Lightness and Brightness and Other Confusions

human colour vision do not follow linear paths within a symmetrical space.
All geometric representations of colour are therefore a compromise between
clarity and accuracy. In colour spaces the compromise has to be made between
two characteristics: symmetry and equal colour difference steps. This
difficulty has led to ever-new mathematical-geometric representations of
colour variables with acronyms such as HSV, HSB, HSL, LCh, CIE Yxy,
CIELAB, CIELUV and CIECAM02. 74 The large number of colour models
might give the impression that the difficulty lies in the complex nature of
light, computers, digital reproduction or other physical challenges. It does
not. The difficulty lies in finding a model that is sophisticated enough to
truthfully simulate human colour vision.
Primary colour
The artificial results of mixing paints is doubtless what has led to the
idea of ’primary colors’, such as red, yellow, and blue. If any special set
of colors deserves to be called primary, it is the set of red, blue, yellow,
and green. – – (W)hat justification all four have as candidates for primaries
has little to do with the three cones and much to do with the subsequent
wiring in the retina and brain.
– David Hubel (1995)
The idea that all colours are physically or physiologically reducible to a limited
number of elementary or primary colours has intrigued artists, philosophers
and colour scientists ever since ancient times. There is an air of transcendence
to the notion of primary colours and even more so to the relatively
recent idea that they are three in number. This idea is so deeply ingrained in
the thinking and vocabulary of at least all those who are used to working with
additive and subtracting colour mixing systems, that it seems almost blasphemous
to doubt this principle. Yet, the deeper one delves into the paradox
of the primaries, the more likely it appears that there might not be any one
irreducible set of colours that are the origin of all other colours.
There are two separate aspirations in seeking the primaries in colour – and
some of the confusions start with getting these aspirations mixed. One is
purely technological: how to get the most hues, tints and shades from the
least number of pigments, inks, lights or pixels. The other is more philosophical
and cultural and is entwined with such usages and traditions as heraldry
Some colour systems, of which two of the most important are the Natural Colour
System NCS and Munsell Color differ from these in that they do not attempt to describe
any device-dependent properties of light or theories of the trichromacy of the human
visual system. They merely attempt to map colour as perceived by humans without any
claims about how or why we see colour.
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