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+/*M///////////////////////////////////////////////////////////////////////////////////////
+//
+//  IMPORTANT: READ BEFORE DOWNLOADING, COPYING, INSTALLING OR USING.
+//
+//  By downloading, copying, installing or using the software you agree to this license.
+//  If you do not agree to this license, do not download, install,
+//  copy or use the software.
+//
+//
+//                           License Agreement
+//                For Open Source Computer Vision Library
+//
+// Copyright (C) 2000-2008, Intel Corporation, all rights reserved.
+// Copyright (C) 2009, Willow Garage Inc., all rights reserved.
+// Third party copyrights are property of their respective owners.
+//
+// Redistribution and use in source and binary forms, with or without modification,
+// are permitted provided that the following conditions are met:
+//
+//   * Redistribution's of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//
+//   * Redistribution's in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//
+//   * The name of the copyright holders may not be used to endorse or promote products
+//     derived from this software without specific prior written permission.
+//
+// This software is provided by the copyright holders and contributors "as is" and
+// any express or implied warranties, including, but not limited to, the implied
+// warranties of merchantability and fitness for a particular purpose are disclaimed.
+// In no event shall the Intel Corporation or contributors be liable for any direct,
+// indirect, incidental, special, exemplary, or consequential damages
+// (including, but not limited to, procurement of substitute goods or services;
+// loss of use, data, or profits; or business interruption) however caused
+// and on any theory of liability, whether in contract, strict liability,
+// or tort (including negligence or otherwise) arising in any way out of
+// the use of this software, even if advised of the possibility of such damage.
+//
+//M*/
+
+#ifndef OPENCV_FEATURES_2D_HPP
+#define OPENCV_FEATURES_2D_HPP
+
+#include "opencv2/core.hpp"
+#include "opencv2/flann/miniflann.hpp"
+
+/**
+  @defgroup features2d 2D Features Framework
+  @{
+    @defgroup features2d_main Feature Detection and Description
+    @defgroup features2d_match Descriptor Matchers
+
+Matchers of keypoint descriptors in OpenCV have wrappers with a common interface that enables you to
+easily switch between different algorithms solving the same problem. This section is devoted to
+matching descriptors that are represented as vectors in a multidimensional space. All objects that
+implement vector descriptor matchers inherit the DescriptorMatcher interface.
+
+@note
+   -   An example explaining keypoint matching can be found at
+        opencv_source_code/samples/cpp/descriptor_extractor_matcher.cpp
+    -   An example on descriptor matching evaluation can be found at
+        opencv_source_code/samples/cpp/detector_descriptor_matcher_evaluation.cpp
+    -   An example on one to many image matching can be found at
+        opencv_source_code/samples/cpp/matching_to_many_images.cpp
+
+    @defgroup features2d_draw Drawing Function of Keypoints and Matches
+    @defgroup features2d_category Object Categorization
+
+This section describes approaches based on local 2D features and used to categorize objects.
+
+@note
+   -   A complete Bag-Of-Words sample can be found at
+        opencv_source_code/samples/cpp/bagofwords_classification.cpp
+    -   (Python) An example using the features2D framework to perform object categorization can be
+        found at opencv_source_code/samples/python/find_obj.py
+
+  @}
+ */
+
+namespace cv
+{
+
+//! @addtogroup features2d
+//! @{
+
+// //! writes vector of keypoints to the file storage
+// CV_EXPORTS void write(FileStorage& fs, const String& name, const std::vector<KeyPoint>& keypoints);
+// //! reads vector of keypoints from the specified file storage node
+// CV_EXPORTS void read(const FileNode& node, CV_OUT std::vector<KeyPoint>& keypoints);
+
+/** @brief A class filters a vector of keypoints.
+
+ Because now it is difficult to provide a convenient interface for all usage scenarios of the
+ keypoints filter class, it has only several needed by now static methods.
+ */
+class CV_EXPORTS KeyPointsFilter
+{
+public:
+    KeyPointsFilter(){}
+
+    /*
+     * Remove keypoints within borderPixels of an image edge.
+     */
+    static void runByImageBorder( std::vector<KeyPoint>& keypoints, Size imageSize, int borderSize );
+    /*
+     * Remove keypoints of sizes out of range.
+     */
+    static void runByKeypointSize( std::vector<KeyPoint>& keypoints, float minSize,
+                                   float maxSize=FLT_MAX );
+    /*
+     * Remove keypoints from some image by mask for pixels of this image.
+     */
+    static void runByPixelsMask( std::vector<KeyPoint>& keypoints, const Mat& mask );
+    /*
+     * Remove duplicated keypoints.
+     */
+    static void removeDuplicated( std::vector<KeyPoint>& keypoints );
+
+    /*
+     * Retain the specified number of the best keypoints (according to the response)
+     */
+    static void retainBest( std::vector<KeyPoint>& keypoints, int npoints );
+};
+
+
+/************************************ Base Classes ************************************/
+
+/** @brief Abstract base class for 2D image feature detectors and descriptor extractors
+*/
+class CV_EXPORTS_W Feature2D : public virtual Algorithm
+{
+public:
+    virtual ~Feature2D();
+
+    /** @brief Detects keypoints in an image (first variant) or image set (second variant).
+
+    @param image Image.
+    @param keypoints The detected keypoints. In the second variant of the method keypoints[i] is a set
+    of keypoints detected in images[i] .
+    @param mask Mask specifying where to look for keypoints (optional). It must be a 8-bit integer
+    matrix with non-zero values in the region of interest.
+     */
+    CV_WRAP virtual void detect( InputArray image,
+                                 CV_OUT std::vector<KeyPoint>& keypoints,
+                                 InputArray mask=noArray() );
+
+    /** @overload
+    @param images Image set.
+    @param keypoints The detected keypoints. In the second variant of the method keypoints[i] is a set
+    of keypoints detected in images[i] .
+    @param masks Masks for each input image specifying where to look for keypoints (optional).
+    masks[i] is a mask for images[i].
+    */
+    CV_WRAP virtual void detect( InputArrayOfArrays images,
+                         CV_OUT std::vector<std::vector<KeyPoint> >& keypoints,
+                         InputArrayOfArrays masks=noArray() );
+
+    /** @brief Computes the descriptors for a set of keypoints detected in an image (first variant) or image set
+    (second variant).
+
+    @param image Image.
+    @param keypoints Input collection of keypoints. Keypoints for which a descriptor cannot be
+    computed are removed. Sometimes new keypoints can be added, for example: SIFT duplicates keypoint
+    with several dominant orientations (for each orientation).
+    @param descriptors Computed descriptors. In the second variant of the method descriptors[i] are
+    descriptors computed for a keypoints[i]. Row j is the keypoints (or keypoints[i]) is the
+    descriptor for keypoint j-th keypoint.
+     */
+    CV_WRAP virtual void compute( InputArray image,
+                                  CV_OUT CV_IN_OUT std::vector<KeyPoint>& keypoints,
+                                  OutputArray descriptors );
+
+    /** @overload
+
+    @param images Image set.
+    @param keypoints Input collection of keypoints. Keypoints for which a descriptor cannot be
+    computed are removed. Sometimes new keypoints can be added, for example: SIFT duplicates keypoint
+    with several dominant orientations (for each orientation).
+    @param descriptors Computed descriptors. In the second variant of the method descriptors[i] are
+    descriptors computed for a keypoints[i]. Row j is the keypoints (or keypoints[i]) is the
+    descriptor for keypoint j-th keypoint.
