diff --git a/lib/visfd/filter1d.hpp b/lib/visfd/filter1d.hpp
index 491e12b..742cb71 100644
--- a/lib/visfd/filter1d.hpp
+++ b/lib/visfd/filter1d.hpp
@@ -18,7 +18,8 @@ namespace visfd {
 
 
 
-
+/// @class Filter1D
+/// @brief A simple class for general linear (convolutional) filters in 1D
 
 template<typename Scalar, typename Integer>
 
@@ -305,12 +306,6 @@ class Filter1D {
   }
 
 
-  void Init() {
-    halfwidth = -1;
-    afH = nullptr;
-  }
-
-
   void Alloc(Integer set_halfwidth) {
     halfwidth = set_halfwidth;
     array_size = 1 + 2*halfwidth;
@@ -334,6 +329,12 @@ class Filter1D {
   }
 
 
+  void Init() {
+    halfwidth = -1;
+    afH = nullptr;
+  }
+
+
   void Resize(Integer set_halfwidth) {
     Dealloc();
     Alloc(set_halfwidth);
@@ -351,6 +352,13 @@ class Filter1D {
   }
 
 
+  // destructor, copy and move constructor, swap, and assignment operator
+
+  ~Filter1D() {
+    Dealloc();
+  }
+
+
   Filter1D(const Filter1D<Scalar, Integer>& source) {
     Init();
     Resize(source.halfwidth); // allocates and initializes afH
@@ -360,17 +368,19 @@ class Filter1D {
     std::copy(source.afH, source.afH + array_size, afH);
   }
 
-
-  ~Filter1D() {
-    Dealloc();
-  }
-
   void swap(Filter1D<Scalar, Integer> &other) {
     std::swap(afH, other.afH);
     std::swap(halfwidth, other.halfwidth);
     std::swap(array_size, other.array_size);
   }
 
+  // Move constructor (C++11)
+  Filter1D(Filter1D<Scalar, Integer>&& other) {
+    Init();
+    this->swap(other);
+  }
+
+  // Using the "copy-swap" idiom for the assignment operator
   Filter1D<Scalar, Integer>&
     operator = (Filter1D<Scalar, Integer> source) {
     this->swap(source);
diff --git a/lib/visfd/filter2d.hpp b/lib/visfd/filter2d.hpp
index 01d1269..f117442 100644
--- a/lib/visfd/filter2d.hpp
+++ b/lib/visfd/filter2d.hpp
@@ -19,6 +19,11 @@ using namespace std;
 namespace visfd {
 
 
+/// @class Filter2D
+/// @brief A simple class for general linear (convolutional) filters in 2D
+///
+/// @note  In practice, this class is not used often because most operations
+///        we need can be performed with separable filters which are faster.
 
 template<typename Scalar, typename Integer>
 
@@ -271,19 +276,6 @@ class Filter2D {
   }
 
 
-  Filter2D(const Filter2D<Scalar, Integer>& source) {
-    Init();
-    Resize(source.halfwidth); // allocates and initializes afH and aafH
-    //for(Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
-    //  for(Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
-    //    aafH[iy][ix] = source.aafH[iy][ix];
-    // -- Use std:copy() instead: --
-    std::copy(source.afH,
-              source.afH + (array_size[0] * array_size[1]),
-              afH);
-  }
-
-
   void Init() {
     halfwidth[0] = -1;
     halfwidth[1] = -1;
@@ -305,11 +297,26 @@ class Filter2D {
   }
 
 
+  // destructor, copy and move constructor, swap, and assignment operator
+
   ~Filter2D() {
     Dealloc();
   }
 
 
+  Filter2D(const Filter2D<Scalar, Integer>& source) {
+    Init();
+    Resize(source.halfwidth); // allocates and initializes afH and aafH
+    //for(Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
+    //  for(Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
+    //    aafH[iy][ix] = source.aafH[iy][ix];
+    // -- Use std:copy() instead: --
+    std::copy(source.afH,
+              source.afH + (array_size[0] * array_size[1]),
+              afH);
+  }
+
+
   void swap(Filter2D<Scalar, Integer> &other) {
     std::swap(afH, other.afH);
     std::swap(aafH, other.aafH);
@@ -317,7 +324,13 @@ class Filter2D {
     std::swap(array_size, other.array_size);
   }
 
+  // Move constructor (C++11)
+  Filter2D(Filter2D<Scalar, Integer>&& other) {
+    Init();
+    this->swap(other);
+  }
 
