Colour perception

2.1 Color Perception
PSYC 579 Topic Presentation,
University of British Columbia
Diliara Nasirova
School of Interactive Art and Technology,
Simon Fraser University
January 26, 2011

2
Outline
1.  The Physical Description of Light
■  Light Components
■  Electromagnetic Spectrum
2.  The Psychological Description of Color
■  Color Space
3.  Theories of Color Vision
■  Trichromatic Theory
■  Opponent Process Theory
Diliara Nasirova | PSYC 579 | Jan 26, 2011
4.  Basic Phenomena
■  Color Blindness
■  Color Afterimage
■  Color Contrast
5.  Application to Visual Design
■  Color Specification Interfaces
■  Color for Labeling

3
References
1.  C. Ware, “Information Visualization: Perception for Design”, ch. 4 “Color”
2.  SE. Palmer, “Vision Science”
3.  E. Tufte, “Envisioning Information”, ch. 5 “Color and information”
4.  P Rheingans. (1999). “Task-based Color Scale Design”
5.  CA Brewer. (2005). “Designing Better Maps”, ch. 5 “Color Decisions for
Mapping”
6.  C. Ware, “Visual Thinking for Design”, ch. 4 “Color”
7.  M. Stone, “Color in Information Display” workshop, Vis08

4
The Physical Description of Light
Light Components
•  Sir Isaac Newton, 1666

5
Electromagnetic Spectrum

6
The Psychological Description of Color
Color Space
•  All colors experiences can be
described in terms of three
dimensions:
■  Hue
■  Value (lightness)
■  Saturation (chroma)

7
Color Space
•  Color space:
■  A three dimensional coordinate
system
■  Each color can be represented as a
single point with a unique position.

8
Color Space
•  Color solid: Subset of color space
Lightness
Hue
Saturation

9
Theories of Color Vision
Trichromatic Theory
•  Trichromacy:
Three color receptors (cones) in
retinas that are active at normal
light levels
•  Young-Helmholtz Trichromatic
Theory

10
Spectral Diagram
•  Human cone sensitivity
functions.
•  Cones sensitive to
■  S (blue)
■  M (green)
■  L (red)

11
Spectral Diagram: Short wavelength sensitive cones
Blue text on a dark background
is to be avoided. We have very few
short-wavelength sensitive cones in
the retina and they are not very
sensitive.
sensitive.

12
Spectral Diagram: Short wavelength sensitive cones
sensitive.
sensitive.

13
Opponent Process Theory
•  Ewald Hering Opponent Process
Theory
•  Six elementary colors arranged as
opponent pairs along three axes:
■  black-white,
■  red-green,
■  yellow-blue.

14
Opponent Process Theory: Physiological basis
•  Input from the cones is processed into 3 distinct channels

15
Opponent Process Theory: Scientific evidence
1.  Unique Hues:
black, white, red, green…

16
2.  Naming and Cross-Cultural Naming:
“yellowish green”, but no “yellowish blue”

17
3.  Neurophysiology: cells in visual
cortexes of monkeys that have
properties of opponency

18
3.  Categorical Colors:
■  Evidence that confusion
between colors is affected by
color categories

19

20
Opponent Process Theory: Color Channels Properties
•  Chromatic channels carry ~1/3
the amount of detail carried by
the black–white channel.
•  Difficult to read the text where
luminance is equal, despite a
large chromatic difference

21
•  Form: Form perception processed mainly through the luminance channel
Floor, Duomo di Siena

22
•  Form: Pseudocolor sequences for maps

23
Basic Phenomena
Color Contrast
•  Colors are perceived relative to their overall context

24
Basic Phenomena
Color Blindness
•  ~10% of the male and ~1% of the female population have some form of
color vision deficiency.
Original
Deuteranope (r/g)
Protanope (r/g)
Tritanope (y/b)

25
Basic Phenomena
Color Blindness

26
Basic Phenomena
Color Blindness
Normal
vision: no
number
Color blind
vision: “45”

27
Basic Phenomena
Color Afterimage

28
Basic Phenomena
Color Afterimage
.

29
Basic Phenomena
Color Afterimage
•  BMW commercial:
http://www.huffingtonpost.com/2010/12/16/bmw-ad-vide-burns-logo-into-eyes-
_n_797981.html

30
Application to Visual Design
Color Specification Interfaces
•  One of the most widely used color
interfaces in computer graphics is
based on the HSV color space
saturation
hue value

31
Color Specification Interfaces

32
Color for Labeling
•  Labeling: nominal information
coding
•  Color can be extremely effective
as a nominal code.

33
Color for Labeling
•  Perceptual factors to be considered:
1.  Distinctness
2.  Unique hues
3.  Contrast with background
4.  Color blindness
5.  Number
6.  Field size
7.  Conventions

34
Color for Labeling
1.  Distinctness
2.  Unique hues
5.  Number
6.  Field size
7.  Conventions

35
Color for Labeling
1.  Distinctness
2.  Unique hues
5.  Number
6.  Field size
7.  Conventions

36
Color for Labeling
1.  Distinctness
2.  Unique hues
5.  Number
6.  Field size
7.  Conventions

37
Color for Labeling
1.  Distinctness
2.  Unique hues
5.  Number
6.  Field size
7.  Conventions

38
Color for Labeling
1.  Distinctness
2.  Unique hues
5.  Number
6.  Field size
7.  Conventions

39
Color for Labeling
1.  Distinctness
2.  Unique hues
5.  Number
6.  Field size
7.  Conventions

40
Color for Labeling
•  12 colors recommended for use in coding.

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