Deriving the extended PSF of an image is very important in many aspects of the analysis of the objects within it. Gnuastro has a set of installed scripts, designed to simplify the process following the recipes that were initially introduced in Infante-Sainz et al. 2020 and further improved in Eskandarlou et al. 2025 with more visualizations to help follow the process as they are implemented now in Gnuastro.
This tutorial is for those who are not yet familiar with the process and would like to start from scratch on a pre-defined dataset and lots of extra information on how to interpret the result. For more advanced users (who have already read this), the full documentation of each of the scripts is available in PSF construction and subtraction and an overview of the process is given in Overview of the PSF scripts.
GNU Astronomy Utilities 0.24 manual, November 2025.