example_19-03.cpp

// Example 19-3. Stereo calibration, rectification, and correspondence
#pragma warning(disable : 4996)
#include <opencv2/opencv.hpp>
#include <iostream>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

using namespace std;

void help(char *argv[])
{
    cout
        << "\n\nExample 19-3. Stereo calibration, rectification, and correspondence"
        << "\n    Reads in list of locations of a sequence of checkerboard calibration"
        << "\n    objects from a left,right stereo camera pair. Calibrates, rectifies and then"
        << "\n    does stereo correspondence."
        << "\n"
        << "\n    This program will run on default parameters assuming you created a build directory"
        << "\n    directly below the Learning-OpenCV-3 directory and are running programs there."
        << "\n\n  NOTE: the list_of_stereo_pairs> must give the full path name to the left right images, in alternating"
        << "\n    lines: left image, right image, one path/filename per line, see"
        << "\n    stereoData/example_19-03_list.txt file, you can comment out lines"
        << "\n    there by starting them with #."
        << "\n"
        << "\n    Default Call (with parameters: board_w = 9, board_h = 6, list = ../stereoData_19-03_list.txt):"
        << "\n"
        << argv[0] << "\n"
        << "\nManual call:"
        << "\n"
        << argv[0] << " [<board_w> <board_h> <path/list_of_stereo_pairs>]"
        << "\n\n PRESS ANY KEY TO STEP THROUGH RESULTS AT EACH STAGE."
        << "\n"
        << endl;
}

static void StereoCalib(const char *imageList, int nx, int ny,
                        bool useUncalibrated)
{
    bool displayCorners = true;
    bool showUndistorted = true;
    bool isVerticalStereo = false; // horiz or vert cams
    const int maxScale = 1;
    const float squareSize = 1.f;

    // actual square size
    FILE *f = fopen(imageList, "rt");
    int i, j, lr;
    int N = nx * ny;
    cv::Size board_sz = cv::Size(nx, ny);
    vector<string> imageNames[2];
    vector<cv::Point3f> boardModel;
    vector<vector<cv::Point3f>> objectPoints;
    vector<vector<cv::Point2f>> points[2];
    vector<cv::Point2f> corners[2];
    bool found[2] = {false, false};
    cv::Size imageSize;

    // READ IN THE LIST OF CIRCLE GRIDS:
    //
    if (!f)
    {
        cout << "Cannot open file " << imageList << endl;
        return;
    }
    for (i = 0; i < ny; i++)
        for (j = 0; j < nx; j++)
            boardModel.push_back(
                cv::Point3f((float)(i * squareSize), (float)(j * squareSize), 0.f));
    i = 0;
    for (;;)
    {
        char buf[1024];
        lr = i % 2;
        if (lr == 0)
            found[0] = found[1] = false;
        if (!fgets(buf, sizeof(buf) - 3, f))
            break;
        size_t len = strlen(buf);
        while (len > 0 && isspace(buf[len - 1]))
            buf[--len] = '\0';
        if (buf[0] == '#')
            continue;
        cv::Mat img = cv::imread(buf, 0);
        if (img.empty())
            break;
        imageSize = img.size();
        imageNames[lr].push_back(buf);
        i++;

        // If we did not find board on the left image,
        // it does not make sense to find it on the right.
        //
        if (lr == 1 && !found[0])
            continue;

        // Find circle grids and centers therein:
        for (int s = 1; s <= maxScale; s++)
        {
            cv::Mat timg = img;
            if (s > 1)
                resize(img, timg, cv::Size(), s, s, cv::INTER_CUBIC);
            // Just as example, this would be the call if you had circle calibration
            // boards ...
            //      found[lr] = cv::findCirclesGrid(timg, cv::Size(nx, ny),
            //      corners[lr],
            //                                      cv::CALIB_CB_ASYMMETRIC_GRID |
            //                                          cv::CALIB_CB_CLUSTERING);
            //...but we have chessboards in our images
            found[lr] = cv::findChessboardCorners(timg, board_sz, corners[lr]);

            if (found[lr] || s == maxScale)
            {
                cv::Mat mcorners(corners[lr]);
                mcorners *= (1. / s);
            }
            if (found[lr])
                break;
        }
        if (displayCorners)
        {
            cout << buf << endl;
            cv::Mat cimg;
            cv::cvtColor(img, cimg, cv::COLOR_GRAY2BGR);

