Transparency is the whole question with a PNG. The Background panel opens first: pick white, black, any colour, a colour sampled from the edges, or click a pixel of the picture to use its colour — every tile is your own picture on that colour.
What changes when a PNG becomes a JPG
PNG is lossless and can be transparent. JPEG is lossy and cannot. So two things happen on the way: the transparent parts are painted with a colour you choose, and the picture goes through the JPEG encoder for the first time, which throws away detail the eye is least likely to miss.
The first decision is the one people regret. A logo cut out on a transparent ground and converted onto white looks wrong on a dark page; the same logo converted onto black looks wrong on a light one. Choosing the colour of the page the JPG will sit on — or picking it straight from the picture — is the fix.
Step by step
- Drop one PNG or a whole selection on the panel. Each row reads the file's own bytes, so a PNG named .jpg is still treated as a PNG.
- In Background, choose the colour behind transparency. Pick from the photo lets you click any opaque pixel on the stage to use its exact colour.
- Check the edge in Split or Original view at 100%.
- Leave quality on Measured, or choose Fixed or a Target size in KB in the Quality panel.
- Press Download JPG. More than three files download as a single ZIP.
Edges, fringes and the honest limit
Anti-aliased edges are semi-transparent pixels, and they are blended with the colour you choose. If the PNG was cut out from a different background, a faint halo of the old colour can remain at the edge. The Original and Split views show the edge before anything is written; an automatic fringe clean-up is not part of this converter yet, and is not claimed.