Multi-image-distance imaging system for extending depth-of-field

Depth of field (DoF) defines the longitudinal range of objects in sharp focus. Imaging systems for machine vision are generally limited to a small DoF by various conditions, constraining the visual inspection of objects with large depth. In this paper, we develop a multi-image-distance imaging system, which can extend the DoF by capturing multi-focus images for fusion. A three-way beam-splitter prism is designed to support independent imaging of three image sensors. Through adjusting the sensors to different back focal lengths, multiple images focusing at different depths are captured in a single exposure. Finally, the focused regions of each image are fused for extending the DoF. Analyses of the proposed DoF extension strategy illustrate excellent enhancement more than three times. Moreover, we introduce a DoF measurement method based on the estimation of the point spread function, and measurement experiments are conducted using the fabricated prototype. Imaging experiments for various scenes demonstrate great imaging quality and DoF extension performance. The proposed multi-image-distance imaging system provides an effective and practical DoF extension solution for close-range visual inspection.