cs781 - Colour for Computer Graphics - Winter 2012

Course Notes

Lecture 21 - Functional Use of Colour

And Now from our Sponsor

1. Projects
   • April 2: All
2. Tables of useful colour data
3. My deadline for grade submission is May 1st.
4. Joseph Albers Interaction of Color is in the Rare Book Room of the Dana Porter Library.

What is Special about Colour?

Why do animals create the capability of seeing colour? Why do plants make parts of the plant colourful?

• If an animal can see colour a plant can create a signal that something an animal wants is available?
• If a plant labels useful things by colouring them then colour vision gives animals the opportunity of finding them.

That is, colour and colour vision co-evolve allowing animals and plants to specialize.

• Plants specialize in mining. They combine
  • energy from the sun with
  • water, minerals and organic matter from the ground,

  to produce stuff that moving organisms find it hard to produce

  • carbohydrates: sugars and starchs
  • minerals in useful forms: e.g. nitrogen and sulphur covalently bonded to carbon, oxygen and hydrogen, dissolved calcium and sodium, etc.
• Animals specialize in moving. They receive elements of life
  • energy in the form of sugars and fats
  • structural materials

  from plants, and move cargo such as

  • pollen
  • seeds
  • fertilizer

  to places inaccessible to a plant.

To do so, plants must mark the things that animals want, commonly by colouring them.

Examples

1. Pollination
   • Butterfly, moth, bat, bird visits flower
     • gets something to eat
     • leaves behind pollen, or leaves with pollen
   • Some plants are generalists
     • any animal will do
     • be generally attractive

     some are specialists

     • only one specific animal will do
     • be attractive only to that animal
   • Use of ultraviolet: look at figure 7.28
2. Seed Distribution
   • Plant holds back the benefit until the seeds are ready
   • Benefit is added when seeds are ready
   • Distinctive colour means benefit is available

Lots of evidence showing that colour and shape are combined very effectively.

• Both colour and shape must contrast well with the background
  • Toronto police cars

Other Uses of Colour in the Natural World

1. Finding a mate
   • Important to do this without making yourself vulnerable to predators
   • Colour production as an indicator of health (= good genes, or so the evolutionary psychologists say)
2. Making a disguise
   • Often the disguise is easy to penetrate for a visual system different from that of the predator.
   • Dull females, colourful males (birds, non-human primates). Why?
3. Advertising
   • that you are poisonous
     • pigeon colour vision and one trial learning
     • mimicking strategy
   • that you are healthy

Human Interference in Natural Colour

Patterning of colour is controlled by a very small number of genes, which makes it easy for plant breeders

Human Taste in Colour

explored in the fruit and vegetable section of a grocery store

Assignment

1. Go to a big grocery store, like Zehr's or Sobey's
2. Look at the fruit asking what do the fruit/vegetables that look good to eat have in common
3. Buy a few nice-looking ones.
4. Take them home and wait until dark
5. Turn on your kitchen light and try to remember the colour they were at the store.

The same thing works, though somewhat differently, with meat.

How does this Specialness Manifest itself in Human Perception and Cognition?

Visual Search for a Specific Colour

• Specific colour might well be hard-wired in small-brained animals, not in mammals
• Combines well with shape, but only using conjunction
• Well-integrated with higher level thought
  • Stroop effect.

Solving Occlusion Problems Using Colour

• Colour works well with good continuation

Making Colour Work for You

1. Finding is much more common task than you think

2. Solving occlusion problems is much more common than you think

3. Grouping things together using colour is very common

• Surrounding a group of items with a coloured border works just as well, and often better, than colouring the items

Some hints for doing it better

1. Colour is a property of areas, not of lines
2. Use visually distinct characteristics
   • such as brightness, hue, saturation
   • and not red, green, blue

   If they look distinct to you they probably are distinct.

3. Pattern, another property of areas, goes well with colour
4. Legends are effective for attaching meaning to colour.
   • What is a legend?
   • Legends are generally handled well on maps: map designers have gone to map school to get degrees in map design.
   • Aerial photographs, a la Google, are a more serious problem. You actually have to learn how to see them
   • beware of simultaneous contrast.

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