Run the opencv official website example code facedetect.py

#!/usr/bin/env python

'''
face detection using haar cascades

USAGE:
    facedetect.py [--cascade <cascade_fn>] [--nested-cascade <cascade_fn>] [<video_source>]
'''

# Python 2/3 compatibility
from __future__ import print_function

import numpy as np
import cv2 as cv

# local modules
from video import create_capture
from common import clock, draw_str


def detect(img, cascade):
    rects = cascade.detectMultiScale(img, scaleFactor=1.3, minNeighbors=4, minSize=(30, 30),
                                     flags=cv.CASCADE_SCALE_IMAGE)
    if len(rects) == 0:
        return []
    rects[:,2:] += rects[:,:2]
    return rects

def draw_rects(img, rects, color):
    for x1, y1, x2, y2 in rects:
        cv.rectangle(img, (x1, y1), (x2, y2), color, 2)

def main():
    import sys, getopt

    args, video_src = getopt.getopt(sys.argv[1:], '', ['cascade=', 'nested-cascade='])
    try:
        video_src = video_src[0]
    except:
        video_src = 0
    args = dict(args)
    cascade_fn = args.get('--cascade', "data/haarcascades/haarcascade_frontalface_alt.xml")
    nested_fn = args.get('--nested-cascade', "data/haarcascades/haarcascade_eye.xml")

    
    cascade = cv.CascadeClassifier(cv.samples.findFile(cascade_fn))
    nested = cv.CascadeClassifier(cv.samples.findFile(nested_fn))
    cam = create_capture(video_src, fallback='synth:bg={}:noise=0.05'.format(cv.samples.findFile('data/lena.jpg')))#此处的data文件夹是从opencv示例simple包中复制到该项目中。

    
    while True:
        _ret, img = cam.read()
        gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
        gray = cv.equalizeHist(gray)

        t = clock()
        rects = detect(gray, cascade)
        vis = img.copy()
        draw_rects(vis, rects, (0, 255, 0))
        if not nested.empty():
            for x1, y1, x2, y2 in rects:
                roi = gray[y1:y2, x1:x2]
                vis_roi = vis[y1:y2, x1:x2]
                subrects = detect(roi.copy(), nested)
                draw_rects(vis_roi, subrects, (255, 0, 0))
        dt = clock() - t

        draw_str(vis, (20, 20), 'time: %.1f ms' % (dt*1000))
        cv.imshow('facedetect', vis)

        if cv.waitKey(5) == 27:
            break

    print('Done')

if __name__ == '__main__':
    print(__doc__)
    main()
    cv.destroyAllWindows()

Problem description

Running the above code reports the following error:

[ WARN:[email protected]] global D:\a\opencv-python\opencv-python\opencv\modules\core\src\utils\samples.cpp (61) cv::samples::findFile cv::samples::findFile('data/haarcascades/haarcascade_frontalface_alt.xml') => ''
Traceback (most recent call last):
  File "E:\Pycharm\Pycharm7\facedetect.py", line 81, in <module>
    main()
  File "E:\Pycharm\Pycharm7\facedetect.py", line 48, in main
    cascade = cv.CascadeClassifier(cv.samples.findFile(cascade_fn))
cv2.error: OpenCV(4.6.0) D:\a\opencv-python\opencv-python\opencv\modules\core\src\utils\samples.cpp:64: error: (-2:Unspecified error) OpenCV samples: Can't find required data file: data/haarcascades/haarcascade_frontalface_alt.xml in function 'cv::samples::findFile'

Cause analysis:

According to the error location:

cascade = cv.CascadeClassifier(cv.samples.findFile(cascade_fn))

It can be found that the file paths of “haarcascade_frontalface_alt.xml” and “data/haarcascades/haarcascade_eye.xml” are not correct.

Solution:

“haarcascade_frontalface_alt.xml” and “data/haarcascades/haarcascade_eye.xml” are under the cv2 package installed in python, just change the path in the code to a relative path.

The code is changed as follows:

cascade_fn = args.get('--cascade', "D:/Python/yingyong/Lib/site-packages/cv2/data/haarcascades/haarcascade_frontalface_alt.xml")
    nested_fn  = args.get('--nested-cascade', "D:/Python/yingyong/Lib/site-packages/cv2/data/haarcascades/haarcascade_eye.xml")

Run again to run normally.