colour andrew hanson and emma woolliams 3 rd july 2006
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Colour
Andrew Hanson and Emma Woolliams
3rd July 2006
Where does colour fit into measurement?
Cryogenic Radiometry
Spectral Responsivity
Photometry
Spectral radiometry
Pyrometry
Solar Remote Sensing Lighting Transport Aerospace Medicine Industry Environment
SI
Appearance
Emma’s background
Emma’s background
00:00 00:05 00:10 00:15 00:20 00:25 00:30 00:35 00:40 00:45
Top 10 bizarre things to measure
• White lines down the middle of the road (and yellow, red, blue)
Top 10 bizarre things to measure
• Glossiness of cats
Top 10 bizarre things to measure
• Camouflage (including NIR)
Top 10 bizarre things to measure
• Chocolate
Top 10 bizarre things to measure
• How Hampton Court tapestries change colour with light exposure
Top 10 bizarre things to measure
• Human organs(skin, teeth, internal organs)
Top 10 bizarre things to measure
• 150 chickens (as they would appear to other chickens)
Top 10 bizarre things to measure
• Amsterdam, lit blue It would not appear completely blue as fluorescent objects would appear in their colours.
• Light
The Optical Window
• Optical Window lets E/M radiation bathe earth’s surface – window of visual opportunity.
Non human vision
• Insects see buttercups striped
Sampling the spectrum
• Humans 3: Trichromacy • Birds 4, • Bulls 1, • Shrimps 13.
Models
What is colour?
• Colour is human coding of light.
Making colour
• Trichromacy exploited by colour making processes:
• Colour displays R,G,B (additive)
• Printing/film photography –R,-G,-B (C,M, Y) (subtractive) (except for Autochrome RGB system)
• Paints – 18 primary pigments? Immiscibility, gamut, cost, metamerism.
Spectra
Human sampling of the spectrum
• Human vision covers about an octave, using three sensors (Trichromacy) in a ‘good engineering’ comparison system:
L vs MM vs SS vs L
(after Vos, J. J. & Walraven, P. L.).
Defining colour
• Measuring Colour
How do you measure colour?
• What is actually measured?
• Need three things for colour:• Light source• Medium• Eye• (Or bang on the back of the head/psychotropic drugs)
How do you measure colour?
• Measure amounts of X, Y, Z.
Defining colour
How do you measure colour?
• Measure emitted light, (source directly, or off media)
How do you measure colour?
• or for given media, the ratio transmitted or reflected light and multiply by a light source’s spectral distribution
How do I know what you call green
isn’t what I see as red?
• Not just philosophy, this is a real problem of perception touching on fundamental issues for modelling vision:
• We’re all different
• It is impossible to see through someone else's eyes.
Looking at the world
• Much processing reduces data into usable informationEyes accept ~700 Mb/s:
• Scene>Eye>Brain<Memory
• Data reduction processes cause many optical illusions.
Optical illusions
• Chromatic induction on a weave.
Akiyoshi KITAOKA, Japan
Human sampling of the spectrum
• Human vision covers about an octave, using three sensors (Trichromacy) in a ‘good engineering’ comparison system:
L vs MM vs SS vs L
(after Vos, J. J. & Walraven, P. L.).
Colour blindness
Subjects tasting visible drinks always identified drink taste correctly. When, however, they could not see drink color….
What People Said (%)
Real Flavor Grape LL Cherry Orange other
Grape 70 15 5 0 10
Lemon-Lime 15 50 5 15 15
Cherry 0 40 30 10 20
Orange 0 50 5 20 25
(Correctly identified in BOLD).
Colour – a matter of tasteColour – a matter of taste
So why is the sky blue?
Why 7 colours in the rainbow?
ROYGBIV
Reasons for colour(Things which happen differently for different wavelengths)
Vibrations, simple excitations, rotations
incandescence Flames
gas excitations neon tube,
Aurora
rotations blue ice and water
Ligand-field-effect colours
transition-metal compounds
turquoise,
chrome-oxide green
impurities ruby, emerald
Molecular orbitals
organic compounds indigo, chlorophyll
charge-transfer compounds
blue sapphire,
lapis lazuli
Reasons for colour(Things which happen differently for different wavelengths)
Energy bands
metals and alloys gold, brass
semiconductors cadmium yellow, vermilion
doped semiconductors
blue and yellow diamond
colour centres amethyst, topaz
Geometrical and physical optics
dispersive refraction rainbow, green flash
scattering blue sky, blue eyes, red sunset
interference soap bubbles, iridescent beetles
diffraction the corona aureole, opal
Question to you:
What is the overall efficiency of conversion of sunlight to incandescent light?