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.