The Experience called Colours - The Human Eye
Color plays an important role in the world we live in.
Colors can influence the way we think, the things we feel and the way we act.
They can change our mood, raise our blood pressure or even suppress our
appetite. From intelligent marketing strategies to energy consumption, the
application of colours is everywhere.
To understand the colourful world we live in, we must first
understand our relationship with colours.
Light
Electromagnetic radiation is characterized by its wavelength
and its intensity. When the wavelength is within the visible spectrum (400 nm
to 700 nm), it is known as "visible light". Visible light is a small
part within the electromagnetic spectrum that human eyes are sensitive to.
Visible light waves are essentially the electromagnetic waves
we can see. They consist of different wavelengths. Each wavelength is a
particular colour. The colour we see is a result of which wavelengths are
reflected back to our eyes. Red has the longest wavelength, and violet has the
shortest wavelength. When all the waves are seen together, they make white
light.
Human Eye
When light hits an object, the object absorbs some of that
light and reflects the rest of it. The reflected light enters the human eye
first through the cornea. The cornea bends light toward the pupil, which
controls the amount of light (exposure) that hits the lens. The lens then focuses
the light on the retina.
The ability of the human eye to distinguish colors is based
upon the varying sensitivity of different cells in the retina to light of
different wavelengths. Our retina has two different types of photoreceptors (cells
that detect and respond to light) — rods and cones.
Cone
Cones are stimulated in brighter environments and contain three
“color-detecting” molecules that give us our colur vision. They are concentrated
in the center of our retina. Each type of cone is sensitive to different
wavelengths of visible light, namely:
·
L cones (long-wavelength cones or, Red Cones) - 60%
·
M cones (middle-wavelength cones or, Green
Cones) - 30%
·
S cones (short-wavelength cones or, Blue Cones)
- 10%
Thus, cones influence color perception and make humans
trichromatic.
Rod
Rods are sensitive to light levels and help give us good
vision in low light. They are concentrated in the outer areas of the retina and
give us peripheral vision. This is why our peripheral vision is less sharp and
colourful than our front-on vision. Rods are 500 - 1,000 times more sensitive
to light than cones. It is the rods that help our eyes adjust when we enter a
darkened room.
When light is bright enough, rods play virtually no role in
vision at all. On the other hand, in dim light, the cones are understimulated,
leaving only the signal from the rods, resulting in a colourless response.
The retina has approximately 120 million rods and 6 million
cones. One could say that; while cones help the human brain interpret the hue
of what we see, rods help it to interpret the contrast.
Stages of Colour Production
The experience of colour is a three stage process. It
involves a light source, a spectral filter and a resolving detector.
A spectral filter is essentially an object we are looking
at. Depending on the material of the object, it will selectively transmit light
of different wavelengths
The human eye and the brain acts as a resolving detector. Together
they translate light into color. Light receptors within the eye transmit
messages to the brain, which produces the sensations of color.
Objects appear different colours because they absorb some colours (wavelengths) and reflected or transmit other colours. The colours we see are the wavelengths that are reflected or transmitted.
The surface of the apple is red because, it is reflecting
the wavelengths we see as red and absorbing all the other wavelengths. An
object appears white when it reflects all wavelengths and black when it absorbs
them all.
Additive and Subtractive Colouring
The way a colour is produced or transmitted from a
television screen is quite different from the way we see it on paper or on
clothes. While one adds the wavelengths of light to produce a colour, the other
absorbs the same to do so.
Additive Colouring
When coloured lights are mixed together, it is called
additive mixing. Red, green and blue are the additive primary colors normally
used in additive color systems. If all of these colours of light are shone onto
a screen at the same time, we will see white light.
This is how TV and computer screens work. If we look closely
at a screen, we would be able to see that only these three colours are being
used. For example, a combination of red and green lights is used to make our
brain perceive an image as yellow.
Subtractive Colouring
Subtractive coloring uses dyes, inks, pigments, paints or
filters to absorb some wavelengths of light and reflect others. The color that
a surface displays comes from the parts of the visible spectrum that are not
absorbed and therefore remain visible.
When a pigment or ink is added to fabrics or papers, colours
(wavelengths) are absorbed or "subtracted" from white light, so light
of another color reaches the eye. Each time another colour of paint is mixed
in, there are more colours absorbed and less are reflected. For example, if red
paint is viewed under pure blue light, it will appear as black. Red paint gets
its colour by scattering or reflecting, red components of the visible spectrum.
If it is illuminated by blue light, it will absorb it completely, creating the
appearance of a black object.
The primary colours for adding paints or dyes, are yellow,
magenta and cyan. If we mix all of these colours together, they will absorb all
the light and we will only see black, because no light will be reflected back
to your eyes. This is also the reason a separate black ink cartridge along with
the yellow, magenta and cyan ink cartridges is provided in an inkjet printer to
make it cost effective.
Complementary colors
Complementary colours are pairs of colors which, when
combined or mixed, cancel each other out. When placed next to each other, they
create the strongest contrast for themselves. Complementary colors are also
called opposite colors.
