Image Formats Explained: JPEG, PNG, WebP, AVIF & GIF

Introduction

Picking the right image format is essential for fast, beautiful websites. Each format has its own way of compressing images, its own strengths, and its own quirks. Choose poorly, and you might end up with slow load times, blurry pictures, or missing features like transparency.

In this guide, we’ll walk through the five formats you’ll see most often on the web: JPEG, PNG, WebP, AVIF, and GIF. You’ll see what makes each one tick, where it shines, and when it’s the right tool for the job.

JPEG: The Classic Photo Format

JPEG is everywhere. Since 1992, it’s been the standard for web photos and images with lots of color and detail. If you’ve ever uploaded a picture online, chances are it was a JPEG.

How JPEG Works

JPEG uses lossy compression to shrink file sizes, which means it throws away some data for good. It chops images into 8×8 pixel blocks and uses math (the Discrete Cosine Transform) to toss details our eyes won’t miss.

Strengths of JPEG

• Great for photos: JPEG can shrink photo files by 10–20x and still look good.
• Works everywhere: Every browser and device supports JPEG, no questions asked.
• Quality control: You can dial in the compression level to balance size and appearance.
• Progressive loading: Progressive JPEGs show a blurry preview first, then sharpen as the image loads.

Weaknesses of JPEG

• No transparency: JPEG can’t do transparent backgrounds, so it’s a no-go for logos or overlays.
• Compression artifacts: Crank up the compression and you’ll spot blocky “artifacts,” especially around edges.
• Not for sharp graphics: Text and crisp lines get blurry or messy in JPEG.
• Quality loss on every save: Each time you re-save a JPEG, you lose a little more quality.

When to Use JPEG

Pro Tip: Let the content decide the format—photos and graphics have different needs.

JPEG is perfect for photos, images with lots of colors or gradients, and anything where a bit of quality loss is worth the smaller size. Reach for JPEG with hero images, product shots, user uploads, or backgrounds.

PNG: Sharp Graphics and Transparency

PNG arrived in 1996 as a free alternative to GIF, and quickly took over as the go-to for graphics that need transparency or perfect quality.

How PNG Works

PNG uses lossless compression, so your image comes out exactly the same as it went in—no data lost. It relies on the DEFLATE algorithm (the same as ZIP files), plus some clever filtering to boost compression.

PNG-8 vs PNG-24

There are two main flavors of PNG. PNG-8 handles up to 256 colors (like GIF) and offers on/off transparency. PNG-24 supports millions of colors and smooth, gradient transparency thanks to its alpha channel.

Strengths of PNG

• Lossless compression: Keeps your image pixel-perfect—no artifacts, ever.
• Alpha transparency: Supports smooth, variable transparency for beautiful overlays.
• Great for graphics: Delivers razor-sharp edges, ideal for logos, icons, and illustrations.
• Universal support: PNG works in every browser and on every device.

Weaknesses of PNG

• Big files for photos: Photos saved as PNG can be 2–5x larger than JPEG.
• No animation: PNG isn’t for animations (APNG exists, but isn’t widely supported).
• Slower to compress: Creating small, optimized PNGs can take extra time.

When to Use PNG

Pro Tip: PNG shines with crisp graphics and transparency—not with photos.

Reach for PNG with logos, icons, screenshots, illustrations, or any image that needs transparency or perfect quality. If you’ll be editing an image repeatedly, PNG is a safe bet—it never loses quality.

WebP: Modern and Efficient

WebP is Google’s answer to web images. Launched in 2010, it was built for the web from the ground up, offering both lossy and lossless compression—usually beating JPEG and PNG in file size.

How WebP Works

WebP compresses images with predictive coding. For lossy images, it borrows from the VP8 video codec. For lossless, it uses entropy coding and a dictionary of pixel values. The result? Smaller files than JPEG or PNG for most images.

Strengths of WebP

• High-efficiency compression: WebP images are usually 25–35% smaller than JPEG at the same quality.
• Lossy and lossless: One format can handle both photos and graphics.
• Alpha transparency: Supports full transparency, just like PNG—but smaller.
• Animation support: Can handle animations better than GIF.
• Modern browser support: Works in almost every browser (over 95% of users).

Weaknesses of WebP

• Not for old browsers: Internet Explorer and some ancient Safari versions can’t display WebP.
• Needs modern tools: You’ll need up-to-date software to create and optimize WebP images.
• Editing support is spotty: Not every image editor supports WebP out of the box.

When to Use WebP

Pro Tip: WebP can often replace both JPEG and PNG—just remember to provide fallbacks for older browsers!

Use WebP as your go-to format for most modern sites. It works for photos, graphics, illustrations, and images with transparency. Just make sure to serve JPEG or PNG as a backup for browsers that don’t support it.

