[Insight-developers] Gaussian filters

[Stephen R. Aylward]

This would also be a great place to use an image adaptor to make the 
image look like a float/double image.

s

Joshua Cates wrote:

> Hi Mark,
> 
> I will add more documentation on DiscreteGaussianImageFilter as soon as I
> have some spare minutes.  In the meantime, ignore the MaximumError
> parameter.  The default setting is fine for most applications.
> 
> Currently, the DiscreteGaussianImageFilter will only give reasonable
> output for real numbers (floats, doubles) so you need to use
> CastImageFilter to convert your input to floats (and back).  In the
> future this conversion will be handled internally within the filter
> and be transparent to the user.  I will be sure to include this caveat in
> the documentation.
> 
> Thanks for the feedback,
> 
> Josh.
> 
> ______________________________
>  Josh Cates
>  School of Computer Science
>  University of Utah
>  Email: cates@sci.utah.edu
>  Phone: (801) 587-7697
>  URL:   www.cs.utk.edu/~cates
> 
> 
> On Wed, 24 Jul 2002, mark foskey wrote:
> 
> 
>>I'm new to the group and still learning ITK, and I've noticed a couple
>>of apparent anomalies with the various Gaussian filter classes.
>>
>>1. RecursiveGaussianImageFilter has a SetSigma method, while
>>DiscreteGaussianImageFilter has a SetVariance method.  I think it would
>>be helpful if the method were the same in both filters.
>>
>>2. DiscreteGaussianImageFilter yielded an apparently blank image for all
>>variance values I tried other than 0.  I am including the test program I
>>used below.  I may be doing something wrong.
>>
>>3. Perhaps most serious is that it was hard to figure out how to use
>>these filters from their documentation.  Programmers are likely to
>>assume that RecursiveGaussianImageFilter simply blurs an image; only if
>>they read the documentation for RecursiveSeparableImageFilter will they
>>learn that the filter must be applied once for each dimension.  Also,
>>for DiscreteGaussianImageFilter, the SetMaximumError method isn't
>>documented.  I'm not clear on what the m_MaximumError parameter controls
>>in this context.  I have not read the code yet, but the point is that I
>>think the meaning of the parameter should be documented.
>>
>>4. It would be nice if there were a convenience filter that would
>>internally chain together instances of the RecursiveGaussianImageFilter
>>for each dimension, since most users will want to filter along all n dims.
>>
>>I'm sorry for my first message to the group to come across as a
>>complaint, but I'm seeing ITK somewhat as a new user will, and I think
>>we have to be aware things that frustrate beginners.
>>
>>Here's the test program:
>>
>>#include <itkImage.h>
>>#include <itkImageFileReader.h>
>>#include <itkImageFileWriter.h>
>>#include <itkPNGImageIO.h>
>>#include <itkDiscreteGaussianImageFilter.h>
>>
>>typedef itk::Image<unsigned char, 2> ImageType ;
>>
>>int main(int argc, char* argv[])
>>{
>>      if (argc < 2)
>>      {
>>          std::cout
>>              << "usage: VerySimpleFilter [inputfile] [outputfile]"
>>              << std::endl;
>>          exit(0);
>>      }
>>
>>      // Create an IO object for PNG files, to be used by both the
>>      // reader and the writer.
>>      typedef itk::PNGImageIO PNGIOType;
>>      PNGIOType::Pointer png = PNGIOType::New();
>>
>>      // Instantiate a reader for the file.
>>      typedef itk::ImageFileReader<ImageType> ImageReaderType;
>>      ImageReaderType::Pointer reader = ImageReaderType::New();
>>      reader->SetImageIO(png);
>>      reader->SetFileName(argv[1]);
>>
>>      // Instantiate a filter and attach it to the reader.
>>      typedef itk::DiscreteGaussianImageFilter<ImageType, ImageType>
>>          GaussianFilterType;
>>      GaussianFilterType::Pointer myFilter = GaussianFilterType::New();
>>      myFilter->SetInput(reader->GetOutput());
>>      myFilter->SetVariance(0.1);
>>
>>      // Instantiate a writer and attach it to the filter.
>>      typedef itk::ImageFileWriter<ImageType> ImageWriterType;
>>      ImageWriterType::Pointer writer = ImageWriterType::New();
>>      writer->SetImageIO(png);
>>      writer->SetInput(myFilter->GetOutput());
>>      writer->SetFileName(argv[2]);
>>
>>      writer->Write();
>>
>>      return 0;
>>
>>}
>>--
>>Mark Foskey    (919) 843-5436   Computer-Aided Diagnosis and Display Lab
>>mark_foskey@unc.edu             Department of Radiology, CB 7515, UNC
>>http://www.cs.unc.edu/~foskey   Chapel Hill, NC  27599-7515
>>
>>
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>>
>>
> 
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-- 
===============================================
Dr. Stephen R. Aylward
Assistant Professor of Radiology
Adjunct Assistant Professor of Computer Science
http://caddlab.rad.unc.edu
aylward@unc.edu
(919) 966-9695