How to Convert JPG to PNG in Your Browser

How JPG becomes PNG

1. The file is checked against a real JPEG signature before anything else, so a renamed or corrupted file fails safely rather than producing a broken image.
2. The browser’s JPEG decoder reconstructs the DCT-compressed data into a full grid of pixel values — whatever detail survived the original JPEG compression is what gets decoded here, nothing more.
3. Since JPEG has no alpha channel, every pixel decodes as fully opaque; there’s no transparency data to carry forward at this step.
4. The decoded pixel grid is written out as PNG using lossless compression, so the exact pixels the decoder produced are what get saved, with no further quality loss applied.

What changes when you convert

Quality doesn’t change, but the numbers around it can be misleading. PNG stores the decoded pixels exactly, without further loss — but those pixels already carry whatever compression artifacts JPEG introduced when the file was first saved. PNG simply stops that loss from getting worse; it doesn’t reverse what already happened.

File size usually goes up, sometimes considerably. JPEG’s lossy compression is generally much more space-efficient than PNG’s lossless approach for photographic content, so the same image can grow several times larger purely from switching containers — with no corresponding gain in visual detail.

Transparency is never added. JPG never had an alpha channel, so there’s nothing for the PNG to inherit — the output is fully opaque, same as the source.

When PNG is the right choice — and when it isn’t

Converting makes sense when a tool or workflow specifically requires PNG — some editors, upload forms, and design pipelines reject JPG outright — or when you want to keep re-saving the image multiple times during editing without compounding JPEG’s lossy compression further.

It’s not worth it purely to try to improve a low-quality or heavily compressed JPG; PNG can’t recover detail that’s already gone, and you’ll just end up with a much larger file carrying the same limitations. If the JPG already looks the way you want, converting to PNG mainly matters for compatibility, not quality.

Limitations and privacy

This conversion is a one-way step in the sense that it can’t undo JPEG’s original compression — whatever the decoder reconstructs is what gets saved, and there’s no quality slider here since PNG output isn’t a lossy process. Metadata like EXIF camera and location data is also not carried into the PNG.

The file is validated against a genuine JPEG signature before conversion starts, so mismatched extensions or corrupted files are caught early. Everything happens locally: decoding and PNG encoding both run in your browser, with the JPG never uploaded to a Looty Tools server.