Luminance, hue and saturation
Any colour has three characteristics to specify its visual information. These are (i) luminance, (ii) hue or tint, and (iii) saturation. These are defined as follows:
(i) Luminance or Brightness
- This is the amount of light intensity as perceived by the eye regardless of the colour.
- In black and white pictures, better lighted parts have more luminance than the dark areas.
- This is the predominant spectral colour of the received light.
- Thus the colour of any object is distinguished by its hue or tint.
- The green leaves have green hue and red tomatoes have red hue.
- This is the spectral purity of the colour light.
- Since single hue colours occur rarely alone, this indicates the amounts of other colours present.
- Thus saturation may be taken as an indication of how little the colour is diluted by white.
- A fully saturated colour has no white.
- As an example. Vivid green is fully saturated and when diluted by white it becomes light green.
- The hue and saturation of a colour put together is known as chrominance. Chrominance is also called chroma.