Bring back the colour

When a coloured document is faxed on a black-and-white machine, one might assume that the colour information is lost.

Not necessarily, according to Karen M. Braun, a Xerox imaging scientist. She is the co-developer of the first way to encode documents so that the colours of the original image can be recovered from a print made on a black-and-white printer, fax or copier.

Together with Ricardo L. deQueiroz, who's on the faculty of the Universidade de Brasilia in Brazil, Braun began with a common problem. When a colour image is copied, printed or faxed on a black-and-white device, the colours are converted to shades of grey.

Two different colours with the same luminance - or perceived brightness - may "map" to the same shade of grey, making it impossible to interpret the information the colours carry. When that happens on graphics like pie charts or bar charts, two colours will look the same and the chart loses its information value.

While trying to understand how to retain the information conveyed in colour graphs and pictures, the researchers looked for new ways to represent colour images in black-and-white.

The method they developed turns each colour into a different texture or pattern in the grey parts of an image. It makes it easy to identify colours with similar luminance value, making the pictures more pleasing and the graphs more useful.

The new method also had an unexpected benefit, according to Braun. "When you map colour to textures in this way, the textures can later be decoded and converted back to colour," she said.

Thus the recipient of a black-and-white fax could recover the colours of the original. It would also allow colours to be retrieved from a printed black-and-white hardcopy.

How might the technology someday be used? In practice, the part of the algorithms that code the colours could be integrated within the software of a black-and-white printer so colours could be transformed to textured greys.

The decoding part of the algorithms could be part of a multifunction system's scanner, recovering the original colours so the document could be switched back to vivid colour for display or print.

Xerox has applied for a patent on the technology. For more information, visit www.xerox.com/innovation.