Schlieren unwrapped: distortion correction in digital focusing schlieren

Benjamin D. Buckner; Drew L'Esperance

doi:10.1117/12.2528081

3 September 2019 Schlieren unwrapped: distortion correction in digital focusing schlieren

Proceedings Volume 11102, Applied Optical Metrology III; 111020R (2019) https://doi.org/10.1117/12.2528081
Event: SPIE Optical Engineering + Applications, 2019, San Diego, California, United States

Abstract

Digital focusing schlieren relies on accurate mapping between a camera and a digital modulator or display system. Our early development of the technology was challenged by higher-order distortions in the optical systems. A simple perspective transform was adequate for lower-power lenses and smaller fields of view, but for wide fields and for highly sensitive configurations such as dark-field schlieren, correction terms were necessary. The Brown-Conrady model fitting implemented by OpenCV offered little improvement, so we developed a new distortion correction method that empirically optimizes the schlieren filter performance and constructs a map with phase unwrapping techniques borrowed from interferometry. This approach allows operation even with wider-angle lenses and finally makes dark-field schlieren practical. It also appears to improve the resilience of the grid generation with lower resolution camera systems, which is important for implementation in high speed schlieren imaging.

Conference Presentation

Citation Download Citation

Benjamin D. Buckner and Drew L'Esperance "Schlieren unwrapped: distortion correction in digital focusing schlieren", Proc. SPIE 11102, Applied Optical Metrology III, 111020R (3 September 2019); https://doi.org/10.1117/12.2528081

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