Changed extract_image_chips() so that it doesn't build image pyramids larger

than necessary when pulling out chips.

dlib/image_transforms/interpolation.h

@@ -1556,7 +1556,8 @@ namespace dlib
     {
         chip_details() : angle(0), rows(0), cols(0) {}
         chip_details(const rectangle& rect_) : rect(rect_),angle(0), rows(rect_.height()), cols(rect_.width()) {}
-        chip_details(const drectangle& rect_) : rect(rect_),angle(0), rows(rect_.height()), cols(rect_.width()) {}
+        chip_details(const drectangle& rect_) : rect(rect_),angle(0), 
+          rows((unsigned long)(rect_.height()+0.5)), cols((unsigned long)(rect_.width()+0.5)) {}
         chip_details(const drectangle& rect_, unsigned long size) : rect(rect_),angle(0) 
         { compute_dims_from_size(size); }
         chip_details(const drectangle& rect_, unsigned long size, double angle_) : rect(rect_),angle(angle_) 
@@ -1617,6 +1618,8 @@ namespace dlib
             const double relative_size = std::sqrt(size/(double)rect.area());
             rows = static_cast<unsigned long>(rect.height()*relative_size + 0.5);
             cols  = static_cast<unsigned long>(size/(double)rows + 0.5);
+            rows = std::max(1ul,rows);
+            cols = std::max(1ul,cols);
         }
     };
 
@@ -1738,22 +1741,36 @@ namespace dlib
         // interpolation.  So we use an image pyramid to make sure the interpolation is
         // fast but also high quality.  The first thing we do is figure out how deep the
         // image pyramid needs to be.
+        rectangle bounding_box;
         for (unsigned long i = 0; i < chip_locations.size(); ++i)
         {
             long depth = 0;
+            double grow = 2;
             drectangle rect = pyr.rect_down(chip_locations[i].rect);
             while (rect.area() > chip_locations[i].size())
             {
                 rect = pyr.rect_down(rect);
                 ++depth;
+                // We drop the image size by a factor of 2 each iteration and then assume a
+                // border of 2 pixels is needed to avoid any border effects of the crop.
+                grow = grow*2 + 2;
             }
+            drectangle rot_rect;
+            const vector<double,2> cent = center(chip_locations[i].rect);
+            rot_rect += rotate_point<double>(cent,chip_locations[i].rect.tl_corner(),chip_locations[i].angle);
+            rot_rect += rotate_point<double>(cent,chip_locations[i].rect.tr_corner(),chip_locations[i].angle);
+            rot_rect += rotate_point<double>(cent,chip_locations[i].rect.bl_corner(),chip_locations[i].angle);
+            rot_rect += rotate_point<double>(cent,chip_locations[i].rect.br_corner(),chip_locations[i].angle);
+            bounding_box += grow_rect(rot_rect, grow).intersect(get_rect(img));
             max_depth = std::max(depth,max_depth);
         }
+        //std::cout << "max_depth: " << max_depth << std::endl;
+        //std::cout << "crop amount: " << bounding_box.area()/(double)get_rect(img).area() << std::endl;
 
         // now make an image pyramid
         dlib::array<array2d<typename image_traits<image_type1>::pixel_type> > levels(max_depth);
         if (levels.size() != 0)
-            pyr(img,levels[0]);
+            pyr(sub_image(img,bounding_box),levels[0]);
         for (unsigned long i = 1; i < levels.size(); ++i)
             pyr(levels[i-1],levels[i]);
 
@@ -1777,7 +1794,7 @@ namespace dlib
 
                 // figure out which level in the pyramid to use to extract the chip
                 int level = -1;
-                drectangle rect = chip_locations[i].rect;
+                drectangle rect = translate_rect(chip_locations[i].rect, -bounding_box.tl_corner());
                 while (pyr.rect_down(rect).area() > chip_locations[i].size())
                 {
                     ++level;
@@ -1795,7 +1812,7 @@ namespace dlib
 
                 // now extract the actual chip
                 if (level == -1)
-                    transform_image(img,chips[i],interpolate_bilinear(),trns);
+                    transform_image(sub_image(img,bounding_box),chips[i],interpolate_bilinear(),trns);
                 else
                     transform_image(levels[level],chips[i],interpolate_bilinear(),trns);
             }