[Insight-users] Re: radius computation in itkHoughTransform2DCirclesImageFilter

[Peter Roesch]

Hi Carlos,

I came across the same source file when I was playing with
the Hough transform a while ago. My conclusions were

1. The iteration 
	radius = (radius + distance)/2 
	is probably meant to be some average value, but in fact
	is not as you pointed out in your posting.
	A possible way to correct this is to simply add up the
	distances  in the loop you quote
	...
	m_RadiusImage->SetPixel(index, m_RadiusImage->GetPixel(index)+distance);
	...

	and to add another loop to do the averaging, something like

	for index in m_RadiusImage:
 		m_RadiusImage->SetPixel(index, 
			m_RadiusImage->GetPixel(index) / outputImage->GetPixel(index));
	...

2. However, even with corrected average value computation, the filter is
	not capable of detecting concentric circles, as two 2D histograms
	(one for the radii and one for the centre positions) are used.
	In order to store more than one radius per centre position, a 
	3D histogram (more memory and computation time ..) is required.

Greetings
Peter