[R] using a custom color sequence for image()

[Jim Lemon]

On 10/17/2009 01:25 AM, Rajarshi Guha wrote:
> Hi, I'd like to use a custom color sequence (black - low values, green -
> high values) in am image() plot. While I can specify colors (say a  sequence
> of grays) to the col argument, the ordering is getting messed up. I have two
> questions:
>
> 1. How can I get a sequence of say 256 colors starting from black and ending
> in green?
> 2. How is this specified to image() such that it uses the colors in the
> proper ordering?
>    
Hi Rajarshi,
Adding to what Albert wrote, if you mean that you want black to gray and 
then gray to green, you can get it by creating two sequences of colors 
and then joining them together:

ccolors<-c(rgb(seq(0,0.5,length.out=128),
  seq(0,0.5,length.out=128),seq(0,0.5,length.out=128)),
  rgb(seq(0.5,0,length.out=128),seq(0.5,1,length.out=128),
  seq(0.5,0,length.out=128)))
image(...,col=ccolors,...)

See the examples in "color2D.matplot" for more information.

Jim