R: Choose Textcolor Depending on Background Color

TextContrastColor {DescTools} | R Documentation

## 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, method = c("glynn", "sonego"))

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

### 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 #000060 if L >= 0.2 and #FFFFA0 else.

### Value

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

### Author(s)

Andri Signorell <andri@signorell.net> based on code of Earl F. Glynn, Stowers Institute for Medical Research, 2004

### References

http://research.stowers.org/mcm/efg/R/Color/Chart/index.htm

(Reference for Sonego??)

### 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"))

[Package DescTools version 0.99.26 Index]