Color

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Slide 1

Today

Measuring color

Spectral power distributions

Color mixing

Color matching experiments

Color spaces

Uniform color spaces

Perception of color

Human photoreceptors

Environmental effects, adaptation

Using color in machine vision systems

Slide 2

What is color?

The result of interaction between physical light in the environment and our visual system.

A psychological property of our visual experiences when we look at objects and lights, not a physical property of those objects or lights.

Slide credit: Lana Lazebnik

Slide 3

Color and light

Color of light arriving at camera depends on

Spectral reflectance of the surface light is leaving

Spectral radiance of light falling on that patch

Color perceived depends on

Physics of light

Visual system receptors

Brain processing, environment

Slide 4

Color and light

Newton 1665

Image from http://micro.magnet.fsu.edu/

White light: composed of about equal energy in all wavelengths of the visible spectrum

Slide 5

Image credit: nasa.gov

Electromagnetic spectrum

Human Luminance Sensitivity Function

Slide 6

Measuring spectra

Foundations of Vision, B. Wandell

Spectroradiometer: separate input light into its different wavelengths, and measure the energy at each.

Slide 7

The Physics of Light

Any source of light can be completely described

physically by its spectrum: the amount of energy emitted

(per time unit) at each wavelength 400 - 700 nm.

© Stephen E. Palmer, 2002

Slide 8

Spectral power distributions

Some examples of the spectra of light sources

© Stephen E. Palmer, 2002

Slide 9

Surface reflectance spectra

Some examples of the reflectance spectra of surfaces

Wavelength (nm)

% Photons Reflected

© Stephen E. Palmer, 2002

Slide 10

Color mixing

Source: W. Freeman

Cartoon spectra for color names:

Slide 11

Additive color mixing