Measure the space the image occupies
Identify whether the image spans the page, sits in a card or appears as a small logo. Its displayed width changes with the layout and device pixel density. A single large source can make small screens download more detail than they need. Start with a few useful sizes based on actual placements rather than creating many arbitrary variants.
Connect sources to the layout
Use srcset to describe available image widths and sizes to describe the expected display width. Keep a sensible fallback source. Check the browser’s selected currentSrc at representative widths and pixel densities; the smallest file is not always the correct choice. An inaccurate sizes value can undermine an otherwise well-prepared set of responsive images.
Keep dimensions and loading priorities deliberate
Reserve space with appropriate dimensions or aspect-ratio rules to reduce layout movement. The main visible image may need eager loading and high priority, while images lower on the page can usually wait. Do not lazy-load every image indiscriminately. Confirm that decorative images have appropriate alternative-text treatment and informative images retain a meaningful description.
Compare bytes and appearance
Review compressed variants at their actual display size, including logos, fine text and gradients. Preserve the original asset so derivatives can be regenerated. Compare transferred bytes and the user experience before claiming a speed improvement. A smaller file is helpful only if the page still communicates the intended content clearly and loads it at the right time.
Your practical checklist
- Match variants to actual image placements
- Verify srcset, sizes and selected sources
- Set dimensions and loading priorities
- Review visual quality and transferred bytes
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