Digital photography could soon be accessible to all, thanks to a new system developed by Kodak. Paul Rodgers reports
A picture can speak a thousand words - but Kodak, the world's largest photographic film company, argues the figure is actually closer to 2 million.

While Kodak's calculations may underestimate the descriptive value of words, they accurately reflect the computer memory needed to store a high- resolution photograph - up to 18 megabytes, against eight for the average English word.

That sheer volume of data has limited the introduction of digital photography to specialist professional applications - until now. Kodak says it has found a way - with the help of partners such as the computer firms IBM, Apple and Microsoft and the Sprint telephone company - to make the technology available to anyone. "Kodak is changing the picture," boasted George Fisher, the company's chief executive, when he unveiled the system two weeks ago.

Initially, some steps in the process will still require a trip to the high-street chemists or a self-serve kiosk in a shopping mall to get pictures scanned into digital format. But eventually, amateur photographers will be able to shoot with digital cameras, store the images in a central warehouse on the Internet, enhance them on home computers and send them by telephone anywhere in the world. They will be able to filter out common problems such as red eye, erase ugly background features such as telephone wires, merge pictures taken of relatives in distant parts of the world, and even edit out former family members after a messy divorce. Individuals and small businesses will also be able to incorporate their pictures in documents. Job-hunters could put a self-portrait on their CVs while mums could include snaps of the kids in an e-mail letter to grandma.

Digital cameras work just like analogue ones, with a shutter and lenses to focus the picture. But instead of exposing a sheet of silver halide film, the image shines on a very large computer chip. The chip is covered with millions of microscopic charge couple devices (CCDs), each of which develops an electrical charge varying according to the brightness of the light landing on it.

CCDs do not register colour, however. To solve this problem, some digital cameras take three separate exposures one after another, each through a different colour filter. Others use a prism to split the image into red, green and blue beams, which shine on different parts of the CCD array. Kodak's latest digital camera groups the CCDs in fours, each with its own tiny filter. "We use a red, a blue and two green filters because the human eye is more sensitive to green," says Phil Fennessy, a Kodak client support executive and co-author of An Introduction to Electronic Imaging for Photographers.

A microprocessor in the camera measures the charge on each CCD and assigns it a number describing the exact hue at that particular point. These numbers are stored in order from top left to bottom right, usually on a credit- card size PCMCIA hard disk. The camera can then be plugged directly into the serial port at the back of the computer or the file can be sent via modem and telephone line.

Digital cameras now cost £1,000 or more. Although Kodak predicts that will drop to as little as £150 in a few years, it is encouraging people to switch to digital now by using scanners. These work much like digital cameras, but instead of shooting from real life, use an old-fashioned analogue negative or print as their original.

Most of digital photography's problems occur when pictures are transferred from camera to computer to printer. The first problem is colour management. Although colours can be numerically defined using a standard system - much like the way letters are universally represented by ASCII code - they may be distorted on different monitors and printing devices.

Without a standard system of colour management, a picture might look too green on a computer monitor, prompting the operator to adjust the levels of red and blue. When it is then transferred to a printer, another operator might decide it had too much magenta and add more cyan to compensate. The result could look quite different from the original.

To ensure that a picture looks right, Kodak has come up with a way to calibrate different machines. Using a colorimeter, technicians measure how different models "see" each colour and set up a chart of values telling the computer how to modify them for display. When the file is passed to a printer, that machine will have its own, unique chart depending on the types of inks it uses. At all times, the file contains the original values recorded by the digital camera or scanner.

The second problem is image management. This is a system to ensure that data is not accidentally lost or damaged during transmission. The most common problem occurs when an entire line of information is scrambled, resulting in what appears to be a horizontal scratch across the picture.

To avoid this, Kodak uses a check sum - essentially, a number at the end of the file calculated from all the values in the file. When a computer receives a picture file, it repeats the calculation and compares the result it obtains to the check sum number sent with the file. If there is a discrepancy, it can ask for the file to be sent again.

The final, and possibly most serious problem, is size. Sending a 35mm picture down a telephone line, even with a fast modem, can take more than an hour. If a picture has to be sent back and forth between computers on different sides of the world - from an ad agency in London, say, to a client in Sydney - this can be time-consuming and expensive.

The traditional way to solve this problem is to expand the bandwidth of the communications channels linking the machines, for example, by switching to fibre optics from normal telephone lines. But as a high bandwidth global network is still years from completion, Kodak decided it would be easier to find a way to reduce the amount of information sent to just 200k.

To do this it is combining its existing Photo CD format, which stores pictures on CDs at five different levels of resolution, with a new computer program called Functional Interpolating Transformation System (Fits), developed by the French software company Live Picture.

The idea is to store the bulky high-resolution files in a central photo library on the Internet, and give users low-resolution copies to view, modify and transfer between computers. The Fits program incorporates any changes they make to these copies into the original. Only when a high- resolution print is wanted will the full file be sent from the library to a printer.

While several elements of the system have been independently developed by different companies, Kodak is the first to unite them in one package. By licensing the system to its competitors, it hopes to establish a global standard. If it succeeds, ordinary computer users could find playing with pictures as easy as they now find playing with words.