tim.colors: 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

Value

A vector giving the colors in a hexadecimal format.

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. two.colors is really about three different colors. For other colors try fields.color.picker to view possible choices. start="darkgreen", end="azure4" are the options used to get a nice color scale for rendering aerial photos of ski trails. (See http://www.image.ucar.edu/Data/MJProject.)

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 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

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

leaves the choice of the colors to Dr. R after a thunderstorm.

Examples

Run this code

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()