Proposal to introduce maximum contrast ratio

[cawa-93]

Success Criterion 1.4.6 Contrast (Enhanced)
(Level AAA)

The visual presentation of text and images of text has a contrast ratio of at least 7:1

However, this also means that the contrast ratio can be much higher. Here are common example: white text on black background.

This text fully meets all Contrast Criterion AAA level (Contrast Ratio for Me 21:1). However, it is absolutely not readable.

I propose to introduce the maximum along with the minimum contrast ratio.

[JAWS-test]

I think the text with high contrasts is very readable in itself. Of course, there are people who might have problems reading such a text. I think defining a maximum contrast is not a good idea. It would be better if adapting colors to user needs works well and WCAG supports such adaptability (e.g. via Custom Styles, Windows High Contrast Mode, etc.).

[mraccess77]

I personally would be negatively impacted by a contrast maximum. I understand other people need low contrast. I agree with JAWS Test that we need ways to allow the user to adjust contrast to meet individual needs. There are combinations such as the image with small white text on black background that would be difficult for most users to read and so I agree there are some specific bad combinations. I wonder if there is a better calculation other than current contrast that could be used. I believe Andrew Summers has been working on something to calculate situations like this.

[bruce-usab]

I agree that white text on a black background is a reasonably common barrier for accessibility. That said, I am not sure how to address this issue in the context of WCAG 2.x, even at AAA, because flagging plain black-on-white body text seems crazy to me.

Yes, WCAG3 is looked at better algorithms, see: www.myndex.com/APCA

[NathanInnes]

Take twitters branding revamp as a case note to note the importance for the necessity of a maximum contrast, it passes beyond the standard but a lot of their users found it very difficult to read and straining on the eyes.

[Myndex]

The text in the OP is unreadable as too small and too crowded in the example, not to mention it's all Loren Ipsum Gack Filler.

There is a maximum contrast that we are considering in WCAG 3 for certain instances of large and bold text, but in WCAG 3 we have a perceptually uniform contrast math called APCA. WCAG 2 does not. This topic is much more complicated than an arbitrary cap can rescue, and personalization is a large part of the user needs. My more complete objection and additional discussion is below. I've attempted to be succinct.

OBJECTION

The WCAG 2 contrast math is not even remotely capable of calculating a perceptually accurate value. And without that, you can't specify a maximum contrast without significant unintended consequences.

It's bad enough that the WCAG 2 math overstates the minimum contrast for dark colors and fails in other ways — if you were to try and use it to set a maximum, it will not achieve the desired result, and create even more unreadable pages than it does now.

To be clear: the contrast value calculated by the WCAG 2 math is essentially meaningless, as has been demonstrated, thoroughly examined, and reported by myself and others. What it does show is an unfortunate confirmation bias situation that we are working diligently to correct. But trying to use it for ANY further SCs is a terrible idea, especially something as supra threshold as a maximum contrast cap, where it will not only fail to provide a useful solution, it will continue the misunderstandings of how contrast and readability function.

BUT WAIT THERE'S MORE

Maximum contrast is usually NOT the actual problem, it is more often an excessively bright screen — A screen that a user has turned excessively bright because there is now so much LOW contrast out in the wild that users have to increase the brightness to read it, so when they encounter a site with good contrast, it blasts them out. Duck and cover!

Trying to set a maximum contrast using WCAG 2 contrast math is like trying to fix a broken leg by breaking the other leg.

Example of excess luminance:

In this example, assuming a typically adjusted monitor, we can see that it is excessive luminance of #fff that is the issue, not so much the contrast ratio.

TL;DR

Let's not please.

Thank you for reading,

Andy

Andrew Somers
W3 AGWG LVTF Silver Invited Expert
Senior Color Perception Scientist @
Myndex Perception Research

THE REVOLUTION WILL BE READABLE

[Myndex]

Maximum Contrast Status Update:

1. Light Mode¹

• There is no "maximum contrast" for light mode¹.
  • However there is definitely a maximum luminance (aka screen brightness).
  • The setting for peak luminance is a user control, and not the content author per se.
  • There are best practices the author can take to reduce visual fatigue.

2. Paper Emulation

• For reducing visual fatigue with light mode, design best practices for keeping the background under body text at 85% of the adaptation state, similar to diffuse paper.
  • "The Paper Reading Experience" is an example (under study).
  • A work in progress internal draft, paper-reading-experience.

3. Dark Mode²

• There is definitely a reasonable, maximum contrast for some dark mode² schemes.
  • For many users, excessively bright text on a dark background can result in halation, glare, and other issues.
  • Setting a guideline for maximum contrast requires a perceptually uniform contrast appearance model, WCAG 2.x contrast math/method cannot perform this function.
  • Under study: a lightness-contrast value of Lc -90 as a maximum for body text, and Lc -85 for larger text. These are interim experimental values using APCA 0.0.98G4g, under evaluation (see ambient considerations).

4. Ambient & Multi-Mode

• There is clearly space for at least two dark mode schemes, one for bright/day environments, and one for dark/night environments.
  • It is an open question regarding user display adjustment for peak luminance for a given dark mode scheme, vs author responsibilities here.
    • This question is influenced by the darkness of the screen background and the ambient illumination.
    • Further complicated by the range of device output capabilities, and automatic ambient adjustment.
• Other modes, such as daltonized schemes, schemes for photophobia, schemes for "Meares-Irlen syndrome", most likely will have alternate maximum values or guidelines.

Thank you for reading

¹ "Light mode" meaning dark text on a light background
² "Dark mode" meaning light text on a dark background