DescTools (version 0.99.56)

TextContrastColor: Choose Textcolor Depending on Background Color

Description

Text of a certain color when viewed against certain backgrounds can be hard to see. TextContrastColor returns either black or white depending on which has the better contrast.

Usage

TextContrastColor(col, white = "white", black = "black", method = c("glynn", "sonego"))

Value

a vector containing the contrast color (either black or white)

Arguments

col

vector of any of the three kind of R colors, i.e., either a color name (an element of colors()), a hexadecimal string of the form "#rrggbb" or "#rrggbbaa" (see rgb), or an integer i meaning palette()[i]. Non-string values are coerced to integer.

white

the color for the dark backgrounds, default is "white".

black

the color for the bright backgrounds, default is "black"

method

defines the algorithm to be used. Can be one out of "glynn" or "sonego". See details.

Author

Andri Signorell <[e-mail]> based on code of Earl F. Glynn, Stowers Institute for Medical Research, 2004

Details

A simple heuristic in defining a text color for a given background color, is to pick the one that is "farthest" away from "black" or "white". The way Glynn chooses to do this is to compute the color intensity, defined as the mean of the RGB triple, and pick "black" (intensity 0) for text color if the background intensity is greater than 127, or "white" (intensity 255) when the background intensity is less than or equal to 127. Sonego calculates L <- c(0.2, 0.6, 0) %*% col2rgb(color)/255 and returns "black" if L >= 0.2 and "white" else.

Examples

# works fine for grays
PlotArea( y=matrix(rep(1, times=3, each=8), ncol=8), x=1:3,
  col=gray(1:8 / 8), ylab="", xlab="", axes=FALSE )
text( x=2, y=1:8-0.5, levels(d.pizza$driver),
  col=TextContrastColor(gray(1:8 / 8)))

# and not so fine, but still ok, for colors
par(mfrow=c(1,2))
PlotArea( y=matrix(rep(1, times=3, each=12), ncol=12), x=1:3,
  col=rainbow(12), ylab="", xlab="", axes=FALSE, main="method = Glynn" )
text( x=2, y=1:12-0.5, levels(d.pizza$driver),
  col=TextContrastColor(rainbow(12)))

PlotArea( y=matrix(rep(1, times=3, each=12), ncol=12), x=1:3,
  col=rainbow(12), ylab="", xlab="", axes=FALSE, main="method = Sonego" )
text( x=2, y=1:12-0.5, levels(d.pizza$driver),
  col=TextContrastColor(rainbow(12), method="sonego"))