How to convert images from PNG to JPEG in bulk on Mac

You’ve been hoarding screenshots for two years and the Desktop folder is 14 GB. PNG is overkill for most screenshots once you’re done with them — JPEG at quality 85 is usually 10x smaller and visually identical for everything except UI with hard text edges.

Two paths

Native macOS. Two options:

• Preview. Select PNGs in Finder, open them all in one Preview window, Cmd+A in the sidebar, File → Export Selected Images, set format to JPEG, pick quality, save. Works, but Preview slows down with hundreds of files.

• Terminal sips in a loop. The classic scriptable approach:

  for f in *.png; do
    sips -s format jpeg -s formatOptions 85 "$f" --out "${f%.png}.jpg"
  done
  

  Fast, handles thousands of files, leaves the PNGs in place so you can verify before deleting. Note that JPEG doesn’t support transparency — any transparent pixels become black or white depending on the encoder, which sips doesn’t warn you about.

Melt. A drag-and-drop Mac app ($9.99 one-time) built for batch conversion. Drag the folder in, set output to JPEG, run.

Bulk convert PNG to JPEG in Melt

1. Open Melt.
2. Drag your folder of PNGs in.
3. Set output format to JPEG.
4. Pick a quality — 85 is the sweet spot for screenshots; go higher for graphics.
5. Click Compress. JPEGs are written alongside the PNGs (or to an output folder, depending on your settings).

Honest tradeoffs

The big one: JPEG has no transparency. A PNG with a transparent background becomes JPEG with a solid background, which is fine for screenshots but breaks logos, icons, and any image you planned to layer over something else. If transparency matters, keep those as PNG and only convert the rest.

The other tradeoff is text sharpness. JPEG’s compression creates faint halos around hard edges — usually invisible at quality 85+, but if your screenshots are mostly small text on flat colour, you may notice. For those, either bump quality to 92+ or keep them as PNG and compress them in place instead.