Centroiding Undersampled PSFs with a Lookup Table

TL;DR

This paper introduces a lookup table method for accurately determining the centroid of undersampled PSFs without dithering, outperforming traditional fitting algorithms especially under noisy conditions.

Contribution

The paper proposes a novel lookup table approach for centroiding undersampled PSFs, leveraging simulated PSFs to improve accuracy over existing fitting methods.

Findings

Lookup table method yields more accurate centroid positions than fitting algorithms.

Method performs well across different PSF sizes and noise levels.

Improves centroiding accuracy when dithering is not possible.

Abstract

We present a method of centroiding undersampled point spread functions (PSFs) that may be useful, especially when dithering is not an option. If the profile of the expected PSF is known fairly well through characterization of the telescope and detector used for observing, one can simulate the undersampled PSF at many positions on a simulated pixel grid. The true centroid positions are known since the PSFs are simulated, and so one can match up each undersampled PSF images to its true centroid location, thus forming a lookup table. One then assigns the centroid position of an observed PSF to the position associated with the PSF in the lookup table that has the smallest squared residual with respect to the observed PSF. We examine a few PSF sizes and demonstrate that the lookup table provides better centroid positions compared to a fitting algorithm when the PSFs are undersampled, even in the presence of noise.