| % File src/library/grDevices/man/rgb.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2014 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{rgb} |
| \title{RGB Color Specification} |
| \usage{ |
| rgb(red, green, blue, alpha, names = NULL, maxColorValue = 1) |
| } |
| \alias{rgb} |
| \description{ |
| This function creates colors corresponding to the given |
| intensities (between 0 and \code{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 |
| \code{0} means fully transparent and \code{max} means opaque). If |
| \code{alpha} is not specified, an opaque colour is generated. |
| |
| The \code{names} argument may be used to provide names for the |
| colors. |
| |
| The values returned by these functions can be used with a |
| \code{col=} specification in graphics functions or in \code{\link{par}}. |
| } |
| \arguments{ |
| \item{red, blue, green, alpha}{numeric vectors with values in \eqn{[0, M]} |
| where \eqn{M} is \code{maxColorValue}. When this is \code{255}, the |
| \code{red}, \code{blue}, \code{green}, and \code{alpha} |
| values are coerced to integers in \code{0:255} and the result is |
| computed most efficiently.} |
| \item{names}{character vector. The names for the resulting vector.} |
| \item{maxColorValue}{number giving the maximum of the color values |
| range, see above.} |
| } |
| \details{ |
| The colors may be specified by passing a matrix or data frame as argument |
| \code{red}, and leaving \code{blue} and \code{green} missing. |
| In this case the first three columns of \code{red} are taken to be |
| the \code{red}, \code{green} and \code{blue} values. |
| |
| Semi-transparent colors (\code{0 < alpha < 1}) are supported only on |
| some devices: at the time of writing on the \code{\link{pdf}}, |
| \code{windows}, \code{quartz} and \code{X11(type = "cairo")} devices and |
| associated bitmap devices (\code{jpeg}, \code{png}, \code{bmp}, |
| \code{tiff} and \code{bitmap}). They are supported by several |
| third-party devices such as those in packages \CRANpkg{Cairo}, |
| \CRANpkg{cairoDevice} and \CRANpkg{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. |
| |
| \code{NA} values are not allowed for any of \code{red}, \code{blue}, |
| \code{green} or \code{alpha}. |
| } |
| \value{ |
| A character vector with elements of 7 or 9 characters, \code{"#"} |
| followed by the red, blue, green and optionally alpha values in |
| hexadecimal (after rescaling to \code{0 ... 255}). The optional alpha |
| values range from \code{0} (fully transparent) to \code{255} (opaque). |
| |
| \R does \strong{not} use \sQuote{premultiplied alpha}. |
| } |
| \seealso{ |
| \code{\link{col2rgb}} for translating \R colors to RGB vectors; |
| \code{\link{rainbow}}, \code{\link{hsv}}, \code{\link{hcl}}, |
| \code{\link{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) |
| } |
| \keyword{color} |