for the error "index exceeds matrix dimensions" it is far simpler for you to debug it and learn from it. All you need to do is just put a debug breakpoint at that spot or a try-catch debug code to catch the error at which iteration.
Without digging all your code I can venture a guess just by looking at the error line. I am pretty certain you're incrementing x and y in the loop. And at some point you're doing x= x+1 or y = y+1 one too many times such that it no longer within the dimensions of im(). So to correct this your while conditional statement should be adjusted or pick when you're incrementing x or y such that you don't exceed dimensions of im().
