Mikko Toivonen defends his PhD thesis on Practical Spectral Diffraction Imaging
On Wednesday the 25th of May 2022, M.Sc. (Tech) Mikko Toivonen defends his doctoral thesis on Practical Spectral Diffraction Imaging. The thesis is related to research done in the Department of Computer Science and in the Multi-Source Probabilistic Inference group.

M.Sc. (Tech) Mikko Toivonen defends his doctoral thesis Practical Spectral Diffraction Imaging on Wednesday the 25th of May 2022 at 13 o'clock in the University of Helsinki Exactum building, Auditorium CK112 (Pietari Kalmin katu 5, ground floor). His opponent is Associate Professor Esa Rahtu (Tampereen University, Finland) and custos Associate Professor Arto Klami  (University of Helsinki). The defence will be held in English.

The thesis of Mikko Toivonen is a part of research done in the Department of Computer Science and in the Multi-Source Probabilistic Inference group at the University of Helsinki. His supervisor has been Associate Professor Arto Klami (University of Helsinki).

Practical Spectral Diffraction Imaging

Spectral imaging has proved to be an invaluable tool in many industries and research areas. Spectral images can be used for material identification, food quality monitoring, as an aid in cancer diagnostics, the analysis of paintings, and land cover type detection, to name a few tasks. Despite the high utility of spectral images, spectral imaging devices are often expensive or technically impaired for many use cases and hence they are not used as widely as they could. The computed tomography imaging spectrometer (CTIS) is a special type of spectral imaging device capable of capturing snapshot spectral imaging using a commodity digital camera, together with a modified objective lens containing a diffraction grating. This offers a cost-effective and fast way of spectral imaging that is potentially accessible to a large audience.

In this thesis, we introduce the diffraction imaging add-on, an alternative design to the CTIS, and several algorithms for spectral image production and device calibration. We make the following four contributions: First, we discuss the salient aspects of the design of a diffraction imaging add-on together with two design examples for two cameras, which can be 3D printed with a commodity-grade 3D printer. Second, we present three use cases for diffraction imaging, which also discuss related practical issues of spectral imaging by diffraction imaging. Third, we introduce calibration procedures needed to produce physically correct spectra estimates. Calibration procedures are supported from the perspective of the three use cases. Lastly, we discuss possible shortcomings of the methods presented in the use cases and present improvement suggestions.

Avail­ab­il­ity of the dis­ser­ta­tion

An electronic version of the doctoral dissertation is available on the e-thesis site of the University of Helsinki at http://urn.fi/URN:ISBN:978-951-51-8166-4.

Printed copies will be available on request from Mikko Toivonen: mikko.e.toivonen@helsinki.fi