[Insight-users] Sobel operator gives fat edges

[Emma Ryan]

Hi All,

   Any guesses as to how I can address this 'fat edge' issue.  Or does anybody have an idea  how Matlab manages to get the thin lines ?

Thank you,
Emma

    



________________________________
 From: Sergio Vera <sergio.vera at alma3d.com>
To: Emma Ryan <eryanvtk at yahoo.com> 
Cc: "insight-users at itk.org" <insight-users at itk.org> 
Sent: Wednesday, March 14, 2012 1:22 AM
Subject: Re: [Insight-users] Sobel operator gives fat edges
 

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
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 T. (+34) 932 380 592
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