Pick the most distinguishable colors from one or more palettes

Pools the colors of the named palettes and selects the n that are hardest to confuse with one another on a given kind of plot: light background, dark background, or output that will be read in grayscale. Optionally judges distinctness under simulated color-vision deficiency. Use it when a single character's palette does not have enough usable colors, or when you want a team's or a faction's colors but only the ones that hold up on a chart.

Usage

tf_pick(
  palettes,
  n = 5,
  style = c("light", "dark", "grayscale"),
  colorblind = FALSE,
  medium = "toy",
  background = NULL,
  min_contrast = 3
)

Arguments

palettes: Character vector of one or more palette names; see tf_palette_names(). Team names are not accepted; use tf_palette_names(team = ...) to expand a team.
n: Number of colors wanted.
style: One of "light" (white background), "dark" (near-black background) or "grayscale" (white background, judged by lightness alone).
colorblind: Logical. Require the colors to stay distinct under simulated deuteranopia, protanopia and tritanopia?
medium: Medium for plain palette names; see tf_media().
background: Optional background color overriding the one implied by style, as a hex string.
min_contrast: Minimum WCAG 2 contrast ratio a color must have against the background to be considered. Set to 1 to disable the filter.

Value

A character vector of n hex colors with class "tf_palette", named by the palette each color came from, and with attributes min_distance (smallest pairwise distance under the chosen criterion), style, colorblind and background.

Details

The selection runs in three steps.

Pool. The colors of every palette in palettes are combined, with duplicates removed. Names may be plain ("optimus_prime") or carry a medium suffix ("optimus_prime_cartoon"); plain names use medium.
Filter for the background. Colors whose WCAG 2 contrast ratio against the background is below min_contrast are dropped, so a light-mode selection never contains a near-white and a dark-mode selection never contains a near-black. The background is white for "light" and "grayscale" and near-black ("#121212") for "dark" unless background is given. The default of 3 is the WCAG minimum for graphical objects; lower it to keep more colors, raise it for text.
Choose. Every pair of remaining colors is scored by its distance in CIE Lab (CIE76). With colorblind = TRUE the distance is the smallest of the normal-vision distance and the distances after simulating deuteranopia, protanopia and tritanopia (Machado, Oliveira and Fernandes 2009), so two colors only count as distinct if every viewer can tell them apart. With style = "grayscale" only the lightness difference counts, so the colors survive conversion to gray. The n colors whose closest pair is farthest apart are chosen (a maximum-dispersion subset, found exhaustively when the pool is small and by greedy seeding plus swap search otherwise), then ordered so that each color is as different as possible from those before it.

The result is a categorical palette: it does not try to build a gradient. The smallest pairwise distance in the selection is returned as the min_distance attribute; values above about 20 are comfortably distinct, and below about 12 two colors will be hard to tell apart. If the pool cannot supply n colors after filtering, the function errors and says how many it had, so add palettes or lower min_contrast.

Examples

# five colors for a white-background plot, from the two leaders
tf_pick(c("optimus_prime", "megatron"), n = 5)
#> Transformers pick of 5 colors from optimus_prime + megatron
#> light background #FFFFFF, min distance 21.7
#> optimus_prime = #D0202A
#> optimus_prime = #1F3E8F
#> megatron = #8C9095
#> megatron = #2A2A2A
#> megatron = #6B3FA0


# the same for a dark theme, and color-blind safe
tf_pick(c("optimus_prime", "megatron"), n = 4, style = "dark", colorblind = TRUE)
#> Transformers pick of 4 colors from optimus_prime + megatron
#> dark background #121212, colorblind-safe, min distance 22
#> optimus_prime = #D0202A
#> megatron = #C9CBCF
#> optimus_prime = #F2D23C
#> megatron = #8C9095


# a whole team, cartoon colors, printable in grayscale
tf_pick(tf_palette_names(team = "Combaticons"), n = 4,
        style = "grayscale", medium = "cartoon")
#> Transformers pick of 4 colors from onslaught_cartoon + brawl_cartoon + swindle_cartoon + blast_off_cartoon + vortex_cartoon + bruticus_cartoon
#> grayscale background #FFFFFF, min distance 4.5
#> onslaught_cartoon = #2B2B2B
#> onslaught_cartoon = #4E6E3E
#> swindle_cartoon = #5A3E8A
#> onslaught_cartoon = #2E5A8A


library(ggplot2)
cols <- tf_pick(tf_palette_names(team = "Predacons"), n = 3, colorblind = TRUE)
ggplot(mpg, aes(displ, hwy, colour = drv)) +
  geom_point(size = 2.5) +
  scale_colour_manual(values = unname(cols)) +
  theme_minimal()