diff --git a/image.cpp b/image.cpp
index a5082c32..387b7be3 100644
--- a/image.cpp
+++ b/image.cpp
@@ -23,54 +23,20 @@ using util::image::buffer;
 
 //-----------------------------------------------------------------------------
 template <typename T>
-util::image::buffer<T>::buffer (util::extent2u _size):
-    buffer<T> (_size.w, _size.h)
+util::image::buffer<T>::buffer (util::extentu<2> _size):
+    m_size (_size),
+    m_stride (1, _size.w),
+    m_data (std::make_unique<T[]> (_size.area ()))
 { ; }
 
 
-//-----------------------------------------------------------------------------
-template <typename T>
-util::image::buffer<T>::buffer (size_t _w, size_t _h, size_t _s):
-    w (_w),
-    h (_h),
-    s (_s),
-    m_data (std::make_unique<T[]> (_h * _s))
-{
-    CHECK_NEQ (w * h, 0);
-    CHECK_GE (s, w);
-}
-
-
-//-----------------------------------------------------------------------------
-template <typename T>
-util::image::buffer<T>::buffer (size_t _w, size_t _h):
-    buffer<T> (_w, _h, _w)
-{ ; }
-
-
-//-----------------------------------------------------------------------------
-template <typename T>
-util::image::buffer<T>::buffer (size_t _w,
-                                size_t _h,
-                                size_t _s,
-                                std::unique_ptr<T[]> &&_data):
-    w (_w),
-    h (_h),
-    s (_s),
-    m_data (std::move (_data))
-{
-    CHECK_NEQ (w * h, 0);
-    CHECK_GE (s, w);
-}
-
-
 //-----------------------------------------------------------------------------
 template <typename T>
 template <typename U>
 util::image::buffer<U>
 util::image::buffer<T>::alloc (void) const
 {
-    return buffer<U> (w, h, s);
+    return buffer<U> (m_size);
 }
 
 
@@ -102,8 +68,7 @@ template <typename T>
 const T&
 buffer<T>::operator[] (point<2,size_t> p) const
 {
-    CHECK_LT (p.x, w);
-    CHECK_LT (p.y, h);
+    CHECK (util::all (p < size ()));
 
     return begin ()[offset (p)];
 }
@@ -114,8 +79,7 @@ template <typename T>
 T&
 buffer<T>::operator[] (point<2,size_t> p)
 {
-    CHECK_LT (p.x, w);
-    CHECK_LT (p.y, h);
+    CHECK (util::all (p < size ()));
 
     return begin ()[offset (p)];
 }
@@ -126,7 +90,7 @@ template <typename T>
 const T&
 buffer<T>::operator[] (size_t idx) const
 {
-    CHECK_LT (idx, h * s);
+    CHECK_LT (idx, size ());
 
     return begin ()[idx];
 }
@@ -137,7 +101,7 @@ template <typename T>
 T&
 buffer<T>::operator[] (size_t idx)
 {
-    CHECK_LT (idx, h * s);
+    CHECK_LT (idx, size ());
 
     return begin ()[idx];
 }
@@ -166,7 +130,7 @@ template <typename T>
 T*
 buffer<T>::end (void)
 {
-    return begin () + h * s;
+    return begin () + m_size.back () * m_stride.back ();
 }
 
 
@@ -211,7 +175,7 @@ template <typename T>
 const T*
 buffer<T>::cend (void) const
 {
-    return cbegin () + h * s;
+    return cbegin () + m_size.back () * m_stride.back ();
 }
 
 
diff --git a/image.hpp b/image.hpp
index 7ccea0ce..a089d30a 100644
--- a/image.hpp
+++ b/image.hpp
@@ -31,13 +31,13 @@ namespace util { namespace image {
         typedef T value_type;
 
         //---------------------------------------------------------------------
-        buffer (util::extent2u);
-        buffer (size_t w, size_t h);
-        buffer (size_t w, size_t h, size_t s);
-        buffer (size_t w, size_t h, size_t s, std::unique_ptr<T[]> &&data);
+        buffer (util::extentu<2>);
+        buffer (util::extentu<2>, std::unique_ptr<T[]> &&data);
 
         buffer (const buffer<T>&) = delete;
         buffer (buffer<T> &&) = default;
+        buffer& operator= (const buffer<T>&) = default;
+        buffer& operator= (buffer<T>&&) = default;
 
         //---------------------------------------------------------------------
         /// allocate and return a buffer of the same dimensions. contents are undefined.
@@ -54,10 +54,6 @@ namespace util { namespace image {
 
         constexpr bool is_packed (void) const;
 
-        size_t w;
-        size_t h;
-        size_t s;
-
         //---------------------------------------------------------------------
         constexpr size_t offset (point<2,size_t>) const;
 
@@ -80,6 +76,8 @@ namespace util { namespace image {
         const T* cend   (void) const;
 
     private:
+        util::extent2u m_size;
+        util::vector2u m_stride;
         std::unique_ptr<T[]> m_data;
     };
 } }
diff --git a/image.ipp b/image.ipp
index b96e2f33..3fc32a4f 100644
--- a/image.ipp
+++ b/image.ipp
@@ -25,7 +25,7 @@ namespace util { namespace image {
     constexpr extent2u
     buffer<T>::extent (void) const
     {
-        return { w, h };
+        return m_size;
     }
 
 
@@ -34,7 +34,7 @@ namespace util { namespace image {
     constexpr vector2u
     buffer<T>::stride (void) const
     {
-        return { 1, s };
+        return m_stride;
     }
 
 
@@ -52,7 +52,7 @@ namespace util { namespace image {
     constexpr size_t
     buffer<T>::size (void) const
     {
-        return extent ()[1] * stride ()[1];
+        return extent ().back () * stride ().back ();
     }
 
 
@@ -61,6 +61,6 @@ namespace util { namespace image {
     constexpr bool
     buffer<T>::is_packed (void) const
     {
-        return stride ()[1] == extent ()[0];
+        return stride ().back () == extent ().back ();
     }
 } }
diff --git a/test/image.cpp b/test/image.cpp
index 75e70792..657bd480 100644
--- a/test/image.cpp
+++ b/test/image.cpp
@@ -10,7 +10,7 @@ main (void)
 
     constexpr size_t W = 64;
     constexpr size_t H = 128;
-    util::image::buffer<uint16_t> img (W, H);
+    util::image::buffer<uint16_t> img ({W, H});
 
     if (!img.is_packed ())
         tap.skip ("linear position probe requires packed image allocation");