April 2018Martin Bailey, CTO, Global Graphics
Software
Avoiding the orange peel
180329
Copyright © Global Graphics Software Limited 2018

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

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

Global Graphics Software: digital print customers
Plus many others still under NDA
Copyright © Global Graphics Software Limited 2018

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 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

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

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

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

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

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

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

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

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

Widely applicable
 Advanced Inkjet
Screens can be used
for both binary and
multi-level devices
Copyright © Global Graphics Software Limited 2018

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

Using software to help with ‘hardware’
issues
2: Non-uniformity
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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

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
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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

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

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