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Measurement of large, discontinuous displacement from digital images
Author(s) -
Luo Zhilei,
Hu Xu,
Wang Linlin,
Lu Yangxiao
Publication year - 2020
Publication title -
strain
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.477
H-Index - 47
eISSN - 1475-1305
pISSN - 0039-2103
DOI - 10.1111/str.12349
Subject(s) - digital image correlation , subpixel rendering , pixel , discontinuity (linguistics) , mathematics , algorithm , image (mathematics) , norm (philosophy) , differentiable function , displacement (psychology) , computer science , computer vision , mathematical analysis , optics , physics , law , political science , psychology , psychotherapist
Abstract One main limitation of conventional digital image correlation (DIC) methods is their incapacity to treat with large, discontinuous displacements. This paper seeks to resolve this issue using a variational method. Specifically, the objective function is written in a form of L 1 ‐norm instead of L 2 ‐norm for discontinuity preservation. This convex, non‐differentiable objective function is resolved by a proximal gradient method. Then, the entire correlation process is embedded into a multi‐level image pyramid, enabling large displacements to be measured accurately. The proposed method is first validated on images with prescribed small displacements; its performance to treat with discontinuous, large displacements is then examined. The results show that the proposed method exhibits an acceptable performance when measuring some extreme displacements up to 16.5 pixels in a 500 × 500 pixels resolution image. Concerning subpixel accuracy, the errors can be lessened to a very low level with optimised parameters even for a dense correlation at each pixel. Good performance is also demonstrated in forms of noise proof and illumination fluctuation tolerance. Finally, an application is conducted on an experiment concerned with cracking in desiccated soils, in which the proposed method succeeds in tracking the nucleation and propagation processes of multiple cracks.