Details:
Summary:
Sigg described Grey Component Replacement (GCR) as a four color printing reproduction technique, where in any given image location, the least predominant of the three primary printing inks is used to calculate a partial substitution for some or all of the primaries by black. Early GCR images were judged to be commercially unacceptable. This condition is now eliminated or reduced by the practice of adding additional densities, Undercolor Addition (UCA), to each of the primary colors at the upper portion of their GCR tonal curve. GCR plus UCA has proven to be an effective combination to insure excellent commercial application. By convention, colored or toned black inks are routinely used for printing black and white reproductions, as well as four color reproduction. If the black ink used is not neutral, or the dot ratios of the UCA three color combinations are not a balanced grey, an off-color image will occur. Each ink has its own spectrophotometric characteristics. The GCR/UCA scanner program must be especially adjusted to the ink and the press fingerprint at the individual printing and therefore the above difficulties may be overlooked. By convention, colored or toned black inks are routinely used for printing black and white reproductions, as well as four color reproduction. If the black ink used is not neutral, or the dot ratios of the UCA three color combinations are not a balanced grey, an off-color image will occur. Each ink has its own spectrophotometric characteristics. The GCR/UCA scanner program must be especially adjusted to the ink and the press fingerprint at the individual printing and therefore the above difficulties may be overlooked. It is the intent of this paper to compare densitometric and colorimetric techniques in determining the correct UCA levels for various GCR black printer values. It is hoped that this work will provide some insight into specifications and techniques to facilitate optimum GCR.UCA levels.