Merge pull request opencv#17643 from pemmanuelviel:pev--new-flann-demo

* Add a FLANN example showing how to search a query image in a dataset

* Clean: remove warning

* Replace dependency to boost::filesystem by calls to core/utils/filesystem

* Wait for escape key to exit

* Add an example of binary descriptors support

* Add program options for saving and loading the flann structure

* Fix warnings on Win64

* Fix warnings on 3.4 branch still relying on C++03

* Add ctor to img_info structure

* Comments modification

* * Demo file of FLANN moved and renamed

* Fix distances type when using binary vectors in the FLANN example

* Rename FLANN example file

* Remove dependency of the flann example to opencv_contrib's SURF.

* Remove mention of FLANN and other descriptors that aimed at giving hint on the other options

* Cleaner program options management

* Make waitKey usage minimal in FLANN example

* Fix the conditions order

* Use cv::Ptr

Author: pemmanuelviel

samples/cpp/flann_search_dataset.cpp

@@ -0,0 +1,250 @@
+// flann_search_dataset.cpp
+// Naive program to search a query picture in a dataset illustrating usage of FLANN
+
+#include <iostream>
+#include <vector>
+#include "opencv2/core.hpp"
+#include "opencv2/core/utils/filesystem.hpp"
+#include "opencv2/highgui.hpp"
+#include "opencv2/features2d.hpp"
+#include "opencv2/flann.hpp"
+
+using namespace cv;
+using std::cout;
+using std::endl;
+
+#define _ORB_
+
+const char* keys =
+    "{ help h | | Print help message. }"
+    "{ dataset | | Path to the images folder used as dataset. }"
+    "{ image |   | Path to the image to search for in the dataset. }"
+    "{ save |    | Path and filename where to save the flann structure to. }"
+    "{ load |    | Path and filename where to load the flann structure from. }";
+
+struct img_info {
+    int img_index;
+    unsigned int nbr_of_matches;
+
+    img_info(int _img_index, unsigned int _nbr_of_matches)
+        : img_index(_img_index)
+        , nbr_of_matches(_nbr_of_matches)
+    {}
+};
+
+
+int main( int argc, char* argv[] )
+{
+    //-- Test the program options
+    CommandLineParser parser( argc, argv, keys );
+    if (parser.has("help"))
+    {
+        parser.printMessage();
+        return -1;
+    }
+
+    const cv::String img_path = parser.get<String>("image");
+    Mat img = imread( samples::findFile( img_path ), IMREAD_GRAYSCALE );
+    if (img.empty() )
+    {
+        cout << "Could not open the image "<< img_path << endl;
+        return -1;
+    }
+
+    const cv::String db_path = parser.get<String>("dataset");
+    if (!utils::fs::isDirectory(db_path))
+    {
+        cout << "Dataset folder "<< db_path.c_str() <<" doesn't exist!" << endl;
+        return -1;
+    }
+
+    const cv::String load_db_path = parser.get<String>("load");
+    if ((load_db_path != String()) && (!utils::fs::exists(load_db_path)))
+    {
+        cout << "File " << load_db_path.c_str()
+             << " where to load the flann structure from doesn't exist!" << endl;
+        return -1;
+    }
+
+    const cv::String save_db_path = parser.get<String>("save");
+
+    //-- Step 1: Detect the keypoints using a detector, compute the descriptors
+    //   in the folder containing the images of the dataset
+#ifdef _SIFT_
+    int minHessian = 400;
+    Ptr<Feature2D> detector = SIFT::create( minHessian );
+#elif defined(_ORB_)
+    Ptr<Feature2D> detector = ORB::create();
+#else
+    cout << "Missing or unknown defined descriptor. "
+            "Only SIFT and ORB are currently interfaced here" << endl;
+    return -1;
+#endif
+
+    std::vector<KeyPoint> db_keypoints;
+    Mat db_descriptors;
+    std::vector<unsigned int> db_images_indice_range; //store the range of indices per image
+    std::vector<int> db_indice_2_image_lut;           //match descriptor indice to its image
+
+    db_images_indice_range.push_back(0);
+    std::vector<cv::String> files;
+    utils::fs::glob(db_path, cv::String(), files);
+    for (std::vector<cv::String>::iterator itr = files.begin(); itr != files.end(); ++itr)
+    {
+        Mat tmp_img = imread( *itr, IMREAD_GRAYSCALE );
+        if (!tmp_img.empty())
+        {
+            std::vector<KeyPoint> kpts;
+            Mat descriptors;
+            detector->detectAndCompute( tmp_img, noArray(), kpts, descriptors );
+
+            db_keypoints.insert( db_keypoints.end(), kpts.begin(), kpts.end() );
+            db_descriptors.push_back( descriptors );
+            db_images_indice_range.push_back( db_images_indice_range.back()
+                                              + static_cast<unsigned int>(kpts.size()) );
+        }
+    }
+
+    //-- Set the LUT
+    db_indice_2_image_lut.resize( db_images_indice_range.back() );
+    const int nbr_of_imgs = static_cast<int>( db_images_indice_range.size()-1 );
+    for (int i = 0; i < nbr_of_imgs; ++i)
+    {
+        const unsigned int first_indice = db_images_indice_range[i];
+        const unsigned int last_indice = db_images_indice_range[i+1];
+        std::fill( db_indice_2_image_lut.begin() + first_indice,
+                   db_indice_2_image_lut.begin() + last_indice,
+                   i );
+    }
+
+    //-- Step 2: build the structure storing the descriptors
+#if defined(_SIFT_)
+    cv::Ptr<flann::GenericIndex<cvflann::L2<float> > > index;
