Recovering data from noisy fringe patterns from a portable digital speckle pattern interferometer for in-situ inspection of a painting hanging on the wall
Authors: Memmolo P., Arena G., Paturzo M., Fatigati G., Fatigati G., Grilli M., Pezzati L., Ferraro P.
Autors Affiliation: Ctr Adv Biomat, I-80125 Naples, Italy; CNR, Inst E Caianiello, I-80078 Pozzuoli, Italy; Univ Suor Orsola Benincasa, I-80135 Naples, Italy; Ist Tecn Ind A Righi, I-80125 Naples, Italy; CNR, Natl Opt Inst, Florence, Italy; INNOVA SCARL, Ctr Sviluppo & Trasferimento Innovaz Nel Settore, I-80078 Pozzuoli, Italy
Abstract: We report on a method for recovering data from a simple portable Digital Speckle Pattern Interferometer intended for utilization outside of laboratory conditions, without anti-vibration devices. We used the system for monitoring the structural behavior of a painting on wood, hanging on a wall. In such a situation, fringes, produced by the object displacements, were affected by random distortions caused by environment noise. However a satisfactory number of undistorted, or barely distorted, fringe patterns were found and utilized for processing.
We performed fast continuous acquisitions of consecutive interferograms, picking usable fringe patterns out of a large amount of recorded frames. This is the crucial task in the measurement procedure. For this purpose we developed a software routine, based on jointly analysis of both spectral content and fringe image sharpne ss, as selection rule. From the selected frames, by using a simple approach based on Hilbert Transform and Phase Unwrapping, via MAx-flow (PUMA) algorithm, we were able to evaluate the painting whole structure deformations, caused by environmental thermohygrometric fluctuations.
KeyWords: Artwork diagnostics; DSPI; Holography; Interferometry; NDT; Wooden paintings