+    */
+    CV_WRAP virtual void compute( InputArrayOfArrays images,
+                          CV_OUT CV_IN_OUT std::vector<std::vector<KeyPoint> >& keypoints,
+                          OutputArrayOfArrays descriptors );
+
+    /** Detects keypoints and computes the descriptors */
+    CV_WRAP virtual void detectAndCompute( InputArray image, InputArray mask,
+                                           CV_OUT std::vector<KeyPoint>& keypoints,
+                                           OutputArray descriptors,
+                                           bool useProvidedKeypoints=false );
+
+    CV_WRAP virtual int descriptorSize() const;
+    CV_WRAP virtual int descriptorType() const;
+    CV_WRAP virtual int defaultNorm() const;
+
+    CV_WRAP void write( const String& fileName ) const;
+
+    CV_WRAP void read( const String& fileName );
+
+    virtual void write( FileStorage&) const;
+
+    virtual void read( const FileNode&);
+
+    //! Return true if detector object is empty
+    CV_WRAP virtual bool empty() const;
+};
+
+/** Feature detectors in OpenCV have wrappers with a common interface that enables you to easily switch
+between different algorithms solving the same problem. All objects that implement keypoint detectors
+inherit the FeatureDetector interface. */
+typedef Feature2D FeatureDetector;
+
+/** Extractors of keypoint descriptors in OpenCV have wrappers with a common interface that enables you
+to easily switch between different algorithms solving the same problem. This section is devoted to
+computing descriptors represented as vectors in a multidimensional space. All objects that implement
+the vector descriptor extractors inherit the DescriptorExtractor interface.
+ */
+typedef Feature2D DescriptorExtractor;
+
+//! @addtogroup features2d_main
+//! @{
+
+/** @brief Class implementing the BRISK keypoint detector and descriptor extractor, described in @cite LCS11 .
+ */
+class CV_EXPORTS_W BRISK : public Feature2D
+{
+public:
+    /** @brief The BRISK constructor
+
+    @param thresh AGAST detection threshold score.
+    @param octaves detection octaves. Use 0 to do single scale.
+    @param patternScale apply this scale to the pattern used for sampling the neighbourhood of a
+    keypoint.
+     */
+    CV_WRAP static Ptr<BRISK> create(int thresh=30, int octaves=3, float patternScale=1.0f);
+
+    /** @brief The BRISK constructor for a custom pattern
+
+    @param radiusList defines the radii (in pixels) where the samples around a keypoint are taken (for
+    keypoint scale 1).
+    @param numberList defines the number of sampling points on the sampling circle. Must be the same
+    size as radiusList..
+    @param dMax threshold for the short pairings used for descriptor formation (in pixels for keypoint
+    scale 1).
+    @param dMin threshold for the long pairings used for orientation determination (in pixels for
+    keypoint scale 1).
+    @param indexChange index remapping of the bits. */
+    CV_WRAP static Ptr<BRISK> create(const std::vector<float> &radiusList, const std::vector<int> &numberList,
+        float dMax=5.85f, float dMin=8.2f, const std::vector<int>& indexChange=std::vector<int>());
+};
+
+/** @brief Class implementing the ORB (*oriented BRIEF*) keypoint detector and descriptor extractor
+
+described in @cite RRKB11 . The algorithm uses FAST in pyramids to detect stable keypoints, selects
+the strongest features using FAST or Harris response, finds their orientation using first-order
+moments and computes the descriptors using BRIEF (where the coordinates of random point pairs (or
+k-tuples) are rotated according to the measured orientation).
+ */
+class CV_EXPORTS_W ORB : public Feature2D
+{
+public:
+    enum { kBytes = 32, HARRIS_SCORE=0, FAST_SCORE=1 };
+
+    /** @brief The ORB constructor
+
+    @param nfeatures The maximum number of features to retain.
+    @param scaleFactor Pyramid decimation ratio, greater than 1. scaleFactor==2 means the classical
+    pyramid, where each next level has 4x less pixels than the previous, but such a big scale factor
+    will degrade feature matching scores dramatically. On the other hand, too close to 1 scale factor
+    will mean that to cover certain scale range you will need more pyramid levels and so the speed
+    will suffer.
+    @param nlevels The number of pyramid levels. The smallest level will have linear size equal to
+    input_image_linear_size/pow(scaleFactor, nlevels).
+    @param edgeThreshold This is size of the border where the features are not detected. It should
+    roughly match the patchSize parameter.
+    @param firstLevel It should be 0 in the current implementation.
+    @param WTA_K The number of points that produce each element of the oriented BRIEF descriptor. The
+    default value 2 means the BRIEF where we take a random point pair and compare their brightnesses,
+    so we get 0/1 response. Other possible values are 3 and 4. For example, 3 means that we take 3
+    random points (of course, those point coordinates are random, but they are generated from the
+    pre-defined seed, so each element of BRIEF descriptor is computed deterministically from the pixel
+    rectangle), find point of maximum brightness and output index of the winner (0, 1 or 2). Such
+    output will occupy 2 bits, and therefore it will need a special variant of Hamming distance,
+    denoted as NORM_HAMMING2 (2 bits per bin). When WTA_K=4, we take 4 random points to compute each
+    bin (that will also occupy 2 bits with possible values 0, 1, 2 or 3).
+    @param scoreType The default HARRIS_SCORE means that Harris algorithm is used to rank features
+    (the score is written to KeyPoint::score and is used to retain best nfeatures features);
+    FAST_SCORE is alternative value of the parameter that produces slightly less stable keypoints,
+    but it is a little faster to compute.
+    @param patchSize size of the patch used by the oriented BRIEF descriptor. Of course, on smaller
+    pyramid layers the perceived image area covered by a feature will be larger.
+    @param fastThreshold
+     */
+    CV_WRAP static Ptr<ORB> create(int nfeatures=500, float scaleFactor=1.2f, int nlevels=8, int edgeThreshold=31,
+        int firstLevel=0, int WTA_K=2, int scoreType=ORB::HARRIS_SCORE, int patchSize=31, int fastThreshold=20);
+
+    CV_WRAP virtual void setMaxFeatures(int maxFeatures) = 0;
+    CV_WRAP virtual int getMaxFeatures() const = 0;
+
+    CV_WRAP virtual void setScaleFactor(double scaleFactor) = 0;
+    CV_WRAP virtual double getScaleFactor() const = 0;
+
+    CV_WRAP virtual void setNLevels(int nlevels) = 0;
+    CV_WRAP virtual int getNLevels() const = 0;
+
+    CV_WRAP virtual void setEdgeThreshold(int edgeThreshold) = 0;
+    CV_WRAP virtual int getEdgeThreshold() const = 0;
+
+    CV_WRAP virtual void setFirstLevel(int firstLevel) = 0;
+    CV_WRAP virtual int getFirstLevel() const = 0;
+
+    CV_WRAP virtual void setWTA_K(int wta_k) = 0;
+    CV_WRAP virtual int getWTA_K() const = 0;
+
+    CV_WRAP virtual void setScoreType(int scoreType) = 0;
+    CV_WRAP virtual int getScoreType() const = 0;
+
+    CV_WRAP virtual void setPatchSize(int patchSize) = 0;
+    CV_WRAP virtual int getPatchSize() const = 0;
+
+    CV_WRAP virtual void setFastThreshold(int fastThreshold) = 0;
+    CV_WRAP virtual int getFastThreshold() const = 0;
+};
+
+/** @brief Maximally stable extremal region extractor
+
+The class encapsulates all the parameters of the %MSER extraction algorithm (see [wiki
+article](http://en.wikipedia.org/wiki/Maximally_stable_extremal_regions)).
+
+- there are two different implementation of %MSER: one for grey image, one for color image
+
+- the grey image algorithm is taken from: @cite nister2008linear ;  the paper claims to be faster
+than union-find method; it actually get 1.5~2m/s on my centrino L7200 1.2GHz laptop.
+
+- the color image algorithm is taken from: @cite forssen2007maximally ; it should be much slower
+than grey image method ( 3~4 times ); the chi_table.h file is taken directly from paper's source
+code which is distributed under GPL.
