Colour Theory Helge Seetzen University of British Columbia Presentation and Outline at

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 Lighting Film Mirrored Endcap Extractor

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: Cone Sensitivity

Perception of monochromatic light of 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 nm

Red and green cone are stimulated equally The Psychologist: Stimulation

We have a perception of yellow The Psychologist: Perception

Colour: Bringing it all together =

Integration of each cone signal =

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.