[Insight-developers] Gaussian filter performance

[Ken Martin]

The RadiusFactors in VTK (or tail or quality etc) are a critical factor
in the timing of a Gaussian. The actual kernel size in VTK is
std_dev*rad_factor*2 + 1 Adjusting the radius_factor will significantly
modify the timings. VTK defaults to a fairly rough 1.5 radius factor
(meaning the Gaussian is reduced to zero beyond 1.5 standard deviations)
It would be interesting to see what timings result with all three
filters using the same kernel size. Also interesting to see if they
produce the same result... 

Ken

> I have been trying to choose an appropriate Gaussian blurring filter
to
> use in the SnAP project.  While doing so, I tried to compare the
> performance of three candidates from ITK and VTK on a sample image.
The
> candidates were itk::DiscreteGaussianImageFilter,
> itk::RecursiveGaussianImageFilter and vtkImageGaussianSmooth .  I ran
> the filters with default parameters, only changing the standard
deviation.
> 
> Perhaps the result is useful to others, so I post it here.  For one
> thing, it shows that the recursive gaussian filter seems to perform
> better on even very small sigmas.  What is the error of the recursive
> filter w.r.t to the true solution for subpixel values of sigma?
> 
> The times listed below are for VC6 Release program running on a
> two-month old machine.
> 
> Loaded image     : image01.mha
> Image size       : 7109137 bytes
> Image dimensions : 181 x 217 x 181
> Component count  : 1
> File type        : Binary
> File byte order  : Little Endian
> 
> Standard Deviation: 0.5
>    ITK Discrete Gaussian   : 3688ms.
>    ITK Recursive Gaussian  : 515ms.
>    VTK Gaussian            : 1907ms.
> 
> Standard Deviation: 1.5
>    ITK Discrete Gaussian   : 4578ms.
>    ITK Recursive Gaussian  : 484ms.
>    VTK Gaussian            : 2281ms.
> 
> Standard Deviation: 2.5
>    ITK Discrete Gaussian   : 5672ms.
>    ITK Recursive Gaussian  : 485ms.
>    VTK Gaussian            : 2406ms.
> 
> Standard Deviation: 3.5
>    ITK Discrete Gaussian   : 7079ms.
>    ITK Recursive Gaussian  : 500ms.
>    VTK Gaussian            : 2781ms.
> 
> Standard Deviation: 4.5
>    ITK Discrete Gaussian   : 8578ms.
>    ITK Recursive Gaussian  : 484ms.
>    VTK Gaussian            : 3078ms.
> 
> Paul.
> 
> 
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