Converting spectral data for given Observer/Illuminant to another Observer/Illuminant

Question

I'm working on a simple Measuring Software for HunterLab (Color) instruments (EZ line) (screenshot here) and I hope someone can help out here.

They deliver spectral data from 400nm...700nm by 10nm using a D65 light source and 10° Observer.

I have the observer functions for ASTM D65 which work great and I can reproduce any value from the instrument 1:1, as long as i measure in D65, 10° (converting to XYZ and then CIELab using tristimulus references for perfect reflecting diffuser).

That was done mostly using algorithms from brucelindbloom.com and easyrgb.com, both have some great information!

Now I want to add the ability to convert the spectral data to another observer or another illuminant (or both). But I cant wrap my head around how to do that.

I guess some directions would be enough but I dont know if I would need even more references for that (references for illuminants by wavelength?) or if its done by some other means.

Answer 1

OK, here is the answer :)

Spectral data from most spectrophotometers is already corrected in so far that the hardware illuminant and angle dont matter.

What you do is just use the observer functions for every single angle/illuminant, as written in ASTM E308, to convert the spectral data to XYZ instead of only using the table which corresponds to the hardware illuminant/angle.

Thats a lot of reference values but it works perfect.