级联分类器（Cascade Classifier）是一种基于Haar特征的对象检测算法，首先需要手动的去训练自己的模型，如人脸识别官网有训练好的，可以直接拿来用
链接直达
官方代码示例：
from __future__ import print_function
import cv2 as cv
import argparsedef detectAndDisplay(frame):frame_gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)frame_gray = cv.equalizeHist(frame_gray)# -- 检测面部faces = face_cascade.detectMultiScale(frame_gray)for (x, y, w, h) in faces:center = (x + w // 2, y + h // 2)frame = cv.ellipse(frame, center, (w // 2, h // 2), 0, 0, 360, (255, 0, 255), 4)faceROI = frame_gray[y:y + h, x:x + w]# -- 在每张面部上检测眼睛eyes = eyes_cascade.detectMultiScale(faceROI)for (x2, y2, w2, h2) in eyes:eye_center = (x + x2 + w2 // 2, y + y2 + h2 // 2)radius = int(round((w2 + h2) * 0.25))frame = cv.circle(frame, eye_center, radius, (255, 0, 0), 4)cv.imshow('Capture - Face detection', frame)parser = argparse.ArgumentParser(description='Code for Cascade Classifier tutorial.')
parser.add_argument('--face_cascade', help='Path to face cascade.', default='haarcascade_frontalface_alt.xml')
parser.add_argument('--eyes_cascade', help='Path to eyes cascade.', default='haarcascade_eye_tree_eyeglasses.xml')
parser.add_argument('--camera', help='Camera divide number.', type=int, default=0)
args = parser.parse_args()
face_cascade_name = args.face_cascade
eyes_cascade_name = args.eyes_cascade
face_cascade = cv.CascadeClassifier()
eyes_cascade = cv.CascadeClassifier()
# -- 1. 加载级联
if not face_cascade.load(cv.samples.findFile(face_cascade_name)):print('--(!)Error loading face cascade')exit(0)
if not eyes_cascade.load(cv.samples.findFile(eyes_cascade_name)):print('--(!)Error loading eyes cascade')exit(0)
camera_device = args.camera
# -- 2. 读取视频流
cap = cv.VideoCapture(camera_device)
if not cap.isOpened:print('--(!)Error opening video capture')exit(0)
while True:ret, frame = cap.read()if frame is None:print('--(!) No captured frame -- Break!')breakdetectAndDisplay(frame)if cv.waitKey(10) == 27:break
