Hue, Saturation and Lightness

More sophisticated image editors provide separate adjustments for the three main components of colour: hue, saturation and lightness. Together they enable us to describe colours with a high degree of precision.

Hue is what we usually define as colour. For painters (and many other artists), the term ‘hue’ refers to a pure colour; in other words, red, green, blue or yellow. For scientists, hue refers to a specific waveband in the visible spectrum. Everyday photographers generally think of hue as referring simply to a specific colour.

Saturation (or ‘chroma’) defines the intensity of a hue. Vivid primary colours are highly saturated, while pastel colours are unsaturated. Monochrome (black and white) prints are totally de-saturated since they lack colour intensity.

Lightness (which is sometimes referred to as ‘value’ or ‘tone’) relates to the amplitude of the colour – or its proximity to the white or black end of the tonal scale. A colour with low value is close to black, while one with high value is close to white.

Photographers use the ‘low’ and ‘high’ value terms to define the ‘key’ of pictures. High-key photographs contain mainly light tones, while low-key images are pitched towards the dark end of the tonal scale. Examples are shown below.

A typical high-key image containing mostly light tones.

A typical low-key image containing mostly dark tones.
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