R: Add an Alpha Channel To a Color

SetAlpha {DescTools} | R Documentation

## Add an Alpha Channel To a Color

### Description

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.

### Usage

    SetAlpha(col, alpha = 0.5)

### 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.

### 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(s)

Andri Signorell <andri@signorell.net>

### See Also

`ColToHex`, `col2rgb`

### Examples

    SetAlpha("yellow", 0.2)
    SetAlpha(2, 0.5)   # red

    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" )

[Package DescTools version 0.99.26 Index]