python - 在python中使用cv2.findContours()时发生ValueError。 ->没有足够的值来解压(预期3，得到2)

Question

出现错误:

Traceback (most recent call last):
    File "motion_detector.py", line 21, in <module>
        (_, cnts, _) = cv2.findContours(thresh_frame.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE) 
ValueError: not enough values to unpack (expected 3, got 2)

在检测图像轮廓时遇到问题。从本教程中进行了双重检查，并从堆栈溢出处进行了检查，以了解我错过了什么，但是找不到解决方案。使用Python 3.6.4和OpenCV 4.0.0。谢谢您的帮助!

代码在这里:

import cv2, time

first_frame = None

video = cv2.VideoCapture(0)

while True:
    check, frame = video.read()

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    gray = cv2.GaussianBlur(gray,(21,21),0) 

    if first_frame is None:
        first_frame = gray 

    delta_frame = cv2.absdiff(first_frame, gray)
    thresh_frame = cv2.threshold(delta_frame, 30, 255, cv2.THRESH_BINARY)[1]
    thresh_frame = cv2.dilate(thresh_frame, None, iterations = 2) 

    (_, cnts, _) = cv2.findContours(thresh_frame.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

    for contour in cnts:
        if cv2.contourArea(contour) < 1000: 
            continue
        (x, y, w, h) = cv2.boundingRect(contour)
        cv2.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 3)

    cv2.imshow("Gray Frame", gray)
    cv2.imshow("Delta Frame", delta_frame)
    cv2.imshow("Threshold Frame", thresh_frame)
    cv2.imshow("Color Frame", frame)

    key = cv2.waitKey(1)
    print(gray)
    print(delta_frame)

    if key == ord('q'):
        break

video.release()
cv2.destroyAllWindows

Answer 1

我也遇到了同样的问题，如果您使用的是旧教程cv2.findContours()函数将返回3值，但是如果您使用的是更高版本，它将返回2值，因此您可以删除第一个变量赋值并像这样使用

cnts, _ = cv2.findContours(thresh_frame.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)