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What do bruised fruit, crime scenes and the United States of America’s Declaration of Independence have in common? Our understanding of all three areas has been enhanced through the use of hyperspectral imaging.
The University of Strathclyde in Glasgow, Scotland is holding the UK’s second academic conference on Hyperspectral Imaging (HSI 2011) from 16-18 May 2011. The conference will bring together academic and industrial practitioners to share their knowledge of innovation of hyperspectral imaging technology.
Accepted papers will describe in detail critical implementation issues and the latest applications of hyperspectral imaging technology such as microscopy and fluorescence imaging; data processing techniques and environmental monitoring.
The conference will feature oral and poster sessions, a tutorial programme, demo presentations, invited speakers and an exhibition space. HSI 2011 offers an exciting opportunity to learn more about this radical and groundbreaking technology.
Increased relevance of hyperspectral imaging
Hyperspectral imaging cameras can determine if objects being viewed are hot or cold, wet or dry, their fat and sugar content and the presence of certain chemical elements. Therefore, it has a diverse range of applications in areas such as pharmaceuticals, food technology and homeland security. Whereas conventional colour cameras capture light in just three spectral windows, hyperspectral cameras have the ability to capture an entire section of the electromagnetic spectrum at every pixel.
There are a number of different techniques for hyperspectral image capture including push broom and tunable filter. New capture techniques are also being developed, some of which will be showcased at HSI 2011.
In the past hyperspectral cameras were bulky and expensive and so were mostly used by the military for remote sensing and surveillance applications. Today’s hyperspectral cameras are almost as small as a standard video camera. These latest developments in camera technology are moving hyperspectral imaging from the aircraft and the military surveillance station to the laboratory and the factory.
Applications of hyperspectral imaging
The astonishing range of industries that have laboratories and factories which use hyperspectral imaging emphasises the relevance and importance of the growth of this technology. Food technology specialists, Campden BRI are using hyperspectral imaging in the inspection of food to measure everything from the freshness of fish to the tenderness of beef to the salt and starch content of oven ready chips.
Professor Sam Millar is Campden BRI’s Director of Cereals and Cereal Processing and was a speaker at last year’s HSI 2010 conference. He believes: “Hyperspectral imaging is an important new technology informing us of the structure, composition and quality of the food we are eating today.” In agriculture, hyperspectral imaging can be used to determine if soft fruit, such as apples, is bruised below the surface and likely to have a short shelf life. Similarly, the technology can be used in Biomedical Engineering to reveal the extent of burns and bruises below the skin of the human body.
As with any camera, it is possible to attach a microscope to a hyperspectral imaging camera and view the world at different magnifications. Such techniques may be used to observe real time lifetime fluorescence. This has numerous applications in bioscience.
Hyperspectral imaging has many other uses for medical science. For instance, in a research project sponsored by one of the world’s leading pharmaceutical companies, Astra Zenica, the University of Strathclyde is currently investigating the use of hyperspectral imaging to distinguish between different types of polymers. The technology can also be used to discriminate between different types of pills which look identical to the naked eye.
Professor Clive Wilson from Bio-Images Research, and a speaker at HSI 2010, declares: “Hyperspectral Imaging has the potential to revolutionise the interpretation of image data in the pharmaceutical industry.”
Hyperspectral imaging is playing an increasingly important role in forensic technologies. The detection of fingerprints at crime scenes and the analysis of inks to detect forged documents can both be performed using the technology.
Hyperspectral imaging has even helped to bring new insights to old documents. The Library of Congress’ Preservation Research and Testing Division used hyperspectral imaging on discarded drafts of the American Declaration of Independence in order to uncover crossed out words. This research has helped to give modern historians a deeper understanding into Thomas Jefferson’s thought process.
Hyperspectral imaging is also being used to provide solutions to problems for which imaging solutions have not previously been considered, such as using a hyperspectral imaging cameras to inform a paper mill’s feedback control system of the correct amount of heat required to dry paper.
Hyperspectral imaging tools
The optical and spectral characteristics of a hyperspectral imaging system are largely determined by the application requirements. However, all systems have the same three basic components in common: a means to image the object, a means to provide both spectral and spatial resolution and a means of detection.
The classic, though inefficient, method to make spectral images has been to sequentially take the same ‘photograph’ through a series of wavelength bandpass filters and construct an image spectral cube data set – X-position versus Y-position versus wavelength.
Traditional methods of wavelength selection have used dielectric optical bandpass filters but the use of either an Acousto-Optic Tunable Filter or a Liquid Crystal Tunable Filter have permitted electronic sweeping of the spectral bandpass.
In each of these cases, an image is collected one wavelength after the other and the Field of View of the imaging system is fixed. Filter based methods place a huge burden on the sample and illumination stability as well as being an intensive process in terms of time and computation.
At the very minimum it is necessary to wait until all wavelength images have been recorded. This can take up to hours of measurement time depending upon samples, illumination and integration conditions. Therefore, if an object is moving or is spectrally unstable due to its chemical, physical or physiological characteristics, the integrity of the resulting hyperspectral data cube may seriously be in question.
True spectral imaging requires all of the wavelengths to be recorded simultaneously so a wavelength dispersive system is required. In this case, the Field of View is generated sequentially and the hyperspectral integrity of the data is maintained for each and every measurement, even if the sample dynamics are changing or if the sample is moving.
An image of the Field of View is collected by translating the sample across the slit aperture of the spectrograph in a method known as push broom acquisition. Thus the wavelength or spectral data are measured simultaneously and the image or Field of View is generated sequentially.
There is essentially no delay in acquisition. This guarantees the integrity of spectral data and ratios. The spectral image builds up in real time and can be stopped at any time, which means that spectral snapshots are possible without the need to take the full image field of view.
In principle, the data collected in either the filter or push broom approach are complementary to each other in terms of the basic concept.
University of Strathclyde’s HSI Centre
Generally, end users in laboratories or factories only need a standalone turnkey system to solve a particular problem, such as whether a pharmaceutical product is counterfeit or the extent of bruising in the fruit. Such systems require new and state of the art signal processing algorithms to reach correct decisions in real time.
The University of Strathclyde, in partnership with Gilden Photonics, is opening the UK’s first Hyperspectral Imaging Centre later this year. The Centre will help to deliver these signal processing algorithms. It will provide an interface with industry and the public sector to advise and supply turnkey solutions to specific imaging problems.
The Hyperspectral Imaging Centre is an excellent example of knowledge exchange between academia and industry as fundamental university research will be transferred to usable end products.
Dr John Gilchrist, Managing Director of Gilden Photonics and HSI 2010 speaker, says: “Hyperspectral imaging is fast becoming the method of choice when one wants to evaluate a wide range of industrial process and environmental problems. The advantages of being able to determine chemical composition, size and distribution are invaluable.
“We are delighted to be sponsoring the new Hyperspectral Imaging Centre and see HSI 2011 as a key tool in promoting the techniques and, more importantly, the signal processing requirements that can vary from application to application.
Published: 10th Mar 2011 in AWE International
