Is it possible to desaturate a ggplot easily?

Question

Is it possible to desaturate a ggplot easily?

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In principle, there could be two possible strategies.
First, apply some function to a ggplot object (or, possibly, Grob object) to desaturate all colors. Second, some trick to print ggplot desaturated while rendering a .rmd file. Both strategies would be ok for me, but first one is, of course, more promissing.
Creating ggplot in greys from the beginning is not a good option as the idea is to have the same plot as if it was printed in shades of grey.

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There were some similar questions and remarkably good answers on how to perform desaturation in R. Here is a convenient way to desaturate color palette. And here is the way of desaturating a raster image. What I'm looking for, is a simple way of desaturating the whole ggplot.

Answer 1

Just came across this question. The experimental package colorblindr (written by Claire McWhite and myself) contains a function that can do this in a generic way. I'm using the example figure from @hrbrmstr:

library(ggplot2)
library(viridis)

gg <- ggplot(mtcars) + 
  geom_point(aes(x=mpg, y=wt, fill=factor(cyl), size=factor(carb)), 
             color="black", shape=21) + 
  scale_fill_viridis(discrete = TRUE) +
  scale_size_manual(values = c(3, 6, 9, 12, 15, 18)) +
  facet_wrap(~am)
gg

Now let's desaturate this plot, using the edit_colors() function from colorblindr:

library(colorblindr) # devtools::install_github("clauswilke/colorblindr")
library(colorspace) # install.packages("colorspace", repos = "http://R-Forge.R-project.org") --- colorblindr requires the development version
# need also install cowplot; current version on CRAN is fine.

gg_des <- edit_colors(gg, desaturate)
cowplot::ggdraw(gg_des)

The function edit_colors() takes a ggplot2 object or grob and applies a color transformation function (here desaturate) to all colors in the grob.

We can provide additional arguments to the transformation function, e.g. to do partial desaturation:

gg_des <- edit_colors(gg, desaturate, amount = 0.7)
cowplot::ggdraw(gg_des)

We can also do other transformations, e.g. color-blind simulations:

gg_des <- edit_colors(gg, deutan)
cowplot::ggdraw(gg_des)

Finally, we can manipulate line colors and fill colors separately. E.g., we could make all filled areas blue. (Not sure this is useful, but whatever.)

gg_des <- edit_colors(gg, fillfun = function(x) "lightblue")
cowplot::ggdraw(gg_des)

Answer 2

As per my comment above, this might be the quickest/dirtiest way to achieve the desaturation for a ggplot2 object:

library(ggplot2)

set.seed(1)
p <- qplot(rnorm(50), rnorm(50), col="Class")
print(p)

pdf(file="p.pdf", colormodel="grey")
  print(p)
dev.off()

Answer 3

I tried this with the new viridis color palette since it desaturates well (i.e. it should be noticeable between the colored & non-colored plots):

library(ggplot2)
library(grid)
library(colorspace)
library(viridis) # devtools::install_github("sjmgarnier/viridis") for scale_fill_viridis

gg <- ggplot(mtcars) + 
  geom_point(aes(x=mpg, y=wt, fill=factor(cyl), size=factor(carb)), 
             color="black", shape=21) + 
  scale_fill_viridis(discrete = TRUE) +
  scale_size_manual(values = c(3, 6, 9, 12, 15, 18)) +
  facet_wrap(~am)

gb <- ggplot_build(gg)
gb$data[[1]]$colour <- desaturate(gb$data[[1]]$colour)
gb$data[[1]]$fill <- desaturate(gb$data[[1]]$fill)

gt <- ggplot_gtable(gb)

grid.newpage()
grid.draw(gt)

You end up having to manipulate on the grob level.

Here's the plot pre-desaturate:

and here's the plot post-desature:

I'm trying to figure out why the legend got skipped and this may miss other highly customized ggplot aesthetics & components, so even while it's not a complete answer, perhaps it might be useful (and perhaps someone else can tack on to it or expand on it in another answer). It should just be a matter of replacing the right bits in either the gb object or gt object.

UPDATE I managed to find the right grob element for the legend:

gt$grobs[[12]][[1]][["99_9c27fc5147adbe9a3bdf887b25d29587"]]$grobs[[4]]$gp$fill <- 
    desaturate(gt$grobs[[12]][[1]][["99_9c27fc5147adbe9a3bdf887b25d29587"]]$grobs[[4]]$gp$fill)
gt$grobs[[12]][[1]][["99_9c27fc5147adbe9a3bdf887b25d29587"]]$grobs[[6]]$gp$fill <- 
    desaturate(gt$grobs[[12]][[1]][["99_9c27fc5147adbe9a3bdf887b25d29587"]]$grobs[[6]]$gp$fill)
gt$grobs[[12]][[1]][["99_9c27fc5147adbe9a3bdf887b25d29587"]]$grobs[[8]]$gp$fill <- 
    desaturate(gt$grobs[[12]][[1]][["99_9c27fc5147adbe9a3bdf887b25d29587"]]$grobs[[8]]$gp$fill)

grid.newpage()
grid.draw(gt)

The machinations to find the other gp elements that need desaturation aren't too bad either.