• Easy Intro to APCA? This is the simple, plain-language introduction to APCA that you've been looking for. This is an ideal place to start and is an easier version of WhyAPCA.

• linktr.ee/Myndex In an effort to pare down the mountain of material, this linktree is composed of the essential links, with the most basic at the top.

• Basic Tool & Quickstart Docs The basic APCA demonstration tool with live font examples and general design guidance for designers and developers.
• APCA Readability Criterion In depth guidelines for accomodating user needs regarding visual content, includes testing methods, conformance models, best practices, and more. Public Working Draft.

• Why APCA? This brief introduction into APCA describes how it solves the problems of WCAG_2 contrast. See Easy Intro to APCA? for the plain language version.
• APCA in a Nutshell Basic overview for using APCA, including simple use-case based conformance levels. This is a bare bones version, for the deeper dive see APCA Readability Criterion
• APCA FAQ APCA Frequenty Asked Questions (in development)
• Easy Intro to APCA? This is the simple plain-language introduction to APCA that you've been looking for. This is a simpler version of WhyAPCA above.

• APCA W3 Functions/API Using the API of the APCA W3 package.
• Links To Tools & Apps Some of the tools,apps, and design systems that have adopted APCA.
• Main Readme Doc (HTML version) Includes the math and walkthroughs, and additional resources.
• Documentation Index An index of APCA related documentation relating to code libraries.
• The Main List This page, i.e. you are HERE.

• APCA Forum Discuss, ask questions, fend off lions...
• Tangled Web Andrew's Tangled Web Tech Blog
• Social Medieval
  • Myndex on Twitter
  • Myndex on Mastodon
  • Andrew on LinkedIn
  • Inclusive Reading Technologies on Twitter
  • Inclusive Reading Technologies on Mastodon

Maths! Theory! Vision Science! Photons on Parade!

• The Realities And Myths Of Contrast And Color A plain language, in-depth primer to vision, color, and contrast for design, with an emphasis on typography and readability needs. Published in Smashing Magazine.
• The base APCA-W3 formula in LaTeX math for your viewing and calculating pleasure.
• Regarding Exponents Some notes and explaination regarding the powercurve exponents.
• Standard Observer Model Draft standardized environment.

• Repo List List of APCA and related respositories.
• Important Change Notices Current constants refer to 0.0.98G-4g
• List Your Tool Here! Have you created a tool using APCA or BridgePCA? Let us know!
  • Third Party Tools Letting us know gets your tool onto the official third party tool listing.
• APCA™ Integration Compliance Discusses levels of implementation.
• How to Contribute Contributions welcome — in particular we need to redesign the apcacontrast.com tool for responsiveness, set up rollup for builds, and a few other things. Help wanted!

• APCA Documentation Repository The docs repo and forum for APCA and SACAM
• APCA W3 Repository The W3 version code repo for web content
• Max Contrast A very simple, APCA compatible text color flipper. Flips from black to white text at middle contrast.
• Inclusive Reading Technologies The repo for IRC and the APCA Readability Criterion.
• Bridge PCA Repository Bridge PCA - the WCAG 2 compatible version
• DeltaPhiStar Repository A simplified general purpose contrast algorithm using L*
• Color Parsley Repository Fast and easy color string parsing — a NodeJS dependency for many of the SAPC libraries.
• SeeStars Repository A microlibrary for calculating L*
• Missing Intro Repository A correction and rebuttle to a flawed analysis
• FancyFontFlipping Repository At what point should text flip from black to white? This repo houses experiments and discussion of "font flipping". See also Max Contrast, above.
• Tiny Trim This is a CSS sheet of terse classes, useful for quick adjustments without having to add a style="" great for site development when you have a client watching and breathing down your back, LOL.

• APCA Use Cases, Conformance, Research, and Glossary Discussion of use cases for text and non-text elements, and references to the relevant research. Conformance considerations and rational basis for guidelines.
• Inline text links theory and practice Draft guidance regarding link identification.
• WCAG 2 vs APCA Comparisons Direct head to head comparisons.
• Discuss Maximum Contrast Here
• HDR Displays, Dark Mode Color Palettes, and APCA
• Glossary: Terminology Emerging From APCA Research
• Contrast Arising from Text Spatial Frequency

A separate page comprised of the following listing of reviews is also available at APCA Reviewed, which is updated more frequently.

