Multispectral systems have several applications and there are different possible configurations in which they can be implemented. Different characteristics make them useful, but the basic one is the access to spectral information of a scene or sample with high spatial resolution. In this thesis , the main objective has been the design and implementation of a multispectral system that covers part of the UV, the visible, and part of theIR ranges of the electromagnetic spectrum to be applied to artwork studies.
The main part of the thesis is dedicated to the design, characterization and application of a multispectral system based on
multiplexed illumination using light emitting diodes (LED). This system comprises two modules : Module 1 UV-Vis, with a CCD camera sensitive between 370nm and 930nm , coupled to a source of LEDs with 16 different channels, i.e. 16 wavelengths of emission; and Module 2 IR with an lnGaAs camera with sensitivity between 930nm and 1650nm coupled to an LED source with 7 emission wavelengths. Thus , the complete system covers from 370nm to 1650nm with a total of23 channels obtained with LED illumination.
The system elements were characterized and simulations were performed to assess their performance in the reconstruction of spectral reflectance under ideal conditions , and also under conditions of quantization noise and additive noise. Its performance was evaluated using the formula CIEDE2000 color difference, the mean square error (RMSE) and the
goodness-of-fit coefficient (GFC) . The simulation results showed a good overall system performance, but with better results for module 1 UV -Vis due to the increased amount of LED channels in its spectral range.
Computer programs with their respective graphical interfaces to control the hardware and processing the information provided by the system were implemented. For the spectral reconstruction we employed the method based on direct interpolation using splines , and the methods based on training set of samples with known digital system responses and spectral reflectances: the undetermined pseudo-inverse (PSE -1) and simple pseudo-inverse (PSE). The equipment was evaluated over real samples of the Color Checker Chart CCCR and a series of frescoes patches painted with pigments used in artworks. The results of the metrics CIEDE2000, RMSE and GFC showed that the methods ofthe PSE-1 and PSE have similar performance, with slightly better results for the second one. The interpolation method presented a slightly lower performance, but it has the practical value of not needing training. The results for the PSE method were similar to those obtained through simulation, and proved again that the module 2 IR has lower performance. lt was concluded that overall system performance was good with CIEDE2000 and RMSE average values for the methods based on PSE in the order of 1 unit.
The developed system was applied to artworks in the museum ofPedralbes Monastery in Barcelona, and the churches of Sant Pere in Terrassa. Different images of murals of the chapel of San Miguel in the Monastery of Pedralbes were captured. The evaluation of the system performance for this museum application showed similar performance to the reported one in laboratory. We also captured a painting of large format, oil on wood named: La Virgen de la Leche. For this artwork the modular design and easy movement of the system was used to generate a complete picture by composition from several smaller images. At the churches of Sant Pere, we explored wall paintings dating from the Visigoth (VI-VII) and Romance times (XII -XIII) to assess whether there were features in the paintings that were not evident in the visible range, but in other spectral ranges. Enhancement algorithms were implemented for this task. The results obtained in this thesis demonstrate the potential of the developed multispecral system for obtaining spectral information in the ultraviolet, visible and infrared regions. / Los sistemas multiespectrales tienen la caracteristica principal de proporcionar acceso a informaci6n espectral de una muestra con alta resoluci6n espacial. En esta tesis, como principal objetivo, se ha disefiado e implementado un sistema multiespectral para aplicarlo al estudio de obras de arte. Este sistema comprende dos m6dulos: el m6dulo 1 UV-Vis, con una camara CCD con sensibilidad entre 370nm y930nm, acoplada