Which target format, when
Most image-conversion pain is really a destination problem: the file is fine, the receiving system is picky. Pick by destination, not by habit: upload forms, old software and print shops want JPG; editing pipelines and assets with transparency want PNG; your own website wants WebP for the bandwidth; avatars want a transparent circle. Converting "up" never restores quality — a JPG turned into PNG is a faithful copy of the JPG, not a better photo — so every page here documents what a conversion keeps, what it loses, and when not to run it.
Format compatibility at a glance
| Format | Browsers | Windows/Office | Transparency | Best role |
|---|---|---|---|---|
| JPG | All | All | No | Sharing, upload forms, print |
| PNG | All | All | Yes | Editing masters, UI assets |
| WebP | All modern | Patchy (old apps) | Yes | Web delivery |
| HEIC | Effectively none | Needs HEVC extension | Yes | iPhone storage |
| SVG | All (as image) | Design tools | Yes | Icons, logos — keep vector |
Every conversion here runs on your device — the image decoders and encoders are your browser's own plus WebAssembly for HEIC, and the How it works page shows how to verify that nothing uploads.