Registax

RegiStax is image processing software for amateur astrophotographers, released as freeware, which runs under Windows.

Its purpose is to produce enhanced images of astronomic observations through combining consecutive photographs (an image "stack") of the same scene that were taken over a short period of time. The process relies on the subject (e.g. a planet) being unchanged between photographs, so that any differences can be assumed to be random noise or atmospheric interference.