a una fuente de diodos emisores de luz(LED) con 16 canales diferentes, es decir 16 1ongitudes de onda de emisi6n; yel m6dulo 2 IR, con una camara lnGaAs con sensibilidad entre 930nm y 1650nm, acoplada a una fuente LED con 71ongitudes de onda de emisi6n. Por tanto, el sistema completo abarca desde 370nm a 1650nm con un total de 23 canales. Se caracterizaron Ios elementos del sistema y se han realizado simulaciones para evaluar su rendimiento en la reconstrucci6n de reflectancias espectrales bajo condiciones ideales, condiciones de ruido de cuantificaci6n y aditivo. Su rendimiento se evalu6 empleando la formula de diferencia de color CIEDE2000,el error cuadratico medio (RMSE) y el coeficiente de bondad del ajuste (GFC). Los resultados de las simulaciones mostraron un buen rendimiento general del sistema, aunque con mejores resultados para el m6dulo 1 UV-Vis debido a la mayor cantidad de canales LED en su rango espectral. Paralelamente se implementaron Ios programas computacionales con sus respectivas interfaces graficas necesarias para el control del hardware usado y para el procesamiento de la informaci6n proporcionada por el sistema. Para la reconstrucci6n espectral empleamos un metodo de interpolaci6n directa basado en splines, y Ios metodos de pseudoinversa indeterminada (PSE-l) y pseudoinversa simple (PSE) que necesitan de un entrenamiento con un conjunto de muestras con respuestas digitales del sistema y reflectancias espectrales conocidas. El equipo se evalu6 sobre muestras reales de la carta de colores Color Checker CCCR y sobre un conjunto de pinturas alfresco realizadas con pigmentos comunmente presentas en obras de arte. Los resultados de las metricas CIEDE2000,RMSE yGFC mostraron que Ios metodos de la PSE-1 y PSE tienen desempefios similares,con resultados ligeramente mejores para el segundo metodo. El metodo de interpolaci6n present6 un rendimiento ligeramente menor, aunque tiene el valor practico de no necesitar entrenamiento. Los resultados reales para el metodo del PSE fueron similares a Ios obtenidos mediante simulaci6n, y se mostr6 una vez m as que el m6dulo 2 IR tiene un rendimiento inferior. Se concluy6 que en general el desempefio del sistema era bueno, con valores CIEDE2000 y RMSE promedio para Ios metodos basados en PSE del orden de 1 unidad en ambos casos. El sistema desarrollado fue aplicado a obras de arte en elmuseo de Monasterio de Pedralbes, en Barcelona, y Ias lglesias de Sant Pere, en Terrassa.En el Monasterio de Pedralbes se capturaron diferentes imagenes de pinturas murales de la capilla de San Miguel y se evalu6 el desempefio del sistema para esta aplicaci6n de museo, mostrando un desempeno similar al reportado en las pruebas de laboratorio. Tambien se accedi6 a la obra Virgen de la Leche que es un 61eo en tabla de gran formato. En esta obra se aprovech6 el diseno modular y de facil movimiento del sistema para generar por composici6n una imagen completa a partir de varias imagenes menores.En las iglesias de Sant Pere se exploraron pinturas murales que se estima datan de las epocas visigoda (siglos VI-VII) y romanica (siglos XII-XIII) para evaluar si existian caracteristicas en Ias pinturas que no fueran evidentes en el rango visible y que silo fueran en otros rangos espectrales. Para ello se implementaron algoritmos de realce de la informaci6n. Los resultados obtenidos en esta tesis doctoral ponen de manifiesto las potencialidades del sistema multiespecral desarrollado para la obtenci6n de informaci6n espectral en las regiones ultravioleta, visible e infrarrojo
| Identifer | oai:union.ndltd.org:TDX_UPC/oai:www.tdx.cat:10803/277543 |
| Date | 25 March 2014 |
| Creators | Herrera Ramírez, Jorge A. |
| Contributors | Vilaseca Ricart, Meritxell, Pujol i Ramo, Jaume, Universitat Politècnica de Catalunya. Departament d'Òptica i Optometria |
| Publisher | Universitat Politècnica de Catalunya |
| Source Sets | Universitat Politècnica de Catalunya |
| Language | Spanish |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | 184 p., application/pdf |
| Source | TDX (Tesis Doctorals en Xarxa) |
| Rights | info:eu-repo/semantics/openAccess, L'accés als continguts d'aquesta tesi queda condicionat a l'acceptació de les condicions d'ús establertes per la següent llicència Creative Commons: http://creativecommons.org/licenses/by-sa/3.0/es/ |
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