BUG: Fix ImageRegionSplitters with zero sized image

When the image had a zero size, undefined results of division by zero
occoured. For both the ImageRegionSplitterSlowDimension and the
ImageRegionSplitterDirection classes when a region's size is zero, the
region has one "split" region of a zero sized region.

Author: blowekamp

Modules/Core/Common/src/itkImageRegionSplitterDirection.cxx

@@ -41,9 +41,10 @@ ImageRegionSplitterDirection::GetNumberOfSplitsInternal(unsigned int         dim
                                                         const SizeValueType  regionSize[],
                                                         unsigned int         requestedNumber) const
 {
+  requestedNumber = std::max(1u, requestedNumber);
   // split on the outermost dimension available
   int splitAxis = dim - 1;
-  while (regionSize[splitAxis] == 1 || splitAxis == (int)m_Direction)
+  while (regionSize[splitAxis] <= 1 || splitAxis == (int)m_Direction)
   {
     --splitAxis;
     if (splitAxis < 0)
@@ -71,7 +72,7 @@ ImageRegionSplitterDirection::GetSplitInternal(unsigned int   dim,
   // split on the outermost dimension available
   // and avoid the current dimension
   int splitAxis = dim - 1;
-  while (regionSize[splitAxis] == 1 || splitAxis == (int)m_Direction)
+  while (regionSize[splitAxis] <= 1 || splitAxis == (int)m_Direction)
   {
     --splitAxis;
     if (splitAxis < 0)

Modules/Core/Common/src/itkImageRegionSplitterSlowDimension.cxx

@@ -30,9 +30,10 @@ ImageRegionSplitterSlowDimension::GetNumberOfSplitsInternal(unsigned int
                                                             const SizeValueType  regionSize[],
                                                             unsigned int         requestedNumber) const
 {
+  requestedNumber = std::max(1u, requestedNumber);
   // split on the outermost dimension available
   int splitAxis = dim - 1;
-  while (regionSize[splitAxis] == 1)
+  while (regionSize[splitAxis] <= 1)
   {
     --splitAxis;
     if (splitAxis < 0)
@@ -57,10 +58,9 @@ ImageRegionSplitterSlowDimension::GetSplitInternal(unsigned int   dim,
                                                    IndexValueType regionIndex[],
                                                    SizeValueType  regionSize[]) const
 {
-
   // split on the outermost dimension available
   unsigned int splitAxis = dim - 1;
-  while (regionSize[splitAxis] == 1)
+  while (regionSize[splitAxis] <= 1)
   {
     if (splitAxis == 0)
     { // cannot split

Modules/Core/Common/test/itkImageRegionSplitterDirectionTest.cxx

@@ -38,6 +38,7 @@ itkImageRegionSplitterDirectionTest(int, char *[])
 
   const itk::ImageRegion<2> lpRegion = region;
 
+  ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 0), 1);
   ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 1), 1);
   ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 2), 2);
   ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 3), 3);
@@ -66,6 +67,13 @@ itkImageRegionSplitterDirectionTest(int, char *[])
   ITK_TEST_EXPECT_EQUAL(region.GetSize(0), 5);
   ITK_TEST_EXPECT_EQUAL(region.GetSize(1), 11);
 
+  const itk::ImageRegion<2> lpRegion2{}; // default zero sized
+  region = lpRegion2;
+  ITK_TEST_EXPECT_EQUAL(1, splitter->GetNumberOfSplits(lpRegion2, 1));
+  ITK_TEST_EXPECT_EQUAL(1, splitter->GetSplit(1, 1, region));
+  ITK_TEST_EXPECT_EQUAL(region.GetSize(0), 0);
+  ITK_TEST_EXPECT_EQUAL(region.GetSize(1), 0);
+
 
   return EXIT_SUCCESS;
 }

Modules/Core/Common/test/itkImageRegionSplitterSlowDimensionTest.cxx

@@ -37,7 +37,7 @@ itkImageRegionSplitterSlowDimensionTest(int, char *[])
   region.SetIndex(1, 10);
 
   const itk::ImageRegion<2> lpRegion = region;
-
+  ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 0), 1);
   ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 1), 1);
   ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 2), 2);
   ITK_TEST_EXPECT_EQUAL(splitter->GetNumberOfSplits(lpRegion, 3), 3);
@@ -58,6 +58,12 @@ itkImageRegionSplitterSlowDimensionTest(int, char *[])
   ITK_TEST_EXPECT_EQUAL(region.GetSize(0), 10);
   ITK_TEST_EXPECT_EQUAL(region.GetSize(1), 5);
 
+  const itk::ImageRegion<2> lpRegion2{}; // default zero sized
+  region = lpRegion2;
+  ITK_TEST_EXPECT_EQUAL(1, splitter->GetNumberOfSplits(lpRegion2, 1));
+  ITK_TEST_EXPECT_EQUAL(1, splitter->GetSplit(1, 1, region));
+  ITK_TEST_EXPECT_EQUAL(region.GetSize(0), 0);
+  ITK_TEST_EXPECT_EQUAL(region.GetSize(1), 0);
 
   return EXIT_SUCCESS;
 }

Modules/Filtering/LabelMap/test/itkLabelImageToLabelMapFilterTest.cxx

@@ -20,6 +20,19 @@
 #include "itkLabelImageToLabelMapFilter.h"
 #include "itkTestingMacros.h"
 
+void
+zeroSizeCase()
+{
+  // test filter with zero sized image
+  auto p_filter = itk::LabelImageToLabelMapFilter<itk::Image<unsigned char, 3>>::New();
+  auto p_image = itk::Image<unsigned char, 3>::New();
+  p_image->SetRegions(itk::Size<3>{ 0, 0, 0 });
+  p_image->Allocate(true);
+
+  p_filter->SetInput(p_image);
+  p_filter->Update();
+}
+
 int
 itkLabelImageToLabelMapFilterTest(int argc, char * argv[])
 {
@@ -131,5 +144,8 @@ itkLabelImageToLabelMapFilterTest(int argc, char * argv[])
 
   conversion->Print(std::cout);
 
+  zeroSizeCase();
+
+
   return EXIT_SUCCESS;
 }