How to use convexityDefects in Opencv 2.4

Question

I try to use convexHull and convexityDefects to define a hand. But when the program hit the convexityDefects, there is always an error

Answer 1

It looks like the issue is that convexityDefects() expects an array for the contourDefects parameter:

void convexityDefects(InputArray contour, InputArray convexhull, OutputArray convexityDefects);

Both contours and hull are vector> types, which is correct, but defects also needs to be a vector>. That way when you loop through the contours array, defects[i] will contain an array to pass to convexityDefects():

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vector> defects( contours.size() ); 

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Later on in your code, you will have to loop through the defects[i] vector to print the depth as well, if that is what you were trying to do.