Return a colour palette function or vector from the cpt-city archive

cpt extracts a named colour palette from the internal cpt-city database and returns either a character vector of n interpolated hex colours or the underlying colorRampPalette function itself. The package ships 7140 colour gradients from https://phillips.shef.ac.uk/pub/cpt-city/.

cpt(
  pal = "mpl_inferno",
  n = 100,
  colorRampPalette = FALSE,
  rev = FALSE,
  frgb = rep(1, 3)
)

Arguments

pal: Character. Name or position of the colour gradient in the cpt-city archive. Default "mpl_inferno".
n: Integer. Number of colours to return when colorRampPalette = FALSE. Ignored when colorRampPalette = TRUE.
colorRampPalette: Logical. If FALSE (default), returns a character vector of n hex colours. If TRUE, returns a colorRampPalette *function* — this is what you need for plot (pal =) and scale_fill_gradientn (colours =).
rev: Logical. If TRUE, reverses the order of colours before interpolation.
frgb: Numeric vector of length 3. Per-channel scaling factors for c(red, green, blue). Values > 1 boost the channel, < 1 reduce it. Default c(1, 1, 1) (no scaling).

Value

A character vector of hex colours (length n) when colorRampPalette = FALSE, or a colorRampPalette function when colorRampPalette = TRUE.

Details

**`sf` / `ggplot2` users:** use colorRampPalette = TRUE. The sf plot method and ggplot2's scale_*_gradientn need a *function*, not a character vector. See the examples below.

Examples

library(cptcity)

# Character vector — use with base graphics
image(matrix(1:100), col = cpt(pal = "mpl_inferno"))

image(matrix(1:100), col = cpt("idv_temperature", rev = TRUE))


# colorRampPalette function — use with sf and ggplot2
if (FALSE) { # \dontrun{
library(sf)
nc <- st_read(system.file("shape/nc.shp", package = "sf"))
plot(nc["AREA"], pal = cpt("mpl_inferno", colorRampPalette = TRUE))

library(ggplot2)
ggplot(faithfuld, aes(waiting, eruptions)) +
  geom_raster(aes(fill = density)) +
  scale_fill_gradientn(colours = cpt(n = 100, pal = "mpl_inferno"))
} # }

# Search for palettes by keyword
find_cpt("temperature")
#> [1] "arendal_temperature"    "idv_temperature"        "jjg_misc_temperature"  
#> [4] "kst_03_red_temperature"
image(matrix(1:100), col = cpt("idv_temperature"))


# Tint the palette by scaling the red channel down
image(matrix(1:100), col = cpt("mpl_inferno", frgb = c(0.3, 1, 1)))