Search results for "Point spread function"
showing 10 items of 75 documents
Left-handed metamaterial coatings for subwavelength-resolution imaging
2012
We report on a procedure to improve the resolution of far-field imaging by using a neighboring high-index medium that is coated with a left-handed metamaterial. The resulting plot can also exhibit an enhanced transmission by considering proper conditions to retract backscattering. Based on negative refraction, geometrical aberrations are considered in detail since they may cause a great impact in this sort of diffraction-unlimited imaging by reducing its resolution power. We employ a standard aberration analysis to refine the asymmetric configuration of metamaterial superlenses. We demonstrate that low-order centrosymmetric aberrations can be fully corrected for a given object plane. For su…
Optoelectronic morphological image processor.
2009
A morphological optoelectronic image processor based on the threshold decomposition concept is described and demonstrated. Binary slices of a gray-scale input image are optically convolved with a binary structuring element of arbitrary size and shape in a noncoherent convolver. The slices are displayed on a liquid-crystal spatial light modulator of 320 × 264 pixels. The kernels are implemented as modifications of the system impulse response. The processor’s convolution patterns are recorded with a CCD camera and fed into a PC by a frame grabber. Subsequent elementary morphological operations are looped. Examples of processing an input image of 256 × 256 pixels and 16 gray levels with kernel…
Variational multiframe restoration of images degraded by noisy (stochastic) blur kernels
2013
This article introduces and explores a class of degradation models in which an image is blurred by a noisy (stochastic) point spread function (PSF). The aim is to restore a sharper and cleaner image from the degraded one. Due to the highly ill-posed nature of the problem, we propose to recover the image given a sequence of several observed degraded images or multiframes. Thus we adopt the idea of the multiframe approach introduced for image super-resolution, which reduces distortions appearing in the degraded images. Moreover, we formulate variational minimization problems with the robust (local or nonlocal) L^1 edge-preserving regularizing energy functionals, unlike prior works dealing wit…
Exceeding the resolving imaging power using environmental conditions
2007
We present two approaches that use the environmental conditions in order to exceed the classical Abbe's limit of resolution of an aperture-limited imaging system. At first we use water drops in order to improve the resolving capabilities of an imaging system using a time-multiplexing approach. The limit for the resolution improvement capabilities is equal to the size of the rain drops. The rain drops falling close to the imaged object act as a sparse and random high-resolution mask attached to it. By applying proper image processing, the center of each falling drop is located, and the parameters of the encoding grating are extracted from the captured set of images. The decoding is done digi…
Iterative Regularization Techniques in Image Reconstruction
2000
In this survey we review recent developments concerning the efficient iterative regularization of image reconstruction problems in atmospheric imaging. We present a number of preconditioners for the minimization of the corresponding Tikhonov functional, and discuss the alternative of terminating the iteration early, rather than adding a stabilizing term in the Tikhonov functional. The methods are examplified for a (synthetic) model problem.
Merits of vision in presence of light scattering using Tiffen ProMist filters
2020
Light scattering caused by Tiffen ProMist photographic filters of various grades at different laser radiation 640 nm, 532 nm and 405 nm was objectively studied and compared. The lack of removal of speckles from the scene of laser radiation scattering did not allow an accurate assessment of the effect of scattering on the decrease in image contrast. Subjective deterioration in visual acuity using various contrast optotypes and contrast sensitivity was assessed by scattering induction using filters up to grade #5. Vision contrast sensitivity diminishes within all studied spatial frequency range 0.5-18 cpd. The degradation of the impact factor to visual acuity without scattering filters when t…
Optical and visual quality comparison of implantable Collamer lens and laser in situ keratomileusis for myopia using an adaptive optics visual simula…
2012
Purpose. To compare optical and visual quality of the implantable Collamer lens (ICL) and laser in situ keratomileusis (LASIK) for myopia. Methods. An adaptive optics visual simulator (CRX1, Imagine Eyes, France) was used to simulate the vision after ICL implantation and LASIK procedure from the wavefront aberration pattern for -3 and -6 D. Monocular visual acuity (VA) at different contrasts and contrast sensitivity (CS) at 10, 20, and 25 cycles/degree (cpd) were measured for 3- and 5-mm pupils. Modulation transfer function (MTF) and point spread function (PSF) were calculated for a 5-mm pupil. Results. The ICL showed a MTF near of diffraction-limited MTF, but the post-LASIK of MTF worsened…
Axial apodization in 4Pi-confocal microscopy by annular binary filters
2002
We present a novel technique for considerably decreasing the sidelobe height of the axial point-spread function of one-photon 4Pi-confocal microscopes. By means of a numerical example, in which the ratio between the excitation and the fluorescence wavelengths was set to epsilon = lambdaexc/lambdadet = 0.8, we show that simply inserting a pair of properly designed two-ring binary masks in the illumination set allows the height of the axial sidelobes to be reduced from 20% to 5% of the height of the central peak. This allows one to receive the full benefit of the strong narrowness of the central lobe provided by the 4Pi-confocal technique.
Wavefront Recovery: Shack-Hartmann Aberrometry vs PhaseLift Using a Single Binary Amplitude Modulating Mask
2019
We investigate whether a wavefront can be recovered by using a single mask rotated in four different positions. Results show that PhaseLift can recover the wavefront from intensity measurements using such a kind of modulation.
Combining hectometric and decametric satellite observations to provide near real time decametric FAPAR product
2017
Abstract A wide range of ecological, agricultural, hydrological and meteorological applications at local to regional scales requires decametric biophysical data. However, before the launch of SENTINEL-2A, only few decametric products are produced and most of them remain limited by the small number of available observations, mostly due to a moderate revisit frequency combined with cloud occurrence. Conversely, kilometric and hectometric biophysical products are now widely available with almost complete and continuous coverage, but the associated spatial resolution limits the application over heterogeneous landscapes. The objective of this study is to combine unfrequent decametric spatial res…