Table of Contents


Part I - Introduction

Part II - Spectral Power Distribution

Part III - Metamerism and Color Matching

Part IV - The Optical System of the Human Eye

Part V - Chromaticity Coordinates and the Color Triangle

Part VI - Color Spaces and the CIE-XYZ System

Works Consulted


Up to the seventeenth century, most theories attributed color to some sort of modification of light that was thought to occur when light interacted with matter. Light, in its purest form (such as sunlight) was thought to be colorless. However, progress in understanding color was made by Isaac Newton when in 1666 he was able to show that normal white light already contained all the colors of the spectrum, which could be separated using a prism. He also concluded from his experiments that objects have color because they selectively reflect certain colors of the spectrum while absorbing light of other colors.

Light is the small part of the electromagnetic spectrum that can affect the human sense of sight. The visible part of the spectrum (for us) ranges from 400 nm (blue) to 700 nm (red). Each wavelength value within the visible band corresponds to a distinct colour.

Figure 1.1
The visible portion of the spectrum

Parameters of light that are of interest to us:
    Wavelength - the length of one light-wave cycle
    Frequency - the number of wavelengths per second

Three attributes are used to specify a color: hue, saturation and brightness. These describe only the perception of light, not its physical properties.

  1. Hue - a feature of monochromatic light that varies with wavelength and used to denote the various regions of the spectrum (in other words, the basic color from the spectrum).
  2. Saturation - how much a color differs from white (ie vivid pure color versus pastel color)
  3. Brightness - the perceived intensity of light
Figure 1.2 shows three different pairs of squares of color. Part (a) shows two squares that are of different hue. Part (b) shows two squares of the same hue but different saturation. The square on the right is less saturated than the square on the left. Part (c) shows two squares that are of different brightness. The square on the left is much brighter than the square on the right.

Figure 1.2
Examples of (a)different hues, (b)different saturation, and (c)different brightness