Colorimetric control of photographic prints: the problem of fluorescence

Abstract

The colorimetric control of photographic prints is an important issue of color reproduction quality. Concentration series of the three photographic dyes Yellow, Magenta and Cyan on photographic paper are very often measured without considering the optical quality of the substrate. However, this substrate, the photographic paper, produces problems for colorimetry because it emits luminenscent light from optical brighteners. Many instruments used in colorimetry are not adapted to measure such an output correctly. Here, an experimental investigation is presented which quantifies systematic shifts of spectral curves and colorimetric values of photographic paper and dyes for various measuring parameters. Several spectrophotometers equipped with different sources for irradiation such as Tungsten halogen lamp, Xenon flash lamp, D65 simulator, and two Xenon lamps with adjustable UV-filter were referenced against the results of two-monochromator spectrophotometer. In the photographic paper the largest color-difference extended to approximately 10 CIELAB-units between irradiation by a Tungsten halogen and a Xenon lamp. These differences diminished with increasing concentration of the photographic dyes, however, did not die away at the highest concentration of the dyes used. The correct colorimetric values for D65 irradiation were halfway between those for the two former lamps and near to measures received from Xenon lamp irraditoin with adjustable UV-filter. Therefore, such spectrophotometers may be used for colorimetric control of photographic prints to attain an accuracy below 3 CIELAB units, or else, two measurements with a Tungsten halogen and a Xenon lamp should be averaged.