import cv2 import numpy as np import glob ################################################################################ print 'criteria and object points set' # termination criteria criteria = (3L, 30, 0.001) # prepare object points, like (0,0,0), (1,0,0), (2,0,0) ....,(8,5,0) objpoint = np.zeros((9 * 6, 3), np.float32) objpoint[:,:2] = np.mgrid[0:9, 0:6].T.reshape(-1,2) # arrays to store object points and image points from all the images # 3d point in real world space objpoints = [] # 2d points in image plane imgpoints = [] ################################################################################ print 'Load Images' images = glob.glob('images/Phone Camera/*.bmp') for frame in images: img = cv2.imread(frame) imgGray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY) # find chess board corners ret, corners = cv2.findChessboardCorners(imgGray, (9,6), None) # print ret to check if pattern size is set correctly print ret # if found, add object points, image points (after refining them) if ret == True: # add object points objpoints.append(objpoint) cv2.cornerSubPix(imgGray, corners, (11,11), (-1,-1), criteria) # add corners as image points imgpoints.append(corners) # draw corners cv2.drawChessboardCorners(img, (9,6), corners, ret) cv2.imshow('Image',img) cv2.waitKey(0) cv2.destroyAllWindows() ################################################################################ print 'camera matrix' ret, camMat, distortCoffs, rotVects, transVects = cv2.calibrateCamera(objpoints, imgpoints, imgGray.shape[::-1],None,None) ################################################################################ print 're-projection error' meanError = 0 for i in xrange(len(objpoints)): imgpoints2, _ = cv2.projectPoints(objpoints[i], rotVects[i], transVects[i], camMat, distortCoffs) error = cv2.norm(imgpoints[i], imgpoints2, cv2.NORM_L2) / len(imgpoints2) meanError += error print "total error: ", meanError / len(objpoints) ################################################################################ def drawAxis(img, corners, imgpoints): corner = tuple(corners[0].ravel()) cv2.line(img, corner, tuple(imgpoints[0].ravel()), (255,0,0), 5) cv2.line(img, corner, tuple(imgpoints[1].ravel()), (0,255,0), 5) cv2.line(img, corner, tuple(imgpoints[2].ravel()), (0,0,255), 5) return img ################################################################################ def drawCube(img, corners, imgpoints): imgpoints = np.int32(imgpoints).reshape(-1,2) # draw ground floor in green color cv2.drawContours(img, [imgpoints[:4]], -1, (0,255,0), -3) # draw pillars in blue color for i,j in zip(range(4), range(4,8)): cv2.line(img, tuple(imgpoints[i]), tuple(imgpoints[j]), (255,0,0), 3) # draw top layer in red color cv2.drawContours(img, [imgpoints[4:]], -1, (0,0,255), 3) return img ################################################################################ print 'pose calculation' axis = np.float32([[3,0,0], [0,3,0], [0,0,-3]]).reshape(-1,3) axisCube = np.float32([[0,0,0], [0,3,0], [3,3,0], [3,0,0], [0,0,-3], [0,3,-3], [3,3,-3], [3,0,-3]]) for frame in glob.glob('images/Phone Camera/*.bmp'): img = cv2.imread(frame) gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY) ret, corners = cv2.findChessboardCorners(gray, (9,6), None) if ret == True: # find the rotation and translation vectors. rotVects, transVects, inliers = cv2.solvePnPRansac(objpoint, corners, camMat, distortCoffs) # project 3D points to image plane ''' imgpoints, jac = cv2.projectPoints(axis, rotVecs, transVecs, camMat, distortCoffs) img = drawAxis(img, corners, imgpoints) ''' imgpoints, jac = cv2.projectPoints(axisCube, rotVects, transVects, camMat, distortCoffs) img = drawCube(img, corners, imgpoints) cv2.imshow('Image with Pose', img) cv2.waitKey(0) cv2.destroyAllWindows()