            // draw chessboard corners works for circle grids too
            cv::drawChessboardCorners(cimg, cv::Size(nx, ny), corners[lr], found[lr]);
            cv::imshow("Corners", cimg);
            if ((cv::waitKey(0) & 255) == 27) // Allow ESC to quit
                exit(-1);
        }
        else
            cout << '.';
        if (lr == 1 && found[0] && found[1])
        {
            objectPoints.push_back(boardModel);
            points[0].push_back(corners[0]);
            points[1].push_back(corners[1]);
        }
    }
    fclose(f);

    // CALIBRATE THE STEREO CAMERAS
    cv::Mat M1 = cv::Mat::eye(3, 3, CV_64F);
    cv::Mat M2 = cv::Mat::eye(3, 3, CV_64F);
    cv::Mat D1, D2, R, T, E, F;
    cout << "\nRunning stereo calibration ...\n";
    cv::stereoCalibrate(
        objectPoints, points[0], points[1], M1, D1, M2, D2, imageSize, R, T, E, F,
        cv::CALIB_FIX_ASPECT_RATIO | cv::CALIB_ZERO_TANGENT_DIST |
            cv::CALIB_SAME_FOCAL_LENGTH,
        cv::TermCriteria(cv::TermCriteria::COUNT | cv::TermCriteria::EPS, 100,
                         1e-5));
    cout << "Done! Press any key to step through images, ESC to exit\n\n";

    // CALIBRATION QUALITY CHECK
    // because the output fundamental matrix implicitly
    // includes all the output information,
    // we can check the quality of calibration using the
    // epipolar geometry constraint: m2^t*F*m1=0
    vector<cv::Point3f> lines[2];
    double avgErr = 0;
    int nframes = (int)objectPoints.size();
    for (i = 0; i < nframes; i++)
    {
        vector<cv::Point2f> &pt0 = points[0][i];
        vector<cv::Point2f> &pt1 = points[1][i];
        cv::undistortPoints(pt0, pt0, M1, D1, cv::Mat(), M1);
        cv::undistortPoints(pt1, pt1, M2, D2, cv::Mat(), M2);
        cv::computeCorrespondEpilines(pt0, 1, F, lines[0]);
        cv::computeCorrespondEpilines(pt1, 2, F, lines[1]);

        for (j = 0; j < N; j++)
        {
            double err = fabs(pt0[j].x * lines[1][j].x + pt0[j].y * lines[1][j].y +
                              lines[1][j].z) +
                         fabs(pt1[j].x * lines[0][j].x + pt1[j].y * lines[0][j].y +
                              lines[0][j].z);
            avgErr += err;
        }
    }
    cout << "avg err = " << avgErr / (nframes * N) << endl;

    // COMPUTE AND DISPLAY RECTIFICATION
    //
    if (showUndistorted)
    {
        cv::Mat R1, R2, P1, P2, map11, map12, map21, map22;

        // IF BY CALIBRATED (BOUGUET'S METHOD)
        //
        if (!useUncalibrated)
        {
            stereoRectify(M1, D1, M2, D2, imageSize, R, T, R1, R2, P1, P2,
                          cv::noArray(), 0);
            isVerticalStereo = fabs(P2.at<double>(1, 3)) > fabs(P2.at<double>(0, 3));
            // Precompute maps for cvRemap()
            initUndistortRectifyMap(M1, D1, R1, P1, imageSize, CV_16SC2, map11,
                                    map12);
            initUndistortRectifyMap(M2, D2, R2, P2, imageSize, CV_16SC2, map21,
                                    map22);
        }

        // OR ELSE HARTLEY'S METHOD
        //
        else
        {

            // use intrinsic parameters of each camera, but
            // compute the rectification transformation directly
            // from the fundamental matrix
            vector<cv::Point2f> allpoints[2];
            for (i = 0; i < nframes; i++)
            {
                copy(points[0][i].begin(), points[0][i].end(),
                     back_inserter(allpoints[0]));
                copy(points[1][i].begin(), points[1][i].end(),
                     back_inserter(allpoints[1]));
            }
            cv::Mat F = findFundamentalMat(allpoints[0], allpoints[1], cv::FM_8POINT);
            cv::Mat H1, H2;
            cv::stereoRectifyUncalibrated(allpoints[0], allpoints[1], F, imageSize,
                                          H1, H2, 3);
            R1 = M1.inv() * H1 * M1;
            R2 = M2.inv() * H2 * M2;

