bugfix

src/interface.cpp

@@ -61,7 +61,7 @@ public:
 
     //! 2. cast cv::Mat to numpy.ndarray
     static handle cast(const cv::Mat& mat, return_value_policy, handle defval){
-        UNUSED(defval);
+        // UNUSED(defval);
 
         std::string format = format_descriptor<unsigned char>::format();
         size_t elemsize = sizeof(unsigned char);