# Compress PNG — Compress PNG images on Mac

Shrink PNGs by 60–80% by reducing colours, keeping transparency — ideal for screenshots, logos and icons. Part of OneMacTools, 151 private tools in one native Mac app (macOS 26 or later); category: Images. Runs on your Mac; nothing is uploaded.

Re-saving a PNG rarely makes it smaller. Compress PNG reduces the image to a palette of 256, 128, 64, 32 or 16 colours with optional smoothing for gradients, the technique behind popular PNG compressors, and keeps transparency. It never hands back a bigger file: if a palette wouldn't help, it saves the smallest lossless version instead. A live preview shows the result and the new size before you start.

Page: https://www.onemactools.com/tools/compress-png · Download: https://www.onemactools.com/download · Pricing: https://www.onemactools.com/pricing

## How to use it
1. **Drop your PNGs.** Add screenshots, logos, icons or interface images, as many as you like.
2. **Choose the colours.** 256 colours is a safe default. Fewer colours make smaller files; watch the live preview for the new size and any visible change.
3. **Decide on smoothing.** Leave Smooth gradients on for shadows, gradients and photos inside the image; turn it off for flat graphics.
4. **Click Compress.** Each PNG is saved with “compressed” in its name, and you see the total saving.
5. **Use the smaller files.** They're saved in a new dated folder in Downloads › OneMacTools. Check them with the Preview (eye) button or Show in Finder.

## Options
- **Colours:** 256, 128, 64, 32 or 16 colours, or Lossless (keep every colour). A palette of 256 colours is usually indistinguishable from the original for screenshots and graphics. Lossless re-saves the PNG without changing a pixel, which helps less but is completely safe.
- **Smooth gradients (dithering):** On by default, shown when you reduce the colours. Mixes nearby palette colours in a fine pattern to avoid visible bands in gradients and shadows. Turn it off for flat logos and icons, where it can add speckles and makes files slightly bigger.

## Tips
- Start at 256 colours and only go lower if you need a smaller file and the preview still looks right.
- Flat icons and simple logos often look perfect at 32 or 16 colours, with dithering off.
- For photos, save as JPEG or WebP instead. They're made for smooth colour and will be much smaller than any PNG.
- Resize oversized screenshots first. A Retina screenshot shown at half size on a website carries four times the pixels it needs.

## Questions
**How does it make PNGs so much smaller?**
It reduces the image to a palette of up to 256 colours and stores each pixel as a small index into it, the technique popular PNG compressors use. Screenshots, logos and icons usually look identical at a fraction of the size.

**Will it work on photos?**
Less well: smooth gradients need many colours and can show banding. Keep 256 colours with smoothing on, or use Compress Images to save photos as JPEG.

**Is transparency kept?**
Yes. Transparent and semi-transparent pixels are kept in the palette.

**How do I compress a PNG without losing quality?**
Choose Lossless (keep every colour). Every pixel stays exactly the same; the saving is smaller, but nothing changes.

**Can the file get bigger?**
No. If a palette or re-saving wouldn't make a PNG smaller, the original is copied as it is.

**How many colours should I use?**
256 for screenshots and anything with gradients or photos, 64 to 128 for simple interfaces, and 16 to 32 for flat icons and logos. The live preview shows the result before you start.