R: Create colour spaces

make.rgb {grDevices} | R Documentation

## Create colour spaces

### Description

These functions specify colour spaces for use in `convertColor`.

### Usage

    make.rgb(red, green, blue, name = NULL, white = "D65",
             gamma = 2.2)

    colorConverter(toXYZ, fromXYZ, name, white=NULL)

### Arguments

`red,green,blue` | Chromaticity (xy or xyY) of RGB primaries
`name` | Name for the colour space
`white` | Character string specifying the reference white (see ‘Details’.)
`gamma` | Display gamma (nonlinearity). A positive number or the string `"sRGB"`
`fromXYZ` | Function to convert from XYZ tristimulus coordinates to this space
`toXYZ` | Function to convert from this space to XYZ tristimulus coordinates.

### Details

An RGB colour space is defined by the chromaticities of the red, green and blue primaries. These are given as vectors of length 2 or 3 in xyY coordinates (the Y component is not used and may be omitted). The chromaticities are defined relative to a reference white, which must be one of the CIE standard illuminants: "A", "B", "C", "D50", "D55", "D60", "E" (usually "D65").

The display gamma is most commonly 2.2, though 1.8 is used for Apple RGB. The sRGB standard specifies a more complicated function that is close to a gamma of 2.2; `gamma="sRGB"` uses this function.

Colour spaces other than RGB can be specified directly by giving conversions to and from XYZ tristimulus coordinates. The functions should take two arguments. The first is a vector giving the coordinates for one colour. The second argument is the reference white. If a specific reference white is included in the definition of the colour space (as for the RGB spaces) this second argument should be ignored and may be `...`.

### Value

An object of class `colorConverter`

### References

Conversion algorithms from http://www.brucelindbloom.com

### See Also

`convertColor`

### Examples

    (pal <- make.rgb(red=  c(0.6400,0.3300),
                     green=c(0.2900,0.6000),
                     blue= c(0.1500,0.0600),
                     name = "PAL/SECAM RGB"))

    ## converter for sRGB in #rrggbb format
    hexcolor <- colorConverter(toXYZ = function(hex,...) {
                                rgb <- t(col2rgb(hex))/255
                                colorspaces$sRGB$toXYZ(rgb,...) },
                               fromXYZ = function(xyz,...) {
                                  rgb <- colorspaces$sRGB$fromXYZ(xyz,..)
                                  rgb <- round(rgb,5)
                                  if (min(rgb) < 0 || max(rgb) > 1)
                                       as.character(NA)
                                  else
                                       rgb(rgb[1],rgb[2],rgb[3])},
                               white = "D65", name = "#rrggbb")

    (cols <- t(col2rgb(palette())))
    (luv <- convertColor(cols,from="sRGB", to="Luv", scale.in=255))
    (hex <- convertColor(luv, from="Luv",  to=hexcolor, scale.out=NULL))

    ## must make hex a matrix before using it
    (cc <- round(convertColor(as.matrix(hex), from= hexcolor, to= "sRGB",
                              scale.in=NULL, scale.out=255)))
    stopifnot(cc == cols)

[Package grDevices version 2.8.1 Index]