Deleting a selected area in Illustrator
How do I chop out regions of a bitmap in Illustrator, revealing the transparency beneath?
I'm starting with a raster graphic imported from Photoshop. The goal is to cut off a precisely-measured triangular section at each corner of the image.
My intuition is to use the pen tool to mark out the exact area I want to cut out, then hit the delete button and watch everything within the path bounds vanish back to transparency. And that's the goal. But it doesn't seem to work. Hitting delete, once I've laid out the path with the pen tool, has no effect. Using the eraser tool inside the path has no effect. I don't see a way to convert the path to a selection.
Create an object that is the shape of the opaque areas of your bitmap. Make sure it is above your bitmap. Select both objects and hit Ctrl + 7 to mask your bitmap.