colour andrew hanson and emma woolliams 3 rd july 2006

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?