Biomedical Engineering Reference
In-Depth Information
range, then we can rely on new technical and emerging systems, e.g., the night
vision systems built on IR-technology. Actually, important distinction of these
technologies will not allow us to see new colours, instead the artificial devices
allow us to get a glimpse into a different wavelength or range.
The shades of colours are, as much of the human efforts to sort and classify
different states, often described in standardised terms. A colour can be described
in different shades, which are related to a general classification system of colours.
In the text below, some useful colour related terms are explained to show that there
is an attempt to structure and organise the varieties of existing colours.
- Hue is the local colour of an object, defined in the seven major colours: red,
orange, yellow, green, blue, indigo, and violet.
-A value is the degree of lightness or darkness of a hue, defined as a light related
valueaddedbeforeacolour.
- Saturation is the relative intensity of a hue when compared to grey.
- Temperature is the term describing whether a colour is relativly warm or cool.
Colours containing of blue, green, or purple or undertones thereof are cool
colours. Similarly, colours containing red, orange, or yellow or undertones
thereof are warm colours. The concept of color temperature is of importance
in photography and digital imaging.
2.2.1 Colour Deficiency
Colour deficiency affects an individual's ability in the sense that he may identify
the colour spectrum slightly different than another person. The degree of differ-
ence in experiencing the colour qualities may, of course, vary between individuals
and the variety of colour sensation individually perceived can also be a limitation
in daily life. But nature also plays an important role in experiencing the perception
of colours, when we find huge varieties and nuances in different shades and places.
The sensory effects of colours are also dependent on their context, indicating that
the colours are in a way dependent on each other. This effect can be shown when
experiencing that a particular red colour may appear more intensely red when rel-
atively compared to an adjacent colour of green than if it is surrounded with grey.
Also the surrounding light intensity relative to the colour and seen from different
angles will affect our perception.
Most people will, when ageing, have decreased vision ability, mainly due to
natural reasons, like age related factors such as deteriorated pupil size. This nor-
mally results in an effect whereby the incoming light to the retina may have re-
duced ability to discern contrasts, Winn (1994). Ageing also affects colour vision
in the sense that the vision effect is reduced in discriminating between different
blue and blue-green colours. This effect is believed to be caused when the lens
turns slightly yellow, which will drastically reduce perception, as it will affect the
abilities to distinguish between colours.
The human eye sensations arise when light stimulates the retina. The retina
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