Browsing by Author "Romero L.A."

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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)
A Structure-from-Motion Pipeline for Generating Digital Elevation Models for Surface-Runoff Analysis
(Institute of Physics Publishing, 2019) Meza J.; Marrugo A.G.; Ospina G.; Guerrero M.; Romero L.A.; Perez-Taborda J.A.; Avila Bernal A.G.
Digital Elevation Models (DEMs) are used to derive information from the morphology of a land. The topographic attributes obtained from the DEM data allow the construction of watershed delineation useful for predicting the behavior of systems and for studying hydrological processes. Imagery acquired from Unmanned Aerial Vehicles (UAVs) and 3D photogrammetry techniques offer cost-effective advantages over other remote sensing methods such as LIDAR or RADAR. In particular, a high spatial resolution for measuring the terrain microtopography. In this work, we propose a Structure from Motion (SfM) pipeline using UAVs for generating high-resolution, high-quality DEMs for developing a rainfall-runoff model to study flood areas. SfM is a computer vision technique that simultaneously estimates the 3D coordinates of a scene and the pose of a camera that moves around it. The result is a 3D point cloud which we process to obtain a georeference model from the GPS information of the camera and ground control points. The pipeline is based on open source software OpenSfM and OpenDroneMap. Encouraging experimental results on a test land show that the produced DEMs meet the metrological requirements for developing a surface-runoff model. © Published under licence by IOP Publishing Ltd.
A structure-from-motion pipeline for topographic reconstructions using unmanned aerial vehicles and open source software
(Springer Verlag, 2018) Meza J.; Marrugo A.G.; Sierra E.; Guerrero M.; Meneses J.; Romero L.A.; Serrano C. J.E.; Martínez-Santos, Juan Carlos
In recent years, the generation of accurate topographic reconstructions has found applications ranging from geomorphic sciences to remote sensing and urban planning, among others. The production of high resolution, high-quality digital elevation models (DEMs) requires a significant investment in personnel time, hardware, and software. Photogrammetry offers clear advantages over other methods of collecting geomatic information. Airborne cameras can cover large areas more quickly than ground survey techniques, and the generated Photogrammetry-based DEMs often have higher resolution than models produced with other remote sensing methods such as LIDAR (Laser Imaging Detection and Ranging) or RADAR (radar detection and ranging). In this work, we introduce a Structure from Motion (SfM) pipeline using Unmanned Aerial Vehicles (UAVs) for generating DEMs for performing topographic reconstructions and assessing the microtopography of a terrain. SfM is a computer vision technique that consists in estimating the 3D coordinates of many points in a scene using two or more 2D images acquired from different positions. By identifying common points in the images both the camera position (motion) and the 3D locations of the points (structure) are obtained. The output from an SfM stage is a sparse point cloud in a local XYZ coordinate system. We edit the obtained point in MeshLab to remove unwanted points, such as those from vehicles, roofs, and vegetation. We scale the XYZ point clouds using Ground Control Points (GCP) and GPS information. This process enables georeferenced metric measurements. For the experimental verification, we reconstructed a terrain suitable for subsequent analysis using GIS software. Encouraging results show that our approach is highly cost-effective, providing a means for generating high-quality, low-cost DEMs. © Springer Nature Switzerland AG 2018.
A vision-based system for the dynamic measurement of in-plane displacements
(Institute of Electrical and Electronics Engineers Inc., 2014) Marrugo W.; Sierra E.; Marrugo J.; Camacho C.; Romero L.A.; Marrugo A.G.; Marrugo A.G.
Computer vision has advanced markedly in the last decade and has had new applications such as the analysis of the behavior of structures. The analysis of displacement and deformation of structures is an important process in Structural Health Monitoring (SHM). There are different techniques and devices for measuring strains and displacements, such as linear-variable-differential-transducers (LVDTs) and the global position system (GPS), which can be expensive and may not provide sufficient accuracy. This paper proposes vision-based methods for non-contact measurement of displacements and deformations. These methods allow for accurate non-contact measurements at low cost using off-the-shelf components, basically a camera, a computer, and a target. In this work, we test propose a vision based method for the measurement of displacements and we discuss the trade-offs in terms of robustness, computational complexity and accuracy. Encouraging results show that the displacement of a structure can be both determined accurately and fast enough in real time. © 2014 IEEE.
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.
Developing a Robust Acquisition System for Fringe Projection Profilometry
(Institute of Physics Publishing, 2019) Pineda J.; Marrugo A.G.; Romero L.A.; Perez-Taborda J.A.; Avila Bernal A.G.
