To allow the nature of human perception to contribute to a measuring result in a controlled manner, it was necessary to define a standard for human vision. This standardized vision was then defined in the so-called CIE standard observers. |
Firstly, the standard observer is defined in that the observer perceives colors without any interference. Moreover, CIE took into account that humans perceive colors most exactly in the eye if the colors impinge in the region of the fovea (fovea centralis).
Since this region, for a standard observation distance from a color sample, deviates from the optical axis of the eye by approx. 2°, the angle under which the standard observer sees was defined to be exactly these 2°. Accordingly, the so-called CIE 1931 2° standard observer was defined as early as in 1931.
|But the eye sees more distant objects under a different viewing angle. Therefore, another standard viewing angle was defined in 1964, the CIE 1964 10° standard observer, in order to take these circumstances into account as well. |
The underlying standard observer needs to be specified as well in color calculations from a spectral measurement; usually this is a software setting.