I recently tried to bulk resize several hundred large photos in OS X Preview. This repeatedly failed (spinning wheel of death).
In search of a method to resize these images, I found an easy way using Terminal.
- Open up your Terminal app (can open Spotlight and search terminal).
- cd into the desired image directory (e.g. if they are in your Pictures directory, you may: type “cd Pictures/”).
- Enter “sips -Z 1500 *.jpg” (with no “” marks).
- Press enter. It will output every .jpg file in the directory you are in into a max of 1500 width or height.
- Change the “1500” to the max resolution you want.
- It keeps the aspect ratio (-Z is the command for keeping aspect ratio).
- Keep a back up of the full resolution images!