python - Google Colab 中的 OpenCV Python 用于多个图像：max Contour 函数不起作用

Question

我目前正在使用 Google Colab 编写用于面部图像的脚本。我正在使用 Haar 正面面部检测，为其拟合一个矩形，使用该区域内的最大轮廓将椭圆拟合到面部。当我尝试将函数 max() 用于轮廓“cnts”时，我收到错误“ValueError: max() arg is an empty sequence”。打印时的 Cnts 具有值，并且列表已填充。max() 函数适用于单个图像。关于如何让它再次运行的任何建议？TIA

    from collections import Iterable
import math
def flatten(lis):
     for item in lis:
         if isinstance(item, Iterable) and not isinstance(item, str):
             for x in flatten(item):
                 yield x
         else:        
             yield item

detector = cv2.CascadeClassifier(cv2.data.haarcascades + 'haarcascade_frontalface_default.xml')

for i in range (0, len(X_data)):
  gray = cv2.cvtColor(X_data[i], cv2.COLOR_RGB2GRAY)
  rects = detector.detectMultiScale(gray, scaleFactor=1.05,                             #rects returns the values of the bounding boxes
      minNeighbors=5, minSize=(30, 30),
      flags=cv2.CASCADE_SCALE_IMAGE)

  # loop over the bounding boxes
  for (x, y, w, h) in rects:
    crop_img = gray[y-5:(y+h+5) , x-5:(x+w+5)]                                                        #crop each image with a border of 10 pixels for each with the bounding box
    th, threshed = cv2.threshold(crop_img, 100, 255, cv2.THRESH_BINARY)                                #thresholding image to aid finding contours within the cropped image, possible improvement needed
    cnts, hiers = cv2.findContours(threshed, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE, offset=(x,y))  #find contours in the thresheld image
    print(cnts)
    
    c = max(cnts, key = cv2.contourArea)                                                             #find maximum contour in the image
    cnt_list=list(flatten(c))
    print (cnt_list)                                                                         #flatten the largest contour
    ellipse=cv2.fitEllipse(c)
    cv2.ellipse(X_data[i], ellipse, (23, 184, 80), 3)
    #print ('ellipse: ',ellipse)
    print(ellipse[0][0])
    centre_x=ellipse[0][0]
    centre_y=ellipse[0][1]
    minor_b=ellipse[1][0]
    major_a=ellipse[1][1]
    angle=ellipse[2]

标签： pythonopencvmax