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April 2018Martin Bailey, CTO, Global Graphics
Software
Avoiding the orange peel
180329
Copyright © Global Graphics Softwar...
Who are Global Graphics Software?
A software technology supplier for print OEMs,
especially for inkjet presses
Harlequin S...
Global Graphics Software is
 A global company
• US office in Sarasota, FL
• R & D in Cambridge, UK;
• Technical office in...
Global Graphics Software: digital print customers
Plus many others still under NDA
Copyright © Global Graphics Software Li...
Using software to help with ‘hardware’
issues
1: Halftoning
Copyright © Global Graphics Software Limited 2018
What is halftoning?
Black separation only
Copyright © Global Graphics Software Limited 2018
Digital halftones … the story so far
Screens for offset, flexo etc
Binary (1-bit, on or off)
Clustered
Sometimes called AM...
So what’s the problem?
Irregular drop positioning
leads to drops ‘randomly’
coalescing on the media:
These microscopic eff...
In response …
 We developed
advanced
screening
technology for
inkjet presses
 And launched a
service to develop
custom s...
Several projects later
 We’ve now worked on
screening for at least a
dozen single-pass inkjet
presses
• Mainly UV, plus a...
Fairly absorbent and/or wettable substrates
 Drops coalesce on the substrate surface
 Direction of coalescence is not ra...
Non-absorbent, poorly wettable substrates
 Prints show a mottle
effect
• Looks like orange peel
• Especially in areas wit...
We’re told: “I can fix that with …”
 Inter-station pinning, corona pre-
treatment etc to enhance ink adhesion
• Yes, redu...
Where does all this lead?
 Global Graphics has launched
Advanced Inkjet
Screens
 Innovative halftone screening
 Greatly...
Two common problems; two solutions
MIRROR
A screen designed to avoid orange peel mottle
on non-absorbent, poorly wettable ...
Widely applicable
 Advanced Inkjet
Screens can be used
for both binary and
multi-level devices
Copyright © Global Graphic...
So were we wrong …?
 To offer a press-by-press
halftone tuning service?
 No.
• There will always be some
presses with un...
Using software to help with ‘hardware’
issues
2: Non-uniformity
Copyright © Global Graphics Software Limited 2018
No good deed goes unpunished
 Improved screening takes
away noise that masks
other effects
• So now we have to fix those!...
What causes non-uniformity?
 Variation within a head
• Commonly a ‘smile’ shape
• Caused by pressure or voltage changes
...
We’re told: “I can fix that by tuning voltages! …”
 Not all heads have sufficient adjustment points to
correct the smile
...
Much better to do this in software
 Very fine granularity
• Can address every nozzle separately
• On any head/electronics...
Next steps
 Several inkjet OEMs are using
everything I’ve discussed today
 We’re always looking for new
partners to help...
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Global Graphics IJCUSA 2018 - Avoiding the orange peel

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At the recent Inkjet Conference in Chicago Global Graphics CTO Martin Bailey provided an update on mitigating texture artifacts on inkjet presses using halftone screens: streaking, coalescence, tone steps and the dreaded orange peel mottling.

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Global Graphics IJCUSA 2018 - Avoiding the orange peel

