python校准失真校正错误

我正在尝试opencv图像校准和校正失真。它没有错误，但它给了我意想不到的结果

下图为“2.jpg”

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问题是什么？但是不能使用单个图像计算摄影机矩阵，在可以校正图像后，需要N个图像来计算摄影机矩阵

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((4*7,3), np.float32)
objp[:,:2] = np.mgrid[0:7,0:4].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.

fname = '2.jpg'
img = cv2.imread(fname)
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
# Find the chess board corners
ret, corners = cv2.findChessboardCorners(gray, (7,4),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)
    img = cv2.drawChessboardCorners(img, (7, 4), corners2, ret)
    ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, gray.shape[::-1], None, None)

    img = cv2.imread('2.jpg')

    h, w = img.shape[:2]
    newcameramtx, roi = cv2.getOptimalNewCameraMatrix(mtx, dist, (w, h), 1, (w, h))

    mapx, mapy = cv2.initUndistortRectifyMap(mtx, dist, None, newcameramtx, (w, h), 5)
    dst = cv2.remap(img, mapx, mapy, cv2.INTER_LINEAR)

    # crop the image
    x, y, w, h = roi
    dst = dst[y:y + h, x:x + w]
    cv2.imwrite('calibresult.png', dst)