Canny edge detection

Hey everyone,

I am writing a Canny edge detection algorithm. I'm testing it on simple shapes right now, such as circles and squares. It does great at detecting lines that are close to horizontal and vertical, however, it fails when the lines approach 45 degrees (or 135 or 225 or 315). Is it common for this algorithm to fail at corners? Anyone worked with this algorithm before and come up with the same issues?

Best, Adam