How to reduce image file size on a Mac

Image file size comes down to three levers: pixel dimensions, format, and compression. Pull all three and a 6 MB photo becomes a few hundred kilobytes with no visible difference.

Lever 1: Resize to the dimensions you actually need

The biggest wins are free. A 4032×3024 iPhone photo displayed in a 800px-wide blog column wastes 90% of its pixels. In Preview: Tools → Adjust Size…, set the width you need. Do this before compressing — no compressor can beat simply having fewer pixels.

Lever 2: Pick the right format

• Photos: JPEG or HEIC (HEIC is roughly 40% smaller at the same quality, but less universally supported).
• Screenshots, UI, logos, anything with transparency: PNG.
• Web delivery: WebP or AVIF give the best sizes for modern browsers.

Wrong-format images are everywhere — a photo saved as PNG can be 5–10× larger than it needs to be.

Lever 3: Compress properly

This is where TinyPresso comes in. Drop images in, press Compress, and PNGs typically come out 60–80% smaller while JPEGs get slimmed down to a leaner quality. It can convert formats in the same pass — set Format to JPEG, HEIC, WebP or AVIF in the sidebar. In our benchmarks, a 2.3 MB portrait dropped to 734 KB with no visible change.

Three properties make it safe to use on everything: it's free, it never inflates a file (if there are no savings, the original is kept), and it's 100% offline, so private photos stay private.

A workflow that always works

1. Resize to target dimensions (Preview or your design tool).
2. Decide the format: photo → JPEG/HEIC, graphics/transparency → PNG, web → WebP/AVIF.
3. Drop the results on TinyPresso and let it squeeze out the rest.

More detail per use case: compressing PNGs, converting HEIC to JPG, and images for the web.