Best Mac Image Compressors: 8 Apps That Work Offline

You'd think a smaller image file has to look worse. Often it doesn't, at least not at first. A photo straight off a phone or out of an export carries location data, camera details, thumbnails and encoding that wasn't written with file size in mind. Strip and repack that and the file shrinks with no change you could see. Only after that point do you start trading quality for bytes, and that's where the choice of app starts to matter.

Every app below is a Mac app that does the work locally. Your client's product shots and your family photos never leave the machine.

Four mistakes that make any compressor look bad

Compressing when you should be resizing. A phone photo is several thousand pixels wide. If your website shows it at 1,200 pixels, resizing it first will save far more than any amount of clever compression on the full-size file. Compress after you resize, never instead of it.

Squeezing the same JPEG again and again. Each lossy save throws a little more away. Run a file through three tools in a row, or recompress something you downloaded that was already compressed, and you'll see blocky skies and smeared edges. Keep an original and always compress from it.

Letting the app overwrite your only copy. Some batch tools replace the files you drop on them. That's convenient for a website folder and a disaster for the only copy of a shoot. Duplicate the folder first, or find the setting that saves to a new location.

Paying monthly for a one-job utility. This is a cheap category. Two of the apps here are free software, and the paid ones that publish a price sell a one-time licence of about $6 to $15, one of them priced at €15, rather than a subscription. Where a paid app has a free download, the limit it publishes is a daily image count, so you can judge the output on your own files before spending anything.

Lossless, lossy and the setting in between

Lossless compression keeps every pixel. It removes metadata and repacks the file more tightly, so the saving is modest but free. Lossy compression throws away detail your eye is unlikely to miss: fine colour variation, noise, the texture in a flat sky. The saving is much larger, and so is the risk if you push it.

Most apps here let you set how far to go, either with a quality slider or a single "lossy on or off" switch. How much you save depends on the file, and none of these apps publishes a typical figure; the one number on offer, Caesium's "up to 90%", is a best case. A sensible starting point for web photos is the app's default, then check the result at 100% zoom on a busy area like hair or foliage. If it looks fine there, it'll look fine anywhere.

One detail people miss: stripping metadata can also remove the colour profile. Without that tag, some photos can look a little different on screen. If colours look flat after compression, look for a setting that keeps the colour profile while dropping everything else. And yes, removing metadata also strips the GPS location from phone photos, which is a good reason to do it before you post anything taken at home.

Drop a folder in, get smaller files back

ImageOptim

Open-source Mac app for people who want to drag images onto a window and get them back stripped of metadata and recompressed.

Caesium

Cross-platform compressor with a macOS download alongside Windows builds, aimed at shrinking pictures heavily while keeping them looking the same.

Optimage

Designed to compress at a consistent quality level, so a batch of mixed photos and graphics comes out evenly rather than file by file.

Komprixo

A Mac compressor that keeps processing on your machine and adds format conversion and resizing in the same window.

JPEGmini

Photographers who live in JPEG use this desktop app, which also plugs into editing workflows so exports come out smaller.

Squash

Part batch photo editor, part compressor: resize, convert and shrink a stack of photos in one go, including HEIC to JPG.

Compressors that live in Finder or the menu bar

Clop

Menu bar utility that optimises images, video and PDFs the moment you copy them or drop them into its zones.

Compress Image

If you'd rather never open an app at all, this one works from Finder: select an image and compress it in two clicks.

Window, Finder or clipboard: match it to how you work

Once the output is good enough, pick by where the app sits in your day. It's the thing you'll notice every time you use it.

A batch window suits anyone who prepares images in sessions: a blog post's worth of screenshots, a product shoot, a folder for a client. You drag the lot in, wait a few seconds and move on. Web developers and bloggers should start here with a free open-source app, and only move on if they hit a specific gap.

Finder integration suits people who deal with one or two files at a time and don't want another window open. Right-click, compress, done.

Clipboard and drop zones suit the person pasting screenshots into Slack, email and documents all day. Copy large, paste small, without thinking about it. If you share screen recordings too, an app that handles video as well as images saves you a second tool.

Export-time compression suits photographers delivering JPEGs: a JPEG specialist that plugs into the editor shrinks files as they're exported. If you're still choosing the editor itself, see our pick of photo editing software for Mac.

Format support is the other fork. If your problem is mostly iPhone photos in HEIC that a website or a client can't open, you want a batch editor that converts and compresses in one pass. If you publish to the web and want next-generation formats, our guide to WebP converters covers that job in more depth.

Why browser compressors aren't here

Web compressors work well, but they upload your images to someone else's server first. For client work under an agreement, unreleased product shots or personal photos, that's a step you may not be allowed to take. They also need a connection, which a Mac app doesn't. A Mac app does the same job offline, in bulk, with nothing leaving the machine.

Do you make image compressors or Mac utilities for photos? Tool makers can ask to be considered for a featured place on this list.

Before you choose: try three on the same folder

Give yourself an hour and a copy of a real folder: ten phone photos, five screenshots and a couple of logos with transparent backgrounds.

• Run the same copy through one free batch app, one paid app and one clipboard or Finder tool, each on its default setting.
• Sort each output folder by size in Finder and note the total next to the original.
• Open the same three files from each set at 100% zoom: a face, a screenshot with small text, and a logo edge. Look for halos round text and banding in gradients.
• Check one photo's colours against the original side by side. If one set looks duller, that app dropped the colour profile.
• Time how long the whole folder took, then think about how often you'll do this. A few extra seconds a batch doesn't matter weekly and matters a lot every hour.

Whichever gives the smallest total with no visible damage on those three test files is your app. It's rarely the same answer for a photographer and a developer.

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