Search results for "transfer function"
showing 10 items of 152 documents
Multiframe image restoration in the presence of noisy blur kernel
2009
We wish to recover an original image u from several blurry-noisy versions f k , called frames. We assume a more severe degradation model, in which the image u has been blurred by a noisy (stochastic) point spread function. We consider the problem of restoring the degraded image in a variational framework. Since the recovery of u from one single frame f is a highly ill-posed problem, we formulate two minimization problems based on the multiframe approach proposed for image super-resolution by Marquina-Osher [13]. Several experimental results for image restoration are shown, illustrating that the proposed models give visually satisfactory results.
Through-focus response of multifocal intraocular lenses evaluated with a spatial light modulator
2012
A new testing technique based on the use of a liquid crystal spatial light modulator (SLM) is proposed to analyze the optical quality of multifocal intraocular lenses (MIOLs). Different vergences and decentrations of the incident beam can be programmed onto the SLM in order to record the point spread function (PSF) for different object positions. From these axial PSFs, the through-focus modulation transfer function is computed. Because there are no moving parts in the experimental setup, this method is fast and versatile to assess MIOLs. Experimental results confirm the potential of the proposed method.
Optical Characterization Method for Tilted or Decentered Intraocular Lenses
2016
Purpose To test and validate a method for measuring the optical quality and optical power of monofocal intraocular lenses (IOLs) in the presence of a tilt or a decentration as well as its optical power. Methods The experimental system consists of an artificial eye (wet-cell) and a commercial aberrometer with a Shack-Hartmann sensor. Optical image quality parameters such as point spread function (PSF), modulation transfer function (MTF), and the simulations of the retinal image of an extended object are computed from the in vitro wavefront data of an IOL. Repeatability and reproducibility of the system are tested. Mathematical and ray-tracing simulations are used to ascertain the precision a…
Note: Precise radial distribution of charged particles in a magnetic guiding field.
2015
Current high precision beta decay experiments of polarized neutrons, employing magnetic guiding fields in combination with position sensitive and energy dispersive detectors, resulted in a detailed study of the mono-energetic point spread function (PSF) for a homogeneous magnetic field. A PSF describes the radial probability distribution of mono-energetic electrons at the detector plane emitted from a point-like source. With regard to accuracy considerations, unwanted singularities occur as a function of the radial detector coordinate which have recently been investigated by subdividing the radial coordinate into small bins or employing analytical approximations. In this note, a series expa…
Three-dimensional point spread function and generalized amplitude transfer function of near-field flat lenses.
2010
We derive a nonsingular, polarization-dependent, 3D impulse response that provides unambiguously the wave field scattered by a negative-refractive-index layered lens and distributed in its image volume. By means of a 3D Fourier transform, we introduce the generalized amplitude transfer function in order to gain a deep insight into the resolution power of the optical element. In the near-field regime, fine details containing some depth information may be transmitted through the lens. We show that metamaterials with moderate absorption are appropriate for subwavelength resolution keeping a limited degree of depth discrimination.
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.
Data quality oriented procedure, for detailed mapping of heavy metals in urban topsoil as an approach to human health risk assessment
2021
Abstract Urban soils' health is important to the community because of the soils' potential use for recreational activities. A data quality-oriented approach to sampling design is proposed for performing soil representative surveys that gives support to defensible and statistically-based decisions. Krowoderski park in Cracow (Poland) was selected as a study case to investigate heavy metals (HMs) accumulation and to assess human risk exposure according to simulated scenarios. Statistical power was computed for optimizing the number of samples to compare HMs concentration against legal upper tolerance levels (LUTL). The samples' location was iteratively designed as random spatial distribution …
Researches Regarding Optimising the Contouring Precision of CNC Laser Cutting Machines
2014
This paper presents some experimental researches regarding the manufacturing accuracy of a profiling machine together with an approach to eliminate the positioning and contouring errors. A mathematical model based on transfer functions is used as starting approach in order to tune the feed drives of the machine. The accuracy of the profiling machine is tested before and after the tuning process, in order to validate the proposed approach. There are unfolded both positioning tests along one axis and contouring tests on two axes.
The modulation transfer function and signal-to-noise ratio of different digital filters: a technical approach.
2011
The aim of this study was to illustrate the influence of digital filters on the signal-to-noise ratio (SNR) and modulation transfer function (MTF) of digital images. The article will address image pre-processing that may be beneficial for the production of clinically useful digital radiographs with lower radiation dose.Three filters, an arithmetic mean filter, a median filter and a Gaussian filter (standard deviation (SD) = 0.4), with kernel sizes of 3 × 3 pixels and 5 × 5 pixels were tested. Synthetic images with exactly increasing amounts of Gaussian noise were created to gather linear regression of SNR before and after application of digital filters. Artificial stripe patterns with defin…