[Insight-users] Some questions in understanding the N4ITK

[Nicholas Tustison]

Hi Wenwu,

> There are some problems when I learn the N4ITK. Firstly, in the paper-"N4ITK:Nick's N3 ITK Implementation For MRI Bias Field Correction" , I found there are 9 parameters (m_MaskMabel, m_numberOfHistogamBins, m_WeinerFilterNoise, m_BiasFieldFullWitdthAtHalfMaximum... ,)need to set, it can also be found in the N4ITK package.  However, in the lastest ITK4.0, in the project-ITKBiasCorrectionTestDriver, I open the CMakeLists.txt, and some code is as followiing:
>  
> itk_add_test(NAME itkN4BiasFieldCorrectionImageFilterTest1
>       COMMAND ITKBiasCorrectionTestDriver
>       --compare DATA{Baseline/N4ControlPoints_3D.nii.gz}
>                ${ITK_TEST_OUTPUT_DIR}/N4ControlPoints_3D.nii.gz
>     itkN4BiasFieldCorrectionImageFilterTest
>     2
>     DATA{${ITK_DATA_ROOT}/Input/HeadMRVolumeCompressed.mha}            # input
>     ${ITK_TEST_OUTPUT_DIR}//N4ControlPoints_3D.nii.gz                  # control point lattice  . , I also can not understand the mean of this parameter
> 
>     3                                                                       # shrink factor
>     10x10x10                                                           # number of iterations
>     none                                                               # mask
>     150                                                                # spline distance
>     )
> 

The control point lattice is the output defining the bias field.  
You need to remember that this is a test, not a user-level
application which is what N4.cxx encapsulates.

Nick

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