Ratio (contrast) calculation & vision:
WCAG: (Lw+0.05) / (Lk+0.05)
Weber(mod): ((Lw^1.6)-(Lk^1.6)+0.05) / (Lk^1.6+0.05)
Sources:
myndex,
johndcook
Author:
Tom Jewett, for WCAG LVTF
Wish list: more vision & contrast options
Ratio color coding, WCAG 2.0:
7.0–21.0 OK all sizes (AA, AAA)
4.5–6.99 >=18/
14 (AAA); < same (AA)
3.0–4.49 OK >=18/
14pt (AA)
1.0–2.99 Not OK at any size