findcontour points order

asked 2017-06-20 11:47:51 -0600

Rok
41 ●2 ●4

Hi, I'm using this function:

cv::findContours(frame, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);

Debugging my application I noticed that for any contour detected, the first point, contour[0], always is the topmost point, with the lowest y value. Is that really true? I didn't find any reference in the documentation about the point order. Is this a reliable way to find the topmost point of a contour?

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answered 2017-06-20 11:58:34 -0600

matman
1001 ●6 ●16

That's correct. The algorithm scans the image row by row and column by column until it finds the first point of a contour. After that the contour is traced by checking the points neighbours. So I think this should be a legal way to find topmost point of the contour.