Convert JPG to PNG when you need a lossless file to edit without cumulative quality loss, or a format that can later hold transparency. The PNG will be larger than the JPG — that is the cost of being lossless — but it stops degrading every time you save, which matters for graphics you will revise repeatedly.
Stopping generation loss before you start editing
JPG has a quiet flaw that bites anyone who edits photos: generation loss. Each time you open a JPG, change it, and save, the encoder re-compresses the whole image and discards a little more detail. Edit and re-save a dozen times and the degradation becomes obvious — softer edges, muddier colour, creeping blocks. Converting to PNG first breaks that cycle. PNG is lossless, so once you are in it every save is identical no matter how many rounds of retouching you do. This is exactly why graphic workflows keep working files as PNG and only export to JPG at the very end. When that final export comes, send the finished image through Convert to JPG to get a small, share-ready file.
PNG for transparency, overlays, and platform rules
The other big reason to move from JPG to PNG is transparency. A JPG is always a solid rectangle, but once it is a PNG you can erase the background and composite the subject over any colour or texture — essential for logos, product cut-outs, and layered designs. Many platforms also mandate PNG outright for icons, stickers, and store assets, so converting up front avoids a rejected upload. Bear in mind the PNG will be larger, since lossless storage keeps every pixel; that is the price of an editable, non-degrading file. If you later need it smaller for the web while keeping transparency, JPG to WebP compresses hard with an alpha channel, and the jpgoo hub covers the rest of the round trip.