Scegliere il formato immagine giusto: La guida decisionale definitiva

One of the most common questions in web development and digital design is: "Which image format should I use?" The answer depends on multiple factors including content type, quality requirements, browser support, and performance goals.

This guide provides a comprehensive decision framework to help you choose the optimal format for any situation.

The Format Landscape in 2025

We now have more image format options than ever:

• Classic formats: JPG, PNG, GIF
• Modern formats: WebP, AVIF
• Vector format: SVG
• Specialized formats: HEIC, JPEG XL, JPEG 2000

Each has specific strengths. Let's break down when to use each one.

Decision Tree: Start Here

Step 1: What Type of Content?

Vector graphics (logos, icons, simple illustrations)?

• → Use SVG (best choice)
• → Fallback: PNG for raster version

Photograph or complex raster image?

• → Continue to Step 2

Animation?

• → Modern: WebP or AVIF (animated)
• → Legacy: GIF (only if required for compatibility)
• → Complex: MP4 or WebM video

Step 2: Do You Need Transparency?

Yes, need transparency:

• → Modern: WebP with alpha
• → Universal: PNG-24
• → Cutting edge: AVIF with alpha

No transparency needed:

• → Continue to Step 3

Step 3: What Are Your Priorities?

Maximum quality, file size less critical:

• → PNG (lossless)
• → Or WebP lossless

Balance of quality and file size:

• → WebP at 80-85% quality
• → Fallback: JPG at 80-85% quality

Smallest possible file size:

• → AVIF (best compression)
• → Fallback: WebP
• → Universal fallback: JPG

Universal compatibility required:

• → JPG for photos
• → PNG for graphics

Format Deep Dive

SVG: Best for Vector Graphics

Use for:

• Company logos
• Icons and UI elements
• Simple illustrations
• Data visualizations
• Decorative elements

Advantages:

• Infinitely scalable with no quality loss
• Typically 1-10KB file sizes
• Can be animated and styled with CSS
• Accessible and SEO-friendly (text is searchable)
• Works perfectly on any screen resolution

When NOT to use:

• Photographs (use raster formats)
• Complex illustrations with many gradients
• When you need to hide source code

Implementation tip:

<!-- Inline SVG for styling -->
<svg width="24" height="24" viewBox="0 0 24 24">
  <path d="..." fill="currentColor"/>
</svg>

<!-- External SVG -->
<img src="logo.svg" alt="Company Logo">

JPG: Best for Photographs

Use for:

• Photographs and portraits
• Complex images with many colors
• Images with gradients
• When file size is more important than pixel-perfect quality

Advantages:

• Excellent compression for photos
• Adjustable quality/size tradeoff
• Universal browser and device support
• Small file sizes (can be 80% smaller than PNG for photos)

When NOT to use:

• Graphics with sharp edges or text
• Images requiring transparency
• Images that will be edited multiple times
• Screenshots with text

Quality recommendations:

• 90-100%: Professional photography, portfolio work
• 80-85%: General website photos, optimal balance
• 70-75%: Background images, thumbnails
• Below 70%: Only when absolutely necessary

PNG: Best for Graphics and Transparency

Use for:

• Logos and brand assets (when SVG isn't possible)
• UI elements and icons
• Screenshots
• Images requiring transparency
• Graphics with text or sharp lines

PNG-8 vs PNG-24:

• PNG-8: Up to 256 colors, smaller files, binary transparency
• PNG-24: Millions of colors, larger files, full alpha transparency

Advantages:

• Lossless compression (perfect quality)
• Full alpha channel transparency
• Universal support
• Perfect for text and sharp edges

When NOT to use:

• Photographs (use JPG or WebP instead - 3-5x smaller)
• When maximum compression is needed
• Complex images without transparency

WebP: Modern All-Purpose Format

Use for:

• Any image on modern websites
• E-commerce product photos
• Blog images
• Responsive images
• Mobile-first designs

Advantages:

• 25-35% smaller than JPG at same quality
• 26% smaller than PNG for same quality
• Supports both lossy and lossless compression
• Supports alpha transparency
• Supports animation
• Now supported in 95%+ of browsers

