PIPP, as the full title suggests, is an application for preparing a collection of images, either as single images or as a video clip, to make them ready for stacking. The preparation can include steps such as cropping frames to a region of interest, calibrating frames using dark and/or flat frames, and ensuring a planet is centred in the frame.

The application can also make a quality measurement on each frame and rank them, allowing the poorest quality frames to be discarded to prevent them from compromising the final image quality.

What PIPP does not do is stack the frames. It simply prepares the frames ready for stacking in another application, such as Autostakkert or Registax.

The PIPP website seems to have been offline for some time, but I have a copy of the installer file that can be downloaded from here.