There are several independent researchers evaluating APCA, and additional third party comparitive reviews that include demonstrations of the functional superiority to existing methods. The first few listed below are technical reviews by peers evaluating the APCA math and methods, including journal published peer reviewed papers. Some in comparison to WCAG 2 contrast methods and guidelines.

APCA has been developed in the open for open peer review and discussion, and the reviews listed below were performed independently, the majority were completed without consulting the APCA developers. Reviews listed first are peer or academically oriented, and deal with theory, while reviews listed later are targeted more toward practicioners, designers, and developers.

• Book-Published Peer Review: Applying APCA and Huetone for Color Accessibility of User Interfaces, by Kirill Ulitin, published by Springer 2023. Part of the Communications in Computer and Information Science book series (CCIS,volume 1833)
• Journal-Published Peer Review: Color in Interface (In Russian) Ulitin, K.V. (2021) in Culture and Technologies Studies. Vol. 6, № 4. P. 225-234. DOI: 10.17586/2587-800X-2021-6-4-225-234
• WCEU 2022 (video) Conference Presentation on Contrast: by Vicent Sanchis, PhD in optometry and an accessibility specialist. This in depth presentation on contrast was given at WCEU 2022, covering both WCAG 2 and APCA, with comparisons.
  • The general contrast presentation starts @ 1:06:20 - Click Here
  • Then @ 1:21:30 are comparisons
  • APCA is specifically reviewed @ 1:26:40
• Does the contrast ratio actually predict the legibility of website text? by Sam Waller PhD, a researcher within the Inclusive Design Group, University of Cambridge, UK & published at the Engineering Design Centre, University of Cambridge, UK. April 2022. Paper is a comparison of WCAG 2 math and APCA math, with interactive examples.
• Color Contrast Is Not As Black And White As It Seems by Roger Attrill, UX Specialist for Linguamatics, Dec. 2021. A technical analysis of some of the problems with WCAG 2 contrast math, and comparing and analyzing APCA math methods.
• It’s Time For A More Sophisticated Color Contrast Check by dataviz expert and author Lisa Charlotte Muth, Jan 2022. A review of APCA and comparison to WCAG 2 contrast, for the use case of dataviz.
• Don't rely on WCAG 2's contrast calculation, try APCA Comparative peer-review of APCA by Gu Wei of the Yunjiang Design and Research Factory in China. This is a Google translate link (Original is Mandarin), you may need to clear a dialog that pops up. Many comparisons and real-world examples.
• The Hubris of Contrast Ratio by DLyons, in Canvas LMS, Aug. 2022 — a further discussion of APCA, citing Dan Hollick's review, by Silicon Valley based research scientist/author Richard Lyons.
• Start optimising UI designs for readability instead of old-school WCAG 2 contrast by Andy Pillip, February 18, 2023. Discussion of APCA tools for designers, and practical considerations for integrating APCA into workflows.
• 3 Reasons Why the WCAG 2.1 Color Contrast Guidelines Don't Work by Shimanta Krishna Bhuyan, Nov. 2022. Well written, in-depth comparative analysis.
• Good color contrast: make sure you see everything well by Bart Pluijms, a quick comparative review. This is a Google translate link (Original is Dutch), you may need to clear a dialog that pops up. Includes a number of visual real-world examples.
• 9 Decisions were made when developing a unified Dark Mode by Simon Schmidt, UI Designer/author, Published in Idealo Tech Blog, March 2023. An in-depth discussion of a real-world development process for a design system, integrating APCA.
• APCA: the new algorithm for accessible colour contrast by Juan Ruitiña, May 2022. A brief comparative review comparing WCAG2 contrast to APCA.
• Stop using WCAG 2 for color contrast. by Simon Schmidt, UI Designer/author, Medium, Jan 2023.
• Improving accessibility with the new APCA A review of APCA by Nik Bailey, Lightflows, Jan. 2022
• Adv. Perceptual Contrast Algorithm Don Hollick's review and discussion of APCA vs WCAG 2. Typefully, Dec. 2021
• Accessible Palette: stop using HSL for color systems by Eugene Fedorenko, this is largely a discussion of his new color pallette tool, but APCA figures into that, and he discusses the integration into the tool vs WCAG 2 contrast.

The problems of 4.5:1 as a target for a guideline is that it not only impact those with impairments, but impacts standard vision as well. WCAG 2 contrast SCs affect 100% of sighted users. The inherent problems with the WCAG 2 contrast math have been known for some time and widely critisized. Including studies by others showing that color insensitive types are not well served.

