Same compression power. Modern UI, built-in resize, and format conversion — for $2.99 once instead of free-but-clunky.
Verdict
ImageOptim is excellent, free, and twelve years old. Kompressor does the same compression job — and adds resize, format conversion and an interface built for 2026 — for $2.99 once. Pick Kompressor if a clean UI and resize matter. Stick with ImageOptim if you only need lossless PNG/JPG and don't mind hunting through Preferences.
| Feature | Kompressor | ImageOptim |
|---|---|---|
| Price | $2.99 one-time | Free (open source, GPL v2) |
| Free tier | 10 images / day, no card | Unlimited |
| Platform | macOS 11+ (Apple Silicon + Intel) | macOS only |
| Drag & drop folder | Yes, recursive | Yes, recursive |
| Output formats | JPEG, PNG, WebP | JPG, PNG, GIF, SVG (no conversion) |
| Resize | 5 presets + original | No |
| Privacy (local processing) | 100% local | 100% local |
| Speed | Very fast (Rust, parallel) | Variable; slow on PNG with all algorithms enabled |
| Quality control | Visible slider (10–100) | Hidden in Preferences |
| Interface era | 2026 native, TWK Continental | 2014, system Helvetica |
ImageOptim's window has not meaningfully changed since around 2014. It is a list of files with a coloured savings column, a help button, and that is essentially it. The quality slider — the single most important control for any compressor — lives buried in Preferences. Most ImageOptim users compress in lossless mode without realising they could halve file sizes again with a tiny perceptual hit. Kompressor puts that slider front and centre, in a window styled to feel like a 2026 macOS app rather than a Snow Leopard relic. Same engine class underneath; vastly cleaner glass on top.
ImageOptim does not resize. If you need to ship 800-pixel-wide web images from a folder of 6000-pixel DSLR shots, you compress in ImageOptim, then resize in Preview or Sips, then compress again. Kompressor caps the longest side in one drop — pick 800, 1200, 1600, 2400, 3200 px or keep the original. The image is downscaled with a Lanczos filter and then encoded in your target format. One step, web-ready out, no second app.
ImageOptim writes back the same format you fed it. JPG in → smaller JPG out. PNG in → smaller PNG out. Kompressor lets you drop a folder of any supported input — JPG, PNG, WEBP, TIFF, BMP, GIF, HEIC — and pick the output: JPEG, PNG, or WebP. Want a folder of WebPs from a folder of PNG screenshots for your new website? One drag, one click. Want JPEGs from your iPhone HEICs to email? Same flow.
Kompressor is written in Rust with the image
crate and lives in a 6 MB universal binary. Batches run in
parallel on every CPU core. A folder of 200 photos that takes
ImageOptim 35–60 seconds with all algorithms enabled comes
out of Kompressor in 6–10 seconds. The visual progress bar is
actually slowed down on purpose so you can see something
happen — without that, most batches would finish before the
rainbow gradient even starts moving.
ImageOptim costs nothing and never will. It is open source under GPL v2, run by a single dev who has shipped consistently since 2010, and you can audit every byte if you want. For students, hobbyists, or anyone who only compresses two photos a month, that price is unbeatable. Kompressor's free tier (10 images a day) is generous, but if you genuinely process zero to two images a month and never resize, ImageOptim wins.
Kompressor reads GIF but writes only JPEG, PNG, or WebP. It ignores SVG entirely. ImageOptim has SVGO and Gifsicle baked in and runs them automatically. If your job involves a steady stream of vector icons or animated GIFs that need to stay small, ImageOptim is the better fit. Kompressor's roadmap includes neither for 2026.
On lossless PNG specifically, ImageOptim chains MozJPEG, pngquant, Pngcrush, 7zip, SVGO and Zopfli to squeeze out the last 1–3% of file size. Kompressor uses a single high-quality PNG encoder and does not try to win every byte. For most users this difference is invisible. For a designer shipping PNG sprites where every kilobyte counts and time does not, ImageOptim's brute-force pipeline still has an edge.
ImageOptim is free. Kompressor is $2.99 once for one Mac, or $9.99 once for up to five Macs. Neither has a subscription.
Over three years of use, ImageOptim costs $0. Kompressor costs $2.99 — roughly the price of a small coffee, paid once, forever. If you compress one image a week for those three years, the per-image cost on Kompressor is just under two cents. If you compress a hundred a week, it is well below a tenth of a cent. The "is it worth it" question is genuinely short: if you would happily trade a single coffee for built-in resize, format conversion, and a window you actually enjoy looking at, the answer is yes.
You ship images regularly to websites, social media, or email and want them small and resized and in the right format — in one drop.
You appreciate a clean modern UI, a visible quality slider, and a window that fits a 2026 Mac.
You sometimes need WebP output for the modern web, or want to convert HEIC iPhone photos to JPEG.
You only ever compress JPG and PNG losslessly, never need resize, and never need format conversion.
You handle SVG icons or animated GIFs regularly and want one tool for all of them.
You strongly prefer open-source software and the price tag matters.
10 images every day, no email, no card. Decide for yourself if the modern UI and resize are worth the coffee.
macOS 11+ · 6 MB universal binary · refundable within 14 days
Better is the wrong word — Kompressor is different. Both compress JPG and PNG well. ImageOptim wins on price (free) and aggressive lossless PNG. Kompressor wins on UI, resize, format conversion (JPEG, PNG, WebP output), and a visible quality slider. Pick based on what you actually do, not on what is cheapest.
On JPEG and standard PNG output the file size and visual quality are within a few percent of each other. ImageOptim can squeeze a little more out of PNG with its multi-algorithm pipeline if you enable every option. For 95 percent of users that difference is invisible at normal viewing distance.
For a modern macOS interface, an exposed quality slider, built-in resize presets, and format conversion (JPEG, PNG, WebP). $2.99 once is the cost of a coffee — and unlike ImageOptim you can also output WebP and resize for the web in the same drop.
No. Like ImageOptim, Kompressor processes everything locally on your Mac. Your images never touch a server. There is no telemetry, no account, and no internet needed to compress.
No, Kompressor is macOS only (Apple Silicon and Intel, macOS 11+). It is built natively in Rust and Tauri, sized at about 6 MB. There are no plans for a Windows version in 2026.