Colour

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Colour

• Andrew Hanson and Emma Woolliams
• 3rd July 2006

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Where does colour fit into measurement?
Cryogenic Radiometry
SI
Spectral Responsivity
Spectral radiometry
Pyrometry
Photometry
Appearance
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Emmas background
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Emmas background
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Top 10 bizarre things to measure

• White lines down the middle of the road (and
  yellow, red, blue)

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Top 10 bizarre things to measure

• Glossiness of cats

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Top 10 bizarre things to measure

• Camouflage (including NIR)

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Top 10 bizarre things to measure

• Chocolate

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Top 10 bizarre things to measure

• How Hampton Court tapestries change colour with
  light exposure

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Top 10 bizarre things to measure

• Human organs(skin, teeth, internal organs)

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Top 10 bizarre things to measure

• 150 chickens (as they would appear to other
  chickens)

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Top 10 bizarre things to measure

• Amsterdam, lit blue It would not appear
  completely blue as fluorescent objects would
  appear in their colours.

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• Light

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The Optical Window

• Optical Window lets E/M radiation bathe earths
  surface window of visual opportunity.

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Non human vision

• Insects see buttercups striped

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Sampling the spectrum

• Humans 3 Trichromacy
• Birds 4,
• Bulls 1,
• Shrimps 13.

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Models
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What is colour?

• Colour is human coding of light.

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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.

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Spectra
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Human sampling of the spectrum

• Human vision covers about an octave, using three
  sensors (Trichromacy) in a good engineering
  comparison systemL vs MM vs SS vs
  L (after Vos, J. J. Walraven, P.
  L.).

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Defining colour
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• Measuring Colour

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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)

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How do you measure colour?

• Measure amounts of X, Y, Z.

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Defining colour
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How do you measure colour?

• Measure emitted light, (source directly, or off
  media)

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How do you measure colour?

• or for given media, the ratio transmitted or
  reflected light and multiply by a light sources
  spectral distribution

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How do I know what you call green isnt what I
see as red?

• Not just philosophy, this is a real problem of
  perception touching on fundamental issues for
  modelling vision
• Were all different
• It is impossible to see through someone else's
  eyes.

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Looking at the world

• Much processing reduces data into usable
  informationEyes accept 700 Mb/s

• ScenegtEyegtBrainltMemory
• Data reduction processes cause many optical
  illusions.

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Optical illusions
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• Chromatic induction on a weave.

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Akiyoshi KITAOKA, Japan
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Human sampling of the spectrum

• Human vision covers about an octave, using three
  sensors (Trichromacy) in a good engineering
  comparison systemL vs MM vs SS vs
  L (after Vos, J. J. Walraven, P.
  L.).

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Colour blindness
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Colour a matter of taste
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So why is the sky blue?
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Why 7 colours in the rainbow?
ROYGBIV
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Reasons for colour(Things which happen
differently for different wavelengths)
Vibrations, simple excitations, rotations incandescence Flames
Vibrations, simple excitations, rotations gas excitations neon tube, Aurora
Vibrations, simple excitations, rotations rotations blue ice and water
Ligand-field-effect colours transition-metal compounds turquoise, chrome-oxide green
Ligand-field-effect colours impurities ruby, emerald
Molecular orbitals organic compounds indigo, chlorophyll
Molecular orbitals charge-transfer compounds blue sapphire, lapis lazuli
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Reasons for colour(Things which happen
differently for different wavelengths)
Energy bands metals and alloys gold, brass
Energy bands semiconductors cadmium yellow, vermilion
Energy bands doped semiconductors blue and yellow diamond
Energy bands colour centres amethyst, topaz
Geometrical and physical optics dispersive refraction rainbow, green flash
Geometrical and physical optics scattering blue sky, blue eyes, red sunset
Geometrical and physical optics interference soap bubbles, iridescent beetles
Geometrical and physical optics diffraction the corona aureole, opal
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• Question to you What is the overall efficiency
  of conversion of sunlight to incandescent light?