The modular spectral imaging (MOSI) system was developed at the Max-Planck Institute for Marine Microbiology in Bremen to enable imaging of pigments in cells and mixed microbial communities, such as microbial mats, biofilms and sediments (Polerecky et al. AEM 2009). It is a versatile system, allowing spectral imaging at scales ranging from a single-cell level up to areas several tens of cm in size. Also, both reflectance and auto-fluorescence measurements can be done. Last but not least, the system can be used in the lab and in field measurements.