Web Accessibility

Optimising Images

Meeting WCAG 2.0

A To claim Single A conformance, all of your pages and documents must meet all Single A requirements for all content

A A To claim Double A, all of your pages and documents must meet all Single A and all Double A requirements

A A A To claim Triple A, all of your pages and documents must meet all Single A, Double A and Triple A requirements

Images are the quickest way to add bulk to a web page or any other document (Powerpoint, PDF etc) and slow it down. If your web page is aimed at external (off campus) users, then it should load in no more than 8 seconds. Documents can take a little longer, but you must include the file size in the link text.

When you have optimised your images, follow the accessibility guidelines for

Optimise Images to Reduce Download Speed

  • Reduce images dimensions properly in an image editor: If you just change the width and height attribute to shrink it, the image will still take the same amount of time to download because it is still the same size in bytes
  • Crop extraneous information: Either change the size of the image 'canvas', or remove coloured areas
  • Save at a lower resolution or quality: How far you reduce the image will depend on what it is for, and what looks OK on the screen:
    - Reducing the quality of JPEG or JPG images will make the image blurry
    - Reducing the number of colours used in GIF files will make the image blotchy. GIF is a good format for images that have few colours, such as logos

Optimise Images With Software

Optimise Images Online