[Insight-users] Find circle with Hough Transform

[Julien Jomier]

Hi Georges,

You may have to tune the parameters a little.

1) Are you getting a "good" approximation of the real radius?
The current implementation of the Hough Transform is looking for =
different
radii, you can try to reduce the range of the radii if you know the size =
of
the circle you are looking for, this might help with the location.

2) The sigma value of the gradient computation (7th parameter) is also
another important factor for the location of the circle. The Hough =
Transform
filter computes the gradient at each point internally, using the =
derivative
of a gaussian at a scale sigma and increments the accumulator only in =
the
direction of the gradient, if the computation of the gradient is not
performed correctly (bad sigma value) the direction may be wrong and the
resulting location off.

3) The 6th parameter is the SweepAngle (in radians), this means that the
accumulator is incremented in the direction of the gradient(as in 2)) =
but
also in the cone defined by the sweep angle. You may want to try to =
increase
the SweepAngle.

4) The accumulator variance might be another factor, if you blur the
accumulator too much, the location of the circle might be off by a small
amount.

I hope this helps,
Best regards,

Julien

> -----Original Message-----
> From: insight-users-admin at itk.org=20
> [mailto:insight-users-admin at itk.org] On Behalf Of Georges Le Goualher
> Sent: Friday, January 23, 2004 5:52 AM
> To: insight-users at itk.org
> Cc: Georges Le Goualher
> Subject: [Insight-users] Find circle with Hough Transform
>=20
>=20
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> I have a very simple image containing a 2D circle. I'm trying to=20
> localize
> this circle with the HoughTransform2DCirclesImageFilter test,=20
> unfortunately the algorithm fails to accurately detect the=20
> circle. In fact the detected circle in systematicly few=20
> pixels  away from the correct position.
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> This is the command line I used:
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> ./HoughTransform2DCirclesImageFilter=20
> /data/dataImageCell/default/guide/s3.png=20
> /data/dataImageCell/default/guide/s3H.png 1 1 300 0 1 5 10
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> Upon request, I can send you the test image.
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> Regards,
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> Georges
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> --
> Georges Le Goualher
> Ingenieur de Recherche / Research Engineer
> Mauna Kea Technologies, Paris
> www.maunakeatech.com
> tel: 33 1 48 24 24 96
> fax: 33 1 48 24 12 18
> ---------------------------------------------------------------------
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