+
+- (Python) A complete example showing the use of the %MSER detector can be found at samples/python/mser.py
+*/
+class CV_EXPORTS_W MSER : public Feature2D
+{
+public:
+    /** @brief Full consturctor for %MSER detector
+
+    @param _delta it compares \f$(size_{i}-size_{i-delta})/size_{i-delta}\f$
+    @param _min_area prune the area which smaller than minArea
+    @param _max_area prune the area which bigger than maxArea
+    @param _max_variation prune the area have simliar size to its children
+    @param _min_diversity for color image, trace back to cut off mser with diversity less than min_diversity
+    @param _max_evolution  for color image, the evolution steps
+    @param _area_threshold for color image, the area threshold to cause re-initialize
+    @param _min_margin for color image, ignore too small margin
+    @param _edge_blur_size for color image, the aperture size for edge blur
+     */
+    CV_WRAP static Ptr<MSER> create( int _delta=5, int _min_area=60, int _max_area=14400,
+          double _max_variation=0.25, double _min_diversity=.2,
+          int _max_evolution=200, double _area_threshold=1.01,
+          double _min_margin=0.003, int _edge_blur_size=5 );
+
+    /** @brief Detect %MSER regions
+
+    @param image input image (8UC1, 8UC3 or 8UC4, must be greater or equal than 3x3)
+    @param msers resulting list of point sets
+    @param bboxes resulting bounding boxes
+    */
+    CV_WRAP virtual void detectRegions( InputArray image,
+                                        CV_OUT std::vector<std::vector<Point> >& msers,
+                                        CV_OUT std::vector<Rect>& bboxes ) = 0;
+
+    CV_WRAP virtual void setDelta(int delta) = 0;
+    CV_WRAP virtual int getDelta() const = 0;
+
+    CV_WRAP virtual void setMinArea(int minArea) = 0;
+    CV_WRAP virtual int getMinArea() const = 0;
+
+    CV_WRAP virtual void setMaxArea(int maxArea) = 0;
+    CV_WRAP virtual int getMaxArea() const = 0;
+
+    CV_WRAP virtual void setPass2Only(bool f) = 0;
+    CV_WRAP virtual bool getPass2Only() const = 0;
+};
+
+/** @overload */
+CV_EXPORTS void FAST( InputArray image, CV_OUT std::vector<KeyPoint>& keypoints,
+                      int threshold, bool nonmaxSuppression=true );
+
+/** @brief Detects corners using the FAST algorithm
+
+@param image grayscale image where keypoints (corners) are detected.
+@param keypoints keypoints detected on the image.
+@param threshold threshold on difference between intensity of the central pixel and pixels of a
+circle around this pixel.
+@param nonmaxSuppression if true, non-maximum suppression is applied to detected corners
+(keypoints).
+@param type one of the three neighborhoods as defined in the paper:
+FastFeatureDetector::TYPE_9_16, FastFeatureDetector::TYPE_7_12,
+FastFeatureDetector::TYPE_5_8
+
+Detects corners using the FAST algorithm by @cite Rosten06 .
+
+@note In Python API, types are given as cv2.FAST_FEATURE_DETECTOR_TYPE_5_8,
+cv2.FAST_FEATURE_DETECTOR_TYPE_7_12 and cv2.FAST_FEATURE_DETECTOR_TYPE_9_16. For corner
+detection, use cv2.FAST.detect() method.
+ */
+CV_EXPORTS void FAST( InputArray image, CV_OUT std::vector<KeyPoint>& keypoints,
+                      int threshold, bool nonmaxSuppression, int type );
+
+//! @} features2d_main
+
+//! @addtogroup features2d_main
+//! @{
+
+/** @brief Wrapping class for feature detection using the FAST method. :
+ */
+class CV_EXPORTS_W FastFeatureDetector : public Feature2D
+{
+public:
+    enum
+    {
+        TYPE_5_8 = 0, TYPE_7_12 = 1, TYPE_9_16 = 2,
+        THRESHOLD = 10000, NONMAX_SUPPRESSION=10001, FAST_N=10002,
+    };
+
+    CV_WRAP static Ptr<FastFeatureDetector> create( int threshold=10,
+                                                    bool nonmaxSuppression=true,
+                                                    int type=FastFeatureDetector::TYPE_9_16 );
+
+    CV_WRAP virtual void setThreshold(int threshold) = 0;
+    CV_WRAP virtual int getThreshold() const = 0;
+
+    CV_WRAP virtual void setNonmaxSuppression(bool f) = 0;
+    CV_WRAP virtual bool getNonmaxSuppression() const = 0;
+
+    CV_WRAP virtual void setType(int type) = 0;
+    CV_WRAP virtual int getType() const = 0;
+};
+
+/** @overload */
+CV_EXPORTS void AGAST( InputArray image, CV_OUT std::vector<KeyPoint>& keypoints,
+                      int threshold, bool nonmaxSuppression=true );
+
+/** @brief Detects corners using the AGAST algorithm
+
+@param image grayscale image where keypoints (corners) are detected.
+@param keypoints keypoints detected on the image.
+@param threshold threshold on difference between intensity of the central pixel and pixels of a
+circle around this pixel.
+@param nonmaxSuppression if true, non-maximum suppression is applied to detected corners
+(keypoints).
+@param type one of the four neighborhoods as defined in the paper:
+AgastFeatureDetector::AGAST_5_8, AgastFeatureDetector::AGAST_7_12d,
+AgastFeatureDetector::AGAST_7_12s, AgastFeatureDetector::OAST_9_16
+
+For non-Intel platforms, there is a tree optimised variant of AGAST with same numerical results.
+The 32-bit binary tree tables were generated automatically from original code using perl script.
+The perl script and examples of tree generation are placed in features2d/doc folder.
+Detects corners using the AGAST algorithm by @cite mair2010_agast .
+
+ */
+CV_EXPORTS void AGAST( InputArray image, CV_OUT std::vector<KeyPoint>& keypoints,
+                      int threshold, bool nonmaxSuppression, int type );
+//! @} features2d_main
+
+//! @addtogroup features2d_main
+//! @{
+
+/** @brief Wrapping class for feature detection using the AGAST method. :
+ */
+class CV_EXPORTS_W AgastFeatureDetector : public Feature2D
+{
+public:
+    enum
+    {
+        AGAST_5_8 = 0, AGAST_7_12d = 1, AGAST_7_12s = 2, OAST_9_16 = 3,
+        THRESHOLD = 10000, NONMAX_SUPPRESSION = 10001,
+    };
+
+    CV_WRAP static Ptr<AgastFeatureDetector> create( int threshold=10,
+                                                     bool nonmaxSuppression=true,
+                                                     int type=AgastFeatureDetector::OAST_9_16 );
+
+    CV_WRAP virtual void setThreshold(int threshold) = 0;
+    CV_WRAP virtual int getThreshold() const = 0;
+
+    CV_WRAP virtual void setNonmaxSuppression(bool f) = 0;
+    CV_WRAP virtual bool getNonmaxSuppression() const = 0;
+
+    CV_WRAP virtual void setType(int type) = 0;
+    CV_WRAP virtual int getType() const = 0;
+};
+
+/** @brief Wrapping class for feature detection using the goodFeaturesToTrack function. :
+ */
+class CV_EXPORTS_W GFTTDetector : public Feature2D
+{
+public:
+    CV_WRAP static Ptr<GFTTDetector> create( int maxCorners=1000, double qualityLevel=0.01, double minDistance=1,
+                                             int blockSize=3, bool useHarrisDetector=false, double k=0.04 );
+    CV_WRAP virtual void setMaxFeatures(int maxFeatures) = 0;
+    CV_WRAP virtual int getMaxFeatures() const = 0;
+
+    CV_WRAP virtual void setQualityLevel(double qlevel) = 0;
+    CV_WRAP virtual double getQualityLevel() const = 0;
+
+    CV_WRAP virtual void setMinDistance(double minDistance) = 0;
+    CV_WRAP virtual double getMinDistance() const = 0;
+
+    CV_WRAP virtual void setBlockSize(int blockSize) = 0;
+    CV_WRAP virtual int getBlockSize() const = 0;
+
+    CV_WRAP virtual void setHarrisDetector(bool val) = 0;
+    CV_WRAP virtual bool getHarrisDetector() const = 0;
+
+    CV_WRAP virtual void setK(double k) = 0;
+    CV_WRAP virtual double getK() const = 0;
+};
+
+/** @brief Class for extracting blobs from an image. :
+
+The class implements a simple algorithm for extracting blobs from an image:
+
+1.  Convert the source image to binary images by applying thresholding with several thresholds from
+    minThreshold (inclusive) to maxThreshold (exclusive) with distance thresholdStep between
+    neighboring thresholds.