  1. 1. April 2018Martin Bailey, CTO, Global Graphics Software Avoiding the orange peel 180329 Copyright © Global Graphics Software Limited 2018
  2. 2. Who are Global Graphics Software? A software technology supplier for print OEMs, especially for inkjet presses Harlequin ScreenPro BreakThrough Very fast, high- quality PDF, PostScript etc rendering with extensive color management Stand-alone screening engine. Can be used with RIPs from other vendors, or where original designs are delivered as rasters/TIFF, as well as with Harlequin Professional services with expertise in building Digital Front Ends (DFEs), RIP integration, color management, halftone screening and problem solving Copyright © Global Graphics Software Limited 2018
  3. 3. Global Graphics Software is  A global company • US office in Sarasota, FL • R & D in Cambridge, UK; • Technical office in Tokyo, Japan  A Global Graphics company; sister to: • Meteor Inkjet • Specialists in industrial printhead driver solutions • www.meteorinkjet.com • URW type foundry • Designers and developers of digital fonts and font technology used by OEMs • www.urwpp.de Copyright © Global Graphics Software Limited 2018
  4. 4. Global Graphics Software: digital print customers Plus many others still under NDA Copyright © Global Graphics Software Limited 2018
  5. 5. Using software to help with ‘hardware’ issues 1: Halftoning Copyright © Global Graphics Software Limited 2018
  6. 6. What is halftoning? Black separation only Copyright © Global Graphics Software Limited 2018
  7. 7. Digital halftones … the story so far Screens for offset, flexo etc Binary (1-bit, on or off) Clustered Sometimes called AM screens E.g. Harlequin Precision Screening (HPS) Stochastic screens Used for offset, EP, some inkjet Binary Dispersed Sometimes called FM screens E.g. Harlequin Dispersed Screening (HDS) Multi-level screens Used for some EP, most inkjet 2-7 ink levels (drop sizes etc) Dispersed Copyright © Global Graphics Software Limited 2018
  8. 8. So what’s the problem? Irregular drop positioning leads to drops ‘randomly’ coalescing on the media: These microscopic effects cause visible artefacts, often described as mottling or streaking: Synthetic image with exaggerated artefacts in order to be visible on a projector, or reproduced on another print process Copyright © Global Graphics Software Limited 2018
  9. 9. In response …  We developed advanced screening technology for inkjet presses  And launched a service to develop custom screens for each press in early 2016 Copyright © Global Graphics Software Limited 2018
  10. 10. Several projects later  We’ve now worked on screening for at least a dozen single-pass inkjet presses • Mainly UV, plus aqueous and others • Various heads & electronics • Lots of different media • With and without chillers, corona pre-treatment etc  And … There is more commonality than we thought What matters most is … the media There are two distinct groups of behavior Reasonably absorbent and/or wettable Non-absorbent, poorly wettable Paper, inkjet coated etc Flexible plastics, metal etc Copyright © Global Graphics Software Limited 2018
  11. 11. Fairly absorbent and/or wettable substrates  Drops coalesce on the substrate surface  Direction of coalescence is not random • Tends to be along the substrate  Coalescence causes visible streaking • Especially in mid- and three-quarter tones These issues are quite amenable to correction in a halftone With compensating halftone Uncorrected  Some influence from: • Head geometry, e.g. saw-tooth nozzle patterns • Timing issues for different drop sizes • Head stitching Copyright © Global Graphics Software Limited 2018
  12. 12. Non-absorbent, poorly wettable substrates  Prints show a mottle effect • Looks like orange peel • Especially in areas with reasonably high total area coverage (TAC)  Triggered by ink shrinkage during cure Copyright © Global Graphics Software Limited 2018
  13. 13. We’re told: “I can fix that with …”  Inter-station pinning, corona pre- treatment etc to enhance ink adhesion • Yes, reduces the tonal mottle • BUT increases color mottle • by reducing fluid ink mixing on the substrate  Ink reduction with UCR/GCR etc • Yes, reduces tonal mottle • BUT increases apparent noise/grain • by reducing area covered by ink and increasing local contrast between ink and light colored substrate The orange peel CAN be corrected with a halftone with specially designed characteristics Without increasing color mottle, noise or grain Copyright © Global Graphics Software Limited 2018
  14. 14. Where does all this lead?  Global Graphics has launched Advanced Inkjet Screens  Innovative halftone screening  Greatly improves quality on the majority of inkjet presses  Advanced Inkjet Screens can be used in both the Harlequin RIP and in ScreenPro Copyright © Global Graphics Software Limited 2018
  15. 15. Two common problems; two solutions MIRROR A screen designed to avoid orange peel mottle on non-absorbent, poorly wettable substrates PEARL A screen specifically created to counteract streaking on reasonably absorbent and/or wettable substrates Copyright © Global Graphics Software Limited 2018
  16. 16. Widely applicable  Advanced Inkjet Screens can be used for both binary and multi-level devices Copyright © Global Graphics Software Limited 2018
  17. 17. So were we wrong …?  To offer a press-by-press halftone tuning service?  No. • There will always be some presses with unique properties  Global Graphics has continued to develop our Chameleon design tools for creation of unique halftones for these cases Copyright © Global Graphics Software Limited 2018
  18. 18. Using software to help with ‘hardware’ issues 2: Non-uniformity Copyright © Global Graphics Software Limited 2018
  19. 19. No good deed goes unpunished  Improved screening takes away noise that masks other effects • So now we have to fix those!  Non-uniformity across the web is the next project Both uncorrected Original Blurred to make the density variation more obviou Copyright © Global Graphics Software Limited 2018
  20. 20. What causes non-uniformity?  Variation within a head • Commonly a ‘smile’ shape • Caused by pressure or voltage changes  Variation between heads • Especially as heads become field replaceable  Head wear Density ONE HEAD Copyright © Global Graphics Software Limited 2018
  21. 21. We’re told: “I can fix that by tuning voltages! …”  Not all heads have sufficient adjustment points to correct the smile  Often time-consuming work for an expert • Increases time and cost of installation or head replacement  Not readily automated for closed-loop correction  Difficult in head overlap/stitching regions  Reduces jetting stability and (anecdotally) head lifetime • Especially risky to tweak heads beyond warranty limits  Causes ink pressure and timing/drop speed variation • Which increase ink coalescence on the substrate … • Which causes texture artifacts … That sounds familiar! That’s where I started today! Copyright © Global Graphics Software Limited 2018
  22. 22. Much better to do this in software  Very fine granularity • Can address every nozzle separately • On any head/electronics  Almost instant once output is measured • Can be automated for closed-loop correction  Doesn’t affect • Jetting stability or head lifetime • Warranty compliance • Ink pressure and timing/drop speed variation • Ink coalescence on the substrate • Halftoning Corrected in software Original Blurred Original Blurred Uncorrected Copyright © Global Graphics Software Limited 2018
  23. 23. Next steps  Several inkjet OEMs are using everything I’ve discussed today  We’re always looking for new partners to help expand our knowledge  We love to develop new technologies to help bring better products to market faster Martin.Bailey@GlobalGraphics.com www.GlobalGraphics.com Copyright © Global Graphics Software Limited 2018

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