Write alt text that preserves a research figure's message
Describe a research figure’s essential information, separate short alt text from longer detail and check descriptions against the final figure version.
About 5 min read · Allow extra time for the practical checks
Describe what a reader needs to understand from the figure, rather than listing its colours or copying its filename. For a complex chart, prepare a short identification and an accessible longer description or data table that carries the essential information. Check how your journal or document format expects you to supply these parts.
Alt text has a different job from a visible caption. AIP Publishing’s accessibility guidance distinguishes a concise description of the visual from caption material that develops the article’s interpretation. Keep the caption’s labels, scope and notes accurate too; one piece of text does not automatically do every job.
Decide what the figure contributes
Write a working sentence about the information the reader needs from this display. A chart may compare categories; a process diagram may explain a sequence and a decision branch. Identify that purpose before choosing details for the description.
W3C’s image decision tree bases the alternative on the image’s role in context. It distinguishes meaningful images, functional images and decoration, and directs authors of complex graphics to make their information available elsewhere on the page. Do not label an evidence-bearing chart decorative simply because the surrounding paragraph mentions its subject.
This is also a useful point to ask whether you have chosen a chart that answers the intended question. Describing an unsuitable display more carefully does not repair the display itself.
Separate a short identification from the detail
W3C’s complex-image guidance describes a two-part text alternative: a short description identifies the image, while a longer one conveys essential information. Depending on the image, that information can include values, scale, relationships or sequence. The guidance offers ways to make longer descriptions available in the surrounding content.
Use the short part to orient the reader. Put substantial detail where it can be read and navigated properly, following the publication’s implementation. If the short description points to a table or heading, make sure the named destination actually exists in the submitted version.
There is no reason to invent a universal character limit for every journal and format. Follow the applicable instructions, and avoid squeezing a full complex figure into one dense sentence merely to meet a limit you assumed.
Work through an original fictional example
Imagine a proposed horizontal bar chart of requests logged at a fictional help desk during one invented week. The categories and counts below are entirely synthetic. They illustrate description choices, not research findings or actual service activity.
| Request category | Number of requests |
|---|---|
| Account access | 18 |
| Room booking | 12 |
| Equipment loan | 6 |
Suppose the horizontal axis is labelled Number of requests, runs from 0 to 20, and the bars follow the table’s order. A weak short description would be: “Three green bars.” That describes appearance while omitting what the bars represent.
A more useful proposed short description is: “Horizontal bar chart comparing three help-desk request categories during one fictional week; values are listed in the table below.” This wording is suitable only if the accessible table really follows the figure.
A proposed longer description is: “The chart uses a count scale from 0 to 20 requests. Account access has 18 requests, room booking 12, and equipment loan 6. Account access has the largest count and equipment loan the smallest. The accompanying table gives the three values.”
These are draft descriptions for the stipulated design. If you reorder the bars or remove the table, revise them. Do not describe a planned version while submitting a different figure.
Avoid adding “Account problems caused most delays.” Neither the hypothetical counts nor their ordering establish a cause or say anything about delay duration. The description should preserve the information shown without importing a new conclusion.
Keep the description attached to the right version
Use a working record containing the figure number, image filename, caption, proposed alt text and location of any longer description. When someone replaces an image, check the corresponding record rather than assuming that an unchanged figure number means unchanged content.
For a multi-panel figure, check that each panel’s contribution remains understandable. A description that mentions two panels will not fit a revised three-panel figure. Resolve unfamiliar symbols with the author who knows the figure; do not guess from how a mark looks.
AIP notes that some workflows can generate preliminary alt text but that authors remain responsible for reviewing its accuracy. Compare any suggested wording with the actual image and its context. In the fictional chart, a suggestion that calls the categories months would need correction even if its counts were right.
Review the complete reading path
Read the caption, short alternative, longer description and nearby paragraph together. Check that they agree on figure identity, units, scope and values. Remove needless repetition while preserving the information readers need to follow the argument.
Confirm that the required text was supplied in the journal’s designated fields or files and survived export where you control it. If you cannot inspect how the production system associates the description with the figure, ask the production contact about that association. Writing good text and delivering it through the required channel are separate checks.