+2.  Extract connected components from every binary image by findContours and calculate their
+    centers.
+3.  Group centers from several binary images by their coordinates. Close centers form one group that
+    corresponds to one blob, which is controlled by the minDistBetweenBlobs parameter.
+4.  From the groups, estimate final centers of blobs and their radiuses and return as locations and
+    sizes of keypoints.
+
+This class performs several filtrations of returned blobs. You should set filterBy\* to true/false
+to turn on/off corresponding filtration. Available filtrations:
+
+-   **By color**. This filter compares the intensity of a binary image at the center of a blob to
+blobColor. If they differ, the blob is filtered out. Use blobColor = 0 to extract dark blobs
+and blobColor = 255 to extract light blobs.
+-   **By area**. Extracted blobs have an area between minArea (inclusive) and maxArea (exclusive).
+-   **By circularity**. Extracted blobs have circularity
+(\f$\frac{4*\pi*Area}{perimeter * perimeter}\f$) between minCircularity (inclusive) and
+maxCircularity (exclusive).
+-   **By ratio of the minimum inertia to maximum inertia**. Extracted blobs have this ratio
+between minInertiaRatio (inclusive) and maxInertiaRatio (exclusive).
+-   **By convexity**. Extracted blobs have convexity (area / area of blob convex hull) between
+minConvexity (inclusive) and maxConvexity (exclusive).
+
+Default values of parameters are tuned to extract dark circular blobs.
+ */
+class CV_EXPORTS_W SimpleBlobDetector : public Feature2D
+{
+public:
+  struct CV_EXPORTS_W_SIMPLE Params
+  {
+      CV_WRAP Params();
+      CV_PROP_RW float thresholdStep;
+      CV_PROP_RW float minThreshold;
+      CV_PROP_RW float maxThreshold;
+      CV_PROP_RW size_t minRepeatability;
+      CV_PROP_RW float minDistBetweenBlobs;
+
+      CV_PROP_RW bool filterByColor;
+      CV_PROP_RW uchar blobColor;
+
+      CV_PROP_RW bool filterByArea;
+      CV_PROP_RW float minArea, maxArea;
+
+      CV_PROP_RW bool filterByCircularity;
+      CV_PROP_RW float minCircularity, maxCircularity;
+
+      CV_PROP_RW bool filterByInertia;
+      CV_PROP_RW float minInertiaRatio, maxInertiaRatio;
+
+      CV_PROP_RW bool filterByConvexity;
+      CV_PROP_RW float minConvexity, maxConvexity;
+
+      void read( const FileNode& fn );
+      void write( FileStorage& fs ) const;
+  };
+
+  CV_WRAP static Ptr<SimpleBlobDetector>
+    create(const SimpleBlobDetector::Params &parameters = SimpleBlobDetector::Params());
+};
+
+//! @} features2d_main
+
+//! @addtogroup features2d_main
+//! @{
+
+/** @brief Class implementing the KAZE keypoint detector and descriptor extractor, described in @cite ABD12 .
+
+@note AKAZE descriptor can only be used with KAZE or AKAZE keypoints .. [ABD12] KAZE Features. Pablo
+F. Alcantarilla, Adrien Bartoli and Andrew J. Davison. In European Conference on Computer Vision
+(ECCV), Fiorenze, Italy, October 2012.
+*/
+class CV_EXPORTS_W KAZE : public Feature2D
+{
+public:
+    enum
+    {
+        DIFF_PM_G1 = 0,
+        DIFF_PM_G2 = 1,
+        DIFF_WEICKERT = 2,
+        DIFF_CHARBONNIER = 3
+    };
+
+    /** @brief The KAZE constructor
+
+    @param extended Set to enable extraction of extended (128-byte) descriptor.
+    @param upright Set to enable use of upright descriptors (non rotation-invariant).
+    @param threshold Detector response threshold to accept point
+    @param nOctaves Maximum octave evolution of the image
+    @param nOctaveLayers Default number of sublevels per scale level
+    @param diffusivity Diffusivity type. DIFF_PM_G1, DIFF_PM_G2, DIFF_WEICKERT or
+    DIFF_CHARBONNIER
+     */
+    CV_WRAP static Ptr<KAZE> create(bool extended=false, bool upright=false,
+                                    float threshold = 0.001f,
+                                    int nOctaves = 4, int nOctaveLayers = 4,
+                                    int diffusivity = KAZE::DIFF_PM_G2);
+
+    CV_WRAP virtual void setExtended(bool extended) = 0;
+    CV_WRAP virtual bool getExtended() const = 0;
+
+    CV_WRAP virtual void setUpright(bool upright) = 0;
+    CV_WRAP virtual bool getUpright() const = 0;
+
+    CV_WRAP virtual void setThreshold(double threshold) = 0;
+    CV_WRAP virtual double getThreshold() const = 0;
+
+    CV_WRAP virtual void setNOctaves(int octaves) = 0;
+    CV_WRAP virtual int getNOctaves() const = 0;
+
+    CV_WRAP virtual void setNOctaveLayers(int octaveLayers) = 0;
+    CV_WRAP virtual int getNOctaveLayers() const = 0;
+
+    CV_WRAP virtual void setDiffusivity(int diff) = 0;
+    CV_WRAP virtual int getDiffusivity() const = 0;
+};
+
+/** @brief Class implementing the AKAZE keypoint detector and descriptor extractor, described in @cite ANB13 . :
+
+@note AKAZE descriptors can only be used with KAZE or AKAZE keypoints. Try to avoid using *extract*
+and *detect* instead of *operator()* due to performance reasons. .. [ANB13] Fast Explicit Diffusion
+for Accelerated Features in Nonlinear Scale Spaces. Pablo F. Alcantarilla, Jesús Nuevo and Adrien
+Bartoli. In British Machine Vision Conference (BMVC), Bristol, UK, September 2013.
+ */
+class CV_EXPORTS_W AKAZE : public Feature2D
+{
+public:
+    // AKAZE descriptor type
+    enum
+    {
+        DESCRIPTOR_KAZE_UPRIGHT = 2, ///< Upright descriptors, not invariant to rotation
+        DESCRIPTOR_KAZE = 3,
+        DESCRIPTOR_MLDB_UPRIGHT = 4, ///< Upright descriptors, not invariant to rotation
+        DESCRIPTOR_MLDB = 5
+    };
+
+    /** @brief The AKAZE constructor
+
+    @param descriptor_type Type of the extracted descriptor: DESCRIPTOR_KAZE,
+    DESCRIPTOR_KAZE_UPRIGHT, DESCRIPTOR_MLDB or DESCRIPTOR_MLDB_UPRIGHT.
