Image Formats Explained

Image formats proliferate because they make different trade-offs between size, quality, features and compatibility. None is "best" — each was designed with a specific job in mind, and picking the right one is mostly about knowing what that job was. Here is each format in plain language, followed by a decision table you can bookmark.

JPG — the universal photo carrier

Born in 1992, JPG compresses photographs by discarding detail human vision barely registers. It remains the world's default for one reason: everything opens it. No transparency, no animation, and quality erodes with each re-save — but for shipping a photo anywhere, to anyone, on anything, JPG is never the wrong answer. Use quality 80–90 for publishing. (Full comparison: PNG vs JPG.)

PNG — the lossless workhorse

PNG keeps every pixel exactly and supports full alpha transparency, which makes it the standard for logos, screenshots, UI graphics and any image with sharp edges or text. The price is weight on photographic content — a photo saved as PNG is typically 5–10× its JPG size for no visible benefit. Use PNG as your lossless master and for graphics; convert photos out of it with a PNG to JPG converter before publishing.

WebP — the web's efficient all-rounder

Google's WebP (2010) does both lossy and lossless compression, supports transparency and animation, and compresses photos roughly 25–35% smaller than equivalent-quality JPG. Browser support has been universal for years, and it's now a safe default for web images. Its remaining weakness is the world outside the browser: some desktop software, older devices and print workflows still greet .webp files with a shrug. Publish WebP on your own site; hand JPG/PNG to clients and third parties. Our Image Resizer exports it directly.

AVIF — the compression champion with caveats

AVIF, derived from the AV1 video codec, compresses hardest of all — often 40–50% smaller than JPG at comparable quality, with transparency and HDR support. All major browsers now decode it. The friction is on the production side: encoding is slow, tooling is patchier, and very large images can hit encoder limits. Adopt AVIF when your build pipeline or CDN generates it automatically; it's rarely worth manual effort today.

GIF — the meme that refuses to die

GIF is technologically obsolete: maximum 256 colours, huge files for what it delivers, clumsy binary transparency. It survives on one feature — universally auto-playing looped animation — and on culture. For anything animated that you control, an MP4 or animated WebP is a fraction of the size at far better quality. For static images, there is no reason to ever choose GIF.

SVG — not pixels at all

SVG stores instructions for drawing — shapes, paths, text — rather than pixels. The consequences are magical for the right content: infinite sharpness at any zoom, tiny files, editable in a text editor, styleable with CSS. Logos, icons and diagrams belong in SVG whenever a vector source exists. Photographs can't be meaningfully vectorized, so SVG simply doesn't apply to them. One caution: SVG files can embed scripts, so only use SVGs from sources you trust and sanitize user uploads.

HEIC — the iPhone's private dialect

Apple's HEIC halves photo sizes on-device, which is why iPhones default to it. Outside the Apple ecosystem, support remains inconsistent — web browsers don't display it, and many platforms silently convert or reject it. Treat HEIC as a camera-storage format, not an interchange format: export to JPG before sharing beyond Apple devices.

The decision table

Three principles that outlive any format

1. Master lossless, publish lossy. Keep one pristine PNG/RAW original; generate compressed copies per destination. You can always make a smaller copy from a master — never the reverse.
2. Match the format to the content, not to habit: photographic content wants lossy photographic codecs (JPG/WebP/AVIF); synthetic content — text, edges, flat colour — wants lossless (PNG/SVG).
3. Compatibility is a feature. The 10% smaller file is a bad deal if a recipient can't open it. The newer the format, the more you should control both ends of the pipe before using it.

Formats will keep evolving — JPEG XL is waiting in the wings, AVIF adoption keeps climbing — but these principles have held for thirty years of format churn, and the optimization workflow built on them will survive the next thirty too.