Compress a Mac screenshot before sharing it

You hit ⌘⇧4, dragged a selection, and now there’s a 3.8 MB PNG on your desktop with a name like “Screenshot 2026-05-14 at 11.42.13.png.” It’s a screenshot — there’s no reason it should be that big. Here’s how to fix it.

Why this happens

macOS saves screenshots as PNG by default. PNG is lossless and uses 24-bit colour with an 8-bit alpha channel — 32 bits per pixel before compression. On a Retina display, even a modest selection runs to several million pixels. The format isn’t doing anything wrong; it’s just optimised for fidelity, not size.

The faster screenshot itself

Two changes worth knowing about, regardless of compression:

• Default to JPEG. From Terminal: defaults write com.apple.screencapture type jpg && killall SystemUIServer. Every screenshot you take from then on is a JPEG, usually 70-85% smaller than the PNG equivalent.
• Skip the shadow on window grabs. defaults write com.apple.screencapture disable-shadow -bool true && killall SystemUIServer. Window screenshots (⌘⇧4 then space) stop including the drop shadow padding, which also shaves a chunk.

The native way to compress one

If switching the default isn’t an option (lots of Slack channels expect PNG, and some text-on-UI compresses badly as JPEG), compress the existing PNG:

Preview. Open it, File → Export, switch format to JPEG, set quality to 80, save.

Terminal sips:

sips -s format jpeg -s formatOptions 80 screenshot.png —out screenshot.jpg

For a folder of screenshots:

cd ~/Desktop && for f in Screenshot*.png; do sips -s format jpeg -s formatOptions 80 “$f” —out ”${f%.png}.jpg”; done

The faster way

For ongoing screenshot work — recording bug reports, doing design QA, putting together a support ticket — Download Melt. Drag any number of screenshots in, get them out the other side much smaller.

1. Download Melt and open it.
2. Drag your screenshots in.
3. Set output to JPEG at quality 80, or keep PNG if you need transparency. Both work.
4. Click Compress.

If you keep PNG, Melt runs pngquant-style quantization and still gets you 70-85% smaller. Switching to JPEG gets you a bit more on top.

How much smaller will it really get?

A typical Retina screenshot of a UI: 3-5 MB as PNG. After Melt at PNG quality 80: 400-700 KB. Converted to JPEG at quality 80: 200-400 KB. Slack previews instantly, email attachments stop bouncing, and your Desktop folder stops looking like a hard drive backup.