[R] image() and non-well-ordered colours

From: Robin Hankin <r.hankin_at_noc.soton.ac.uk>
Date: Tue 24 May 2005 - 21:07:58 EST


Hi.

I want to use image() with colours that are indexed by two variables. Indexing by one variable is easy:

library(colorspace)
x <- seq(from=0, to=1,len=30)
z <- outer(x,1i*x,"+")
image(Re(z),col=hcl(seq(from=0,to=100,len=15),c=100))

OK, so far so good. Now, I want the colour to be a more complicated function
of z, in which both the hue and luminance change (thus the colours cannot
be ordered):

f <- function(z){hcl(h=100*Re(z),l=100*Im(z))}

I want to draw z in terms of the colour defined by f():

image(z,col=f)
image(f(z))

but these don't work as intended. How do I use image() to get what I want?
I can get close using plot():

x <- runif(1000)
y <- (1:1000)/10
g <- function(x){hcl(h=80*x,l=(1:1000)/10,c=300)}
plot(x,y,col=g(x),pch=16)

[note that one cannot draw nontrivial "contour lines" joining points of identical colours on this
plot: top left to lower right goes from pink to black; top right to low left goes from yellow to reddy orange]

It'd be nice to make image() do what I want. Anyone?

--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743

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Received on Tue May 24 21:12:03 2005

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