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Section 508 ICT Testing Baseline

8. Contrast

Accessibility Requirements

  • WCAG SC 1.4.3 Contrast (minimum) – The visual presentation of text and images of text has a contrast ratio of at least 4.5:1, except for the following:
    • Large Text: Large-scale text and images of large-scale text have a contrast ratio of at least 3:1;
    • Incidental: Text or images of text that are part of an inactive user interface component, that are pure decoration, that are not visible to anyone, or that are part of a picture that contains significant other visual content, have no contrast requirement.
    • Logotypes: Text that is part of a logo or brand name has no contrast requirement.

Test Method Rationale

This test is conducted to evaluate equal access to information for all users, including those who may experience difficulty in discerning between items with low contrast.

Limitations, Assumptions, or Exceptions

  • Exception: The following types of text and images of text are not included in this test:
    • Logotypes: logo or brand name
    • Inactive (disabled) user interface components
    • Pure decoration purposes and not meaningful, having no functionality
    • Contained within a picture that contains significant other visual content
  • Testing of text contrast changes includes changes due to mouse hover and selection status.
  • Disabled input elements do not receive keyboard focus, cannot be selected, and cannot be modified. These are not required to meet contrast ratio requirements. Note: Read-only and disabled interface components are not the same. Disabled interface components can be considered inactive interface components; read-only interface components are active interface components and must meet contrast ratio requirements.
  • Large scale text is at least 18 point text or 14 point bold text.

8.A Test Procedure for Contrast (minimum)

Baseline Test ID: 8.A-ContrastMinimum

Identify Content

All visible text **AND** images of text (except those noted in Limitations, Assumptions, or Exceptions above)

Test Instructions

  1. Determine the contrast ratio of foreground text and background.
  2. Check that the contrast ratio is at least 4.5:1. [SC 1.4.3]
  3. If the contrast ratio is less than 4.5:1, check that the ratio is at least 3:1 AND the font meets one of the following criteria: [SC 1.4.3]
    • At least 18 point (24 pixels)
    • At least 14 point (18.5 pixels) AND bold (at least 700 font weight)

Test Results

If both of the above checks fail, then Baseline Test 8.A-ContrastMinimum fails.

Advisory: Tips for streamlined test processes

  • There are a variety of color contrast tools that can perform the algorithms necessary to determine the contrast. See Sufficient Technique G18 for possible testing tools that use an appropriate algorithm.
  • Use contrast tools that do not round values. A ratio of 4.499:1 would not meet the 4.5:1 threshold.
  • WCAG 2.2 Understanding 1.4.3: Contrast (Minimum) suggests using foreground and background colors obtained from the user agent, or the underlying markup and stylesheets for the contrast ratio computation, rather than the text as presented on screen.
  • While text contained in logos rendered as images is exempt from this requirement, the image must still provide alternative text (e.g., via an alt attribute).

WCAG 2.2 Techniques

The following sufficient techniques and/or common failures were considered when developing this test procedure for this baseline requirement:

Contact the ICT Baseline Working Group

Related Projects

The Baseline Alignment for Web is being developed to aid in determining if a test process aligns with the ICT Baseline for Web.