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- 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 minimum contrast requirement.
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.
- 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 defined as at least 18 point text or 14 point bold text.
Baseline Test ID: 8.1-ContrastMinimum
All visible text AND images of text (except those noted in Limitations, Assumptions, or Exceptions above)
- Determine the contrast ratio of foreground text and background.
- Check that the contrast ratio is at least 4.5:1. [SC 1.4.3]
- 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 (23.94 pixels)
- At least 14 point (18.62 pixels) AND bold (at least 700 font weight)
If both of the above checks fail, then Baseline Test 8.1-ContrastMinimum fails.
- There are a variety of color contrast tools that can perform the algorithms necessary to determine the contrast. See http://www.w3.org/TR/WCAG20-TECHS/G18.html for possible testing tools that use an appropriate algorithm.
- 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).
- The following sufficient techniques and/or common failures were considered when developing this test procedure for this baseline requirement:
- G18: Ensuring that a contrast ratio of at least 4.5:1 exists between text (and images of text) and background behind the text
- G145: Ensuring that a contrast ratio of at least 3:1 exists between text (and images of text) and background behind the text (when the text is at least 18 point if not bold and at least 14 point if bold).