+  // Using the "copy-swap" idiom for the assignment operator
   Filter2D<Scalar, Integer>&
     operator = (Filter2D<Scalar, Integer> source) {
     this->swap(source);
diff --git a/lib/visfd/filter3d.hpp b/lib/visfd/filter3d.hpp
index 090375e..d3355a3 100644
--- a/lib/visfd/filter3d.hpp
+++ b/lib/visfd/filter3d.hpp
@@ -23,10 +23,10 @@ namespace visfd {
 
 
 /// @class Filter3D
-/// @brief A simple class for general linear (convolutional) filters in 3D
+/// @brief A class for general linear (convolutional) filters in 3D
 ///
-/// @note  In practice, this class is not used often because separable filters
-///        based on Gaussians are much faster.
+/// @note  In practice, this class is not used often because most operations
+///        we need can be performed with separable filters which are faster.
 
 template<typename Scalar, typename Integer>
 
@@ -194,18 +194,19 @@ class Filter3D {
   } // Apply()
 
 
-
-  Filter3D(const Filter3D<Scalar, Integer>& source) {
-    Init();
-    Resize(source.halfwidth); // allocates and initializes afH and aaafH
-    //for(Integer iz=-halfwidth[2]; iz<=halfwidth[2]; iz++)
-    //  for(Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
-    //    for(Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
-    //      aaafH[iz][iy][ix] = source.aaafH[iz][iy][ix];
-    // -- Use std:copy() instead: --
-    std::copy(source.afH,
-              source.afH + (array_size[0] * array_size[1] * array_size[2]),
-              afH);
+  /// @ brief   Make sure the sum of the filter weights (in aaafH) is 1
+  void Normalize() {
+    Scalar total = 0.0;
+    for (Integer iz=-halfwidth[2]; iz<=halfwidth[2]; iz++)
+      for (Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
+        for (Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
+          total += aaafH[iz][iy][ix];
+            
+    assert(total > 0.0);
+    for (Integer iz=-halfwidth[2]; iz<=halfwidth[2]; iz++)
+      for (Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
+        for (Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
+          aaafH[iz][iy][ix] /= total;
   }
 
 
@@ -220,11 +221,27 @@ class Filter3D {
   }
 
 
+  // destructor, copy and move constructor, swap, and assignment operator
+
   ~Filter3D() {
     Dealloc();
   }
 
 
+  Filter3D(const Filter3D<Scalar, Integer>& source) {
+    Init();
+    Resize(source.halfwidth); // allocates and initializes afH and aaafH
+    //for(Integer iz=-halfwidth[2]; iz<=halfwidth[2]; iz++)
+    //  for(Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
+    //    for(Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
+    //      aaafH[iz][iy][ix] = source.aaafH[iz][iy][ix];
+    // -- Use std:copy() instead: --
+    std::copy(source.afH,
+              source.afH + (array_size[0] * array_size[1] * array_size[2]),
+              afH);
+  }
+
+
   void swap(Filter3D<Scalar, Integer> &other) {
     std::swap(afH, other.afH);
     std::swap(aaafH, other.aaafH);
@@ -232,7 +249,13 @@ class Filter3D {
     std::swap(array_size, other.array_size);
   }
 
+  // Move constructor (C++11)
+  Filter3D(Filter3D<Scalar, Integer>&& other) {
+    Init();
+    this->swap(other);
+  }
 
+  // Using the "copy-swap" idiom for the assignment operator
   Filter3D<Scalar, Integer>&
     operator = (Filter3D<Scalar, Integer> source) {
     this->swap(source);
@@ -240,20 +263,11 @@ class Filter3D {
   }
 
 
-  /// @ brief   Make sure the sum of the filter weights (in aaafH) is 1
-  void Normalize() {
-    Scalar total = 0.0;
-    for (Integer iz=-halfwidth[2]; iz<=halfwidth[2]; iz++)
-      for (Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
-        for (Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
-          total += aaafH[iz][iy][ix];
-            
-    assert(total > 0.0);
-    for (Integer iz=-halfwidth[2]; iz<=halfwidth[2]; iz++)
-      for (Integer iy=-halfwidth[1]; iy<=halfwidth[1]; iy++)
-        for (Integer ix=-halfwidth[0]; ix<=halfwidth[0]; ix++)
-          aaafH[iz][iy][ix] /= total;
-  }
+
+  // Miscellaneous functions
+  //    (COMMENT: Most of these functions are no longer needed.
+  //              I may remove them in the future. -A 2021-7-11)
+  
 
   /// @brief Calculate the (weighted) average value of the filter array aaafH
   /// @param aaafW optional weights used when calculating the averages