tim.colors {fields} | R Documentation |
Several color scales useful for image plots: a pleasing rainbow style color table patterned after that used in Matlab by Tim Hoar and also some simple color interpolation schemes between two or more colors. There is also a function that converts between colors and a real valued vector.
tim.colors(n = 64, alpha=1.0) two.colors(n=256, start="darkgreen", end="red", middle="white", alpha=1.0) designer.colors( n=256, col= c("darkgreen", "white", "darkred"), x= seq(0,1,, length(col)) ,alpha=1.0) color.scale( z, col=tim.colors(256), zlim =NULL, transparent.color="white", eps= 1e-8)
alpha |
The transparency of the color – 1.0 is opaque and 0 is transparent. This is useful for overlays of color and still being able to view the graphics that is covered. |
n |
Number of color levels. The setting |
start |
Starting color for lowest values in color scale |
end |
Ending color. |
middle |
Color scale passes through this color at halfway |
col |
A list of colors (names or hex values) to interpolate |
x |
Positions of colors on a [0,1] scale. Default is to assume that the x values are equally spacesd from 0 to 1. |
z |
Real vector to encode in a color table. |
zlim |
Range to use for color scale. Default is the |
transparent.color |
Color value to use for NA's or values outside |
eps |
A small inflation of the range to avoid boundary values of |
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.
A vector giving the colors in a hexadecimal format, two extra hex digits are added for alpha channel.
topo.colors, terrain.colors, image.plot, quilt.plot, grey.scale, fields.color.picker
tim.colors(10) # returns an array of 10 character strings encoding colors in hex format # e.g. (red, green, blue) values of (16,255, 239) # translates to "#10FFEF" # rgb( 16/255, 255/255, 239/255, alpha=.5) # gives "#10FFEF80" note extra "alpha channel" # veiw some color table choices set.panel( 2,3) z<- outer( 1:20,1:20, "+") obj<- list( x=1:20,y=1:20,z=z ) image( obj, col=tim.colors( 200)) # 200 levels image( obj, col=two.colors() ) # using tranparency without alpha the image plot would cover points plot( 1:20,1:20) image(obj, col=two.colors(alpha=.5), add=TRUE) coltab<- designer.colors(col=c("blue", "grey", "green"), x= c( 0,.3,1) ) image( obj, 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 # some random color values set.seed(123) z<- rnorm(100) hex.codes<- color.scale(z, col=two.colors()) N<-length( hex.codes) # take a look at the coded values # or equivalently create some Xmas wrapping paper! image( 1:N, N, matrix(1:N, N,1) , col=hex.codes, axes=FALSE, xlab="", ylab="") set.panel()