236 research outputs found

    Spectral responsivity vs. action spectrum in digital photography

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    We propose an experimental and theoretical methodology based on spectroradiometric procedures to determine the spectral sensitivity of digital still cameras (DSC). The opto-electronic conversion spectral functions (OECSF's) are obtained from normalized digital level (NDL) vs. spectral exposure data, fitted by a typical sigmoidal transition curve. At this stage, we define spectral responsivity r(λ, H) and action spectrum a(λ, NDL), which are conceptual derivations of the general concept of spectral sensitivity of any image sensor. Then, the real spectral responsivity and action spectrum are represented as 3-dimensional functions, where r(λ, H = constant) and a(λ, NDL = constant) profiles are scaled relatively to determine the valid linear output range of the digital image capture device. This range would serve to design the colorimetric profile of the camera with CIE-1931 XYZ standard observer, which is considered as a linear color image sensor.This research was supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT) (Spain) under grants TAP96-0887 and TAP99-0856

    Creació d'una eina multimèdia d'autoaprenentatge que proporciona indicadors de l'aprenentatge al professor

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    Les eines d’autoaprenentatge, en si mateixes no proporcionen informació al professor sobre l’evolució de l’aprenentatge dels alumnes. La innovació del projecte radica en el desenvolupament e inclusió d’indicadors que quantifiquen la evolució de l’aprenentatge de l’estudiant i que el professor rep. L’eina d’autoaprenentatge ha estat desenvolupada en un entorn web amb accés via internet e implementada en llenguatge PHP i fent servir bases de dades MySQL. L’eina d’autoaprenentatge consta de dos mòduls principals; el mòdul interacció amb l’estudiant i el mòdul de gestió de continguts. El mòdul interacció amb l’estudiant té un doble funcionament, per una banda l’alumne té a la seva disposició tota una sèrie de test que pot realitzar quant desitgi, i per l’altra es pot utilitzar per realitzar exàmens tipu test. Els indicadors de l’autoaprenentatge que rep el professor són: temps i durada de realització del test, tema seleccionat i resultat del mateix. Quant l’eina d’autoapranentatge s’utilitza per fer un exàmen tipu test la correcció es automàtica i en temps real. L’eina d’autoaprenentatge es va posar en funcionament en el primer quatrimestre del curs 03-04 en la assignatura òptica fisiològica I. En aquest quatrimestre no es feia servir per realitzar exàmens tipu test. Durant el segon quatrimestre del curs 03-04 es va adaptar l’eina per poder dur a terme exàmens tipu test. En el primer quatrimestre del curs 04-05 és va realitzar el primer examen tipu test. La utilització de l’eina ha evolucionat del 5% inicial fins el 53% dels alumnes. Actualment, l’eina d’autoaprenentatge es troba en la fase d’incorporació a les assignatures d’instruments optomètrics i òptica fisiològica II, així com, la generació automàtica dels indicadors, la creació de nous indicadors i de les accions de coordinació vertical derivades de l’implantació en altres assignatures

    Visual outcome of penetrating keratoplasty, deep anterior lamellar keratoplasty and Descemet membrane endothelial keratoplasty

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    Purpose: A single-center, cross-sectional study was designed to assess and compare objective and subjective quality of vision of patients intervened with penetrating keratoplasty (PK), deep anterior lamellar keratoplasty (DALK) and Descemet membrane endothelial keratoplasty (DMEK). Methods: Forty-six patients previously intervened with PK (22 eyes), DALK (7 eyes) and DMEK (17 eyes) were recruited. Visual evaluation included spherical and cylindrical refraction, distance corrected visual acuity (DCVA), photopic contrast sensitivity (CS), optical quality, measured with the HD Analyzer (objective scattering index [OSI], MTF cut-off and Strehl ratio), and ocular and corneal aberrometry, measured with the KR-1W Wavefront Analyzer. Results: Statistically significant between-group differences were found in age (p = 0.006, DMEK patients were older) and time since surgery (p <. 0.001, longest time for PK patients). No statistically significant differences were found in DCVA between the techniques. Between-group differences were encountered in CS at 12 (p = 0.007) and 18 (p <. 0.001) cycles per degree, with DMEK and DALK obtaining the best and worst outcomes, respectively. Differences in optical quality were found between the techniques (OSI, p = 0.004; MTF cut-off, p = 0.048; Strehl ratio p = 0.022), with DMEK displaying the best outcomes. Highest and lowest values in ocular and corneal aberrations were for DALK and DMEK patients, respectively. Between-group differences were found in corneal astigmatism (p <. 0.001; -3.31. ±. 2.00 D in PK; -2.68. ±. 0.94 D in DALK; -1.09. ±. 0.62 D in DMEK). Conclusion: Overall, DMEK proved superior over PK and DALK in terms of quality of vision, with PK offering slightly better outcomes than DALK in most visual function parameters under evaluation.Preprin

    New methodology of light source spectral distribution selection and design for use in museums to properly exhibit and preserve artwork

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    A new methodology to select light source spectral distribution for use in museums is presented. It is based upon obtaining the Representative Spectral Reflectance Curve (RSRC) for each artwork and then lighting it with a light source the spectral power distribution of which is coincident in shape with the objects RSRC. This should cause minimum damage due to radiation on the object, as the deterioration of the object due to radiation is an effect of energy absorbed. In order to evaluate quality of presentation, colour differences were calculated for the three primal colours present in an artwork sample, illuminated under Illuminants D65 and under a simulated illuminant the spectral power distribution of which matches the RSRC of the illuminated object. Results are in general lower than 3 CIELAB units, considered the limit for strict tolerance in normal colour reproduction.Postprint (author's final draft

    Effect of Experimental Conditions in the Accommodation Response in Myopia

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    SIGNIFICANCE The accommodative response is more affected by the type of refractive error than the method of stimulation, field of view (FOV), or stimulus depth. PURPOSE This study aims to analyze the effect of stimulation method, stimulus depth, and FOV on the accommodation response (AR) for emmetropes (EMM), late-onset myopes (LOM), and early-onset myopes (EOM). METHODS Monocular AR was measured in 26 young observers (n = 9 EMM, n = 8 LOM, n = 9 EOM) under 60 different viewing conditions that were the result of permuting the following factors: (1) stimulation method (free space or Badal lens viewing), (2) stimulus depth (flat or volumetric), (3) FOV (2.5, 4, 8, 10, and 30°), and (4) accommodative stimulus (AS: 0.17, 2.50, and 5.00 diopters [D]). RESULTS Mixed analysis of variance for 2.50 D of AS resulted in a significant effect of refractive group (F = 6.77, P < .01) and FOV (F = 1.26, P = .04). There was also a significant interaction between stimulus depth and FOV (F = 2.73, P = .03) and among stimulation method, FOV, and refractive group (F = 2.42, P = .02). For AS of 5.00 D, there was a significant effect of refractive group (F = 13.88, P < .01) and stimulation method (F = 5.16, P = .03). There was also a significant interaction of stimulation method, stimulus depth, and refractive group (F = 4.08, P = .03). When controlling for all interactions, LOM showed larger lags than EMM and EOM; the AR did not significantly change for fields of 8, 10, and 30°, and it did not significantly differ for different stimulation methods or stimulus depth. CONCLUSIONS Previously reported differences in AR when using lens-based methods compared with free space viewing may be explained by the effect of other factors such as the FOV or the depth of the stimulus. Targets with an FOV of 8 or 10° may be optimal for accurate ARs.Preprin
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