I have a wide angle lens (>160 degrees). I have tried both the Pinhole and Fisheye models and they seem to provide clear rectified images with a little FOV sacrifice. So I decided to give a try with the Omnidirectional Model.
With the Omnidirectional model:
double rms = cv::omnidir::stereoCalibrate(Omni_L.RealP, Omni_L.ImageP, Omni_R.ImageP, Omni_L.img.size(), Omni_R.img.size(), K1, xi1, D1, K2, xi2, D2, rvec, tvec, rvecsL, tvecsL, flags, critia);
std::cout << "RMS : " << rms << std::endl;
I Get the following results after the Stereo-calibration
RMS : 0.527522
Camera_Matrix1 :
[773.9380049495828, 0, 394.6697338356358;
0, 776.2094223216956, 382.016762545214;
0, 0, 1]
Xi-1 :[1.804945374650817]
Distortion Parameters1:
[0, 0, -0.009983732008104793, -0.004530718062523464]
Camera_Matrix2:
[783.1807043871861, 0, 393.2120687911561;
0, 784.4790955477508, 386.7954078861521;
0, 0, 1]
Xi-2 :[1.837909340970556]
Distortion Parameters2:
[0, 0, -0.009779422171305124, -0.003723193186299092]
rvec :[-0.003821627764900316;
0.005567569400892289;
0.001491183114878044]
tvec:[-63.09243360480385;
0.1195353275271446;
0.9082801155496641]
R:
[1, 0, 0;
0, 1, 0;
0, 0, 1]
P:
[773.9380049495828, 0, 394.6697338356358;
0, 776.2094223216956, 382.016762545214;
0, 0, 1]
Then I do undistortion:
cv::Mat R = cv::Mat::eye(3, 3, CV_32FC1);
cv::Mat Mapx, Mapy;
cv::Mat P(3, 3, CV_32FC1);
P = K1;
cv::Mat orid = cv::imread("Left\\1.jpg");
std::cout << orid.size();
std::cout << "R : "<<R<<std::endl;
std::cout << "P : " << P << std::endl;
cv::Size s= orid.size();
try {
cv::omnidir::initUndistortRectifyMap(K1, D1, xi1, R, P, s, CV_32FC1, Mapx, Mapy, cv::omnidir::RECTIFY_PERSPECTIVE);// Knew, new_size);
cv::remap(orid, DC, Mapx, Mapy, cv::INTER_CUBIC);
}
catch (cv::Exception & e)
{
std::cerr << e.msg << std::endl; // output exception message
}
std::string Save_Original = "Distorted_Original" + std::to_string(10) + EXT;
cv::imwrite(Save_Original, orid);
std::string Save_Corrected = "Distorted_Corrected" + std::to_string(10) + EXT;
cv::imwrite(Save_Corrected, DC);
Question 1:
Why the Radial distortion is zero?
Question 2:
The output of the undistortion image with rectification drastically reduces the FOV. Is there something wrong in my code?
Original Image:
Distortion Corrected Image:
Question 3:
What does the P and R do in the cv::omnidir::initUndistortRectifyMap() function?
Question 4:
Need Ideas on how to get good rectified images with more FoV with omnidirectional calibration?
Post Trials:
suggested by @sushi(commented below) to try RECTIFY_CYLINDRICAL for the same image and below is the result:
cv::omnidir::RECTIFY_CYLINDRICAL
-> Results are worse
First I recommend you to read this tutorial: https://docs.opencv.org/master/dd/d12/tutorial_omnidir_calib_main.html Answering your questions:
This is the result of my approach using RECTIFY_PERSPECTIVE, I don't know why RECTIFY_CYLINDRICAL does not work in this case:
To achieve it simply undistort your image like this:
cv::Size s = orid.size();
cv::Mat Knew = cv::Mat(cv::Matx33f(s.width / 4, 0, s.width / 2,
0, s.height / 4, s.width / 2,
0, 0, 1));
cv::MAt undistorted;
cv::omnidir::undistortImage(orid, undistorted, K1, D1, xi1, cv::omnidir::RECTIFY_PERSPECTIVE, Knew, orid.size());