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Compressing image files

This guide explains how to compress image files in Windows or Mac OS. This is useful when you want to integrate a lot of images into an external environment (e.g., a learning platform, website or presentation) or share them externally (e.g., by storing them in a cloud service or sending it by email) but the files take up too much space.

Good to know: the lower the quality, the smaller the file. Very large original images will retain sufficient quality even with high compression.

Windows: Caesium

Download Caesium for Microsoft Windows.

The Caesium user interface looks like this:

This is how to compress image files in Caesium:

  1. Click the “Add” button to select the images you wish to compress. Alternatively, drag and drop them into the application directly.
  2. Use the slider in the “Compression Options” menu to set the quality of the compressed images To set the same compression level for all images, select “Same for all.” To confirm your selection, click “Set Quality.”
  3. You can select a storage location for your compressed images under “Output File.” To save all files in the same folder as the originals, select “Same folder as input.”
    To save all files in a different folder, deselect “Same folder as input” and select a new folder using the “[...]” button.
    By default, compressed files are saved with the suffix “_compressed” in the file name to distinguish them from the originals. You can change this setting by entering a different suffix into the “Suffix” field.
  4. Once you are happy with all settings, click “Compress!” to start the process for each image. When the process has completed, you will see a notification and a list showing you the file sizes of the compressed images.
  5. You will find your compressed video in the location you specified earlier.

Mac OS: Preview

In Mac OS, you can use the standard “Preview” program to compress images.

This is how to compress image files in Preview:

  1. Open the image you wish to compress in Preview and click “File” in the top menu. Select “Export...” in the drop-down menu.
  2. Choose a file name for the image you wish to compress and select a storage location. Use the slider to specify the quality of the compressed image. You will see the resulting file size right away. Click “Save” to create the compressed image.
  3. You will find your compressed image file in the location you specified earlier.