+    if (load_db_path != String())
+        index = cv::makePtr<flann::GenericIndex<cvflann::L2<float> > >(db_descriptors,
+                                                             cvflann::SavedIndexParams(load_db_path));
+    else
+        index = cv::makePtr<flann::GenericIndex<cvflann::L2<float> > >(db_descriptors,
+                                                             cvflann::KDTreeIndexParams(4));
+
+#elif defined(_ORB_)
+    cv::Ptr<flann::GenericIndex<cvflann::Hamming<unsigned char> > > index;
+    if (load_db_path != String())
+        index  = cv::makePtr<flann::GenericIndex<cvflann::Hamming<unsigned char> > >
+                (db_descriptors, cvflann::SavedIndexParams(load_db_path));
+    else
+        index  = cv::makePtr<flann::GenericIndex<cvflann::Hamming<unsigned char> > >
+                (db_descriptors, cvflann::LshIndexParams());
+#else
+    cout<< "Descriptor not listed. Set the proper FLANN distance for this descriptor" <<endl;
+    return -1;
+#endif
+    if (save_db_path != String())
+        index->save(save_db_path);
+
+
+    // Return if no query image was set
+    if (img_path == String())
+        return 0;
+
+    //-- Detect the keypoints and compute the descriptors for the query image
+    std::vector<KeyPoint> img_keypoints;
+    Mat img_descriptors;
+    detector->detectAndCompute( img, noArray(), img_keypoints, img_descriptors );
+
+
+    //-- Step 3: retrieve the descriptors in the dataset matching the ones of the query image
+    // /!\ knnSearch doesn't follow OpenCV standards by not initialising empty Mat properties
+    const int knn = 2;
+    Mat indices(img_descriptors.rows, knn, CV_32S);
+#if defined(_SIFT_)
+#define DIST_TYPE float
+    Mat dists(img_descriptors.rows, knn, CV_32F);
+#elif defined(_ORB_)
+#define DIST_TYPE int
+    Mat dists(img_descriptors.rows, knn, CV_32S);
+#endif
+    index->knnSearch( img_descriptors, indices, dists, knn, cvflann::SearchParams(32) );
+
+    //-- Filter matches using the Lowe's ratio test
+    const float ratio_thresh = 0.7f;
+    std::vector<DMatch> good_matches; //contains
+    std::vector<unsigned int> matches_per_img_histogram( nbr_of_imgs, 0 );
+    for (int i = 0; i < dists.rows; ++i)
+    {
+        if (dists.at<DIST_TYPE>(i,0) < ratio_thresh * dists.at<DIST_TYPE>(i,1))
+        {
+            const int indice_in_db = indices.at<int>(i,0);
+            DMatch dmatch(i, indice_in_db, db_indice_2_image_lut[indice_in_db],
+                          static_cast<float>(dists.at<DIST_TYPE>(i,0)));
+            good_matches.push_back( dmatch );
+            matches_per_img_histogram[ db_indice_2_image_lut[indice_in_db] ]++;
+        }
+    }
+
+
+    //-- Step 4: find the dataset image with the highest proportion of matches
+    std::multimap<float, img_info> images_infos;
+    for (int i = 0; i < nbr_of_imgs; ++i)
+    {
+        const unsigned int nbr_of_matches = matches_per_img_histogram[i];
+        if (nbr_of_matches < 4) //we need at leat 4 points for a homography
+            continue;
+
+        const unsigned int nbr_of_kpts = db_images_indice_range[i+1] - db_images_indice_range[i];
+        const float inverse_proportion_of_retrieved_kpts =
+                static_cast<float>(nbr_of_kpts) / static_cast<float>(nbr_of_matches);
+
+        img_info info(i, nbr_of_matches);
+        images_infos.insert( std::pair<float,img_info>(inverse_proportion_of_retrieved_kpts,
+                                                       info) );
+    }
+
+    if (images_infos.begin() == images_infos.end())
+    {
+        cout<<"No good match could be found."<<endl;
+        return 0;
+    }
+
+    //-- if there are several images with a similar proportion of matches,
+    // select the one with the highest number of matches weighted by the
+    // squared ratio of proportions
+    const float best_matches_proportion = images_infos.begin()->first;
+    float new_matches_proportion = best_matches_proportion;
+    img_info best_img = images_infos.begin()->second;
+
+    std::multimap<float, img_info>::iterator it = images_infos.begin();
+    ++it;
+    while ((it!=images_infos.end()) && (it->first < 1.1*best_matches_proportion))
+    {
+        const float ratio = new_matches_proportion / it->first;
+        if( it->second.nbr_of_matches * (ratio * ratio) > best_img.nbr_of_matches)
+        {
+            new_matches_proportion = it->first;
+            best_img = it->second;
+        }
+        ++it;
+    }
+
+    //-- Step 5: filter goodmatches that belong to the best image match of the dataset
+    std::vector<DMatch> filtered_good_matches;
+    for (std::vector<DMatch>::iterator itr(good_matches.begin()); itr != good_matches.end(); ++itr)
+    {
+        if (itr->imgIdx == best_img.img_index)
+            filtered_good_matches.push_back(*itr);
+    }
+
+    //-- Retrieve the best image match from the dataset
+    Mat db_img = imread( files[best_img.img_index], IMREAD_GRAYSCALE );
+
+    //-- Draw matches
+    Mat img_matches;
+    drawMatches( img, img_keypoints, db_img, db_keypoints, filtered_good_matches, img_matches, Scalar::all(-1),
+                 Scalar::all(-1), std::vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS );
+
+    //-- Show detected matches
+    imshow("Good Matches", img_matches );
+    waitKey();
+
+    return 0;
+}