+    @param descriptor_size Size of the descriptor in bits. 0 -\> Full size
+    @param descriptor_channels Number of channels in the descriptor (1, 2, 3)
+    @param threshold Detector response threshold to accept point
+    @param nOctaves Maximum octave evolution of the image
+    @param nOctaveLayers Default number of sublevels per scale level
+    @param diffusivity Diffusivity type. DIFF_PM_G1, DIFF_PM_G2, DIFF_WEICKERT or
+    DIFF_CHARBONNIER
+     */
+    CV_WRAP static Ptr<AKAZE> create(int descriptor_type=AKAZE::DESCRIPTOR_MLDB,
+                                     int descriptor_size = 0, int descriptor_channels = 3,
+                                     float threshold = 0.001f, int nOctaves = 4,
+                                     int nOctaveLayers = 4, int diffusivity = KAZE::DIFF_PM_G2);
+
+    CV_WRAP virtual void setDescriptorType(int dtype) = 0;
+    CV_WRAP virtual int getDescriptorType() const = 0;
+
+    CV_WRAP virtual void setDescriptorSize(int dsize) = 0;
+    CV_WRAP virtual int getDescriptorSize() const = 0;
+
+    CV_WRAP virtual void setDescriptorChannels(int dch) = 0;
+    CV_WRAP virtual int getDescriptorChannels() const = 0;
+
+    CV_WRAP virtual void setThreshold(double threshold) = 0;
+    CV_WRAP virtual double getThreshold() const = 0;
+
+    CV_WRAP virtual void setNOctaves(int octaves) = 0;
+    CV_WRAP virtual int getNOctaves() const = 0;
+
+    CV_WRAP virtual void setNOctaveLayers(int octaveLayers) = 0;
+    CV_WRAP virtual int getNOctaveLayers() const = 0;
+
+    CV_WRAP virtual void setDiffusivity(int diff) = 0;
+    CV_WRAP virtual int getDiffusivity() const = 0;
+};
+
+//! @} features2d_main
+
+/****************************************************************************************\
+*                                      Distance                                          *
+\****************************************************************************************/
+
+template<typename T>
+struct CV_EXPORTS Accumulator
+{
+    typedef T Type;
+};
+
+template<> struct Accumulator<unsigned char>  { typedef float Type; };
+template<> struct Accumulator<unsigned short> { typedef float Type; };
+template<> struct Accumulator<char>   { typedef float Type; };
+template<> struct Accumulator<short>  { typedef float Type; };
+
+/*
+ * Squared Euclidean distance functor
+ */
+template<class T>
+struct CV_EXPORTS SL2
+{
+    enum { normType = NORM_L2SQR };
+    typedef T ValueType;
+    typedef typename Accumulator<T>::Type ResultType;
+
+    ResultType operator()( const T* a, const T* b, int size ) const
+    {
+        return normL2Sqr<ValueType, ResultType>(a, b, size);
+    }
+};
+
+/*
+ * Euclidean distance functor
+ */
+template<class T>
+struct CV_EXPORTS L2
+{
+    enum { normType = NORM_L2 };
+    typedef T ValueType;
+    typedef typename Accumulator<T>::Type ResultType;
+
+    ResultType operator()( const T* a, const T* b, int size ) const
+    {
+        return (ResultType)std::sqrt((double)normL2Sqr<ValueType, ResultType>(a, b, size));
+    }
+};
+
+/*
+ * Manhattan distance (city block distance) functor
+ */
+template<class T>
+struct CV_EXPORTS L1
+{
+    enum { normType = NORM_L1 };
+    typedef T ValueType;
+    typedef typename Accumulator<T>::Type ResultType;
+
+    ResultType operator()( const T* a, const T* b, int size ) const
+    {
+        return normL1<ValueType, ResultType>(a, b, size);
+    }
+};
+
+/****************************************************************************************\
+*                                  DescriptorMatcher                                     *
+\****************************************************************************************/
+
+//! @addtogroup features2d_match
+//! @{
+
+/** @brief Abstract base class for matching keypoint descriptors.
+
+It has two groups of match methods: for matching descriptors of an image with another image or with
+an image set.
+ */
+class CV_EXPORTS_W DescriptorMatcher : public Algorithm
+{
+public:
+   enum
+    {
+        FLANNBASED            = 1,
+        BRUTEFORCE            = 2,
+        BRUTEFORCE_L1         = 3,
+        BRUTEFORCE_HAMMING    = 4,
+        BRUTEFORCE_HAMMINGLUT = 5,
+        BRUTEFORCE_SL2        = 6
+    };
+    virtual ~DescriptorMatcher();
+
+    /** @brief Adds descriptors to train a CPU(trainDescCollectionis) or GPU(utrainDescCollectionis) descriptor
+    collection.
+
+    If the collection is not empty, the new descriptors are added to existing train descriptors.
+
+    @param descriptors Descriptors to add. Each descriptors[i] is a set of descriptors from the same
+    train image.
+     */
+    CV_WRAP virtual void add( InputArrayOfArrays descriptors );
+
+    /** @brief Returns a constant link to the train descriptor collection trainDescCollection .
+     */
+    CV_WRAP const std::vector<Mat>& getTrainDescriptors() const;
+
+    /** @brief Clears the train descriptor collections.
+     */
+    CV_WRAP virtual void clear();
+
+    /** @brief Returns true if there are no train descriptors in the both collections.
+     */
+    CV_WRAP virtual bool empty() const;
+
+    /** @brief Returns true if the descriptor matcher supports masking permissible matches.
+     */
+    CV_WRAP virtual bool isMaskSupported() const = 0;
+
+    /** @brief Trains a descriptor matcher
+
+    Trains a descriptor matcher (for example, the flann index). In all methods to match, the method
+    train() is run every time before matching. Some descriptor matchers (for example, BruteForceMatcher)
+    have an empty implementation of this method. Other matchers really train their inner structures (for
+    example, FlannBasedMatcher trains flann::Index ).
+     */
+    CV_WRAP virtual void train();
+
+    /** @brief Finds the best match for each descriptor from a query set.
+
+    @param queryDescriptors Query set of descriptors.
+    @param trainDescriptors Train set of descriptors. This set is not added to the train descriptors
+    collection stored in the class object.
+    @param matches Matches. If a query descriptor is masked out in mask , no match is added for this
+    descriptor. So, matches size may be smaller than the query descriptors count.
+    @param mask Mask specifying permissible matches between an input query and train matrices of
+    descriptors.
+
+    In the first variant of this method, the train descriptors are passed as an input argument. In the
+    second variant of the method, train descriptors collection that was set by DescriptorMatcher::add is
+    used. Optional mask (or masks) can be passed to specify which query and training descriptors can be
+    matched. Namely, queryDescriptors[i] can be matched with trainDescriptors[j] only if
+    mask.at\<uchar\>(i,j) is non-zero.
+     */
+    CV_WRAP void match( InputArray queryDescriptors, InputArray trainDescriptors,
+                CV_OUT std::vector<DMatch>& matches, InputArray mask=noArray() ) const;
+
+    /** @brief Finds the k best matches for each descriptor from a query set.
+
+    @param queryDescriptors Query set of descriptors.
+    @param trainDescriptors Train set of descriptors. This set is not added to the train descriptors
+    collection stored in the class object.
+    @param mask Mask specifying permissible matches between an input query and train matrices of
+    descriptors.
+    @param matches Matches. Each matches[i] is k or less matches for the same query descriptor.
+    @param k Count of best matches found per each query descriptor or less if a query descriptor has
+    less than k possible matches in total.
+    @param compactResult Parameter used when the mask (or masks) is not empty. If compactResult is
+    false, the matches vector has the same size as queryDescriptors rows. If compactResult is true,
+    the matches vector does not contain matches for fully masked-out query descriptors.
+
+    These extended variants of DescriptorMatcher::match methods find several best matches for each query
+    descriptor. The matches are returned in the distance increasing order. See DescriptorMatcher::match
+    for the details about query and train descriptors.
+     */
+    CV_WRAP void knnMatch( InputArray queryDescriptors, InputArray trainDescriptors,
+                   CV_OUT std::vector<std::vector<DMatch> >& matches, int k,
+                   InputArray mask=noArray(), bool compactResult=false ) const;
+
+    /** @brief For each query descriptor, finds the training descriptors not farther than the specified distance.
