Properties of Colour

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Color Theory
Which colours is white light made of?
Color Mixing
Color can be perceived either from
1) a luminous object (TV, monitor,
projector) using the Additive
Approach
2) reflected pigment or ink
(printouts, materials) using the
Subtractive Approach
Additive Color Model

Used by luminous objects
ex. Computers, TV, projectors

When light energy is added,
a color appears brighter

The additive primary colours
are (RGB):
– Red
– Green
– Blue

Secondary colours produced are (CMY)
– Cyan – Magenta – Yellow

Different percentages of red, green, & blue light
are used to generate different colours

White light is created when Red, Blue and Green
are mixed together

There is no way of making black by adding red,
green and blue light sources, the screen must be
black to start with.

http://dev.physicslab.org/asp/ap
plets/additivecolors/default.asp
Our Eyes
Our eyes use the additive colour
approach, but how do we see
colour if all wavelengths are
coming in from the sun (white
light)?
Objects absorb all colors
except the color being seen,
which is reflected
White light
Green Surface
White Light
reflected
White light
Green Light
reflected
Blue Light
reflected
White light
White Surface
Blue Surface
White light
Red Light
reflected
White light
No Light reflected
Red Surface
Black Surface

Objects absorb all colors except
the color being seen, which is
reflected
White surface = all wavelengths
(blue, red, green) are being reflected
 Black surface = all wavelengths are
being absorbed.
 Red surface = blue and green
wavelengths are absorbed, red is
reflected
 Green surface = blue and red
wavelengths are absorbed, green is
reflected.

DEMO

Questions, why are clouds
white?

Why is it not a good idea to
wear black in the summer?
Subtractive Color Model

Used in the print media
ex. inks, fabrics, paints, crayons, etc.

When more color is added,
a color appears darker

The subtractive primary colours are (CMY):
– Cyan
– Magenta
– Yellow
 Secondary colours produced by CMY colours are
– Red
– Green
– Blue
What do you
notice about the
primary
& magenta & yellow
 Different percentages
of cyan,
light are used tosecondary
generate different colours
colours?

There is no way of making white by adding CMY
colour sources, the paper/canvas must be white
to start with.
Computers DON’T use
the subtractive theory.
16
Because printers work
on subtractive colour
system and computers
don’t, it’s hard to
reproduce the same
picture.
Cookie Wheel
Colour Blindness

1 out of 10 men and 1 out of 200
women have some type of color
deficiency.

The most common type is
mistaking red and green.

The second most common type
is mistaking blue and yellow
Blind Spot – not just on
cars!

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