Stereo Camera Calibration Using OpenCV C++

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This repository contains some sources to calibrate the intrinsics of individual cameras and also the extrinsics of a stereo pair.

Dependencies

• OpenCV

% brew install opencv

Compilation

Compile all the files using the following commands.

% mkdir cmake-build-debug
% cd cmake-build-debug
% cmake ..
% make

Make sure you are in the cmake-build-debug folder to run the exeutables.

% ./stereo-camera-calibration

Data Analysis(calib_data)

File name	Description
calib_data/20220208_4cm/ opencv_algo/raw/left_xx.jpg	4cm means the camera baseline and left_xx.jpg or right_xx.jpg refers to the sequence of the captured image from the stereo pair.
../raw/stereo_calib.xml	this xml file determines the sequence of the raw images.
../result/extrinsics.yml	this yml file denotes the extrinsic parameters including rotational matrix, translational matrix, the decomposition of the homography matrix (reprojection) of the stereo pair.
../result/intrinsics.yml	this yml file denotes the intrinsic parameters including each of the intrinsic matrix and distortion coefficients (either rational or tangential).
../result/rectified.png	this png file presents the epipolar rectification.
../result/error_metrics.png	this png file presents the RMS error and average epipolar error (per pixel).

How to modify the filepath

input path in main.cpp:

int main(int argc, char** argv){

    calibrate_stereo calibrateStereo;
    cv::Size boardSize;
    std::string imagelistfn;
    std::string filePath = "/Desktop/stereo-camera-calibration/calib_data/20220208_4cm/opencv_algo/raw/";
    bool showRectified;
    cv::CommandLineParser parser(argc, argv, "{w|11|}{h|8|}{s|0.3|}{nr||}{help||}{@input|" + filePath + "stereo_calib.xml|}");
...
return 0;
}

output path in calibrate_stereo.cpp:

void calibrate_stereo::StereoCalib(const std::vector<std::string> &imagelist, cv::Size boardSize, float squareSize,
                                   bool displayCorners, bool useCalibrated, bool showRectified) {
...
    // save intrinsic parameters
    cv::FileStorage fs("/Desktop/stereo-camera-calibration/calib_data/20220208_4cm/opencv_algo/result/intrinsics.yml", cv::FileStorage::WRITE);

...
    stereoRectify(cameraMatrix[0], distCoeffs[0],
                  cameraMatrix[1], distCoeffs[1],
                  imageSize, R, T, R1, R2, P1, P2, Q,
                  cv::CALIB_ZERO_DISPARITY, 1, imageSize, &validRoi[0], &validRoi[1]);
    fs.open("/Desktop/stereo-camera-calibration/calib_data/20220208_4cm/opencv_algo/result/extrinsics.yml", cv::FileStorage::WRITE);
...
}

References

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[1] Bradski, G., 2000. The OpenCV Library. Dr. Dobb's Journal of Software Tools.

[2] Zhang, Z., 2000. A flexible new technique for camera calibration. IEEE Transactions on pattern analysis and machine intelligence, 22(11), pp.1330-1334.

[3] Loop, C.T. and Zhang, Z., 1999, January. Computing Rectifying Homographies for Stereo Vision. In CVPR.