Ra11y: A collection of accessibilty features for ggplot2 charts

• Colour blindness
• Alt text
  • Auto-generating alt text
• Contrast
• Todo

There are a few functions here that I wrote for personal/professional use. Feel free to use them or suggest new ones.

Install like this:

remotes::install_github("nicucalcea/Ra11y")

Then load it.

library(Ra11y)

Colour blindness

Ra11y includes a function that automatically extracts geom fill and colour properties and checks if they’re safe to use together. If they are not, it will print out the possibly unsafe combinations to the console and suggest a simulation of what the plot looks like with different types of colour blindness.

Let’s look at an example.

library(ggplot2)

starwars <- dplyr::starwars |> 
  tidyr::drop_na(height, mass, gender)

starwars_plot <- starwars |>
  ggplot(aes(x = height, y = mass, colour = gender)) +
  geom_point(size = 4) +
  scale_colour_manual(values = c("red", "darkgreen")) +
  labs(title = "Jabba the Hutt outweighs the competion",
       subtitle = "Height and mass of Star Wars characters")

starwars_plot

This chart uses two colours, red and darkgreen. While those colours look very distinct to most people, they could look similar for some with colour blindness, in this case, protanomaly.

Let’s test that theory.

test_plot(starwars_plot, test = "cvd") # CVD stands for Colour Vision Deficiency

If you run the suggested command (you’ll need a separate package for that), you can see exactly where the problem is. The protanomaly version of the chart has nearly identical colours for both sets of dots.

colorblindr::cvd_grid(starwars_plot)

You should change the colours to something a bit easier to differentiate.

Note that the warning is just a suggestions, colours that are deemed unsafe could be okay to use if, for example, the difference is shown with another dimension (shape, size, etc). This is just a reminder to check.

Alt text

ggplot2 has some rudimentary support for alt text. So far, it gets automatically embedded in R Markdown (what you’re reading now) and Quarto documents and outputed to HTML. This function nudges you to add alt text if you don’t have it, and displays it in the console if you do.

test_plot(starwars_plot, test = "alt")

Let’s add some alt text.

starwars_plot_with_alt <- starwars_plot +
  labs(alt = paste0("Scatter plot of Star Wars characters, with height plotted on the x-axis and mass on the y-axis. The dots are coloured by gender. Generally-speaking, height and mass are correlated. The heaviest character is ", starwars$name[starwars$mass == max(starwars$mass)], "."))

test_plot(starwars_plot_with_alt, test = "alt")

My particular use case is to have a reminder to write good, descriptive alt text for charts that end up being published online.

Of course, you can run both tests in one go.

test_plot(starwars_plot_with_alt)

Additionally, I would recommend checking your plot’s spelling (including the alt text) with ggspell.

Auto-generating alt text

You can also generate alt text automatically using ✨AI✨.

alt_text_suggest(starwars_plot)

## ℹ Scatter plot comparing the height and mass of Star Wars characters, with gender represented by color. Jabba Desilijic Tiure stands out as an outlier with a mass of 1358 and a height of 175.

Contrast

There are some recommendations for setting foreground and background colours that provide enough contrast with the background. This library includes a function that checks if two colours are contrasting enough to use together.

contrast_check("purple", "white")

You can set the colour of text to light or dark depending on, say, the colour of the background.

You can use contrast() to automatically set the text colour so that it’s legible on your background.

contrast_bg("darkred") # returns white

## [1] "white"

contrast_bg("yellow", dark_col = "#222222") # returns off-black

## [1] "#222222"

Or you can use this nifty shortcut.

grid_data <- expand.grid(X = LETTERS[1:10], Y = paste0("var", seq(1, 10)))
grid_data$Z <- runif(100, 0, 5)

ggplot(grid_data, aes(X, Y, fill = Z)) + 
  geom_tile() +
  geom_text(aes(label = Y, !!!autocontrast))

Todo

• Check for minimum text size
• Implement a contrast check for plots. Here’s an example for HTML and one for CSS.
• Check if alt text is too short, too long, doesn’t contain certain keywords (chart, graph, graphic, plot, etc.). Perhaps only activated with a strict param.
• Test other AI models like VisText