Automatic Frames Extraction and Visualization From Noisy Fringe Sequences for Data Recovering in a Portable Digital Speckle Pattern Interferometer for NDI

Abstract

We report on a method for recovering data from a simple portable Digital Speckle Pattern Interferometer, we used for monitoring structural behavior of a painting on wood, hanging on a wall, outside of laboratory conditions, without anti-vibration devices. In such a situation, fringes produced by the object displacements were affected by unpredictable distortions caused by environment vibrations. However, an sufficient number of suitable, i.e., undistorted or barely distorted, fringe patterns usable for processing was found. We performed multiple acquisitions at a frame rate as high as possible. The main task was picking out usable interferograms from large amount of frames. We developed a PC-based method based on jointly analysis of spectral content and fringe image sharpness as selection rules. The selected frames were utilized for off-line processing by using an approach based on Hilbert Transform and Phase Unwrapping via MAx-flow (PUMA) algorithm. We obtained a collection of displacement-maps, that allowed for evaluating the whole structure deformations, caused by environmental thermo-hygrometric fluctuations.

Defect Isolation from Whole to Local Field Separation in Complex Interferometry Fringe Patterns through Development of Weighted Least-Squares Algorithm

“…Schematic representation of the DHSPI optical geometry satisfying fundamental holographic interferometry operation principle. The collected interferometric data provides hundreds of images depending on the initial excitation and the conservation state of the examined artwork [13]. The complex interferometry field is combined by the displacement due to the induced excitation and the impact of subsurface defects that are displaced with their own dynamic.…”

“…Digital holographic speckle pattern interferometry (DHSPI) provides a non-destructive non contacting remote operation portable prototype especially developed for cultural heritage applications, which signifies that the out-of-plane deformation common in expanding processes as artworks respond to the daily fluctuations of the environment. Coherent interferometry enables the structural diagnosis many advantages over the current practices as non-contact non-destructive full-field imaging with high resolution inherently quantitative data visualizing all sorts of different defects, in which they profile the depth from the surface to many tenths of a millimeter deep [12,13]. The plethora of advantages upgraded the method as the most promising one in cultural heritage structural diagnosis, creating a variety of techniques [14].…”

A Portable Compact System for Laser Speckle Correlation Imaging of Artworks Using Projected Speckle Pattern

“…The applications include the structural evaluation of restoration processes (such as consolidation, cleaning or protective treatments), the detection of alterations induced by aging (such as cracks or subsurface defects) and the real-time monitoring of deformation due to microclimate variations [ 14 , 15 , 16 , 17 ]. As the nature of many artifacts makes their transport to a dedicated facility not possible, many research efforts are addressing the problem of in situ diagnostics with portable speckle-based techniques [ 14 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ].…”

Strategies for reducing speckle noise in digital holography

“…DH has the unique property of retrieving the entire complex wavefront of a recorded object, thereby allowing the measurement and manipulation of both amplitude and phase information 11 . The incredible technological development of digital sensors and optical elements has made DH the primary approach in several research fields, such as quantitative phase 3D imaging of biological samples 12 – 17 , microfluidics 18 , 19 , optofluidics 20 , 21 , 3D particle tracking 22 , 23 , 3D optical display 24 – 26 , homeland security 27 , optical security and encryption 28 , cultural heritage 29 , and compressive holographic imaging 30 , 31 .…”