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Substrate correction experiment

In graphic arts colour reproduction it is common for a final print to be produced on a paper that is not identical to that used for the proof, or which does not exactly match one of the target reference papers specified in the a process control standard such as ISO DIS 12647-2. To achieve an accurate colorimetric match on the actual paper it would be necessary to generate characterization data for the printing process on the new paper. However, in many cases it is not practical to generate this data empirically by printing samples and measuring them. In addition, there will be some degree of adaptation to the new paper white point, so that a colorimetric match may not be a desirable reproduction goal.

It is therefore useful to be able compute new characterization data to take account of the change in paper colour, in a way that preserves the appearance of the original when printed on the new paper. Commonly this is done by applying a media-relative adjustment to the data, so that the actual production paper white becomes the target media white and other colorimetric data is scaled in the same way. This approach uses the same equations as those used to convert to and from media-relative colorimetry defined in the ICC specification.

To determine what range of media white points this approach is valid, a series of experiments is being carried out, led by Kwame Baah at London College of Communication. Prints are prepared with the media-relative correction applied, and observers are asked to judge the perceptibility and acceptability of the colour differences from the reference colours.

A preliminary paper on the experiment has been published at AIC 2012, which found that the difference in paper colour itself was the main factor in determining the threshold of acceptability for the media-relative correction.

Further work is continuing, and experts are invited to contribute to this work by generating samples and carrying out further psychophysical experiments to evaluate acceptability and perceptibility thresholds.

A protocol and record sheet for the coordinated experiment are available. Further results will be reported here when completed.

To take part in the experiment, contact the ICC Technical Secretary