//高低值通道
study(title="highest_lowest", shorttitle="highest_lowest_channel", overlay=true)

length = input(defval=30,title='length',minval=10)

highest_value = highest(high,length)
lowest_value = lowest(low,length)

plot(highest_value, color=color.red, linewidth=1)
plot(lowest_value, color=color.red, linewidth=1)