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\name{color.scale}
\alias{color.scale}
\title{Turn values into colors.}
\description{Transform numeric values into colors}
\usage{
color.scale(x,redrange=c(0,1),greenrange=c(0,1),bluerange=c(0,1),
extremes=NA,na.color=NA,xrange=NULL)
}
\arguments{
\item{x}{a numeric vector, matrix or data frame}
\item{redrange,greenrange,bluerange}{color ranges into which
to scale \samp{x}}
\item{extremes}{The colors for the extreme values of \samp{x}.}
\item{na.color}{The color to use for NA values of \samp{x}.}
\item{xrange}{An explicit range to use in the transformation.}
}
\details{
\samp{color.scale} calculates a sequence of colors by a linear
transformation of the numeric values supplied into the ranges
for red, green and blue. If only one number is supplied for a
color range, that color remains constant for all values of \samp{x}.
If more than two values are supplied, the \samp{x} values will be
split into equal ranges (one less than the number of colors) and
the transformation carried out on each range. Values for a color
range must be between 0 and 1.
If \samp{extremes} is not NA, the ranges will be calculated from
its values using \samp{col2rgb}, even if ranges are also supplied.
\samp{extremes} allows the user to just pass the extreme color values
in any format that \samp{col2rgb} will accept.
If the user wants to specify a range of values with \samp{xrange},
it must at least include the range of x values. This can be useful
when there is a notional range like 0-100% that the values do not
cover, or when several series of values with different ranges are
to be assigned the same color scale.
The user may not want the color scheme to be continuous across some
critical point, often zero. In this case, color scale can be called
separately for the values below and above zero. See the second example
for \samp{color2D.matplot}.
}
\note{
The function is useful for highlighting a numeric dimension or adding
an extra "dimension" to a plot.
There are quite a few R functions that transform numeric values into
colors or produce colors that can be used to represent values. Two
packages that might be of interest are \pkg{RColorBrewer} and
\pkg{colourschemes}.
}
\value{A vector or matrix of hexadecimal color values.}
\author{Jim Lemon}
\seealso{\link{rescale}, \link{col2rgb}, \link{smoothColors}}
\examples{
# go from green through yellow to red with no blue
x<-rnorm(20)
y<-rnorm(20)
# use y for the color scale
plot(x,y,col=color.scale(y,c(0,1,1),c(1,1,0),0),main="Color scale plot",
pch=16,cex=2)
}
\keyword{misc}
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