def reduce_bbox_size(bbox, width_frac=1., height_frac=1.):
    """
    bbox (list): 
    -- [x, y, w, h] 
    frac_of_original (float): 
    -- new box area will be frac_of_original times original area
    """
    x, y, w, h = bbox
    bbox_center = (x + w / 2., y + h / 2.)
    new_w = width_frac * w
    new_h = height_frac * h
    new_x = bbox_center[0] - new_w / 2.
    new_y = bbox_center[1] - new_h / 2.
    resized_bbox = [new_x, new_y, new_w, new_h]
    resized_bbox = [int(round(_)) for _ in resized_bbox]
    return resized_bbox