[OT] two question about color space.

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

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))

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

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