Drawing Function of Keypoints and Matches

drawMatches

Draws the found matches of keypoints from two images.

C++: void drawMatches(const Mat& img1, const vector<KeyPoint>& keypoints1, const Mat& img2, const vector<KeyPoint>& keypoints2, const vector<DMatch>& matches1to2, Mat& outImg, const Scalar& matchColor=Scalar::all(-1), const Scalar& singlePointColor=Scalar::all(-1), const vector<char>& matchesMask=vector<char>(), int flags=DrawMatchesFlags::DEFAULT )

C++: void drawMatches(const Mat& img1, const vector<KeyPoint>& keypoints1, const Mat& img2, const vector<KeyPoint>& keypoints2, const vector<vector<DMatch>>& matches1to2, Mat& outImg, const Scalar& matchColor=Scalar::all(-1), const Scalar& singlePointColor=Scalar::all(-1), const vector<vector<char>>& matchesMask=vector<vector<char> >(), int flags=DrawMatchesFlags::DEFAULT )

Parameters:

• img1 – First source image.
• keypoints1 – Keypoints from the first source image.
• img2 – Second source image.
• keypoints2 – Keypoints from the second source image.
• matches1to2 – Matches from the first image to the second one, which means that keypoints1[i] has a corresponding point in keypoints2[matches[i]] .
• outImg – Output image. Its content depends on the flags value defining what is drawn in the output image. See possible flags bit values below.
• matchColor – Color of matches (lines and connected keypoints). If matchColor==Scalar::all(-1) , the color is generated randomly.
• 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.
• matchesMask – Mask determining which matches are drawn. If the mask is empty, all matches are drawn.
• 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). The structure DrawMatchesFlags is defined as follows:

struct DrawMatchesFlags
{
    enum
    {
        DEFAULT = 0, // Output image matrix will be created (Mat::create),
                     // i.e. existing memory of output image may be reused.
                     // Two source images, matches, and single keypoints
                     // will be drawn.
                     // For each keypoint, only the center point will be
                     // drawn (without a circle around the keypoint with the
                     // keypoint size and orientation).
        DRAW_OVER_OUTIMG = 1, // Output image matrix will not be
                       // created (using 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.
    };
};

drawKeypoints

Draws keypoints.

C++: void drawKeypoints(const Mat& image, const vector<KeyPoint>& keypoints, Mat& outImage, const Scalar& color=Scalar::all(-1), int flags=DrawMatchesFlags::DEFAULT )

Parameters:

• image – Source image.
• keypoints – Keypoints from the source image.
• outImage – Output image. Its content depends on the flags value defining what is drawn in the output image. See possible flags bit values below.
• color – Color of keypoints.
• flags – Flags setting drawing features. Possible flags bit values are defined by DrawMatchesFlags. See details above in drawMatches() .