Abstract
A photographic shutter regulates the duration of light reaching a photosensitive surface. Modern digital cameras employ diverse mechanical, electronic, or hybrid shutter technologies to synchronise light admission with a sensor's capacity to collect and reset charge. To clarify longstanding terminological inconsistencies, this paper first introduces a systematic, four-dimensional framework for classifying camera shutters alongside standardised terminology for describing key temporal quantities in the image-formation pipeline. It then focuses on progressive (i.e., rolling) exposure mechanisms in CMOS-based cameras, where sequential row-integration results in intra-frame temporal offsets across the image sensor that distort image geometry during camera or subject motion. A simple experimental setup utilising a 1,000 Hz flickering LED enables direct measurement of these temporal offsets, revealing substantial delays in electronic rolling shutters compared to mechanical or hybrid rolling-blind focal-plane types. Here, these effects are described by refining the broadly adopted notion of sensor readout into the proposed concept of shutter transit time. Finally, real-world image-based 3D modelling experiments on architectural case studies in Vienna, Austria, highlight the impact of slow shutter transit times in two typical rolling-shutter sensors. Subsequent bundle adjustments in Agisoft Metashape Professional demonstrate that even imperceptible rolling-shutter artefacts can significantly degrade camera exterior orientation and 3D surface quality, although the use of compensation algorithms markedly improves results. Overall, the paper highlights that sensor readout architecture—rather than exposure duration alone—is a decisive factor in determining the geometric fidelity of image-based 3D surface reconstructions.