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Spectral and XYZ Color Functions

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Spectral and XYZ Color Functions

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01 Mar 2005 (Updated )

Label plots with spectra. Convert wavelengths to RGB. Functions for color matching and illuminants.

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Description

This is the beginning of a set of functions for working with color as wavelengths (spectral color) and in the xyY and XYZ color spaces.

Current functionality includes:

spectrumLabel - Add a color bar containing the visible spectrum to a plot's X axis.

spectrumRGB - Converts wavelengths of light to equivalent RGB values (in the sRGB space).

colorMatchFcn - Raw data of popular color matching functions (spectra to XYZ) for various standard observers:
  * CIE 1931 2-degree
  * CIE 1964 10-degree
  * CIE 1931 2-degree modified by Judd (1951)
  * CIE 1931 2-degree modified by Judd (1951) and Vos (1978)
  * Stiles and Burch 2-degree (1955)
  * Stiles and Burch 10-degree (1959)

illuminant - Raw data for the A, D65, and E standard illuminants.

Acknowledgements

This file inspired Perceptually Improved Colormaps.

Required Products Image Processing Toolbox
MATLAB release MATLAB 7.0.1 (R14SP1)
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Comments and Ratings (21)
28 Mar 2014 Liviu Ivanescu

I'm surprised that you don't obtain a unique RGB value for a given wavelength, as your RGB functions are truncated, saturated at 1. For example, in the range 512-548 nm you have the same RGB value: a pure green 0-1-0. Also in the range 611-641 you give constant pure red 1-0-0. I guess the eye should perceive a difference along those ranges, so the results are not realistic. Correct?

04 Sep 2013 Tim Zaman  
23 Jul 2012 Filipe

Dear Jeff Mather,
can you please provide/indicate the reference (paper, scientific publication) in which these algorithms have been based?

Thank you very much in advance!

07 Jul 2012 hongli

very help ful,excellent work!

25 Mar 2012 Alexander Brodsky

Very helpful!
Thank you.

07 Feb 2012 Guido

Help!
I'm trying to use spectrumLabel for a calculated absorption spectrum.
It works fine from the command window, but I'm not able to put the color axis in a plot which is rendered to a GUI.
Here is the piece of code that I put in the .m file. The plot of the extinction, scattering and absorption spectra are sent to the axes style GUI handles.axes1:
----------------------------
axes(handles.axes1);
plot(wave,qext,wave,qsca,wave,qabs);
title('Spectrum');
xlabel('Wavelength (nm)');
ylabel('Arbitrary units');
spectrumLabel(handles.axes1);
-------------------------------
Apparently, the spectrumLabel is put at the right position but with zero or very small vertical dimension.
Thank you!

01 Jan 2012 Li

I got this error information:
"the selected cell cannot be evaluated because it contains an invalid statement".
"??? Input argument "formulary" is undefined."
Any idea why this happen? Thank you!

04 Sep 2011 springface

but there seems to be a scale off. I don't know how to solve that. Please help!

04 Sep 2011 springface

Thanks to this excellent work, I've been able to image a spectrum plot with both the characteristic peaks marked in colors and intensity plot shown. The code is as following.

%%%%%%%%%%%%%%%%%%%%%%
function SpecRGB_Intensity(wavelength,intensity, peak_threshold)
% wavelength and intensity are vectors
% the characteristic peaks are chosen if the value of the peak
% is bigger than the peak_threshold.
% by springface

sRGB = spectrumRGB(wavelength);

%% Transform spectrum plot into an image, marked by colors
len_wave = length(wavelength);
len_inten = 1000;
intensity_plot = max(intensity):-max(intensity)/(len_inten-1):0;
wavelength_plot = wavelength;

intensity_num = ones(size(intensity));

for cc = 1: len_wave
if intensity(cc)>=0
[C,I] = min(abs(intensity(cc)- intensity_plot));
intensity_num(cc) = len_inten-I;
end
end

im_plot = ones(len_inten,len_wave,3);

for cc = 1: len_wave
im_plot(1:intensity_num(cc),cc,:) = repmat(sRGB(1,cc,:),intensity_num(cc),1);
end

%% mark the non-peak area as black
spec_idx = intensity < peak_threshold;
sRGB(1,spec_idx,:) = zeros(1,sum(spec_idx),3);

%% Plot figures
figure;

whitegap_len = 2;
RGBspec_len = 100;

RGBspec_range = max(intensity)+whitegap_len+RGBspec_len+1:max(intensity)+1;

imagesc(wavelength_plot,[RGBspec_range,intensity_plot],...
cat(1,repmat(sRGB,RGBspec_len,1),ones(whitegap_len,len_wave,3),im_plot));
set(gca,'YTick',[])
%%%%%%%%%%%%%%%%%%%%%%

20 Sep 2010 Matteo Niccoli

Great submission!

19 May 2010 Mike Vasilescu

how do I get the spectrumon jpg?

07 Oct 2008 Franck Riberi

Need demo files absolutely.

12 Dec 2007 Neeraj Adsul  
20 Jun 2007 jeongwoon lee  
26 Apr 2007 NOne None

None

03 Jan 2007 Vishnuvenkatesh Dhage  
06 Apr 2006 ben taylor

Does anyone know hot to convert it the other way? I have an RGB image of black body radiation and I am writing a program that will give me a 3d temperature plot, but I need to convert from RGB to wavelength to temperature.

Thanks,

28 Oct 2005 Levent Onural

Thanks a lot, I have been looking for how I could generate the matching functions for 5 hours. Excellent piece of work...

18 Oct 2005 marwan reyadh

please how can i convert an image from RGB of size n*n*3 to an image with of size n*n*n

01 Oct 2005 colour rainbow

could you able to create function for r2xyz
for 1xm or 1xn matrix

21 Jul 2005 Wu John

Good job! Thank you,but how about the other light source in illuminate.m?

Updates
08 Nov 2010

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