First apply Canny Edge Detector on the current image,
then apply Hugh transform to find circles

C# | Visual Basic | Visual C++ |
public Circle<float>[][] HughCircles( TColor cannyThreshold, TColor accumulatorThreshold, double dp, double minDist, int minRadius, int maxRadius )

- cannyThreshold (TColor)
- The higher threshold of the two passed to Canny edge detector (the lower one will be twice smaller).
- accumulatorThreshold (TColor)
- Accumulator threshold at the center detection stage. The smaller it is, the more false circles may be detected. Circles, corresponding to the larger accumulator values, will be returned first
- dp (Double)
- Resolution of the accumulator used to detect centers of the circles. For example, if it is 1, the accumulator will have the same resolution as the input image, if it is 2 - accumulator will have twice smaller width and height, etc
- minDist (Double)
- Minimum distance between centers of the detected circles. If the parameter is too small, multiple neighbor circles may be falsely detected in addition to a true one. If it is too large, some circles may be missed
- minRadius (Int32)
- Minimal radius of the circles to search for
- maxRadius (Int32)
- Maximal radius of the circles to search for

[Missing <returns> documentation for M:Emgu.CV.Image`2.HughCircles(`0,`0,System.Double,System.Double,System.Int32,System.Int32)]