Transcript here

Colour Theory
Helge Seetzen
University of British Columbia
[email protected]
Presentation and Outline at
http:\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
Extractor
Mirrored Endcap
Optical Lighting
Film
Input Window
LED Array
The Artist: The Colour Wheel
• 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 Physicist: What is Light?
• wave?
• particle?
• ray?
The Physicist: Defining a Wave
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: Visible Spectrum
The Physicist: Additive Colours
Mixing colours
created by light.
- Video Cameras
- Computer Screens
- Television Lights
- Video Monitors
Primary Colours
- Red
- Green
- Blue
Additive Colours
The Physicist: But…
Subtractive Colours
• Used for mixing inks
for printing.
• Primary colors are:
- Yellow
- Cyan
- Magenta
The Physicist: Subtractive Colours
The Psychologist: And the Eye?
The Psychologist: And the Eye?
The Psychologist: Cone Sensitivity
The Psychologist: An Example
Perception of monochromatic light
of a laser at 640 nm
The Psychologist: Incoming Light
640 photons
The Psychologist: Stimulation
Red cone is stimulated more than green cone
The Psychologist: Perception
We have a perception of red
The Psychologist: Trickier Case
Perception of yellow light
The Psychologist: Incoming Light
Incoming light of 560-580nm
The Psychologist: Stimulation
Red and green cone are stimulated equally
The Psychologist: Perception
We have a perception of yellow
5
2.5
0
400
500
600
Wavelength(nm)
700
1
0.5
0
400
=
500
600
Wavelength(nm)
700
Intensity
Reflectance
Intensity
Colour: Bringing it all together
3
2
1
0
400
500
600
Wavelength(nm)
700
Colour: Bringing it all together
500
600
Wavelength(nm)
700
1
0.5
0
400
=
500
600
700
Stimulation
3
2
1
0
400
Cone Response
Intensity
5.5
1.5
0.3
1
0.5
0
400
Wavelength(nm)
Integration of each cone signal
500
600
Wavelength(nm)
700
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.