c++ - 如何从相机矩阵中找到焦距？

Question

我有用于计算相机矩阵和修复图像失真的 OpenCV 代码。

这里是OpenCV和C++的部分代码。

//default capture width and height
const int FRAME_WIDTH = 1288;
const int FRAME_HEIGHT = 964;
//max number of objects to be detected in frame
const int MAX_NUM_OBJECTS=50;
//minimum and maximum object area
const int MIN_OBJECT_AREA = 2*2;
const int MAX_OBJECT_AREA = FRAME_HEIGHT*FRAME_WIDTH/1.5;

Mat DistortedImg;                                           //storage for copy of the image raw
Mat UndistortedImg;                                         //

double cameraM[3][3] = {{1103.732864, 0.000000, 675.056365}, {0.000000, 1100.058630, 497.063376}, {0, 0, 1}}; //camera matrix to be edited
Mat CameraMatrix = Mat(3, 3, CV_64FC1, cameraM);

double distortionC[5] = {-0.346476, 0.142352, -0.000084, -0.001727, 0.000000};              //distortioncoefficient to be edited
Mat DistortionCoef = Mat(1, 5, CV_64FC1, distortionC);                          

double rArray[3][3] = {{1, 0, 0}, {0, 1, 0}, {0, 0, 1}};
Mat RArray = Mat(3, 3, CV_64FC1, rArray);                   //originally CV_64F

double newCameraM[3][3] = {{963.436584, 0.000000, 680.157832}, {0.000000, 1021.688843, 498.825528}, {0, 0, 1}};
Mat NewCameraMatrix = Mat(3, 3, CV_64FC1, newCameraM);
Size UndistortedSize(1288,964);

Mat map1;
Mat map2;       

string intToString(int number)
{
    std::stringstream ss;
    ss << number;
    return ss.str();
}

void imageCb(const sensor_msgs::ImageConstPtr& msg)                               //callback function defination
{
   cv_bridge::CvImagePtr cv_ptr;                                                       
   try
   {
        cv_ptr = cv_bridge::toCvCopy(msg, sensor_msgs::image_encodings::BGR8);              //convert ROS image to CV image and make copy of it storing in cv_ptr(a pointer)
   }
   catch (cv_bridge::Exception& e)
   {
      ROS_ERROR("cv_bridge exception: %s", e.what());
      return;
   }

    /*  image working procedure starting from here inside the main function.
     *  The purpose of the image processing is to use the existing video to working out the 
     *  cordinate of the detected object, using color extraction technique.
     */

    bool trackObjects = true;
    bool useMorphOps = true;

    Mat cameraFeed; 
    Mat HSV;    
    Mat threshold;
    Mat ideal_image;

    //x and y values for the location of the object
    int x=0, y=0;
    createTrackbars();

    //store image to matrix
    cv_ptr->image.copyTo(DistortedImg);                                         //=Tan= copy the image from ardrone to DistortedImg for processing
    initUndistortRectifyMap(CameraMatrix, DistortionCoef, RArray, NewCameraMatrix, UndistortedSize, CV_32FC1, map1, map2);
    remap(DistortedImg, cameraFeed, map1, map2, INTER_LINEAR, BORDER_CONSTANT, Scalar(0,0,0));      

    cvtColor(cameraFeed,HSV,COLOR_BGR2HSV);                                  //convert frame from BGR to HSV colorspace

    //output the after-threshold matrix to Mat threshold
    inRange(HSV,Scalar(iLowH_1, iLowS_1, iLowV_1),Scalar(iHighH_1, iHighS_1, iHighV_1),threshold);      
    //inRange(HSV,Scalar(0, 87, 24),Scalar(9, 255, 255),threshold);  //red

    morphOps(threshold);
    GaussianBlur( threshold, ideal_image, Size(9, 9), 2, 2 );

    trackFilteredObject1(x,y,ideal_image,cameraFeed);


    namedWindow( "Image with deal1", 0 );
    namedWindow( "Original Image", 0 );

    imshow("Image with deal1",ideal_image);
    imshow("Original Image", cameraFeed);

    //delay 30ms so that screen can refresh.
    //image will not appear without this waitKey() command
    cv::waitKey(30);
}

我不确定如何使用此代码从相机矩阵中找到焦距。这段代码应该计算相机矩阵并根据需要找到焦距。但是有些我不确定这是获取相机矩阵然后获取焦距的方法。相机矩阵 3x3 矩阵。但是这些参数是如何计算的呢？

有什么帮助吗？

Answer 1

首先介绍一下相机矩阵:

相机矩阵的形式如下:

f_x  s    c_x
0    f_y  c_y
0    0    1

其中 f_x 是 x 轴上的相机焦距，以像素为单位

f_y 是以像素为单位的 y 轴相机焦距

s是一个skew参数(一般不用)

c_x 是 x 中的光学中心

c_y 是 y 方向的光学中心

通常 f_x 和 f_y 是相同的，但也有可能不同。在 this link您可以获得有关它的更多信息。

现在让我们回到您的代码。

在你的代码中，相机矩阵是硬编码的，不是计算的!，具体在这里:

double cameraM[3][3] = {{1103.732864, 0.000000, 675.056365}, {0.000000, 1100.058630, 497.063376}, {0, 0, 1}}; //camera matrix to be edited
Mat CameraMatrix = Mat(3, 3, CV_64FC1, cameraM);

并且在您的代码的任何部分中都有关于计算它的内容。

相机的标定有几个步骤:

1. 获取棋盘状图像

2. 找出图片中正方形的交点 ( findChessBoardCorners

3. 然后使用 CalibrateCamera获取矩阵等信息的函数

关于它的更多信息here .

一旦你得到相机矩阵，你就可以得到焦距，如果你想要以毫米为单位，你需要相机的传感器尺寸(你必须询问制造商或在互联网上找到它)