OpenCV Java camera calibration

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Hello,

I have been struggling to calibrate my camera in a Java application .

I have used the python tutorial code Python and when I tranformed it to my Java application the results are different( On the exact same image!!). Even the camera matrix has no resemblance. I don't understand why that may be.

Here is the java code

found_chess = Calib3d.findChessboardCorners(gray, patternSize, actual_corners,  Calib3d.CALIB_CB_ADAPTIVE_THRESH + Calib3d.CALIB_CB_NORMALIZE_IMAGE);
if(found_chess)
{

    corners.add(actual_corners);
    //cornersubPix() irrelevant since all the corners are found in findChessBoard
    //Imgproc.cornerSubPix(gray, actual_corners, new Size(SIZE_Y*2+1,SIZE_X*2+1), new Size(-1,-1), new TermCriteria(TermCriteria.EPS+TermCriteria.MAX_ITER,30,0.1));

    MatOfPoint3f points;

    Mat a = new MatOfPoint3f();
        for(int x=0; x<SIZE_X; ++x) 
        {
            for(int y=0; y<SIZE_Y; ++y)
            {
                points = new MatOfPoint3f(new Point3(y, x, 0));
                a.push_back(points);
            }
        }

    object_points.add(a);
    Calib3d.calibrateCamera(object_points, corners, gray.size(), cameraMatrix, distCoeffs, rvecs, tvecs);
 }

The corners position is exactly the same in both implementations. I have no clue on why this disparity between programs (Maybe the way I am initializing the object_points?)

I hope someone could provide me a solution,

Thank you in advance