Extended Depth-of-Field Projector by Fast Focal Sweep Projection

Abstract

A simple and cost-efficient method for extending a projector's depth-of-field (DOF) is proposed. By leveraging liquid lens technology, we can periodically modulate the focal length of a projector at a frequency that is higher than the critical flicker fusion (CFF) frequency. Fast periodic focal length modulation results in forward and backward sweeping of focusing distance. Fast focal sweep projection makes the point spread function (PSF) of each projected pixel integrated over a sweep period (IPSF; integrated PSF) nearly invariant to the distance from the projector to the projection surface as long as it is positioned within sweep range. This modulation is not perceivable by human observers. Once we compensate projection images for the IPSF, the projected results can be focused at any point within the range. Consequently, the proposed method requires only a single offline PSF measurement; thus, it is an open-loop process. We have proved the approximate invariance of the projector's IPSF both numerically and experimentally. Through experiments using a prototype system, we have confirmed that the image quality of the proposed method is superior to that of normal projection with fixed focal length. In addition, we demonstrate that a structured light pattern projection technique using the proposed method can measure the shape of an object with large depth variances more accurately than normal projection techniques.

Accommodation-invariant computational near-eye displays

“…EDOF displays have also been proposed to extend the focal range of projectors. For example, Grosse et al [2010] used adaptive coded apertures in combination with image deconvolution to achieve an EDOF effect whereas Iwai et al [2015] employed focus-tunable optics instead to maximize the light throughput. Von Waldkirch et al [2005] simulated the depth of field of focus-tunable lens-based retinal projectors with partially and fully coherent light.…”

“…where f (t ) maps time to temporally-varying focal length. Oftentimes, 1 f (t ) , the focal length in dioptric space, is a periodic trianglelike function [Iwai et al 2015;Miau et al 2013;Nagahara et al 2008], ensuring that the blur diameter varies linearly in time.…”

EyeAR: Refocusable Augmented Reality Content through Eye Measurements

“…In order to achieve the required optical power, we are now considering programmable optical elements. This approach has been successfully demonstrated in the dual problem of increasing the DoF of projectors through coded apertures [52] and fast focal sweep based on a shape-changing lens [53].…”

Recent Advances in Projection Mapping Algorithms, Hardware and Applications

“…Example of extended DOF projection based on the focal sweep technique [IMS15]. Upper left: A prototype system.…”

“…For example, researchers apply coded apertures that have two‐dimensional complex patterns instead of an ordinary circular aperture to make the PSFs more broadband [GWGB10, MSD*13]. Another strategy is to apply a focus tunable lens (FTL) to sweep the focusing distance through the scene to make the PSF invariant to scene depths [IMS15] (Figure ).…”