scott schrieb:

>> Experiments were conducted to measure this per-wavelength response (a 
>> bit indirectly) in a manner that, to my understanding, only yielded 
>> /relative/ results:
> 
> No, I think they were able to generate pretty accurate colour matching 
> functions, which mapped exactly how the intensity of each wavelength 
> corresponded to the tristimulus values.  You end up with a chart like 
> the one on wikipedia:

Not really: They used various other assumtions to get to the XYZ color 
model, which were not part of the original tristimulus experiments (for 
instance results from an experiment that tested for how people percieve 
the brightness of spectral colors in relation to one another).

> http://en.wikipedia.org/wiki/File:CIE_1931_XYZ_Color_Matching_Functions.svg
> 
>> Thus, the immediate conclusions drawn from these experiments left open 
>> the question what "white" is
> 
> The only universal "scientific" definition of "white" I can think of is 
> equal energy at all wavelengths, this gives XYZ=(1,1,1).  Other whites 
> are usually related to the colour of a hot object, eg D65 is the colour 
> of an object at 6500K.

Given that "white" is what we humans /percieve/ as "white", that 
equal-energy definition is not really reliable.

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