+
+    @param queryDescriptors Query set of descriptors.
+    @param trainDescriptors Train set of descriptors. This set is not added to the train descriptors
+    collection stored in the class object.
+    @param matches Found matches.
+    @param compactResult Parameter used when the mask (or masks) is not empty. If compactResult is
+    false, the matches vector has the same size as queryDescriptors rows. If compactResult is true,
+    the matches vector does not contain matches for fully masked-out query descriptors.
+    @param maxDistance Threshold for the distance between matched descriptors. Distance means here
+    metric distance (e.g. Hamming distance), not the distance between coordinates (which is measured
+    in Pixels)!
+    @param mask Mask specifying permissible matches between an input query and train matrices of
+    descriptors.
+
+    For each query descriptor, the methods find such training descriptors that the distance between the
+    query descriptor and the training descriptor is equal or smaller than maxDistance. Found matches are
+    returned in the distance increasing order.
+     */
+    CV_WRAP void radiusMatch( InputArray queryDescriptors, InputArray trainDescriptors,
+                      CV_OUT std::vector<std::vector<DMatch> >& matches, float maxDistance,
+                      InputArray mask=noArray(), bool compactResult=false ) const;
+
+    /** @overload
+    @param queryDescriptors Query set of descriptors.
+    @param matches Matches. If a query descriptor is masked out in mask , no match is added for this
+    descriptor. So, matches size may be smaller than the query descriptors count.
+    @param masks Set of masks. Each masks[i] specifies permissible matches between the input query
+    descriptors and stored train descriptors from the i-th image trainDescCollection[i].
+    */
+    CV_WRAP void match( InputArray queryDescriptors, CV_OUT std::vector<DMatch>& matches,
+                        InputArrayOfArrays masks=noArray() );
+    /** @overload
+    @param queryDescriptors Query set of descriptors.
+    @param matches Matches. Each matches[i] is k or less matches for the same query descriptor.
+    @param k Count of best matches found per each query descriptor or less if a query descriptor has
+    less than k possible matches in total.
+    @param masks Set of masks. Each masks[i] specifies permissible matches between the input query
+    descriptors and stored train descriptors from the i-th image trainDescCollection[i].
+    @param compactResult Parameter used when the mask (or masks) is not empty. If compactResult is
+    false, the matches vector has the same size as queryDescriptors rows. If compactResult is true,
+    the matches vector does not contain matches for fully masked-out query descriptors.
+    */
+    CV_WRAP void knnMatch( InputArray queryDescriptors, CV_OUT std::vector<std::vector<DMatch> >& matches, int k,
+                           InputArrayOfArrays masks=noArray(), bool compactResult=false );
+    /** @overload
+    @param queryDescriptors Query set of descriptors.
+    @param matches Found matches.
+    @param maxDistance Threshold for the distance between matched descriptors. Distance means here
+    metric distance (e.g. Hamming distance), not the distance between coordinates (which is measured
+    in Pixels)!
+    @param masks Set of masks. Each masks[i] specifies permissible matches between the input query
+    descriptors and stored train descriptors from the i-th image trainDescCollection[i].
+    @param compactResult Parameter used when the mask (or masks) is not empty. If compactResult is
+    false, the matches vector has the same size as queryDescriptors rows. If compactResult is true,
+    the matches vector does not contain matches for fully masked-out query descriptors.
+    */
+    CV_WRAP void radiusMatch( InputArray queryDescriptors, CV_OUT std::vector<std::vector<DMatch> >& matches, float maxDistance,
+                      InputArrayOfArrays masks=noArray(), bool compactResult=false );
+
+
+    CV_WRAP void write( const String& fileName ) const
+    {
+        FileStorage fs(fileName, FileStorage::WRITE);
+        write(fs);
+    }
+
+    CV_WRAP void read( const String& fileName )
+    {
+        FileStorage fs(fileName, FileStorage::READ);
+        read(fs.root());
+    }
+    // Reads matcher object from a file node
+    virtual void read( const FileNode& );
+    // Writes matcher object to a file storage
+    virtual void write( FileStorage& ) const;
+
+    /** @brief Clones the matcher.
+
+    @param emptyTrainData If emptyTrainData is false, the method creates a deep copy of the object,
+    that is, copies both parameters and train data. If emptyTrainData is true, the method creates an
+    object copy with the current parameters but with empty train data.
+     */
+    CV_WRAP virtual Ptr<DescriptorMatcher> clone( bool emptyTrainData=false ) const = 0;
+
+    /** @brief Creates a descriptor matcher of a given type with the default parameters (using default
+    constructor).
+
+    @param descriptorMatcherType Descriptor matcher type. Now the following matcher types are
+    supported:
+    -   `BruteForce` (it uses L2 )
+    -   `BruteForce-L1`
+    -   `BruteForce-Hamming`
+    -   `BruteForce-Hamming(2)`
+    -   `FlannBased`
+     */
+    CV_WRAP static Ptr<DescriptorMatcher> create( const String& descriptorMatcherType );
+
+    CV_WRAP static Ptr<DescriptorMatcher> create( int matcherType );
+
+protected:
+    /**
+     * Class to work with descriptors from several images as with one merged matrix.
+     * It is used e.g. in FlannBasedMatcher.
+     */
+    class CV_EXPORTS DescriptorCollection
+    {
+    public:
+        DescriptorCollection();
+        DescriptorCollection( const DescriptorCollection& collection );
+        virtual ~DescriptorCollection();
+
+        // Vector of matrices "descriptors" will be merged to one matrix "mergedDescriptors" here.
+        void set( const std::vector<Mat>& descriptors );
+        virtual void clear();
+
+        const Mat& getDescriptors() const;
+        const Mat getDescriptor( int imgIdx, int localDescIdx ) const;
+        const Mat getDescriptor( int globalDescIdx ) const;
+        void getLocalIdx( int globalDescIdx, int& imgIdx, int& localDescIdx ) const;
+
+        int size() const;
+
+    protected:
+        Mat mergedDescriptors;
+        std::vector<int> startIdxs;
+    };
+
+    //! In fact the matching is implemented only by the following two methods. These methods suppose
+    //! that the class object has been trained already. Public match methods call these methods
+    //! after calling train().
+    virtual void knnMatchImpl( InputArray queryDescriptors, std::vector<std::vector<DMatch> >& matches, int k,
+        InputArrayOfArrays masks=noArray(), bool compactResult=false ) = 0;
+    virtual void radiusMatchImpl( InputArray queryDescriptors, std::vector<std::vector<DMatch> >& matches, float maxDistance,
+        InputArrayOfArrays masks=noArray(), bool compactResult=false ) = 0;
+
+    static bool isPossibleMatch( InputArray mask, int queryIdx, int trainIdx );
+    static bool isMaskedOut( InputArrayOfArrays masks, int queryIdx );
+
+    static Mat clone_op( Mat m ) { return m.clone(); }
+    void checkMasks( InputArrayOfArrays masks, int queryDescriptorsCount ) const;
+
+    //! Collection of descriptors from train images.
+    std::vector<Mat> trainDescCollection;
+    std::vector<UMat> utrainDescCollection;
+};
+
+/** @brief Brute-force descriptor matcher.
+
+For each descriptor in the first set, this matcher finds the closest descriptor in the second set
+by trying each one. This descriptor matcher supports masking permissible matches of descriptor
+sets.
+ */
+class CV_EXPORTS_W BFMatcher : public DescriptorMatcher
+{
+public:
+    /** @brief Brute-force matcher constructor (obsolete). Please use BFMatcher.create()
+     *
+     *
+    */
+    CV_WRAP BFMatcher( int normType=NORM_L2, bool crossCheck=false );
+
+    virtual ~BFMatcher() {}
+
+    virtual bool isMaskSupported() const { return true; }
+
+    /* @brief Brute-force matcher create method.
