如何從相機矩陣中找到焦距？

Question

我有OpenCV代碼用於計算相機矩陣和修復圖像中的失真。

這是OpenCV和C ++中代碼的一部分。

//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);
}

我不知道如何使用此代碼來從相機矩陣中找到焦距。 這段代碼應該計算相機矩陣並從需要找到焦點長度。 但有些人如何不確定這是獲得相機矩陣然后焦點長度的方法。 相機矩陣3x3矩陣。 但是如何計算這些參數？

有幫助嗎？

Answer 1

首先談談相機矩陣：

相機矩陣具有以下形式：

f_x  s    c_x
0    f_y  c_y
0    0    1

其中f_x是x軸上的相機焦距，以像素為單位

f_y是y軸上的相機焦距，以像素為單位

s是一個偏斜參數（通常不使用）

c_x是x中的光學中心

c_y是y中的光學中心

通常f_x和f_y相同但可能不同。 在此鏈接中，您可以獲得有關它的更多信息。

現在讓我們回到你的代碼。

在您的代碼中，相機矩陣是硬編碼的，而不是計算！，具體在這里：

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);

在代碼的任何部分，都有關於計算它的任何信息。

相機的校准有幾個步驟：

1. 獲得像棋盤一樣的棋盤圖像

2. 找到此圖像中正方形的交點（ findChessBoardCorners

3. 然后使用CalibrateCamera函數獲取矩陣和其他信息

關於它的更多信息在這里 。

獲得相機矩陣后，您可以獲得焦距，如果您想要以毫米為單位，則需要相機傳感器的尺寸（您必須詢問制造商或在互聯網上找到它）