How to compute an offset master image under ISIS



The offset (or bias) is a spurious signal produced by an electronic shift of the camera. We observe that signal in an image taken with an exposure time of almost zero and in darkness. The offset signal is present in all images

Offset must be subtracted in the process stage for extracting clean signal of the observed star.

Right, the Audela software acquisition panel during offset sequence acquistion.


From "Master images" tab, we compute an offset image from individual o-1 o-2, ..., o-15. The result is image in the working directory.

Tip: make a habit of adopting the same name for yourcalibration images calibration. A generic name such as "o-xxx"is easy to type during acquisition. Do not complicate your life. A name like "" is also explicit.

Above all, do you make a strict protocol and did not deviate!