def _convert_yolo(size, box):
    """ Used to normalize bounding box """
    dw = 1.0 / size[0]
    dh = 1.0 / size[1]
    x = (box[0] + box[2]) / 2.0
    y = (box[1] + box[3]) / 2.0
    w = box[2] - box[0]
    h = box[3] - box[1]
    x = x * dw
    w = w * dw
    y = y * dh
    h = h * dh
    return x, y, w, h
