opencv - How can i fit points to curve using c++?

Question

There a is an ellipse on the picture,just as following.

I have got the points of the contour by using opencv. But you can see the pictrue,because the resolution is low, there is a straight line on the contour.How can i fit it into curve like the blue line?

Answer 1

One Of the method to solve your problem is to vectorize your shape (moving from simple intensity space to vectors space).

I am not aware of the state-of-art in this field. However, from school information, I can suggest this solution.

Bezier curves, you can try to model your shape using simple bezier curve.This is not a hard operation you can google for dozen of them. Then, you can resizing it as much as you want after that you may render it to simple image. Be aware that you may also Splines instead of Bezier.

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Another method would be more simple but less efficient. Since you mentioned OpenCV, you can apply the cv::fitEllipse on the points. Be aware that this will return a RotatedRect which contains the ellipse. You can infer your ellipse simply like this:

Center = Center of RotatedRect.
Longest Radius = The Line which pass from the center and intersect with the two small sides of the RotatedRect.
Smallest Radius = The Line which pass from the center and intersect with the two long sides of the RotatedRect.

After you got your Ellipse Parameters, You can resize it as you want then just repaint it in the size you want using cv::ellipse.

I know that this is a pseudo answer. However, I think every thing is easy to apply. If you faced any problem implementing it, just give me a comment.