'A face in the crowd'

(Article Precis, 15/Aug/1998, Issue 2147, Fp37_39)
"Forget powerful digital processors. To match one image with another you need a machine that works with pure light, report Sunny Bains and Justin Mullins"
Sunny Bains and Justin Millins report on new developments in computer image recognition.

Establishing what an image is, or identifying a feature within an image, can be difficult, whether that image is a face, a target on a battlefield, or a tumour in a medical scan. Existing techniques compare individual pixels of a target image with known image pixel types in a variety of ways to identify similarities. However, experts in the field say these methods will not be successful in the long term due to the enormous amount of computation required to process ever-increasing image sizes.

Researchers are instead developing an analogue technique which examines all of an image at the same time. Imagine overlaying target images with known comparison images: if they were the same, the images would overlap exactly. But identifying the differences isn't easy because a target image may be displaced or rotated, etc. If one could compare different images and their differences directly, without having to worry about precise alignment, analysis would be considerably easier.

When two images are optically overlapped and illuminated by laser light, a special form of Fourier analysis can produce a transform that is unique and is not affected by the images' relative positions. Thus, comparing the features of these different Fourier transforms is all that a computer needs to do to perform an image comparison.

Much work has gone into developing methods that can scan images at an appropriate level of quality, involving fast-siwtching lasers, high quality LCDs and special optical sensors that can record the image transforms. Only now have these technologies become advanced enough for this new technique, termed 'optical correlation', to be economically realised. The authors describe various devices made by companies such as Lockheed Martin Astronautics which have the equivalent of several dozen Crays in compute power, yet are no bigger than a shoe box and consume very little energy. Such devices permit the analysis of images for specific patterns in real-time.

Researchers for the companies involved, which so far have targeted military applications such as missile guidance, say they now want to expand into the industrial, commercial and home markets, where the possibilties for advanced medical, industrial, security and other areas such as crime prevention (eg. finger print analysis) and the searching of personal archives are considerable.

Note: In order to comply with copyright law, I have ommited many details from the original article. Thus, for a complete insight into the topic covered here, please either consult your local library for the issue concerned, purchase the relevant issue from your local newsagent, or back-order it from the publishers.

Precised by Ian Mapleson, 16/Aug/1998.