I have a image file which has a large number of card images, each in its own layer. I would like to crop these images to the proper size with rounded-rectangle corners. (I got the images as formatted for printing, with extra bleed.) I can easily crop the entire image to a rectangle, and I can make a selection that has just the triangular corner regions. But how do I clear all the triangular corners simultaneously in GIMP, without going through each layer individually? Do I need to write a script to do this?
I am using GIMP 2.8.20 on Debian GNU/Linux.