This International Standard specifies colour-matching functions for use in colorimetry. Two
sets of colour-matching functions are specified.
a) Colour-matching functions for the CIE 1931 standard colorimetric observer
This set of colour-matching functions is representative of the colour-matching properties of
observers with normal colour vision for visual field sizes of angular subtense from about 1° to
about 4°, for vision at photopic levels of adaptation.
b) Colour-matching functions for the CIE 1964 standard colorimetric observer
This set of colour-matching functions is representative of the colour-matching properties of
observers with normal colour vision for visual field sizes of angular subtense greater than
about 4°, for vision at sufficiently high photopic levels and with spectral power distributions
such that no participation of the rod receptors of the retina is to be expected.