1 Common Interfaces of Descriptor Extractors
2 ==========================================
6 Extractors of keypoint descriptors in OpenCV have wrappers with a common interface that enables you to easily switch
7 between different algorithms solving the same problem. This section is devoted to computing descriptors
8 represented as vectors in a multidimensional space. All objects that implement the ``vector``
9 descriptor extractors inherit the
10 :ocv:class:`DescriptorExtractor` interface.
16 .. ocv:class:: DescriptorExtractor : public Algorithm
18 Abstract base class for computing descriptors for image keypoints. ::
20 class CV_EXPORTS DescriptorExtractor
23 virtual ~DescriptorExtractor();
25 void compute( const Mat& image, vector<KeyPoint>& keypoints,
26 Mat& descriptors ) const;
27 void compute( const vector<Mat>& images, vector<vector<KeyPoint> >& keypoints,
28 vector<Mat>& descriptors ) const;
30 virtual void read( const FileNode& );
31 virtual void write( FileStorage& ) const;
33 virtual int descriptorSize() const = 0;
34 virtual int descriptorType() const = 0;
36 static Ptr<DescriptorExtractor> create( const string& descriptorExtractorType );
43 In this interface, a keypoint descriptor can be represented as a
44 dense, fixed-dimension vector of a basic type. Most descriptors
45 follow this pattern as it simplifies computing
46 distances between descriptors. Therefore, a collection of
47 descriptors is represented as
48 :ocv:class:`Mat` , where each row is a keypoint descriptor.
52 DescriptorExtractor::compute
53 --------------------------------
54 Computes the descriptors for a set of keypoints detected in an image (first variant) or image set (second variant).
56 .. ocv:function:: void DescriptorExtractor::compute( const Mat& image, vector<KeyPoint>& keypoints, Mat& descriptors ) const
58 .. ocv:function:: void DescriptorExtractor::compute( const vector<Mat>& images, vector<vector<KeyPoint> >& keypoints, vector<Mat>& descriptors ) const
62 :param images: Image set.
64 :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).
66 :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.
69 DescriptorExtractor::create
70 -------------------------------
71 Creates a descriptor extractor by name.
73 .. ocv:function:: Ptr<DescriptorExtractor> DescriptorExtractor::create( const string& descriptorExtractorType )
75 :param descriptorExtractorType: Descriptor extractor type.
77 The current implementation supports the following types of a descriptor extractor:
79 * ``"SIFT"`` -- :ocv:class:`SIFT`
80 * ``"SURF"`` -- :ocv:class:`SURF`
81 * ``"ORB"`` -- :ocv:class:`ORB`
82 * ``"BRISK"`` -- :ocv:class:`BRISK`
83 * ``"BRIEF"`` -- :ocv:class:`BriefDescriptorExtractor`
85 A combined format is also supported: descriptor extractor adapter name ( ``"Opponent"`` --
86 :ocv:class:`OpponentColorDescriptorExtractor` ) + descriptor extractor name (see above),
87 for example: ``"OpponentSIFT"`` .
90 OpponentColorDescriptorExtractor
91 --------------------------------
92 .. ocv:class:: OpponentColorDescriptorExtractor : public DescriptorExtractor
94 Class adapting a descriptor extractor to compute descriptors in the Opponent Color Space
95 (refer to Van de Sande et al., CGIV 2008 *Color Descriptors for Object Category Recognition*).
96 Input RGB image is transformed in the Opponent Color Space. Then, an unadapted descriptor extractor
97 (set in the constructor) computes descriptors on each of three channels and concatenates
98 them into a single color descriptor. ::
100 class OpponentColorDescriptorExtractor : public DescriptorExtractor
103 OpponentColorDescriptorExtractor( const Ptr<DescriptorExtractor>& dextractor );
105 virtual void read( const FileNode& );
106 virtual void write( FileStorage& ) const;
107 virtual int descriptorSize() const;
108 virtual int descriptorType() const;
115 BriefDescriptorExtractor
116 ------------------------
117 .. ocv:class:: BriefDescriptorExtractor : public DescriptorExtractor
119 Class for computing BRIEF descriptors described in a paper of Calonder M., Lepetit V.,
120 Strecha C., Fua P. *BRIEF: Binary Robust Independent Elementary Features* ,
121 11th European Conference on Computer Vision (ECCV), Heraklion, Crete. LNCS Springer, September 2010. ::
123 class BriefDescriptorExtractor : public DescriptorExtractor
126 static const int PATCH_SIZE = 48;
127 static const int KERNEL_SIZE = 9;
129 // bytes is a length of descriptor in bytes. It can be equal 16, 32 or 64 bytes.
130 BriefDescriptorExtractor( int bytes = 32 );
132 virtual void read( const FileNode& );
133 virtual void write( FileStorage& ) const;
134 virtual int descriptorSize() const;
135 virtual int descriptorType() const;