Batch Convert Image

Converting between image formats is rarely neutral, because the formats do not hold the same things. Knowing what a given conversion discards is the difference between a deliberate choice and an unpleasant surprise.

JPEG is lossy and designed for photographs. It has no transparency, so anything transparent is flattened onto a background colour, usually white. Every save re-encodes and loses a little more, which is why an image edited and saved repeatedly as JPEG degrades visibly over time even if nothing was changed. It is the right choice for photographic content and the wrong one for flat graphics and text, where its artefacts cluster around hard edges.

PNG is lossless and supports transparency. It is the right choice for screenshots, logos, diagrams, and anything with sharp edges or text, where it is often smaller than JPEG as well as cleaner. For photographs it is usually much larger, because lossless compression of continuous tone data cannot do what a lossy encoder does.

WebP does both: a lossy mode competitive with JPEG at smaller sizes and a lossless mode with transparency. The practical caveat is not quality but compatibility, and it is smaller every year; the remaining cases are older systems, some email clients, and tools that predate it.

The conversions that lose something are worth naming. PNG to JPEG discards transparency and introduces lossy artefacts. JPEG to PNG does not restore anything: the artefacts are already baked in, and you get a larger file containing the same damaged image. Any lossy format to any other lossy format re-encodes and accumulates loss, so converting JPEG to WebP and back is worse than either alone.

Metadata is the part people forget, and it matters beyond file size. Photographs carry EXIF data that can include the camera, the timestamp and often the GPS coordinates where the picture was taken. Some conversions preserve it and some strip it. If images are going to be published, stripping location data is usually what you want, and it is worth checking rather than assuming.

All of this runs in your browser through WebAssembly, so the images are decoded and re-encoded on your machine and never uploaded.