fix, for funtion undist source and dest shoudl be not equal

Demo.cpp

@@ -378,12 +378,13 @@ int main(int argc, char * argv[])
             {
                 //! step 0 we take care about the lense distortion
                 //! correct lense distortion
-                //Mat imgLenseCorrection = img_input.clone();
-                cv::undistort(img_input, img_input, intrinsicsCameraMatrix, distortionCoeff);
+                Mat imgLenseCorrection = img_input.clone();
+                //see https://docs.opencv.org/2.4/modules/imgproc/doc/geometric_transformations.html#undistort
+                cv::undistort(img_input, imgLenseCorrection, intrinsicsCameraMatrix, distortionCoeff);
 
                 //! we cut out a smaller ROI,
                 //! step 1)
-                img_input = TToolBox::cropImageCircle(img_input,circleCenterX,circleCenterY,circleRadius);
+                img_input = TToolBox::cropImageCircle(imgLenseCorrection,circleCenterX,circleCenterY,circleRadius);
 
                 //!  normal bgs processing
                 //! step 2)