There is No Such Thing as G7 Proofing Media: CGS Offers Tips for Updating Your Inkjet Proofing Substrate
Tuesday, October 30, 2018
Press release from the issuing company
by Lynn Leppo, National Media Sales Manager
Are you ready?
In the many calls and emails I receive, before the important questions are asked and addressed, there is always a mention of: “but we/they are a ‘G7’ shop.” This is great—and aligning to the G7 methodology is fantastic—however, a common misunderstanding regarding G7 is that it suggests an applicable media white point or Characterized Reference Print Condition (CRPC). The truth is, it does not. G7 Neutral Print Density Curves and gray balance are ‘paper-relative.’ The same is true of all substrates. The secret is out: G7 works on any substrate, without change.
What ‘paper-relative’ refers to in this application, is 'white point'. G7 looks at 'white point' from a relative perspective, indicating that its methodology is able to account for varying media white points. There is not one specific G7 media option, rather, any media can be G7 aligned.
Being ‘paper-relative’ is a perspective based on comparison rather than seeing something as an individual entity—in this case, it refers specifically to individual white point. This concept differs from ‘absolute,’ which is also often used in industry language. G7 does not mandate a CIE LAB for media white point. G7 is paper-relative.
What To Consider, When Shopping for Media:
OBA, if you are unfamiliar, refers to optical brightening agents. OBAs are becoming more and more prevalent in both proofing and production media—whiter whites impress, and they make paper production cheaper. The presence of OBAs influence the visual appearance of media based on the amount of UV in the viewing condition spectrum. In the past, we proofed on OBA-excluded proofing media because of the influence the paper had on viewing color. Because there has been a resurgence of OBAs in press stock, we are now running proofing media that are OBA-included.
We can account for the influence of OBAs utilizing a measurement condition referred to as ‘M1.’ While determining whether you are OBA-included or OBA-excluded, knowing if you are M1 capable will also be a beneficial step for the media-selecting process. An easy way to determine the level of OBA in a substrate, is by measuring the native paper and evaluating the b* value. If you have a -4 b*, for example, you’ve likely got a moderate level of OBA. Whereas, if you encounter a b* of -6 or -9 on a reading, you’re running a higher level of OBA. You will want to consider balancing OBAs in prepress and your press room, by selecting a media with a similar level of OBA for prepress as you see in your press stock. If I’ve lost you, do not worry. You can send me, or another technical resource samples to evaluate for you. Anyone with a measurement device will be able to offer a hand.
When establishing which CRPC you target, keep in mind that G7 is not GRACoL. If you are a G7 certified printer, it doesn’t necessarily mean that you target GRACoL. Specifications in printing use a precise characterization data set for a specific print process and substrate. Specifications such as GRACoL, or SWOP are NOT paper-relative—they dictate a LAB measurement. If you need a refresher on the different CRPC’s or help determining which you target, the Idealliance website is great place to start. If you find that you do not fit within a white point designated by your specification, the specification dataset can be modified to accommodate your substrate. Aligning to G7 in this instance, is still entirely possible utilizing Substrate-Corrected Colorimetric Aims, or SCCA. More information on SCCA can be found, here: http://connect.idealliance.org/g7/education/g7masterfaq.
A Final Note:
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