How to increase performance of OpenCV cv2.VideoCapture(0).read()

问题

I'm running this script on Kali linux with intel core i7-4510u:

import cv2
from datetime import datetime
vid_cam = cv2.VideoCapture(0)
vid_cam.set(cv2.CAP_PROP_FPS, 25)
vid_cam.set(cv2.CAP_PROP_FRAME_WIDTH, 640)
vid_cam.set(cv2.CAP_PROP_FRAME_HEIGHT, 360)

lastDate = datetime.now().second
fcount = 0
while(vid_cam.isOpened()):
    if(datetime.now().second>lastDate):
        lastDate = datetime.now().second
        print("Fps: " + str(fcount))
        fcount = 0
    else:
        fcount += 1
    ret, image_frame = vid_cam.read()
    cv2.imshow('frame', image_frame)
    if cv2.waitKey(100) & 0xFF == ord('q'):
        break
vid_cam.release()
cv2.destroyAllWindows()

If I run it, it prints Fps: 4.
If I check Task Manager my cpu is at about 2%.
Where can the problem be?

回答1:

One potential reason could because of I/O latency when reading frames. Since cv2.VideoCapture().read() is a blocking operation, the main program is stalled until the frame is read from the camera device and returned. A method to improve performance would be to spawn another thread to handle grabbing frames in parallel instead of relying on a single thread to grab frames in sequential order. We can improve performance by creating a new thread that only polls for new frames while the main thread handles processing the current frame. Here's a snippet for multithreading frames.

from threading import Thread
import cv2, time

class VideoStreamWidget(object):
    def __init__(self, src=0):
        self.capture = cv2.VideoCapture(src)
        # Start the thread to read frames from the video stream
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True
        self.thread.start()

    def update(self):
        # Read the next frame from the stream in a different thread
        while True:
            if self.capture.isOpened():
                (self.status, self.frame) = self.capture.read()
            time.sleep(.01)

    def show_frame(self):
        # Display frames in main program
        cv2.imshow('frame', self.frame)
        key = cv2.waitKey(1)
        if key == ord('q'):
            self.capture.release()
            cv2.destroyAllWindows()
            exit(1)

if __name__ == '__main__':
    video_stream_widget = VideoStreamWidget()
    while True:
        try:
            video_stream_widget.show_frame()
        except AttributeError:
            pass

来源：https://stackoverflow.com/questions/54933801/how-to-increase-performance-of-opencv-cv2-videocapture0-read