Browsing by Author "Vargas R."

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A flexible and simplified calibration procedure for fringe projection profilometry
(SPIE, 2019) Vargas R.; Marrugo A.G.; Pineda J.; Romero L.A.; Bodermann B.; Frenner K.
Fringe Projection Profilometry (FPP) is a widely used technique for optical three-dimensional (3D) shape measurement. Among the existing 3D shape measurement techniques, FPP provides a whole-field 3D reconstruction of objects in a non-contact manner, with high resolution, and fast data processing. The key to accurate 3D shape measurement is the proper calibration of the measurement system. Currently, most calibration procedures in FPP rely on phase-coordinate mapping (PCM) or back-projection stereo-vision (SV) methods. The PCM technique consists in mapping experimental metric XYZ coordinates to recovered phase values by fitting a predetermined function. However, it requires accurately placing 2D or 3D targets at different distances and orientations. Conversely, in the SV method, the projector is regarded as an inverse camera, and the system is modeled using triangulation principles. Therefore, the calibration process can be carried out using 2D targets placed in arbitrary positions and orientations, resulting in a more flexible procedure. In this work, we propose a hybrid calibration procedure that combines SV and PCM methods. The procedure is highly flexible, robust to lens distortions, and has a simple relationship between phase and coordinates. Experimental results show that the proposed method has advantages over the conventional SV model since it needs fewer acquired images for the reconstruction process, and due to its low computational complexity the reconstruction time decreases significantly. © 2019 SPIE.
A particle swarm optimization approach to log-gabor filtering in fourier transform profilometry
(OSA - The Optical Society, 2018) Pineda J.; Meza J.; Marrugo A.G.; Vargas R.; Romero L.A.
In this work, we propose a particle Swarm Optimization approach to Log-Gabor filtering in Fourier transform profilometry. Encouraging experimental results show the advantage of the proposed method. © 2018 The Author(s)
An experimental study on deformation analysis of an indented pipe via fringe projection profilometry and digital image correlation
(OSA - The Optical Society, 2018) Forero N.; Marrugo A.G.; Vargas R.; Pineda J.; Useche Vivero, Jairo; Romero L.A.
We studied the surface displacement of a steel pipe during indentation via Fringe Projection Profilometry and 2D-Digital Image Correlation. Experimental results show that a 3D strain approximation is possible for comparison with numerical simulation. © 2018 The Author(s)
Background intensity removal in Fourier transform profilometry: A comparative study
(OSA - The Optical Society, 2016) Vargas R.; Pineda J.; Romero L.A.; Marrugo A.G.
We study the removal of the background intensity of fringe patterns via Empirical Mode Decomposition and the Hilbert Transform. Simulation results show that the latter provides a suitable background compensation with minimal error 3D-reconstruction. © OSA 2016.
Background intensity removal in structured light three-dimensional reconstruction
(Institute of Electrical and Electronics Engineers Inc., 2016) Vargas R.; Pineda J.; Marrugo A.G.; Romero L.A.; Altuve M.
In Fourier Transform Profilometry, a filtering procedure is performed to separate the desired information (first order spectrum) from other unwanted contributions such as the background component (zero-order spectrum). However, if the zero-order spectrum and the high order spectra component interfere the fundamental spectra, the 3D reconstruction precision decreases. In this paper, we test two recently proposed methods for removing the background intensity so as to improve Fourier Transform Profilometry reconstruction precision. The first method is based on the twice piece-wise Hilbert transform. The second is based on Bidimensional Empirical Mode Decomposition, but the decomposition is carried out by morphological operations In this work, we present as a novel contribution, the sequential combination of these two methods for removing the background intensity and other unwanted frequencies close to the first order spectrum, thus obtaining the 3D topography of the object. Encouraging experimental results show the advantage of the proposed method. © 2016 IEEE.
Evaluating the influence of camera and projector lens distortion in 3D reconstruction quality for fringe projection profilometry
(OSA - The Optical Society, 2018) Vargas R.; Marrugo A.G.; Pineda J.; Meneses J.; Romero L.A.
We study the influence of geometric distortions of the camera and projector lenses on 3D reconstruction quality for fringe projection profilometry. Experimental results on real objects and their 3D models show the accuracy is improved. © 2018 The Author(s).
On the compensation of uneven illumination in retinal images for restoration by means of blind deconvolution
(Institute of Electrical and Electronics Engineers Inc., 2016) Marrugo A.G.; Vargas R.; Contreras Ortiz, Sonia Helena; Millan M.S.; Altuve M.
