Camera calibration with opencv (Assertion failed fault) - c++

Question

I am trying to get camera calibration parameters by using opencv camera calibration functions. I have a video and trying to find the calibration parameters and find the points in the video which inclused a checkboard in different psoitions. But i couldnt passed the calibration phase yet. I can find the corner of the checkboard and show them in openCV window but when it comes to line:
calibrateCamera(objectPoints,imagePoints..............)
it throws exception and stops.
I get the following error: OpenCV error: Assertion failed 0 &&nimages==int imagePoints1.total ()&&
Here is my code:
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "C:/opencv/include/opencv/cv.h"
#include <iostream>
#include <math.h>
using namespace cv;
using namespace std;
std::vector<cv::Point2f> imageCorners;
std::vector<cv::Point3f> objectCorners;
std::vector<std::vector<cv::Point3f>> objectPoints;
std::vector<std::vector<cv::Point2f>> imagePoints;
void addPoints(const std::vector<cv::Point2f>&imageCorners, const std::vector<cv::Point3f>& objectCorners)
{
// 2D image points from one view
imagePoints.push_back(imageCorners);
// corresponding 3D scene points
objectPoints.push_back(objectCorners);
}
int main()
{
int key;
cv::Mat image;
cv::Mat gray_image;
VideoCapture cap("here goes path of the file");
if (!cap.isOpened()) // check if we succeeded
cout<<"failed";
else
cout<<"success";
cvNamedWindow( "video",0);
cv::Size boardSize(8,6);
// output Matrices
cv::Mat cameraMatrix;
std::vector<cv::Mat> rvecs, tvecs;
cv::Mat distCoeffs;
for (int i=0; i<boardSize.height; i++)
{
for (int j=0; j<boardSize.width; j++)
{
objectCorners.push_back(cv::Point3f(i, j, 0.0f));
}
}
int frame=1;
int corner_count=0;
while(1)
{
if(cap.read(image))
{
frame++;
if(frame%20==0)
{
if(waitKey(30) >= 0) break;
bool found = cv::findChessboardCorners(image, boardSize, imageCorners);
cvtColor( image, gray_image, CV_RGB2GRAY );
addPoints(imageCorners, objectCorners);
//bool found = cv::findChessboardCorners(image,boardSize, imageCorners);
cv::drawChessboardCorners(gray_image,boardSize, imageCorners,found);
imshow( "video", gray_image );
}
}
else
break;
}
int flag=0;
std::string text="";
for (int i=1; i<imagePoints.size();i++)
{
std::stringstream out;
out << imagePoints[i];
text=out.str();
cout<<text<<endl;
}
calibrateCamera(objectPoints,imagePoints,gray_image.size(), cameraMatrix, distCoeffs, rvecs, tvecs, flag);
return 0;
}

Answer 1

Print the size of all your std::vector, I suspect you are passing an empty vector to that function.
EDIT:
I've shared some instructions in this answer on how to do camera calibration. Those references include working source code. You'll probably have to do a small adaptation on those programs so they work with video instead.

Answer 2

you should look at this:
http://docs.opencv.org/modules/calib3d/doc/camera_calibration_and_3d_reconstruction.html#bool findChessboardCorners(InputArray image, Size patternSize, OutputArray corners, int flags)
it says your Source chessboard view must be an 8-bit grayscale or color image.
so you must use this:
bool found = cv::findChessboardCorners(gray_image, boardSize, imageCorners);