Colour Perception (Feb 25 , 2013)
“Red” apple does not have the quality of “red”. How would you explain this quality
that you call “red” to a person that who is blind?
The ability to see in colour is not because the objects or surfaces themselves are
inherently colourful. The reason we see different colours around us is because the
objects and surfaces we look at reflect certain wavelengths of the visible spectrum,
and these reflected wavelengths trigger specific patterns of response in our brains
that give rise to our subjective experience of colour. That is, colour is a creation of
our minds. The subjective experience relates to how the different wavelengths of
light affect certain cones in our retina.
Colour obviously adds to the richness of our visual experience. (Black and white
forest scene is difficult for us to pick out individual tree, but with the colour scene,
it’s much easier to tell the trees apart.)
Evolution of Colour Perception: Why and Who
Ex: when the matador takes off his red cape and waves it at the incensed bull who
charges. Presumably, the bull charges because the flash of the red cape infuriated
him. But what is the bull is really responding to? – It turns out that bulls don’t see
the cape as red, they just see a piece of grey, moving cloth. They are responding to
Who has colour vision?
Many birds, fish, reptiles and insects have excellent colour vision.
Among mammals, colour vision is limited to primates, including humans. This
means dog, cats, along with the bull, can only see in shades of grey.
How did primates end up evolving the ability for colour vision?
Primates have three different kinds of cones for colour vision, especially well-suited
to distinguish red and yellow against a greed background. This adaptation helps
immensely with foraging for fruit in the bushes and trees. In this way, one possible
biological advantage of colour vision for primates is the ability to detect colourful
objects in the wild. The ability to perceive color is an important advantage for
detecting predators on prey against a background, determining the ripeness of
fruit, the richness f the soil, or even using the color of sunsets as a means to predict
Colour vision is also an important part of the lives of many non-mammalian
species. Birds, fish and insects are able to see colors we don’t see at all, including
colors at the UV end of the spectrum.
(ex: for birds, the color of a potential mates’ feathers provides signals to other birds
about how healthy that bird is, and can influence how likely that bird is chosen as a
mate. So a bird that may look ordinarily colored to human eyes, may look
particularly brightly colored to other birds. -This type of coloration system would
help the birds communicate with each other about how sexy and healthy they are, while still remaining inconspicuous in the forest to potential predators who are
unable to see this bright coloration.
In addition to use in mating behaviour, color vision in non-Mammalia animals can
also be used for foraging. We can’t assume that the red rose we see must be
irresistible to the bee. The bee might be attracted to flowers that look dull to human
eyes, because it’s responding to specific patterns and colors on the flower that we
are unaware of. Some flowers have adapted patterns on the petals that are
invisible to us, but serve as “nectar maps” to the bee.
The human eye processes color information using principles that have been known
to artists for centuries. We don’t need to have millions of color receptors to deal
with every conceivable color out there in the world. Instead, we just need a few
receptor types whose activity can be combined in various proportions to make
every conceivable color.
Primary colors: the three colors that can be combined in various proportions to
make every color in the spectrum. They are base color, that can’t be reduced into
other colors. There are no colors that can e mixed together to make a primary color, but primary color can be mixed together to make all the other colors.
Subtractive color mixing: when colored pigments selectively absorb some
wavelengths and reflect others. (mix the color blue and yellow paint to make
green, or red and yellow to make orange.)
Subtractive color mixing applies to the mixing of pigments, dyes, or paints, and its
is called “subtractive” because every reflective surface absorbs (or subtracts)the
colors that it does not reflect. Adding other pigments to that surface alters the
combination wavelengths subtracted.
The primary color with subtractive color mixing is blue, yellow and red. They all
can be mixed in various proportions to make all colors in rainbow.
Blue object looks blue because all wavelengths are being absorbed by the
object except short, blue waves, which are being reflected back to our eye and