Cleaned up code and pushed is_rgb_image and is_grayscale_image somewhere more accessible.

dlib/image_processing/generic_image.h

@@ -4,6 +4,7 @@
 #define DLIB_GeNERIC_IMAGE_Hh_
 
 #include "../assert.h"
+#include "../pixel.h"
 
 namespace dlib
 {
@@ -128,6 +129,13 @@ namespace dlib
                 image_traits<image_type>::pixel_type
     !*/
 
+    template <typename image_type>
+    struct is_rgb_image { const static bool value = pixel_traits<typename image_traits<image_type>::pixel_type>::rgb; };
+
+    template <typename image_type>
+    struct is_grayscale_image { const static bool value = pixel_traits<typename image_traits<image_type>::pixel_type>::grayscale; };
+
+
 // ----------------------------------------------------------------------------------------
 // ----------------------------------------------------------------------------------------
 //                   UTILITIES TO MAKE ACCESSING IMAGE PIXELS SIMPLER

dlib/image_saver/image_saver.h

@@ -423,13 +423,6 @@ namespace dlib
             }
         };
 
-        template <typename image_type>
-        struct is_rgb_image
-        {
-            typedef typename image_traits<image_type>::pixel_type pixel_type;
-            const static bool value = pixel_traits<pixel_type>::rgb;
-        };
-
         template <typename image_type>
         struct save_dng_helper<image_type,typename enable_if<is_rgb_image<image_type> >::type>
         {

dlib/image_transforms/interpolation.h

@@ -705,11 +705,6 @@ namespace dlib
 
 // ----------------------------------------------------------------------------------------
 
-    template <typename image_type>
-    struct is_rgb_image { const static bool value = pixel_traits<typename image_traits<image_type>::pixel_type>::rgb; };
-    template <typename image_type>
-    struct is_grayscale_image { const static bool value = pixel_traits<typename image_traits<image_type>::pixel_type>::grayscale; };
-
     // This is an optimized version of resize_image for the case where bilinear
     // interpolation is used.
     template <