python - cv2.videoCapture.release() 是什么意思？

Question

我正在使用树莓派捕捉视频的前 20 帧。现在这更像是一个概念问题，但是在浏览 videoCapture 上的 openCV 文档时，他们强调了在此代码中发布捕获的重要性(如他们网站上发布的那样):

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()

    # Our operations on the frame come here
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Display the resulting frame
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

cap.release() 的重要性是什么？忽略这一行是否对内存有影响？如果是，它们是什么，为什么？

Answer 1

当您调用 cap.release() 时，则:

1. 发布软件资源
2. 释放硬件资源

---

在调用 cap.release() 之前，您可以尝试创建另一个实例 cap2 = cv2.VideoCapture(0)。

cap = cv2.VideoCapture(0)
#cap.release() 

cap2 = cv2.VideoCapture(0)

因为你还没有释放相机设备资源，那么它会引发错误，如Device or resource busy，导致引发OpenCV Exception。

libv4l2: error setting pixformat: Device or resource busy
VIDEOIO ERROR: libv4l unable to ioctl S_FMT
libv4l2: error setting pixformat: Device or resource busy
libv4l1: error setting pixformat: Device or resource busy
VIDEOIO ERROR: libv4l unable to ioctl VIDIOCSPICT

libv4l2: error setting pixformat: Device or resource busy
OpenCV Error: Unspecified error (GStreamer: unable to start pipeline
) in cvCaptureFromCAM_GStreamer, file /home/xxx/Programs/OpenCV/src/opencv-master/modules/videoio/src/cap_gstreamer.cpp, line 887
VIDEOIO(cvCreateCapture_GStreamer(CV_CAP_GSTREAMER_V4L2, reinterpret_cast<char *>(index))): raised OpenCV exception:

/home/xxx/Programs/OpenCV/src/opencv-master/modules/videoio/src/cap_gstreamer.cpp:887: error: (-2) GStreamer: unable to start pipeline
 in function cvCaptureFromCAM_GStreamer