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, vectorized = FALSE)

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.
`vectorized`	Whether `fromXYZ` and `toXYZ` are vectorized internally to handle input color matrices.

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 ....

As of R 3.6.0 the built in color converters along with convertColor were vectorized to process three column color matrices in one call, instead of row by row via apply. In order to maintain backwards compatibility, colorConverter wraps fromXYZ and toXYZ in a apply loop in case they do not also support matrix inputs. If the fromXYZ and toXYZ functions you are using operate correctly on the whole color matrix at once instead of row by row, you can set vectorized=TRUE for a performance improvement.

Value

An object of class colorConverter

References

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

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())))
zapsmall(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)

## Internally vectorized version of hexcolor, notice the use
## of `vectorized = TRUE`:

hexcolorv <- 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)
                              oob <- pmin(rgb[,1],rgb[,2],rgb[,3]) < 0 |
                                     pmax(rgb[,1],rgb[,2],rgb[,3]) > 0
                              res <- rep(NA_character_, nrow(rgb))
                              res[!oob] <- rgb(rgb[!oob,,drop=FALSE])},
                           white = "D65", name = "#rrggbb",
                           vectorized=TRUE)
(ccv <- round(convertColor(as.matrix(hex), from = hexcolor, to = "sRGB",
                           scale.in = NULL, scale.out = 255)))
stopifnot(ccv == cols)

[Package grDevices version 4.4.1 Index]