luminance: Get or set the relative brightness of colors

In jiho/chroma: Parse and Manipulate Colors, Create Perceptually Correct Color Palettes

Get or set the relative brightness of colors

Description

Get or set the relative brightness of colors

Usage

luminance(x)

luminance(x) <- value

Arguments

x	vector of colors specified as hex strings or named R colors.
value	the luminance value, as a number in [0,1]

Details

luminance gets the relative brightness of colors, normalised to 0 for darkest black and 1 for lightest white according to the WCAG definition http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef.

luminance<- sets the relative brightness by interpolating with black or white until the appropriate relative luminance is found. The changes in luminance are not reversible because the interpolation to black or white changes various aspects of the color simultaneously: its lightness of course but also its intensity and even possibly its hue (at the extreme, black or white have no well-defined hue).

Value

For luminance, a vector of luminance values, each in [0,1].

For luminance<-, the updated object(s).

See Also

channel to extract or set a given channel, in particular the lightness channel in HSL, HCL, or L*a*b* color spaces.

Other color manipulation functions: average(), blend(), channel(), darken(), mix(), saturate()

Examples

luminance("black")
luminance("white")
luminance("red")

# Colors along a HSV rainbow have very different relative brightness
luminance(rainbow(6))
# but brightness is much more homogenous along a HCL "rainbow"
luminance(hcl(h=seq(0, 360, length.out=6)))

# Change the luminance
col <- "red"
luminance(col) <- 0.5
show_col(c("red", col))

# This can even be used to create color ramps, although the steps in
# perceived brightness may not be regular at the extremes
col <- "red"
luminance(col) <- seq(0, 1, length.out=10)
show_col(col)
# Better to avoid the extremes then
col <- "red"
luminance(col) <- seq(0.1, 0.9, length.out=10)
show_col(col)

jiho/chroma documentation built on Nov. 26, 2022, 2:39 a.m.