pfctrl is a command line application for controlling the scientific cameras "pixelfly" and "pixelfly qe" manufactured by PCO. It allows setting all parameters and capturing images. A video mode intended for adjusting the objective is also provided.
To get a list of available options, just run it without parameters. Most options should be self explanatory.
The purpose of the daemon mode is to allow faster image capturing. If a daemon is running, further calls of pfctrl automatically communicate with the daemon. This way the camera needs only to be initialized once.
The subtraction of images is intended for elimination of pixel errors which is especially useful if long exposure times are used.