ThevenonP's profile - activity

Hello everyone,

I have an issue implementing one recipe from the book "OpenCV 2 Computer vision Application Programming" that I see around, which uses knnMatch.

Here is the code I use:

#include <iostream>
#include <opencv2\core\core.hpp>
#include <opencv2\imgproc\imgproc.hpp>
#include <opencv2\features2d\features2d.hpp>
#include <opencv2\nonfree\features2d.hpp>
#include <opencv2\calib3d\calib3d.hpp>
#include <opencv2\highgui\highgui.hpp>

using namespace cv;
using namespace std;

int main() {
    Mat image1 = imread(filename_object, CV_LOAD_IMAGE_GRAYSCALE);
    Mat image2 = imread(filename_scene, CV_LOAD_IMAGE_GRAYSCALE);

    // 1a. Detection of the features
    SIFT detector;
    vector<KeyPoint> keypoints1, keypoints2;
    detector.detect(image1,keypoints1);
    detector.detect(image2,keypoints2);
    cout << keypoints1.size() << " features found in image 1.\n";
    cout << keypoints2.size() << " features found in image 2.\n";

    // 1b. Extraction of features' descriptors
    Mat descriptors1, descriptors2;
    SiftDescriptorExtractor extractor;
    extractor.compute(image1,keypoints1,descriptors1);
    extractor.compute(image2,keypoints2,descriptors2);
    cout << descriptors1.size() << " descriptors found in image 1.\n";
    cout << descriptors2.size() << " descriptors found in image 2.\n";

    // 2. Match the two image descriptors
    // Construction of the matcher
    BFMatcher matcher;
    vector<vector<DMatch>> matches_multiple_1, matches_multiple_2;
    matcher.knnMatch(descriptors1,descriptors2,matches_multiple_1,2);
    matcher.knnMatch(descriptors2,descriptors1,matches_multiple_2,2);

    cout << matches_multiple_1.size() << " simple 1->2 matches found.\n";
    for (int i=0; i<9; i++)
        cout << "1->2 - query descriptor #" << i+1 << " - number of neighbours: " << matches_multiple_1[i].size() << "\n";
    cout << matches_multiple_2.size() << " simple 2->1 matches found.\n";
    for (int i=0; i<9; i++)
        cout << "2->1 - query descriptor #" << i+1 << " - number of neighbours: " << matches_multiple_2[i].size() << "\n";

    waitKey();
    exit(0);
}

When I run this code, I obtain the following text in my console:

142 features found in image 1.
2269 features found in image 2.
[128 x 142] descriptors found in image 1.
[128 x 2269] descriptors found in image 2.
189 simple 1->2 matches found.
1->2 - query descriptor #1 - number of neighbours: 2
1->2 - query descriptor #2 - number of neighbours: 312192029373266162
1->2 - query descriptor #3 - number of neighbours: 18134552044336285451
1->2 - query descriptor #4 - number of neighbours: 0
1->2 - query descriptor #5 - number of neighbours: 2
1->2 - query descriptor #6 - number of neighbours: 312192029373199793
1->2 - query descriptor #7 - number of neighbours: 18134552044336351820
1->2 - query descriptor #8 - number of neighbours: 0
1->2 - query descriptor #9 - number of neighbours: 2
3025 simple 2->1 matches found.
2->1 - query descriptor #1 - number of neighbours: 2
2->1 - query descriptor #2 - number of neighbours: 312192029372759970
2->1 - query descriptor #3 - number of neighbours: 18134552044336791643
2->1 - query descriptor #4 - number of neighbours: 0
2->1 - query descriptor #5 - number of neighbours: 2
2->1 - query descriptor #6 - number of neighbours: 312192029372759985
2->1 - query descriptor #7 - number of neighbours: 18134552044336791628
2->1 - query descriptor #8 - number of neighbours: 0
2->1 - query descriptor #9 - number of neighbours: 2

What I do not understand, is why some elements of the Vector matches_multiple_1 and _2 have not the right size, notably, the zero value and the very large values.

I tried to go back from scratch several ... (more)