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5D HSI Measures Shape and Spectral Characteristics as a Function of Time

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JENA, Germany, Aug. 29, 2018 — A 5D hyperspectral imaging system (HSI) — so-called because it captures multiple wavelengths of light plus spatial coordinates as a function of time — has been developed by a team at Friedrich Schiller University Jena and the Fraunhofer Institute for Applied Optics and Precision Engineering, in collaboration with a group from Ilmenau University of Technology.

5D Hyperspectral Imaging System, Fraunhofer Institute et al.
The new hyperspectral imager contains two cameras and measures just 425 × 200 mm. With further miniaturization, it could be incorporated into smartphones for personal use. Courtesy of Stefan Heist, Friedrich Schiller University/Fraunhofer IOF.

The compact system operates in the visible-to-NIR spectral range and provides high degrees of spatial and spectral resolution, depth accuracy, and high frame rates. It could be used for a variety of applications, including optical-based sorting of products and identity authentication.

The researchers have created a prototype system with a footprint of 200 × 425 mm (about the size of a laptop). The prototype uses two hyperspectral snapshot cameras to form 3D images and obtain depth information. By identifying specific points on the object’s surface that are present in both camera views, the system can create a complete set of data points in space for the object. However, this approach only works if the object has enough texture or structure to unambiguously identify points.

To capture both spectral information and the surface shape of objects that may not be highly texturized or structured, the researchers incorporated a custom high-speed projector into their system. Through mechanical projection, a series of aperiodic light patterns are created and used to artificially texture the object surface. This allows robust and accurate 3D reconstruction of the surface. The spectral information obtained by the different channels of the hyperspectral cameras is then mapped onto these points.

“Our earlier development of a system projecting aperiodic patterns by a rotating wheel made it possible to project pattern sequences at potentially very high frame rates and outside the visible spectral range,” said research team leader Stefan Heist. "New hyperspectral snapshot cameras were also an important component because they allow spatially and spectrally resolved information to be captured in a single image, without any scanning."

The researchers characterized the prototype by analyzing the spectral behavior of the cameras and the 3D performance of the entire system. They showed that the system could capture visible-to-NIR 5D images as fast as 17 frames per second.

Because the new imaging system does not require contact with the object, it could be used to record valuable artifacts or artwork. To demonstrate, the researchers used it to digitally document a historical relief globe from 1885.

The team also created NIR 5D models of a person’s hand, showing that the system could be used as a simple way to detect veins. The imager could also be used for agricultural applications, which the researchers showed by using it to capture the 5D change in reflection spectrum of citrus plant leaves as they were absorbing water.

The researchers plan to optimize their prototype by using hyperspectral cameras with a higher signal-to-noise ratio or that exhibit less crosstalk between the different spectral channels. Ideally, the system would be tailored to specific applications. For example, cameras with high imaging rates could be used to analyze dynamically changing object properties, while sensors with high resolution in the IR wavelength could be used for detecting chemical leaks. With further miniaturization, the imager could enable smartphone-based inspection of fruit ripeness or personal medical monitoring.

The research was published in Optics Express, a publication of OSA, The Optical Society (doi: 10.1364/OE.26.023366).
Aug 2018
hyperspectral imaging
Methods for identifying and mapping materials through spectroscopic remote sensing. Also called imaging spectroscopy; ultraspectral imaging.
Research & TechnologyeducationEuropeimagingopticsspectroscopycamerasinfrared camerashyperspectral imagingagricultureBiophotonicsConsumermedicalindustrialFraunhofer Institute for Applied Optics and Precision EngineeringEuro News

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