The printing process depends on “transforms” – mathematical instructions that tell machines how much of each ink or toner is needed so that the colours on paper replicate the colours we see with the human eye. Currently, the standard industry approach to printer calibration uses “one-dimensional transforms,” which individually adjust each of a printer’s colours – cyan, magenta, yellow and black (CMYK) – one at a time.
One-dimensional transforms are appealing because of their low cost and simplicity. But if a machine’s colour-print output changes, as it might when wear or other factors change the way colour toner is transferred onto paper, changing an individual colour won’t correct the entire system.
On the other hand, three- and four-dimensional calibrations can handle the problem and simultaneously adjust the red, green, blue or the CMYK values, but the cost of incorporating the more complex adjustment system in printers and the manpower required to account for changes in the printer’s behaviour would be prohibitive.
The answer, according to the Xerox scientists is two-dimensional calibration, which combines the advantages of both approaches.
“We see two-dimensional calibration as adding affordable quality,” said Raja Bala, the research’s presenter and a principal scientist at Xerox’s Imaging and Services Technology Centre. “Our research focuses on the once-forgotten two-dimensional realm as a cost-effective means of providing more accurate colour output in not only printers but even colour LCD devices.”
At a recent conference, Bala highlighted Xerox’s work in developing full-resolution two-dimensional calibration tables, on which patents are pending. The Xerox scientists wrote software to mathematically construct the two-dimensional tables, which allow for simultaneous corrections of the primary printing colours as well as greys and flesh tones, to which the human eye is quite sensitive.
Today’s one-dimensional calibration is far more limited, forcing manufacturers to choose between the control of one colour or another.
Bala showed samples of printer colour correction accomplished with minimal additional mathematical computations, using less computer space. Results show significant improvement in colour accuracy and stability when compared to traditional one-dimensional calibration.
“A few years ago, the half a megabyte of computer disk space required for two-dimensional calibration would have been considered prohibitive,” Bala said. Recent advances in technology, however, will make it more possible for manufacturers to inexpensively embed the new two-dimensional calibration tables inside printers or print controllers.