标定结果如下。左图出现锯齿状折线说明找到模式,右图为多个坐标轴的组成的正方体的可视化。每个正方体的边长为3,测得黑格和白格的边长即可获得物体的实际长度,所以用在视觉测量方面很方便,即测量图像中物体的实际长度。
<pre name="code" class="python">################################################################################ print 'SIFT Keypoints and Descriptors' sift = cv2.SIFT() keypoint1, descriptor1 = sift.detectAndCompute(img1, None) keypoint2, descriptor2 = sift.detectAndCompute(img2, None) ################################################################################ print 'SIFT Points Match' FLANN_INDEX_KDTREE = 0 index_params = dict(algorithm = FLANN_INDEX_KDTREE, trees = 5) search_params = dict(checks = 50) # flann = cv2.FlannBasedMatcher(index_params, search_params) bf = cv2.BFMatcher() matches = bf.knnMatch(descriptor1, descriptor2, k = 2) ################################################################################ good = [] points1 = [] points2 = [] ################################################################################ for i, (m, n) in enumerate(matches): if m.distance < 0.7 * n.distance: good.append(m) points1.append(keypoint1[m.queryIdx].pt) points2.append(keypoint2[m.trainIdx].pt) points1 = np.float32(points1) points2 = np.float32(points2) F, mask = cv2.findFundamentalMat(points1, points2, cv2.RANSAC) # We select only inlier points points1 = points1[mask.ravel() == 1] points2 = points2[mask.ravel() == 1]
基础矩阵适用于未标定的摄像头,假设空间点在两个物理成像平面中的坐标分别为p = (u, v)和p' = (u', v'),则满足transpose(p) *F*p = 0,*表示矩阵乘法。根据基础矩阵的定义F = inverse(transpose(K)) * E * inverse(K)计算出本征矩阵E。
################################################################################ # camera matrix from calibration K = np.array([[517.67386649, 0.0, 268.65952163], [0.0, 519.75461699, 215.58959128], [0.0, 0.0, 1.0]]) # essential matrix E = K.T * F * K
W = np.array([[0., -1., 0.], [1., 0., 0.], [0., 0., 1.]]) U, S, V = np.linalg.svd(E) # rotation matrix R = U * W * V # translation vector t = [U[0][2], U[1][2], U[2][2]] checkValidRot(R) P1 = [[R[0][0], R[0][1], R[0][2], t[0]], [R[1][0], R[1][1], R[1][2], t[1]], [R[2][0], R[2][1], R[2][2], t[2]]] P = [[1., 0., 0., 0.], [0., 1., 0., 0.], [0., 0., 1., 0.]]
################################################################################ print 'points triangulation' u = [] u1 = [] Kinv = np.linalg.inv(K) # convert points in gray image plane to homogeneous coordinates for idx in range(len(points1)): t = np.dot(Kinv, np.array([points1[idx][0], points1[idx][1], 1.])) t1 = np.dot(Kinv, np.array([points2[idx][0], points2[idx][1], 1.])) u.append(t) u1.append(t1) ################################################################################ # re-projection error reprojError = 0 # point cloud (X,Y,Z) pointCloudX = [] pointCloudY = [] pointCloudZ = [] for idx in range(len(points1)): X = linearLSTriangulation(u[idx], P, u1[idx], P1) pointCloudX.append(X[0]) pointCloudY.append(X[1]) pointCloudZ.append(X[2]) temp = np.zeros(4, np.float32) temp[0] = X[0] temp[1] = X[1] temp[2] = X[2] temp[3] = 1.0 print temp # calculate re-projection error reprojPoint = np.dot(np.dot(K, P1), temp) imgPoint = np.array([points1[idx][0], points1[idx][1], 1.]) reprojError += math.sqrt((reprojPoint[0] / reprojPoint[2] - imgPoint[0]) * (reprojPoint[0] / reprojPoint[2] - imgPoint[0]) + (reprojPoint[1] / reprojPoint[2] - imgPoint[1]) * (reprojPoint[1] / reprojPoint[2] - imgPoint[1])) print 'Re-project Error:', reprojError / len(points1)绘制空间点的在三维空间中的位置,但没有根据黑白格边长作长度单位的转换。实验结果如下图所示。上面两幅图为步骤(2)和(3)的实验结果,所有极线的交点为极点,都在图像之外。图像中匹配合格的特征点有相同的编号。根据编号的相对位置关系判断重建可以是否合理。