Image Optimization for Core Web Vitals
Optimize images for Core Web Vitals improvement. Learn how LCP, CLS, and INP are affected by image delivery and how to improve all three.
How Images Affect Core Web Vitals
Google's Core Web Vitals measure real user experience through three key metrics. Images directly impact all three:
Largest Contentful Paint (LCP)
LCP measures loading performance. The LCP element is usually a hero image or banner. Large, unoptimized images directly increase LCP time.
Fix: Compress LCP images to under 100KB, use AVIF/WebP, add preload hints, serve via CDN.
Cumulative Layout Shift (CLS)
CLS measures visual stability. Images without width/height attributes cause layout shifts as they load, pushing content down.
Fix: Always declare width and height on img tags, use aspect-ratio CSS, reserve space for images before they load.
Interaction to Next Paint (INP)
INP measures interactivity. Large images block the main thread during decoding, delaying responses to user interactions.
Fix: Use smaller image files, modern formats with faster decoding (AVIF, WebP), lazy loading for offscreen content.
| Metric | Image Impact | Optimization |
|---|---|---|
| LCP | Hero image load time | Compress, AVIF/WebP, preload |
| CLS | Missing dimensions | Width/height, aspect-ratio |
| INP | Decode blocking | Smaller files, lazy load |