HYPERSPECTRAL IMAGING Super spectral in sight
Optical design is crucial in enabling wider adoption of hyperspectral imaging, finds Andy Extance
Te spectroscopic signature resulting
from the toxin’s chemical makeup is visible to hyperspectral imaging used for quality control in processing, Pust added. But bringing hyperspectral imaging into wider use is challenging for optical technology. ‘You measure at least in 2D with good spatial resolution,’ Pust said. ‘You also want to measure spectra at high fidelity and good resolution. Spatial spectral measurement has challenges.’ Such optical demands have slowed
T
he ability to spot poisonous food visually sounds so miraculous it’s little wonder that it’s not part of our
natural eyesight. Yet it is a possibility offered by hyperspectral imaging, and judging food quality is perhaps the most striking use driving this technology’s adoption. Tat’s thanks to chemical information
beyond the visible spectrum, explained Oliver Pust, vice president of sales and marketing at Danish firm Delta Optical Tin Film. ‘If you have nuts on the conveyor belt, and one nut has a toxin, it can spoil one tonne of produce,’ he said.
hyperspectral imaging’s growth, according to Boris Lange, manager of imaging Europe at Edmund Optics. Te technology combines a two dimensional image made up with a third dimension comprising pixels spanning many wavelengths containing spectroscopic chemical information. Together, these measurements build a hyperspectral imaging data cube. Te various approaches that can produce such a data cube each have their own challenges. Pushbroom systems continuously capture spectra across a single line at the same time, often being fixed while objects move past on a conveyor belt. Whiskbroom captures spectra as a sensor whisks from the top to the bottom of an image, before then moving horizontally and back to the top. By contrast, snapshot captures a single image at once.
Across these approaches, new technology helps hyperspectral imaging grow. Transmission and wavelength correction
are significant challenges in each of these data collection approaches, Lange explained. Te optics must span very broad colour ranges, for example from 470 to 900nm or 1,100 to 1,650nm, but perform consistently at each wavelength, so that the data cube is built up evenly. Tis is not typically possible with a single glass lens – but an imaging lens assembly for a hyperspectral imaging camera might contain up to ten individual lenses. ‘If you want to correct the lens over a
wide waveband range, the optical designer needs to use a lot of different materials, and combine them. Tis drives cost, because there might be more exotic glass materials.’
‘Optical design benefits can be simplified by clever use of different optical materials and combination of refractive and reflective components’
RGB image of nuts before and after classification as ‘good’ and ‘bad’, using Specim’s FX17 camera 14 IMAGING AND MACHINE VISION EUROPE OCTOBER/NOVEMBER 2020 @imveurope |
www.imveurope.com
Specim
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