How to used the edge detection in opencv python to return number of edge?

[Vivian]

Hi I have the following picture, how to use edge detection to return the result which is equal to 4?

[Larz60+]

see: http://www.scipy-lectures.org/advanced/i...edges.html
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[nilamo]

Why would it be 4? Those are corners, so shouldn't it be 9? Two for each corner, and then another for the bottom right corner? Also, I feel like it'd be hard to avoid getting false positives on all the "1"s...