Fundamental Chromaticity Diagram with Physiological Axes – Part 2: Spectral Luminous Efficiency Functions and Chromaticity Diagrams
|Publication Date:||1 January 2015|
Introduction to Part 2
Since colorimetry was established in 1931, considerable improvements in the metrology of the colour stimulus and immense advances in the knowledge of colour vision have been made.
The colour sensation results from physiological processes, the first of which is the capture of photons by the cones of the retina. The fundamental sensitivities of the cones need to be precisely known to accurately specify a colour stimulus from a given spectral power distribution.
Part 1 of this report provides the scientific community with cone fundamentals, which are the relative spectral sensitivities of the long-wave sensitive (LWS), middle-wave sensitive (MWS) and short-wave sensitive (SWS) cones as measured at the entrance of the eye. The cone fundamentals have been derived from the best set of colour-matching functions experimentally collected on a 10° field. In particular, the 2° cone fundamentals, which have been reconstructed from the 10° data by guidance of psychophysical data for 2° field size, represent the best proposal available today.
Part 2 of the report aims at providing the user with practical
colorimetric tools, in the form of chromaticity diagrams. The
chromaticity diagram is a two-dimensional representation of colour,
independent of the luminance of the colour stimulus. The hypothesis
that luminous quantity as measured by flicker photometry (referred
to as LM-luminance in this report) relies only on the sum of the
activity of the LWS and MWS cones has been recognized, and a
conefundamental- based spectral luminous efficiency function is
implemented in Clause 7. As outlined in 8.1, this hypothesis offers
the possibility of proposing an equi-luminant chromaticity diagram
directly based on cone fundamentals, which is a considerable
advantage for understanding colour. In addition, to allow for
comparison with the traditional CIE procedures, a transformation of
the cone fundamentals in the form of cone-fundamentalbase
Part 2 ends by concluding that a link has been established between colorimetry and physiology. Such a reasoning, which has been developed by several scientists in the past, is a modern CIE approach that will improve the understanding of colour. It will be useful for education and will offer novel opportunities of solving problems of colour measurement and colour perception in everyday life and in industry.
NOTE The clause numbers in this document are continuous with respect to Part 1 of the report, i.e. start with Clause 7.