Image Formats Explained
Choosing the right image format affects both quality and performance. Each format makes different tradeoffs between file size, quality, features, and browser support. Understanding these tradeoffs helps you optimize images for the web.
Compression Types
Image compression falls into two categories:
Lossy compression discards information to reduce file size. You can't recover the original — some detail is permanently lost. The benefit is dramatically smaller files. JPEG uses lossy compression.
Lossless compression reduces file size without losing any information. The original can be perfectly reconstructed. Files are larger than lossy but maintain full quality. PNG uses lossless compression.
Format Comparison
| Format | Type | Best For | Compression |
|---|---|---|---|
| JPEG | Raster | Photos | Lossy |
| PNG | Raster | Graphics, transparency | Lossless |
| GIF | Raster | Simple animations | Lossless, 256 colors |
| WebP | Raster | Modern web | Both |
| AVIF | Raster | Next-gen web | Both |
| SVG | Vector | Icons, logos | N/A (text-based) |
JPEG excels at photographs where small quality losses are imperceptible. Compression levels let you balance quality against size.
PNG preserves every pixel perfectly and supports transparency. Use it for screenshots, graphics with text, or images needing transparent backgrounds.
GIF supports animation but limits colors to 256. Fine for simple animated graphics, but video formats work better for complex animation.
WebP offers both lossy and lossless modes with better compression than JPEG and PNG. Most modern browsers support it.
AVIF provides even better compression than WebP but has less browser support. It's the future, but you'll need fallbacks today.
Practical Guidelines
Photo → JPEG or WebP
Logo → SVG
Screenshot → PNG or WebP
Icon → SVG
Simple animation → GIF
Complex animation → Video format
Modern web → WebP with JPEG fallback
Optimization Practices
Resize to display size. Don't serve a 4000px image that displays at 400px. The browser downloads unnecessary data.
Compress appropriately. JPEG quality of 80-85% usually looks identical to 100% at a fraction of the size.
Use modern formats. WebP typically saves 25-35% over JPEG at equivalent quality. Serve WebP to supporting browsers with JPEG fallback.
Lazy load below-fold images. Images users haven't scrolled to yet don't need to load immediately.