Module contrast 

How far apart two colours are, in the two ways the colour roles are held to: contrast for an ink on a fill, and separation for a fill that has to be seen on another.

The design system tables are tested against these, an application’s palette is checked against them, and the Renderer chooses an ink with the same arithmetic.

Constants

DIFF_ROLES

Each diff ink with its line background and its word background.

MIN_SEPARATION

How far apart, summed over three eight bit channels, two fills have to be before one can be seen on the other. The same figure the system tables are tested against.

SYNTAX_ROLES

The fifteen syntax inks.

Functions

apart

Summed channel distance in eight bit terms.

contrast

The WCAG contrast ratio of two opaque colours, from 1 to 21.

luminance

Relative luminance, as WCAG defines it.