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Can 'Fast Radial Transform' algorithm detect ellipses?

asked 2018-05-16 05:13:00 -0500

Macho gravatar image

I am detecting ellipses and tried different methods,

I tried Hough Circle and it is detecting only perfect circles

I tried Fit Ellipse after applying it on Find Contours and it is doing pretty well.

I came across Fast Radial Transform and i was wondering would it detects perfect circles only or it will also detect Ellipses?


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"I tried Hough Circle and it is detecting only perfect circles" NO

FastRadialTransform can you give a link in opencv doc?

LBerger gravatar imageLBerger ( 2018-05-16 07:16:43 -0500 )edit

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answered 2018-05-16 09:39:56 -0500

kbarni gravatar image

updated 2018-05-16 09:43:08 -0500

Probably the radial transform (Loy&Zelinsky) is not the best way to detect ellipses.

From the definition of the transform, every pixel affects only the pixels along the gradient vector in the current pixel and to a given distance n. This is perfect to detect circles, as the radius vector is always perpendicular to the contour and the distance to the center of the circle is constant (=radius).

However in the case of ellipses, the contour isn't perpendicular to the radius, and the radius varies also; so it won't give a single bright pixel in the accumulator space.

Maybe with some adaptations you could obtain some results (by varying the sigma parameter) , but I think there are better suited algorithms for ellipse detection.

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Asked: 2018-05-16 05:13:00 -0500

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Last updated: May 16 '18