[Insight-users] Issues with the canny edge detection class

[Bill Lorensen]

The CannyEdgeDetectionImageFilter has a SetVariance method. The variance is
sigma squared. Are you specifying a variance of 900?

Bill


On 6/25/06, Shlomo Kashani. <shlomo_kashani at yahoo.com> wrote:
>
> Hi All,
> I am trying to use the class CannyEdgeDetectionImageFilter in an iris
> recognition system. One of the first steps is segmenting the iris and the
> pupil by and edge detector and then finding the radii of the pupil and the
> iris using a circular Hough Transform. I have several questions regarding
> the canny edge detector implementation in ITK:
>
> 1-I understand that in the original paper by Canny a first derivative of a
> Gaussian was used while ITK uses a LoG operator (second derivative of a
> Gaussian). Why was this method chosen over the original suggested method?
>
> 2-in the class CannyEdgeDetectionImageFilter, I noticed that there is no
> way of specifying the SIZE of the Gaussian kernel that the canny edge
> detector would use (by a call to DiscreteGaussianImageFilter I guess ???),
> rather only the standard deviation can be specified and I understand that
> the kernel size is determined automatically from the standard deviation. Is
> that correct and is there a way to over ride this behavior?
>
> 3-I noticed that when using ITK I have to use a standard deviation as
> large as *30* which would probably result in a huge Gaussian and Gaussian
> derivative kernel size while when using MATLAB (which uses a first
> derivative of a Gaussian) a standard deviation of 5 is enough. How come
> there is such a hug difference?
>
> Any help would be appreciated,
>
> Shlomo Kashani.
>
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