The observer is a set of three color-matching functions that turn a reflectance spectrum into tristimulus values X, Y and Z. The 2-degree version represents small viewed areas and the 10-degree version larger patches, and the same sample gives slightly different color numbers under each. Paper specs always pair an observer with an illuminant, such as C/2 for printing opacity or D65/10 for CIE whiteness.
Supplier reports on the 2-degree standard observer and we use 10, so those b-star values aren't comparable.
Mixing 2-degree and 10-degree data is one of the most common reasons two labs disagree on b* by several tenths.
Also heard as
- CIE standard observer
- CIE observer
Related terms
Luminance factor
Tristimulus Y: the overall lightness of a sample as the eye sees it under a given illuminant and observer.
CIELAB
Color space describing a color by lightness L* plus a* for red-green and b* for yellow-blue.
Illuminant C
Standard CIE light distribution approximating average daylight, with relatively little ultraviolet.
Illuminant D65
Standard CIE daylight at about 6500 K, with enough ultraviolet to excite optical brighteners strongly.