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How to Optimize Images for Better Performance and Core Web Vitals?

Updated on 12. 6. 2025

Image Optimization Overview

Image optimization is crucial for website performance, user experience, and Core Web Vitals scores. ZiziCache provides comprehensive image optimization features including lazy loading, responsive images, automatic LCP detection, priority hints, and intelligent preloading strategies.

Image Lazy Loading

Enable Image Lazy Loading

Activate intelligent image lazy loading:

  1. Navigate to ZiziCache � Optimization
  2. Find the Image Optimization section
  3. Check “Lazy Load Images”
  4. Configure exclusion settings as needed

Lazy Loading Benefits

  • Faster initial page load: Only above-the-fold images load immediately
  • Reduced bandwidth usage: Images load only when needed
  • Better mobile performance: Especially important for mobile users
  • Improved Core Web Vitals: Better LCP and FID scores
  • Server resource savings: Reduced server load and bandwidth

Lazy Loading Configuration

Exclude Count

Configure how many images to exclude from lazy loading:

  • Default: 2 images (recommended for most sites)
  • Blog sites: 1-2 images (featured image and hero)
  • E-commerce: 3-4 images (product grid considerations)
  • Image-heavy sites: 2-3 images (balance performance and UX)

Lazy Loading Exclusions

Specify images that should never be lazy loaded:

hero-image
banner
logo
above-fold
critical-image
product-main

Use CSS classes, image names, or URL patterns to exclude specific images.

Responsive Images

Enable Responsive Images

Activate automatic responsive image generation:

  1. In Image Optimization section
  2. Check “Responsive Images”
  3. ZiziCache will automatically generate and serve appropriate image sizes

Responsive Images Benefits

  • Device optimization: Serves appropriate sizes for different screens
  • Bandwidth savings: Mobile users get smaller images
  • Better performance: Faster loading on all devices
  • Automatic generation: No manual intervention required
  • Retina support: High-density display optimization

Responsive Image Implementation

ZiziCache automatically:

  • Generates multiple image sizes
  • Adds srcset and sizes attributes
  • Implements picture element when beneficial
  • Optimizes for different pixel densities
  • Maintains aspect ratios across sizes

Missing Width and Height Attributes

Add Width/Height Attributes

Prevent layout shifts by adding missing dimensions:

  1. In Image Optimization section
  2. Check “Add Missing Width/Height”
  3. ZiziCache will analyze and add missing image dimensions

Layout Stability Benefits

  • Prevents CLS: Eliminates Cumulative Layout Shift issues
  • Better UX: Stable layout during image loading
  • SEO improvement: Better Core Web Vitals scores
  • Accessibility: Better experience for screen readers

Dimension Detection Process

ZiziCache automatically:

  1. Scans HTML for images missing dimensions
  2. Analyzes image files to determine actual dimensions
  3. Adds width and height attributes to HTML
  4. Preserves existing dimensions when present
  5. Handles both local and external images

Priority Hints and Performance

Enable Priority Hints

Implement fetchpriority and importance attributes:

  1. In Image Optimization section
  2. Check “Priority Hints”
  3. Automatically optimizes image loading priorities

Priority Hints Implementation

ZiziCache automatically adds:

  • fetchpriority=”high”: For critical above-the-fold images
  • fetchpriority=”low”: For below-the-fold or decorative images
  • importance=”high”: For LCP candidate images
  • loading=”eager”: For critical images that must load immediately
  • loading=”lazy”: For non-critical images

Intelligent Priority Assignment

Priority hints are assigned based on:

  • Image position in viewport
  • Image size and potential LCP impact
  • Semantic importance (hero images, logos)
  • User interaction patterns

Automatic LCP Detection

Enable LCP Detection

Activate automatic Largest Contentful Paint optimization:

  1. In Image Optimization section
  2. Check “Automatic LCP Detection”
  3. Optionally enable public debug mode for testing

LCP Detection Features

  • Real-time analysis: Uses Layout Instability API
  • Automatic optimization: Optimizes detected LCP elements
  • Priority assignment: Assigns high priority to LCP images
  • Preload generation: Automatically preloads LCP images
  • Performance monitoring: Tracks LCP improvements

LCP Optimization Process

  1. JavaScript monitors page loading
  2. Identifies potential LCP elements
  3. Records LCP candidates for optimization
  4. Applies priority hints and preloading
  5. Monitors performance improvements

Image Preloading

Enable Image Preloading

Activate intelligent image preloading:

  1. In Image Optimization section
  2. Check “Image Preloading”
  3. Configure for above-the-fold and critical images

Preloading Strategy

ZiziCache preloads images based on:

  • Above-the-fold position: Images visible on initial load
  • LCP candidates: Images likely to be Largest Contentful Paint
  • Hero images: Primary visual elements
  • Critical content: Essential visual components

Preload Implementation

Automatic preload link generation:

<link rel="preload" as="image" href="/path/to/critical-image.jpg" fetchpriority="high">

Gravatar Optimization

Localhost Gravatar Serving

Optimize Gravatar loading for better performance:

