Person: Quiroga Mellado, Juan Antonio
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 10 of 28
PublicationMeasurement of surface topography by RGB Shadow-Moiré with direct phase demodulation(Elsevier Sci. Ltd., 2006-12) Quiroga Mellado, Juan Antonio; Gómez Pedrero, José Antonio; Terrón López, M. José; Crespo Vázquez, DanielIn this paper we present the application of a direct demodulation method for the measurement of surface topography by means of Shadow-Moiré. In our set-up, we use three LEDs (with green, red and blue peak wavelengths) to illuminate the grating. Due to the different position of these light sources, a polychromatic Shadow-Moiré fringe pattern is produced, which can be described as the superposition of three monochromatic (red, green and blue) fringe patterns. Taking the image of this polychromatic fringe pattern with a RGB CCD camera, we get a monochromatic fringe pattern stored at each RGB channel of the CCD. The direct demodulation algorithm employed uses these fringe patterns to calculate the wrapped phase map. After unwrapping the phase map using a standard multi-grid technique, we implemented an automatic procedure to detect the area of interest of the phase map by removing low modulation zones and to calculate the absolute value of the phase. In this way it is possible to determine the topography of a surface with a single RGB snapshot maintaining a simple experimental set-up, which is an important feature, especially for the study of dynamic phenomena such as deformations. We present the experimental results obtained after measuring different objects with both smooth and rough surface textures. PublicationWavefront measurement by solving the irradiance transport equation for multifocal systems(Spie-Soc Photo-Optical Instrumentation Engineers, 2001-12) Quiroga Mellado, Juan Antonio; Gómez Pedrero, José Antonio; Martínez Antón, Juan CarlosA method for sensing wavefronts is presented. The method is based on the resolution of the irradiance transport equation, which relates the irradiance distribution and the shape of the wavefront of a light beam propagating along a given direction. The method presents no restrictions in the locations of the measurement planes and incorporates an improved procedure to geometrically correct the acquired images to take into account the effect of ray deflection in the propagation of the irradiance distributions. With the proposed technique, we measure the wavefront at the exit pupil of a progressive addition lens and find good agreement with an alternative deflectometric method. PublicationRecent advances in automatic demodulation of single fringe patterns(Springer Verlag Berlin, 2006) Quiroga Mellado, Juan Antonio; Crespo Vázquez, Daniel; Gómez Pedrero, José Antonio; Martínez Antón, Juan Carlos PublicationImproved method for isochromatic demodulation by RGB calibration(The Optical Society of America, 2002-06-10) Quiroga Mellado, Juan Antonio; García Botella, Ángel; Gómez Pedrero, José AntonioThe red-blue-green (RGB) calibration technique consists in constructing an a priori calibration table of the isochromatic retardation versus the triplet of RGB values obtained with a RGB CCD camera. In this way a lookup table (LUT) is built in which the entry is the corresponding RGB triplet and the output is the given retardation. This calibration (a radiometric quantity) depends on the geometric and chromatic parameters of the setup. Once the calibration is performed, the isochromatic retardation at a given point of the sample is computed as the one that minimizes the Euclidean distance between the measured RGB triplet and the triplets stored in the LUT. We present an enhanced RGB calibration algorithm for isochromatic fringe pattern demodulation. We have improved the standard demodulation algorithm used in RGB calibration by changing the Euclidean cost function to a regularized one in which the fidelity term corresponds to the Euclidean distance between RGB triplets; the regularizing term forces piecewise continuity for the isochromatic retardation. Additionally we have implemented a selective search in the RGB calibration LUT. We have tested the algorithm with simulated as well as real photoelastic data with good results. PublicationIncremental PCA algorithm for fringe pattern demodulation(The Optical Society Of America, 2022-04-11) Gómez Pedrero, José Antonio; Estrada, Julio César; Alonso Fernández, José; Quiroga Mellado, Juan Antonio; Vargas Balbuena, JavierThis work proposes a new algorithm for demodulating fringe patterns using principal component analysis (PCA). The algorithm is based on the incremental implantation of the singular value decomposition (SVD) technique for computing the principal values associated with a set of fringe patterns. Instead of processing an entire set of interferograms, the proposed algorithm proceeds in an incremental way, processing sequentially one (as minimum) interferogram at a given time. The advantages of this procedure are twofold. Firstly, it is not necessary to store the whole set of images in memory, and, secondly, by computing a phase quality parameter, it is possible to determine the minimum number of images necessary to accurately demodulate a given set of interferograms. The proposed algorithm has been tested for synthetic and experimental in ter ferograms showing a good performance. