On 14 Mar 2009, at 13:08, Jinsong Zhao wrote:
Hi,
For a good discussion of the link between colour and spectra I would
suggest,
http://www.fourmilab.ch/documents/specrend/
which provides an open-source C code to perform the conversion you
ask
for. I asked for some advice on how to wrap a R function around this
code last week but sadly I didn't get anywhere. Do let me know if you
succeed. (alternatively, one could port the implementation in pure R
as the code is not too complicated or computationally demanding).
Hope this helps,
baptiste
I have visited the site before I posted my question. I don't know
what's
the relationship between black body spectra and specific wavelength.
And frankly, I don't understand C.
The black body radiation in that code is only provided as a test case,
as far as i see it.
I have translate a Fortran code
(http://www.isc.tamu.edu/~astro/color/spectra.html) to R as given
below,
however, I don't know how to modify it and make it could accept a
vector, e.g., 380:780, as input.
if you don't mind about the efficiency of your program, just use ?
sapply on a range of wavelengths. I'm not particularly keen on the
implementation of the FORTRAN program you used compared to the one I
suggested, it seems like a very crude convolution.
And when plot a line, how to color the line using different color?
The easiest way I know of is using ggplot2, see the last example of
this page:
http://had.co.nz/ggplot2/geom_path.html
In base graphics, you could use segments to join the observations and
supply a vector of colours of appropriate length.
Hope this helps,
baptiste
Thanks in advance!
Jinsong
wl2rgb <- function(wl, gamma) {
if (missing(gamma)) gamma <- 1
if (wl >= 380 & wl <= 440) {
r <- -1 * (wl - 440) / (440 - 380)
g <- 0
b <- 1
}
if (wl >= 440 & wl <= 490 ) {
r <- 0
g <- (wl - 440) / (490 - 440)
b <- 1
}
if (wl >= 490 & wl <= 510) {
r <- 0
g <- 1
b <- -1 * (wl - 510) / (510 - 490)
}
if (wl >= 510 & wl <= 580) {
r <- (wl - 510) / (580 - 510)
g <- 1
b <- 0
}
if (wl >= 580 & wl <= 645) {
r <- 1
g <- -1 * (wl - 645) / (645 - 580)
b <- 0
}
if (wl >= 645 & wl <= 780) {
r <- 1
g <- 0
b <- 0
}
s <- 1
if (wl > 700) {
s <- .3 + .7 * (780 - wl) / (780 - 700)
}
if ( wl < 420) {
s <- .3 + .7 * (wl - 380) / (420 - 380)
}
r <- as.integer(255 * (s * r)^gamma)
g <- as.integer(255 * (s * g)^gamma)
b <- as.integer(255 * (s * b)^gamma)
return(rgb(r, g, b, maxColorValue = 255))
}
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_____________________________
Baptiste Auguié
School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK
Phone: +44 1392 264187
http://newton.ex.ac.uk/research/emag
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
