Kompressor vs ImageOptim
ImageOptim makes PNG and JPEG files smaller without a format change. Kompressor converts between formats. This is how the two Mac apps differ and when to use which.
The short answer
The two apps do different jobs, and many people use both. ImageOptim makes existing PNG, JPEG and GIF files smaller and keeps their format. Kompressor converts images to a different format, such as WebP, AVIF or HEIC, and resizes them.
Comparison
| Kompressor | ImageOptim | |
|---|---|---|
| Price | $14.99 one-time, 3 free conversions | Free and open source |
| Main job | Convert, compress and resize | Optimize files in their current format |
| Input formats | More than 50, among them HEIC, WebP, AVIF, RAW | PNG, JPEG, GIF, SVG |
| Output formats | More than 20, among them WebP, AVIF, HEIC | The same format as the input |
| Original files | Kept. Kompressor asks before it replaces a file | Replaced by the optimized files. The originals go to the Trash |
| Result preview | Original and result side by side, with file size | No preview |
| Resize | Yes | No |
| Remove metadata | Yes, by default | Yes, by default |
| System | macOS 14 or later (macOS 13 from the Mac App Store) | macOS 11 or later |
What ImageOptim does well
ImageOptim combines several open-source optimizers, among them MozJPEG, pngquant, Pngcrush, Zopfli and SVGO, and keeps the smallest result. By default it is lossless: the pixels stay the same and only the file becomes smaller. It is free, simple and very good at this job. If your website must stay with PNG and JPEG files, ImageOptim is the correct tool.
When Kompressor is the better tool
- You want a modern format. A change of format saves much more than an optimization. In our test, 30 PNG files became 93% smaller as WebP. ImageOptim does not write WebP, AVIF or HEIC.
- Your images are HEIC or RAW files. ImageOptim does not read them.
- You want to see the result first. Kompressor shows the original next to the result with the real file size.
- You want to keep your originals in place. ImageOptim saves the optimized image over the original file and moves the original to the Trash. Kompressor writes new files and asks before it replaces an existing file.
- You need a different pixel size. ImageOptim does not resize.
Facts about other apps are from their official websites, as of November 2026.
Kompressor in short
Kompressor is an image converter and compressor for Mac (macOS 14 or later, or macOS 13 or later from the Mac App Store). It reads more than 50 formats, among them HEIC, WebP, AVIF and camera RAW, and writes more than 20, among them JPEG, PNG, WebP, AVIF and HEIC. It converts files and whole folders with drag and drop, shows the result and its file size before you convert, and works offline with no analytics. You get 3 free conversions with as many images as you want. A license is a one-time payment of $14.99.