We propose a non-permanent add-on that enables plenoptic imaging with standard cameras. Our design is based on a physical copying mechanism that multiplies a sensor image into a number of identical copies that still carry the plenoptic information of interest. Via different optical filters, we can then recover the desired information. A minor modification of the design also allows for aperture subsampling and, hence, light-field imaging. As the filters in our design are exchangeable, a reconfiguration for different imaging purposes is possible. We show in a prototype setup that high dynamic range, multispectral, polarization, and light-field imaging can be achieved with our design.
International audienceLight field imaging offers powerful new capabilities through sophisticated digital processing techniques that are tightly merged with unconventional optical designs. This combination of imaging technology and computation necessitates a fundamentally different view of the optical properties of imaging systems and poses new challenges for the traditional signal and image processing domains. In this article, we aim to provide a comprehensive review of the considerations involved and the difficulties encountered in working with light field data
A method for numerical reconstruction of digitally recorded holograms with variable magnification is presented. The proposed strategy allows for smaller, equal, or larger magnification than that achieved with Fresnel transform by introducing the Bluestein substitution into the Fresnel kernel. The magnification is obtained independent of distance, wavelength, and number of pixels, which enables the method to be applied in color digital holography and metrological applications. The approach is supported by experimental and simulation results in digital holography of objects of comparable dimensions with the recording device and in the reconstruction of holograms from digital in-line holographic microscopy.
This article compares the treatment of Colombia in large cross-country conflict datasets with the information of a unique dataset on the Colombian conflict (CERAC). The big datasets display a strong tendency to record fewer killings than does CERAC. Moreover, when the big datasets provide annual time series on the conflict, these figures look either erratic or flat compared to CERAC’s and often move in different directions. The article also examines the criteria of the Uppsala Conflict Data Program (UCDP) for dataset inclusion and finds them considerably more restrictive than CERAC’s. The primary differences are that UCDP generally excludes attacks purely on civilians and any activity of illegal right-wing paramilitary groups. It is argued here that these omissions impoverish our perception of many civil wars. A calculated modified series based on UCDP methodology and CERAC raw information closes 56% of the gap between the two approaches. The remainder appears to derive mainly from a number of small events in CERAC but not UCDP, reflecting the limits of English-language press coverage of Colombia, upon which UCDP data is based. The gap with other big datasets is also closed. The dynamics of the lower-bound UCDP curve clearly resemble the modified CERAC curve, so UCDP does reasonably well on its own terms. A brief Northern Ireland case study is consistent with our Colombia conclusions. The article concludes with a recommendation for conflict researchers to prioritize the construction of more micro-datasets that will facilitate detailed studies of conflict intensity and its dynamics.
We present an automatic procedure for 3D tracking of micrometer-sized particles with high-NA digital lensless holographic microscopy. The method uses a two-feature approach to search for the best focal planes and to distinguish particles from artifacts or other elements on the reconstructed stream of the holograms. A set of reconstructed images is axially projected onto a single image. From the projected image, the centers of mass of all the reconstructed elements are identified. Starting from the centers of mass, the morphology of the profile of the maximum intensity along the reconstruction direction allows for the distinguishing of particles from others elements. The method is tested with modeled holograms and applied to automatically track micrometer-sized bubbles in a sample of 4 mm3 of soda.
Light-field photography is an extension of traditional photography that enables among other effects refocusing, viewpoint change, and aperture synthesis of still images by digital post-processing. It achieves this capability by recording 4-dimensional radiance information rather than 2-dimensional integrated sensor irradiance. Consequently, optical design tools need to change in order to design these new devices. In this article, we propose an optical first-order model that abstracts the architecture of any light-field camera as an Equivalent Camera Array (ECA). This model enables a comparison between different designs and allows for a simulation of the effects of parameter modifications to a design. We present equations for optical properties such as the depth of field, the angle of view, as well as important parameters for algorithmic performance such as the triangulation baseline. We provide an experimental validation of our model by measuring the properties of a real light-field camera. We are able to extract unknown physical parameters of the system such as the focal length of the main lens.
The phase-space representation of interference based on the marginal power spectrum gives new insight on interference, enlarging its potential applications by means of the principle of spatial coherence modulation. Carrier and (0,pi)-rays produced by three different types of supports are introduced for describing interference as the result of adding the radiant energy propagated by the carriers and the modulating energy (which can be positive or negative) propagated by the (0,pi)-rays. Numerical examples are presented.
The aberrations of an optical system can be described in terms of the wave aberrations, defined as the departure from the ideal spherical wavefront; or the ray aberrations, which are in turn the deviations from the paraxial ray intersections measured in the image plane. The classical connection between the two descriptions is an approximation, the error of which has, so far, not been quantified analytically. We derive exact analytical equations for computing the wavefront surface, the aberrated ray directions, and the transverse ray aberrations in terms of the wave aberrations (OPD) and the reference sphere. We introduce precise conditions for a function to be an OPD function, show that every such function has an associated wavefront, and study the error arising from the classical approximation. We establish strict conditions for the error to be small. We illustrate our results with numerical simulations. Our results show that large numerical apertures and OPD functions with strong gradients yield larger approximation errors.
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