There are a few things you need to know if you want to crop a diagonal line in Photoshop. First, make sure that the line is on a straight line. If it’s not, you’ll have to crop the line in some way. Second, make sure that the line is of the right size. Third, make sure that the line is in focus. Finally, use the following commands to crop the line:
Command
Crop (x,y)
Crop (width/height)
