MantisBT - ITK
When NormalizeAcrossScale is set to true, the response of itkHessianRecursiveGaussianImageFilter is not consistent in scale-space. See attached test for reproducing the error: by creating objects at different widths and same peak intensities and computing the Hessian at the same sigma, the response is different across scales, while it should stay the same.
The bug has been there since the introduction of the class, and it is severe as it makes scale-space Hessian-based filters (vesselness, etc) fail to work correctly in 3D.
The problem is related to the battery of extra smoothing filters in itkHessianRecursiveGaussianImageFilter (itkHessianRecursiveGaussianImageFilter.txx, line 64), that are created for dimensions 3 and greater.
In SetNormalizeAcrossScale, line 107, NormalizeAcrossScale is set to true for the derivative filters *and* for the smoothing filters. This is incorrect, since only derivative filters should have the flag turned on, since they are used to fill in the Hessian matrix with correct values in scale-space. If the flag is on in the extra smoothing filters, the integral of the kernel function is not 1, and the values of the Hessian end-up with extra-rescaling, leading to incorrect scaling in scale-space.
The solution to the bug is to remove the call to SetNormalizeAcrossScale( normalize ); for the smoothing filters in the battery.
itkHessianRecursiveGaussianFilterScaleSpaceTest.cxx (4,062) 2010-04-23 03:04https://public.kitware.com/Bug/file/3060/itkHessianRecursiveGaussianFilterScaleSpaceTest.cxx