OpenCV displaying a 2-channel image (optical flow)

Question

I have optical flow stored in a 2-channel 32F matrix. I want to visualize the contents, what\'s the easiest way to do this?

How do I convert a CV_32FC2 to R

Answer 1

imshow can handle only 1-channel gray-scale and 3-4 channel BRG/BGRA images. So you need do a conversion yourself.

I think you can do something similar to:

//extraxt x and y channels
cv::Mat xy[2]; //X,Y
cv::split(flow, xy);

//calculate angle and magnitude
cv::Mat magnitude, angle;
cv::cartToPolar(xy[0], xy[1], magnitude, angle, true);

//translate magnitude to range [0;1]
double mag_max;
cv::minMaxLoc(magnitude, 0, &mag_max);
magnitude.convertTo(magnitude, -1, 1.0 / mag_max);

//build hsv image
cv::Mat _hsv[3], hsv;
_hsv[0] = angle;
_hsv[1] = cv::Mat::ones(angle.size(), CV_32F);
_hsv[2] = magnitude;
cv::merge(_hsv, 3, hsv);

//convert to BGR and show
cv::Mat bgr;//CV_32FC3 matrix
cv::cvtColor(hsv, bgr, cv::COLOR_HSV2BGR);
cv::imshow("optical flow", bgr);

cv::waitKey(0);