Improved the behavior of assign_image_scaled()

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403978

dlib/image_transforms/assign_image.h

@@ -54,10 +54,10 @@ namespace dlib
             << "\n\t thresh: " << thresh 
             );
 
-        // If the source and destination have the same range of values in their pixels then we don't need to do any
-        // special scaling.  So just call the regular assign_image().
-        if (pixel_traits<typename dest_image_type::type>::max() == pixel_traits<typename src_image_type::type>::max() &&
-            pixel_traits<typename dest_image_type::type>::min() == pixel_traits<typename src_image_type::type>::min() )
+        // If the destination has a dynamic range big enough to contain the source image data then just do a 
+        // regular assign_image()
+        if (pixel_traits<typename dest_image_type::type>::max() >= pixel_traits<typename src_image_type::type>::max() &&
+            pixel_traits<typename dest_image_type::type>::min() <= pixel_traits<typename src_image_type::type>::min() )
         {
             assign_image(dest, src);
             return;
@@ -83,16 +83,28 @@ namespace dlib
                 rs.add(get_pixel_intensity(src[r][c]));
             }
         }
+        typedef typename pixel_traits<typename src_image_type::type>::basic_pixel_type spix_type;
+
+        if (std::numeric_limits<spix_type>::is_integer)
+        {
+            // If the destination has a dynamic range big enough to contain the source image data then just do a 
+            // regular assign_image()
+            if (pixel_traits<typename dest_image_type::type>::max() >= rs.max() &&
+                pixel_traits<typename dest_image_type::type>::min() <= rs.min() )
+            {
+                assign_image(dest, src);
+                return;
+            }
+        }
 
         // Figure out the range of pixel values based on image statistics.  There might be some huge
         // outliers so don't just pick the min and max values.
         const double upper = std::min(rs.mean() + thresh*rs.stddev(), rs.max());
         const double lower = std::max(rs.mean() - thresh*rs.stddev(), rs.min());
 
-        typedef typename pixel_traits<typename dest_image_type::type>::basic_pixel_type dpix_type;
 
-        const dpix_type dest_min = pixel_traits<typename dest_image_type::type>::min();
-        const dpix_type dest_max = pixel_traits<typename dest_image_type::type>::max();
+        const double dest_min = pixel_traits<typename dest_image_type::type>::min();
+        const double dest_max = pixel_traits<typename dest_image_type::type>::max();
 
         const double scale = (upper!=lower)? ((dest_max - dest_min) / (upper - lower)) : 0;
 

dlib/image_transforms/assign_image_abstract.h

@@ -53,10 +53,12 @@ namespace dlib
         ensures
             - #dest_img.nc() == src_img.nc()
             - #dest_img.nr() == src_img.nr()
-            - if (dest_image_type and src_image_type both contain pixels with the same dynamic
-              range as determined by the min() and max() pixel_traits properties) then
+            - if (dest_img's pixels have a wide enough dynamic range to contain all the
+              pixels in src_img.  (Note that dynamic range is determined by the min() and 
+              max() pixel_traits properties)) then
                 - performs: assign_image(dest_img, src_img) 
-                  (i.e. in this case, no scaling is performed. )
+                  (i.e. in this case, no scaling is performed.  Just a normal color space 
+                  conversion and copy )
             - else
                 - #dest_img will be converted to a grayscale image
                 - scales the contents of src_img into the dynamic range of dest_img and then