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Surf and Brisk have terrible accuracy

asked 2017-10-31 13:41:33 -0500

I have been trying both Surf and Brisk and none of them seem to recognize a single object in a photo.

Matches

I have tried with a lot of photos like these:

A cocacola can

A cocacola can in scene

A tonica can

A tonica can in scene

I also have tried with books and other sort of objects but with no result!

Code of brisk and surf implementations below:

   BRISK
const char * PimA="image1.jpg";   // object
const char * PimB="image2.jpg"; // image

cv::Mat GrayA = getMatByName(PimA);
cv::Mat GrayB = getMatByName(PimB);
std::vector<cv::KeyPoint> keypointsA, keypointsB;
cv::Mat descriptorsA, descriptorsB;
//set brisk parameters

int Threshl=10;
int Octaves=4;
float PatternScales=1.0f;
//declare a variable BRISKD of the type cv::BRISK

cv::BRISK  BRISKD(Threshl,Octaves,PatternScales);//initialize algoritm
BRISKD.create("Feature2D.BRISK");

BRISKD.detect(GrayA, keypointsA);
BRISKD.compute(GrayA, keypointsA,descriptorsA);

BRISKD.detect(GrayB, keypointsB);
BRISKD.compute(GrayB, keypointsB,descriptorsB);


cv::FlannBasedMatcher matcher(new cv::flann::LshIndexParams(20,10,2));


std::vector<cv::DMatch> matches;
matcher.match(descriptorsA, descriptorsB, matches);


std::vector<cv::DMatch> goodMatches;
int min = 1000, max = 0;
for(int i=0; i<matches.size(); i++){
   if(matches[i].distance < min)
       min = matches[i].distance;
   if(matches[i].distance > max)
        max = matches[i].distance;
}

printf("min - max %d %d\n", min, max);

for(int i=0; i<matches.size(); i++)
   if(matches[i].distance < min*3)
     goodMatches.push_back(matches[i]);

cv::Mat all_matches;
cv::drawMatches( GrayA, keypointsA, GrayB, keypointsB,
                 goodMatches, all_matches, cv::Scalar::all(-1), cv::Scalar::all(-1),
                 vector<char>(),cv::DrawMatchesFlags::DEFAULT );
showImage(all_matches, 1);




std::vector<Point2f> obj;
std::vector<Point2f> scene;

for( int i = 0; i < goodMatches.size(); i++ )
{
    //-- Get the keypoints from the good matches
        obj.push_back( keypointsA[ goodMatches[i].queryIdx ].pt );
     scene.push_back( keypointsB[ goodMatches[i].trainIdx ].pt );
}


Mat H = findHomography(obj, scene, CV_RANSAC);

std::vector<Point2f> obj_corners(4);
obj_corners[0] = cvPoint(0,0);
obj_corners[1] = cvPoint( GrayA.cols, 0 );
obj_corners[2] = cvPoint( GrayA.cols, GrayA.rows );
obj_corners[3] = cvPoint( 0, GrayA.rows );
std::vector<Point2f> scene_corners(4);

perspectiveTransform( obj_corners, scene_corners, H);

//-- Draw lines between the corners (the mapped object in the scene - image_2 )
line( GrayB, scene_corners[0] + Point2f( GrayA.cols, 0), scene_corners[1] + Point2f( GrayA.cols, 0), Scalar(0, 0, 255), 4 );
line( GrayB, scene_corners[1] + Point2f( GrayA.cols, 0), scene_corners[2] + Point2f( GrayA.cols, 0), Scalar( 0, 0, 255), 4 );
line( GrayB, scene_corners[2] + Point2f( GrayA.cols, 0), scene_corners[3] + Point2f( GrayA.cols, 0), Scalar( 0, 0, 255), 4 );
line( GrayB, scene_corners[3] + Point2f( GrayA.cols, 0), scene_corners[0] + Point2f( GrayA.cols, 0), Scalar( 0, 0, 255), 4 );


showImage(GrayB, 1);






 SURF    

  Mat img_object = imread( "image1.jpg", CV_LOAD_IMAGE_GRAYSCALE );
  Mat img_scene = imread( "image2.jpg", CV_LOAD_IMAGE_GRAYSCALE );

  if( !img_object.data || !img_scene.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<KeyPoint> keypoints_object, keypoints_scene;

  detector.detect( img_object, keypoints_object );
  detector.detect( img_scene, keypoints_scene );

  //-- Step 2: Calculate descriptors (feature vectors)
  SurfDescriptorExtractor extractor;

  Mat descriptors_object, descriptors_scene;

  extractor.compute( img_object, keypoints_object, descriptors_object );
  extractor.compute( img_scene, keypoints_scene, descriptors_scene );

  //-- Step 3: Matching descriptor vectors using FLANN matcher
  FlannBasedMatcher matcher;
  std::vector< ...
(more)
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Comments

Have you tried different matching methods? In my experience BruteForceMatcher (takes longer) achieves better results. You could also try to implement a symmetry test so good matches will just be taken if matches1to2 == matches2to1 Here are different approaches: https://stackoverflow.com/questions/1... It also seems to me that the smaller images are quite blurred. Shouldn't be a problem for SURF though, I think.

Grillteller gravatar imageGrillteller ( 2017-11-01 05:35:58 -0500 )edit

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answered 2017-11-02 18:16:53 -0500

Eduardo gravatar image

It should work:

Matches1 Matches2

Code (needs OpenCV 3 or later):

  cv::Ptr<cv::Feature2D> surf = cv::xfeatures2d::SURF::create();
  cv::Mat ref = cv::imread("15094723456792949.jpg");
  cv::Mat img = cv::imread("15094723542694177.jpg");
//  cv::Mat ref = cv::imread("1509472382233744.jpg");
//  cv::Mat img = cv::imread("15094725804738763.jpg");
  std::vector<cv::KeyPoint> keypoints_ref, keypoints_img;
  cv::Mat descriptors_ref, descriptors_img;

  surf->detectAndCompute(ref, cv::noArray(), keypoints_ref, descriptors_ref);
  surf->detectAndCompute(img, cv::noArray(), keypoints_img, descriptors_img);

  cv::Ptr<cv::DescriptorMatcher> matcher = cv::DescriptorMatcher::create("BruteForce");
  std::vector<std::vector<cv::DMatch> > matches;
  matcher->knnMatch(descriptors_ref, descriptors_img, matches, 2);

  std::vector<cv::DMatch> matches_filtered;
  for(size_t i = 0; i < matches.size(); i++) {
    if(matches[i].size() >= 2) {
      float ratio = matches[i][0].distance / matches[i][1].distance;

      if (ratio < 0.7) {
        matches_filtered.push_back(cv::DMatch(matches[i][0].queryIdx, matches[i][0].trainIdx, matches[i][0].distance));
      }
    }
  }

  cv::Mat img_matches;
  cv::drawMatches(ref, keypoints_ref, img, keypoints_img, matches_filtered, img_matches);
  cv::imshow("Matches", img_matches);
  cv::imwrite("matches.png", img_matches);
  cv::waitKey();
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Comments

Oh thank you Eduardo, It works much better!

cpp_opencv gravatar imagecpp_opencv ( 2017-11-08 12:42:01 -0500 )edit
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Asked: 2017-10-31 13:41:33 -0500

Seen: 454 times

Last updated: Nov 08 '17