- Colour vision relies on colour constancy to enable an observer to perceive the colour of an object as almost unchanged as levels of illumination change and the spectral distributions of light changes.
- A human observer will often not notice when the colour of object changes as the source of illumination changes e.g. sunlight to artificial light.
- Colour vision allows us to distinguish different objects by their colour. In order to do so, colour constancy can keep the perceived colour of an object relatively unchanged when the illumination changes among various broad (whitish) spectral distributions of light.
- Colour constancy is achieved by chromatic adaptation. The International Commission on Illumination defines white (adapted) as “a colour stimulus that an observer who is [chromatically] adapted to the viewing environment would judge to be perfectly achromatic and to have a luminance factor of unity. The colour stimulus that is considered to be the adapted white may be different at different locations within a scene.
- The effect of changes in colour balance is very noticeable when comparing photographs of the same subject taken in different lighting conditions. Cameras use white balance to compensate for changes in illumination.