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Technique F13:Failure of Success Criterion 1.1.1 and 1.3.3 due to having a text alternative that provides information relying on color differences only

About this Technique

This technique relates to:

This failure applies to all technologies.

Failure techniques show examples of how content can fail particular WCAG success criteria. However, content may still satisfy those criteria if it includes equivalent/alternative content or functionality that does meet the normative requirements. See About WCAG Techniques.

Description

The objective of this technique is to describe the failure that occurs when the text alternative for an image relies on color differences only. This can cause problems for people who are blind or have low vision, because they will not be able to perceive the visual cues the alternative text refers to.

Note

Depending on its visual appearance, such an image might or might not fail Success Criterion 1.4.1 Use of Color. For example, bar charts, such as the one described in the following section, can provide information based on color alone (which represents a failure) or using a combination of color and pattern for their bars (which is a pass). Please remember that 1.4.1 Use of Color addresses the needs of sighted users, who are able to perceive images and don't usually rely on text alternatives.

Examples

  • A bar chart of sales data is provided as an image. The chart includes yearly sales figures for four employees in the Sales Department. The text alternative for the image says: "Bar chart showing the yearly sales figures for the Sales Department. Mary sold 3.1 Million; Fred, 2.6 Million; Bob, 2.2 Million; and Andrew, 3.4 Million. The red bars indicate sales that were below the yearly quota". Information about the employees not meeting the yearly quota is not provided anywhere else on the page. This alternative fails to provide all the relevant information, since blind users cannot perceive the bars of the chart, nor their color. The text alternative should indicate which people did not meet the sales quota rather than referencing the visual appearance of the image.

Tests

Procedure

For all images in the content that convey information by way of color differences:

  1. Check that the information provided in the text alternative relies solely on color differences.
  2. Check that the same information is not provided anywhere else on the page in a way that does not rely solely on color differences.

Expected Results

  • If check #1 and #2 are true, then this failure condition applies and content fails the Success Criterion.
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