Dr. Elsa S. R. Fonseca Profile

Dr. Elsa S. R. Fonseca

Professor at Univ da Beira Interior

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Publications (6)

Proceedings Article | 3 October 2019 Paper

Influence of pupil function in pseudophakia

Elsa S. Fonseca, Paulo Fiadeiro, Renato Gomes, Angel Sanchez Trancon, António M. Baptista, Pedro Serra

Proceedings Volume 11207, 112071N (2019) https://doi.org/10.1117/12.2527412

KEYWORDS: Eye models, Eye, Visualization, Data modeling, Visual process modeling, Image quality, Spherical lenses, Statistical modeling, Modulation transfer functions, Surgery

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Proceedings Article | 17 September 2018 Presentation + Paper

A digital hologram compression scheme for representation on the object plane

Marco Bernardo, Elsa Fonseca, Paulo Fiadeiro, António Pinheiro, Manuela Pereira

Proceedings Volume 10752, 107520J (2018) https://doi.org/10.1117/12.2323442

KEYWORDS: Holograms, Digital holography, Holography, Computer generated holography, Image compression

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Digital holography is a growing field that owes its success to the provided three-dimensional imaging representation. This is achieved by encoding the wave field transmitted or scattered by an object in the form of an interference pattern with a reference beam. While in conventional imaging systems it is usually impossible to recover the correct focused image from a defocused one, with digital holography the image can be numerically retrieved at any distance from the hologram. Digital holography also allows the reconstruction of multiple objects at different depths. In a previous study, the benchmark of the main available image coding standard solutions JPEG, JPEG-XT, JPEG 2000 and the HEVC intra mode was performed for digital holographic data represented on the object plane. The HEVC intra main coding profile outperforms the other standards while JPEG 2000 results in very similar compression performance. In the current work, a scheme based on the HEVC intra mode codec for holographic information compression on the object plane is proposed. In the base layer, a 2D version of the object (amplitude information on object plane) is coded with HEVC intra main coding profile. Previously was observed that the phase information requires much higher bit rates than the amplitude information, as standardized codecs are not adapted for the compression of this type of information. In this paper we propose a model where the amplitude information is encoded with the HEVC intra mode codec, while the phase is represented by encoding the real information and the signal of the imaginary information. The real information is also encoded using the HEVC intra mode as it already revealed appropriate for compression of this type of information. The imaginary information signal is encoded with JBIG. The advantage of this scheme is that the amplitude information provides a direct 2D representation of the hologram while the phase information can be considered as a 3D enhancement layer. The results show that the proposed scheme outperforms the state of the art in holography compression, while allowing compatibility with the current standards and direct 2D visualization.

Proceedings Article | 17 July 2007 Paper

Estimation of biomedical optical properties by simultaneous use of diffuse reflectometry and photothermal radiometry: investigation of light propagation models

E. S. Fonseca, M. E. de Jesus

Proceedings Volume 6631, 66310C (2007) https://doi.org/10.1117/12.728251

KEYWORDS: Scattering, Absorption, Monte Carlo methods, Diffuse reflectance spectroscopy, Diffusion, Anisotropy, Tissue optics, Biomedical optics, Light scattering, Optical properties

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The estimation of optical properties of highly turbid and opaque biological tissue is a difficult task since conventional purely optical methods rapidly loose sensitivity as the mean photon path length decreases. Photothermal methods, such as pulsed or frequency domain photothermal radiometry (FD-PTR), on the other hand, show remarkable sensitivity in experimental conditions that produce very feeble optical signals. Photothermal Radiometry is primarily sensitive to absorption coefficient yielding considerably higher estimation errors on scattering coefficients. Conversely, purely optical methods such as Local Diffuse Reflectance (LDR) depend mainly on the scattering coefficient and yield much better estimates of this parameter. Therefore, at moderate transport albedos, the combination of photothermal and reflectance methods can improve considerably the sensitivity of detection of tissue optical properties. The authors have recently proposed a novel method that combines FD-PTR with LDR, aimed at improving sensitivity on the determination of both optical properties. Signal analysis was performed by global fitting the experimental data to forward models based on Monte-Carlo simulations. Although this approach is accurate, the associated computational burden often limits its use as a forward model. Therefore, the application of analytical models based on the diffusion approximation offers a faster alternative. In this work, we propose the calculation of the diffuse reflectance and the fluence rate profiles under the δ-P₁ approximation. This approach is known to approximate fluence rate expressions better close to collimated sources and boundaries than the standard diffusion approximation (SDA). We extend this study to the calculation of the diffuse reflectance profiles. The ability of the δ-P₁ based model to provide good estimates of the absorption, scattering and anisotropy coefficients is tested against Monte-Carlo simulations over a wide range of scattering to absorption ratios. Experimental validation of the proposed method is accomplished by a set of measurements on solid absorbing and scattering phantoms.

Proceedings Article | 1 March 2006 Paper

Combined photothermal-photometric method for the determination of tissue optical properties

E. S. R. Fonseca, M. E. P. de Jesus

Proceedings Volume 6084, 60840N (2006) https://doi.org/10.1117/12.644120

KEYWORDS: Absorption, Scattering, Monte Carlo methods, Diffuse reflectance spectroscopy, Diffusion, Tissue optics, Optical properties, Epoxies, Signal detection, Modulation

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Proceedings Article | 22 October 1999 Paper

Time and range averaging of lidar echoes using APD-based receivers

Jose Dias, Elsa Fonseca, David Resendes

Proceedings Volume 3757, (1999) https://doi.org/10.1117/12.366429

KEYWORDS: Receivers, Avalanche photodetectors, Speckle, Interference (communication), Palladium, LIDAR, Signal to noise ratio, Statistical analysis, Signal processing, Avalanche photodiodes

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Proceedings Article | 4 October 1999 Paper

Nonlinear stochastic filtering technique for radar/lidar inversion

Jose Dias, Elsa Fonseca

Proceedings Volume 3809, (1999) https://doi.org/10.1117/12.364048

KEYWORDS: Nonlinear filtering, Signal attenuation, Stochastic processes, Backscatter, Mass attenuation coefficient, Autoregressive models, Digital filtering, LIDAR, Electronic filtering, Remote sensing

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Showing 5 of 6 publications

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