Merge pull request #2784 from mapycz/fix-benchmark

fix benchmark

benchmark/compare_images.hpp

@@ -23,8 +23,11 @@ namespace benchmark {
             throw mapnik::image_reader_exception("Failed to load: " + src_fn);
         }
 
-        image_rgba8 const& dest = util::get<image_rgba8>(reader1->read(0,0,reader1->width(), reader1->height()));
-        image_rgba8 const& src = util::get<image_rgba8>(reader1->read(0,0,reader1->width(), reader1->height()));
+        const image_any desc_any = reader1->read(0,0,reader1->width(), reader1->height());
+        const image_any src_any = reader2->read(0,0,reader2->width(), reader2->height());
+
+        image_rgba8 const& dest = util::get<image_rgba8>(desc_any);
+        image_rgba8 const& src = util::get<image_rgba8>(src_any);
 
         unsigned int width = src.width();
         unsigned int height = src.height();