Add an Alpha Channel To a Color

Add transparency to a color defined by its name or number. The function first converts the color to RGB and then appends the alpha channel. Fade() combines ColToOpaque(SetAlpha(col)).

SetAlpha(col, alpha = 0.5)
Fade(col, ...)

Arguments

col

vector of two kind of R colors, i.e., either a color name (an element of colors()) or an integer i meaning palette()[i].

alpha

the alpha value to be added. This can be any value from 0 (fully transparent) to 1 (opaque). NA is interpreted so as to delete a potential alpha channel. Default is 0.5.

...

the dots in Fade are passed on to SetAlpha.

Details

All arguments are recyled as necessary.

Value

Vector with the same length as col, giving the rgb-values extended by the alpha channel as hex-number (#rrggbbaa).

Author

Andri Signorell <andri@signorell.net>

See also

ColToHex, col2rgb, adjustcolor, ColToOpaque

Examples

SetAlpha("yellow", 0.2)
#>      yellow 
#> "#FFFF0033" 
SetAlpha(2, 0.5)   # red
#> [1] "#DF536B80"

Canvas(3)
DrawCircle(x=c(-1,0,1), y=c(1,-1,1), r.out=2, col=SetAlpha(2:4, 0.4))


x <- rnorm(15000)
par(mfrow=c(1,2))
plot(x, type="p", col="blue" )
plot(x, type="p", col=SetAlpha("blue", .2), main="Better insight with alpha channel" )