— IRIS is more sensitive to colour than the human eye and can easily show doctors the distribution of oxygenated (red) and deoxygenated (cyan) blood in the human retina (Image: Andrew Harvey)
A handheld device sensitive to changes in colour not detectable by the human eye could be used to spot objects hidden by camouflage or foliage.
The Image Replication Imaging Spectrometer (IRIS) system was developed by Andrew Harvey and colleagues at Heriot-Watt University in the UK.
The cells in the human retina that detect coloured light are sensitive to only certain parts of the spectrum red, green or blue. All perceived colours are a mixture of this basic palette of colours. Digital cameras work in a similar way, also using separate red, green and blue filters or sensors.
By contrast, the IRIS system has a greater basic palette, of 32 or more "colours" bands of the light spectrum. It works by dividing an image into 32 separate snapshots, each containing only the light from one of its 32 spectral bands. This allows it to pick out features that blend into one for a human observer. "In a single snapshot we can capture subtle differences in colour that the eye can't," Harvey told New Scientist.
The 32 snapshots are projected onto a detector side by side, allowing the device to analyse them all simultaneously. "Until now this kind of imaging was achieved by looking at the different spectral bands sequentially in time," says Harvey, "this method is much faster." What IRIS sees can be translated into false colour images to allow a human to make use of its abilities.
Two British defence firms, Quinetiq and Selex, are working on handheld versions of the device, Harvey says, which are similar in size to a video camera: "It should be useful in, for example, a situation where they need to know if there are any artificial objects like mines or vehicles hidden in foliage."
IRIS could help reveal what is hidden, "or let soldiers know what needs further investigation", he adds.
The device is also being tested as a medical tool, in collaboration with Andy McNaught at Cheltenham General Hospital in the UK. He is using it to diagnose eye disease by looking at blood flow within the retina. This is because IRIS is sensitive enough to tell the different between oxygenated and deoxygenated blood.
Images like the one to the right can be used to look for problems with retinal blood flow, such as diabetic retinopathy a complication of diabetes that can lead to blindness.