This repository contains filters for Preview on macOS, which can downsample images to 150/300/600DPI when you export files using File => Export.

To install these filters:

1. Open Finder
2. Choose from menu: Go => Go to Folder, or press Cmd-Shift-G
3. Enter "/Library" in the dialog, and press Enter. This brings you to /Library
4. Copy Filter in this repo into /Library (i.e., afterwards there will be a new folder /Library/Filter containing a set of *.qfilter files); your password will be asked
5. Done! Restart Preview to use the newly installed filters

Acknowledgement

Originally from https://discussions.apple.com/message/6109398