Pairette

Contrast matrix

A contrast matrix is a palette held against itself: every color paired with every other, measured, and checked against what the guidelines require. It answers the question a palette alone cannot — which of these colors may sit on which, and which pairing looks settled to the designer and falls apart for the reader.

The pairing has a direction: a row is the text color, a column the ground it sits on. The diagonal is a color on itself and is left out, because a color has no contrast to itself. Contrast is only ever compared within one medium — a color that carries a print rendition is measured through the printing condition, never against a screen value.

Every pair is measured by several procedures at once, and they disagree: they model different things and are defined for different media. Which of them take part is set in the display options beside the matrix, and with them which results are worth seeing.

The two selections combine differently, and on purpose. Within one procedure the results ticked are alternatives: AA and AA-L side by side keep every pair that reached either of them. Across procedures they add up — a pair stays only if every procedure that judged it landed on one of its ticked results, because a single lenient procedure would carry the whole matrix. A procedure that judged nothing never excludes a pair: nothing examined is not the same as failed.

WCAG 2

Screen. The ratio of the two luminances, from 1:1 to 21:1. It reads contrast off luminance alone and is deliberately symmetric: which of the two colors is the text makes no difference to it.

AAA
Body text, 7:1
AAA-L
Large text, 4.5:1
AA
Body text, 4.5:1
AA-L
Large text, 3:1
AA-G
Graphics and user interface components, 3:1

APCA

Screen. Lightness contrast, Lc 0 to about 106, and polarity sensitive: dark text on a light ground and light text on a dark ground are judged differently, because they really are read differently.

Lc 90
Body text, preferred, Lc 90
Lc 75
Body text, minimum, Lc 75
Lc 60
Other content text, Lc 60
Lc 45
Large bold text, Lc 45
Lc 30
Non-text, essential, Lc 30

Delta Phi Star

Screen. A perceptual difference in lightness, 0 to 101, derived from CIE L*. It says how far apart two colors are without saying what is far enough.

It publishes no thresholds, so it reaches no verdict: the value is shown and nothing is concluded from it.

DIN 32975

Print, Spot color. The Michelson formula on the luminance factor, K 0 to 1, for surfaces that reflect light rather than emit it. A second condition rides along: the lighter of the two colors has to reflect at least half of the incident light, or the pair fails however far apart the two are.

Text
Text, K 0.7
Surfaces
Surfaces and markings, K 0.4

Pairette helps you find colors that hold up next to each other — readable on screen, in print and as spot colors. Put together the palette you want to work on, and it says which pairs carry and which do not.

Display options
Procedures
Target

A goal you set, not a verdict a standard reaches. Minimum holds WCAG 2 to level AA, APCA to Lc 75 and DIN 32975 to K 0.7; Enhanced raises the first two to level AAA and Lc 90, and DIN 32975 publishes nothing above its own.

WCAG 2 results
APCA results
DIN 32975 results
Cell size / details
Cell color

The print preview converts the print colors back to the screen through the profile. On an uncalibrated monitor that is an indication, not a binding statement.

Printing condition

Applies to deriving print values. The luminance factor used for measuring contrast is always determined absolute colorimetric, independently of this.

Palette

Add a color

Print color (CMYK in %)
Spot color (measured L, a, b)

The screen color takes any notation CSS admits. Fields left empty are converted from the lead color; where that conversion strays too far from the original, the application says so. A spot color is measured, never calculated.

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