comparative color viewing, color management, predicting outcomes on press, and
print process control. Implementation of the ISO 3664:2009 specified viewing
conditions will expose color complications that might arise from the presence of
optical brighteners in the printing system; allowing those challenges to be realized
earlier in the color management workflow where they can be addressed
preemptively and more efficiently.
For the purpose of illustration, consider a printed image and a contract color
proof which are a “metameric” match when viewed under a certain lighting condition
void of significant U.V. energy (e.g., such as office lighting or even in a viewing booth
equipped with the “old style” 5000K/D50 lamps). When viewed outdoors or in
lighting conditions that contain U.V. energy, the two no longer match. What
happened? The presence of U.V. energy in the light source causes the optical
brighteners in the printed piece (e.g., fine paper + ink + aqueous coating) to
fluoresce and re-emit color (light) in the lower spectral wavelengths—dramatically
affecting the color of the printed image. Since the particular proofing media in our
example contains little to no optical brighteners, the color of the contract proof
appears virtually the same as it did in the non-U.V. lighting condition. The result:
color mismatch (metameric failure) between the print and the proof. Color
differences resulting from the effects of optical brighteners are generally most
noticeable in the lower end of the tonal scale (highlight to mid-tone)—areas where
the optical contributions of paper and overcoats are highly relevant.5
As demonstrated by the illustration, creating a metameric color “match” (i.e.,
the creation of a unique metameric pair) in one specific viewing environment (one
which typically excludes U.V. from the illuminant) is generally not a practical or
widely useful match. In reality, a metameric color match can be highly misleading
and may create false expectations of a printed product. To guard against this
phenomenon, ISO 3664:2009 mandates a much lower tolerance for metamerism (i.e.,
a lower metamerism index) than did the previous version of ISO 3664 by specifying a
close approximation of the standard CIE D50 illuminant that contains precisely
balanced spectral power distribution—including U.V. wavelengths. Therefore, ISO
3664:2009 prevents the “surprise” of unexpected metameric failure; i.e., as the color
of two objects may match under one light source and viewing condition but not in
another.