I want to calculate x and y coordinate of a given color in CIE 1931 color space. What is the practical formula for that? I am attaching herewith the information I got from internet
In order to calculate x, y coordinates we need to calculate X,Y and Z which is called the tristimulus values of a color.
You also need to decide what source of light you are using. CIE Standard Illuminant A (representative of incandescent light) or CIE Standard Illuminant D65 (representative of a phase pf day;right) are the two most used, but others are possible. Send me your spectral reflectance or transmittance data 380-780 nm in either 5 nm or 10 nm steps and I will send you an excel spread sheet
Thank you for your response Dr Dain but I am afraid I do not have the requisite instrument to measure the spectral reflectance or transmittance.
Alternatively, can we use linear R,G and B to calculate the x and y? As I got in one paper. I am attaching herewith the paper
If I'm not confnusing, M(λ) must be dependent of the illuminant (D65, A, C...) and the reflectance (or transmission) spectrum.
I found D65 spectrum in: http://www.cie.co.at/publ/abst/datatables15_2004/std65.txt
Yes that is one method. I am referring the alternative method. Actually the problem with the alternative method is that I am unable to figure out the difference between R,G,B and linear R,G,B.
One of us is missing something here. CIE x, y and Y are calculated for an object (transmitting or reflecting or emitting). To do that you need data on the object. That would be the spectral transmittance or reflectance or radiance. Otherwise, I have no idea what it is that you want, or even why you w its!! CIE RGB was simply a system that was adopted to lead up to XYZ, it was never actually intended to be used.
All I can think is that you want to get from the computer specification that is R,G,B. Is that the case? In that case it depends on what computer and what display you are using. So you still need to be able to measure the display to get from computer RGB (which is not the same as CIE RGB) to CIE x,y,Y.
Try this answer: http://stackoverflow.com/questions/12524623/what-are-the-practical-differences-when-working-with-colors-in-a-linear-vs-a-no
You can find different matrixes to convert XYZ to RGB as well as RGB to XYZ based on various standards (Adobe RGB, Apple RGB, CIE RGB, ...) here:
http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
Hello Stephen John,
If we have the reflectance or transmittance or emission spectrum of the material, can we calculate the color coordinates (x, y and Y values)?. If it is so, it will help me a lot.
By excel : (one by one)
Easy , you can feed your data here to get desired XYZ for most of the Illuminant observer pair.
http://www.brucelindbloom.com/index.html?SpectCalcSpreadsheets.html
For By Matlab: (for lots of data)
many options from Prof. Stepland , Colour tool box, optproperties
https://www.mathworks.com/matlabcentral/fileexchange/40640-computational-colour-science-using-matlab-2e?focused=3779525&tab=function
You can ask if need code, its a simple loop function
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