Retinal eye fundus images are used for diagnostic purposes, but despite controlled conditions in acquisition they often suffer from uneven illumination and blur. In this work, we propose the use of multi-channel blind deconvolution for the restoration of blurred retinal images. The estimation of an adequate point-spread function (PSF) is highly dependent on the registration of at least two images from the same retina, which undergo illumination compensation. We use the bi-dimensional empirical mode decomposition (BEMD) approach to model the illumination distribution as a sum of non-stationary signals. The BEMD approach enables an artifact-free compensation of the illumination in order to estimate an adequate PSF and carry out the best restoration possible. Encouraging experimental results show significant enhancement in the retinal images with increased contrast and visibility of subtle details like small blood vessels. © 2016 IEEE.
On the illumination compensation of retinal images by means of the bidimensional empirical mode decomposition
(SPIE, 2015) Marrugo A.G.; Vargas R.; Chirino M.; Millán M.S.; Garcia-Arteaga J.D.; Brieva J.; Lepore N.
Retinal images are used for diagnostic purposes by ophthalmologists. However, despite controlled conditions in acquisition retinal images often suffer from non-uniform illumination which hinder their clinical use. In this work we propose the compensation of the illumination by modeling the intensity as a sum of non-stationary signals using bidimensional empirical mode decomposition (BEMD). We compare the estimation and compensation of the background illumination with a widely used technique based retinal image pixel classification. The proposed method has shown to provide a better estimation of the background illumination, particularly in complicated areas such as the optic disk (usually bright) and the periphery of fundus images (usually dim). © 2015 SPIE.
Robust automated reading of the skin prick test via 3D imaging and parametric surface fitting
(Public Library of Science, 2019) Pineda J.; Vargas R.; Romero L.A.; Marrugo J.; Meneses J.; Marrugo A.G.
The conventional reading of the skin prick test (SPT) for diagnosing allergies is prone to inter- and intra-observer variations. Drawing the contours of the skin wheals from the SPT and scanning them for computer processing is cumbersome. However, 3D scanning technology promises the best results in terms of accuracy, fast acquisition, and processing. In this work, we present a wide-field 3D imaging system for the 3D reconstruction of the SPT, and we propose an automated method for the measurement of the skin wheals. The automated measurement is based on pyramidal decomposition and parametric 3D surface fitting for estimating the sizes of the wheals directly. We proposed two parametric models for the diameter estimation. Model 1 is based on an inverted Elliptical Paraboloid function, and model 2 on a super-Gaussian function. The accuracy of the 3D imaging system was evaluated with validation objects obtaining transversal and depth accuracies within ± 0.1 mm and ± 0.01 mm, respectively. We tested the method on 80 SPTs conducted in volunteer subjects, which resulted in 61 detected wheals. We analyzed the accuracy of the models against manual reference measurements from a physician and obtained that the parametric model 2 on average yields diameters closer to the reference measurements (model 1: -0.398 mm vs. model 2: -0.339 mm) with narrower 95% limits of agreement (model 1: [-1.58, 0.78] mm vs. model 2: [-1.39, 0.71] mm) in a Bland-Altman analysis. In one subject, we tested the reproducibility of the method by registering the forearm under five different poses obtaining a maximum coefficient of variation of 5.24% in the estimated wheal diameters. The proposed method delivers accurate and reproducible measurements of the SPT. © 2019 Pineda et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Toward an automatic 3D measurement of skin wheals from skin prick tests
(SPIE, 2019) Marrugo A.G.; Romero L.A.; Pineda J.; Vargas R.; Altamar Mercado, Hernando; Marrugo J.; Meneses J.; Harding K.G.; Zhang, Song
The skin prick test (SPT) is the standard method for the diagnosis of allergies. It consists in placing an array of allergen drops on the skin of a patient, typically the volar forearm, and pricking them with a lancet to provoke a specific dermal reaction described as a wheal. The diagnosis is performed by measuring the diameter of the skin wheals, although wheals are not usually circular which leads to measurement inconsistencies. Moreover, the conventional approach is to measure their size with a ruler. This method has been proven prone to inter- and intra-observer variations. We have developed a 3D imaging system for the 3D reconstruction of the SPT. Here, we describe the proposed method for the automatic measurements of the wheals based on 3D data processing to yield reliable results. The method is based on a robust parametric fitting to the 3D data for obtaining the diameter directly. We evaluate the repeatability of the system under 3D reconstructions for different object poses. Although the system provides higher accuracy in the measurement, we compare the results to those produced by a physician. Copyright © 2019 SPIE.