Restoring Original Document Colour To Mono Faxes

When a coloured document is faxed on a mono the colour of the item is not necessarily gone for good, according to Xerox,which has claimed it can recover the original image's colour.

When a coloured document is faxed on a mono the colour of the item is not necessarily gone for good, according to Xerox, which has claimed it can recover the original image's colour.

Karen M Braun is a Xerox imaging scientist and co-developer of what is said to be the first way to encode documents so that the colours of the original image can be recovered from a print made on a mono fax or copier.

Braun and deQueiroz 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, such as pie charts or bar charts, two colours will look the same and the chart loses its information value, said Xerox.

Whilst trying to work out 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.

Their method turns each colour in to a microscopically different texture or pattern in the grey parts of an image.

It is claimed to make 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." Therefore, 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.

Xerox has applied for a patent on the technology.

Xerox added that, in practice, the part of the algorithms that code the colours, could be integrated within the software of a mono printer so that colours could be transformed to textured greys.

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

Braun is part of a contingent of Xerox researchers sharing their work at the annual conference for colour scientists at the Society for Imaging Science and Technology's annual Colour Imaging Conference in Scottsdale, Arizona (USA).

Braun and Ricardo L deQueiroz, who are on the faculty of the Universidade de Brasilia in Brazil, described their work in a paper called 'Colour to Grey and Back: Colour Embedding into Textured Grey Images'.

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