Speaker
Description
The Timepix4 provides time of arrival (ToA) and time over threshold (ToT) information on detected events, enabling sub-pixel position reconstruction beyond simple pixel-centre assignment [1]. We present an evaluation of centroiding methods for Timepix4 electron clusters, aimed at improving spatial resolution by combining the complementary information carried by ToT and ToA. Using Allpix2 simulated data, we compare conventional ToT-weighted centroiding, ToA-based localisation, and a scaled-centroid approach designed to retain the sharpness of an anchor-pixel method, while recovering fractional position information from the cluster charge distribution.
The study investigates how the cluster ToT distribution can be used to estimate a physically motivated sub-pixel offset, based on the observation that the ToT-weighted centroid reflects the overall cluster shape, while the earliest ToA is often located close to the particle entry point and can therefore serve as an anchor for reconstruction. Several methods are explored to calculate this scaled centroid, including corrections derived from the displacement of the ToT-weighted centroid relative to the anchor pixel centre, and shape-dependent offsets informed by characteristic cluster topologies.
A comparison of the different centroiding strategies is performed on simulated datasets to assess their effect on sub-pixel hit distributions and imaging performance. The results show that pure ToT centroiding can introduce strong topology-dependent biases, while ToA anchoring preserves localisation near the point of entry but lacks fractional precision. The scaled-centroid approach provides a compromise between these two limits, maintaining proximity to the early-ToA anchor while introducing controlled sub-pixel shifts based on the cluster charge pattern. We discuss the physical interpretation of these methods and apply the centroiding approaches to 200 keV electron data acquired in a transmission electron microscope in order to study their impact on modulation transfer function and position reconstruction in electron imaging applications.
[1] N Dimova et al., NIMA 1075 (2025), 170335