RE: Checking text on image colour contrast compliance (when a colour gradient is applied)

We mostly use a colour contrast analyser tool that has a colour picker, which allows us to pick the combinations of colours with the lowest received contrast ratio. It’s still rather subjective because it depends on how much of the text has a contrast ratio below the required level. If it’s only a few pixels, should it really be classed as non-conformant?

A tool that does all the work and gives you the answer isn’t going to be any more accurate – in fact it’s probably going to be less accurate. Such tools take different approaches. For instance, https://www.brandwood.com/a11y/ takes measurements at 8 fixed points on a rectangle, which may not be good choices.

SortSite once reported a contrast issue with text on a background gradient, but it turns out that they just calculate the lowest contrast that could occur if it was possible for the text to be placed anywhere on the gradient (the top right corner in my case because it was a diagonal gradient). There was a large amount of padding around the text, so the contrast ratio that SortSite reported could never occur. I tested it at every possible window width and zoom level just to be sure.

Steve Green
Managing Director
Test Partners Ltd


From: Louise Lister <Louise.Lister@iop.org>
Sent: 25 June 2021 11:56
To: w3c-wai-ig@w3.org
Subject: Checking text on image colour contrast compliance (when a colour gradient is applied)


Hello,

Please would anyone be able to recommend a good tool to check contrast on the brand story images that have a filter applied. We currently have a homepage image slot which applies a darker colour gradient over an image to allow the text on top of it to stand out.  The text can also be in different sizes.

I’ve tried WCAG contrast checker but that doesn’t seem to allow for the gradient and tried Chrome colour contrast analyser instead. I don’t think that gives me a definitive picture on whether I am compliant other than the contrast on some text has a better outline than other bits of text.

If there’s any other options people can suggest that would be amazing!

Kind regards
Louise





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