c++ - OpenCV calibrateCamera 断言失败

Question

几天来，我一直在用棋盘示例进行相机校准。一切都很好(找到并显示角，然后馈送到数组)直到我调用最终函数 calibrateCamera。比我得到断言错误:

OpenCV 错误:calibrateCamera 断言失败(nimages > 0)，文件/home/ig/Downloads/opencv-2.4.8/modules/calib3d/src/calibration.cpp，第 3415 行

这是经典代码:

    #include <iostream>
    #include <fstream>
    #include <vector>

    #include "opencv2/core/core.hpp"
    #include "opencv2/highgui/highgui.hpp"
    #include "opencv2/calib3d/calib3d.hpp"
    #include "opencv2/imgproc/imgproc.hpp"

    using namespace cv;
    using namespace std;

    int main(int argc, char* argv[])
    {
        VideoCapture captR(0); // open the video camera no. 0 (RIGHT)

        if (!captR.isOpened())  // if not success, exit program
        {
            cout << "Cannot open the video cam 0" << endl;
            return -1;
        }

        namedWindow("MyVideo (RIGHT)",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"

        namedWindow("Grayscale",CV_WINDOW_AUTOSIZE); //create a window called "Grayscale"

        int a = 0;  // Frame counter

        int numCornersHor = 7; // Chessboard dimensions
        int numCornersVer = 5;
        int numSquares = numCornersHor * numCornersVer;
        Size boardSize = Size(numCornersHor, numCornersVer);

        Mat frameR;
        //      Mat frameL;
        Mat gray_frame;

        vector<Point3f> obj;
        vector<Point2f> corners;  // output vectors of image points

        for (int i=0; i<boardSize.height; i++) {
            for (int j=0; j<boardSize.width; j++) {
                obj.push_back(Point3f(i, j, 0.0f));
            }
        }

        while (1){

            int key = waitKey(30);

            bool bCaptSuccessR = captR.read(frameR); // read a new frame from video

            if (!bCaptSuccessR) //if capture not succeded, break loop
            {
                 cout << "Cannot read a frame from video stream" << endl;
                 break;
            }

            vector<vector<Point3f> > object_points;
            vector<vector<Point2f> > image_points;

            // make grayscale frame version for conerSubPix
            cvtColor(frameR, gray_frame, CV_BGR2GRAY);

            // Get the chessboard corners
            bool found = findChessboardCorners(frameR, boardSize, corners);

            if (found) {
                // Increase accuracy by subpixels
                cornerSubPix(gray_frame, corners, Size(11, 11), Size(-1, -1), TermCriteria(CV_TERMCRIT_EPS | CV_TERMCRIT_ITER, 30, 0.1));
                drawChessboardCorners(gray_frame, boardSize, corners, found);
                imshow("Grayscale", gray_frame);

                ////////////////////////////////////////////
                if(key==32){  // Save good found by pressing [space]
                    image_points.push_back(corners);
                    object_points.push_back(obj);
                    cout << "Captured good calibration image, No " << a << endl;
                    cout << "corners: " << corners << endl;
                    //cout << "obj: " << obj << endl;
                    a++;
                }
            }

            imshow("MyVideo (RIGHT)", frameR); //show right webcam frame in "MyVideo" window

            if (key == 27) {    //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
                cout << "esc key is pressed by user" << endl;
                break;
            }

            if (key == 115){ // If 'S' key pressed begin calibration

                //////////// BEGIN CALIBRATION ////////////////////////
                cout << "Callibration started..." << endl;

                Mat cameraMatrix = Mat(3, 3, CV_64F);
                cameraMatrix.at<double>(0,0) = 1.0;

                Mat distCoeffs;
                distCoeffs = Mat::zeros(8, 1, CV_64F);

                vector<Mat> rvecs;
                vector<Mat> tvecs;

                Size imageSize = frameR.size();

                calibrateCamera(object_points, image_points, imageSize, cameraMatrix, distCoeffs, rvecs, tvecs);

                cout << "Callibration ended." << endl;



            }//callibration
        }

        captR.release();

        return 0;

    }

这是带有行号的 OpenCV 文件摘录:

3400    double cv::calibrateCamera( InputArrayOfArrays _objectPoints,
3401                                InputArrayOfArrays _imagePoints,
3402                                Size imageSize, InputOutputArray _cameraMatrix, InputOutputArray _distCoeffs,
3403                                OutputArrayOfArrays _rvecs, OutputArrayOfArrays _tvecs, int flags, TermCriteria criteria )
3404    {
3405        int rtype = CV_64F;
3406        Mat cameraMatrix = _cameraMatrix.getMat();
3407        cameraMatrix = prepareCameraMatrix(cameraMatrix, rtype);
3408        Mat distCoeffs = _distCoeffs.getMat();
3409        distCoeffs = prepareDistCoeffs(distCoeffs, rtype);
3410        if( !(flags & CALIB_RATIONAL_MODEL) )
3411            distCoeffs = distCoeffs.rows == 1 ? distCoeffs.colRange(0, 5) : distCoeffs.rowRange(0, 5);
3412
3413        int    i;
3414        size_t nimages = _objectPoints.total();
3415        CV_Assert( nimages > 0 );
3416        Mat objPt, imgPt, npoints, rvecM((int)nimages, 3, CV_64FC1), tvecM((int)nimages, 3, CV_64FC1);
3417        collectCalibrationData( _objectPoints, _imagePoints, noArray(),
3418                                objPt, imgPt, 0, npoints );
3419        CvMat c_objPt = objPt, c_imgPt = imgPt, c_npoints = npoints;
3420        CvMat c_cameraMatrix = cameraMatrix, c_distCoeffs = distCoeffs;
3421        CvMat c_rvecM = rvecM, c_tvecM = tvecM;
3422
3423        double reprojErr = cvCalibrateCamera2(&c_objPt, &c_imgPt, &c_npoints, imageSize,
3424                                              &c_cameraMatrix, &c_distCoeffs, &c_rvecM,
3425                                              &c_tvecM, flags, criteria );
3426
3427        bool rvecs_needed = _rvecs.needed(), tvecs_needed = _tvecs.needed();
3428
3429        if( rvecs_needed )
3430            _rvecs.create((int)nimages, 1, CV_64FC3);
3431        if( tvecs_needed )
3432            _tvecs.create((int)nimages, 1, CV_64FC3);
3433

使用 Linux Ubuntu 12.04、OpenCV 2.4.8、gcc 4.6.3、Eclipse，...

Answer 1

您正在 while 循环内声明 object_points 和 image_points，但可能希望将声明放在循环之外。否则，列表将在每次迭代后(有效地)被清除。

用户按下第一个键，检测棋盘。板被写入 object_points 和 image_points。然后用户按下键来校准相机。第一个键的处理结束，object_points 和 image_points 松散范围(并被清除)，第二个键的处理开始，调用 calibrateCamera一个空的 object_points 数组并失败。

在调用 calibrateCamera 之前，您还应该检查 object_points 是否不为空。