variable increment in python beginner error

Question

I am trying to increment the counter each time it detects an object.

count=0

def detect_and_draw(img, cascade):
    # allocate temporary images
    gray = cv.CreateImage((img.width,img.height), 8, 1)
    small_img = cv.CreateImage((cv.Round(img.width / image_scale),
                   cv.Round (img.height / image_scale)), 8, 1)

    # convert color input image to grayscale
cv.CvtColor(img, gray, cv.CV_BGR2GRAY)

# scale input image for faster processing
cv.Resize(gray, small_img, cv.CV_INTER_LINEAR)
cv.EqualizeHist(small_img, small_img)

if(cascade):
    t = cv.GetTickCount()
    faces = cv.HaarDetectObjects(small_img, cascade, cv.CreateMemStorage(0),
                                 haar_scale, min_neighbors, haar_flags, min_size)
    t = cv.GetTickCount() - t
    print "time taken for detection = %gms" % (t/(cv.GetTickFrequency()*1000.))
    if faces:

        for ((x, y, w, h), n) in faces:
            # the input to cv.HaarDetectObjects was resized, so scale the
            # bounding box of each face and convert it to two CvPoints
            pt1 = (int(x * image_scale), int(y * image_scale))
            pt2 = (int((x + w) * image_scale), int((y + h) * image_scale))
            cv.Rectangle(img, pt1, pt2, cv.RGB(255, 0, 0), 3, 8, 0) 
            count += 1
            print count

But I can't get why it has this error .I tried to do the increment just after if but still same error. It's the first time to use python so I can't get the scoping rules. what should I modify?

 File "detect.py", line 42, in detect_and_draw
    count +=1
UnboundLocalError: local variable 'count' referenced before assignment

Answer 1

You have a global count. The function doesn't know it.

def detect_and_draw(img, cascade):
    global count