When NOT to use:

• When supporting Internet Explorer is required
• When you can't provide fallback images
• Email templates (limited support)

Implementation with fallback:

<picture>
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Description">
</picture>

AVIF: Next-Generation Compression

Use for:

• High-performance modern websites
• Hero images and LCP elements
• High-resolution images
• When maximum compression is critical

Advantages:

• Best compression available (50% smaller than JPG)
• 20-30% smaller than WebP
• Supports HDR and wide color gamut
• Supports transparency
• Growing browser support

When NOT to use:

• When encoding speed matters (AVIF is slow to encode)
• When maximum compatibility is needed
• For real-time image generation

Browser support (2025):

• Chrome, Firefox, Opera: Full support
• Safari: iOS 16+, macOS Ventura+
• Edge: Full support
• Always provide WebP and JPG fallbacks

Three-tier implementation:

<picture>
  <source srcset="image.avif" type="image/avif">
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Description">
</picture>

GIF: Legacy Animation Format

Use for:

• Simple animations when WebP/AVIF aren't supported
• When compatibility with very old systems is required

Advantages:

• Universal support
• Simple animation format
• Works everywhere

When NOT to use:

• Modern websites (use animated WebP instead - 10x smaller)
• High-quality images (limited to 256 colors)
• Anything requiring smooth edges (only binary transparency)

Better alternatives:

• Animated WebP (much smaller, better quality)
• MP4/WebM video (even better for longer animations)

Use Case Matrix

Performance Considerations

File Size Comparison (Same Quality)

For a typical 1200x800 photo:

• PNG-24: ~850KB (baseline)
• JPG 85%: ~180KB (79% savings)
• WebP 85%: ~120KB (86% savings)
• AVIF 85%: ~85KB (90% savings)

Encoding Speed

When generating images server-side:

• JPG: Very fast (baseline)
• PNG: Fast
• WebP: Moderate (2-3x slower than JPG)
• AVIF: Slow (10-20x slower than JPG)

Recommendation: Pre-generate AVIF for static images, use WebP for dynamic images.

Browser Support Strategy

The Progressive Enhancement Approach

1. Provide best format first (AVIF)
2. Fallback to widely supported (WebP)
3. Universal fallback (JPG/PNG)

<picture>
  <source srcset="hero.avif" type="image/avif">
  <source srcset="hero.webp" type="image/webp">
  <img src="hero.jpg" alt="Hero Image" width="1200" height="800">
</picture>

When to Skip Modern Formats

• Email newsletters: Stick with JPG/PNG
• Microsoft Office documents: Use JPG/PNG
• Print materials: Use TIFF or high-quality PNG
• When serving very old browsers: Check your analytics

Quick Reference Checklist

When choosing an image format, ask yourself:

1. □ Is this a vector graphic? → Use SVG
2. □ Do I need transparency? → Use PNG or WebP
3. □ Is this a photograph? → Use WebP or JPG
4. □ Is maximum compatibility required? → Use JPG or PNG
5. □ Is file size critical? → Use AVIF with WebP and JPG fallbacks
6. □ Is this for email? → Use JPG or PNG only
7. □ Will this be animated? → Use animated WebP or video

Tools for Format Conversion

• ConvToSomething: Free online converter supporting all major formats
• Squoosh: Google's advanced web app with side-by-side comparison
• ImageMagick: Command-line tool for batch conversion
• cwebp/cavif: Official encoders for WebP and AVIF
• Sharp (Node.js): Fast image processing library

Conclusion

There's no single "best" image format - the right choice depends on your content, audience, and requirements. For modern websites in 2025, the winning strategy is:

• SVG for logos and icons
• WebP (with AVIF for high-performance sites) for photos and graphics
• JPG/PNG as universal fallbacks
• Always optimize and compress

Use this guide's decision tree and matrix to choose confidently. Test your choices on real devices, measure the impact, and iterate. The format that delivers the best balance of quality, file size, and compatibility for your specific use case is the right format.