ENH: Support H5::PredType::NATIVE_SCHAR for signed char

Mapped `H5::PredType::NATIVE_CHAR` to either `IOComponentEnum::CHAR` or
`IOComponentEnum::UCHAR`, depending on the signedness of `char`.

Author: N-Dekker

Modules/IO/HDF5/src/itkHDF5ImageIO.cxx

@@ -24,6 +24,7 @@
 #include "itkMakeUniqueForOverwrite.h"
 
 #include <algorithm>
+#include <type_traits> // For is_signed_v.
 
 namespace itk
 {
@@ -83,19 +84,20 @@ GetType()
   }
 
 GetH5TypeSpecialize(float, H5::PredType::NATIVE_FLOAT) GetH5TypeSpecialize(double, H5::PredType::NATIVE_DOUBLE)
+  GetH5TypeSpecialize(signed char, H5::PredType::NATIVE_SCHAR) GetH5TypeSpecialize(char, H5::PredType::NATIVE_CHAR)
+    GetH5TypeSpecialize(unsigned char, H5::PredType::NATIVE_UCHAR)
 
-  GetH5TypeSpecialize(char, H5::PredType::NATIVE_CHAR) GetH5TypeSpecialize(unsigned char, H5::PredType::NATIVE_UCHAR)
+      GetH5TypeSpecialize(short, H5::PredType::NATIVE_SHORT)
+        GetH5TypeSpecialize(short unsigned int, H5::PredType::NATIVE_USHORT)
 
-    GetH5TypeSpecialize(short, H5::PredType::NATIVE_SHORT)
-      GetH5TypeSpecialize(short unsigned int, H5::PredType::NATIVE_USHORT)
+          GetH5TypeSpecialize(int, H5::PredType::NATIVE_INT)
+            GetH5TypeSpecialize(unsigned int, H5::PredType::NATIVE_UINT)
 
-        GetH5TypeSpecialize(int, H5::PredType::NATIVE_INT) GetH5TypeSpecialize(unsigned int, H5::PredType::NATIVE_UINT)
+              GetH5TypeSpecialize(long, H5::PredType::NATIVE_LONG)
+                GetH5TypeSpecialize(long unsigned int, H5::PredType::NATIVE_ULONG)
 
-          GetH5TypeSpecialize(long, H5::PredType::NATIVE_LONG)
-            GetH5TypeSpecialize(long unsigned int, H5::PredType::NATIVE_ULONG)
-
-              GetH5TypeSpecialize(long long, H5::PredType::NATIVE_LLONG)
-                GetH5TypeSpecialize(unsigned long long, H5::PredType::NATIVE_ULLONG)
+                  GetH5TypeSpecialize(long long, H5::PredType::NATIVE_LLONG)
+                    GetH5TypeSpecialize(unsigned long long, H5::PredType::NATIVE_ULLONG)
 
 /* The following types are not implemented.  This comment serves
  * to indicate that the full complement of possible H5::PredType
@@ -105,13 +107,24 @@ GetH5TypeSpecialize(float, H5::PredType::NATIVE_FLOAT) GetH5TypeSpecialize(doubl
 
 #undef GetH5TypeSpecialize
 
-                  inline IOComponentEnum PredTypeToComponentType(H5::DataType & type)
+                      inline IOComponentEnum PredTypeToComponentType(H5::DataType & type)
 {
   if (type == H5::PredType::NATIVE_UCHAR)
   {
     return IOComponentEnum::UCHAR;
   }
   if (type == H5::PredType::NATIVE_CHAR)
+  {
+    if constexpr (std::is_signed_v<char>)
+    {
+      return IOComponentEnum::CHAR;
+    }
+    else
+    {
+      return IOComponentEnum::UCHAR;
+    }
+  }
+  else if (type == H5::PredType::NATIVE_SCHAR)
   {
     return IOComponentEnum::CHAR;
   }
@@ -166,7 +179,7 @@ ComponentToPredType(IOComponentEnum cType)
     case IOComponentEnum::UCHAR:
       return H5::PredType::NATIVE_UCHAR;
     case IOComponentEnum::CHAR:
-      return H5::PredType::NATIVE_CHAR;
+      return H5::PredType::NATIVE_SCHAR;
     case IOComponentEnum::USHORT:
       return H5::PredType::NATIVE_USHORT;
     case IOComponentEnum::SHORT:
@@ -784,6 +797,10 @@ HDF5ImageIO::ReadImageInformation()
       {
         this->StoreMetaData<char>(&metaDict, localMetaDataName, name, metaDataDims[0]);
       }
+      else if (metaDataType == H5::PredType::NATIVE_SCHAR)
+      {
+        this->StoreMetaData<signed char>(&metaDict, localMetaDataName, name, metaDataDims[0]);
+      }
       else if (metaDataType == H5::PredType::NATIVE_UCHAR)
       {
         if (doesAttrExist(metaDataSet, "isBool"))