Integration in the Fourier domain for restoration of a function from its slope : comparison of four methods

Altres ajuts: European Community project CTB556-01-4175.In some measurement techniques the profile, f(x), of a function should be obtained from the data on measured slope f'(x) by integration. The slope is measured in a given set of points, and from these data we should obtain the profile with the highest possible accuracy. Most frequently, the integration is carried out by numerical integration methods [Press et al., Numerical Recipes: The Art of Scientific Computing (Cambridge U. Press, Cambridge, 1987)] that assume different kinds of polynomial approximation of data between sampling points. We propose the integration of the function in the Fourier domain, by which the most-accurate interpolation is automatically carried out. Analysis of the integration methods in the Fourier domain permits us to easily study and compare the methods' behavior

Phase-only filter with improved discrimination

The optimization of a phase-only filter (POF) in terms of discrimination capability is presented. The notion of a phase-difference histogram and its modification are proposed for selecting the support function of the POF. Some numerical results obtained with the conventional POF and the optimized POF are given. The discrimination capability is increased significantly

Optical pattern recognition based on color vision models

A channel transformation based on opponent-color theory of the color vision models is applied to optical pattern recognition so that the conventional red, green, and blue (RGB) channels are transformed into bright-dark, red-green, and yellow-blue (ATD) channels. Matched filtering and correlation are performed over the new components of the target and the scene in the ATD system. The proposed transformation allows us to reduce the number of channels commonly used in color pattern recognition, passing from the three RGB channels to the two red-green and yellow-blue opponent-color channels

Color pattern recognition with circular component whitening

Polychromatic object recognition based on circular whitening preprocessing of red-green-blue components and multichannel matched filtering is described. Computer simulations and experimental results are provided to facilitate recognizing a color target among objects of similar shape but with different color contents. Experimental results are obtained with an optical correlator with two spatial light modulators, one to introduce the scene and the second one to introduce the filter

Clinical leishmaniosis in a domestic ferret (Mustela putorius furo) treated with miltefosine plus allopurinol: Serological and clinical follow-up

The published information on the treatment of mustelid leishmaniosis is extremely scarce because there are only two case reports available. In one case, a domestic ferret (Mustela putorius furo) was treated with a combination of meglumine antimoniate plus allopurinol and, in the other case, a therapeutic regimen with allopurinol was administrated to a Eurasian otter (Lutra lutra). This article describes for the first time a combined therapeutic protocol with miltefosine (2 mg/kg once a day during 28 days per os), and allopurinol (10 mg/kg twice a day PO sine die) in a domestic ferret with splenomegaly, lymphadenomegaly and a facial pyogranulomatous dermatitis, with a moderate level of antibodies to Leishmania infantum. © 2021 Elsevier B.V

Characterization of the Liquid Crystal Display Modulation. Optimization for Some Applications

In this paper we revise recent results of our team in the optimization of twisted nematic liquid crystal displays to be used as spatial light modulators for image processing and diffractive optics. In general two kind of responses are desired for the mentioned applications: amplitude-only and phase-only modulations. However, it is not a trivial task to find the polarization configurations for which these responses are obtained. We show that a reverse-engineering approach is needed to optimize the liquid crystal display response. According to this reverse-engineering approach the modulation characteristics can be calibrated by evaluating the modulation response in a few polarization configurations. These results are used to fit the liquid crystal display behavior to a simplified physical model, which uses two modulation parameters. We demonstrate that the degree of accuracy of this model is very high, thus enabling the prediction of the modulation behavior of the display at other polarization configurations. Therefore, we can perform computer searches for the optimum orientation of the polarizing elements to obtain the required optical transmission. We demonstrate the need to use short wavelengths and the need to insert wave plates in front and behind the liquid crystal displays to obtain either amplitude-only or phase-only regime

Characterization of the anamorphic and frequency dependent phenomenon in Liquid Crystal on Silicon displays

The diffractive efficiency of Liquid Crystal on Silicon (LCoS) displays can be greatly diminished by the appearance of temporal phase fluctuations in the reflected beam, depolarization effects and also because of phase modulation depths smaller than 2π. In order to maximize the efficiency of the Diffractive Optical Elements (DOEs) implemented in the LCoS device, the Minimum Euclidean Distance principle can be applied. However, not all the diffractive elements can be corrected in the same way due to the anamorphic and frequency dependent phenomenon, which is related to the LCoS response, largely dependending on the period and the spatial orientation of the generated DOE. Experimental evidence for the anamorphic and frequency dependent phenomenon is provided in this paper, as well as a comparative study between the efficiency obtained for binary gratings of different period

Optical pattern recognition based on color vision models

A channel transformation based on opponent-color theory of the color vision models is applied to optical pattern recognition so that the conventional red, green, and blue (RGB) channels are transformed into bright-dark, red-green, and yellow-blue (ATD) channels. Matched filtering and correlation are performed over the new components of the target and the scene in the ATD system. The proposed transformation allows us to reduce the number of channels commonly used in color pattern recognition, passing from the three RGB channels to the two red-green and yellow-blue opponent-color channels

Time fluctuations of the phase modulation in a liquid crystal on silicon display: characterization and effects in diffractive optics

In this paper we provide evidence of the temporal fluctuations of the phase modulation property of a liquid crystal on silicon (LCoS) display, and we analyze its effect when the device is used for displaying a diffractive optical element. We use a commercial twisted nematic LCoS display configured to produce a phase-only modulation, and we provide time resolved measurements of the diffraction efficiency that show rapid fluctuations of the phase modulation, in the millisecond order. We analyze how these fluctuations have to be considered in two typical methods for the characterization of the phase modulation: two beam interference and diffraction from a binary grating. We finally provide experimental results on the use of this device for displaying a computer generated hologram. A reduction of the modulation diffraction efficiency results from the phase modulation fluctuation.We acknowledge financial support from the Spanish Ministerio de Educación y Ciencia (grants FIS2006-13037-C02-01 and FIS2006-13037-C02-02) and from Generalitat de Catalunya (grant ACI2003-42). C. Iemmi gratefully acknowledges the support of the Universidad de Buenos Aires and CONICET (Argentina)