Accessible Text on Images: Nail the Contrast Ratio

• rainbow

  1 1 3.2 JavaScript

  Rainbow — Accessibility Contrast Tool for Text on Images (by rodneylab)

The Rainbow tool was built using a static site generator. It's power lies in a Rust serverless function which does the maths. It works by finding the pixel (in the image) with the lowest contrast to the text colour. Then it uses a bit of High School Maths (the Newton-Raphson numerical technique) to work out the overlay transparency which satisfies the contrast ratio supplied (4.5 by default). There are a few optimisations built in such as resizing the image before getting going to speed up the later calculations. The code is open source and you can view the Rainbow Site code on the Rodney Lab Git Hub page. Now you know what the Rainbow tool is shall we look at how to use it?

• SurveyJS

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