s a normal behavior.
Because I already did my screenshots when I read this, thus in the screenshot please just look at the red arrows not the blue
Typically, this filter is used on a single image that ultimately comes from a camera, so an alpha channel isn’t expected, and is removed if found; in default behavior it uses the alpha channel during the creation of a mask image.
In operation, the filter lets you specify (at least one, and as many as four) luminosity ranges that might interest you. In its default input/output behavior, the filter alpha-masks out all but the regions of the image that fall within the specified luminosity range(s).
This masked image is created as a new layer; the original image is retained as the background layer. The typical workflow is to modify the masked image, then flatten layers into an aggregate image.
Because it can use the alpha channel for masking purposes, it removes previously created alpha channels.
I would say that us, non programmers but simple users, are always using filters in an unexpected way
Thank you very much @grosgood for your explanations