Since Fringe Projection Profilometry (FPP) is an intensity-based coding strategy, it is prone to improper optical setup arrangement, surface texture and reflectance, uneven illumination distribution, among others. These conditions introduce errors in phase retrieval which lead to an inaccurate 3-D reconstruction. In this paper, we describe a dynamic approach toward a robust FPP acquisition in challenging scenes and objects. Our aim is to acquire the best possible fringe pattern image by adjusting the object closer to an ideal system-object setup. We describe the software implementation of our method and the interface design using LabVIEW. Experimental results demonstrate that the proposed method greatly reduces sources of error in 3-D reconstruction. © Published under licence by IOP Publishing Ltd.
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).
Noise-Robust Processing of Phase Dislocations using Combined Unwrapping and Sparse Inpainting with Dictionary Learning
(Institute of Electrical and Electronics Engineers Inc., 2019) Pineda J.; Meza J.; Barrios E.M.; Romero L.A.; Marrugo A.G.
The problem of phase unwrapping from a noisy and also incomplete wrapped phase map arises in many optics and image processing applications. In this work, we propose a noise-robust approach for processing regional phase dislocations. Our approach combines phase unwrapping and sparse-based inpainting with dictionary learning to recover the continuous phase map. The method is validated both using numerically simulated data with strong additive white Gaussian noise and phase dislocations; and experimental data from fringe projection profilometry. Comparisons with other phase inpainting method referred to as PULSI+INTERP, show the suitability of the proposed method for phase restoration even in extremely noisy phases. The error given by the proposed method on the highest level of noise (RMSE=0.0269 Rad) remains the smallest compared to the error given by PULSI+INTERP for noise-free data (RMSE=0.0332 Rad). © 2019 IEEE.
Programmable diffractive lens for ophthalmic application
(SPIE, 2014) Millán M.S.; Pérez-Cabré E.; Romero L.A.; Ramírez N.
Pixelated liquid crystal displays have been widely used as spatial light modulators to implement programmable diffractive optical elements, particularly diffractive lenses. Many different applications of such components have been developed in information optics and optical processors that take advantage of their properties of great flexibility, easy and fast refreshment, and multiplexing capability in comparison with equivalent conventional refractive lenses. We explore the application of programmable diffractive lenses displayed on the pixelated screen of a liquid crystal on silicon spatial light modulator to ophthalmic optics. In particular, we consider the use of programmable diffractive lenses for the visual compensation of refractive errors (myopia, hypermetropia, astigmatism) and presbyopia. The principles of compensation are described and sketched using geometrical optics and paraxial ray tracing. For the proof of concept, a series of experiments with artificial eye in optical bench are conducted. We analyze the compensation precision in terms of optical power and compare the results with those obtained by means of conventional ophthalmic lenses. Practical considerations oriented to feasible applications are provided. © 2014 Society of Photo-Optical Instrumentation Engineers.
Programmable diffractive optical elements for extending the depth of focus in ophthalmic optics
(SPIE, 2015) Romero L.A.; Millán M.S.; Jaroszewicz Z.; Kołodziejczyk A.; Romero E.; Lepore N.
The depth of focus (DOF) defines the axial range of high lateral resolution in the image space for object position. Optical devices with a traditional lens system typically have a limited DOF. However, there are applications such as in ophthalmology, which require a large DOF in comparison to a traditional optical system, this is commonly known as extended DOF (EDOF). In this paper we explore Programmable Diffractive Optical Elements (PDOEs), with EDOF, as an alternative solution to visual impairments, especially presbyopia. These DOEs were written onto a reflective liquid cystal on silicon (LCoS) spatial light modulator (SLM). Several designs of the elements are analyzed: the Forward Logarithmic Axicon (FLAX), the Axilens (AXL), the Light sword Optical Element (LSOE), the Peacock Eye Optical Element (PE) and Double Peacock Eye Optical Element (DPE). These elements focus an incident plane wave into a segment of the optical axis. The performances of the PDOEs are compared with those of multifocal lenses. In all cases, we obtained the point spread function and the image of an extended object. The results are presented and discussed. © 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.
Wide-field 3D imaging with an LED pattern projector for accurate skin feature measurements via Fourier transform profilometry
(SPIE, 2019) Marrugo A.G.; Romero L.A.; Meneses J.; Harding K.G.; Zhang, Song
Accurate 3D imaging of human skin features with structured light methods is hindered by subsurface scattering, the presence of hairs and patient movement. In this work, we propose a wide-field 3D imaging system capable of reconstructing large areas, e.g. the whole surface of the forearm, with an axial accuracy in the order of 10 microns for measuring scattered skin features, like lesions. By pushing the limits of grating projection we obtain high-quality fringes within a limited depth of field. We use a second projector for accurate positioning of the object. With two or more cameras we achieve independent 3D reconstructions automatically merged in a global coordinate system. With the positioning strategy, we acquire two consecutive images for absolute phase retrieval using Fourier Transform Profilometry to ensure accurate phase-to-height mapping. Encouraging experimental results show that the system is able to measure precisely skin features scattered in a large area. Copyright © 2019 SPIE.