Recently, researchers in Jena, Germany, have developed a compact imaging system that can measure the shape and light reflection characteristics of objects with high speed and high precision. Because it can capture multiple wavelengths of light, plus spatial coordinates as a function of time, this 5D hyperspectral imaging system can be used in a variety of applications, including optical-based product classification and identification in airport security zones. Through further miniaturization, the imager can implement smartphone-based fruit ripening or personal medical monitoring.
More importantly, Stefan Heist, head of the research team at the Fraunhofer Institute for Applied Optics and Precision Engineering at Friedrich Schiller-Jena University in Germany, says "because our imaging system does not need to be in contact with objects, it Can be used to record artifacts or artworks of historical value." He added that this can be used to create detailed and accurate digital archives while also studying the material composition of objects.
The 5D hyperspectral imager includes two cameras measuring only 425mm x 200mm and can be integrated into a smartphone for personal use with further miniaturization.
Hyperspectral imagers can detect dozens to hundreds of colors or wavelengths instead of the three colors detected by ordinary cameras. Each pixel of a conventional hyperspectral image contains a wavelength dependent radiation intensity within a particular range associated with the two dimensional coordinates. The new hyperspectral imaging system was developed in collaboration with the Gunther Notni research team at the Technical University of Ilmenau, Germany, and the system advances this imaging method by acquiring additional dimensional information.
In the Optics Express, a journal of the Optical Society of America, the researchers described how each pixel of their new 5D hyperspectral imager contains time, (x, y, z) spatial coordinates, based on the visible to near-infrared portion of the electromagnetic spectrum. Information on the light reflectivity. “The most advanced systems designed to determine the shape of an object and its spectral properties are based on multiple sensors with low accuracy or long measurement times,†Heist said. “In contrast, our approach is in a single, compact system. Combines excellent spatial and spectral resolution with extremely high depth accuracy and high frame rate."
Compact prototype
The researchers created a prototype system that measures only 200mm x 425mm, which is about the size of a laptop. It uses two hyperspectral fast cameras to form a 3D image and obtain depth information. By identifying a specific point on the surface of an object that exists in two camera views, you can create a complete set of data points in the space of that object. However, this method works only if the object has enough texture or structure to clearly identify the point.
To capture spectral information and surface shapes without highly textured or structured objects, researchers have integrated specially developed high-speed projectors into the system. Using a mechanical projection method, a series of non-periodic light patterns artificially form the surface of the target object. And allow surface 3D reconstruction. The spectral information obtained by the different channels of the hyperspectral camera is then mapped to these points.
“A system that we developed early to project aperiodic mode by rotating the wheel makes it possible to project a sequence of patterns outside of the very high frame rate and visible spectral range,†Heist said. “The new hyperspectral fast cameras are also an important part because they allow for the capture of spatial and spectrally resolved information in a single image without any scanning.â€
The researchers described their prototypes by analyzing the spectral behavior of the camera and the 3D performance of the entire system. The results show that visible near-infrared 5D images can be captured at speeds of up to 17 frames per second, significantly faster than other similar systems.
To prove that the prototype is analyzing the utility of culturally significant items, the researchers used the system to digitally record the 1885 historical embossed earth. They also created a near-infrared 5D model of the human hand, which showed that the system could be used as a simple method of detecting veins. The imager can also be used in agricultural production, where researchers use the system to capture 5D changes in the reflectance spectrum of citrus leaves when they absorb water.
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