What is Image optimisation?
Also called: Image optimization, Image compression
The short answer
Image optimisation is serving images at the right size, format and quality for each device, so pages load fast without visibly losing quality.
Image optimisation, explained
It means responsive sizes (srcset), modern formats (WebP, AVIF), compression, lazy loading below the fold and explicit dimensions to prevent layout shift.
Images are usually the heaviest part of a page, so this is often the single biggest speed win.
Questions people ask about Image optimisation
What is Image optimisation?
Image optimisation is serving images at the right size, format and quality for each device, so pages load fast without visibly losing quality.
What size should images be on a website?
No bigger than they display: generate several widths and let the browser choose the right one for each screen.
Related terms
WebP and AVIF are modern image formats that compress photos and graphics much smaller than JPEG and PNG at similar visual quality, supported by current browsers.
Lazy loadingLazy loading delays downloading images, video, scripts or components until they are about to be needed, usually when they scroll into view.
Largest Contentful PaintLargest Contentful Paint measures how long it takes for the largest visible element, usually the hero image or headline, to appear; good is 2.5 seconds or less.
Cumulative Layout ShiftCumulative Layout Shift measures how much page content moves unexpectedly while loading; good is below 0.1.
Part of the Web Encyclopedia by Apex Flow Digital. Definitions are general knowledge, kept current, with no invented statistics.