Lightness and Brightness and Other Confusions

Current physiological brain research works very much with finding patterns
of correspondence between outer stimuli and neural responding and processing.
This is done by monitoring the electrical activity of brain cells or by scanning
the activity of the brain as a whole with methods such as PET and MRI.
The results of such research could eventually add much to our understanding
of vision and perception, and could possibly be made useful in the measuring
of experienced colour and light.
The use of standardised colour samples
Colour sample selections can be made for various purposes, with various
demands on production stability, physical and visual constancy, and notation
accuracy. To function as references for industrial colour production and reproduction
they need to meet very high demands in all these aspects. To do
so, standardised colour samples are specified colorimetrically with very narrow
variation tolerances. (Hård & Nilsson 1994).
When it comes to the Natural Colour System, it is based on visual concepts.
Once you know the system, you do not need reference samples to understand
from the NCS code how the colour looks or how it visually relates to another
colour. As an illustration of the concepts and their relationships, a choice of
colour samples has been made, based on visual assessments by many observers
in a controlled viewing situation. Once the samples and their visual notations
have been established, they are colorimetrically measured and standardised.
These colorimetric specifications can then serve as references when
measuring other surfaces, e.g. in a portable colour scanner as mentioned
earlier. However, as there are always some differences between different
instruments and measuring conditions, measurements without direct access
to the reference samples cannot claim very high accuracy.
The physical colour samples can also be used as visual measuring rods. As
mentioned above, the nominal colour can be defined as “perceived colour
under standardised viewing conditions”. This means that the colour code
printed on an NCS sample denotes its nominal colour. These colour samples
can be used for visual measuring of the nominal colour of objects outside the
standard situation, a procedure that cannot claim the same accuracy as technical
measuring under controlled conditions. 64 One advantage with the visual
method is, however, that it can be used also for comparing surfaces with different
surface qualities, i.e. gloss, structure etc. (Fig. 15)
64
Fridell Anter 2000, pp 59–64. For further discussion see the article Lightness and
brightness in this volume.
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