opencv (cv2) 在我的代码中检测运动的问题

Question

我已经编写了一个代码来通过网络摄像头检测运动，但每当我启动该代码时，它都能正常工作，但它会检测整个全屏，而不是检测屏幕中移动的对象。我注意到如果我关闭相机，它似乎会删除检测；这是代码：

import cv2

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
        continue

    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) < 4000:
            continue

        (x,y, w, h)= cv2.boundingRect(contour)
        cv2.rectangle(frame, (x, y), (x + w, y + h),(0,225,0),3)


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

    key = cv2.waitKey(5)

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

video.release()
cv2.destroyAllWindows()

代码应该只能检测屏幕中的移动对象。

Answer 1

我刚开始使用 opencv 时遇到过类似的问题；该程序的问题是第一帧，第一帧捕获了黑屏。第一帧（first_frame）与下一帧（灰色）的 cv2.absdiff 检测到的差异足够大，以至于 cv2.findContours 显示在整个屏幕上。这可能是相机延迟造成的

可以通过在摄像头加载到程序使用 time.sleep() 记录第一帧 (first_frame) 之间加入轻微的延迟来解决。试试这个：

import cv2, time


first_frame = None

video = cv2.VideoCapture(0)
# the camera has some lag time hence the starting of video.read outside loop and sleep
video.read()
time.sleep(2)

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
        continue

    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) < 4000:
            continue

        (x,y, w, h)= cv2.boundingRect(contour)
        cv2.rectangle(frame, (x, y), (x + w, y + h),(0,225,0),3)


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

    key = cv2.waitKey(5)

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

video.release()
cv2.destroyAllWindows()

time.sleep 负责相机启动的延迟时间。试试代码，它在这里工作

opencv (cv2) 在我的代码中检测运动的问题

Problem with opencv (cv2) detecting motion in my code

python

opencv

cv2