yahvuu wrote:
> That was thought as "color data that is defined in an absolute color space, 
> or can
> be unambiguously transformed into such a color space". Perhaps a better term 
> is
> 'unambiguous color data'.

Unfortunately, due to the adaptability of human vision, there is
really no such thing as an absolute unambiguous color space.

But for practical purposes there is something that everyone uses,
and that is the CIE standard observer tri-stimulus space, XYZ.

But note there are still many subtleties. The most popular
XYZ spaces come in two flavours, 2 degree and 10 degree,
referring to the viewing angle, since we have different
type of color sensitive cells in the central and peripheral
viewing regions of our eyes. For practical use, there is often
the assumption that the viewer is perfectly adapted to the white
point of the scene (ICC relative colorimetric), and XYZ is typically
an absolute coordinate system, that doesn't normalise to any white
point, hence the use of chromatic adaptation transforms. CIE XYZ
assumes a set of standard viewing conditions (absolute brightness level,
surround color etc.), whereas the real world probably has different viewing
conditions, hence CIECAM02 etc.

ICC device profiles codify a transformation from device colorspaces
to/from PCS (Profile connection space), which is defined in terms

Psudo device independent spaces such as scRGB, sRGB, Adobe RGB are
defined in terms of XYZ too. Note that there is some controversy
of how to handle the white point adaptation to these spaces though,
although this is only of relevance in specialised applications where
absolute XYZ is required.

Graeme Gill.
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