Spot the Difference

There are many possible uses for this type of technology but one major area is for optical comparators. By taking an input image and displaying it against a reference image any changes between the two can be analysed. For instance, this type of process is currently being applied to quality control of the 'best before' date stamps on food. Small errors in printing can lead to an "8" being mistaken for a "0" for instance. At present, the date stamps have to be checked by eye to make sure they are legible and correct - a tedious process for the operator involved. Using an optical comparator such as that described above, date stamps can be checked automatically for legibility at a rate of 2000 images per second.

The process of comparing a reference image with an incoming image has many other potential applications including monitoring the platforms of underground stations for overcrowding (a common cause of delay for underground trains) and the docking of spacecraft with space stations.

The product is at present at the prototype stage, but the team are looking to mass production. A particular concern is to make the product mechanically robust. "We can make these devices insensitive to thermal and mechanical instabilities" says Tim Wilkinson, "and the setting up tolerances are reasonable, of the order of millimetres rather than microns, which has overcome many of the problems people normally have with optical systems."

For the science behind these devices, please go to the Photonics and Sensors Group web site. For more information, please e-mail Dr Tim Wilkinson -