ggplot writes to pdf and png with very different sizes

Question

I create a grid with 4 plots and then write it to a pdf as well as to a png. For reasons I don't understand, the charts and fonts plot differently (much smaller in the png than in the pdf). The commands I use are:

pdf("Cusum Page 1.pdf")
  grid.arrange(log_return_plot, tracking_error_plot, 
               ir_graph, excess_vol, 
               layout_matrix = rbind(c(1, 2), c(3, 4)))
dev.off()

and

png(filename = "Cusum Page 1.png", width = 800, height = 800, units = "px",
    pointsize = 12, bg = "white", res = NA, family = "", restoreConsole = TRUE,
    type = c("windows", "cairo", "cairo-png"), antialias = "d")   

  grid.arrange(log_return_plot, tracking_error_plot, 
               ir_graph, excess_vol, 
               layout_matrix = rbind(c(1, 2), c(3, 4)))

dev.off()

I have tried changing and cutting out various options in the png call, with no success - I just can't make my png and pdf look identical. Is the root cause of this problem known? I'd greatly appreciate suggestions on settings that I should try changing in order to make the two exports identical.

Sincerely and with many thanks in advance

Thomas Philips

Answer 1

I suspect this is something to do with setting the width and height arguments of each option and making the png::res (nominal resolution) and pdf::pointsize (defaults to 12) agree.

pdf dimensions default to inches so I've made the png follow suit.

Here's an initial attempt at a resolution.

library(gridExtra)
library(ggplot2)


pdf("Cusum Page 1.pdf", width = 6, height = 6)
grid.arrange(p1, p2, p3, p4, 
             layout_matrix = rbind(c(1, 2), c(3, 4)))
dev.off()



png(filename = "Cusum Page 2.png", width = 6, height = 6, units = "in",
    pointsize = 12, bg = "white", res = 144, family = "", restoreConsole = TRUE,
    type = c("windows", "cairo", "cairo-png"), antialias = "d")   

grid.arrange(p1, p2, p3, p4, 
             layout_matrix = rbind(c(1, 2), c(3, 4)))

dev.off()

graphs

p1 <- 
  ggplot(iris) + 
  geom_histogram(aes(Sepal.Length))

p2 <-  
  ggplot(iris) + 
  geom_histogram(aes(Sepal.Width))

p3 <- 
  ggplot(iris) + 
  geom_histogram(aes(Petal.Length))

p4 <-  
  ggplot(iris) + 
  geom_histogram(aes(Petal.Width))

^{Created on 2021-07-12 by the reprex package (v2.0.0)}

png

pdf - converted to jpg to enable uploading