The WCAG 2 contrast specs often cause enough problems for designers that it is ignored and today, some 86% of websites are failing WCAG_2 contrast per an automated survey—though some of these failures are not due to poor actual accessibility, but due to the perceptual inaccuracies of WCAG_2 contrast.

The unfortunate end result is a grave distrust of the WCAG 2.x accessibility standards overall, despite the many other important aspects of those standards.

• APCA Demonstrator The APCA contrast technology demonstrator—it's not as slick as a production tool, but presents the essential functions for design guidance.
• Bridge-PCA Calculator Bridge-PCA or BPCA is a drop-in replacement for WCAG_2 contrast that is backwards compatible with the existing guideline, but is using APCA technology for improved readability.

• Color Vision Deficiency Simulator This simulator demonstrates the way someone with a Color Vision Deficiency (incorrectly labeled "color blind") sees colors. This simulator uses the clinically accurate Brettel/Viénot model of CVD simulation for the primary (deuteranopia, protanopia, tritanopia) and there is an experimental blue cone monochromacy sim, based on the Brettel/Viénot concepts.

• The Realities And Myths Of Contrast And Color This popular article is an in-depth primer to vision, color, and contrast for design, written in the most plain language way possible. Features an emphasis on typography and readability needs. Published by Smashing Magazine.

• Better reading on the web Published by UX Collective (uxdesign.cc). This article discusses and demonstrates the problems with automated testing and WCAG 2 contrast math, methods, and guidelines.

• Published at Tangled Web (TangledWeb.xyz):

  • Small Text is Medium’s Large Fail The Medium platform has a lot of good features going for it, yet it literally ignores visual accessibility. For a platform that is entirely based around readable content, one would think that it’d be close to State of the Art, instead of the State of Unreadable.
  • Hats off to ALL CAPS Myth-busting the misunderstandings regarding accessibility: are dyslexia fonts useful and the shift in using ALL UPPERCASE LETTERS for various text elements.
  • Getting the Wrong, Right? What does it mean to get something right, if the underlying foundation of that thing is ultimately wrong?
  • Busy Background Breaks Bulletin Examples of how to destroy readability by choosing the wrong image as a background. And also, how to fix it.
  • Please Stop Using Grey Text Debunking one of the worst myths regarding design contrast. THis article went viral in early 2022.
  • What's Red & Black & Also Not Read? Do the WCAG 2 Contrast Guidelines help users with color vision issues? While this is a widely held belief, the truth may surprise you.
  • A Contrast of Errors A look into the history of the WCAG 2 contrast guidelines and some of the problems created by them, and a discussion of the proposed replacement, the APCA (Accessible Perceptual Contrast Algorithm).

• Contrasting Theories Article at Tangled Web
• A Contast of Contrasts Article at Tangled Web
• Luminance is King LinkedIn post on the iportance of luminance fore reading.
• Human Contrast Sensitivity Curve LinkedIn post on the nature of human contrast sensitivity.
• Legally Readable LinkedIn post on the value of actual accessibility vs arbitrary law.
• (Legacy) Basics of Luminance Contrast Written before APCA. A precursor to the Contrast FAQ.
• (Legacy) Creating Color Gradients, Part I Experiments and discussion of color spaces for gradient creation.
• (Legacy) Color Gradients, Part II More experiments and more color spaces.
• (Legacy) PDF on Accessible Fonts A PDF that discusses key factors in fonts for readability.

Mini articles on technical topics, with examples

• brintness is an integer brightness/lightness/darkness calculation. This is part of an experiment in estimating a perceived brightness while remaining in integer math and using bitshifts to maximize performance.

• Kelly's 22 Colors of Some Contrast (revised) An object of Kelly's 22 colors, as for "maximum contrast", I do not endorse that claim.

• Phi Alternate Expression a formula for phi, reduced to a positive exponent, multiplication, and addition...

• What's Up With Markdown GitHub Flavored Markdown Cheat Sheet.

• Three Part Series on WCAG 2 contrast problems with comparisons to perceptually uniform models.

