I'm trying to get the corners of this rectangle:

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I tried using cv2.cornerHarris(rectangle, 2, 3, 0.04) , but the left edges are not showed due to image brightness, I guess. So I tried applying a threshold before using cornerHarris, but the image produced showed a lot of vertices along the edges, not being possible to filter the corners.

I know that I need to filter it before using cornerHarris, but I don't know how. Could someone help me with this problem?

Ps. I've already tried to use blur, but it also doesn't work.