Saturation

How it is measured

The CIE defines saturation as the colourfulness of an area judged in proportion to its own brightness. The HSL and HSV figures that most software reports are simpler: both come from the spread between the largest and smallest RGB channel, divided by the largest channel in HSV and by a term that depends on lightness in HSL. Both run from 0% to 100% and neither is a measurement of how saturated a colour looks.

Worked example

Cream scores 100% in HSL and 18% in HSV. HSL measures saturation against the most saturated colour possible at that lightness, and near white almost nothing is possible, so a faint yellow counts as fully saturated. Navy blue scores 100% in HSV with a chroma of 80.3, lower than Red's, because it is dark. Colourwise's muted, vivid and neutral labels use the HSV column for this reason.

How this was calculated: HSL and HSV saturation and CIELAB chroma (the length of the a*, b* vector) from each catalogue HEX value.

Often confused with

Chroma

Chroma is judged against a white under the same light; saturation is judged against the colour's own brightness. A deep red in shadow keeps its saturation and loses chroma. A dark colour can be highly saturated and still have little chroma.

Colourfulness

Colourfulness is the absolute impression, and it rises with the light level: the same flowerbed looks more colourful in sun than under cloud. Saturation divides that out, so it stays roughly constant as the light changes.

Vivid colour

Vivid is a label Colourwise applies above a threshold of HSV saturation. Saturation is the scale; vivid is one end of it.

Where it matters in practice

Where to go next

• HSL and HSV — Colour systems
• Highlight clipping and hue shifts — Photography
• The great desaturation: what the evidence shows — Colour through time
• Colour Converter — tool