Efficient and robust image registration for two-dimensional micro-X-ray fluorescence measurements

• Published in: Journal of analytical atomic spectrometry 2023-05, Vol.38 (5), p.121-131
• Main Authors: Bock, Felix, Gruber, Andreas, Leopold, Kerstin, Bruhn, Henning
• Format: Article
• Language: English
• Subjects: Algorithms; Image registration; Image resolution; Pixels; Registration; X ray fluorescence analysis
• ISSN: 0267-9477; 1364-5544
• DOI: 10.1039/d2ja00347c

X-ray fluorescence spectrometry (XRF) is a technique that allows determining non-destructively the composition of elements within a sample. Focussing the excitation X-ray beam to a small spot that is moved in the x - y -direction relative to the sample adds lateral information. Such a two-dimensional micro-X-ray fluorescence (2D µ-XRF) spectrometer for desktop use is commercially available providing a resolution down to approximately 10 µm. With a µ-XRF spectrometer, it is inexpensive to take many scans of the same sample. With super-resolution methods, these can potentially be combined into a higher-resolution image. As a prerequisite, the misalignments of multiple scans (shifts and rotation) in the subpixel range have to be detected. We present a method for image registration of multiple images based on expander graphs that provides adjustable tradeoffs between registration quality and running time. We evaluate the algorithms on artificial and real µ-XRF data and we argue that our findings show that subpixel information is present in real µ-XRF data. This is a necessary condition for the applicability of multi-image super-resolution techniques to µ-XRF data in future work. Solving image registration problem in micro-X-ray uorescence spectrometry (µ-XRF) is a first step towards application of multi-image super-resolution technique.