Tracking in StarTools makes sure that every module and algorithm can trace back how a pixel was modified at any point in time. It is the Tracking engine's job to allow modules and algorithms "travel in time" to consult data and even change data (changing the past), and then forward-propagate the changes to the present.
The latter sees the Tracking module re-apply every operation made since that point in time, however with the changed data as a starting point; changing the past for a better future. This is effectively signal processing in three dimensions; X, Y and time (X, Y, t).
I'm relatively new to image processing and just wanted to say how straight forward and powerful StarTools is.
The Color module is very powerful - offering capabilities surpassing most other software - yet it is simple to use.
The PSF radius input for the chosen synthetic model, is controlled by the 'Synthetic PSF Radius' parameter.
All light in your image is spread according to a Point Spread Function (PSF), not just the stars.
You can convert everything you see to a format you find convenient. Give it a try!