% fields, Tools for spatial data
% Copyright 2004-2007, Institute for Mathematics Applied Geosciences
% University Corporation for Atmospheric Research
% Licensed under the GPL -- www.gpl.org/licenses/gpl.html

\name{tim.colors}
\alias{tim.colors}
\alias{two.colors}
\alias{designer.colors}
\title{ Some useful color tables for images. }
\description{
Two color scales useful for image plots:
a pleasing rainbow style color table patterned after that used in 
Matlab by Tim Hoar and also a simple colr interpolation between two 
colors passing through white. 
}
\usage{
tim.colors(n = 64)
two.colors(n=256, start="darkgreen", end="red", middle="white")
designer.colors( n=256, col= c("darkgreen", "white", "darkred"),
                              x= seq(0,1,, length(col)) )

}
\arguments{
  \item{n}{ Number of color levels. The setting \code{n}=64 is the orignal 
definition.}
\item{start}{Starting color for lowest values in color scale}
\item{end}{ Ending color.}
\item{middle}{Color scale passes through this color at halfway}
\item{col}{A list of colors (names or hex values) to interpolate}
\item{x}{Positions of colors on a [0,1] scale. Default is to assume that
the x values are equally spacesd from 0 to 1.}
}

\details{
 The color in R can be represented as three vectors in RGB coordinates
and these coordinates are interpolated separately using a cubic spline
to give color values that intermediate to the specified colors.  

 Ask Tim Hoar about tim.colors! He is a matlab black belt and this is
his favorite scale in that system.  \code{two.colors} is really about
three different colors. For other colors try \code{fields.color.picker}
to view possible choices.   \code{start="darkgreen", end="azure4"} are
the options used to get a nice color scale for rendering aerial photos
of ski trails.  (See \url{http://www.image.ucar.edu/Data/MJProject}.)

 \code{designer.color} is the master function for two.colors and
tim.colors.  It can be useful if one wants to customize the color table
to match quantiles of a distribution.  e.g. if the median of the data is
at .3 with respect to the range then set \code{x} equal to c(0,.3,1) and
specify three colors to provide a transtion that matches the median
value. In fields language this function interpolates between a set of
colors at locations x. While you can be creative about these colors just
using another color scale as the basis is easy. For example

\code{designer.color( 256, rainbow(4), x= c( 0,.2,.8,1.0))}

leaves the choice of the colors to Dr. R after a thunderstorm.
 
}
\value{
A vector giving the colors in a hexadecimal format. 

}
\seealso{ topo.colors, terrain.colors, image.plot, quilt.plot, grey.scale,
fields.color.picker }
\examples{

tim.colors(10) 
# returns an array of 10 strings in hex format
#e.g. (red, green,  blue) values of   (16,255, 239)
# translates to "#10FFEF" .

# veiw some color table choices
set.panel( 1,3)
par( pty="s")
z<- outer( 1:20,1:20, "+")

image( z, col=tim.colors( 200)) # 200 levels

image( z, col=two.colors() )

coltab<- designer.colors(col=c("blue", "grey", "green"),  x= c( 0,.3,1) ) 
image( z, col= coltab )

# peg colors at some desired quantiles  of data.
# NOTE need 0 and 1 for the color scale to make sense
x<- quantile( c(z), c(0,.25,.5,.75,1.0) )
# scale these to [0,1]
zr<- range( c(z))
x<- (x-zr[1])/ (zr[2] - zr[1])  

coltab<- designer.colors(256,rainbow(5), x)
image( z, col= coltab ) # see image.plot for adding all kinds of legends

# colors now change at quantiles of data

set.panel()

}
\keyword{ aplot}