r - 如何使用ggplot2在R中制作具有透明背景的图形？

Question

我需要将 ggplot2 图形从 R 输出到具有透明背景的 PNG 文件。基本 R 图形一切正常，但 ggplot2 不透明:

d <- rnorm(100) #generating random data

#this returns transparent png
png('tr_tst1.png',width=300,height=300,units="px",bg = "transparent")
boxplot(d)
dev.off()

df <- data.frame(y=d,x=1)
p <- ggplot(df) + stat_boxplot(aes(x = x,y=y)) 
p <- p + opts(
    panel.background = theme_rect(fill = "transparent",colour = NA), # or theme_blank()
    panel.grid.minor = theme_blank(), 
    panel.grid.major = theme_blank()
)
#returns white background
png('tr_tst2.png',width=300,height=300,units="px",bg = "transparent")
p
dev.off()

有没有办法用ggplot2获得透明背景？

Answer 1

创建初始图:

library(ggplot2)
d <- rnorm(100)
df <- data.frame(
  x = 1,
  y = d,
  group = rep(c("gr1", "gr2"), 50)
)
p <- ggplot(df) + stat_boxplot(
  aes(
    x = x,
    y = y,
    color = group
  ), 
  fill = "transparent" # for the inside of the boxplot
)

修改上图以获得完全透明背景的最快方法是设置 theme()的 rect 参数，因为所有矩形元素都继承自 rect:

p <- p + theme(rect = element_rect(fill = "transparent"))
          
p

更受控制的方法是单独设置 theme() 的更具体参数:

p <- p + theme(
  panel.background = element_rect(fill = "transparent",
                                  colour = NA_character_), # necessary to avoid drawing panel outline
  panel.grid.major = element_blank(), # get rid of major grid
  panel.grid.minor = element_blank(), # get rid of minor grid
  plot.background = element_rect(fill = "transparent",
                                 colour = NA_character_), # necessary to avoid drawing plot outline
  legend.background = element_rect(fill = "transparent"),
  legend.box.background = element_rect(fill = "transparent"),
  legend.key = element_rect(fill = "transparent")
)

p

<小时/>

ggsave()提供专用参数bg来设置

Background colour. If NULL, uses the plot.background fill value from the plot theme.

使用透明背景将 ggplot 对象 p 写入磁盘上的 filename:

ggsave(
  plot = p,
  filename = "tr_tst2.png",
  bg = "transparent"
)