def normalize_box(box,w,h):
    """ Input: [ymin, xmin,ymax,xmax]
        Output: normalized by width and height of image
    """
    nbox = box.copy()
    nbox[:,0] = nbox[:,0]/h
    nbox[:,1] = nbox[:,1]/w
    nbox[:,2] = nbox[:,2]/h
    nbox[:,3] = nbox[:,3]/w
    return nbox