R: Adjust Colors in One or More Directions Conveniently

adjustcolor {grDevices}

R Documentation

Adjust Colors in One or More Directions Conveniently

Description

Adjust or modify a vector of colors by “turning knobs” on one or more coordinates in (r,g,b,\alpha) space, typically by up or down scaling them.

Usage

adjustcolor(col, alpha.f = 1, red.f = 1, green.f = 1, blue.f = 1,
            offset = c(0, 0, 0, 0),
            transform = diag(c(red.f, green.f, blue.f, alpha.f)))

Arguments

col

vector of colors, in any format that col2rgb() accepts

alpha.f

factor modifying the opacity alpha; typically in [0,1]

red.f, green.f, blue.f

factors modifying the “red-”, “green-” or “blue-”ness of the colors, respectively.

offset

numeric vector of length 4 to offset x := c(r,g,b,alpha), where x is the [0,1]-scaled result of col2rgb(col, alpha=TRUE).

transform

a 4x4 numeric matrix applied to x + offset.

Value

a color vector of the same length as col, effectively the result of rgb().

Examples

## Illustrative examples :
opal <- palette("default")
stopifnot(identical(adjustcolor(1:8,       0.75),
                    adjustcolor(palette(), 0.75)))
cbind(palette(), adjustcolor(1:8, 0.75))

##  alpha = 1/2 * previous alpha --> opaque colors
x <- palette(adjustcolor(palette(), 0.5))

sines <- outer(1:20, 1:4, function(x, y) sin(x / 20 * pi * y))
matplot(sines, type = "b", pch = 21:23, col = 2:5, bg = 2:5,
        main = "Using an 'opaque ('translucent') color palette")

x. <- adjustcolor(x, offset = c(0.5, 0.5, 0.5, 0), # <- "more white"
                  transform = diag(c(.7, .7, .7, 0.6)))
cbind(x, x.)
op <- par(bg = adjustcolor("goldenrod", offset = -rep(.4, 4)), xpd = NA)
plot(0:9, 0:9, type = "n", axes = FALSE, xlab = "", ylab = "",
     main = "adjustcolor() -> translucent")
text(1:8, labels = paste0(x,"++"), col = x., cex = 8)
par(op)

## and

(M <- cbind( rbind( matrix(1/3, 3, 3), 0), c(0, 0, 0, 1)))
adjustcolor(x, transform = M)

## revert to previous palette: active
palette(opal)