There are two types of cachers – Threaded and Unthreaded.

The Threaded cacher will always try to fetch an image as soon as possible (in the background). When a new image is available, the cacher's listeners will be notified. You can't get an image from an empty Threaded cacher (for you programmers out there: it will throw an exception). The Threaded cacher is used in chains.

The Unthreaded cacher will not fetch an image until someone asks the cacher for it. This means that the first time someone asks for the image, it will take some time to generate it, but getting the image every time after that will be very fast. The Unthreaded cacher is used by some preview panels to speed up the graphical interface.

A Cacher is a filter that stores the last input image. This saves time/performance, since the image won't have to travel through all the filters every time a setting is changed.

Cachers don't have any settings, and don't show up as separate filters in the filter list. Instead, the text (cached) will be shown after a filter's name.