+    @param normType One of NORM_L1, NORM_L2, NORM_HAMMING, NORM_HAMMING2. L1 and L2 norms are
+    preferable choices for SIFT and SURF descriptors, NORM_HAMMING should be used with ORB, BRISK and
+    BRIEF, NORM_HAMMING2 should be used with ORB when WTA_K==3 or 4 (see ORB::ORB constructor
+    description).
+    @param crossCheck If it is false, this is will be default BFMatcher behaviour when it finds the k
+    nearest neighbors for each query descriptor. If crossCheck==true, then the knnMatch() method with
+    k=1 will only return pairs (i,j) such that for i-th query descriptor the j-th descriptor in the
+    matcher's collection is the nearest and vice versa, i.e. the BFMatcher will only return consistent
+    pairs. Such technique usually produces best results with minimal number of outliers when there are
+    enough matches. This is alternative to the ratio test, used by D. Lowe in SIFT paper.
+     */
+    CV_WRAP static Ptr<BFMatcher> create( int normType=NORM_L2, bool crossCheck=false ) ;
+
+    virtual Ptr<DescriptorMatcher> clone( bool emptyTrainData=false ) const;
+protected:
+    virtual void knnMatchImpl( InputArray queryDescriptors, std::vector<std::vector<DMatch> >& matches, int k,
+        InputArrayOfArrays masks=noArray(), bool compactResult=false );
+    virtual void radiusMatchImpl( InputArray queryDescriptors, std::vector<std::vector<DMatch> >& matches, float maxDistance,
+        InputArrayOfArrays masks=noArray(), bool compactResult=false );
+
+    int normType;
+    bool crossCheck;
+};
+
+
+/** @brief Flann-based descriptor matcher.
+
+This matcher trains cv::flann::Index on a train descriptor collection and calls its nearest search
+methods to find the best matches. So, this matcher may be faster when matching a large train
+collection than the brute force matcher. FlannBasedMatcher does not support masking permissible
+matches of descriptor sets because flann::Index does not support this. :
+ */
+class CV_EXPORTS_W FlannBasedMatcher : public DescriptorMatcher
+{
+public:
+    CV_WRAP FlannBasedMatcher( const Ptr<flann::IndexParams>& indexParams=makePtr<flann::KDTreeIndexParams>(),
+                       const Ptr<flann::SearchParams>& searchParams=makePtr<flann::SearchParams>() );
+
+    virtual void add( InputArrayOfArrays descriptors );
+    virtual void clear();
+
+    // Reads matcher object from a file node
+    virtual void read( const FileNode& );
+    // Writes matcher object to a file storage
+    virtual void write( FileStorage& ) const;
+
+    virtual void train();
+    virtual bool isMaskSupported() const;
+
+    CV_WRAP static Ptr<FlannBasedMatcher> create();
+
+    virtual Ptr<DescriptorMatcher> clone( bool emptyTrainData=false ) const;
+protected:
+    static void convertToDMatches( const DescriptorCollection& descriptors,
+                                   const Mat& indices, const Mat& distances,
+                                   std::vector<std::vector<DMatch> >& matches );
+
+    virtual void knnMatchImpl( InputArray queryDescriptors, std::vector<std::vector<DMatch> >& matches, int k,
+        InputArrayOfArrays masks=noArray(), bool compactResult=false );
+    virtual void radiusMatchImpl( InputArray queryDescriptors, std::vector<std::vector<DMatch> >& matches, float maxDistance,
+        InputArrayOfArrays masks=noArray(), bool compactResult=false );
+
+    Ptr<flann::IndexParams> indexParams;
+    Ptr<flann::SearchParams> searchParams;
+    Ptr<flann::Index> flannIndex;
+
+    DescriptorCollection mergedDescriptors;
+    int addedDescCount;
+};
+
+//! @} features2d_match
+
+/****************************************************************************************\
+*                                   Drawing functions                                    *
+\****************************************************************************************/
+
+//! @addtogroup features2d_draw
+//! @{
+
+struct CV_EXPORTS DrawMatchesFlags
+{
+    enum{ DEFAULT = 0, //!< Output image matrix will be created (Mat::create),
+                       //!< i.e. existing memory of output image may be reused.
+                       //!< Two source image, matches and single keypoints will be drawn.
+                       //!< For each keypoint only the center point will be drawn (without
+                       //!< the circle around keypoint with keypoint size and orientation).
+          DRAW_OVER_OUTIMG = 1, //!< Output image matrix will not be created (Mat::create).
+                                //!< Matches will be drawn on existing content of output image.
+          NOT_DRAW_SINGLE_POINTS = 2, //!< Single keypoints will not be drawn.
+          DRAW_RICH_KEYPOINTS = 4 //!< For each keypoint the circle around keypoint with keypoint size and
+                                  //!< orientation will be drawn.
+        };
+};
+
+/** @brief Draws keypoints.
+
+@param image Source image.
+@param keypoints Keypoints from the source image.
+@param outImage Output image. Its content depends on the flags value defining what is drawn in the
+output image. See possible flags bit values below.
+@param color Color of keypoints.
+@param flags Flags setting drawing features. Possible flags bit values are defined by
+DrawMatchesFlags. See details above in drawMatches .
+
+@note
+For Python API, flags are modified as cv2.DRAW_MATCHES_FLAGS_DEFAULT,
+cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS, cv2.DRAW_MATCHES_FLAGS_DRAW_OVER_OUTIMG,
+cv2.DRAW_MATCHES_FLAGS_NOT_DRAW_SINGLE_POINTS
+ */
+CV_EXPORTS_W void drawKeypoints( InputArray image, const std::vector<KeyPoint>& keypoints, InputOutputArray outImage,
+                               const Scalar& color=Scalar::all(-1), int flags=DrawMatchesFlags::DEFAULT );
+
+/** @brief Draws the found matches of keypoints from two images.
+
+@param img1 First source image.
+@param keypoints1 Keypoints from the first source image.
+@param img2 Second source image.
+@param keypoints2 Keypoints from the second source image.
+@param matches1to2 Matches from the first image to the second one, which means that keypoints1[i]
+has a corresponding point in keypoints2[matches[i]] .
+@param outImg Output image. Its content depends on the flags value defining what is drawn in the
+output image. See possible flags bit values below.
+@param matchColor Color of matches (lines and connected keypoints). If matchColor==Scalar::all(-1)
+, the color is generated randomly.
+@param singlePointColor Color of single keypoints (circles), which means that keypoints do not
+have the matches. If singlePointColor==Scalar::all(-1) , the color is generated randomly.
+@param matchesMask Mask determining which matches are drawn. If the mask is empty, all matches are
+drawn.
+@param flags Flags setting drawing features. Possible flags bit values are defined by
+DrawMatchesFlags.
+
+This function draws matches of keypoints from two images in the output image. Match is a line
+connecting two keypoints (circles). See cv::DrawMatchesFlags.
