Perception Research

We are currently researching perceptual contrast for assessing legibility and accessibility on graphically rich web pages and computer displays. Below are links to some of the early live experimental pages, evaluating the issue(s) in detail.

All About APCA

APCA Articles, Documentation, & Reviews

This page contains an organized listing of articles, documentation, third party and peer reviews, code repositories, white papers, and more about the Accessible Perceptual Contrast Algorithm. Comments welcome at the GitHub repo!

A Short List of Key APCA Documents

The Myndex APCA Linktree has a short list of the most important understanding documents about perceptual contrast. And if you are new to APCA, the entry level overview is "Why APCA"

APCA Discussion Area

Have a question? We have answers! Please come and join the discussions at the APCA Forum.


ΔγAPCA Algorithm
APCA Contrast Calculator

This is a basic plain-vanilla javascript tool for predicting perceptual contrast using the SAPC (SLuv Advanced Perceptual Contrast) math methods. The APCA version is designed to support emerging accessibility standards. For a deeper dive, please see this catalog of resources. Comments welcome at the GitHub repo!

CVD Simulator
Color Vision Deficiency Simulation

We developed this web app to simulate how someone with Color Vision Deficiency** sees the world. We accurately simulate Protanopia, Deuteranopia, and Tritanopia using the Brettel '99 &'97 models. We also present some experimental models, such as Blue Cone Monochromacy.

**Color Vision Deficiency is sometimes referred to as "color blind,"
though that is not accurate except in some very rare cases.

The Web Perception Experiment

COMING SOON: a public study that you can be involved in! Currently under development, it will evaluate how people perceive content in real world situations. Stay-tuned here as we prepare to launch that project. Presently delayed due to COVID-19.

☼ Perceptual Contrast
Live Demos & Experiments

x-Height DEMO:

The need for a CSS x-height property demonstrator page

Text Zoom DEMO:

The need for proportional (and not percentage) zoom capabilities demonstrator page

Font Color Flip DEMO:

This demo illustrates the issues with a single "flip point" for flip a text color from black or white. See the interactive demonstration page

Luminance Contrast TUTORIAL:

This covers the basics of luminance contrast. Written before the invention of APCA, it covers the classic maths and concepts. Understanding Luminance Contrast

Please be advised: The below are archives of some of the very early experiments conducted on this project, being left here for legacy purposes. For the current state and more recent data, please see the SAPC-APCA GitHub Catalog of Resources.


Most Recent Experiments First

OF INTEREST   • CE17 SAPC-7 Polarity & Uniformity Test NEW! Dec 15 2019 (Polarity & Uniformity Testing — Updated Dec 15, 2019 These are tests of the effects of normal and reverse polarity on contrast measurements. This is part of an assessment of the Luminance Contrast Module. NEW: SAPC revised! Now SAPC 7, with improved Perceptually Uniform Symmetrical Polarity!

SAPC-6 Experiments — Useful Examples

These SAPC-6 studies are close to the v7 trials. Also, the CE14 size, weight, antialias studies are useful demonstrations regarding spatial frequency.

   • CE16 SAPC-6 Contrast Grid Nov 1 2019 (Dark text on Light BG) Perceptually Uniform grid of contrast patches, demonstrating SAPC-6 and also the cut offs for various font sizes and weights. This is part of an assessment of the Luminance Contrast Module. (Please note this page is NOT responsive, as it is intended for display on our research devices and uses REM to lock in certain sizes. As a result it may not work on your mobile device.) UPDATE: The CE16 studies led to minor improvements and the new method, SAPC-7, see links above.
   • Exp. CE16 — SAPC-6 Eval. Oct 27 2019 (Dark text on Light BG) Further perceptual uniformity Experiment. SAPC-6 is the latest advance in perceptually uniform contrast assessment. This is part of an assessment of the Luminance Contrast Module. This links to the short version with some discussion. Links to the complete study series are on that page. UPDATE: The CE16 studies led to minor improvements and the new method, SAPC-7, see links above.
   • Experiment CE14antialias (Oct 14,2019) Similar to "weight" below, only here the webkit antialiasing is turned ON, and you'll see the dramatic reduction in contrast for the thinner fonts, especially weight 100. In particular, look at Test Panel Four's first two series, and how the last two smaller weight 100 fonts practically disappear.
   • Experiment CE14weight (revised Oct 14,2019) How the stroke width (font weight) affects perceptual uniformity Experiment — font weights were grouped and resized for equivalent stroke widths. IMPORTANT DISCOVERY: The examples on this page demonstrate that when near threshold, stroke width is the primary "size" factor affecting CSF and contrast perception.
   • Experiment CE14size How Stimulus Size affects perceptual uniformity Experiment, also contains parts of CE14 for reference. The examples in this page demonstrate that stimulus size is a CRITICAL FACTOR in perceptual contrast, especially for impaired vision that is forced to function close to threshold.

Older Experiments:

These earlier experiments are set to offline to keep them from being crawled by bots in the interest of preventing confusion. Links availble on request.

   • (link off/available on request) Experiment CE15 — SAPC5 (INV) Evaluation (Light on Dark) Further perceptual uniformity Experiment. See CE14, this is the light text/dark BG version.
   • (link off/available on request) Experiment CE14 — SAPC5 Evaluation (Dark on Light) Further perceptual uniformity Experiment. CE14 and CE15 examine a new formula/algorithm for a perceptually uniform contrast assessment (SAPC-5). OF NOTE: This equation is showing overall promise in real-world ambient light, especially on mobile devices in daylight.
   • (link off/available on request) Experiment CE12 — SAPC3 Evaluation (Light on Dark v02) Perceptual uniformity Experiment. The sRGB values were adjusted for uniformity. Useful to note how polarity inversion affects perceptual contrast in terms of uniformity.
   • (link off/available on request) Experiment CE11 — SAPC3 Evaluation (Light on Dark). A straight inversion of the values used in CE11, see that when inverted the assessment does not indicate perceptual uniformity from bright to dark. See experiment CE12.
   • (link off/available on request) Experiment CE10 — SAPC3 Evaluation (Dark on Light). Sample DIVs with sRGB values that are approximately perceptually uniform with in each target range.
   • (link off/available on request) Experiment CE09 — Comparing several different contrast assessment equations.
   • (link off/available on request) Some initial equation evaluations and considerations. Early experiments solving the perceptual uniformity problem.
   • (link off/available on request) Experiments CEX and CEXI — A layout of the basic experiments but using the current WCAG math for a standard of comparison .
   • (link off/available on request) Initial Page describing the immediately apparent issues with the current standard & methods. Discussion of the genesis of this project, the discovery of the issues with the WCAG contrast standard math. NOTE: This page contains some of the initial reactions, but as with most research projects, many of the preliminary conclusions are superseded by more recent experimental results. Listed here for historical purposes only.