[Insight-users] GradientAnisotropicDiffusionImageFilter and LaplacianSegmentation LevelSetImageFilter

[Lorensen, William E (Research)]

Ingmar,

Jim Miller and I finally had a chance to look at the problem.

In Feb 2004, itkAnisotropicDiffusionFunction.h was changed to correct a bug. The SetConductanceParameter method was changed. Prior to the change, the passed in conductance was squared. This was incorrect and was fixed with this change. We suspect that this was the cause of your differences.

Since your conductance (1.5) the new code is essentially using a smaller diffusion. Can you try passing in 1.5*1.5 as a conductance parameter and see if this fixes the problem?

But I am still puzzled why your change gave good results. Are they exactly the same?

On a related note, there is a bug in itkAnisotropicDiffusionImageFilter. If the m_ConductanceScalingUpdateInterval is not 1, the logic for the Gradient computation is flawed. None of our examples or tests set this value.

Bill



-----Original Message-----
From: Bitter, Ingmar (NIH/CC/DRD) [mailto:IBitter at cc.nih.gov]
Sent: Friday, August 19, 2005 5:29 PM
To: Lorensen, William E (Research); ITK Mailing List
Cc: Franaszek, Marek (NIH/CC/DRD)
Subject: RE: [Insight-users] GradientAnisotropicDiffusionImageFilter and
LaplacianSegmentation LevelSetImageFilter 


it seems that the problem is not in the
LaplacianSegmentationLevelSetImageFilter but the
GradientAnisotropicDiffusionImageFilter

m_FixedAverageGradientMagnitude is initialized to 0.0 in the parent
constructor (AnisotropicDiffusionImageFilter)
m_GradientMagnitudeIsFixed is initialized to false in the same constructor.

However the behavior is as if m_GradientMagnitudeIsFixed was later
overwritten to be true, without changing m_FixedAverageGradientMagnitude.
That way there is no smoothing at all.
This is what we saw in our code. Calling SetFixedAverageGradientMagnitude(1)
brought the GradientAnisotropicDiffusionImageFilter back to performing as it
did in ITK 1.6

Ingmar 


-----Original Message-----
From: Lorensen, William 
Sent: Thursday, August 11, 2005 11:11 AM
To: Bitter, Ingmar (NIH/CC/DRD); ITK Mailing List
Cc: Franaszek, Marek (NIH/CC/DRD)
Subject: RE: [Insight-users] GradientAnisotropicDiffusionImageFilter and
LaplacianSegmentationLevelSetImageFilter 

Ingmar,
 
Could you try the following?
 
In itkLaplacianSegmentationLevelSetFunction.h:
 
remove the SetAdvectionWeight method
 
and retry
 
Bill