cv2.videoCapture.release() 是什么意思? [英] What's the meaning of cv2.videoCapture.release()?

问题描述

我正在使用树莓派来捕捉视频的前 20 帧.现在这更像是一个概念问题，但在浏览关于 videoCapture 的 openCV 文档时，他们强调了在此代码中发布捕获的重要性(如其网站上发布的那样):

I am working with a raspberry pi to capture the first 20 frames of a video. Now this is more of a concepts question but while going through the openCV documentation on videoCapture, they emphasize the importance of releasing capture in this code (as posted on their website):

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?省略这一行是否有任何记忆含义?如果是这样，它们是什么以及为什么?

What is the importance of cap.release()? Does ommmiting this line have any memory implication? If so what are they and why?

推荐答案

当你调用 cap.release() 时:

1. 发布软件资源
2. 释放硬件资源

<小时>

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

---

You can try to make another instance cap2 = cv2.VideoCapture(0) before you call cap.release().

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Device or resource busy等错误，导致引发OpenCV Exception.

Because you haven't release the camera device resource, then it will raise errors like Device or resource busy, leads to raise a 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

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