( All or only upper-left? Upper left suffices)
a dialog pops up saying that the op will remove "some unused pixel".
I wonder why remove image content by default?
I suggest to better enlarge its coords to the nearest multiple of 16 (8).
On all sides (Why that? left-uppers suffices? Correct, but if you intend to
crop a border whose width is no multiple, the adjustment from above will
leave a border upper-left. You will probably want to have it on all sides
)