+ */
+CV_EXPORTS_W void drawMatches( InputArray img1, const std::vector<KeyPoint>& keypoints1,
+                             InputArray img2, const std::vector<KeyPoint>& keypoints2,
+                             const std::vector<DMatch>& matches1to2, InputOutputArray outImg,
+                             const Scalar& matchColor=Scalar::all(-1), const Scalar& singlePointColor=Scalar::all(-1),
+                             const std::vector<char>& matchesMask=std::vector<char>(), int flags=DrawMatchesFlags::DEFAULT );
+
+/** @overload */
+CV_EXPORTS_AS(drawMatchesKnn) void drawMatches( InputArray img1, const std::vector<KeyPoint>& keypoints1,
+                             InputArray img2, const std::vector<KeyPoint>& keypoints2,
+                             const std::vector<std::vector<DMatch> >& matches1to2, InputOutputArray outImg,
+                             const Scalar& matchColor=Scalar::all(-1), const Scalar& singlePointColor=Scalar::all(-1),
+                             const std::vector<std::vector<char> >& matchesMask=std::vector<std::vector<char> >(), int flags=DrawMatchesFlags::DEFAULT );
+
+//! @} features2d_draw
+
+/****************************************************************************************\
+*   Functions to evaluate the feature detectors and [generic] descriptor extractors      *
+\****************************************************************************************/
+
+CV_EXPORTS void evaluateFeatureDetector( const Mat& img1, const Mat& img2, const Mat& H1to2,
+                                         std::vector<KeyPoint>* keypoints1, std::vector<KeyPoint>* keypoints2,
+                                         float& repeatability, int& correspCount,
+                                         const Ptr<FeatureDetector>& fdetector=Ptr<FeatureDetector>() );
+
+CV_EXPORTS void computeRecallPrecisionCurve( const std::vector<std::vector<DMatch> >& matches1to2,
+                                             const std::vector<std::vector<uchar> >& correctMatches1to2Mask,
+                                             std::vector<Point2f>& recallPrecisionCurve );
+
+CV_EXPORTS float getRecall( const std::vector<Point2f>& recallPrecisionCurve, float l_precision );
+CV_EXPORTS int getNearestPoint( const std::vector<Point2f>& recallPrecisionCurve, float l_precision );
+
+/****************************************************************************************\
+*                                     Bag of visual words                                *
+\****************************************************************************************/
+
+//! @addtogroup features2d_category
+//! @{
+
+/** @brief Abstract base class for training the *bag of visual words* vocabulary from a set of descriptors.
+
+For details, see, for example, *Visual Categorization with Bags of Keypoints* by Gabriella Csurka,
+Christopher R. Dance, Lixin Fan, Jutta Willamowski, Cedric Bray, 2004. :
+ */
+class CV_EXPORTS_W BOWTrainer
+{
+public:
+    BOWTrainer();
+    virtual ~BOWTrainer();
+
+    /** @brief Adds descriptors to a training set.
+
+    @param descriptors Descriptors to add to a training set. Each row of the descriptors matrix is a
+    descriptor.
+
+    The training set is clustered using clustermethod to construct the vocabulary.
+     */
+    CV_WRAP void add( const Mat& descriptors );
+
+    /** @brief Returns a training set of descriptors.
+    */
+    CV_WRAP const std::vector<Mat>& getDescriptors() const;
+
+    /** @brief Returns the count of all descriptors stored in the training set.
+    */
+    CV_WRAP int descriptorsCount() const;
+
+    CV_WRAP virtual void clear();
+
+    /** @overload */
+    CV_WRAP virtual Mat cluster() const = 0;
+
+    /** @brief Clusters train descriptors.
+
+    @param descriptors Descriptors to cluster. Each row of the descriptors matrix is a descriptor.
+    Descriptors are not added to the inner train descriptor set.
+
+    The vocabulary consists of cluster centers. So, this method returns the vocabulary. In the first
+    variant of the method, train descriptors stored in the object are clustered. In the second variant,
+    input descriptors are clustered.
+     */
+    CV_WRAP virtual Mat cluster( const Mat& descriptors ) const = 0;
+
+protected:
+    std::vector<Mat> descriptors;
+    int size;
+};
+
+/** @brief kmeans -based class to train visual vocabulary using the *bag of visual words* approach. :
+ */
+class CV_EXPORTS_W BOWKMeansTrainer : public BOWTrainer
+{
+public:
+    /** @brief The constructor.
+
+    @see cv::kmeans
+    */
+    CV_WRAP BOWKMeansTrainer( int clusterCount, const TermCriteria& termcrit=TermCriteria(),
+                      int attempts=3, int flags=KMEANS_PP_CENTERS );
+    virtual ~BOWKMeansTrainer();
+
+    // Returns trained vocabulary (i.e. cluster centers).
+    CV_WRAP virtual Mat cluster() const;
+    CV_WRAP virtual Mat cluster( const Mat& descriptors ) const;
+
+protected:
+
+    int clusterCount;
+    TermCriteria termcrit;
+    int attempts;
+    int flags;
+};
+
+/** @brief Class to compute an image descriptor using the *bag of visual words*.
+
+Such a computation consists of the following steps:
+
+1.  Compute descriptors for a given image and its keypoints set.
+2.  Find the nearest visual words from the vocabulary for each keypoint descriptor.
+3.  Compute the bag-of-words image descriptor as is a normalized histogram of vocabulary words
+encountered in the image. The i-th bin of the histogram is a frequency of i-th word of the
+vocabulary in the given image.
+ */
+class CV_EXPORTS_W BOWImgDescriptorExtractor
+{
+public:
+    /** @brief The constructor.
+
+    @param dextractor Descriptor extractor that is used to compute descriptors for an input image and
+    its keypoints.
+    @param dmatcher Descriptor matcher that is used to find the nearest word of the trained vocabulary
+    for each keypoint descriptor of the image.
+     */
+    CV_WRAP BOWImgDescriptorExtractor( const Ptr<DescriptorExtractor>& dextractor,
+                               const Ptr<DescriptorMatcher>& dmatcher );
+    /** @overload */
+    BOWImgDescriptorExtractor( const Ptr<DescriptorMatcher>& dmatcher );
+    virtual ~BOWImgDescriptorExtractor();
+
+    /** @brief Sets a visual vocabulary.
+
+    @param vocabulary Vocabulary (can be trained using the inheritor of BOWTrainer ). Each row of the
+    vocabulary is a visual word (cluster center).
+     */
+    CV_WRAP void setVocabulary( const Mat& vocabulary );
+
+    /** @brief Returns the set vocabulary.
+    */
+    CV_WRAP const Mat& getVocabulary() const;
+
+    /** @brief Computes an image descriptor using the set visual vocabulary.
+
+    @param image Image, for which the descriptor is computed.
+    @param keypoints Keypoints detected in the input image.
+    @param imgDescriptor Computed output image descriptor.
+    @param pointIdxsOfClusters Indices of keypoints that belong to the cluster. This means that
+    pointIdxsOfClusters[i] are keypoint indices that belong to the i -th cluster (word of vocabulary)
+    returned if it is non-zero.
+    @param descriptors Descriptors of the image keypoints that are returned if they are non-zero.
+     */
+    void compute( InputArray image, std::vector<KeyPoint>& keypoints, OutputArray imgDescriptor,
+                  std::vector<std::vector<int> >* pointIdxsOfClusters=0, Mat* descriptors=0 );
+    /** @overload
+    @param keypointDescriptors Computed descriptors to match with vocabulary.
+    @param imgDescriptor Computed output image descriptor.
+    @param pointIdxsOfClusters Indices of keypoints that belong to the cluster. This means that
+    pointIdxsOfClusters[i] are keypoint indices that belong to the i -th cluster (word of vocabulary)
+    returned if it is non-zero.
+    */
+    void compute( InputArray keypointDescriptors, OutputArray imgDescriptor,
+                  std::vector<std::vector<int> >* pointIdxsOfClusters=0 );
+    // compute() is not constant because DescriptorMatcher::match is not constant
+
+    CV_WRAP_AS(compute) void compute2( const Mat& image, std::vector<KeyPoint>& keypoints, CV_OUT Mat& imgDescriptor )
+    { compute(image,keypoints,imgDescriptor); }
+
+    /** @brief Returns an image descriptor size if the vocabulary is set. Otherwise, it returns 0.
+    */
+    CV_WRAP int descriptorSize() const;
+
+    /** @brief Returns an image descriptor type.
+     */
+    CV_WRAP int descriptorType() const;
+
+protected:
+    Mat vocabulary;
+    Ptr<DescriptorExtractor> dextractor;
+    Ptr<DescriptorMatcher> dmatcher;
+};
+
+//! @} features2d_category
+
+//! @} features2d
+
+} /* namespace cv */
+
+#endif