我寫了以下代碼：import cv2 import lxml.etree as xmlimport osimport shutilfor filename in os.listdir(paths['labels']):    with open(paths['labels']+filename,'r'):        img2 = cv2.imread(filename, cv2.IMREAD_COLOR)         # Reading same image in another          # variable and converting to gray scale.         img = cv2.imread(filename, cv2.IMREAD_GRAYSCALE)         # Converting image to a binary image         # ( black and white only image).         #_, threshold = cv2.threshold(img, 110, 255, cv2.THRESH_BINARY)         blur = cv2.GaussianBlur(img,(5,5),0)        _, threshold = cv2.threshold(blur,0,255,cv2.THRESH_BINARY+cv2.THRESH_OTSU)        # Detecting contours in image.         contours, _= cv2.findContours(threshold, cv2.RETR_TREE,      #here it finds the total number of contours, i.e, number of rectangles in the image file                                       cv2.CHAIN_APPROX_SIMPLE)我在第 18 行中收到錯誤：(blur = cv2.GaussianBlur(img,(5,5),0))錯誤：(-215:Assertion failed) dims <= 2 && step[0] > 0 in function 'cv::Mat::locateROI'代碼之前工作正常，錯誤突然出現。我嘗試將圖像擴展名從jpg更改為png，但錯誤仍然存在。