Run pngquant on Mac (the easy way)

You read somewhere that pngquant is what real PNG optimisers run, and you’d like to try it. Good news: it’s free, it’s open source, and it installs in about thirty seconds on a Mac. Slight catch: it’s a command-line tool. Here’s how to use it both ways.

Why pngquant

pngquant does palette quantization — it picks the best 256 (or fewer) colours to represent your image, then writes a PNG with an indexed colour table. This is where the real PNG size savings come from. macOS’s built-in sips doesn’t do this. Preview doesn’t either. Almost every PNG optimiser you can name — ImageOptim, TinyPNG, Squoosh, OptiPNG (combined with it) — has pngquant somewhere in its pipeline.

The Terminal way

Install with Homebrew:

brew install pngquant

Basic use:

pngquant —quality=65-80 input.png

This writes input-fs8.png next to the original. Flags worth knowing:

• --quality=MIN-MAX — the quality range. 65-80 is the standard sweet spot. If pngquant can’t hit at least MIN, it skips the file.
• --strip — removes metadata (EXIF, colour profile chunks).
• --ext .png --force — overwrite the original with a .png extension instead of the -fs8.png suffix.
• --speed 1 — best quality (slowest). Default is 3. Use --speed 11 for fast batch jobs.

A typical “make this small but invisible” command:

pngquant —quality=70-90 —strip —ext .png —force input.png

For a folder:

for f in *.png; do pngquant —quality=70-90 —strip —ext .png —force “$f”; done

The faster way (no Terminal)

If you’d rather not memorise flags or live in Homebrew updates, Download Melt. It wraps the same pngquant-grade quantization (plus zlib re-compression) in a drag-and-drop app.

1. Download Melt and open it.
2. Drag the PNG (or a folder) in.
3. Pick quality — 80 is the default and matches pngquant's `--quality=65-80` range.
4. Click Compress.

The results are functionally equivalent because the algorithm under the hood is the same. The difference is the friction: drag versus Terminal.

How much smaller will it really get?

A typical UI screenshot or design export: 70-85% smaller. A photographic PNG (which shouldn’t really be PNG): 30-50% smaller. A PNG with very few colours already: maybe 10-20%. pngquant’s “never makes it worse” check means files that wouldn’t benefit get skipped.

Honestly — if you only need it occasionally, the Terminal command is fine. If it’s a regular part of your workflow, the GUI shaves real time.