[Insight-users] Canny Edge Detection Filter Qns., etc.
Luis Ibanez
luis.ibanez at kitware.com
Tue Dec 20 10:26:12 EST 2005
Hi Kalpathi,
1. The thresholds in the Canny Edge Detection filter implemented in
ITK apply to the product of the Second Derivative and the image
Gradient.
Please see the code in
Insight/Code/BasicFilters/
itkCannyEdgeDetectionImageFilter.txx
Lines 370-407
::HysteresisThresholding()
{
// This is the Zero crossings of the Second derivative
// multiplied with the gradients of the image.
// HysteresisThresholding of this image should give
// the Canny output.
typename OutputImageType::Pointer input =
m_MultiplyImageFilter->GetOutput();
2. The .mhd file header is part of the MetaImage file format.
For details about this format, please refer to the
ITK Software Guide:
http://www.itk.org/ItkSoftwareGuide.pdf
and the Data page of www.itk.org
http://www.itk.org/HTML/Data.htm
where you will find instructions on how to create .mhd files
for your raw images.
Also the FAQ:
http://www.itk.org/Wiki/ITK_FAQ#What_3D_file_formats_can_ITK_import_and_export.3F
3. I couldn't find the colon datasets that you are refering to
in your email at nova.nlm.nih.gov.
I presume that they are CT datasets..., is that right ?
You should try using the Example:
Insight/Examples/IO
DicomSeriesReadImageWrite2.cxx
It will convert a Dicom series into another file format
such as Analyze, MetaImage, or GIPL.
What DICOM viewer were you using ?
Regards,
Luis
-------------------------
Kalpathi Subramanian wrote:
> 1. I am wondering about the two hysteresis thresholds (lower and
> upper thresholds) in this filter.
> If I remember this (I implemented all of this in my post-doc BSP tree
> project many, many years back), the thresholds were on the
> CDF(cumulative distr. fn) of the gradient magnitudes. Is this the case
> here? Or are the thresholds on
> just the gradient magnitude (maybe my implementation was based on
> another related implementation, I dont quite remember). Anyhow, this
> had the advantage that I could give these thresholds as percentages
> on the CDF..
>
> 2. - on reading raw data. There is a .mhd file needed
> to read raw data. Can someone point me to its format?
>
> 3. Has anyone read the Colon datasets available from NLM
> (nova.nlm.nih.gov) - I have tried it with the itkDicomSeriesReader
> but have had problems.. will try again but the images didnt
> seem like the original CT data; instead looked like binary images..
>
>
> Thanks.
>
> -- krs
>
>
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