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Comparison between object and image plane cross-correlation for stereoscopic PIV in the presence of pixel locking

Comparison between object and image plane cross-correlation for stereoscopic PIV in the presence of pixel locking
Comparison between object and image plane cross-correlation for stereoscopic PIV in the presence of pixel locking
Pixel locking in stereoscopic particle image velocimetry (SPIV) is often overlooked, albeit the existence of studies demonstrating an influence on turbulent statistics. Such a bias error occurs when the seeding particles have an image diameter in the range of 1-2 pixels. Together with the advent of superior cameras and more powerful lasers, new image-processing techniques enable large field of views to be examined. Under such circumstances, defocusing is not an option and due to the small nature of the particle image diameter, pixel locking is inherent in the data. This study analyses the contrast between object plane-based and image plane-based approach for cross-correlation in the presence of pixel locking in SPIV. By combining experimental data and synthetic images, the sensitivity of pixel locking on single-point statistics is quantified and a protocol is proposed to tackle such an increasingly prevalent condition. A consequence of pixel locking is the occurrence of Moire fringes, whose intensity is observed to be enhanced in the presence of particles with an image diameter less than 2 pixels. Such high frequency artifacts are not only receptive to the fill factor of the sensor but also depend on the residual error of the interpolation from image plane to the object plane. This study discusses the origins of Moire fringes in SPIV and provides a method to mitigate these based on the type of cross-correlation used.
0723-4864
Jankee, Girish, K.
ae50bc76-d591-4ec8-9a60-421b2336f5a7
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Jankee, Girish, K.
ae50bc76-d591-4ec8-9a60-421b2336f5a7
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Jankee, Girish, K. and Ganapathisubramani, Bharathram (2020) Comparison between object and image plane cross-correlation for stereoscopic PIV in the presence of pixel locking. Experiments in Fluids, 61 (3), [89]. (doi:10.1007/s00348-020-2916-x).

Record type: Article

Abstract

Pixel locking in stereoscopic particle image velocimetry (SPIV) is often overlooked, albeit the existence of studies demonstrating an influence on turbulent statistics. Such a bias error occurs when the seeding particles have an image diameter in the range of 1-2 pixels. Together with the advent of superior cameras and more powerful lasers, new image-processing techniques enable large field of views to be examined. Under such circumstances, defocusing is not an option and due to the small nature of the particle image diameter, pixel locking is inherent in the data. This study analyses the contrast between object plane-based and image plane-based approach for cross-correlation in the presence of pixel locking in SPIV. By combining experimental data and synthetic images, the sensitivity of pixel locking on single-point statistics is quantified and a protocol is proposed to tackle such an increasingly prevalent condition. A consequence of pixel locking is the occurrence of Moire fringes, whose intensity is observed to be enhanced in the presence of particles with an image diameter less than 2 pixels. Such high frequency artifacts are not only receptive to the fill factor of the sensor but also depend on the residual error of the interpolation from image plane to the object plane. This study discusses the origins of Moire fringes in SPIV and provides a method to mitigate these based on the type of cross-correlation used.

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Accepted/In Press date: 11 February 2020
e-pub ahead of print date: 3 March 2020

Identifiers

Local EPrints ID: 438384
URI: http://eprints.soton.ac.uk/id/eprint/438384
ISSN: 0723-4864
PURE UUID: d9bd78dc-3e50-4013-8eae-132f90881739
ORCID for Girish, K. Jankee: ORCID iD orcid.org/0000-0002-9178-1070
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

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Date deposited: 09 Mar 2020 17:30
Last modified: 28 Apr 2022 05:13

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Author: Girish, K. Jankee ORCID iD

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