Active depth from defocus system using coherent illumination and a no moving parts camera

Abstract

Presented is an active no moving parts Depth From Defocus (DFD) system for autofocus and three-dimensional (3-D) imaging applications. The proposed system uses highly coherent laser light and its beam conditioning optics to realize an active illumination system suited for long range and large field of view imaging, overcoming the limited field of view in previous active DFD systems. This is the first time an active DFD system is implemented and experimentally demonstrated using an Electronically Controlled Variable Focus Lens (ECVFL) as an imaging lens that electrically varies the focal length to acquire images with different degrees of defocus, necessary for DFD operations. An experimental demonstration of the proposed system acting as a distance sensor is compared to an incoherent illumination projector DFD system tested over a 1m range. Apart from showing the effectiveness of the ECVFL as an imaging optic for cameras implementing DFD based autofocus algorithms, presented experimental results for the novel system indicate a depth measurement percentage error of <11% versus a maximum 40% error obtained using an incoherent illumination source. Applications for the proposed system include imaging scenarios where high performance no moving parts autofocus is desired in weak textured scenarios, specifically for smartphone and tablet cameras where the proposed system can be miniaturized.