addAlpha: Add alpha channel (transparency) to colors

In marchtaylor/sinkr: Collection of functions with emphasis on multivariate data analysis

Add alpha channel (transparency) to colors

Description

Takes a vector of colors and adds an alpha channel at the given level of transparency. See also adjustcolor.

Usage

addAlpha(COLORS, ALPHA)

Arguments

COLORS	Vector of any of the three kinds of R color specifications, i.e., either a color name (as listed by colors()), a hexadecimal string of the form "#rrggbb" or "#rrggbbaa" (see rgb), or a positive integer i meaning palette()[i].
ALPHA	A value (between 0 and 1) indicating the alpha channel (opacity) value.

Examples

# Make background image
x <- seq(-180, 180, length.out=30)
y <- seq(-90, 90, length.out=30)
grd <- expand.grid(x=x,y=y)
z <- sqrt(grd$x^2+grd$y^2)
dim(z) <- c(length(x), length(y))
pal <- colorRampPalette(c(rgb(1,1,1), rgb(0,0,0)))
COLORS <- pal(20)
image(x,y,z, col=COLORS)

# Add semi-transparent layer
z2 <- grd$x^2+grd$y
dim(z2) <- c(length(x), length(y))
pal <- colorRampPalette(c(rgb(0.5,1,0), rgb(0,1,1), rgb(1,1,1)))
COLORS <- addAlpha(pal(20), 0.4) # alpha chanel equals 0.4
image(x,y,z2, col=COLORS, add=TRUE)

marchtaylor/sinkr documentation built on June 15, 2025, 1:17 a.m.