Updated requires clause for the spatial filtering methods to note that you

can't use the add_to or use_abs options with color images.

dlib/image_transforms/spatial_filtering.h

@@ -124,9 +124,7 @@ namespace dlib
         const in_image_type& in_img,
         out_image_type& out_img,
         const matrix_exp<EXP>& filter,
-        T scale,
-        bool use_abs = false,
-        bool add_to = false
+        T scale
     )
     {
         COMPILE_TIME_ASSERT( pixel_traits<typename in_image_type::type>::has_alpha == false );

dlib/image_transforms/spatial_filtering_abstract.h

@@ -36,6 +36,9 @@ namespace dlib
             - scale != 0
             - filter.nr() % 2 == 1  (i.e. must be odd)
             - filter.nc() % 2 == 1  (i.e. must be odd)
+            - if (pixel_traits<typename in_image_type::type>::grayscale == false) then
+                - use_abs == false && add_to == false
+                  (i.e. You can only use the use_abs and add_to options with grayscale images)
         ensures
             - Applies the given spatial filter to in_img and stores the result in out_img (i.e.
               cross-correlates in_img with filter).  Also divides each resulting pixel by scale.  
@@ -88,6 +91,9 @@ namespace dlib
             - is_vector(col_filter) == true
             - row_filter.size() % 2 == 1  (i.e. must be odd)
             - col_filter.size() % 2 == 1  (i.e. must be odd)
+            - if (pixel_traits<typename in_image_type::type>::grayscale == false) then
+                - use_abs == false && add_to == false
+                  (i.e. You can only use the use_abs and add_to options with grayscale images)
         ensures
             - Applies the given separable spatial filter to in_img and stores the result in out_img.  
               Also divides each resulting pixel by scale.  Calling this function has the same