PNG to JPG

JPEG has no alpha channel, so transparency cannot survive the conversion, every see-through pixel has to be painted with something before the file is encoded. This tool composites the image onto one solid colour, white unless you pick another from the swatch. The backdrop is painted underneath what is already drawn rather than over it, so a soft shadow or an anti-aliased edge blends into your chosen colour instead of being replaced by a hard block of it. If the transparency has to stay, keep the PNG or convert to WebP instead.

90% is where the slider starts, and on a photograph the gap between that and 100% is close to invisible while the file is often less than half the size. Drop to 70% for thumbnails. Screenshots of text and flat-colour graphics are the exception, JPEG smears sharp edges, and the original PNG is usually smaller as well as cleaner.

Before compositing, a shrunken copy of each image is drawn to a scratch canvas at 120 px on its longest edge and read back pixel by pixel. Anything below full opacity marks the file, and the result row gets a “Flattened” tag. Shrinking first keeps the readback cheap on a 20-megapixel screenshot without hiding a transparent region, which still averages under full opacity after the shrink.

You can, but nothing comes back. JPEG discards detail on the way out and a PNG made from the result stores those artefacts losslessly at a larger size. Keep the PNG if you expect to keep editing.