Question

I am writing a small script (in Python) that generates and updates a running average of a camera feed. When I call cv.RunningAvg it returns:

cv2.error: func != 0

Where am I stumbling in implementing cv.RunningAvg? Script follows:

import cv

feed = cv.CaptureFromCAM(0)
frame = cv.QueryFrame(feed)
moving_average = cv.QueryFrame(feed)
cv.NamedWindow('live', cv.CV_WINDOW_AUTOSIZE)

def loop():
    frame = cv.QueryFrame(feed)
    cv.ShowImage('live', frame)
    c = cv.WaitKey(10)

    cv.RunningAvg(frame, moving_average, 0.020, None)

while True:
    loop()

Answer 1

I am not sure about the error, but check out the documentation for cv.RunningAvg

It says destination should be 32 or 64-bit floating point.

So I made a small correction in your code and it works. I created a 32-bit floating point image to store running average values, then another 8 bit image so that I can show running average image :

import cv2.cv as cv

feed = cv.CaptureFromCAM(0)
frame = cv.QueryFrame(feed)
moving_average = cv.CreateImage(cv.GetSize(frame),32,3) # image to store running avg
avg_show = cv.CreateImage(cv.GetSize(frame),8,3) # image to show running avg

def loop():
    frame = cv.QueryFrame(feed)
    c = cv.WaitKey(10)

    cv.RunningAvg(frame, moving_average, 0.1, None)
    cv.ConvertScaleAbs(moving_average,avg_show) # converting back to 8-bit to show

    cv.ShowImage('live', frame)
    cv.ShowImage('avg',avg_show)

while True:
    loop()

cv.DestroyAllWindows()

Now see the result :

At a particular instant, I saved a frame and its corresponding running average frame.

Original frame :

You can see the obstacle (my hand) blocks the objects in behind.

Now running average frame :

It almost removed my hand and shows objects in background.

That is how it is a good tool for background subtraction.

One more example from a typical traffic video :

You can see more details and samples here : http://opencvpython.blogspot.com/2012/07/background-extraction-using-running.html