学步园

OpenCV中ORB的类定义

class ORB
{
public:
    /** The patch sizes that can be used (only one right now) */
    struct CommonParams
    {
        enum { DEFAULT_N_LEVELS = 3, DEFAULT_FIRST_LEVEL = 0};

        /** default constructor */
        CommonParams(float scale_factor = 1.2f, unsigned int n_levels = DEFAULT_N_LEVELS,
             int edge_threshold = 31, unsigned int first_level = DEFAULT_FIRST_LEVEL);
        void read(const FileNode& fn);
        void write(FileStorage& fs) const;

        /** Coefficient by which we divide the dimensions from one scale pyramid level to the next */
        float scale_factor_;
        /** The number of levels in the scale pyramid */
        unsigned int n_levels_;
        /** The level at which the image is given
         * if 1, that means we will also look at the image scale_factor_ times bigger
         */
        unsigned int first_level_;
        /** How far from the boundary the points should be */
        int edge_threshold_;
    };

    // c:function::default constructor
    ORB();
    // constructor that initializes all the algorithm parameters
    ORB( const CommonParams detector_params );
    // returns the number of elements in each descriptor (32 bytes)
    int descriptorSize() const;
    // detects keypoints using ORB
    void operator()(const Mat& img, const Mat& mask,
                    vector<KeyPoint>& keypoints) const;
    // detects ORB keypoints and computes the ORB descriptors for them;
    // output vector "descriptors" stores elements of descriptors and has size
    // equal descriptorSize()*keypoints.size() as each descriptor is
    // descriptorSize() elements of this vector.
    void operator()(const Mat& img, const Mat& mask,
                    vector<KeyPoint>& keypoints,
                    cv::Mat& descriptors,
                    bool useProvidedKeypoints=false) const;
};

我们可以看到参数主要有4个

float scale_factor = 1.2f, unsigned int n_levels = DEFAULT_N_LEVELS,
             int edge_threshold = 31, unsigned int first_level = DEFAULT_FIRST_LEVEL

由文献中

In our implementation, smoothing is achieved using an integral image, where each test point is a 5 × 5 subwindow of a 31 × 31 pixel patch

可以知道edge_threshold对应的pixel patch