<br>Hi Alex,<br><br>The RecursiveGaussianImageFilter "approximates" convolution, <br>but it doesn't "perform" convolution.<br><br>This filter implements an IIR filter.<br>For details, please see:<br>
<br> "Fast
Algorithms for Low-Level Vision"<br>R.Deriche in IEEE-PAMI Vol.12, No.1, January 1990, pp 78-87,<br><br>"Recursively Implementing The Gaussian and Its Derivatives",<br>R.
Deriche,<br>INRIA, 1993, <a href="ftp://ftp.inria.fr/INRIA/tech-reports/RR/RR-1893.ps.gz">ftp://ftp.inria.fr/INRIA/tech-reports/RR/RR-1893.ps.gz</a><br><br><br>Note that "convolution" by itself doesn't really<br>
set units, *unless* you take unit conversion into <br>account in the computation of the convolution<br>kernel coefficients.<br><br><br>Using the power of Open Source, things will be <br>a lot clearer if you look at the internals of the code. :-)<br>
<br><br>For example, look at lines 56-69 of<br>Insight/Code/BasicFilters/itkDiscreteGaussianImageFilter.txx<br><br>Which actually performs a convolution with a truncated<br>approximation of the Gaussian kernel.<br><br>Note the use of the "m_UseImageSpacing" variable.<br>
<br>On the other hand, look at the <br><br>itkRecursiveSeparableImageFilter which is the parent<br>class of the itkRecursiveGaussianImageFilter. In particular<br>look at lines 264-267 of itkRecursiveSeparableImageFilter.txx:<br>
<br> const typename InputImageType::SpacingType & pixelSize<br> = inputImage->GetSpacing();<br> <br> this->SetUp( pixelSize[m_Direction] );<br> <br>and their effect on <br>lines 79-256 in itkRecursiveGaussianImageFilter.txx<br>
<br><br><br><br> Regards,<br><br><br> Luis<br><br><br>-----------------------------------------------------------------------------------------------------------------------<br><div class="gmail_quote">On Wed, Sep 9, 2009 at 10:22 AM, Oleksandr Dzyubak <span dir="ltr"><<a href="mailto:adzyubak@gmail.com">adzyubak@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br>
Maybe I am misreading the description.<br>
<br>