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问相机不开放，不能通过Open捕捉视频。
EN

Stack Overflow用户

提问于 2022-10-22 23:22:30

回答 1查看 49关注 0票数 0

下面的代码在Google上运行，它显示“您的会话被压缩，自动重新启动”。我是初学者，我需要用相机捕捉面部表情。

import numpy as np
import cv2 as cv
cap = cv.VideoCapture(-1)
if not cap.isOpened():
    print("Cannot open camera")
    exit()
while True:
    # Capture frame-by-frame
    ret, frame = cap.read()
    # if frame is read correctly ret is True
    if not ret:
        print("Can't receive frame (stream end?). Exiting ...")
        break
    # Our operations on the frame come here
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
    # Display the resulting frame
    cv.imshow('frame', gray)
    if cv.waitKey(1) == ord('q'):
        break
# When everything done, release the capture
cap.release()
cv.destroyAllWindows()

google-colaboratory

webcam

python

opencv

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回答 1

Stack Overflow用户

发布于 2022-10-23 00:48:53

Colab环境中没有本地的视频设备，它运行在云中的某个地方。需要的是浏览器中的一些本地JavaScript来访问用户附近的相机。Colab提供了代码片段示例，其中一个是用于视频捕获的，我已经在下面介绍了这些示例。

先运行这个牢房。

from IPython.display import display, Javascript
from google.colab.output import eval_js
from base64 import b64decode

def take_photo(filename='photo.jpg', quality=0.8):
js = Javascript('''
  async function takePhoto(quality) {
    const div = document.createElement('div');
    const capture = document.createElement('button');
    capture.textContent = 'Capture';
    div.appendChild(capture);

    const video = document.createElement('video');
    video.style.display = 'block';
    const stream = await navigator.mediaDevices.getUserMedia({video: true});

    document.body.appendChild(div);
    div.appendChild(video);
    video.srcObject = stream;
    await video.play();

    // Resize the output to fit the video element.
    google.colab.output.setIframeHeight(document.documentElement.scrollHeight, true);

    // Wait for Capture to be clicked.
    await new Promise((resolve) => capture.onclick = resolve);

    const canvas = document.createElement('canvas');
    canvas.width = video.videoWidth;
    canvas.height = video.videoHeight;
    canvas.getContext('2d').drawImage(video, 0, 0);
    stream.getVideoTracks()[0].stop();
    div.remove();
    return canvas.toDataURL('image/jpeg', quality);
  }
  ''')
display(js)
data = eval_js('takePhoto({})'.format(quality))
binary = b64decode(data.split(',')[1])
with open(filename, 'wb') as f:
  f.write(binary)
return filename

在运行此单元时，必须允许视频访问。

from IPython.display import Image
try:
  filename = take_photo()
  print('Saved to {}'.format(filename))

  # Show the image which was just taken.
  display(Image(filename))
except Exception as err:
  # Errors will be thrown if the user does not have a webcam or if they do not
  # grant the page permission to access it.
  print(str(err))