Determinació del factor de cobertura en teixits de calada per processament de la imatge digital i espectroscòpia de reflexió

In this thesis we applied, in a complementary way, techniques of digital image processing and reflectance spectroscopy to perform cover factor (CF) measurements in monochrome openwork fabrics. To evaluate the results provided by both techniques, we used the average CF obtained by a group of 18 expert observers as a reference. IMAGE PROCESSING PART: We developed a new, automatic and objective method for measuring both total and partial CF, and the width of the threads, from the digital image of the fabric. Two algorithms were developed for total and partial CF determinations. The image processing technique used to measure the total CF was the segmentation of the holes from the fabric threads. Conventional methods of segmentation did not lead to similar results than those of the total visual CF. Therefore, we designed a new algorithm (MSSQ) to measure the total CF of fabrics, independently of their degree of coverage. All the CF obtained in 81 typified textile samples were correlated with the CF obtained visually. The best fit to the Stevens' psychophysical law was achieved with the method MSSQ. These results were also consistent with the construction parameters of fabrics. The determination of partial CF in the warp and weft directions was performed by filtering in the Fourier space the warp and weft threads of the sample. For the design of these filters we applied the Radon transform to the power spectrum of the image of the fabric, in order to determine the direction of the warp and weft harmonics. The values of partial CF were consistent with the parameters that characterize the threads and were logical, expected and confirmed the robustness of the method. The values of the diameters of the threads were also consistent with the parameters of the yarn manufacturing and with the manual measurement performed on the image of the same fabric. This method is easily implementable in a laboratory of textile analysis. REFLECTANCE PART: We modelled the reflectance of a flat layer of fabric arranged on a support of known reflectance using the Kubelka-Munk theory. For this purpose we assumed that the optical behaviour of a layer of fabric could be determined by the superposition of two ideal elements: a neutral density filter with no thickness and with different values of transmittance depending on both the direction of the beam (input or output) and whether the beam passes through the covered part of the yarns or through the holes, plus a uniform and homogeneous layer of a material that meets the assumptions of the theory of Kubelka-Munk. The final model contained CF as a parameter. For a set of different samples of fabrics, the integrated spectral reflectance of a stack of increasing number of layers was experimentally measured with a spectroradiometer, up to stabilize the measure. The experimental reflectances were introduced in the generalized model to calculate the values of the parameters involved, particularly the CF. We solved the resulting system of 101 ¿ (m - 1) equations using the least squares method, where m is the total number of stacked layers of fabric, with 103 unknowns. This yielded a couple of estimates of CF. We established correlations between the measured CF (obtained as the solution of these equations) and the visual CF and analyzed the effect of perturbations in the reflectance measurements to explain the discrepancies between these two estimates of CF. Even if we observed problems of precision in one of the estimates and inaccuracy in the other, arising from an unknown parameter in the model, the intervention of the CF in the described model has been proven.Postprint (published version

Psychophysical Validation of a Digital Method to Assess Ill-Defined Visual Boundaries: An Example with Fabric Openness Factor

Fabric openness factor (OF) is the fraction of the web area that is uncovered by yarns. OF is a critical feature regarding the end-use performance of the fabric and should be accurately assessed. However, digital OF estimates yielded by image binarization algorithms differ among them depending on the criteria used, mainly due to ill-defined boundaries, thus precluding a straightforward assessment of the actual fabric OF value. Lacking any standard to compare actual OF values with measured OF values, we addressed the validation procedure of the digital assessment method from visual OF estimates. OF of 81 distinct fabric samples was evaluated from digital images by a panel of 18 observers using visual binarization technique. Following the psychophysical models of Fechner and Stevens, these visual estimates were correlated with digital estimates yielded by several binarization algorithms. Stevens’ psychophysical model and an automatic binarization algorithm developed by us scored the highest correlation.Preprin

Mesura automàtica i manual del factor de cobertura d’un teixit mitjançant processat digital de la imatge

Postprint (published version

Desenvolupament de nou material docent basat en eines TIC per a la realització de pràctiques relacionades amb l’òptica fisiològica

L’òptica fisiològica és la matèria que estudia el procés visual des d’un punt de vista fonamentalment òptic. S’encarrega de l’estudi de l’ull com a sistema òptic i receptor d’energia radiant, així com de les característiques de la visió binocular. És de fonamental importància en el Grau en Òptica i Optometria, on l’estudiant assoleix i integra les competències bàsiques necessàries per a desenvolupar la seva futura professió, i te un paper significatiu en el Màster d’Optometria i Ciències de la Visió, on l’òptic-optometrista amplia i reforça els seus coneixements. També s’estudia des d’un punt de vista més tècnic i aplicat en el Master in Photonics. Les assignatures relacionades amb l’òptica fisiològica incorporen pràctiques en les que s’avalua la resposta d’un observador a diversos estímuls, mitjançant tècniques psicofísiques de mesura. Gràcies a les recents innovacions tecnològiques, en els laboratoris de recerca més avançats i en algunes universitats espanyoles (com la de València i d’Alacant, les quals han visitat els professors implicats en aquest projecte), la presentació d’estímuls es realitza en monitors d’ordinador calibrats i d’elevada resolució, la qual cosa permet prescindir en gran mesura de muntatges experimentals generalment complexes que s’han utilitzat fins l’actualitat. És per aquest motiu que el principal objectiu del present projecte consisteix en elaborar nou programari específic adaptat a les noves tecnologies que permeti la realització de pràctiques relacionades amb l’òptica fisiològica mitjançant la utilització d’eines TIC, podent així millorar alguns dels muntatges experimentals que s’utilitzaven fins al moment a la Facultat d’Òptica i Optometria de Terrassa (FOOT). El desenvolupament d’aquest material ha permès millorar l’aprenentatge de continguts i habilitats, i per tant de competències específiques i transversals dels estudiants, proporcionant més qualitat docent final de les assignatures vinculades a la matèria d’òptica fisiològica.Peer Reviewe

Classe de problemes sobre el tema de l'ull teòric II

Plantejament i resolució de problemes a l'aula sobre ull teòri

6. Ametropies esfèriques II

2010/201