def getGrayDiff(img,currentPoint,tmpPoint):
    """This function does gray difference between two points.
    Parameters
    ----------
    img : numpy array
        Array containing the image data. 
    currentPoint : numpy array
        Array containing the position of one seed point. 
    tmpPoint : numpy array
        Array containing the position of one of the 8 neighboring points to the seed point. 
    """

    return abs(int(img[currentPoint.x,currentPoint.y]) - int(img[tmpPoint.x,tmpPoint.y]))