I am trying to calibrate camera using OpenCV tools according to the following this guide.
The problem is that function findChessboardCorners
cannot find any chessboard on images I tried. I used a lot of them - even just plain chessboard pattern. In any case, nothing was detected.
Here is the code (almost the same as from link above):
import numpy as np
import cv2
import glob
# termination criteria
criteria = (cv2.TERM_CRITERIA_EPS + cv2.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((6*7,3), np.float32)
objp[:,:2] = np.mgrid[0:7,0:6].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.
images = glob.glob('*.png')
for fname in images:
img = cv2.imread(fname)
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
# Find the chess board corners
ret, corners = cv2.findChessboardCorners(gray, (7,6),None)
# If found, add object points, image points (after refining them)
if ret == True:
objpoints.append(objp)
corners2 = cv2.cornerSubPix(gray,corners,(11,11),(-1,-1),criteria)
imgpoints.append(corners2)
# Draw and display the corners
img = cv2.drawChessboardCorners(img, (7,6), corners2,ret)
cv2.imshow('img',img)
cv2.waitKey(500)
cv2.destroyAllWindows()
The only change I made is that i switched from .jpg files to .png files - for some reason, function imread cannot read jpg images (that's another strange problem for other topic).
Thank you in advance for advices!
Image ref:
Just for other Python newbies that may go down this road. Working code:
import numpy as np
import cv2
import glob
# termination criteria
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.
imgpoints = [] # 2d points in image plane.
images = glob.glob('*.png')
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, (7,7))
# If found, add object points, image points (after refining them)
if ret == True:
cv2.cornerSubPix(gray, corners, (11,11), (-1,-1), criteria)
imgpoints.append(corners)
# Draw and display the corners
cv2.drawChessboardCorners(img, (7,7), corners, ret)
cv2.imshow('img',img)
cv2.waitKey(0)
cv2.destroyAllWindows()
Two main points:
You have to carefully count dimension of you pattern. (7,7) is for usual chessboard.
Line img = cv2.drawChessboardCorners(img, (7,6), corners2,ret)
doesn't work, you have to change it to cv2.drawChessboardCorners(img, (7,6), corners2,ret)
(function doesn't return image).
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