Previously, when using spatially_filter_image(), the intermediate filter computations

were carried out using variables of the same basic type as the input image's pixels.
I changed this to use the scalar type used by the actual filter given to this function
since this should result in fewer surprises (since the filter usually determines what
type is appropriate, not the input image).

dlib/image_transforms/spatial_filtering.h

@@ -71,9 +71,9 @@ namespace dlib
         {
             for (long c = first_col; c < last_col; ++c)
             {
-                typedef typename pixel_traits<typename in_image_type::type>::basic_pixel_type bp_type;
-                typename promote<bp_type>::type p;
-                typename promote<bp_type>::type temp = 0;
+                typedef typename EXP::type ptype;
+                ptype p;
+                ptype temp = 0;
                 for (long m = 0; m < filter.nr(); ++m)
                 {
                     for (long n = 0; n < filter.nc(); ++n)
@@ -170,11 +170,11 @@ namespace dlib
         const long last_row = in_img.nr() - col_filter.size()/2;
         const long last_col = in_img.nc() - row_filter.size()/2;
 
-        typedef typename pixel_traits<typename in_image_type::type>::basic_pixel_type bp_type;
 
         typedef typename out_image_type::mem_manager_type mem_manager_type;
+        typedef typename EXP1::type ptype;
 
-        array2d<typename promote<bp_type>::type,mem_manager_type> temp_img;
+        array2d<ptype,mem_manager_type> temp_img;
         temp_img.set_size(in_img.nr(), in_img.nc());
 
         // apply the row filter
@@ -182,8 +182,8 @@ namespace dlib
         {
             for (long c = first_col; c < last_col; ++c)
             {
-                typename promote<bp_type>::type p;
-                typename promote<bp_type>::type temp = 0;
+                ptype p;
+                ptype temp = 0;
                 for (long n = 0; n < row_filter.size(); ++n)
                 {
                     // pull out the current pixel and put it into p
@@ -199,7 +199,7 @@ namespace dlib
         {
             for (long c = first_col; c < last_col; ++c)
             {
-                typename promote<bp_type>::type temp = 0;
+                ptype temp = 0;
                 for (long m = 0; m < col_filter.size(); ++m)
                 {
                     temp += temp_img[r-col_filter.size()/2+m][c]*col_filter(m);

dlib/image_transforms/spatial_filtering_abstract.h

@@ -38,6 +38,8 @@ namespace dlib
         ensures
             - Applies the given spatial filter to in_img and stores the result in out_img.  Also 
               divides each resulting pixel by scale.  
+            - The intermediate filter computations will be carried out using variables of type EXP::type.
+              This is whatever scalar type is used inside the filter matrix. 
             - Pixel values are stored into out_img using the assign_pixel() function and therefore
               any applicable color space conversion or value saturation is performed.
             - if (pixel_traits<typename in_image_type::type>::grayscale == false) then
@@ -87,6 +89,8 @@ namespace dlib
               effect as calling the regular spatially_filter_image() routine with a filter,
               FILT, defined as follows: 
                 - FILT(r,c) == col_filter(r)*row_filter(c)
+            - The intermediate filter computations will be carried out using variables of type EXP1::type.
+              This is whatever scalar type is used inside the row_filter matrix. 
             - Pixel values are stored into out_img using the assign_pixel() function and therefore
               any applicable color space conversion or value saturation is performed.
             - if (pixel_traits<typename in_image_type::type>::grayscale == false) then