Compress Images for Web Performance | Core Web Vitals & Page Speed

Key takeaways

Image compression is critical for Core Web Vitals and overall page performance

Proper compression can reduce image file sizes by 70-90% without visible quality loss

WebP format offers superior compression compared to JPG and PNG

LCP (Largest Contentful Paint) is most affected by image optimization

CLS (Cumulative Layout Shift) improves with properly sized images

• Compress images before uploading to reduce initial load time
• Use WebP format for 30% better compression than JPG
• Implement responsive images with srcset for different screen sizes
• Set explicit image dimensions to prevent layout shifts
• Use lazy loading for below-the-fold images

Understanding Core Web Vitals and images

Core Web Vitals are Google's metrics for measuring user experience, and images play a crucial role in two of the three main metrics: LCP and CLS. Proper image compression directly impacts these scores.

• LCP: Largest Contentful Paint - measures loading performance
• CLS: Cumulative Layout Shift - measures visual stability
• Images are often the largest elements affecting LCP
• Unsized images cause layout shifts affecting CLS
• Google uses these metrics for search rankings

Best image formats for web performance

Choosing the right image format is essential for web performance. Modern formats offer better compression while maintaining quality.

• WebP: Best compression, supports transparency and animation
• AVIF: Next-generation format with even better compression
• JPG: Good for photographs, widely supported
• PNG: Best for graphics and transparency support
• SVG: Perfect for icons and simple graphics

Compression techniques for different image types

Different types of images require different compression approaches for optimal results.

• Photographs: Use JPG at 80-85% quality for best balance
• Graphics: Use PNG for text and flat colors
• Logos: Use SVG or PNG with transparency
• Screenshots: Use PNG for text clarity
• Backgrounds: Use WebP for maximum compression

Advanced web image optimization

Beyond basic compression, several advanced techniques can further improve web performance.

• Implement responsive images with srcset and sizes attributes
• Use modern image formats with fallbacks for older browsers
• Serve different image sizes based on device capabilities
• Implement CDN delivery for faster image loading
• Use image compression tools as part of build process