從網絡攝像頭獲取最新幀

Question

我正在使用OpenCV2使用攝像頭拍攝一些timelapse照片。我想提取攝像頭看到的最近的視圖。我試圖做到這一點。

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)] 

除了放置在網絡攝像頭前面的圖像沒有顯示。這幾乎就像如果有某種緩衝......

所以我清除該緩衝區，就像這樣：

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)] 

現在這個工作，但它是煩人不科學的和緩慢的。有沒有辦法只專門詢問緩衝區中最新的圖像？或者說，更好的方法來清除緩衝區？

Answer 1

我從Capture single picture with opencv發現了一些代碼，這有助於。我對其進行了修改，使其不斷顯示最新拍攝的圖像。它似乎沒有緩衝區問題，但我可能誤解了你的問題。

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() 

Answer 2

我已閱讀，在VideoCapture對象是有5幀緩衝器，並且在.grab方法，它採用的幀，但不對其進行解碼。

所以，你可以

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