FLANN匹配器- opencv 3-min最大距离

Question

我有一些代码，使用Flann匹配器和ORB检测器来查找一个人的两张图像之间的特征。我在ubuntu上使用opencv 3。我有一些疑问……代码如下:

  #include <iostream>
#include </home/sruthi/opencv/include/opencv2/opencv.hpp>
using namespace cv;
//void readme();
/** @function main */
int main(int argc, char** argv)
{
   if( argc != 3 )
  { //readme(); 
     return -1; }
  Mat img_object = imread( argv[1], IMREAD_GRAYSCALE );
  Mat img_scene = imread( argv[2], IMREAD_GRAYSCALE );

    if (!img_object.data || !img_scene.data)
    {
        std::cout << " --(!) Error reading images " << std::endl; return -1;
    }
    //-- Step 1: Detect the keypoints using ORB Detector
    Ptr<FeatureDetector> detector = ORB::create();
    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)
    Ptr<DescriptorExtractor> extractor = ORB::create();
    Mat descriptors_object, descriptors_scene;
    extractor->compute(img_object, keypoints_object, descriptors_object);
    extractor->compute(img_scene, keypoints_scene, descriptors_scene);
    descriptors_object.convertTo(descriptors_object,CV_32F);
    descriptors_scene.convertTo(descriptors_scene,CV_32F);

    //-- Step 3: Matching descriptor vectors using FLANN matcher
    Ptr<DescriptorMatcher> matcher = DescriptorMatcher::create("FlannBased");
    std::vector< DMatch > matches;
    matcher->match(descriptors_object, descriptors_scene, matches);
    double max_dist = 0; double min_dist = 100;
    //-- Quick calculation of max and min distances between keypoints
    for (int i = 0; i < descriptors_object.rows; i++)
    {
        double dist = matches[i].distance;
        if (dist < min_dist) min_dist = dist;
        if (dist > max_dist) max_dist = dist;
    }
    printf("-- Max dist : %f n", max_dist);
    printf("-- Min dist : %f n", min_dist);
    //-- Draw only "good" matches (i.e. whose distance is less than 3*min_dist )
    std::vector< DMatch > good_matches;
    for (int i = 0; i < descriptors_object.rows; i++)
    {
        if (matches[i].distance < 3 * min_dist)
        {
            good_matches.push_back(matches[i]);
        }
    }
    Mat img_matches;
    drawMatches(img_object, keypoints_object, img_scene, keypoints_scene, good_matches, img_matches, Scalar::all(-1), Scalar::all(-1), std::vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS);
    //-- Localize the object
    std::vector<Point2f> obj;
    std::vector<Point2f> scene;
    for (int i = 0; i < good_matches.size(); i++)
    {
        //-- Get the keypoints from the good matches
        obj.push_back(keypoints_object[good_matches[i].queryIdx].pt);
        scene.push_back(keypoints_scene[good_matches[i].trainIdx].pt);
    }

    //-- Show detected matches
  imshow( "Good Matches", img_matches );
  for( int i = 0; i < (int)good_matches.size(); i++ )
  { printf( "-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  n", i, good_matches[i].queryIdx, good_matches[i].trainIdx ); }
    waitKey(0);
    return 0;

}

1. double max_dist = 0;Double min_dist = 100;为什么我们分别将这些距离声明为0和100 ?作为输出我得到最大距离:488.559113最小距离:100.000000。

2. 如果(匹配[我]。距离& lt;3 * min_dist)｛good_matches.push_back(匹配[我]);}为什么我不能把3*min_dist改成2*min_dist?

3. 是否必须有官方文档中所示的平行线?不会得到平行线。我不能发截图

Answer 1

1. 这些初始化似乎是针对编写此代码的特定情况进行调整的。
2. 这也是由于调优的参数。尝试不同的图像集，你应该会看到一些变化的结果。另外，另一个好的做法是使用次优距离来寻找好的匹配。
3. 正确的匹配应该是平行线，因为两幅图像中匹配的相对位置应该保持不变。任何交叉行都是不正确的匹配。