[Insight-users] Sobel operator gives fat edges

[Emma Ryan]

Hi Bradley and All,


  Thank you for your reply.  But Laplacian is also not doing a good job. I have played around with a few values, but no luck.  I finallly tried Canny, But not sure what my threshold should be.  I apply the Canny filter to a image of type 'double'.  The min and max value in my image is -4.0 to +4.0 .   The necessary edges are seen as weak edges by canny. Not sure how to workaround this.

Any suggestions ?

Thank you,
Emma



________________________________
 From: Bradley Lowekamp <blowekamp at mail.nih.gov>
To: Sergio Vera <sergio.vera at alma3d.com> 
Cc: Emma Ryan <eryanvtk at yahoo.com>; "insight-users at itk.org" <insight-users at itk.org> 
Sent: Wednesday, March 14, 2012 6:59 AM
Subject: Re: [Insight-users] Sobel operator gives fat edges
 

I would also suggest looking at the ZeroCrossingBasedEdgeDetectionImageFilter. This extracts where the laplacian of the image crosses zero.



On Mar 14, 2012, at 4:22 AM, Sergio Vera wrote:

Have you tried CannyEdge Detection Filter? Canny always returns the thinnest edges.
>
>
>Hope to help Regards
>
>
>On Wed, Mar 14, 2012 at 2:59 AM, Emma Ryan <eryanvtk at yahoo.com> wrote:
>
>
>>
>>Hi ,
>>
>>   I am using the sobelOperator provided in itk.  The following is my code snippet. I would like to understand
>>
>>1.  the default setting of the sobel and 
>>2. how I can tune it. There dont seem to be too many member functions to manipulate the sobel.
>>3. If I need to use Erosion filter to thin the edges, how do I design a 'line' structuring element. My code ( also added below) does not seem to allow line (which I am guessing derives from Box, line = 1-D Box)
>>
>>Any help/suggestions is truly appreciated.
>>
>>Thank you,
>>Emma
>>
>>
>>typedef itk::ConstNeighborhoodIterator<ImageType> NeighborhoodIteratorType;
>>    typedef itk::ImageRegionIterator<
 ImageType>        IteratorType;
>>
>>    itk::SobelOperator<PixelType, 2> sobel;
>>    sobel.SetDirection(1);  
>>    itk::Size<2> radius_s;
>>    radius_s.Fill(1);
>>    sobel.CreateToRadius(radius_s);
>>
>>   
>>    NeighborhoodIteratorType::RadiusType radius = sobel.GetRadius();
>>    NeighborhoodIteratorType it( radius, my_image, my_image->GetRequestedRegion() );
>>    itk::NeighborhoodInnerProduct<ImageType> inner_product;
>>
>>    ImageType::Pointer output = ImageType::New();
>>    output->SetRegions(my_image->GetRequestedRegion());
>>    output->Allocate();
>>  
>>    IteratorType out(output, my_image->GetRequestedRegion());
>>    
>>    for (it.GoToBegin(), out.GoToBegin(); !it.IsAtEnd(); ++it, ++out)
>>    {
>>     out.Set( inner_product( it, sobel ) );
>>    }
>>
>>    output->Update();
>>    
>>
>>//Erosion Structuring Element: The following fails to compile if I use '1' instead of '2'
>>typedef itk::FlatStructuringElement<2> StructuringElementType;
>>    StructuringElementType::RadiusType element_radius;
>>    element_radius.Fill(5);
>> 
>>    StructuringElementType strel = StructuringElementType::Box(element_radius);
>>
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>
>
>
>-- 
>Sergio Vera
>
> Alma IT Systems
> C/ Vilana, 4B, 4º 1ª
> 08022 Barcelona
> T. (+34) 932 380 592
> www.alma3d.com
>
_____________________________________
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>
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========================================================
Bradley Lowekamp  
Medical Science and Computing for
Office of High Performance Computing and Communications
National Library of Medicine 
blowekamp at mail.nih.gov
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