From ddcc43a18e866123a415d013e61d11c57b973443 Mon Sep 17 00:00:00 2001
From: Niels Dekker <N.Dekker@lumc.nl>
Date: Tue, 13 Nov 2018 14:06:10 +0100
Subject: [PATCH] PERF: unsharpenedImage iterator in N4Bias...Filter is now
 "WithIndex"

Declared the unsharpenedImage iterator within N4BiasFieldCorrectionImageFilter::SharpenImage as ImageRegionConstIteratorWithIndex, instead of ImageRegionConstIterator.

Observed a significant performance improvement: 10% to 30% reduction of runtime duration on filter->Update().
---
 .../include/itkN4BiasFieldCorrectionImageFilter.hxx            | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Modules/Filtering/BiasCorrection/include/itkN4BiasFieldCorrectionImageFilter.hxx b/Modules/Filtering/BiasCorrection/include/itkN4BiasFieldCorrectionImageFilter.hxx
index 3f653209b1d..37af86611d2 100644
--- a/Modules/Filtering/BiasCorrection/include/itkN4BiasFieldCorrectionImageFilter.hxx
+++ b/Modules/Filtering/BiasCorrection/include/itkN4BiasFieldCorrectionImageFilter.hxx
@@ -24,6 +24,7 @@
 #include "itkBSplineControlPointImageFilter.h"
 #include "itkDivideImageFilter.h"
 #include "itkExpImageFilter.h"
+#include "itkImageRegionConstIteratorWithIndex.h"
 #include "itkImageRegionIterator.h"
 #include "itkImageRegionIteratorWithIndex.h"
 #include "itkImportImageFilter.h"
@@ -242,7 +243,7 @@ N4BiasFieldCorrectionImageFilter<TInputImage, TMaskImage, TOutputImage>
   RealType binMaximum = NumericTraits<RealType>::NonpositiveMin();
   RealType binMinimum = NumericTraits<RealType>::max();
 
-  ImageRegionConstIterator<RealImageType> ItU(
+  ImageRegionConstIteratorWithIndex<RealImageType> ItU(
     unsharpenedImage, unsharpenedImage->GetLargestPossibleRegion() );
 
   for( ItU.GoToBegin(); !ItU.IsAtEnd(); ++ItU )