Hysteresis in Edge Detection

Question

What the hysteresis threshold, and why is it useful in edge detection?

I am trying to write an edge detection program in python, and it seems to work well without using hysteresis, but many sources include it. I was wondering why it would be useful.

Answer 1

If you just have a threshold without hysteresis, then when an image is near the threshold you can have low and high transitions (edges) very near each other. What you likely want are real value transitions in order to recognize an edge. The hysteresis value gives a required change before going from a high edge to a low edge and the other way around.