APCA (Accessible Perceptual Contrast Algorithm) is a new method for predicting contrast for use in emerging web standards (WCAG 3) for determining readability contrast. APCA is derived form the SAPC (S-LUV Advanced Predictive Color) which is an accessibility-oriented color appearance model designed for self-illuminated displays.
APCA™ is the Accessible Perceptual Contrast Algorithm, a new way to predict contrast for text and non-text for content on self-illuminated displays. This repository is for the documentation, for issue tracking, and for the discussion forum.
The correct code to use is apca-w3 which is in its own satellite repository, and is also available at npm i apca-w3
That is the only code that should be used for any development purposes.
The draft independent APCA Readability Criterion is up as a work in progress, still sections to be added and/or adjusted.
For comments or questions on the guidelines, use the ARC forum, that is where we discuss the draft standards & guidelines, and discuss legal & conformance issues.
For comments or questions on theory, math, or the APCA algorithm itself, use the SAPC-APCA forum here, please post all comments, questions, or discussions regarding theory, math, code, third-party tools,third-party tools, and so forth, here and not in the satellite repositories, so they can be tracked and resolved.
These are intended for end users, and those interested in a plain language overview without a lot of the math & theory.
Maths! Vision Science! Photons on Parade!
Curated link collection—an ideal starting point.
The main catalog of related articles, peer reviews, repositories, white papers, and more!
You are here 🔽 this index page is served at the github repo.
Over there is the APCA W3 version, and it's the same as the published npm package "apca-w3".
The BridgePCA is backwards compatible with WCAG 2, and it's the same as the published npm package "bridge-pca".
ColorParsley is a micro library for auto parsing color strings of all kinds, also on npm.
SeeStars is a micro library for creating CIE Lstar $(L*)
$, also on npm.
DeltaPhiStar is an ultra simple general purpose contrast equation.
The canonical demo tool at Myndex
Try out the Bridge PCA tool at Myndex
Color insensitive vision simulation (aka colorblind). Includes deuteranopia, protanopia, tritanopia, and blue cone monochromacy/achromatopsia.
IRT is a California nonprofit, dedicated to developing tecnologies to improve visual accessibility for all, and home to the APCA Readability Criterion.
The APCA base color-pair formula, in math notation. 0.0.98G-4g