a11yTips

Provide meaningful text alternatives for images in PDF documents

Make sure informative images in PDF documents are assigned meaningful text alternatives

Regardless of the format in which information is presented, images that are part of a link, or simply convey information that is relevant to understanding the content have to be reliably interpreted by assistive technologies in order to be conveyed back to users. Images in PDF documents are called “figures”. Though the format and technology vary, the technique to make images accessible in PDF document is similar. While informative images in HTML can be turned into text thanks to meaningful alt attribute values assigned to Img elements, figures that are part of the PDF tag tree need to be given a meaningful alternate text.

To do so, simply assign a descriptive alternate text to figures by accessing the properties of the object in the tag tree, or by using the TouchUp Reading Order dialog box in Adobe Acrobat Pro. Make sure the description assigned to the figure is concise and meaningful, and efficiently describes the information the figure conveys or what its purpose or function is. While it would make sense to assign a descriptive value directly in the authoring source instead of the PDF, most conversion processes to PDF today still cannot preserve the information assigned to a figure, once the document is converted to PDF. As a result, planning on actually assigning the information in the PDF authoring tool after conversion remains the most reliable way to provide text alternatives to images in PDF documents.

User Story

As a visually impaired user using assistive technology, I want every informative image I encounter in a PDF document to be properly described, so that my tools can convey the information and I don’t miss out on any content.

Simple Code Example

Not Applicable

Testing Methodology

Using Adobe Acrobat Pro, access the TouchUp Reading Order dialog box to make all figures in the document editable. Then, right-clicking on a specific figure, select the “Edit Alternate Text” option and validate that the value assigned meaningfully describes the content of the figure or, in the case of controls, the function or purpose.

Specification Details