  • Part I: Orange You Wondering About Contrast? Answering some contrast questions, and demonstrating a real solution to the infamous orange conundrum.
  • Part II: The Lighter Side of Dark Backgrounds An article comparing some parts of APCA with the old WCAG 2 contrast methods, demonstrating how WCAG_2 contrast does not help color vision types.
  • Part III: WCAG 2 vs APCA Contrast Shootout Answering some recent questions regarding APCA, with comparisons and examples of the old (WCAG 2 1.4.3) and the future WCAG 3 / APCA.

• COLORSPACES-The Primal Frontier A brief Look at the math that helps model how we see.

• How Many Colors in a Bushel? Just "how many" colors are there? Is that even an answerable question?

• Part I: For The Luv of Color An article comparing CIE Lab and Luv colorspaces.

• Part II: Will Work for Color A follow-up article on working spaces and related considerations, including how ICC profiles may not be a great choice for web due to their inefficiency. Introduces the concept of "Web Working Spacelets".

• colorPalette.js aka Kelly's 22 colors.

These were some of the larger, in-depth issue threads & posts created on GitHub including the infamous thread #695. These posts contain useful information and research. Some of the information here may be superseded as some of these threads date back to the beginnings of the contrast research project.

• Funny you mention Kodak and Xerox In this response to James Biber’s “Theranos, Polaroid and the legacy of dropouts”, I touch on the law of unintended consequences as has repeatedly manifested in the development of modern technology.
• The Laws of Technodynamics An Illustrated Restatement of Thermodynamics in the Context of Applied Problem Solving Through Technology.
• Climate Deniers Left & Right There are two kinds of climate deniers. Those that deny there is a problem, and those that deny the best way to fix it.
• The Unbearable Cruelty of a Finite Existence At first glance, the concept of soul appears rooted in spirituality and religion. In reality the concept of soul is a manifestation of our ego. This very brief yet nihilistic essay leads to a concept on how to create a sentient AI.
• Ending Polarized Politics Can a 200+ year old piece of math, and modern technology, fix this systemic problem in the US political system?
• Election Fraud & Other Illusions How conspiracy theory websites gave rise to a widely spread disinformation campaign apparently aimed at voter suppression. And it was (and continues) to be a shocking example of using math and statistics to lie, by "baffling" with bull.
• Modern Password Theory in a Nutshell Would it surprise you to know that fistsmash passwords aren't really more secure than one you can actually remember? You could say this is 0u+W!+h+h3_01d-InWithTheNew! — In other words, "Out With The Old - In With The New." It's a realistic discussion on password security, with a useful approach to reducing "crackability". HINT: we've all been doing it wrong, LOL. Article at TangledWeb.xyz
• Improving SEO with Redirects Your server's case sensitivity and URL redirect strategies can affect your search ranking!

• What's Up With Markdown GitHub flavored Markdown cheat sheet.
• Phi Alternate Expression An easier way to remember the formula for Phi. Fo fum.

Myndex is top 3% on Stack Overflow!

• Twitter: MyndexResearch New developments regarding APCA are usually posted here first.
• follow Myndex on Mastodon
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• Inclusive Reading Technologies on Mastodon

In this career, I was using Applied Probability Methodologies for the Risk Assessment of short term ROI predictions related to high-variance cash-flow opportunities in finite-sized non-cooperative bidding groups where information is obliquely concealed as a function of multivariate strategies facilitating the predominately range-based tactics driven by randomized but nevertheless deterministic outcomes.

(…Sooo… this is more commonly known as Texas Hold ’Em Poker…)

For the record, Myndex is pronounced:

mind - ex
\ ˈmīn-ˌdɛks \

When George Eastman invented the word "Kodak" one of his criteria was that "it won't be mispronounced". I guess I missed that day. Ooops.

Just how many patent attornys does it take to rotationally engage a helical conducting thread of an illumination apparatus further comprised of a sealed, evacuated glass envelope containing two or more conducting filament holders which electrically connect and physically support a coiled electrically conducting but resistive filament, preferentially fabricated from a tungsten alloy, to the aforementioned helical threads, which further engage into a helical conducting receptacle, such that when an electrical power source of sufficient voltage and current is applied to the receptacle input conducting connectors, the voltage and current is henceforth transferred to the helical conducting threads of the illumination apparatus and thereto across the conducting filament holders and through said filament such that it shall be caused to incandesce and emit visible irradiance according to the laws of blackbody radiators?

The Answer as to how many: a plurality

Here at the very bottom of the page, we dare to ask the question, "do two lights make a dark?"