Closed iris, long exposure photography improves three-dimensional photogrammetric bone reconstructions

Abstract

Three-dimensional (3D) photogrammetry is being increasingly used for digital reconstruction of physical objects. There has been limited investigation on how picture quality influences 3D photogrammetric reconstructions. The purpose of this research was to experimentally compare reconstructions generated from images taken with larger versus smaller iris openings. Four cadaveric feet (2 left and 2 right) from 2 cadavers were dissected, removing skin, fascia, and muscles. Pictures were taken with the feet placed upright on a turntable. For each foot, 24 pictures were taken at f/3.2 (open iris) and f/11 (closed iris), with respective exposure time and ISO determined using a photography light meter. Bones were digitally reconstructed and the talar dome was visually compared between open versus closed iris reconstructions. Closed iris reconstructions more accurately represented the talar dome, for example having gradual and smooth curved transition between the top surface and the medial and lateral sides. Open iris reconstructions had greater distortion, such as sharp, bulging edges on these transitions. To increase the quality of 3D photogrammetric digital reconstructions, a closed iris, restricting only focused light to pass through the camera's iris to the sensor is recommended. Using a closed iris may be particularly important for bone surfaces covered with hyaline cartilage.