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

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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

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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


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The Physical Description of Light Light Components


•  Sir Isaac Newton, 1666

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The Physical Description of Light Electromagnetic Spectrum


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The Psychological Description of Color Color Space

•  All colors experiences can be described in terms of three dimensions: ■  Hue ■  Value (lightness) ■  Saturation (chroma)


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•  Color space: ■  A three dimensional coordinate

system ■  Each color can be represented as a

single point with a unique position.


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•  Color solid: Subset of color space


Lightness

Hue

Saturation

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Theories of Color Vision Trichromatic Theory

•  Trichromacy: Three color receptors (cones) in retinas that are active at normal light levels

•  Young-Helmholtz Trichromatic Theory


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The Physical Description of Light Spectral Diagram


•  Human cone sensitivity functions.

•  Cones sensitive to ■  S (blue) ■  M (green) ■  L (red)

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The Physical Description of Light 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.


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The Physical Description of Light Spectral Diagram: Short wavelength sensitive cones




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Theories of Color Vision Opponent Process Theory

•  Ewald Hering Opponent Process Theory

•  Six elementary colors arranged as opponent pairs along three axes: ■  black-white, ■  red-green, ■  yellow-blue.


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Theories of Color Vision Opponent Process Theory: Physiological basis

•  Input from the cones is processed into 3 distinct channels


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Theories of Color Vision Opponent Process Theory: Scientific evidence

1.  Unique Hues: black, white, red, green…


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2.  Naming and Cross-Cultural Naming:

“yellowish green”, but no “yellowish blue”


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



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3.  Categorical Colors:

■  Evidence that confusion between colors is affected by color categories



19 Diliara Nasirova | PSYC 579 | Jan 26, 2011


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Theories of Color Vision 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


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•  Form: Form perception processed mainly through the luminance channel

Floor, Duomo di Siena

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•  Form: Pseudocolor sequences for maps

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Basic Phenomena Color Contrast


•  Colors are perceived relative to their overall context

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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)

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Normal vision: no number Color blind vision: “45”

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Basic Phenomena Color Afterimage


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


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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

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Application to Visual Design Color Specification Interfaces


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Application to Visual Design Color for Labeling

•  Labeling: nominal information coding

•  Color can be extremely effective as a nominal code.


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


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•  12 colors recommended for use in coding.

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Conclusion

colour perception

Design

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color decisions formapping6

taskbased color scale

cones sensitive

blue text

dark backgroundis