How to find the orientation of an object (shape)? - Python Opencv

Question

My images are always like this:

But I need to rotate them to be like this:

But to do that, I need to find the orientation of the object, knowing

Answer 1

You have to compute the main axis (it is based on PCA). It will give you a good idea of the main orientation, then you can rotate your image accordingly.

As it was pointed as a comment, you now have to test that the thin part is on the right side of the image, and for that you use the centroid/barycenter: if the centroid is on the left of the bounding box, then the wing is well oriented.

Here is the complete algorithm:

• Compute the main orientation (main axis, computed with PCA)
• Rotate your image according to the main axis orientation.
• Compute the bounding box and centroid/barycenter
• If the centroid is on the left, then your image is well oriented, else rotate it about 180°.

Here are the results...