Gradient of n colors ranging from color 1 and color 2

问题

I often work with ggplot2 that makes gradients nice (click here for an example). I have a need to work in base and I think scales can be used there to create color gradients as well but I\'m severely off the mark on how. The basic goal is generate a palette of n colors that ranges from x color to y color. The solution needs to work in base though. This was a starting point but there\'s no place to input an n.

 scale_colour_gradientn(colours=c(\"red\", \"blue\"))

I am well aware of:

brewer.pal(8, \"Spectral\")

from RColorBrewer. I\'m looking more for the approach similar to how ggplot2 handles gradients that says I have these two colors and I want 15 colors along the way. How can I do that?

回答1:

colorRampPalette could be your friend here:

colfunc <- colorRampPalette(c("black", "white"))
colfunc(10)
# [1] "#000000" "#1C1C1C" "#383838" "#555555" "#717171" "#8D8D8D" "#AAAAAA"
# [8] "#C6C6C6" "#E2E2E2" "#FFFFFF"

And just to show it works:

plot(rep(1,10),col=colfunc(10),pch=19,cex=3)

回答2:

Just to expand on the previous answer colorRampPalettecan handle more than two colors.

So for a more expanded "heat map" type look you can....

colfunc<-colorRampPalette(c("red","yellow","springgreen","royalblue"))
plot(rep(1,50),col=(colfunc(50)), pch=19,cex=2)

The resulting image:

回答3:

Try the following:

color.gradient <- function(x, colors=c("red","yellow","green"), colsteps=100) {
  return( colorRampPalette(colors) (colsteps) [ findInterval(x, seq(min(x),max(x), length.out=colsteps)) ] )
}
x <- c((1:100)^2, (100:1)^2)
plot(x,col=color.gradient(x), pch=19,cex=2)

回答4:

The above answer is useful but in graphs, it is difficult to distinguish between darker gradients of black. One alternative I found is to use gradients of gray colors as follows

palette(gray.colors(10, 0.9, 0.4))
plot(rep(1,10),col=1:10,pch=19,cex=3))

More info on gray scale here.

Added

When I used the code above for different colours like blue and black, the gradients were not that clear. heat.colors() seems more useful.

This document has more detailed information and options. pdf

来源：https://stackoverflow.com/questions/13353213/gradient-of-n-colors-ranging-from-color-1-and-color-2

标签

gradient