Added an overload of flip_image_left_right() that operates inplace.

dlib/image_transforms/interpolation.h

@@ -1035,6 +1035,21 @@ namespace dlib
         return find_affine_transform(from,to);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename image_type
+        >
+    point_transform_affine flip_image_left_right (
+        image_type& img
+    )
+    {
+        image_type temp;
+        auto tform = flip_image_left_right(img, temp);
+        swap(temp,img);
+        return tform;
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <

dlib/image_transforms/interpolation_abstract.h

@@ -440,6 +440,29 @@ namespace dlib
               corresponding location in #out_img.
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename image_type
+        >
+    point_transform_affine flip_image_left_right (
+        image_type& img
+    );
+    /*!
+        requires
+            - image_type == an image object that implements the interface defined in
+              dlib/image_processing/generic_image.h 
+        ensures
+            - This function is identical to the above version of flip_image_left_right()
+              except that it operates in-place.
+            - #img.nr() == img.nr()
+            - #img.nc() == img.nc()
+            - #img == a copy of img which has been flipped from left to right.  
+              (i.e. it is flipped as if viewed though a mirror)
+            - returns a transformation object that maps points in img into their
+              corresponding location in #img.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     template <