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Colour Theory
Helge SeetzenUniversity of British Columbia
Presentation and Outline athttp:\www.sunnybrooktech.com\colour.html
Colour Theory
Artist: Colour is a property of objects!
Physicist: Colour is a property of light!
Psychology: Colour is a property of our vision!
The Physicist: The Lightpipe
LED Array
Input Window
Optical LightingFilm
Mirrored Endcap
Ext
ract
or
• A colour circle, based on red, yellow and blue, is traditional in the field of art and is a way of arranging colours to show a variety of relationships between colours
• Sir Isaac Newton developed the first circular diagram of colours in 1666
The Artist: The Colour Wheel
• wave?
• particle?
• ray?
The Physicist: What is Light?
Wavelength - distance from peak to peak, or trough to trough
Frequency - cycles per second; how many peaks pass a given point in 1 second
The Physicist: Defining a Wave
The Physicist: Visible Spectrum
Mixing colours created by light.- Video Cameras- Computer Screens- Television Lights- Video Monitors
Primary Colours- Red- Green- Blue
The Physicist: Additive Colours
Additive Colours
The Physicist: But…
• Used for mixing inks for printing.
• Primary colors are:- Yellow- Cyan- Magenta
Subtractive Colours
The Physicist: Subtractive Colours
The Psychologist: And the Eye?
The Psychologist: And the Eye?
The Psychologist: Cone Sensitivity
Perception of monochromatic lightof a laser at 640 nm
The Psychologist: An Example
640 photons
The Psychologist: Incoming Light
Red cone is stimulated more than green cone
The Psychologist: Stimulation
We have a perception of red
The Psychologist: Perception
Perception of yellow light
The Psychologist: Trickier Case
The Psychologist: Incoming Light
Incoming light of 560-580nm
Red and green cone are stimulated equally
The Psychologist: Stimulation
We have a perception of yellow
The Psychologist: Perception
Colour: Bringing it all together
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Colour: Bringing it all together
Integration of each cone signal
5.51.50.3
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Colour: There is a lot more to it!
The ‘primary colours’ are A, B, and C.
Then for a given real color, its components with respect to the primaries are as follows:
x = A/(A+B+C)y = B/(A+B+C)z = C/(A+B+C) with x + y + z = 1
The CIE diagram is a plot of X
vs. Y for all visible colors.
