Information

Contrast is not one measurement. Pairette carries four procedures, and which of them applies is decided by the medium rather than by preference: three are defined for self-illuminated displays — WCAG 2, APCA and Delta Phi Star — and one for ink on paper, DIN 32975. A pair is therefore only ever compared within one medium, and the same two colors can carry on screen and fail in print.

Three of the four can be read at the source, free of charge: WCAG 2, APCA and Delta Phi Star.

DIN 32975 cannot. It is sold by DIN Media and may not be passed on, which is why nothing of it is reproduced here. What it prescribes is nevertheless open to anyone: the Michelson formula on the luminance factor, a minimum contrast, and the condition that the lighter of the two colors reflect at least half of the incident light. The German Federation of the Blind and Partially Sighted sets all three out in Kontrastreiche Gestaltung öffentlich zugänglicher Gebäude and gives the brochure away. Anyone doubting a number this application reports for print can check it there rather than having to buy the standard.

Conversion

A print color is a screen color taken through an ICC profile, and taking it there is the work of a color engine this server has to supply. Which one is a matter of what is installed: the numbers are the profile's, not the engine's. Without any of them the screen procedures carry on and print is left out rather than estimated.

• FfiTransformer

Printing conditions

A printing condition is paper, ink and press taken together, described by an ICC profile. The same four ink percentages printed under two of them are two different colors, which is why the profile is a setting beside the matrix and not a constant behind it.