TWO American companies this week demonstrated prototype digital cameras that
can capture much sharper pictures than are possible with a standard film-based
camera. The snag is that the memory needed to store the pictures could be
prohibitively expensive.
Each frame of a 35-millimetre film has billions of silver halide crystals
that are chemically changed by light when the camera鈥檚 shutter opens. A digital
camera records images using a mosaic of sensors that convert light into a
digital signal that鈥檚 stored in a memory card.
The best sensors today have 3 to 4 million pixels. But even at this
resolution, individual pixels may make the image look grainy when it is
enlarged. So at this week鈥檚 Photokina show in Cologne, Germany, Kodak showed a
new charge-coupled device (CCD) sensor based on indium tin oxide. This means
individual detectors can be made small enough to pack into an array 4096 cells
square鈥攇iving more than 16 million pixels.
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An alternative and potentially cheaper sensor鈥攐f similar
density鈥攚as being shown by Foveon, a company in Santa Clara, California.
Unlike CCDs, which need specialised production lines, Foveon鈥檚 CMOS chips can be
made on standard microchip production lines.
CMOS sensors need several transistors to control current flow. This used to
mean that the pixels were too large to give high resolutions. But Foveon uses a
reduced CMOS component spacing of 180 nanometres鈥攈alf the previous
limit.
The first Kodak and Foveon products will go on sale in 18 months, aimed at
professional photographers. But each image will need a 50 megabyte storage
card鈥攚hich costs at least $100. A roll of 35-millimetre film takes
up to 36 times as many photographs for a fraction of the price.