reduce processing time of webcam capture

edit

One thing you can do is you can run a separate thread for grabbing the images from the video capture object, and put that captured images in a queue, and from the main thread get a frame from the queue and do your processing.

So while the main thread is processing the image for 25ms, the grabber thread will be able to grab (25/9)=2 frames in the queue ready for the main thread to process and the main thread wont have to wait 9ms for image to be captured.

this will completely remove that 9ms time that was being added to your total time

So right now its like : grab frame(9ms)+ process(25ms)=total time (34ms)

with a separate thread running:

grabber thread:->grab(9ms)--->grab(9ms)------->grab(9ms)----->grab(9ms)->-

main thread: ---> wait(9ms)->getFrame()->--Process------(25ms)---getFrame().... total time for one process cycle is 25ms

so this way the main thread will only wait 9ms in the beginning for the first frame and wont have to wait again anymore

Update: Did some testing in python by myself to see how much it improves the processing in practical, and this is the result

import threading
import time
import Queue
import cv2
frames = Queue.Queue(5)

class ImageGrabber(threading.Thread):
    def __init__(self, ID):
        threading.Thread.__init__(self)
        self.ID=ID
        self.cam=cv2.VideoCapture(ID)
        self.cam.set(3,1280) # just to increase capture time
        self.cam.set(4,1024) # just to increase capture time
        self.runFlag=True

    def run(self):
        print "sub started"
        global frames
        while self.runFlag:
            ret,frame=self.cam.read()
            frames.put(frame)
            time.sleep(0.01)
        self.cam.release()
    def stop(self):
        self.runFlag=False



##------------------------##
## Some random processing ##
## -----------------------##

def Process(img):
    #img1=cv2.Canny(img,100,200)
    img2=cv2.blur(img,(5,5))

##------------------------##
##    without threading   ##
##------------------------##

cam=cv2.VideoCapture(0)
cam.set(3,1280) # just to increase capture time
cam.set(4,1024) # just to increase capture time
ret,img=cam.read()# to ignore the lag of first capture
sumTime=0
i=0
while i<30:
    i=i+1
    start=time.time()
    ret,img=cam.read()
    capTime=time.time()
    Process(img)
    end=time.time()
    sumTime=sumTime+end-start
    print end-start, "capture time=",capTime-start

print "avarage time without multithread=",sumTime/30    
cam.release()


##------------------------##
##     with threading     ##
##------------------------##
grabber = ImageGrabber(0)
grabber.start()
i=0
sumTime=0
while i<30:
    if(not frames.empty()):
        i=i+1
        start=time.time()
        Currframe=frames.get()
        Process(Currframe)
        end=time.time()
        sumTime=sumTime+end-start
        print end-start
print "avarage time with multithread=",sumTime/30    
grabber.stop()
grabber.join()

And this is the output

0.108999967575 capture time= 0.0929999351501
0.0569999217987 capture time= 0.0420000553131
0.0190000534058 capture time= 0.00499987602234
0.055999994278 capture time= 0.0389997959137
0.0340001583099 capture time= 0.0210001468658
0.0820000171661 capture time= 0.069000005722
0.0350000858307 capture time= 0.0199999809265
0.0660002231598 capture time= 0.0530002117157
0.0350000858307 capture time= 0.0209999084473
0.0629999637604 capture time= 0.0479998588562
0.0239999294281 capture time= 0.00499987602234
0.0440001487732 ...