CODEWITHSUNDEEP
rcolorsggplot2
Jonas Stein
Jonas Stein

Reputation: 7043

Generate pairs of bright and dark colours for ggplot2

brewer.pal(n=8,name="Paired")

Can create up to eight colour pairs, but only few of these colours are good for printing. Is there a more flexible function that will generate a dark pendant? The darker one should

Is there a colourbrewer tool that can already solve that? 

> dark("red")
[1] "FF5555"

I figured out this function, but it can only handle single colours, not a vector. This function would be a nice solution, if it could be "vectorized".

setbrightness <- function(rgbcolour, brightness) {
  ## usage: setbrightness(col2rgb("red", 0.2)
  thiscolour <- rgb2hsv(rgbcolour)
  return(hsv(h=thiscolour[1], s=thiscolour[2], v=brightness))
}

Upvotes: 2

Views: 1267

Answers (1)

Julius Vainora
Julius Vainora

Reputation: 48241

Here is a vectorized function that you can use. The idea is to convert RGB to HSV, where V corresponds to brightness and then go back to RGB:

library(grDevices)
# Every element of r, g, b must be in [0, 255]
# Every element of conv[[3]] must be in [0, 1], 1 is highest brightness
brightness <- function(r, g, b, factor) {
  conv <- as.list(as.data.frame(t(rgb2hsv(r, g, b))))
  conv[[3]] <- pmin(1, conv[[3]] * factor)
  do.call(hsv, conv)
}

# Reducing brightness by 20%
brightness(55, 100, 150, 0.8)
#[1] "#2C5078"

# Increasing by 20%
brightness(55, 100, 150, 1.2)
#[1] "#4278B4"

brightness(55, 100, 150, c(0.8, 1.2))
#[1] "#2C5078" "#4278B4"

x <- rep(LETTERS[1:2], 5)
qplot(x = x, geom = "bar", fill = x) + 
  scale_fill_manual(values = brightness(55, 100, 150, c(0.5, 1.5)))

enter image description here

See ?rgb2hsv, ?hsv and wiki for more details.

Edit: according to your edit it seems that you prefer using names of colours and direct values of brightness. In that case a vectorized function would look very similarly:

# Usage: brightness("red", c(0.1, 0.3, 0.5, 1))
brightness <- function(rgbcol, v) {
  conv <- as.list(as.data.frame(t(rgb2hsv(col2rgb(rgbcol)))))
  conv[[3]] <- v
  do.call(hsv, conv)
}

set.seed(19)
df <- data.frame(a = rlnorm(100), b = 1:10, c = rep(LETTERS[1:10], each = 10))
ggplot(df, aes(x = b, y = a, fill = c)) + geom_area() + theme_bw() +
  scale_fill_manual(values = brightness("red", seq(0.1, 0.7, length = 10)))

enter image description here

Upvotes: 10

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