Convert PNG to JPG
Turn a PNG into a JPEG, choosing the quality and what fills any transparency.
How it works
PNG is a lossless format: it stores every pixel exactly, using DEFLATE compression over rows that have first been run through one of five per-row prediction filters. That works beautifully on flat colour, sharp text and large uniform regions, so screenshots and logos stay small. It works badly on photographs, because sensor noise makes each pixel differ slightly from its neighbour and there is no prediction to exploit.
A 12-megapixel photo saved as PNG is routinely 15–25 MB; the same photo as a JPEG at quality 82 is usually under 2 MB. If a PNG is unexpectedly huge, it is almost always a photograph in the wrong container.
What the quality slider quantises
JPEG gets that reduction by throwing information away deliberately. It converts to a luma/chroma colour space, halves the chroma resolution (most encoders subsample 4:2:0, because the eye resolves colour detail far less sharply than brightness), then applies a discrete cosine transform to 8×8 blocks and quantises the high-frequency coefficients.
The quality slider scales that quantisation table. Around 82 the loss is very hard to see on photographic content; below about 60 the 8×8 blocks start to show in smooth gradients like skies. The same mechanism makes JPEG the wrong choice for screenshots of text and for line art: hard edges produce visible ringing, and PNG will be both smaller and cleaner.
Where the transparency goes
JPEG has no alpha channel. Not a limited one — none at all. Anything transparent in the PNG has to become an actual colour before it can be encoded, so this tool composites the image over the background you select and sets every pixel to fully opaque.
White suits most documents and upload forms; black suits artwork made for a dark page, where a white flatten would leave a bright halo around anti-aliased edges. Partially transparent pixels are blended proportionally rather than snapped to opaque, so soft shadows and anti-aliased type do not develop a jagged fringe. The result panel says when flattening actually happened.
Keep the PNG as master
This conversion is irreversible in both respects. The discarded frequency detail is gone, and the transparency is gone; converting the JPEG back to PNG later re-stores the artifacts losslessly rather than undoing them. Keep the PNG if it is your master copy and treat the JPEG as a delivery format. The work runs on WebAssembly builds of libpng and mozjpeg inside a Web Worker on your own machine. There is no queue, no account and no daily conversion limit.
Questions
Is my image uploaded to a server?
No. Open developer tools, select the Network tab, and convert a file. You will see requests for the page's code and the codec, and no request carrying your image. The bytes are read by the browser and handed straight to a Web Worker; nothing is POSTed anywhere.
What happens to the transparent parts of my PNG?
They are composited onto the background colour you choose, because JPEG cannot store transparency at all. Semi-transparent pixels are blended in proportion to their alpha, so anti-aliased edges stay smooth. If you need transparency to survive, convert to WEBP instead. It keeps a full 8-bit alpha channel.
Which quality should I pick?
82 is a sensible default for photographs and is close to what most cameras and phones write. Push to 90 if the image will be edited or printed; drop to 70 if the file is for a web page and the size matters more than the last few percent of fidelity. Below 60 you will start to see blocking in skies and other smooth gradients.
Can I convert the JPEG back to PNG and recover the original?
No. A JPEG-to-PNG conversion stores the decoded JPEG pixels losslessly, which means it preserves the compression artifacts rather than removing them, and the flattened background cannot be made transparent again. Keep the PNG if you may need the original later.