doc/tutorials/features2d/feature_detection/feature_detection.rst

   1 .. _feature_detection:
   2
   3 Feature Detection
   4 ******************
   5
   6 Goal
   7 =====
   8
   9 In this tutorial you will learn how to:
  10
  11 .. container:: enumeratevisibleitemswithsquare
  12
  13    * Use the :feature_detector:`FeatureDetector<>` interface in order to find interest points. Specifically:
  14
  15      * Use the :surf_feature_detector:`SurfFeatureDetector<>` and its function :feature_detector_detect:`detect<>` to perform the detection process
  16      * Use the function :draw_keypoints:`drawKeypoints<>` to draw the detected keypoints
  17
  18
  19 Theory
  20 ======
  21
  22 Code
  23 ====
  24
  25 This tutorial code's is shown lines below. You can also download it from `here <http://code.opencv.org/projects/opencv/repository/revisions/master/raw/samples/cpp/tutorial_code/features2D/SURF_detector.cpp>`_
  26
  27 .. code-block:: cpp
  28
  29    #include <stdio.h>
  30    #include <iostream>
  31    #include "opencv2/core/core.hpp"
  32    #include "opencv2/features2d/features2d.hpp"
  33    #include "opencv2/highgui/highgui.hpp"
  34
  35    using namespace cv;
  36
  37    void readme();
  38
  39    /** @function main */
  40    int main( int argc, char** argv )
  41    {
  42      if( argc != 3 )
  43      { readme(); return -1; }
  44
  45      Mat img_1 = imread( argv[1], CV_LOAD_IMAGE_GRAYSCALE );
  46      Mat img_2 = imread( argv[2], CV_LOAD_IMAGE_GRAYSCALE );
  47
  48      if( !img_1.data || !img_2.data )
  49      { std::cout<< " --(!) Error reading images " << std::endl; return -1; }
  50
  51      //-- Step 1: Detect the keypoints using SURF Detector
  52      int minHessian = 400;
  53
  54      SurfFeatureDetector detector( minHessian );
  55
  56      std::vector<KeyPoint> keypoints_1, keypoints_2;
  57
  58      detector.detect( img_1, keypoints_1 );
  59      detector.detect( img_2, keypoints_2 );
  60
  61      //-- Draw keypoints
  62      Mat img_keypoints_1; Mat img_keypoints_2;
  63
  64      drawKeypoints( img_1, keypoints_1, img_keypoints_1, Scalar::all(-1), DrawMatchesFlags::DEFAULT );
  65      drawKeypoints( img_2, keypoints_2, img_keypoints_2, Scalar::all(-1), DrawMatchesFlags::DEFAULT );
  66
  67      //-- Show detected (drawn) keypoints
  68      imshow("Keypoints 1", img_keypoints_1 );
  69      imshow("Keypoints 2", img_keypoints_2 );
  70
  71      waitKey(0);
  72
  73      return 0;
  74      }
  75
  76      /** @function readme */
  77      void readme()
  78      { std::cout << " Usage: ./SURF_detector <img1> <img2>" << std::endl; }
  79
  80 Explanation
  81 ============
  82
  83 Result
  84 ======
  85
  86 #. Here is the result of the feature detection applied to the first image:
  87
  88    .. image:: images/Feature_Detection_Result_a.jpg
  89       :align: center
  90       :height: 125pt
  91
  92 #. And here is the result for the second image:
  93
  94    .. image:: images/Feature_Detection_Result_b.jpg
  95       :align: center
  96       :height: 200pt
  97