CIE Standard Observer

The CIE 2° and 10° standard observers refer to two different test configurations used to standardize human color perception for instrumental measurements. The goal of these tests was to determine the specific intensities of red, green, and blue light required to match the color impression of light at a particular wavelength, as perceived by the human eye. The results from multiple test subjects were averaged and standardized, leading to the creation of the spectral value functions ¯x, ¯y, and ¯z, which serve as the basis for all subsequent color calculations.
The original experiment conducted in 1931 had observers viewing the test screen with a 2° angular field of view. In 1964, this experiment was repeated with a larger field of view of 10°, as this better reflects real-world situations. As a result, the 10° standard observer function is generally used today. However, the 2° standard observer is still required by some standards, such as when assessing the color of traffic signs, which are perceived at a significantly smaller angle.