Abstract
Light field microscopy is a new technique for high-speed volumetric imaging of weakly scattering or fluorescent specimens. It employs an array of microlenses to trade off spatial resolution against angular resolution, thereby allowing a 4-D light field to be captured using a single photographic exposure without the need for scanning. The recorded light field can then be used to computationally reconstruct a full volume. In this paper, we present an optical model for light field microscopy based on wave optics, instead of previously reported ray optics models. We also present a 3-D deconvolution method for light field microscopy that is able to reconstruct volumes at higher spatial resolution, and with better optical sectioning, than previously reported. To accomplish this, we take advantage of the dense spatio-angular sampling provided by a microlens array at axial positions away from the native object plane. This dense sampling permits us to decode aliasing present in the light field to reconstruct high-frequency information. We formulate our method as an inverse problem for reconstructing the 3-D volume, which we solve using a GPU-accelerated iterative algorithm. Theoretical limits on the depth-dependent lateral resolution of the reconstructed volumes are derived. We show that these limits are in good agreement with experimental results on a standard USAF 1951 resolution target. Finally, we present 3-D reconstructions of pollen grains that demonstrate the improvements in fidelity made possible by our method.
Highlights
Light field microscopy [1, 2] is a new approach for rapid, scanless volumetric imaging using optical microscopy
In this paper we present a novel approach for light field reconstruction with improved lateral spatial resolution compared to ordinary light field microscopy
Note that the computational super-resolution we describe here is not to be confused with optical “super-resolution” or “super-localization” methods in microscopy such as Structure Illumination Microscopy (SIM), Photo Activated Localization Microscopy (PALM), and Stochastic Optical Reconstruction Microscopy (STORM), which seek to surpass the diffraction limit
Summary
Light field microscopy [1, 2] is a new approach for rapid, scanless volumetric imaging using optical microscopy. By introducing a microlens array into the light path of a conventional microscope, it is possible to image both the lateral and angular distribution of light passing through the specimen volume. We further show that, when constraining the reconstruction to a single z-plane in the case of a planar test target, we achieve up to an 8-fold improvement in resolution over previously reported limits (see Fig. 1) This is achieved by modeling the spatially varying point spread function of the LFM using wave optics and using this model to perform 3-D deconvolution. The reconstruction technique we have developed is closely related to “computational superresolution” methods in the field of computer vision [3] This signal processing technique combines multiple under-sampled and aliased images of a scene to recover an image with sub-pixel (or in our case, sub-lenslet) resolution. To aid in exploring these trade-offs, we propose a theoretical band limit that should prove useful when choosing which objective, microlens array, and camera sensor to use for a given 3-D imaging scenario
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