.. _feature_detection: Feature Detection ****************** Goal ===== In this tutorial you will learn how to: .. container:: enumeratevisibleitemswithsquare * Use the :feature_detector:`FeatureDetector<>` interface in order to find interest points. Specifically: * Use the :surf_feature_detector:`SurfFeatureDetector<>` and its function :feature_detector_detect:`detect<>` to perform the detection process * Use the function :draw_keypoints:`drawKeypoints<>` to draw the detected keypoints Theory ====== Code ==== This tutorial code's is shown lines below. You can also download it from `here `_ .. code-block:: cpp #include #include #include "opencv2/core/core.hpp" #include "opencv2/features2d/features2d.hpp" #include "opencv2/highgui/highgui.hpp" using namespace cv; void readme(); /** @function main */ int main( int argc, char** argv ) { if( argc != 3 ) { readme(); return -1; } Mat img_1 = imread( argv[1], CV_LOAD_IMAGE_GRAYSCALE ); Mat img_2 = imread( argv[2], CV_LOAD_IMAGE_GRAYSCALE ); if( !img_1.data || !img_2.data ) { std::cout<< " --(!) Error reading images " << std::endl; return -1; } //-- Step 1: Detect the keypoints using SURF Detector int minHessian = 400; SurfFeatureDetector detector( minHessian ); std::vector keypoints_1, keypoints_2; detector.detect( img_1, keypoints_1 ); detector.detect( img_2, keypoints_2 ); //-- Draw keypoints Mat img_keypoints_1; Mat img_keypoints_2; drawKeypoints( img_1, keypoints_1, img_keypoints_1, Scalar::all(-1), DrawMatchesFlags::DEFAULT ); drawKeypoints( img_2, keypoints_2, img_keypoints_2, Scalar::all(-1), DrawMatchesFlags::DEFAULT ); //-- Show detected (drawn) keypoints imshow("Keypoints 1", img_keypoints_1 ); imshow("Keypoints 2", img_keypoints_2 ); waitKey(0); return 0; } /** @function readme */ void readme() { std::cout << " Usage: ./SURF_detector " << std::endl; } Explanation ============ Result ====== #. Here is the result of the feature detection applied to the first image: .. image:: images/Feature_Detection_Result_a.jpg :align: center :height: 125pt #. And here is the result for the second image: .. image:: images/Feature_Detection_Result_b.jpg :align: center :height: 200pt