Our verdict: Caesium is a simple, effective way to shrink a folder of photos before you upload or email them. You add files, pick a quality level or a lossless mode, and check a live preview before saving. It handles only JPG, PNG and WebP, so it is not a general format converter.
About Caesium Image Compressor
Caesium Image Compressor is developed by Matteo Paonessa under the GPL v3. The compression engine is the open-source libcaesium library written in Rust; there is also a command-line tool and an online version at caesium.app.
You drop in single images or whole folders, choose lossy or lossless compression, optionally set a maximum size or resolution, and save the results to an output folder. A real-time preview helps you judge the quality, and advanced options control metadata and keep the original folder structure.
What it does well
- Batch compression. Compress hundreds of images or whole folders in one run.
- JPG, PNG and WebP. Lossy and lossless modes for the three most common web formats.
- Resize while compressing. Optionally reduce resolution along with file size.
- Real-time preview. See how the compressed image will look before saving.
- Metadata and folders. Choose whether to keep metadata and preserve the folder structure.
Who it is for
Good fit
Bloggers, web developers and anyone who needs to shrink photos before uploading or sharing.
Look elsewhere
Users who need HEIC, AVIF or RAW support, or a full image editor.
Pros and cons
Pros
- Free and open source
- Good size reduction with little visible loss
- Batch processing of whole folders
- Real-time quality preview
Cons
- Only JPG, PNG and WebP
- No editing tools beyond resizing
How to install Caesium Image Compressor
Download the Windows setup from the official GitHub release; a portable zip is offered too. Windows 10 version 1809 or later is required. Check the output folder setting before your first run so you know where the compressed copies are saved.
Questions about Caesium Image Compressor
Is Caesium Image Compressor free?
Yes. It is open source under the GNU GPL v3 with no paid version.
Does Caesium work on Windows 7?
The current version needs Windows 10 build 1809 or later; the developer points Windows 7 and 8 users to the old 1.x version.
