Fixed is_image_type template always reporting false. This also caused

have_same_dimensions() to be uncallable for images, so that's fixed now too.

dlib/image_processing/generic_image.h

@@ -138,10 +138,10 @@ namespace dlib
 
 
     // Check if T has image_traits<T> defined for it.
-    template <typename T, typename enabled = void>
+    template <typename T, typename enabled = size_t>
     struct is_image_type : public std::false_type{};
     template <typename T>
-    struct is_image_type<T, image_traits<typename std::decay<T>::type>> : public std::true_type{};
+    struct is_image_type<T, decltype(sizeof(image_traits<typename std::decay<T>::type>))> : public std::true_type{};
 
 // ----------------------------------------------------------------------------------------
 // ----------------------------------------------------------------------------------------

dlib/test/dnn.cpp

@@ -3271,6 +3271,24 @@ namespace
             dlog << LINFO << "NOW RUNNING TESTS WITH set_dnn_prefer_smallest_algorithms()";
             set_dnn_prefer_smallest_algorithms();
             run_tests();
+
+
+            {
+                resizable_tensor a(2,3,4,5);
+                resizable_tensor b(2,3,4,5);
+                DLIB_TEST(have_same_dimensions(a,b));
+
+                a.set_size(2,3,4,4);
+                DLIB_TEST(!have_same_dimensions(a,b));
+                a.set_size(2,3,3,5);
+                DLIB_TEST(!have_same_dimensions(a,b));
+                a.set_size(2,2,4,5);
+                DLIB_TEST(!have_same_dimensions(a,b));
+                a.set_size(1,3,4,5);
+                DLIB_TEST(!have_same_dimensions(a,b));
+
+                static_assert(!is_image_type<resizable_tensor>::value, "should be false");
+            }
         }
     } a;
 }

dlib/test/image.cpp

@@ -2070,6 +2070,21 @@ namespace
                 DLIB_TEST(sum(matrix_cast<int>(mat(img))) == 0);
             }
 
+            {
+                matrix<int> a(3,4);
+                array2d<unsigned char> b(3,4);
+                DLIB_TEST(have_same_dimensions(a,b));
+            }
+
+            {
+                matrix<int> a(4,4);
+                array2d<unsigned char> b(3,4);
+                DLIB_TEST(!have_same_dimensions(a,b));
+
+                static_assert(is_image_type<matrix<int>>::value, "should be true");
+                static_assert(!is_image_type<int>::value, "should be false");
+            }
+
             test_partition_pixels();
         }
     } a;