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement PublicationOptical method for the surface topographic characterization of Fresnel lenses(SPIE--The International Society for Optical Engineering, 2011) Martínez Antón, Juan Carlos; Gómez Pedrero, José Antonio; Alonso Fernández, José; Quiroga Mellado, Juan AntonioFresnel lenses and other faceted or micro-optic devices are increasingly used in multiple applications like solar light concentrators and illumination devices. As applications are more exigent this characterization is of increasing importance. We present a technique to characterize the surface topography of optical surfaces. It is especially well adapted to Fresnel lenses where abrupt surface slopes are usually difficult to handle in conventional techniques. The method is based on a new photometric strategy able to codify the height information in terms of optical absorption in a liquid. A detailed topographic map is simple to acquire by capturing images of the surface. Some experimental results are presented. A single pixel height resolution of similar to 0.1 mu m is achieved for a height range of similar to 50 mu m. A surface slope analysis is also made achieving a resolution of similar to +/- 0.15 degrees. PublicationTemporal phase evaluation by Fourier analysis of fringe patterns with spatial carrier(Taylor and Francis Ltd., 2001-11-20) Quiroga Mellado, Juan Antonio; Gómez Pedrero, José AntonioA new method is presented for the temporal evaluation of fringe patterns with spatial carrier. The proposed technique involves recording the irradiance fluctuations obtained when a linear variation of the set-up sensitivity is introduced. In this condition, the use of a spatial carrier introduces a linear temporal carrier frequency. In this way, Fourier analysis can be performed to obtain the phase and, finally, the quantity to be measured. The optimum conditions for the sensitivity variation have been studied in order to minimize the errors associated with the Fourier analysis. The technique has been applied to measure the distribution of ray deflections on the surface of two ophthalmic lenses using a deflectometric set-up. PublicationA isotropic n-dimensional quadrature transform and its applications in fringe pattern processing(SPIE--The International Society for Optical Engineering, 2003) Quiroga Mellado, Juan Antonio; Servín Guirado, Manuel; Marroquín Zaleta, José Luis; Gómez Pedrero, José AntonioIn fringe pattern processing, quadrature operators are useful to obtain the corresponding modulating phase. In the case that a carrier exists (spatial or temporal), there are good methods for phase demodulation as Fourier analysis and asynchronous methods, for example. However, if there is no carrier or is to low, robust demodulation from a single image is a difficult task. In this work we present some recent advances in the processing of single fringe patterns with closed fringes based in a isotropic n-dimensional quadrature transform. In particular we address several problems related with the application of this quadrature operator. One of these problems is the Fringe direction, its role in the demodulation process is discussed and a practical method for its computation is presented. Fringe pattern normalization is also an important subject in the demodulation process from a singe image, taking this into account we present a technique for isotropic fringe pattern normalization based in the n-dimensional quadrature transform. All these techniques together configure a robust method for automatic demodulation of single fringe patterns. The performance and limitations of the method are discussed and illustrated by experimental results. PublicationSteerable spatial phase shifting applied to single-image closed-fringe interferograms(The Optical Society of America, 2009-04-20) Quiroga Mellado, Juan Antonio; Servín Guirado, Manuel; Estrada, Julio César; Gómez Pedrero, José AntonioIt is well known that spatial phase shifting interferometry (SPSI) may be used to demodulate two-dimensional (2D) spatial-carrier-interfrograms. In these crises the application of SPSI is straightforward because the modulating phase is a monotonic increasing function of space. However, this is not true when we apply SPSI to demodulate a single-image interferogram containing closed fringes. This is because using these algorithms, one would obtain a wrongly demodulated monotonic phase all over the 2D space. We present a technique to overcome this drawback and to allow any SPSI algorithm to be used as a single-image fringe pattern demodulator containing closed fringes. We make use of the 2D spatial orientation direction of the fringes to steer (orient) the one-dimensional SPSI algorithm in order to correctly demodulate the nonmonotonic 2D phase all over the interferogram. PublicationStructured light-based NDT techniques of interest in the aerospace industry(The British Institute of Non-Destructive Testing, 2003-04) Quiroga Mellado, Juan Antonio; Martínez Antón, Juan Carlos; Gómez Pedrero, José AntonioStructured light techniques (Moiré, projected fringes and other pattern projection techniques) have been used for many years in the aerospace and other industries for external defect location and characterization, 3D shape, deformation measurements and the like. The application of digital image processing methods to the images generated by these techniques has made possible the realization of fast and automatic systems for quantitative NDT measurements. This work is divided in two parts. First, the principal approaches to structured light-based NDT are reviewed, presenting the basis, performance characteristics as well as their expected ranges and resolutions. The second part concentrates on the digital image processing techniques of interest in the field of structured light-based NDT. As the images produced by these techniques are often in the form of phase-modulated fringe patterns, the branch of image processing that deal with this kind of images is denominated fringe pattern processing. Among the many existing fringe pattern processing techniques, the paper will concentrate on the phase-shifting methods (spatial and temporal) and the regularization and natural demodulation methods. It will be shown how when acquisition time is not critical, and several phase-shifted images can be acquired, phase-shifting techniques are well-suited for phase demodulation. Related with these techniques is the so-called phase unwrapping problem that will be discussed. Finally, fringe pattern processing techniques are discussed which can be applied in cases when acquisition time or the optical set-up only allows the use of one fringe pattern. In this case the problem of demodulating the phase is ill-posed from a mathematical point of view and special techniques as regularization and the so-called natural demodulation are needed.