            // Precompute map for cvRemap()
            //
            cv::initUndistortRectifyMap(M1, D1, R1, P1, imageSize, CV_16SC2, map11,
                                        map12);
            cv::initUndistortRectifyMap(M2, D2, R2, P2, imageSize, CV_16SC2, map21,
                                        map22);
        }

        // RECTIFY THE IMAGES AND FIND DISPARITY MAPS
        //
        cv::Mat pair;
        if (!isVerticalStereo)
            pair.create(imageSize.height, imageSize.width * 2, CV_8UC3);
        else
            pair.create(imageSize.height * 2, imageSize.width, CV_8UC3);

        // Setup for finding stereo corrrespondences
        //
        cv::Ptr<cv::StereoSGBM> stereo = cv::StereoSGBM::create(
            -64, 128, 11, 100, 1000, 32, 0, 15, 1000, 16, cv::StereoSGBM::MODE_HH);

        for (i = 0; i < nframes; i++)
        {
            cv::Mat img1 = cv::imread(imageNames[0][i].c_str(), 0);
            cv::Mat img2 = cv::imread(imageNames[1][i].c_str(), 0);
            cv::Mat img1r, img2r, disp, vdisp;
            if (img1.empty() || img2.empty())
                continue;
            cv::remap(img1, img1r, map11, map12, cv::INTER_LINEAR);
            cv::remap(img2, img2r, map21, map22, cv::INTER_LINEAR);
            if (!isVerticalStereo || !useUncalibrated)
            {

                // When the stereo camera is oriented vertically,
                // Hartley method does not transpose the
                // image, so the epipolar lines in the rectified
                // images are vertical. Stereo correspondence
                // function does not support such a case.
                stereo->compute(img1r, img2r, disp);
                cv::normalize(disp, vdisp, 0, 256, cv::NORM_MINMAX, CV_8U);
                cv::imshow("disparity", vdisp);
            }
            if (!isVerticalStereo)
            {
                cv::Mat part = pair.colRange(0, imageSize.width);
                cvtColor(img1r, part, cv::COLOR_GRAY2BGR);
                part = pair.colRange(imageSize.width, imageSize.width * 2);
                cvtColor(img2r, part, cv::COLOR_GRAY2BGR);
                for (j = 0; j < imageSize.height; j += 16)
                    cv::line(pair, cv::Point(0, j), cv::Point(imageSize.width * 2, j),
                             cv::Scalar(0, 255, 0));
            }
            else
            {
                cv::Mat part = pair.rowRange(0, imageSize.height);
                cv::cvtColor(img1r, part, cv::COLOR_GRAY2BGR);
                part = pair.rowRange(imageSize.height, imageSize.height * 2);
                cv::cvtColor(img2r, part, cv::COLOR_GRAY2BGR);
                for (j = 0; j < imageSize.width; j += 16)
                    line(pair, cv::Point(j, 0), cv::Point(j, imageSize.height * 2),
                         cv::Scalar(0, 255, 0));
            }
            cv::imshow("rectified", pair);
            if ((cv::waitKey() & 255) == 27)
                break;
        }
    }
}

//
// Default Call (with parameters: board_w = 9, board_h = 6, list =
//  ../stereoData_19-03_list.txt):
//./example_19-03
//
// Manual call:
//./example_19-03 [<path/list_of_stereo_pairs> <board_w> <board_h>]
//
// Press any key to step through results, ESC to exit
//

int main(int argc, char **argv)
{
    help(argv);
    int board_w = 9, board_h = 6;
    const char *board_list = "../stereoData/example_19-03_list.txt";
    if (argc == 4)
    {
        board_list = argv[1];
        board_w = atoi(argv[2]);
        board_h = atoi(argv[3]);
    }
    StereoCalib(board_list, board_w, board_h, true);
    return 0;
}