R: RGB Color Specification

rgb {grDevices} | R Documentation

## RGB Color Specification

### Description

This function creates colors corresponding to the given intensities (between 0 and `max`) of the red, green and blue primaries. The colour specification refers to the standard sRGB colorspace (IEC standard 61966).

An alpha transparency value can also be specified (as an opacity, so `0` means fully transparent and `max` means opaque). If `alpha` is not specified, an opaque colour is generated.

The `names` argument may be used to provide names for the colors.

The values returned by these functions can be used with a `col=` specification in graphics functions or in `par`.

### Usage

    rgb(red, green, blue, alpha, names = NULL, maxColorValue = 1)

### Arguments

`red, blue, green, alpha` | numeric vectors with values in [0, M] where M is `maxColorValue`. When this is `255`, the `red`, `blue`, `green`, and `alpha` values are coerced to integers in `0:255` and the result is computed most efficiently.
`names` | character. The names for the resulting vector.
`maxColorValue` | number giving the maximum of the color values range, see above.

### Details

The colors may be specified by passing a matrix or dataframe as argument `red`, and leaving `blue` and `green` missing. In this case the first three columns of `red` are taken to be the `red`, `green` and `blue` values.

Semi-transparent colors (`0 < alpha < 1`) are supported only on some devices: at the time of writing on the `pdf`, `windows`, `quartz` and `X11(type="cairo")` devices and associated bitmap devices (`jpeg`, `png`, `bmp`, `tiff` and `bitmap`). They are supported by several third-party devices such as those in packages Cairo, cairoDevice and JavaGD. Only some of these devices support semi-transparent backgrounds.

Most other graphics devices plot semi-transparent colors as fully transparent, usually with a warning when first encountered.

### Value

A character vector with elements of 7 or 9 characters, `"#"` followed by the red, blue, green and optionally alpha values in hexadecimal (after rescaling to `0 ... 255`). The optional alpha values range from `0` (fully transparent) to `255` (opaque).

R does not use ‘premultiplied alpha’.

### See Also

`col2rgb` for translating R colors to RGB vectors; `rainbow`, `hsv`, `hcl`, `gray`.

### Examples

    rgb(0,1,0)

    rgb((0:15)/15, green=0, blue=0, names=paste("red",0:15,sep="."))

    rgb(0, 0:12, 0, max = 255)# integer input

    ramp <- colorRamp(c("red", "white"))
    rgb( ramp(seq(0, 1, length = 5)), max = 255)

[Package grDevices version 2.15.1 Index]