My image has one layer and doesn't have alpha channel. It is a gray-scale image with rgb mode. Do you know why stencil filter is grayed out?
What is the "stencil filter"? - I don't have anything with that name in my GIMP 2.10.2 installation.
I have found out what is the cause for the filter grayed out. The mode should be the gray mode. I thought any grayscale image would work. Don't bother my question here. Thanks guys.
By the way, stencil filter is filter>Decor>stencil carve in gimp 2.8. I don't know about the gimp 2.10.