Sorry not to have replied before but I was ill yesterday; I'm better now so it's back to my PSP problem!
I create a new image, add a raster layer (100%) then cut a rctangular shape with the selection tool. I save this image as a mask. I then use Selection/Modify/Select Selection Borders. In this, I then tick the Outside box and set the border width to 10. I then Edit/Cut to remove a border from my rectangle and save this image as a mask too.
What I'm trying to do is create a rectangular mask and then create another rectangular mask slightly bigger (or slightly smaller would do just as well). No matter what I do though, the corners of the larger mask are rounded. I must be setting something wrong -just can't figure out what yet. The only way I've managed to square off the corners is by zooming in on each & cutting out the 'corner' pixels. It's very frustrating!
Fiona