MS LED & Color Separation Quality
MS LED plate exposure technology promises to change the rules of flexo color separation. Specifically, the ability to hold small and isolated dots with extreme consistency within large plates and between plates enables the total disregard for dropouts in flexo CMYK separations.
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These sequences of separations shows a typical “low GCR” separation (the above row of images) and a very “high GCR” separation (the below row of images). The high GCR separation was used for the October 2017 FLEXO Magazine cover, resulting in perfect neutral grays, extreme stability on press and ink savings. The fact that high GCR separations contain dropouts and isolated dots in all channels is not an issue with MS LED-exposed plates.
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This, in turn, increases simplicity. A separation is now just a simple profile conversion from RGB to CMYK. It also increases quality. A mathematical profile conversion produces higher quality than manual image editing based on human judgment. All of this opens the door to high GCR color separation where dropouts are present everywhere, in every color (cyan, magenta, yellow and black).
Comparing MS LED to bank light exposure using the “flexo-ized” separation of the past will likely show a small to medium increase in quality for MS LED. However, such a comparison fails to show the total values of MS LED plate exposure technology. Comparing new style color separations—profile conversion separations with high GCR and dropouts everywhere—will show a night-and-day difference. It’s truly the ability of MS LED plate exposure to enable better color separation and screening techniques that makes it the obvious technology of the future.
And in the future, any serious comparison between the future of flexo and digital must conclude that a movement to eliminate spot colors and replace them with 7-color process is critical to flexo’s future. As digital technology is new, it’s all based on the process color model (4-color to 7-color), not a spot color model. With 7-color process flexo, every element of a job—images, solid spot colors, gradients, drop shadows—is converted to 7-color process. Hence, there are dropouts everywhere in a converted 7-color job.
A Brief, Oversimplified History of Hybrid Screening
Hybrid screening was introduced to the flexo industry in the late 1990s and has been run on millions of flexo production jobs ever since. It is the basis of today’s HD flexo screens. The goal of hybrid screening is to eliminate the flexo highlight break and provide lighter highlights. The images below illustrate an admittedly oversimplified history of hybrid screening.
The extreme “dot holding” characteristics of MS LED plate exposure technology are forcing our industry to re-think screening. Observing plates alone might lead one to conclude the original AM dot be revived. While it’s true MS LED-exposed plates can hold AM dots down into tenths of a percent, it’s also true such dots often produce a hard edge on the printed sheet. The screen proving to show the best results over the broadest range of conditions might be called a “minimalist” HD hybrid screen (the final image in this group). The ability of MS LED-exposed plates to hold small and isolated dots enables “just enough” hybrid screening to eliminate the highlight break while limiting its range, so as not to produce “grainy” images.
The AM Screen: MS LED plate exposure technology can hold AM dots well below 1 percent, but such dots will gain on press and may create a hard edge on the printed sheet. As such, even the best plate exposure technology can benefit from hybrid screening.
Dot Deletion: A hybrid screen can be created by deleting dots from an AM screen. Such screens can fade to zero, however the human eye can see the “hole” near the transition point. Hybrid screens with large dots and a long range may also appear “grainy” to the eye.
Dot Deletion with Repositioning: Repositioning some of the dots hides the holes from the human eye. Such screens have been successful; however, the isolated dots in the extreme highlights tend to cause problems with normal bank light plate exposure technology.
Support Dot Hybrid Screen: Mixing small “support” dots with larger “print” dots eliminates the effects of isolated dots. Such screens have been very successful with round top dot flexo plates, but require extreme expertise to optimize on plate and on press.
Minimalist HD Hybrid Screen: MS LED plate exposure technology enables very small and isolated dots to be held on the plate. This allows the use of the minimum amount of the simplest type of hybrid screening—dot deletion with slight repositioning.
Whether your goal is to compete with digital or to run flexo side-by-side with digital and achieve a color match (as we did in the 2017 FLEXO Magazine Cover Project), MS LED-exposed plates make the expanded gamut dream more obtainable for flexo, while increasing quality and stability.
About the Author: Mark Samworth began his career with DuPont, where he held numerous positions in the areas of flexographic plates and electronic imaging. Mark joined Esko in 1997 and is currently focused on consulting in screening, calibration, G7, color management and expanded gamut. He holds 11 patents in digital imaging, including FlexoCal, Hybrid Screening, Plate Cell Patsterning, Concentric Screening, Equinox expanded gamut technology and PressSync. He has authored numerous articles in the industry’s major trade publications and presented many papers at the industry’s major trade forums. In May of 2011, Mark was inducted as the 49th member of the FTA Flexo Hall of Fame. Mark received his B.S. from RIT and his MBA from the University of Delaware. He lives in Wilmington, DE.
Technologies discussed in this article include the Esko XPS plate exposure unit, a winner of the 2017 FTA Technical Innovation Award and a part of the 2017 FLEXO Magazine Cover Project, The XPS is a very specific type of LED plate exposure unit. Based on Esko patented technology, it features advanced LED lighting on a movable platen for increased exposure uniformity and to allow for the optimization of variables which, until now, has been unavailable.
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