AVIF: The Future of Image Compression

AVIF is the latest major format, arriving in 2019 and based on the AV1 video codec. It’s designed to deliver the smallest files at high quality—better than anything before it.

How AVIF Works

AVIF borrows its compression tricks from the AV1 video codec, using advanced video compression for still images. This means ultra-efficient file sizes and great image quality—but it’s more demanding on computers when encoding and decoding.

Strengths of AVIF

• Top-tier compression: AVIF files can be 50% smaller than JPEG at the same quality.
• HDR and wide color: Supports high bit depth and wide color for stunning visuals.
• Great quality at tiny sizes: Keeps images looking sharp, even with heavy compression.
• Modern features: Handles transparency, animation, and even lossless compression.

Weaknesses of AVIF

• Not universal yet: About 85% of browsers support AVIF as of 2024.
• Slow to encode: Creating AVIF images takes more time than other formats.
• Slower to decode: Some devices may struggle to display AVIF instantly, especially on mobile.
• Limited editing support: Few image editors support AVIF natively.

When to Use AVIF

Pro Tip: AVIF gives you the smallest files, but always offer WebP or JPEG as a fallback for full compatibility.

Use AVIF for users with modern browsers—especially for high-quality photos, hero images, or when bandwidth is tight. Always provide WebP or JPEG as a backup so everyone gets a great experience.

GIF: The Animated Veteran

GIF has been around since 1987, making it one of the oldest formats still in use. While newer formats have taken over most tasks, GIF sticks around for simple animations.

How GIF Works

GIF uses lossless LZW compression, but it’s limited to just 256 colors. For animations, it strings together multiple frames, each displaying for a set amount of time.

Strengths of GIF

• Easy animation: Simple to make and universally supported for basic animations.
• Works everywhere: Even the oldest browsers and devices can show GIFs.
• Basic transparency: Supports on/off transparent pixels (but not full alpha transparency).

Weaknesses of GIF

• Color limits: Only 256 colors, so photos look banded or posterized.
• Large file sizes: GIF animations are much bigger than modern videos or animated WebP.
• No audio: GIFs can’t include sound.
• Old-school compression: Much less efficient than today’s formats.

When to Use GIF

Pro Tip: Use modern animation formats (WebP, MP4) whenever possible—save GIF for when nothing else will do.

Only use GIF for simple, low-color animations when video or animated WebP aren’t an option. For most cases, MP4, WebP, or APNG will give you better quality and smaller files. If you need a quick, looping animation with few colors, GIF can still do the job.

Format Comparison Table

Choosing the Right Format

Not sure which format to use? Here’s a quick cheat sheet for picking the best one for your images:

For Photographs and Complex Images

Pro Tip: For photos, use the newest formats you can—but always double-check browser support!

1. Best: Use AVIF for browsers that support it (files are up to 50% smaller than JPEG).
2. Better: Use WebP for browsers that don’t support AVIF (25–35% smaller than JPEG).
3. Good: Use optimized JPEG as a fallback (works everywhere).

For Graphics, Logos, and Illustrations

Pro Tip: Use SVG for anything vector; for crisp raster graphics, stick to WebP or PNG. Never use JPEG for logos!

1. Best: SVG for vector graphics (scales perfectly and tiny files).
2. Better: WebP lossless for raster graphics (smaller than PNG).
3. Good: PNG-8 or PNG-24 as a fallback (supported everywhere).

For Images with Transparency

Pro Tip: If you need transparency, WebP or PNG are your friends—JPEG can’t do it!

1. Best: WebP with alpha channel (much smaller than PNG).
2. Better: PNG-24 with alpha channel (supported everywhere).
3. Avoid: Don’t use JPEG (no transparency support).

For Simple Animations

Pro Tip: Go for video or animated WebP for smooth, efficient animations—leave GIF for last.

1. Best: MP4/WebM video with looping (tiny files, great quality).
2. Better: Animated WebP (beats GIF in most ways).
3. Acceptable: GIF, but only for simple, low-color animations.

Implementing Format Selection

Thankfully, modern HTML makes serving multiple image formats a breeze. Use the <picture> element and srcset to automatically give each browser the best image it can handle. Here’s how:

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

The browser picks the first format it supports, falling back to JPEG if needed. This way, modern browsers get the smallest files, but everyone sees your images.

Conclusion

Knowing your image formats is a huge win for web performance. JPEG and PNG are still important for compatibility, but formats like WebP and AVIF can dramatically cut file sizes without losing quality.

The smartest approach? Use progressive enhancement: serve the latest formats to browsers that support them, and reliable fallbacks for the rest. Image optimization tools (like Squish Image Optimizer) can automate this, converting your images to all the right formats with minimal effort.

Sources and References