Search results for "aperture"
showing 10 items of 182 documents
Evaluation of different InSAR multi-baseline construction methods over a dam in southern Italy
2018
Monitoring dam displacements using different techniques allows an evaluation of their structural behaviour over time. In this study, dam displacements (for the Castello dam, Agrigento, Italy) have been investigated using different Interferometric Synthetic Aperture Radar (InSAR) techniques exploiting a freely available dataset from the EU Copernicus Sentinel-1 SAR built by the European Space Agency (ESA). The dataset includes Sentinel 1A (S1A) images acquired in dual-polarization and Interferometric Wide (IW) swath using the Terrain Observation with Progressive Scans SAR (TOPSAR) mode. Three main Multi-Baseline Construction methods based on the identification of Persistent Scatterers (PS) h…
Multispectral integral imaging acquisition and processing using a monochrome camera and a liquid crystal tunable filter
2012
This paper presents an acquisition system and a procedure to capture 3D scenes in different spectral bands. The acquisition system is formed by a monochrome camera, and a Liquid Crystal Tunable Filter (LCTF) that allows to acquire images at different spectral bands in the [480, 680]nm wavelength interval. The Synthetic Aperture Integral Imaging acquisition technique is used to obtain the elemental images for each wavelength. These elemental images are used to computationally obtain the reconstruction planes of the 3D scene at different depth planes. The 3D profile of the acquired scene is also obtained using a minimization of the variance of the contribution of the elemental images at each …
Proposal of a new diffractive corneal inlay to improve near vision in a presbyopic eye
2020
[EN] A new class of diffraction-based corneal inlays for treatment of presbyopia is described. The inlay is intended to achieve an improvement of the near focus quality over previous designs. Our proposal is a two-zone hybrid device with separated amplitude and phase areas having a central aperture and no refractive power. An array of micro-holes is distributed on the surface of the inlay conforming a binary photon sieve. In this way, the central hole of the disk contributes to the zero order of diffraction, and the light diffracted by the micro-holes in the peripheral photon sieve produces a real focus for near vision. We employed ray-tracing software to study the performance of the new in…
Speckle random coding for 2D super resolving fluorescent microscopic imaging.
2006
In this manuscript we present a novel super resolving approach based upon projection of a random speckle pattern onto samples observed through a microscope. The projection of the speckle pattern is created by coherent illumination of the inspected pattern through a diffuser. Due to local interference of the coherent wave front with itself, a random speckle pattern is superimposed on the sample. This speckle pattern can be scanned over the object. A super-resolved image can be extracted from a temporal sequence of images by appropriate digital processing of the image stream. The resulting resolution is significantly higher than the diffraction limitation of the microscope objective. The new …
Super resolved optical system for objects with finite sizes using circular gratings
2015
We present a real time all optical super resolution method for exceeding the diffraction limit of an imaging system which has a circular aperture. The resolution improvement is obtained using two fixed circular gratings which are placed in predetermined positions. The circular gratings generate synthetic circular duplications of the aperture, thus they are the proper choice for a circular aperture optical system. The method is applicable for both spatially coherent and incoherent illuminations, as well as for white light illumination. The resolution improvement is achieved by limiting the object field of view. The proposed method is presented analytically, demonstrated via numerical simulat…
Superresolved Holographic Microscopy
2008
Superresolution methods in digital holographic microscopy provide a useful tool to overcome the Abbe's diffraction limit when using modest microscope lenses. The process improves the cutoff frequency of the microscope lens by means of the generation of a synthetic aperture based on time multiplexing and using 3 main stages: optical coding, optical decoding, and digital postprocessing. After the whole process, a superresolved image is obtained by Fourier transformation of the synthetic aperture.
Superesolution in digital holographic microscopy
2011
In this contribution, we address with the possibility to overcome the limited resolving power of imaging systems beyond the limit imposed by Abbe's diffraction theory. We first review the mathematical foundations underlying superresolution (SR) from an information theory point of view and then we focus on two multiplexing approaches in digital holographic microscopy (DHM) for achieving SR by synthetic aperture (SA) generation.
Synthetic Aperture Lensless Digital Holographic Microscopy (SALDHM) for Superresolved Biological Imaging
2013
Lensless digital holographic microscopy (LDHM) relates with the capability to achieve microscopic imaging working without lenses in the regime of holography. LDHM uses an extremely simplified setup and provides micron-range lateral and depth resolutions in three-dimensional (3D) imaging. Typically, LDHM uses a pinhole to provide spherical divergent illumination over the sample. Then, two different basic schemes are usually adopted for providing holographic recording. The first one assumes the interference between two in-line waves since diffraction by the sample can be considered as a perturbation of the reference wave. The second scheme uses an external reference beam in an off-line config…
Superresolved phase-shifting Gabor holography by CCD shift
2009
Holography in the Gabor regime is restricted to weak diffraction assumptions. Otherwise, diffraction prevents an accurate recovery of the object's complex wavefront. We have recently proposed a modified Gabor-like setup to extend Gabor's concept to any sample provided that it be non-diffusive. However, the resolution of the final image becomes limited as a consequence of the additional elements considered in the proposed setup. In this paper we present an experimental approach to overcome such a limitation in which the former configuration is used while the CCD camera is shifted to different off-axis positions in order to generate a synthetic aperture. Thus, once the whole image set is reco…
Residents’corner June 2014. PhotogRaphic Clues: Best Settings for Dermatologic Photography
2014
Obtaining digital images either for documentation or research purposes is a daily need for the dermatologist. Photography, as the art of capturing light, relies mainly on three modifiable elements: lens aperture (defined as the opening through which light reaches the camera sensor; expressed as “F-stops”, the smaller the number, the broader the aperture), shutter speed (the total time during which light reaches the sensor; it is indicated as fractions of a second) and ISO sensitivity (the light [...]