从网络摄像头获取最新帧

Question

我正在使用 OpenCV2 使用网络摄像头拍摄一些延时摄影照片。我想提取网络摄像头看到的最新视图。我尝试这样做。

import cv2
a = cv2.VideoCapture(1)
ret, frame = a.read()
#The following garbage just shows the image and waits for a key press
#Put something in front of the webcam and then press a key
cv2.imshow('a',frame); cv2.waitKey(0); cv2.destroyAllWindows(); [cv2.waitKey(25) for i in range(10)]
#Since something was placed in front of the webcam we naively expect
#to see it when we read in the next image. We would be wrong.
ret, frame = a.read()
cv2.imshow('a',frame); cv2.waitKey(0); cv2.destroyAllWindows(); [cv2.waitKey(25) for i in range(10)]

除了放置在网络摄像头前面的图像不显示。这几乎就像有某种缓冲......

所以我像这样清除缓冲区：

import cv2
a = cv2.VideoCapture(1)
ret, frame = a.read()
#Place something in front of the webcam and then press a key
cv2.imshow('a',frame); cv2.waitKey(0); cv2.destroyAllWindows(); [cv2.waitKey(25) for i in range(10)]

#Purge the buffer
for i in range(10): #Annoyingly arbitrary constant
  a.grab()

#Get the next frame. Joy!
ret, frame = a.read()
cv2.imshow('a',frame); cv2.waitKey(0); cv2.destroyAllWindows(); [cv2.waitKey(25) for i in range(10)]

现在这可行，但它非常不科学且速度慢。有没有办法专门询问缓冲区中的最新图像？还是说，有更好的方法来清除缓冲区？

Answer 1

我读到在 VideoCapture 对象中有一个 5 帧缓冲区，并且有 .grab 方法获取帧但不解码。

所以你可以

cap = cv2.VideoCapture(0)
for i in xrange(4):
    cap.grab()
ret, frame = cap.read()
...

Answer 2

我从Capture single picture with opencv 找到了一些有用的代码。我对其进行了修改，使其连续显示最近捕获的图像。它似乎没有缓冲问题，但我可能误解了你的问题。

import numpy as np
import cv2

cap = cv2.VideoCapture(0) # video capture source camera (Here webcam of laptop) 
ret,frame = cap.read() # return a single frame in variable `frame`


while(True):
    ret,frame = cap.read() # return a single frame in variable `frame
    cv2.imshow('img1',frame) #display the captured image
    if cv2.waitKey(1) & 0xFF == ord('y'): #save on pressing 'y' 
        cv2.imwrite('images/c1.png',frame)
        cv2.destroyAllWindows()
        break

cap.release()