Feature sponsored by Test & measurement Image credit: S-MA-C-H
HISTORICAL TEXTILES IN FOCUS
New approaches to investigate damage due to environmental fluctuation on textile artefacts by image processing
an IDS camera and specially developed software for digital image correlation. “Digital image correlation is an image processing technique that can be used to analyse movements and deformations of objects. For this purpose, high-resolution images of the object's surface are captured and then evaluated with the help of software algorithms to detect changes in the shape, position or size of the object,” explains Patrick Schick, IDS Product marketing manager. In the search for the right camera model for the system, parameters such as interface, sensor and price-performance ratio were the main deciding factors. “For the analysis of the tapestry, extremely high-resolution images with low image noise are required to capture the smallest details.” The USB 3 uEye CP meets these requirements thanks to the particularly light-sensitive IMX183 rolling shutter CMOS sensor from Sony’s STARVIS series. With BSI technology (“back-side illumination”), this sensor ensures outstanding image quality even under difficult lighting conditions. “The camera is thus ideally suited for demanding image evaluations such as this monitoring, which takes place in low light for conservation reasons. The USB3 Vision camera records high-resolution images at a very low frequency over a longer period of time,” adds Schick. For the research project, for example, the
Instrumentation Monthly May 2023
monitoring ran around the clock for a month, with only one image capture per hour. “The Python interface of the IDS peak API allowed us to quickly and easily develop software to parameterise the camera and capture images,” explains Gauvin. The images are then processed with DEFTAC3D, a software developed by the French Pprime Institute specifically for digital image correlation.
This results in full-surface measurement data of the object’s surface based on thousands of 2D or 3D coordinates with very high resolution. The displacement of the image points within the examination period is interpreted as a deformation that is due to a mechanical load or stress on the object. Based on the results, full- field strain maps as well as deformation maps are generated. Full-field strain maps illustrate the
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