Saving face

日期:2017-11-03 04:59:29 作者:寿绳损 阅读:

By Mark Ward MUG shots can now be stored on the magnetic strip of a credit card, heralding a new phase in electronic ID. Researchers have managed to squeeze digital photographs of faces into a mere 400 bits (50 bytes) of data. Normally it takes tens of thousands of bits, too much for a magnetic strip to store. Chris Solomon and his colleagues in the physics department at the University of Kent have developed a way of creating a unique identifying code for every face by combining images from a library of “universal” faces. To create this library, the researchers produced digitised images of 290 faces, most of them of students. They then mathematically analysed the images to capture their most important features, such as nose shape or eye width. From this information they created another, smaller library of definitive “universal” face types, which they ranked in the order of the degree to which they represent the diversity of features within the population. Faces that represent the largest sector of the population were put at the top of the list, while the least typical ended up at the bottom. To encode the image of somebody’s face the researchers begin with the “average” face—the most representative one. Then other universal faces are overlaid on this first face, emphasising or playing down features such as eyebrows or noses until the image reaches the closest match with the individual’s face. “It’s possible to show that anybody’s face can be produced by an appropriate combination of these faces,” says Solomon. “With a large enough population, it should be possible to re-create any human face efficiently. “The method differs from the Identikit images police use to build up distinguishing features because it builds up images using whole faces, rather than separate facial sections. The faces in the library are numbered, and the unique combination needed to recreate the face of a person defines their “facial PIN number”. Solomon says it takes between 50 and 100 faces to match an individual’s face adequately. This combination of numbers easily fits into 50 bytes and can be recorded on the kind of magnetic strips used on credit cards. One of the tracks on these strips is largely unused and has 65 bytes of space in it. By contrast, the widely used JPEG image compression standard leads to much more data. “There’s no way on earth that JPEG could get near to 50 bytes,” says Solomon. When a credit card carrying the unique number is swiped through a reader a computer at the checkout could use the PIN to re-create an image of the face for visual identification. Alternatively it could be used as part of an automatic recognition system to control access to a building, or to cash in a bank account. Smart cards, which have tens of kilobytes of memory,