calibrate.py

import numpy as np
import cv2 as cv
# dimension of chessboard
dim = (4, 3)   
criteria = (cv.TERM_CRITERIA_EPS + cv.TERM_CRITERIA_MAX_ITER, 30, 0.001)
# prepare object points, like (0,0,0), (1,0,0), (2,0,0) ....,(6,5,0)
objp = np.zeros((dim[0]*dim[1],3), np.float32)
objp[:,:2] = np.mgrid[0:dim[0],0:dim[1]].T.reshape(-1,2)
# Arrays to store object points and image points from all the images.
objpoints = [] # 3d point in real world space
imgpoints = [] # 2d points in image plane.
cap = cv.VideoCapture(0)
i = 0
# more images for better result
numofimages = 20   
while i < numofimages: 
    _, img = cap.read()
    gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
    # Find the chess board corners
    ret, corners = cv.findChessboardCorners(gray, dim, None)
    # If found, add object points, image points (after refining them)
    if ret == True:
        objpoints.append(objp)
        corners2 = cv.cornerSubPix(gray,corners, (11,11), (-1,-1), criteria)
        imgpoints.append(corners)
        # Draw and display the corners
        cv.drawChessboardCorners(img, dim, corners2, ret)
        cv.imshow('img', img)
        # The interval between frames
        cv.waitKey(1500) 
        i += 1
    if cv.waitKey(1) == ord('q'):
        break
    
cap.release()
cv.destroyAllWindows()
ret, mtx, dist, rvecs, tvecs = cv.calibrateCamera(objpoints, imgpoints, gray.shape[::-1], None, None)