The X-ray microscopy technique at the European X-ray free-electron laser
(EuXFEL), operating at a MHz repetition rate, provides superior contrast and
spatial-temporal resolution compared to typical microscopy techniques at other
X-ray sources. In both online visualization and offline data analysis for
microscopy experiments, baseline normalization is essential for further
processing steps such as phase retrieval and modal decomposition. In addition,
access to normalized projections during data acquisition can play an important
role in decision-making and improve the quality of the data. However, the
stochastic nature of XFEL sources hinders the use of existing flat-flied
normalization methods during MHz X-ray microscopy experiments. Here, we present
an online dynamic flat-field correction method based on principal component
analysis of dynamically evolving flat-field images. The method is used for the
normalization of individual X-ray projections and has been implemented as an
online analysis tool at the Single Particles, Clusters, and Biomolecules and
Serial Femtosecond Crystallography (SPB/SFX) instrument of EuXFEL.Comment: 14 pages, 7 figure