[Insight-users] HoughTransform2DCirclesImageFilter (itk)

[Luis Ibanez]

Hi Ab,


There are two things you could do in this filter
for making it compute the center of the circle
with sub-pixel precision.

Unfortunately both of them involve modifying the
code of the filter.


They are:


1) Modify the size and spacing of the output
    image in this filter.  The output image
    is used as the accumulator for the exploration
    of the circle parametric space.  Using
    an image with higher resolution than your
    input image will in principle give you
    access to sub-pixel resolution. Note however
    that the centers will still be limited by
    the new resolution of the output.


OR


2) Introduce a BSpline interpolator in the
    GenerateData() method of this filter.
    With the BSpline you could compute a
    maximum with subpixel precision in the
    accumulator image, instead of just
    selecting the index of the highest
    pixel as it is done right now.
    (see lines 242 in Insight/Code/BasicFilters/
     itkHoughTransform2DCirclesImageFilter.txx)



Option (2) is probably the best approach.

If you feel motivated to introduce this
modifications, we will be happy to assist
you in the process, and of course will
welcome the modified class back into the
toolkit.



   Regards,



      Luis


-----------------------
Ab Sayeed wrote:

> I want to get the HoughTransform2DCirclesImageFilter 
> to give me the centre of a circle in sub pixel 
> precision. Any idea's on how I could do this or 
> is there another function I can use to do this. 
> 
> Thanks
> 
> Ab 
> 
>