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Image Optimization

Comprehensive guide to optimizing images for performance and quality. Reduce page weight while maintaining visual fidelity.

Beginner30 minutes11 rulesImage delivery and quality

Use this checklist when

Use when image weight dominates page performance or when a team is cleaning up responsive media behavior.

Expected outcome

You reduce page weight and improve delivery quality without guessing where to start on media optimization.

Best for

Junior devLaunch workflow

Done looks like

Formats, compression, responsive sizing, critical image loading, and SVG handling are all reviewed together.

How this differs

This is a media-focused checklist that complements, rather than replaces, the broader performance checklists.

Images typically account for 50-70% of total page weight. Optimizing them is one of the highest-impact performance improvements you can make.

When To Use It

Use this checklist when media weight is a visible performance problem or when a team needs a structured image-delivery pass before tuning deeper rendering behavior.

Who It's For

  • Frontend developers improving page weight
  • Launch teams cleaning up obvious media bottlenecks
  • Reviewers working on responsive media quality

Done Looks Like

You should leave with a clearer image strategy for format choice, compression, responsive sizing, and critical-image loading instead of treating image optimization as one-off fixes.

Why This Matters

  • Page Speed - Smaller images mean faster load times
  • Core Web Vitals - Images directly affect LCP and CLS scores
  • Bandwidth Costs - Optimized images reduce server and CDN costs
  • User Experience - Fast-loading images improve engagement
  • Mobile Users - Critical for users on slower connections

Modern Image Formats

WebP

Widely supported format offering 25-35% smaller files than JPEG/PNG with equivalent quality.

AVIF

Next-generation format with even better compression (50%+ smaller than JPEG). Growing browser support.

When to Use Each

  • AVIF - Primary format for browsers that support it
  • WebP - Fallback for wider compatibility
  • JPEG/PNG - Legacy fallback

Optimization Strategy

Above the Fold

  • Preload critical hero images
  • Use appropriate dimensions (no larger than needed)
  • Consider inline base64 for tiny images

Below the Fold

  • Implement lazy loading with loading="lazy"
  • Use placeholder images or blur-up techniques
  • Load on intersection with viewport

Responsive Images

  • Use srcset for multiple resolutions
  • Use sizes to hint layout width
  • Serve 2x images for Retina displays

Tools for Optimization

  • Squoosh - Browser-based compression
  • Sharp - Node.js image processing
  • ImageOptim - Desktop app for batch optimization
  • Cloudinary/imgix - CDN with on-the-fly optimization
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