Lecture 6 - What is colour? Flashcards
What is wavelength?
(m)- the distance from one point on a wave to the same point on the successive wave
Whatis frequency?
(Hz)- how many waves go by in 1 second
What is period?
(s)- how long a wave takes to go through the full range of motion
What is light characterised by?
wavelength or its frequency
What can looking at the colour of a wave do?
help determine its frequency
What is black?
absorb all frequencies of light
What are the different aspects of colour?
colour temp
blackbody radiator
non-blackbody radiators
What does thermal sources of light do?
emit radiant energy in proportion to their temperature
What does the colour tell us when it emits?
tells us the temperature of the source
Where is the colour temperature commonly observed?
when a piece of metal is heated
What happens when you increase the temperature of the flame to the metal?
the metal will start to glow red
and when its very hot it will turn white and blue
What is a blackbody radiator?
- a perfect blackbody is a theoretical object that would absorb all the radiation/wavelengths that falls on it
- it would not reflect or transmit any radiation
- best possible emitter and absorber of radiation
What are non-blackbody radiator?
white and shiny silvery surfaces which are poor emitters
Why are radiators in home usually painted white?
so that the infrared radiation is emitted gradually
What happens if you increase temp in the blackbody curves?
there is a shift in wavelengths emitted
there is a shift towards shorter wavelengths
What can you call blackbody radiators?
if a particular source radiates energy following those wavelengths (blackbody curve)
How can you specify a blackbody radiator?
by its colour temperature, in degrees Kelvin (K)
What does it mean if you have a red (warm) lamp?
its colour temperature is LOW
What does it mean if you have a cold (white) lamp?
it colour temperature is HIGH
What do people prefer from home lamps?
a colder lamp which gives a warmer sensation/look(so red lamp)
What do people prefer for work/office/school lamps?
a warmer lamp which gives a colder sensation/look (so white lamp)
What system allows us to specify colours graphically?
CIE 1931 (x,y) colour space
What does the CIE system do?
specify x,y,z co-ordinate on the chart- mixture of 3 CIE primaries called tristimulus values
they map a colour with respect to hue and saturation on a 2D CIE colour space
What colour is more saturated?
the further away you are (to edges) the more saturated
What are spectral colours?
one wavelength colour
they are aligned around the outside of the horse-shoe shape and are most saturated
can be correlated to a specific wavelength
What colours are less saturated?
closer to the centre
How can you make a colour?
by combining wavelengths
one colour can be made many different ways - from combinations of colours
What is white light?
can be made of any mixture of different colours
in the middle of CIE spectrum
What else is part of the CIE garph?
line of purples across the bottom.
What else is part of the CIE garph?
line of purples across the bottom.
What is additive colour mixing?
mixing lights of different wavelengths
superposition of red,blue,green lights which can be combined to make visibile light
What are the primary colours?
red , green, blue which make whitw light
What are the complementary colours for R,G,B?
Cyan
magenta
yellow
What do computer monitors use?
additive colour mixing
What is the triangle in the computer monitor?
the computer monitor can only produce those colours by mixing them in different combinations
What do the 3 primaries in the computer monitor do?
produce the triangle
What is the gamet determined by?
in chromaticity space, the gamet is determined by the triangle formed by the chromaticities of the light
Maximum luminance?
determined by the sums of the R,G,B luminances
What is a gamet?
all colours the display can produce
What is subtractive colour mixing?
based on absorption or subtraction of certain wavelengths from white light.
as a result of absorbing different wavelengths of colours
What are the usual colours in colour printing?
cyan, magenta, yellow, black
