The new University of Duisburg-Essen freshwater diatom image data set (UDE Diatoms I)

Here, we introduce a collection of more than 83,000 light microscopy images of individual diatom valves or frustules, covering a broad range of taxa and morphology by more than 320 samples from 15 different river and lake ecotypes. The diatoms were imaged at high resolution (< 0.1 µm/pixel) by transmitted light bright-field microscopy, with focus stacking to artificially increase focal depth up to 25 µm, allowing simultaneous observation of valve ornamentation and shape. Taken from a real-world setting, the images partly also include debris, mineral particles or other diatoms. Four experts identified over 500 diatom species; more than 100 species are represented by at least 100 specimens and about 150 by at least 50 specimens each. This data set is about one order of magnitude larger than previously published diatom data sets, and its high interspecies similarity makes it a valuable resource e.g. for benchmarking fine-grained out-of-distribution (OOD) detection, on which we present a new approach