It has long been known that individuals differ in their response to narrow-band stimuli across the visible spectrum. The CIE LMS functions and the 1931 Standard Colorimetric Observer were the result of averaging the response of 17 observers, and inspection of the Wright and Guild data reveals considerable variation between those who participated in their experiments. The 1931 (2 degree) observer (as well as the more recent 1964 and 2006 observers), has nevertheless been a useful construct in defining tristimulus values for the purpose of colour matching across different media.
Failures of metameric colour matching due to different observer spectral response are rare with surface colours, which exhibit smooth reflectance spectra. In recent years this 'observer metamerism' has emerged as an issue with the increasingly narrow spectral emission of the primaries used in displays, particularly as the display gamut is increased.
To address this problem, it would be necessary to adjust display values to compensate for individual responses. This raises a number of questions, including:
- How to efficiently measure or estimate the response of an individual observer?
- Given an individual response function, how to determine the adjustment needed?
- How to integrate individual observer responses in a colour managed workflow?