Which image format should you use?
Five formats cover essentially everything you will meet: JPG, PNG, WebP, AVIF and HEIC. They are not interchangeable, and the differences are easy to state.
The short answer
- Photograph going to another person or an old system → JPG.
- Screenshot, logo, diagram, or anything with text → PNG.
- Anything going on a website → WebP.
- Website image where size matters more than anything → AVIF.
- HEIC → convert it to one of the above; it is an input format, not an output.
Lossy and lossless — the distinction everything follows from
Lossy formats (JPG, WebP, AVIF, HEIC) throw away detail permanently to save space, and let you choose how much. For photographs this works remarkably well, because the detail discarded is the detail your eye is worst at noticing.
Lossless formats (PNG) keep every pixel exactly. That is essential for text and graphics, where the eye is extremely good at spotting damage — and wasteful for photographs, where it is not.
The corollary catches people out: converting a lossy image to a lossless format does not restore anything. A heavily-compressed JPG saved as PNG is the same damaged image in a much larger file.
The formats, one by one
JPG
Thirty years old and universally supported. No transparency. Still the right answer whenever the file is leaving your control — an email attachment, a form upload, a print shop — because nothing will refuse it. At quality 80 the loss is invisible in ordinary viewing.
PNG
Lossless, with transparency. Designed for flat colour and sharp edges, which is why screenshots and logos should be PNG and photographs generally should not — a photo saved as PNG is often ten times larger than a visually identical JPG.
WebP
The pragmatic modern default for the web: 25–35% smaller than JPG at the same visual quality, with transparency, supported by every current browser. Its weakness is outside the browser — some desktop software and a few upload forms still refuse it.
AVIF
The smallest of the lot, sometimes dramatically. Browser support is good; support elsewhere is patchier, and encoding is noticeably slower. Worth it when bandwidth is the priority.
HEIC
What iPhones produce. Technically excellent, roughly half the size of JPG at similar quality — and awkward everywhere outside Apple’s ecosystem. Windows needs an extra codec; many websites reject it. This is why converting HEIC to JPG is the single most common thing people come here to do.
Transparency, briefly
PNG, WebP and AVIF support it. JPG does not, at all. Converting a transparent image to JPG fills the transparent area — this site uses white, which is what most viewers show anyway — and that cannot be undone. If transparency matters, WebP gives you it at a fraction of PNG’s size.
A rule of thumb worth remembering
Photographs compress well and belong in lossy formats. Graphics with hard edges do not, and belong in lossless ones. Almost every wrong format choice comes from applying one rule to the other kind of image.
Convert an image or read about compressing without wrecking quality.