[R] [OT] two question about color space.

[Thomas Lumley]

The XYZ to RGB conversion is already in convertColor(), and also in the colorspace package.

       -thomas


On Sun, 15 Mar 2009, baptiste auguie wrote:

> I've put together a rough R port of that C code [*] in a package on r-forge:
>
> http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/pkg/spectral/?root=photonics
>
> http://r-forge.r-project.org/R/?group_id=160 ( package spectral,  will be built 
> overnight )
>
>
> There is a lot of optimization and cleaning to do: it seems much slower than it 
> should be, and the documentation is empty at the moment, but it reproduces the 
> result for the black body radiation.
>
>
>> library(spectral)
>> 
>> data(wavelength)
>> data(cie_colour_match)
>> data(colourSystem)
>> 
>> test <- function(bbTemp=5000){
>> 	mxyz <- spectrum_to_xyz(specfun=bb_spectrum, bbTemp=bbTemp)
>> 	rgb <- xyz_to_rgb(colourSystem[3, ], mxyz)
>> 	norm_rgb(constrain_rgb(rgb))
>> }
>> 
>> temperatures <- seq(1000, 10000, by=500)
>> # temperatures <- seq(1000, 10000, length=300)
>> res <- abs(sapply(temperatures, test))
>> 
>> 
>> grid.newpage()
>> 
>> start <- seq(0.1, 0.9, length=dim(res)[2])
>> end <- start + mean(diff(start))
>> grid.segments(x0=start,x1=end, y0=0*start+0.5, y1=0*temperatures+0.5,
>> 	gp=gpar(col=rgb(res[1, ], res[2, ], res[3, ], alpha=1), lwd=10, lineend=3))
>
>
> Best wishes,
>
> baptiste
>
>
>
> [*]  from http://www.fourmilab.ch/documents/specrend/
>
>
> On 14 Mar 2009, at 12:33, baptiste auguie 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
>> 
>> 
>> 
>> 
>> On 14 Mar 2009, at 12:09, Jinsong Zhao wrote:
>> 
>>> Hi there,
>>> 
>>> I try to plot visible light spectrum (380nm~780nm) with color
>>> corresponding to the specific wavelength. However, I don't find a
>>> function that could do this.
>>> 
>>> Another question, it's possible to plot a color space chromaticity
>>> diagram like this:
>>> http://upload.wikimedia.org/wikipedia/commons/thumb/0/02/CIExy1931.svg/300px-CIExy1931.svg.png
>>> 
>>> Thanks in advance!
>>> 
>>> Jinsong
>>> 
>>> ______________________________________________
>>> R-help at 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.
>> 
>> _____________________________
>> 
>> 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
>> ______________________________
>> 
>
> _____________________________
>
> 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 at 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.
>

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle