Colour and Humans

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Colour and Humans

• Human colour perception
• in the context of Mapping
• Map Reading

deep cartographic knowledge
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Human Colour Perception

• how we see colour
• how colour is described
• what colour blindness is

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Elements of Colour
illumination
perception
reflectance
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Visible Spectrum
We perceive electromagnetic energy having
wavelengths in the range 400 700 nm as visable
light
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Hue

• Hue is that psychological dimension of colour
  which roughly corresponds to wavelength.  Hue is
  the common meaning of the word "colour".  Common
  colour names, such as  "red", "green", "yellow",
  etc., are all descriptive of hue.
• Most color wheels have 8 12 hues, no more than
  24
• The most complex maps (soils, geology) generally
  have 12 hues

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16 colours
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• Although colour is often used as though
  synonymous with hue, variations in lightness and
  darkness are just as much a part of colour as
  variations in wavelength

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Value

• Lightness or darkness of color
• Also called tint, shade, tone
• Created by adding white or black to a hue
• 5 values of a color are the most that can be
  easily
• distinguished on a map
• Discrimination depends on background color
  dark vs.
• light

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Brightness
Colors are also described by their
brightness Hue will change with intensity
INTENSITY
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Saturation
hue is less saturated
Among monochromatic lights, short wavelengths
(blue) and long wavelengths (red) appear the most
saturated.  Wavelengths of around 575 nm (yellow)
appear the least saturated.  To illustrate this
phenomenon, ask yourself which hue, blue, red or
yellow, is the most similar to white?
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Chroma

• Saturation, intensity or purity of the color
• referring to the purity of the hue where a
  fully saturated colour transmits or reflects at a
  single (or very narrow) wavelength
• Hue affects chroma level intense yellow
  appears brighter than intense blue-green
• A single colour scale is Achromatic

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The photosensitive part of the eye is called the
retina The retina is largely composed of two
types of cells rods and cones. Only the cones
are responsible for colour perception
Colour-blindness results from a deficiency of one
cone type
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• Approximately 8 percent of all males and 0.5
  percent of all females have a color blindness
  (Hackman 1992, 653). Color blindness or weakness
  has four basic varieties
• green blindness--individuals confuse greens,
  yellows, and reds (6.39 percent)
• red blindness--individuals confuse various
  shades of red (2.04 percent)
• blue blindness--individuals confuse blues (0.003
  percent)
• total color blindness, which affects no more
  than 0.005 percent of both sexes.

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A quick colour blindness test
Both normal and those with all colour vision
deficiencies should read the number 12.
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Normal vision should read the number 29.

Red-green deficiencies should read the number
70. Total colour blindness should not read any
numeral
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Normal colour vision should read the number 5.

Red-Green colour deficiencies should
read the number 2.
Total colour
blindness should not be able to read any numeral.
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Normal colour vision should read the number 6.

The majority of those with colour
vision deficiencies cannot read this number or
will
read it incorrectly.
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Normal colour vision and those with total colour
blindness should not be able to read
any
number.
The majority of those with
red-green deficiencies should read the number 5.
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Understanding Colour Transformations

• red green deficiencies are very similar in terms
  of perception
• red blind protanope
• green blind deuteranope

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these colours look the same
protanopic confusion colours
deuteranopic confusion colours
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Mapping

• inclusive colour palettes
• colour meaning and bias
• figure vs ground
• cartographic convention
• 4 colour theory

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Inclusive Colour Schemes

• developed for Mapping Census 2000 The Geography
  of U.S. Diversity
• will be OK for a majority of colour blind people

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10 Colour Scheme
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Alarm Colours
Think in terms of saturation/chroma rather than
hue
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Meaning of Colours
cool soothing
urgent! important!
natural good
happy fun
royal rich
earth safe
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Colour Bias

• some colours are more attention getting than
  others (culturally and visually)
• some combinations of colours create visual bias

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Low BiasHigh Saturation
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Low BiasLow Saturation
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Low BiasEarth Tones
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High BiasLow saturation with high saturation
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High BiasEarth Tones with saturated tones
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Colour Perception

• Advancing and Retreating colors
• Advancing colors appear closer to the viewer
  than retreating colors
• Advancing colors should be used for figure
  retreating colors used for ground
• Advancing colors warm hues, high values, deep
  saturation (deep, dark reds)
• Retreating colors cool hues, low values, less
  saturation (grayish, light blues)

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Colour Perception

• Perception of a color is modified by its
  environment
• Simultaneous contrast adjacent colors appear
  lighter in the direction of the darker color,
  and darker in the direction of the lighter color
• Successive contrast same color may appear
  lighter against a dark background, and darker
  against a light background

just because it looks good in a linear scale in
your key doesnt mean it will work across a whole
map
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The Same Color?
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The Same Color?
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Figure vs Ground
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Design Strategies

• Developing Figure and Ground Relationships
• Perceptual grouping of colors is a strong
  tendency similar hues or brightness, warm or
  cool colors, etc.
• Since warm colors advance they take on figural
  qualities better than cool colors, which make
  good ground colors
• Color combination affects figure and ground
  development

know what you want to say with your map
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Contrast

• Contrast is the most important design element in
  thematic mapping
• Contrasting Hue ? clarity, legibility, visual
  hierarchy
• Contrasting Value/Saturation ? visual interest,
  quantitative information, high values emerge as
  figure
• Render far away objects in cool tones, close
  objects in warm tones
• Legibility of lettering on maps is greatly
  affected by both text and background colors

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Colour Conventions

• Qualitative Color Conventions (kind/quality)
• Stick with hue variations only
• Blue water, cool temperatures
• Red warm temperatures
• Yellow/Tan arid and sparsely vegetated or sand
• Brown land surface
• Green thick and lush vegetation

no surprises for the map user
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Colour Conventions

• Quantitative Conventions (amount)
• Use gray and simple hues only (arcview
  monochromatic)
• Part-spectral use two colors adjacent on color
  wheel, plus intermediate hues (arcview
  dichromatic)
• Full-spectral use a separate hue for each
  different amount (red highest)
• Double-ended illustrate positive to negative
  values by going from one dark hue, through light
  values, to a second dark hue (i.e. red blue)

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Colour Function

• Simplifying and Clarifying Agent
  differentiate figure vs. ground or unify various
  map elements
• Contributes to General Perceptibility lends
  legibility, visual acuity, clarity of differences
• Elicit Subjective Reactions people respond to
  color

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4 Colour Theory

• How many colours do you really need?

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reference

• Eye of the beholder- designing for colour-blind
  users (http//more.btexact.com/people/rigdence/col
  ours/)
• also has palette files
• Colour vision(http//www.psychology.psych.ndsu.no
  dak.edu/mccourt/website/htdocs/HomePage/Psy460/Col
  or20Vision/Color20Vision.html)
• Choosing colours for Mapping Census 2000 the
  Geography of American Diversity
  (http//www.personal.psu.edu/faculty/c/a/cab38/Cen
  susAtlasCMYK.html)
• Colour Brewer (http//www.personal.psu.edu/faculty
  /c/a/cab38/ColorBrewerBeta.html)