When a colored document is faxed
on a black-and-white machine, is the color gone for good?
Not necessarily, according to Karen M. Braun, a Xerox Corporation imaging scientist and co-developer of
the first way to encode documents so that the colors of the original image can be recovered from a print made
on a black-and-white printer, fax or copier.
At the Society for Imaging
Science and Technology's annual Color Imaging Conference here, Braun and Ricardo L. deQueiroz,
who's on the faculty of the Universidade de Brasilia in Brazil, are describing their work in a
paper called "Color to Gray and Back: Color Embedding into Textured Gray Images."
The presentation is one of six being made by Xerox researchers at the conference this week.
Braun and deQueiroz began with a common problem. When a color image is copied, printed or
faxed on a black-and-white device, the colors are converted to shades of gray. Two different
colors with the same luminance - or perceived brightness - may "map" to the same shade of gray,
making it impossible to interpret the information the colors carry. When that happens on graphics
like pie charts or bar charts, two colors will look the same and the chart loses its information
value.
While trying to figure out how to retain the information conveyed in color graphs and pictures,
the researchers looked for new ways to represent color images in black-and-white. Their method
turns each color into a microscopically different texture or pattern in the gray parts of an image.
It makes it easy to identify colors 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 color to textures
in this way, the textures can later be decoded and converted back to color," she said.
Thus the recipient of a black-and-white fax could recover the colors of the original. It would also
allow colors to be retrieved from a printed black-and-white hardcopy. Xerox has applied for a patent
on the technology.
How might the technology someday be used? In practice, the part of the algorithms that code the
colors could be integrated within the software of a black-and-white printer so colors could be
transformed to textured grays. The decoding part of the algorithms could be part of a multifunction
system's scanner, recovering the original colors so the document could be switched back to vivid
color for display or print.
Braun is part of a contingent of Xerox researchers sharing their work at the annual conference for
color scientists. Others presenting papers and tutorials are Raja Bala, R. Victor Klassen, Martin
Maltz, Jon McElvain, and J. Michael Sanchez - a group that collectively hold 88 patents in the
areas of color control, calibration, characterization and image processing.
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