Digital Photography 101
Chapter 1: Introduction to Film and Digital Cameras
1.8: Basic Science of Light and Colour
In order to take and manipulate a nice photo we must understand
fully the main ingredient to a photo and that is light.
In 1666 in Cambridge, Great Britain the great physicist Sir Isaac
Newton was alive and making his experiments that would give rise
to the amazing world of optics, colour and photography. One of his
greatest achievements was a reflective lens used in telescopes today.
He also discovered the colours of light. He did this with a simple
prism lens and turned white light into the seven-colour spectrum.
Rain drops in the atmosphere have a similar effect to the prism
and depending on where you are standing you will see the colours
in the atmosphere as a rainbow.
He then gave us his colour wheel which, when we spin it, will
go grey white because we are mixing the colours and white light
is a blend of seven main colours.
I have drawn up a subtractive and an additive colour triangle
for you to consider (below). The primary colours of paint are red,
blue and yellow. The primary colours of light are red, green and
blue. By mixing these colours together we create our secondary colours
shown as halfway points on our triangles.
Colours opposite in the triangle are said to be complimentary
to each other because mixed together they will make what is in the
centre of the triangle.
Why is there an additive and a subtractive colour triangle?
Mixing paint is due to a subtractive process. Pure light has already
been manipulated; for example blue paint has absorbed all light
except the blue and green, which it reflects back to our eyes. A
yellow flower is yellow because it will absorb most of the other
colours of white light and reflect only the yellow. Take away the
light and the yellow flower is now dark or black. It is the same
with paint.
When light is coming to us from our computer screens it will be
the additive triangle we will be interested in because our screen
is a light source and we are mixing light to give us the colour
we will see with our eyes. You will have to get used to the RGB
or Red, Green, Blue terminology, as it will crop up all the time
in modern photography.
Sir Isaac Newton also discovered that light travels through space
as electromagnetic radiation at various wavelengths depending on
the visible colour he saw in his rainbows. He was suspicious there
were other colours present beyond the spectrum that the human eye
could not see. Further detailed use of lenses resulted in an amazing
discovery. Infra red and ultra violet light rays.
Ultra violet has shorter wavelengths than visible light and will
cause certain material to fluoresce and also affect photographic
plates. Ultra violet light will also make your skin go brown and
is known to cause damage to the eye and skin cancers, which is why
we must cover up when we are out taking photos in the sun.
Infra red on the other hand is at the other end beyond the visible
spectrum and has longer wavelengths. Sir Isaac noticed how the rays
were not scattered by fine particles as much as rays in the visible
spectrum. Later science would develop cameras, which would make
use of infra red light by building filters that would block all
other wavelengths and photographic plates sensitive to only infra
red light. Photography at night and in hazy, misty conditions became
a reality. Digital systems that do this have also been developed.
In case you are wondering why the sun is yellow? I am sure?
Well light contains more yellow than any other light and there
is balance indifference, which makes the sun look yellow to us.
Remember this because we are now going to have a look at why our
photos can sometimes have a colour cast to them. This is called
the colour temperature or the White Balance.
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