# Compress Images — Compress images on Mac

Shrink photos for email and the web, with a live before-and-after preview. 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-save photos as JPEG, HEIC or AVIF at the quality you choose and optionally cap their size, typically cutting file sizes by 60–90% with no visible difference. A live preview shows a zoomed-in before and after of your first photo and the exact new size as you move the slider.

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

## How to use it
1. **Drop your photos.** Drag in one photo or a whole batch. Or select them in Finder, right-click and choose Quick Actions › OMT: Compress Images, which uses your last settings.
2. **Set the quality.** Move the Quality slider. The live preview shows a zoomed-in before and after from the centre of your first photo, with the old and new size and how much smaller it gets.
3. **Choose the format and size.** Pick JPEG, HEIC or AVIF, and cap the long edge with Max size if the photos are going to email or the web.
4. **Click Compress.** Every photo is re-saved with your settings. Each copy has “compressed” added to its name.
5. **Check the results.** The copies are saved in a new dated folder in Downloads › OneMacTools. Open them with the Preview (eye) button or Show in Finder. Your originals are untouched.

## Options
- **Quality:** From 10% to 100%, 70% by default. Lower means smaller files with more visible compression. Around 70% suits most photos; watch the live preview and stop lowering it as soon as you see a change.
- **Save as:** JPEG, HEIC or AVIF. JPEG opens everywhere. HEIC and AVIF make smaller files at the same quality but aren't accepted by every website or app.
- **Max size:** Keep original, or cap the longest edge at 3840, 2048, 1600 or 1024 px. Smaller photos are never enlarged. Capping the size usually saves more than lowering the quality.

## Tips
- Resize before you squeeze: capping a phone photo at 2048 or 1600 px removes far more data than dropping the quality, and it still looks sharp on screen.
- Find your quality with the preview. Lower the slider until you can see blockiness or smeared detail in the zoomed-in after image, then step back up 5–10%.
- If the preview says “No smaller”, the photo is already well compressed. Saving in the same format never gives you a bigger file: the original is copied unchanged instead.
- Compress Images is made for photos. For screenshots, logos and graphics that must stay PNG, use Compress PNG instead.
- Compressed copies keep the date taken and location. Run Remove Metadata on them first if you're posting them publicly.

## Questions
**What quality should I use?**
Around 70% is a good default for photos: typically 60–90% smaller with no visible difference. The live preview shows a zoomed-in before and after of your first photo with the exact new size, so you can lower it until you see a change and step back.

**Should I also make the photos smaller in pixels?**
Yes, if they're for email or the web. A phone photo is about 4000 pixels wide; capping it at 2048 or 1600 px cuts the size far more than quality alone.

**I need a photo under an exact size, like 50 KB.**
Use Compress Image to Exact KB instead. It searches for the best quality that fits under your limit.

**JPEG, HEIC or AVIF: which should I choose?**
JPEG if the photos are going to other people, websites or forms, because everything opens it. HEIC or AVIF if you're keeping them yourself or your website supports them, since they're smaller at the same quality.

**How do I compress photos for email on a Mac?**
Drop them in, choose JPEG, set Max size to 1600 or 1024 px and leave the quality around 70%. A batch of phone photos usually ends up small enough to attach in one email.

**Can I compress PNG screenshots with this?**
You can, but they'll be saved as JPEG, HEIC or AVIF, and sharp text can blur. To keep them as PNG, use Compress PNG.

**Why is the preview only showing part of my photo?**
It shows the centre of the first file, zoomed in, so compression artefacts are easy to spot. The whole photo is compressed with the same settings.