Over the last 15 years, the trend has shifted from traditional CMYK densitometers to spectrophotometer based densitometers. This shift was mainly driven by more affordable, lower cost technology and the need to know more about the characteristic of the ink that is being printed. This has created a new class of products called Spectro-Densitometers.
Spectro-Densitometers are catching the eyes of press operators everywhere. Historically, they’ve had to rely on their eyes to calibrate the press, and many still do. But let’s face it; this method can be cumbersome at times, somewhat inaccurate, and expensive (in terms of time and materials).
The advantages of a Spectro-Densitometer are:
Accuracy and Reliability. A traditional densitometer uses film filters, such as the Kodak Wratten Gelatin filters, that separate the Cyan, Magenta, Yellow and Black colors from which the density of the ink on paper is measured. These filters are sensitive to moisture and high temperature. When the filter degrades, incorrect measurement values are produced. The CMYK filters are designed to measure the maximum absorbance region of process inks. Non-process inks that are often used in spot colors can be difficult to control using the non-optimal CMYK filters. A Spectro-Densitometer uses 16 or more bandpass functions to divide the visual spectrum up equally. These instruments produce a spectral fingerprint of the material measured. From the spectral data, all forms of color and density data can be accurately derived. The extra data allows a spectrophotometer to be a versatile tool that can control process and non-process inks.
Detection of Ink Contamination. This common problem can be caused by many factors such as by unintentionally laying too much of one color of ink on the paper which then gets carried through the press to another ink fountain. Since contamination impacts the high reflectance region of an ink and not the maximum absorbance region, a densitometer is blind to the phenomenon. The versatility of the spectrophotometer allows it to provide other useful metrics, such as the L*a*b* values and the resulting hue which quickly identify ink contamination. These same capabilities allow for new control strategies such as those described in industry standards like ISO, SWOP, GRAcol G7™ etc.
G7 calibration process. This process monitors a gray series as well as the primary inks to accurately maintain near neutral colors. With such a process, the color fidelity of the printing process is greatly improved. (This process relies heavily on maintaining near neutral color for the gray color by measuring the L*A*B of paper white and subtracting the color of the paper white which is not perfectly neutral white.