Drawing Function of Keypoints and Matches

cv::drawMatches

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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)

This function draws matches of keypints from two images on output image.

Match is a line connecting two keypoints (circles).

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 first source image.
• img2 – Second source image.
• keypoints2 – Keypoints from second source image.
• matches – Matches from first image to second one, i.e. keypoints1[i] has corresponding point keypoints2[matches[i]] .
• outImg – Output image. Its content depends on flags value what is drawn in output image. See below possible flags bit values.
• matchColor – Color of matches (lines and connected keypoints). If matchColor==Scalar::all(-1) color will be generated randomly.
• singlePointColor – Color of single keypoints (circles), i.e. keypoints not having the matches. If singlePointColor==Scalar::all(-1) color will be generated randomly.
• matchesMask – Mask determining which matches will be drawn. If mask is empty all matches will be drawn.
• flags – Each bit of flags sets some feature of drawing. Possible flags bit values is defined by DrawMatchesFlags , see below.

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 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.
        };
};

cv::drawKeypoints

Comments from the Wiki

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

Draw keypoints.

Parameters:

• image – Source image.
• keypoints – Keypoints from source image.
• outImg – Output image. Its content depends on flags value what is drawn in output image. See possible flags bit values.
• color – Color of keypoints

.

Parameters:

• flags – Each bit of flags sets some feature of drawing. Possible flags bit values is defined by DrawMatchesFlags , see above in drawMatches() .