Depending on the color theory we use, the pair of complementary
colours change:
·
Modern color theory uses either the RGB additive
color model or the CMY subtractive color model, and in these, the complementary
pairs are red–cyan, green–magenta, and blue–yellow.
·
Opponent process theory suggests that the most
contrasting color pairs are red–green, and blue–yellow.
·
The black-white color pair is common to all.
This concept is known to designers and has been extensively
used throughout history by artists like Vincent Van Gogh and others.
Subjectivity of Colour Perception
The experience of colour is unique to an individual. It is a
feature of visual perception. But, there are various other factors which influences
the way we perceive the colours around us. These factors make the relationship between
the different wavelengths of light in the visual spectrum and the human
experience of colour far more complex than obvious. The perception of color
depends heavily on the context in which the perceived object is presented.
 |
| The same blue square appears darker in the grey region than in the green region |
Vision Anomalies
Color blindness can occur when one or more of the cone types
are not functioning as expected. Since there are 3 types of cone cells, there
are three kinds of colour blindness. Cones can be absent, nonfunctioning or
detect a different color than normal. Red-green color blindness is the most
common, followed by blue-yellow color blindness. Complete colour blindness is
very rare. Men are more likely to have color blindness than women.
Researchers estimate that up to 12% of females have four
cone types in their retinas, rather than three. These individuals have the
potential to perceive 100 times more colors than the rest of us.
Many birds, insects and fish have four types of cones. With
their different cones, they can see ultraviolet light. Other animals, such as
dogs, have fewer types and numbers of cones, so they may see fewer colors than
humans do.
Age
Color vision can deteriorate as people get older. The lenses
of the eyes become yellowish, causing older people to see everything around
them in sepia tone, as if they were looking through a yellow filter. This can
disrupt the "blue-yellow" vision, preventing individuals in certain
situations from distinguishing blue from purple and yellow from green and
yellow-green.
A cataract surgery can make major difference in such a
condition because, it replaces lenses in the eyes, clearing away the yellowish
film.
Chromatic Adaptation
Chromatic adaptation refers to color constancy; the human
visual system’s ability to preserve the appearance of an object under a wide
range of light sources. It is responsible for the stable appearance of colors of
the objects around us, despite the wide variation of light which might be
reflected from them and observed by our eyes. For example, a white page under
blue, or red light will reflect mostly blue, or red light to the eye,
respectively. The brain, however, compensates for the effect of lighting and is
more likely to interpret the page as white under both the conditions.
A camera with no adjustment for light may register the white
page as having varying color. When the correction occurs in a camera it is
referred to as white balance.
Chromatic adaptation is one aspect of vision that may fool
someone into observing a color-based optical illusion. When an artist uses a
limited color palette, the human eye tends to compensate by seeing any gray or
neutral color as the color which is missing from the color wheel. Here is a quick
experiment:
Look first, at the image in the bottom, and fix your gaze on
the dot. You will notice that the left half of the photograph has a definite
bluish tone, while the right half has a definite yellowish tone. Now, fix your
gaze on the dot between the blue and yellow rectangles above for about 30 seconds.
After 30 seconds, shift your gaze to the dot in the image below. if you keep
your eyes fixed on the dot while examining the picture, you will notice that
now the tone appears same in both halves of the picture. Navigate to other
parts of the images and you will notice the color differences reappearing.
After Image
Photoreceptors of a given type become desensitized after
prolonged exposure to strong light in their sensitivity range. If you keep
looking at a yellow light for prolonged duration, the photoreceptors in your
eye responsible for sensing the yellow colour “switches-off” momentarily, as if
it was bored of seeing yellow. That’s a momentary sensory deprivation. For a
few seconds after the light ceases, they will continue to be in this state.
Colors observed during that period will appear to lack the color component
detected by the desensitized photoreceptors. This effect is responsible for the
phenomenon of afterimages, in which the eye continues to see a bright figure
after looking away from it, but in a complementary color.
Focus on the black dot in the yellow circle for about 60
seconds and then focus on the dot in the white circle. You will momentarily see
a bluish-purplish tinge on the white circle. That’s because your eyes were
tired of looking at yellow for so long.
Afterimage effects have also been utilized by artists,
including Vincent van Gogh.
Synesthesia
Have you ever come across the phrase, “you can hear this
picture” or “you can taste this picture” on the internet? This is because of subjective
color experience triggered by input that is not even light, such as sounds or
shapes. In certain forms of synesthesia, perceiving letters and numbers or,
hearing musical sounds will lead to the unusual additional experiences of
seeing colors, although evoked through a non-standard route.
The possibility of a clean dissociation between color
experience from properties of the world reveals that color is a subjective
psychological phenomenon.
Memory
Memory color is the hue of a type of object, like a banana
or an apple, that human observers acquire through their experiences with
instances of that type. For example, a red apple under a pure blue light should
appear black to us but, our brain still perceives it as red.
Memory colors directly modulate the appearance of the actual
colors of objects we see. It is not about what we see, but, what we think, we
are seeing.
If we perform the after-image experiment with an inverted
image of the Indian flag, the people who are acquainted with the colours and
design of the India flag would find it easier to see them in the after image
than those who are not. This is because they know what they are seeing and try
to recreate the image from their memory.
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