Am 06.03.2012 17:33, schrieb Warp:
>    I don't think "rgb" is generally considered to describe the amount of
> radiant energy (measured in Joules) reflected by a surface (so that for
> example "rgb 0.5" means that the surface reflects half of the incoming
> radiant energy), but rather the *perceived* color of the surface (iow.
> "rgb 0.5" means that the surface *looks* exactly half as bright as
> "rgb 1").
>
>    Measuring things in terms of perceived brightness is way more common than
> in terms of absolute radiant energy. For instance, most SI units related to
> light, such as the lux and the candela, measure perceived brightness.

Careful when using those terms: While the luminous flux (measured in 
lux) and luminous intensity (measured in candela) do include some 
correction to account for /some/ peculiarities of human perception, 
these are limited to wavelength-dependent weighting, and doesn't account 
for gamma-like effects. For any given hue and saturation, the units 
still represent light intensity /linearly/.

Thus, a luminous flux of 0.5 lux is still perceived as about 73% as 
bright as a flux of 1.0 lux.

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