  1. In Image Optimization section
  2. Check “Localhost Gravatar”
  3. Gravatars will be cached and served locally

Gravatar Benefits

  • Faster loading: Local serving eliminates external requests
  • Better privacy: Reduces external connections
  • Improved reliability: No dependency on Gravatar servers
  • Enhanced caching: Better cache control

Advanced Image Optimization

Above-the-Fold Analysis

Configure viewport analysis for image optimization:

  • Viewport height: Default 1200px for above-the-fold detection
  • Device consideration: Accounts for different screen sizes
  • Responsive analysis: Adapts to mobile and desktop viewports
  • Dynamic assessment: Updates based on content changes

Image Format Optimization

ZiziCache optimizes image delivery through:

  • Format selection: Serves best format for each browser
  • Quality optimization: Balances file size and visual quality
  • Progressive loading: Implements progressive JPEG where beneficial
  • Next-gen formats: Supports WebP and AVIF when available

Background Image Optimization

Special handling for CSS background images:

  • Lazy loading for background images
  • Priority hints for critical backgrounds
  • Responsive background image sets
  • Preloading for hero background images

Image Performance Monitoring

Performance Metrics

Monitor image optimization effectiveness:

  • Loading times: Track image download speeds
  • LCP improvements: Monitor Largest Contentful Paint scores
  • CLS reduction: Track layout stability improvements
  • Bandwidth savings: Measure data transfer reduction

Debug Image Issues

Troubleshoot image optimization problems:

  1. Browser DevTools: Check Network tab for image loading
  2. Performance panel: Analyze image loading timeline
  3. LCP monitoring: Identify LCP elements and timing
  4. CLS tracking: Monitor layout shifts during image loading

Image Optimization Troubleshooting

Common Issues and Solutions

Images Not Lazy Loading

  • Check exclusions: Verify exclusion settings and counts
  • JavaScript conflicts: Test for theme or plugin conflicts
  • Browser support: Ensure IntersectionObserver support
  • Viewport detection: Verify above-the-fold detection accuracy

Layout Shift Issues

  • Missing dimensions: Ensure width/height attributes are added
  • Aspect ratio preservation: Verify aspect ratios are maintained
  • CSS conflicts: Check for conflicting CSS rules
  • Image loading timing: Optimize image loading sequence

Poor LCP Performance

  • LCP element identification: Verify correct LCP detection
  • Preload optimization: Ensure LCP images are preloaded
  • Priority hints: Check fetchpriority implementation
  • Image optimization: Optimize LCP image file sizes

Testing and Validation

Validate image optimizations using:

  • Google PageSpeed Insights: Core Web Vitals analysis
  • WebPageTest: Detailed loading analysis
  • Lighthouse: Performance and optimization recommendations
  • Browser DevTools: Real-time performance monitoring

Best Practices for Image Optimization

Implementation Strategy

  1. Start with lazy loading: Immediate performance benefits
  2. Add dimensions: Prevent layout shifts
  3. Enable responsive images: Optimize for all devices
  4. Implement priority hints: Optimize loading priorities
  5. Monitor LCP: Track and optimize Largest Contentful Paint

Content Guidelines

  • Optimize source images: Use appropriate file sizes and formats
  • Consider aspect ratios: Maintain consistent image proportions
  • Alt text optimization: Provide meaningful alt attributes
  • Semantic markup: Use appropriate image markup

Performance Guidelines

  • Above-the-fold priority: Optimize visible images first
  • Mobile-first approach: Prioritize mobile image performance
  • Progressive enhancement: Ensure basic functionality without JavaScript
  • Regular monitoring: Continuously track performance metrics

E-commerce Image Optimization

Product Image Strategy

  • Main product images: Exclude from lazy loading or use low exclude count
  • Gallery images: Implement lazy loading for secondary images
  • Thumbnail grids: Use appropriate lazy loading settings
  • Zoom functionality: Ensure compatibility with image zoom plugins

Category Page Optimization

  • Balance lazy loading with user experience
  • Consider infinite scroll compatibility
  • Optimize for mobile shopping experience
  • Test with various product grid layouts

Image Optimization Impact

Performance Improvements

Image optimization typically provides:

  • Page load speed: 30-50% improvement in loading times
  • LCP scores: Significant Largest Contentful Paint improvements
  • CLS reduction: Eliminated layout shifts
  • Bandwidth savings: 40-60% reduction in data transfer
  • Mobile performance: Dramatic improvements on slower connections

User Experience Benefits

  • Faster perceived page loading
  • Stable layout during loading
  • Better mobile browsing experience
  • Improved accessibility
  • Enhanced visual experience

SEO and Business Impact

  • Better Core Web Vitals scores
  • Improved search engine rankings
  • Higher user engagement
  • Reduced bounce rates
  • Better conversion rates

Image optimization is one of the most impactful performance improvements you can implement. ZiziCache’s comprehensive image optimization features provide automatic, intelligent optimization that improves both technical performance metrics and user experience across all devices and connection speeds.

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