WHY DO OPTICAL BRIGHTENERS IN PAPER MATTER?
In the world of print, optical brightening agents in paper have often been referred to as a ‘game changer’ because of their inherent impact on achieving an acceptable color match. Although G7® has proven to be a valuable method for calibrating printing devices, as well as specifying color, one of the limitations of G7, as well as other calibration methods, has been the problem of paper color. The G7 method is based upon ISO 10128. This means that the LAB values for inks, the traps, and the gray curve are all based on the global print standard, ISO 12647-2. When performed on the stock specified, the process works spectacularly well. Part of the consistent results we see from G7 are due to the fact that G7 sits on top of ISO 12647-2. In the world of standard papers and inks everything works well. But when we use papers that are out of spec then we begin to see color matching problems. The more out of spec the paper is the worse the color match will be.
WHAT IS BEING DONE ABOUT IT?
Idealliance.org: The Introduction of Substrate Corrected Colorimetric Aims
IDEAlliance, the organization that owns G7, GRACoL and SWOP has been aware of this disconnect. Standards like ISO are standards for a reason, and when you stop using standard material (like using an extremely different shade of paper) then the standard becomes broken and does not work as intended. The problem is bigger than just sheetfed printing, where we have more control over the sheets we print on. In other print processes like flexo, or board printing, the substrates are even more out of spec. In order to have a brand render correctly across a variety of substrates, and to give the printer a fair chance at matching color, G7 and additional color management may be required. One member of the IDEAlliance Print Properties & Colorimetric Committee who has thought long and hard about this is David McDowell. David is a color scientist and US ISO delegate. He has developed a formula for paper scaling [SCCA : Substrate Corrected Colorimetric Aims ] which the GRACoL Tolerance Committee is currently testing. The formula has been integrated into a spreadsheet, which contains the GRACoL and SWOP datasets. By typing the paper color into the spreadsheet, the spreadsheet will do the math and recalculate the dataset with new aim points based on using that specific paper color. It’s a very interesting concept and in near future IDEAlliance may release it as a tool with a set of guidelines for printers to test.
Techkon: Implementing Substrate Corrected Colorimetric Aims
We became aware of this new specification, SCCA :Substrate Corrected Colorimetric Aims, and immediately began working on a solution for our line of densitometers and spectrophotometers. We are working towards implementing the ability to measure the paper and based on those measurements and using the SCCA formula we will calculate the new aim points right on the instrument. This feature will allow printers to quickly and easily achieve an acceptable color match regardless of the presence of optical brightening agents in their substrates. The feature will be a simple firmware upgrade available for free on techkonusa.com.
Ron Ellis wrote a great article on this topic. Read the entire article written by Ron Ellis entitled:
G7 and Paper Color: the Challenge of Achieving Acceptable Color Match