Since the road from reflectance data to subjective colour attributes has severals stations inbetween, I wondered for which step you seek an "up-to-date" method. While CIECAM02 is the latest development in colour appearance models, it starts with the tristimulus values of a colour sample, which thus have to be calculated first. 

Assuming that you are talking about *spectral* reflectance values you first must know the spectrum of the light source that is reflected from your patch. In a nutshell you first have to multiply those two spectra with each other, then you have to apply three different weighting functions to the result, and finally you have to integrate (sum up) these latter three results in order to find the tristimulus values X,Y,Z of your colour sample under the given illuminant. Only then you can proceed with the CIECAM model.

You might know all this, but since the exact method of calculation has always been a matter of debate, I thought I could mention that there is a standard from 1994 available detailing the procedure (see attached file).

ps "brightness" is often understood to be the subjective correlate of the luminace of a light source. It may be that "lightness" is what you are after, which is an attribute of a coloured object that varies between the extremes of black and white

I would suggest looking in to "CIE 159:2004 A Colour Appearance Model for Colour Management Systems: CIECAM02" ISBN 978 3 901906 29 9

This would be the most recent authoritative method I can think of. As far as I can gather you need to a specify light source/illuminant to be able to calculate the numbers your are looking for.

Thanks Anders!

Since the road from reflectance data to subjective colour attributes has severals stations inbetween, I wondered for which step you seek an "up-to-date" method. While CIECAM02 is the latest development in colour appearance models, it starts with the tristimulus values of a colour sample, which thus have to be calculated first. 

Assuming that you are talking about *spectral* reflectance values you first must know the spectrum of the light source that is reflected from your patch. In a nutshell you first have to multiply those two spectra with each other, then you have to apply three different weighting functions to the result, and finally you have to integrate (sum up) these latter three results in order to find the tristimulus values X,Y,Z of your colour sample under the given illuminant. Only then you can proceed with the CIECAM model.

You might know all this, but since the exact method of calculation has always been a matter of debate, I thought I could mention that there is a standard from 1994 available detailing the procedure (see attached file).

ps "brightness" is often understood to be the subjective correlate of the luminace of a light source. It may be that "lightness" is what you are after, which is an attribute of a coloured object that varies between the extremes of black and white

Hi Detlef,

I'm trying to quantify bird plumage. I'm looking at color evolution with respect to ambient light condition of birds.

I wanna se how brightness and signalling wavelength varies with light environment in a macroevolutionary perspective.

Oh, that sounds like fascinating research. However, much of the answers to your question so far might be irrelevant unless you consider humans as receivers of the colour signals provided through the plumage. My guess is they are either targeted at  conspecifics for the purpose of mating or at predators or prey for the purpose of camouflage. Whatever species is supposed to read the signals, in theory you would have to use a model of that species' colour vision to know eg what hue an exemplar perceives.

I am aware that we can appreciate the colours of peacocks, birds of paradise etc. so maybe it makes sense to use CIECAM. On the other hand that model is probably overly precise and you might better use the older and simpler CIELAB formulae.

On a sidenote the characterization of "ambient light conditions" - if you cannot directly measure them - requires some kind of model as well. There is a model of the light under the northern sky ("D65") that is often used for object colour computations, but light within say a rainforest might be tinged in green through reflectance from the foliage and so on. 

So altogether your project seems difficult to me, and I am asking myself whether it is more promising to stick with just the light and reflectance spectra and to see in what way they might relate to each other.   

Thank you so much for your valuable insights on my work. I sure will consider those. The light environment classification would be a very crude one, based upon relative closed-open measures, with respect to data gathered by researchers from mid 1900s, and will just be a small portion of a chapter, hopefully :)

Thanks again for your comments!!