删除基本图周围的空白区域

Question

我想删除图周围的空白空间并将其保存为png文件。我真的需要帮助

这是我的代码：

valores=c(12.5,25.0,12.5,25.0)
names(valores)=c("Escrita","Leitura","Comp. Oral","Exp. Oral")
par(mai=c(1,1.2,1,1))
barplot(valores,horiz = TRUE,xaxt="n",xlim=c(0,100),width=0.3,ylim=c(0,5),xlab=c("Nível"),space=c(0.3,0.3,0.3,0.3),
      col="firebrick",las=1)
ticks<-c(0,25,50,75)
axis(1,at=ticks,labels=c("","A1","A2","B1"))