Pretty new to all this and I'm trying to do the calibration for a Webcam following this guide and using the code below. I get the following error ..
OpenCV Error: Assertion failed (ni > 0 && ni == ni1) in collectCalibrationData, file /build/buildd/opencv-2.4.8+dfsg1/modules/calib3d/src/calibration.cpp, line 3193
cv2.error: /build/buildd/opencv-2.4.8+dfsg1/modules/calib3d/src/calibration.cpp:3193: error: (-215) ni > 0 && ni == ni1 in function collectCalibrationData
Can someone explain what this error is and how to fix it?
(Full error at the bottom)
import numpy as np
import cv2
import glob
criteria = (cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 30, 0.001)
# Arrays to store object points and image points from all the images.
objpoints = [] # 3d point in real world
imgpoints = [] # 2d points in image plane.
images = glob.glob('*.png')
objp = np.zeros((6*7,3), np.float32)
objp[:,:2] = np.mgrid[0:7,0:6].T.reshape(-1,2)
objp = objp * 22
for fname in images:
img = cv2.imread(fname)
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret = False
# Find the chess board corners
ret, corners = cv2.findChessboardCorners(gray, (6,9))
# If found, add object points, image points (after refining them)
if ret == True:
objpoints.append(objp)
cv2.cornerSubPix(gray, corners, (11,11), (-1,-1), criteria)
imgpoints.append(corners)
# Draw and display the corners
cv2.drawChessboardCorners(img, (6,9), corners, ret)
cv2.imshow('img',img)
cv2.waitKey(0)
cv2.waitKey(0)
for i in range (1,5):
cv2.waitKey(1)
cv2.destroyAllWindows()
cv2.waitKey(1)
ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, gray.shape[::-1],None,None)
OpenCV Error: Assertion failed (ni > 0 && ni == ni1) in collectCalibrationData, file /build/buildd/opencv-2.4.8+dfsg1/modules/calib3d/src/calibration.cpp, line 3193 Traceback (most recent call last): File "", line 1, in File "/usr/lib/python2.7/dist-packages/spyderlib/widgets/externalshell/sitecustomize.py", line 540, in runfile execfile(filename, namespace) File "/home/students/Test/test.py", line 49, in ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, gray.shape[::-1],None,None) cv2.error: /build/buildd/opencv-2.4.8+dfsg1/modules/calib3d/src/calibration.cpp:3193: error: (-215) ni > 0 && ni == ni1 in function collectCalibrationData
I had this same problem, and your main mistake (which I know because I made it myself) is that you have changed checkerboard size (default in example is 7x6, yours is 6x9), but you have neglected to change the size in the initialization code at the top of the routine
objp = np.zeros((6*7,3), np.float32)
objp[:,:2] = np.mgrid[0:7,0:6].T.reshape(-1,2)
To make this work with multiple checkerboard sizes you could adjust the code like so:
# checkerboard Dimensions
cbrow = 5
cbcol = 7
# prepare object points, like (0,0,0), (1,0,0), (2,0,0) ....,(6,5,0)
objp = np.zeros((cbrow * cbcol, 3), np.float32)
objp[:, :2] = np.mgrid[0:cbcol, 0:cbrow].T.reshape(-1, 2)
.
.
.
ret, corners = cv2.findChessboardCorners(gray, (cbcol, cbrow), None)