import cv2 def back cap while frame cap read gray cv2 cvtColor frame c

import cv2

def back(cap):
    while (1):
        _, frame = cap.read()
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        cv2.imshow('frame', gray)
        k = cv2.waitKey(10)
        if k >= 0:
            break
    cv2.destroyWindow('frame')
    _, background = cap.read()
    return background

def norm(cap):
    while (1):
        _, frame = cap.read()
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        cv2.imshow('frame', gray)
        k = cv2.waitKey(10)
        if k >= 0:
            break
    cv2.destroyWindow('frame')
    _, background = cap.read()
    # gray_bg = cv2.cvtColor(background, cv2.COLOR_BGR2GRAY)
    # h, w = gray_bg.shape[:2]
    # bottom = gray_bg[h / 2 : h, w / 3 : 2 * w / 3]
    h, w = background.shape[:2]
    bottom = background[0 : h, w / 3 : 2 * w / 3]
    return cv2.mean(bottom)

def doIt(img, avg, th):
    if img is None:
        return
    # gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    gray = img[:,:]
    cv2.subtract(gray, avg - th, gray)
    _, gray = cv2.threshold(gray, th, 255, cv2.THRESH_BINARY)
    return gray